- Volume 19, Issue 3, 1985

Yersinia enterocolitica is an important cause of enteritis and mesenteric adenitis in many countries. However the pathogenesis of the disease caused by this organism has not been fully elucidated. Most isolates from clinical material possess two independent properties associated with virulence whose relative contribution to the development of disease is not known. These are the ability to penetrate the intestinal wall, which is thought to be controlled by a plasmid gene, and the production of heat-stable enterotoxin, which is controlled by a chromosomal gene. In this study, we infected neonatal gnotobiotic piglets with strains of Y. enterocolitica expressing these two properties in various combinations. The suitability of the piglet model was shown in experiments in which piglets fed virulent Y. enterocolitica serogroup O3 developed a clinical illness related to the size of the inoculum, which was accompanied by intestinal lesions similar to those reported in naturally and experimentally infected people and animals. The results confirmed the key role of a 47 × 106-mol. wt plasmid in the pathogenicity of Y. enterocolitica, but suggested that penetration of the intestinal wall may be governed by chromosomal rather than plasmid-borne genes. No role for enterotoxin in the pathogenesis of yersiniosis was shown, although there was evidence that enterotoxin may promote intra-intestinal proliferation of Y. enterocolitica, thus favouring increased shedding of bacteria and encouraging their spread between hosts.

Six of 11 test strains of Yersinia enterocolitica and related species that carried other markers of pathogenicity were found to associate with Henle 407 epithelial cells in vitro. All Henle-positive strains were hydrophobic when tested by hydrophobic interaction chromatography with phenyl-Sepharose and by partitioning in an aqueous-hexadecane mixture. Hydrophobicity was also exhibited by some of the Henle-negative strains. None of the test strains aggregated in low concentrations of ammonium sulphate, suggesting that protein structures such as fimbriae were not involved in hydrophobicity or epithelial cell association.

Summary. Group-B streptococci that possess a type-specific surface polysaccharide undergo phagocytosis only in the presence of antibodies to this, and complement. The snail Cepaea hortensis forms a lectin that is specific for sialic acid; treatment with this promoted the phagocytosis of a group-B streptococcus of serotype Ia (strain O90) in the absence of opsonic antibodies. The effect of the lectin was dose-dependent and required the presence of complement. The specificity of the lectin reaction for sialic acid was proved by the inhibition of phagocytosis by bovine submaxillary mucin. The participation of complement in the reaction was confirmed by demonstrating that C3 was bound to the surface of lectin-treated cells.

An animal model is described for quantitative evaluation of pathogenic synergy between Escherichia coli and Bacteroides fragilis in which adjuvants were not required for abscess formation. Two sets of strains of E. coli and B. fragilis isolated from human wound infections were tested. Pathogenic synergy was observed in only one of the two combinations and was dependent on properties of E. coli.

Chemiluminescence (CL) of human polymorphonuclear leukocytes was determined after stimulation with 89 clinical isolates of Klebsiella which differed in serotype and in their virulence for mice. With K1, K2, K4 and K5 strains, a significantly lower CL response was observed than with K3, K6 and K > 6 strains. These results correlated well with virulence: greater virulence could be explained by greater resistance to phagocytosis.

Prior colonisation of clindamycin-treated hamsters with non-toxigenic strains of C. difficile protected them from subsequent colonisation with a toxigenic pathogenic strain. In total, 13 of 18 ‘protected’ hamsters survived for up to 27 days whereas all 27 animals challenged with the toxigenic strain alone died within 48 h. Protection was not evident if a heat-killed suspension was used or if the colonising non-toxigenic strain was first removed with vancomycin. No antitoxic activity could be detected in the faeces of animals colonised with the non-toxigenic strains. Other species of clostridia did not protect against the lethal effects of subsequent exposure to the toxigenic strain. Conversely, non-toxigenic strains would not protect the animals from the lethal effects of a different clostridial pathogen, C. spiroforme. In most cases, even in the protected animals, the toxigenic strain eventually became dominant and caused disease, with translocation across the gut wall occurring early in the disease process. It was also shown that a non-toxigenic strain of C. difficile can adhere to gut mucosa. It is proposed that the protection afforded by the non-toxigenic strains may be due to competition for ecological niches.

