- Volume 61, Issue 9, 2012
Volume 61, Issue 9, 2012
- Review
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Current concepts on the virulence mechanisms of meticillin-resistant Staphylococcus aureus
More LessMeticillin-resistant Staphylococcus aureus (MRSA) strains are prevalent bacterial pathogens that cause both health care and community-associated infections. Increasing resistance to commonly prescribed antibiotics has made MRSA a serious threat to public health throughout the world. The USA300 strain of MRSA has been responsible for an epidemic of community-associated infections in the US, mostly involving skin and soft tissue but also more serious invasive syndromes such as pneumonia, severe sepsis and endocarditis. MRSA strains are particularly serious and potentially lethal pathogens that possess virulence mechanisms including toxins, adhesins, enzymes and immunomodulators. One of these is Panton–Valentine leukocidin (PVL), a toxin associated with abscess formation and severe necrotizing pneumonia. Earlier studies suggested that PVL was a major virulence factor in community-associated MRSA infections. However, some recent data have not supported this association while others have, leading to controversy. Therefore, investigators continue to search for additional mechanisms of pathogenesis. In this review, we summarize the current understanding of the biological basis of MRSA virulence and explore future directions for research, including potential vaccines and antivirulence therapies under development that might allow clinicians to more successfully treat and prevent MRSA infections.
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- Pathogenicity and virulence
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Adhesion to the yeast cell surface as a mechanism for trapping pathogenic bacteria by Saccharomyces probiotics
Recently, much attention has been given to the use of probiotics as an adjuvant for the prevention or treatment of gastrointestinal pathology. The great advantage of therapy with probiotics is that they have few side effects such as selection of resistant bacteria or disturbance of the intestinal microbiota, which occur when antibiotics are used. Adhesion of pathogenic bacteria onto the surface of probiotics instead of onto intestinal receptors could explain part of the probiotic effect. Thus, this study evaluated the adhesion of pathogenic bacteria onto the cell wall of Saccharomyces boulardii and Saccharomyces cerevisiae strains UFMG 905, W303 and BY4741. To understand the mechanism of adhesion of pathogens to yeast, cell-wall mutants of the parental strain of Saccharomyces cerevisiae BY4741 were used because of the difficulty of mutating polyploid yeast, as is the case for Saccharomyces cerevisiae and Saccharomyces boulardii. The tests of adhesion showed that, among 11 enteropathogenic bacteria tested, only Escherichia coli, Salmonella Typhimurium and Salmonella Typhi adhered to the surface of Saccharomyces boulardii, Saccharomyces cerevisiae UFMG 905 and Saccharomyces cerevisiae BY4741. The presence of mannose, and to some extent bile salts, inhibited this adhesion, which was not dependent on yeast viability. Among 44 cell-wall mutants of Saccharomyces cerevisiae BY4741, five lost the ability to fix the bacteria. Electron microscopy showed that the phenomenon of yeast–bacteria adhesion occurred both in vitro and in vivo (in the digestive tract of dixenic mice). In conclusion, some pathogenic bacteria were captured on the surface of Saccharomyces boulardii, Saccharomyces cerevisiae UFMG 905 and Saccharomyces cerevisiae BY4741, thus preventing their adhesion to specific receptors on the intestinal epithelium and their subsequent invasion of the host.
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Adherence of Clostridium difficile spores to Caco-2 cells in culture
More LessClostridium difficile is the causative agent of the majority of antibiotic associated diarrhoea cases. C. difficile spores are recognized as the persistent and infectious morphotype as well as the vehicle of transmission of CDI. However, there is a lack of knowledge on how C. difficile spores interact with the host’s epithelial surfaces. In this context, we have characterized the ability of C. difficile spores to adhere to human Caco-2 cells. Despite the similarities in spore-surface hydrophobicity between spores of C. difficile and Clostridium perfringens (another enteric pathogen that also sporulates in the gut), spores of C. difficile adhere better to Caco-2 cells. Adherence to Caco-2 cells was significantly reduced when C. difficile spores were treated with trypsin. Sonication of C. difficile spores altered the ultrastructure of the outermost exosporium-like structure, releasing two protein species of ~40 kDa and significantly reduced spore hydrophobicity and adherence to Caco-2 cells. Using a trifunctional cross-linker, we were able to co-immunoprecipitate four protein species from the surface of Caco-2 cells. In conclusion, this study provides evidence that C. difficile spores adhere to human intestinal enterocyte-like cells through spore- and enterocytic-surface-specific ligand(s) and/or receptor(s).
