- Volume 47, Issue 7, 1998

Study of the epidemiology of childhood infection reveals that the brunt of disease for a number of invasive bacterial infections is borne by children under the age of 4 years. Haemophilus influenzae type b (Hib), Neisseria meningitidis and Streptococcus pneumoniae, the three most important causes of childhood meningitis, illustrate this phenomenon, which is caused by the inability of infants and young children to mount antibodies to the carbohydrates that form a capsule surrounding these organisms. Carbohydrates are traditionally viewed as T-independent antigens with a number of unique and important immunological properties that are not encountered when inducing an immune response to proteins. These properties include no overt requirement for the presence of T cells to induce an immune response, dominance of IgM, failure to induce memory following immunisation, an absence of affinity maturation following immunisation, and poor immunogenicity in infants, the elderly and the immunocompromised. These properties of carbohydrates have precluded the use of pure carbohydrate vaccines in those patients most at risk. Conjugate vaccine technology, where a carbohydrate antigen is coupled chemically to a protein carrier, has overcome the limitations of carbohydrates as vaccine antigens by rendering the carbohydrate moiety of such vaccines immunogenic, even in the very young. The dramatic success of the Hib conjugate vaccines, the first conjugates licensed clinically for human use, in reducing the incidence of invasive Hib disease has demonstrated the potential value of such conjugate vaccines. Similar technology is, therefore, being applied to a number of other vaccines in development, including N. meningitidis (groups A and C) and S. pneumoniae vaccines. The large number of pneumococcal carbohydrate serotypes that require inclusion in a vaccine makes this conjugate formulation far more complicated than that for Hib, and it is likely that the dramatic success of the Hib conjugate vaccines will be more difficult to repeat for the pneumococcus.

The natural antibiotic susceptibility of 38 Providencia rettgeri, 35 P. stuartii, 23 P. alcalifaciens and 20 P. rustigianii strains was examined. MIC values were determined by a microdilution procedure and evaluated by a table calculation programme. P. stuartii was the least susceptible Providencia sp. and was naturally resistant to tetracyclines, some penicillins, older cephalosporins, sulphamethoxazole and fosfomycin and to antibiotics to which other species of Enterobacteriaceae are also resistant. It was naturally sensitive to modern penicillins and cephalosporins, carbapenems and aztreonam, but its susceptibility to aminoglycosides and quinolones was difficult to assess. P. alcalifaciens and P. rustigianii strains were the most susceptible Providencia spp. They were naturally sensitive or intermediate to tetracyclines and sensitive to aminoglycosides and quinolones. Susceptibility to sparfloxacin, biapenem and sulphamethoxazole permitted the discrimination of P. alcalifaciens and P. rustigianii strains. The natural antibiotic susceptibility of P. rettgeri strains was between that of P. stuartii and that of the other providenciae. P. rettgeri was resistant to tetracyclines and fosfomycin, but more susceptible to aminoglycosides, quinolones, fosfomycin and numerous β-lactam antibiotics than P stuartii. A database is described of the natural antibiotic susceptibilities of Providencia spp. It can be used for the validation of antibiotic susceptibility test results of these micro-organisms.

The aim of this retrospective study was to determine the clinical spectrum of group B streptococcal (GBS) bacteraemia in patients over 70 years old. Sixty-six adults with GBS bacteraemia were reviewed over a 5-year period. Disease characteristics, clinical diagnoses and underlying disease were compared in 33 older patients (mean age 82.4 years) and 33 younger patients (mean age 54.2 years). The older patients were also compared with a control group (mean age 81.3 years). Urinary tract infection (39%), skin infection (33%) and pneumonia (24%) were the most frequent clinical diagnoses in older patients. Urinary tract infection (39% versus 6%) was significantly more frequent in older than in younger patients. One underlying disease and one condition were more frequent in elderly patients: congestive heart failure (39% versus 6%) and being bedridden (36% versus 0%). A comparison with the older control group showed that being bedridden was highly associated with GBS bacteraemia and was an important mortality factor amongst older patients (10% versus 30%). In conclusion, GBS disease in the elderly was found to be a severe clinical problem with a high mortality despite appropriate treatment.

