Of 2458 isolates of Haemophilus influenzae examined in a recent British survey, 42 were resistant to chloramphenicol. Two resistant isolates were of type b and 40 were non-capsulate. Spectrophotometric assay showed that all the resistant isolates produced chloramphenicol acetyltransferase (CAT). CAT activity did not increase following growth onheated blood agar containing chloramphenicol 2 mg/L but was reduced by 84-98% when extracts were treated for 30 min with 5', 5'-dithiobis-2-nitrobenzoate. These data suggest thatH. influenzae CATs resemble the Type-II CATs produced by enterobacteria. Extrachromosomal DNA was detected in five only of the 42 resistant isolates and cured derivatives of two plasmid-containing strains retained their chloramphenicol resistance. These results suggest that the CAT gene is located on the chromosome.
We questioned whether the penicillin binding protein (PBP) profiles of representativestrains from the 19 species varied within the genus Haemophilus and whether these profiles would be of taxonomic value. Seventeen of the 19 representative strains studied had distinct PBP profiles; only those of H. avium and H.paragallinarum wereidentical. The data support the inclusion of H. aegyptius in the genus as a species related to but separate from H. influenzae and could not exclude H. somnus, H.agni, and H. equigenitalis from the genus. Comparative PBP analysis within the genus Haemophilus may therefore be useful taxonomically.
The effects of chlorpromazine (CPZ), berberine and verapamil on intestinal hypersecretion in the rabbit ileal loop model by the heat-labile enterotoxin (LT) of Escherichiacoli were studied in relation to their ability to inhibit the stimulation ofintestinal adenylate cyclase (AC) by LT. CPZ 5 mg by the intraluminal (i.l.) route and 4 mg/kg bythe intramuscular (i.m.) route significantly reduced LT-induced intestinal hypersecretion. Berberine (10 mg) exerted an inhibitory effect, but only after i.l. administration, whereas verapamil did not exert any significant inhibitory effect when administered eitheri.l.(2.5 mg) or i.m. (4 mg/kg). At concentrations of (0.17-1.34) x 10-3 M CPZ, the anti-secretory effect of CPZ correlated with its inhibitory effect on rabbit LT-stimulated intestinal AC. Inhibition of cAMP synthesis was probably not involved in the mechanism of action of the two other substances. These results indicate that CPZ and phenothiazines in general are efficient drugs for reducing LT-induced intestinal hypersecretion and could represent a model for synthesis of new anti-secretory drugs with no tranquiliser side effects.
Dental implant research has been mostly concerned with the biocompatibility of materials for implantation. In this study the effects of titanium dioxide and other metallic salts on seven bacterial species commonly found in dental plaque, two which are uncommon, and a yeast, were determined by agar incorporation and diffusion techniques, and compared with the effects of a titanium implant abutment. Neither the titanium dioxide nor the implant abutment demonstrated any inhibitory activity, although other compounds such as cobalt used in dental alloys had some effects.
The pathogenicity of 20 strains belonging to nine bacterial species isolated from acute dentoalveolar abscesses was assessed individually and in two species combinations by subcutaneous inoculation of mice. Infections were produced by all the bacteria although variations were seen both in the type of lesion produced and the subsequent recovery of viable bacteria. Anaerobic gram-negative bacilli were recovered more often (p0.05) at high concentrations (106-109 cfu/ml) and produced a localised abcess with peripheral necrosis more frequently (p0.001) than either Streptococcus milleri or anaerobic gram-positive cocci. Lesions induced by a combination of bacteria comprising an anaerobic gram-negative bacillus and any other species yielded both strains at high concentration more often (p0.001) than a combination comprising anaerobic gram-positive cocciand S. milleri. It is concluded that anaerobic gram-negative bacilli are major pathogens in acute dentoalveolar abscesses.