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- Diagnostics, typing and identification
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Development of a thermostabilized, one-step, nested, tetraplex PCR assay for simultaneous identification and differentiation of Entamoeba species, Entamoeba histolytica and Entamoeba dispar from stool samples
Entamoeba histolytica is the only Entamoeba species that causes amoebiasis in humans. Approximately 50 million people are infected, with 100 000 deaths annually in endemic countries. Molecular diagnosis of Entamoeba histolytica is important to differentiate it from the morphologically identical Entamoeba dispar to avoid unnecessary medication. Conventional molecular diagnostic tests require trained personnel, cold-chain transportation and/or are storage-dependent, which make them user-unfriendly. The aim of this study was to develop a thermostabilized, one-step, nested, tetraplex PCR assay for the detection of Entamoeba histolytica, Entamoeba dispar and Entamoeba species in cold-chain-free and ready-to-use form. The PCR test was designed based on the Entamoeba small subunit rRNA (SSU-rRNA) gene, which detects the presence of any Entamoeba species, and simultaneously can be used to differentiate Entamoeba histolytica from Entamoeba dispar. In addition, a pair of primers was designed to serve as an internal amplification control to help identify inhibitors in the samples. All PCR reagents together with the designed primers were thermostabilized by lyophilization and were stable at 24 °C for at least 6 months. The limit of detection of the tetraplex PCR was found to be 39 pg DNA or 1000 cells for Entamoeba histolytica and 78 pg DNA or 1000 cells for Entamoeba dispar, and the specificity was 100 %. In conclusion, this cold-chain-free, thermostabilized, one-step, nested, multiplex PCR assay was found to be efficacious in differentiating Entamoeba histolytica from other non-pathogenic Entamoeba species.
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Molecular typing and antifungal susceptibility of Exophiala isolates from patients with cystic fibrosis
The black yeast Exophiala dermatitidis is a frequent agent of colonization of the lungs of patients with cystic fibrosis (CF). A total of 71 clinical isolates of Exophiala from 13 patients were identified at the species level by sequencing the internal transcribed spacer (ITS) regions 1 and 2 of the rDNA genes and typed by random amplification of polymorphic DNA (RAPD), using two different primers, BG-2 and ERIC-1. In vitro susceptibility of these isolates to some systemic antifungal drugs was investigated using the CLSI method. Almost all the isolates were identified as E. dermatitidis, but long-term colonization with the closely related species E. phaeomuriformis was observed in one patient. No clustering was found according to the geographical origin of the isolates, the isolation date or the antifungal susceptibility. Variations were seen in the susceptibility of studied isolates to antifungals but most of them exhibited low susceptibility to amphotericin B and although some patients were successively colonized by two distinct genotypes, most of the isolates were distributed in patient-specific clusters. This phenomenon may be due to genomic variations of E. dermatitidis in the lung environment of CF patients. These results are typical of colonization of the airways of patients by a poorly distributed environmental fungus, which occupies particular reservoirs that need to be defined.
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Characterization of a novel variant of Mycobacterium chimaera
In this study, nonchromogenic mycobacteria were isolated from pulmonary samples of three patients in the Netherlands. All isolates had identical, unique 16S rRNA gene and 16S–23S ITS sequences, which were closely related to those of Mycobacterium chimaera and Mycobacterium marseillense. The biochemical features of the isolates differed slightly from those of M. chimaera, suggesting that the isolates may represent a possible separate species within the Mycobacterium avium complex (MAC). However, the cell-wall mycolic acid pattern, analysed by HPLC, and the partial sequences of the hsp65 and rpoB genes were identical to those of M. chimaera. We concluded that the isolates represent a novel variant of M. chimaera. The results of this analysis have led us to question the currently used methods of species definition for members of the genus Mycobacterium, which are based largely on 16S rRNA or rpoB gene sequencing. Definitions based on a single genetic target are likely to be insufficient. Genetic divergence, especially in the MAC, yields strains that cannot be confidently assigned to a specific species based on the analysis of a single genetic target.