Actinobacillus actinomycetemcomitans is considered to be an aetiological agent in various forms of periodontitis, with serotype b-specific carbohydrate being the immunodominant antigen of A. actinomycetemcomitans Y4 in high-responder patients. Lipopolysaccharide (LPS) of the organism may also be an important antigen. The purpose of the present study was to clarify the importance of LPS as an antigen of A. actinomycetemcomitans. Twenty patients who had high antibody titres to strain Y4 were selected, and the reactivity of their sera with LPS was determined by ELISA and Western blotting. Two groups of patients were observed: group 1 had high IgG titres only to serotype b strain, whereas group 2 had high IgG titres to serotypes a, b and c strains. The results of adsorption tests showed that anti-A. actinomycetemcomitans Y4 antibody in group 1 patients mostly consisted of antibody reactive with the serotype b-specific carbohydrate, whereas the antibody in group 2 patients mostly consisted of antibody reactive with the LPS of all serotypes. These data show that anti-LPS antibody is present and predominant in anti-A. actinomycetemcomitans Y4 antibody from some high-responder patients, and indicate an important role for LPS as an antigen in the humoral immune response to the organism.

Bacteraemia and subsequent sepsis is one possible complication of Clostridium difficile infection. The aim of this study was to examine a correlation between bacterial translocation with morphological changes of intestinal mucosa and shifts of intestinal microflora in experimental models of C. difficile infection. A mouse model was used to study post-antibiotic shifts and mild C. difficile infection, and hamsters were used to study fatal enterocolitis. The influence of pro- and pre-biotics (lactobacilli and xylitol) were also studied in the hamster model. The quantitative composition of luminal and mucosal microflora was evaluated in different intestinal loci, inflammatory changes of mucosa were estimated in histological sections and bacterial translocation was detected in samples from blood, liver, spleen and mesenteric lymph nodes. In cases of mild C. difficile infection, the extent of disturbance of intestinal microflora appeared to be a more important promoting factor in translocation than inflammatory activity in the mucosa. Translocation was frequent in fatal enterocolitis, with facultative species predominating in the intestinal mucosa and also C. difficile in some cases. The combination of lactobacilli and xylitol had some protective effect against C. difficile infection in these models.

A multiplex polymerase chain reaction (PCR), involving detection of the mecA and femB genes, was combined with a novel immunoassay system capable of detecting specific PCR products. The resulting PCR-immunoassay was evaluated in comparison with conventional microbiological techniques used in the routine diagnostic laboratory for the rapid identification of methicillin-resistant Staphylococcus aureus (MRSA), either in pure culture or in overnight broth cultures obtained following enrichment of patient screening swabs. Among the 480 purified isolates of staphylococci and 246 enrichment broths examined, only one ‘false-negative’ result was obtained by PCR, compared with 18 ‘false-negative’ results obtained by conventional methodology and demonstrated by further conventional examination. Five demonstrable ‘false-positive’ results were obtained by conventional methodology, compared with a possible 10 by the PCR-immunoassay, although it was not certain that these 10 PCR results were true ‘false positives’ as, by definition, MRSA could not be isolated by conventional methodology. The results indicated that the routine diagnostic laboratory was encountering difficulties in identifying MRSA correctly, and that the conventional microbiological techniques lacked sensitivity. Overall, the PCR technique was more accurate and sensitive than conventional methodology in detecting MRSA, and results were available within 24 h of screening swabs arriving in the laboratory, compared with a minimum of 48–72 h by conventional techniques. The immunoassay system added to the usefulness of the method by allowing the detection of specific PCR products within 5 min of completing the PCR, without the normal additional step of agarose gel electrophoresis.

CHROMagar, a chromogenic differential culture medium, is claimed to facilitate the isolation and presumptive identification of certain clinically important yeast species, e.g., Candida albicans. This study evaluated the cost-effectiveness and time advantage of using it in comparison with Sabouraud dextrose agar (SDA). Three possible pathways, each of which included the use of one or both media, were compared in a routine laboratory. A total of 21 yeast isolates was cultured from 298 clinical samples from neutropenic and AIDS patients. An overall sensitivity of 95.2% was observed for each medium and primary isolation on CHROMagar was found to be 100% sensitive and 100% specific for C. albicans. For identification purposes, after initial culture the use of CHROMagar provided the most economical and least time-consuming method. Direct inoculation on to CHROMagar is recommended for blood cultures when yeast cells are seen on microscopy and where early appropriate therapy is imperative.

Hepatitis C virus (HCV) is an important human pathogen that can cause acute and chronic hepatitis, liver cirrhosis and hepatocellular carcinoma. Recently, partial and entire sequence data from HCV isolates have been reported, suggesting various genotypes of HCV. The genotype may be correlated with the progression of hepatitis and maybe a prognostic marker of treatment. Thus, the availability of an assay for typing HCV RNA is important. This study developed a convenient method for genotyping HCV into six groups by PCR-RFLP with four restriction endonucleases (BstUI, HaeIII, NciI, RsaI) in the 5′ untranslated region (UTR) of HCV. The HCV genotypes from 169 patients with HCV infections in Korea were analysed. Two genotypes, type 1b and type 2a, accounted for 47.3% and 42.6% of HCV infections, respectively.