Clinical isolates of Staphylococcus aureus from the London Hospital were characterised by genetic analysis of antibiotic-resistance determinants and by restriction endonuclease digestion of chromosomal DNA and compared with isolates from elsewhere in the UK. Restriction enzyme digestion of chromosomal DNA confirmed that a single strain of methicillin-resistant S. aureus (MRSA) persists at the London Hospital, although its antibiotic-resistance profile and plasmid carriage are not constant. Methicillin-sensitive isolates, on the other hand, each had readily distinguishable and unique DNA restriction patterns. The DNA restriction digest pattern of the London Hospital MRSA isolates was identical to that of ‘epidemic’ (E) MRSA isolates from the Thames regions. By contrast, other MRSA isolates had DNA restriction patterns which differed from those of EMRSA isolates and from each other. These results confirm the discriminatory value of restriction pattern analysis as a typing method.
The opsonic activity of human serum from various sources against Campylobacterpylori was compared. All sera, whether from control subjects with no symptoms of gastritis or peptic ulceration, or from symptomatic patients from whom C. pylori had or had not been isolated, opsonised C. pylori equally well. Opsonisation depended on the alternative pathway of complement activation but not on antibody. These findings suggest that antibody plays no role in protection against C.pylori and that the presence of antibody in patients' sera is mainly of diagnostic value.
The virulence of representative strains of the five species of Listeria monocytogenes sensu lato was compared in C57BL/6 and BALB/c mice in terms of LD50 values and ofbacterial growth kinetics and histological changes in mouse livers. L. monocytogenes sensu stricto and L. ivanovii showed relatively low LD50 values and much bacterial growth for 2-3 days before viable counts declined. Histological changes in L. ivanovii infection resembled those caused by L. monocytogenes, with early development of neutrophil-rich micro-abscesses and hepatocyte necrosis followed by macrophage infiltration and formation of granulomas. By contrast, L. innocua, L. welshimeri and L. seeligeri were almost entirely avirulent as shown by high LD50 values, early elimination of viable bacteria and no evidence of growth. Histological changes consisted only of slight, transient infiltration of the liver with neutrophils. Both groups of bacteria were seen infrequently in Kupffer cells early in infection, but only the highly virulent species appeared to replicate. LD50 values for L. monocytogenes and L. ivanovii were (10-20)-fold greater, and for the less virulent bacteria at least two-fold greater, in C57BL/6 than in BALB/c mice. This difference in host susceptibility was not reflected in detectable histological differences between the two mouse strains.
A series of 698 strains of group A β-haemolytic streptococci (GAS) isolated from cildren with streptococcal pyoderma was tested for production of serum opacity factor (OF)and nicotinamide adenine dinucleotide glycohydrolase (NADase). OF was produced by 37% of strains and 40% produced NADase. Classification based on various combinations of OF and NADase reactions showed that 58% belonged to enzyme group e1 and 34% to e2. Correlation with T and M types showed the possible use of this means of classification as an epidemiological marker for GAS. The specificity of such a system in the further classification of various T types of GAS in epidemiological studies, in the light of antigenic variation among M types, is described.
Serological variation in 71 oral isolates and three reference strains of Streptococcus milleri was examined. Antisera were raised by immunising rabbits with cells of 10 selected strains, followed by absorption of non-specific antibodies. Double diffusion of the typing sera and the Rantz and Randall extracts of the strains in agar gel demonstrated that 70 strains were divided into 10 serotypes (a-j) on the basis of cell-surface carbohydrate antigens. Only four strains were untypable. The typing scheme proposed depends on type antigens other than the Lancefield group antigens A, C, F, G and others, although strains belonging to the serotypes a, c and f strictly corresponded to those of the groups A, C and F respectively. Close correlation between the present serotyping scheme and the previously proposed biotyping scheme for S. milleri was demonstrated. Distribution of these strains in dental plaque obtained from young adults was also investigated.
One hundred and fifty isolates of Campylobacter pylori were divided into nine groups by immunoblot fingerprinting. All isolates were typable and reproducibility between immunoblots was good provided both antigen and antibody preparation were standardised. Discrimination was a problem as Groups 1 and 2 accounted for 66% of isolates. Recurrence after bismuth treatment was due to indistinguishable strains in five patients and different strains in three patients.