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- Antimicrobial agents and chemotherapy
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Multidrug-resistant clones of community-associated meticillin-resistant Staphylococcus aureus isolated from Chinese children and the resistance genes to clindamycin and mupirocin
This study aimed to correlate the multidrug resistance (MDR) and sequence type (ST) clones of community-associated (CA) meticillin-resistant Staphylococcus aureus (MRSA) to identify the genes responsible for clindamycin and mupirocin resistance in S. aureus isolates from paediatric hospitals in mainland China. A total of 435 S. aureus isolates were collected. Compared with CA meticillin-susceptible S. aureus (MSSA), the resistance rates of CA-MRSA to ciprofloxacin, chloramphenicol, gentamicin and tetracycline were higher (19.0 vs 2.6 %, P<0.001; 14.7 vs 3.1 %, P<0.001; 14.7 vs 3.1 %, P<0.01; and 46.0 vs 13.3 %, P<0.001, respectively). Compared with hospital-associated (HA)-MRSA, the resistance rates of CA-MRSA to ciprofloxacin, gentamicin, rifampicin, tetracycline and trimethoprim–sulfamethoxazole were lower (19 vs 94.8 %, P<0.001; 14.7 vs 84.4 %, P<0.001; 5.5 vs 88.3 %, P<0.001; 46 vs 94.8 %, P<0.001; and 1.8 vs 9.1 %, P<0.01, respectively). The resistance rates of CA-MRSA, HA-MRSA and CA-MSSA to clindamycin (92.0, 77.9 and 64.1 %, respectively) and erythromycin (85.9, 77.9 and 63.1 %, respectively) were high. The MDR rates (resistance to three or more non-β-lactams) were 49.6, 100 and 14 % in the CA-MRSA, HA-MRSA and CA-MSSA isolates, respectively. Five of seven ST clones in the CA-MRSA isolates, namely ST59, ST338, ST45, ST910 and ST965, had MDR rates of >50 % (67.9, 87.5, 100, 50 and 83.3 %, respectively). The constitutive phenotype of macrolide–lincosamide–streptogramin B (MLSB) resistance (69 %) and the ermB gene (38.1 %) predominated among the MLSB-resistant CA S. aureus strains. The resistance rate to mupirocin was 2.3 % and plasmids carrying the mupA gene varied in size between 23 and 54.2 kb in six strains with high-level resistance as determined by Southern blot analysis. The present study showed that resistance to non-β-lactams, especially to clindamycin, is high in CA-MRSA isolates from Chinese children and that the profile of resistance is related to clonal type. This study revealed distinctive patterns of MLSB-resistant genes among CA S. aureus isolates.
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Comparative in vitro efficacies of ethanol-, EDTA- and levofloxacin-based catheter lock solutions on eradication of Stenotrophomonas maltophilia biofilms
More LessThe aim of this study was to compare the in vitro activity of ethanol, EDTA and levofloxacin (Levo), alone or in combination, on biofilms of Stenotrophomonas maltophilia recovered from patients with catheter-related bloodstream infections (CRBSIs) at a university hospital in Argentina. First, 24 and 48 h biofilms were formed in microtitre plates and challenged with 25 or 40 % ethanol for 1 h. Biofilms, of the 14 local isolates and from the reference strain K279a, were eradicated after both treatments as shown by plate counts and the regrowth technique. Second, 24 h biofilms of all isolates were established in silicone catheter segments and challenged with 25 or 40 % ethanol, Levo (2.5 mg ml−1), EDTA (30 mg ml−1), 25 % ethanol–EDTA or Levo–EDTA for 1, 3 and 24 h. Viable counts of biofilms treated for 1 h with 25 or 40 % ethanol or 25 % ethanol–EDTA were under the limit of detection. Killing of biofilms by Levo or Levo–EDTA was gradual and it was only after 24 h of treatment that no differences could be seen between the effects of these catheter lock solutions (CLSs) and those of ethanol (P>0.05). Levo–EDTA, in combination, did not act synergistically against biofilms. After 24 h of exposure, EDTA did not eradicate biofilms but reduced biofilm survival rates to 1–5 %. The effect of the different CLSs on biomass reduction, estimated by crystal violet staining, was highly dependent on the isolate, and the most effective agents were 25 and 40 % ethanol. Our results suggest that when used as a CLS for short periods, ethanol at low concentrations, alone or in combination with a chelator, can decontaminate the line from S. maltophilia in cases of CRBSI and help, in conjunction with systemic antibiotics, in the retention of precious vascular catheters.
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Evidence for the predominance of a single tet(M) gene sequence type in tetracycline-resistant Ureaplasma parvum and Mycoplasma hominis isolates from Tunisian patients
Resistance to tetracyclines in genital mycoplasmas is due mainly to acquisition of the tet(M) determinant, which is frequently associated with conjugative transposon elements of the Tn916/Tn1545 family. The aim of the present work was to evaluate the prevalence of tet(M) in Tunisian isolates and to gain an insight into its origin and evolution. Twenty Ureaplasma parvum, two Ureaplasma urealyticum and 48 Mycoplasma hominis isolates, recovered from Tunisian patients with urogenital and infertility disorders, were evaluated for their resistance to tetracyclines and interrogated by PCR amplification for the presence of tet(M) and int-Tn, the gene encoding the integrase of Tn916/Tn1545-like transposons. The resistance rates to tetracyclines were 22.72 and 25.0 % among U. parvum and M. hominis isolates, respectively, with high-level resistance observed in 11 of the 12 resistant M. hominis isolates. All resistant isolates harboured both tet(M) and int-Tn sequences. Nucleotide sequence analysis of the tet(M) amplicon revealed a unique sequence shared by all tetracycline-resistant clinical isolates of both species. Molecular typing indicated that the tetracycline-resistant U. parvum and M. hominis isolates were not clonal. Taken together, these data indicate that a single tet(M) gene sequence type, most probably transmitted via a Tn916/Tn1545-like transposon, contributes to most of the tetracycline resistance in U. parvum and M. hominis isolates in Tunisia. Because this tet(M) gene sequence type was harboured by different Mycoplasma spp. and by phylogenetically distinct isolates within these species, one could reasonably argue that it may have benefited from an efficient horizontal transfer context, making it highly competent to spread.
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Infecting mice with recombinant Ad5-BPI23-Fcγ1 virus protects against systemic Escherichia coli challenge
More LessInfections caused by Gram-negative bacteria (GNB) are increasingly common and can result in significant mortality rates due to the development of sepsis. To examine the potential usage of a recombinant Ad5-BPI23-Fcγ1 virus as a biological treatment against systemic infection by GNB, a construct containing the human bactericidal/permeability increasing protein (BPI) gene, encoding the functional N terminus (amino acid residues 1–199) of human BPI, and the Fcγ1 gene, encoding the Fc segment of human immunoglobulin G1, was inserted into an adenovirus serotype 5 (Ad5) chromosome to produce a recombinant Ad5-BPI23-Fcγ1 virus. Human A549 cells in culture and BALB/c mice were infected with the recombinant Ad5-BPI23-Fcγ1 virus and BPI23-Fcγ1 expression was confirmed by Western blot analysis and ELISA. The concentrations of BPI23-Fcγ1 protein were 5.59 µg ml−1 in vitro and 21.37 ng ml−1 in vivo and it was observed that these concentrations were sufficient to decrease endotoxin concentrations while enhancing bactericidal activity. In addition, mice treated with the recombinant Ad5-BPI23-Fcγ1 virus had decreased levels of IL-1β and TNF-α and were protected from an E. coli O111 : B4 challenge. Our data support the concept that Ad5-mediated BPI23-Fcγ1 gene delivery could be used as an ancillary biological treatment in the management of infection caused by GNB.
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Porin alterations present in non-carbapenemase-producing Enterobacteriaceae with high and intermediate levels of carbapenem resistance in Chile
The main goal of this work was to identify the mechanisms responsible for carbapenem resistance in 61 Chilean clinical isolates of Enterobacteriaceae (Enterobacter spp., Serratia marcescens, Morganella morganii, Escherichia coli and Klebsiella pneumoniae) with reduced susceptibility to at least one carbapenem (ertapenem, imipenem or meropenem). All of the isolates were analysed for the presence of carbapenemases, extended spectrum β-lactamases (ESBLs), AmpC enzymes and outer-membrane proteins. None of the isolates exhibited carbapenemase activity nor did they have any of the carbapenemase genes that were screened for. Most of the 61 strains produced at least one ESBL and/or one AmpC enzyme and either lost their porins or had altered porins according to sequence analysis. The distribution of ESBLs and AmpC enzymes was different among the species studied. Resistance in K. pneumoniae and E. coli isolates was associated with ESBLs; in M. morganii isolates, resistance was attributed to overexpression of an AmpC enzyme; and in Enterobacter spp. isolates, resistance was associated with both types of enzymes. In K. pneumoniae isolates, porin integrity was more a determinant of carbapenem resistance than the presence of ESBLs, whereas in isolates of Enterobacter spp., M. morganii and S. marcescens, the presence of an overexpressed AmpC enzyme was associated with higher imipenem and meropenem MIC values. Therefore, carbapenem resistance in Chilean isolates is not due to true carbapenemases but rather to a combination of porin loss/alteration and β-lactamase activity. The fact that carbapenemases were not detected in this study is unique, given that many countries in the region have already reported the presence of these enzymes.
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Discovery of a compound that acts as a bacterial PyrG (CTP synthase) inhibitor
More LessPyrG (CTP synthase) catalyses the conversion of UTP to CTP, an essential step in the pyrimidine metabolic pathway in a variety of bacteria, including those causing community-acquired respiratory tract infections (RTIs). In this study, a luminescence-based ATPase assay of PyrG was developed and used to evaluate the inhibitory activity of 2-(3-[3-oxo-1,2-benzisothiazol-2(3H)-yl]phenylsulfonylamino) benzoic acid (compound G1). Compound G1 inhibited PyrG derived from Streptococcus pneumoniae with a 50 % inhibitory concentration value of 0.091 µM, and the inhibitory activity of compound G1 was 13 times higher than that of acivicin (1.2 µM), an established PyrG inhibitor. The results of saturation transfer difference analysis using nuclear magnetic resonance spectroscopy suggested that these compounds compete with ATP and/or UTP for binding to Strep. pneumoniae PyrG. Finally, compound G1 was shown to have antimicrobial activity against several different bacteria causing RTIs, such as Staphylococcus aureus and Haemophilus influenzae, suggesting that it is a prototype chemical compound that could be harnessed as an antimicrobial drug with a novel structure to target bacterial PyrG.
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- Epidemiology
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Chromosomal bla CTX-M-15 associated with ISEcp1 in Proteus mirabilis and Morganella morganii isolated at the Military Hospital of Tunis, Tunisia
This study investigated the genetic environment of bla CTX-M genes and associated resistance genes in seven Proteus mirabilis and six Morganella morganii extended spectrum β-lactamase (ESBL)-positive isolates. The isolates were recovered from hospitalized patients with respiratory or urinary tract infections at the Military Hospital of Tunis, Tunisia. Twenty-one of the 200 strains exhibited non-susceptibility to third generation cephalosporins and, among these strains, the double-disk synergy test confirmed the ESBL phenotype in 13 isolates. These ESBL producers were co-resistant to chloramphenicol, tetracycline and oflaxacin but remained susceptible to ertapenem (MIC<0.25 mg l−1). The presence and nature of bla CTX-M-15, bla CTX-M-8, bla TEM-24, bla TEM-1 and bla TEM-2 genes was determined by PCR and sequencing. Chromosomal localization of the bla CTX-M-15 gene was confirmed in all strains, with the exception of M. morganii isolate M-17991, by Southern-blot analysis performed either on chromosomal or plasmid DNA. M. morganii M-12012 and M. morganii M-6019 showed the same PFGE pattern, whereas the remaining CTX-M-15-producing isolates were unrelated. The presence of ISEcp1 was ascertained in CTX-M-15-producing isolates. A class 1 integron with different gene cassettes (dfrA1, orfC and aadB) was found in five P. mirabilis and six M. morganii isolates.
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- Clinical microbiology and virology
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Carriage of Clostridium difficile in outpatients with irritable bowel syndrome
Irritable bowel syndrome (IBS) is a common, typically chronic and sometimes disabling gastrointestinal condition of uncertain aetiology. Recently, a variety of links to gastrointestinal infections have been described including the onset of IBS following exposure to enteric pathogens and an apparent predisposition to gastrointestinal infection. The prevalence of Clostridium difficile in a population of IBS outpatients (n = 87) in the absence of established risk factors for the acquisition of C. difficile infection was examined. Overall, 5.7 % of patients (n = 5) carried culturable C. difficile and 4.6 % (n = 4) of isolates were toxigenic, belonging to toxinotype group 0, compared with 1.1 % (n = 1) for the healthy control group (n = 88). These isolates were members of toxigenic PCR ribotype groups 005 and 050 (IBS group) and 062 (control group) and were identified further as three individual strains by PFGE. Although no significant difference was observed between IBS patients and healthy volunteers, these findings support the concept that a subpopulation of IBS patients may be susceptible to gastrointestinal infection.
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Significant association of the dupA gene of Helicobacter pylori with duodenal ulcer development in a South-east Indian population
A novel virulence factor, duodenal ulcer-promoting gene A (dupA), in Helicobacter pylori has been found to be associated with disease in certain populations but not in others. This study analysed a South-east Indian population as part of the debate about the relevance of dupA for the prediction of clinical outcomes. A total of 140 H. pylori strains isolated from duodenal ulcer (DU) (n = 83) and non-ulcer dyspepsia (NUD) patients (n = 57) were screened by PCR and dot-blot hybridization to determine the presence of the ORFs jhp0917 and jhp0918. Part of jhp0917–jhp0918 was sequenced to search for the C/T insertion that characterizes dupA and the levels of dupA transcripts were also assessed. The PCR and dot-blot results indicated the presence of jhp0917 and jhp0918 in 37.3 % (31/83) and 12.2 % (7/57) of H. pylori strains isolated from DU and NUD patients, respectively. Sequencing analysis showed insertion of a C at nt 1386 in the 3′ region of jhp0917, forming the dupA gene in 35 strains. RT-PCR analysis detected the dupA transcript in 28 of these 35 strains. The expression level of the dupA transcript varied from strain to strain, as shown by real-time PCR. The results demonstrated that analysis based on PCR only for dupA may produce an erroneous interpretation. The prevalence of dupA was significantly greater among strains isolated from patients with DU than from patients with NUD in this population (P = 0.001, odds ratio = 4.26, confidence interval = 1.60–11.74). Based on these findings, dupA can be considered a biomarker for DU patients in India. The reported discrepancies for this putative virulence marker in different populations may be due to the genome plasticity of H. pylori.
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Genetic characteristics of one highly multi-drug-resistant strain of Klebsiella ozaenae
More LessOne highly multi-drug-resistant, mucus-producing and foul-smelling strain of Klebsiella ozaenae was isolated from a patient in the ICU of a Chinese tertiary hospital. MICs of several clinical antimicrobials against the strain were obtained using the Vitek-2 Compact System with AST-GN13 cards and resistance genes were evaluated by PCR and gene sequencing. The strain was resistant to most of the β-lactams and quinolones tested and carried several antibiotic resistance genes, including bla KPC-2, bla TEM-98, bla CTX-M-3, bla SHV-26 and qnrS. To our knowledge, this is the first report of β-lactam and quinolone resistance genes co-existing in a K. ozaenae strain in China.
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Re-evaluation of rejection criteria for endotracheal tube (ETT) specimens from adult patients
More LessThe purpose of this study was to determine optimal criteria for microbiology laboratory screening of endotracheal tube (ETT) specimens submitted for bacterial culture from adult patients. ETT specimens from adult patients that were received by two microbiology laboratories were prospectively evaluated and subdivided into one of three study arms with the following criteria: <10 squamous epithelial cells (SECs) per low-power field with bacteria seen on Gram staining (arm 1), >10 SECs per low-power field with bacteria seen on Gram staining (arm 2) and <10 SECs per low-power field with no bacteria seen on Gram staining (arm 3). A fourth study arm (>10 SECs per low-power field with no bacteria seen on Gram staining) was planned but this arm was terminated due to the paucity of specimens meeting these criteria. Isolate evaluation was performed using standard microbiology protocols. A limited chart review was undertaken at one of the institutions, only reviewing patients from which a potential pathogen was recovered on culture. In total, 141 ETT specimens were evaluated. A potential respiratory pathogen was recovered from 54, 37 and 10 % of specimens in study arms 1, 2, and 3, respectively (P<0.0001, comparing between arm 1 and arm 3). For the 23 patients included in the chart review from whom a potential pathogen was recovered on culture, respiratory infection was considered to be present in 50 % (6/12) of patients in arm 1, 66.6 % (6/9) of patients in arm 2 and 100 % (2/2) of patients in arm 3. Therapy was rarely altered based on culture results. In this study, the ETT specimens submitted for bacterial culture were of limited benefit to clinicians. The data presented here support the use of an absence of bacteria on Gram staining as a rejection criterion for ETT specimens. The criterion of >10 SECs per low-power field should be further evaluated in a prospective study of patients with an unequivocal clinical diagnosis of pneumonia.
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- Veterinary microbiology
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A novel intranasal mouse model for mucosal colonization by Streptococcus suis serotype 2
Streptococcus suis causes meningitis and various other diseases in pigs and humans. Healthy piglets carrying virulent Streptococcus suis strains on their mucosal surfaces are epidemiologically very important. The objective of this study was to establish an intranasal Streptococcus suis mouse model for invasion and colonization of the respiratory tract. CD1 mice were infected intranasally with a highly virulent Streptococcus suis serotype 2 strain under different conditions. Clinical, histological and bacteriological screenings revealed that invasion of host tissue occurred in the majority of mice only after predisposition with 12.5 µl 1 % acetic acid per nostril. Severe fibrinosuppurative or purulent necrotizing pneumonia associated with Streptococcus suis was a common manifestation. Furthermore, a novel model to study nasopharyngeal colonization was established by reducing the volume of 1 % acetic acid per nostril to 5 µl prior to Streptococcus suis application. This model mimics asymptomatic carriage in swine, as all mice carried Streptococcus suis on their respiratory mucosa at 7 days post-infection (p.i.) in moderate to high numbers without the development of pneumonia or any other invasive Streptococcus suis disease. This intranasal Streptococcus suis model was applied to investigate the function of suilysin (SLY) in colonization. Although an isogenic SLY mutant was isolated from the upper respiratory tract at a lower recovery rate than its wild-type parental strain at 14 days p.i., the differences were not significant and did not indicate severe attenuation in colonization. In conclusion, this work describes to the best of our knowledge the first intranasal mouse model to study colonization of the respiratory tract by a highly virulent Streptococcus suis pathotype.
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- Models of infection
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Natural and experimental Helicobacter pullorum infection in Brown Norway rats
Helicobacter pullorum is an enterohepatic Helicobacter species (EHS) that was recently reported as a naturally acquired infection in mice. Faecal samples from 18 out of 20 Brown Norway (BN) rats, housed in the same barrier as the H. pullorum-infected mice, were positive for H. pullorum using species-specific PCR. In addition, we determined whether H. pullorum was able to persistently colonize the gastrointestinal tract and/or biliary tree and elicit tissue inflammation as well as a serum IgG response in BN rats. Six (four male, two female) 6-week-old, H. pullorum-negative BN rats were orally dosed with 4×108 c.f.u. of H. pullorum every other day for a total of three doses. At 2 weeks post-infection, all rats were H. pullorum-positive by faecal PCR. Five out of the six BN rats remained H. pullorum-positive for the entire 30 week study. PCR analysis of tissue collected at necropsy confirmed that the colon and caecum were the primary sites of H. pullorum colonization. Rats that were persistently colonized by H. pullorum had a sustained H. pullorum-specific IgG response measured by ELISA. Intestinal or hepatic pathology associated with H. pullorum infection was not noted. To our knowledge, this is the first report documenting that rats can be persistently colonized with an EHS that also infects humans.
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- Case reports
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Life-threatening Escherichia coli cellulitis in patients with haematological malignancies
Cellulitis due to Escherichia coli is rare and usually secondary to a cutaneous portal of entry. Skin and soft tissue infections (SSTI) secondary to E. coli bacteraemia have been reported exclusively in immunodeficient patients. Here, we report two cases of serious cellulitis secondary to E. coli bacteraemia in patients with haematological malignancies. Both isolated strains belonged to phylogenetic group B2 and harboured some of the main virulence factor genes commonly found in extra-intestinal pathogenic E. coli (ExPEC), including neuC, iro and fimH. Cellulitis due to E. coli seems to be linked to the immunocompromised status of patients rather than to a highly virulent clone. Nevertheless, some of the virulence factors appear to be important because both isolates belong to phylogenetic group B2. This aetiology should be considered in SSTI in patients with haematological malignancies.
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Volumes and issues
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Volume 73 (2024)
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Volume 72 (2023 - 2024)
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Volume 71 (2022)
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Volume 70 (2021)
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Volume 69 (2020)
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Volume 68 (2019)
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Volume 67 (2018)
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Volume 66 (2017)
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Volume 65 (2016)
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Volume 64 (2015)
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Volume 63 (2014)
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Volume 62 (2013)
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Volume 61 (2012)
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Volume 60 (2011)
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Volume 59 (2010)
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Volume 58 (2009)
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Volume 57 (2008)
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Volume 56 (2007)
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Volume 55 (2006)
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Volume 54 (2005)
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Volume 52 (2003)
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Volume 51 (2002)
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Volume 49 (2000)
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Volume 48 (1999)
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Volume 47 (1998)
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Volume 46 (1997)
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Volume 45 (1996)
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Volume 44 (1996)
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Volume 43 (1995)
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Volume 42 (1995)
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Volume 41 (1994)
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Volume 40 (1994)
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Volume 39 (1993)
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Volume 38 (1993)
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Volume 37 (1992)
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Volume 36 (1992)
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Volume 35 (1991)
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Volume 34 (1991)
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Volume 33 (1990)
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Volume 32 (1990)
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Volume 31 (1990)
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Volume 30 (1989)
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Volume 29 (1989)
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Volume 28 (1989)
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Volume 27 (1988)
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Volume 26 (1988)
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Volume 25 (1988)
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Volume 24 (1987)
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Volume 23 (1987)
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Volume 22 (1986)
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Volume 21 (1986)
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Volume 20 (1985)
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Volume 19 (1985)
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Volume 18 (1984)
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Volume 17 (1984)
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Volume 16 (1983)
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Volume 15 (1982)
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Volume 14 (1981)
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Volume 13 (1980)
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Volume 12 (1979)
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Volume 11 (1978)
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Volume 10 (1977)
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Volume 9 (1976)
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Volume 8 (1975)
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Volume 7 (1974)
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Volume 6 (1973)
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Volume 5 (1972)
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Volume 4 (1971)
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Volume 3 (1970)
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Volume 2 (1969)
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Volume 1 (1968)