Heated spores (80°C, 10 min) of Clostridium butyricum strain CB 1002 isolated from a fatal case of necrotising enterocolitis in a human neonate were inoculated into ligated intestinal loops prepared in young conventional guinea pigs. Necropsy findings 18 h later included congestion, patchy haemorrhage of the intestinal mucosa and bacteraemia. No abnormalities were observed in control loops given inocula of inactivated spores (heated at 100°C for 10 min) or TYG 6 medium. The results suggest that vascular lesions are produced by C. butyricum in the intestine of young conventional guinea pigs.

Summary. Spirochaetes were recognised in the large bowel of 57 of 59 baboons as a basophilic fringe at the microvillous brush border of the epithelial cells. Both caecum and colon were usually affected, but seven animals had spirochaetes in the caecum alone. Examination of three animals by transmission electronmicroscopy revealed only one type of spirochaete; ring forms and cross-walls were present. Inflammatory changes were not seen in association with the infection, and the distribution of spirochaetes in 10 animals with soft or diarrhoeic faeces resembled that in normal animals.

Summary. Antigen extracts obtained by sonication of 22 strains of Mycobacterium bovis from cattle and badgers together with extracts of strains of M. tuberculosis, M. paratuberculosis, M. avium, M. africanum, M. kansasi, M. leprae and BCG were examined with a panel of 10 monoclonal antibodies to M. tuberculosis or M. leprae. Antigen extracts were coated in aqueous solution (wet coating) and the extracts were also dried on to the polyvinyl plates (dry coating). When dry coating was compared to wet coating, there was a major increase in the binding of monoclonal antibody ML03 to M. avium and M. paratuberculosis, monoclonal antibody ML02 to M. paratuberculosis, and monoclonal antibodies TB71 and TB72 to the majority of M. bovis isolates.

The study confirmed that on wet-coated plates, monoclonal antibodies TB71 and TB72 bind poorly or not at all to M. bovis and that monoclonal antibodies TB68, TB78, TB77 and TB23 each bind to field strains of M. bovis while TB23 binds poorly to BCG in wet-coating conditions. Antibodies TB72 and TB71, originally thought to be specific for M. tuberculosis, each reacted with M. africanum. Antibody TB78 bound to M. paratuberculosis but did not react with M. avium, and M. avium and M. paratuberculosis were distinguished from M. bovis and M. tuberculosis by the binding of antibody ML03 to dry-coated plates. When wet-coated plates were used, ML03 bound strongly only to M. leprae. The panel of monoclonal antibodies did not demonstrate distinct serotype differences between the field isolates of M. bovis.

The outer surface structure of clinical isolates of Pseudomonas aeruginosa resistant to carbenicillin or gentamicin or both was studied by thin-section electronmicroscopy and compared with that of sensitive isolates. The latter had a fairly smooth outer layer. Strains resistant to both antibiotics were characterised by extrusions that appeared to constitute extensions of the outer membrane. The outer membrane appeared wavy with distortion of its tripartite structure. The latter findings were also present in isolates resistant to only one of the two antibiotics. The disorganisation of the outer membrane might contribute to the expression of resistance.

The morphological response of two strains of Legionella pneumophila to ampicillin 10 μg/ml and erythromycin 10 μg/ml in vitro was studied by electronmicroscopy, MIC estimations and viable counts. In the presence of ampicillin, discrete lesions appeared in the bacterial cell walls through which cytoplasmic contents extruded and lysis occurred. A few spheroplasts, together with minicells of 0·15 μm diameter, and apparently normal cells were present after exposure to ampicillin for several hours. Conversely, erythromycin initially resulted in inhibition of division and the formation of filamentous organisms. The cell walls of these filaments were eventually disrupted with numerous small membranous vesicles appearing on their surfaces. On further erythromycin treatment, breakage of the cell wall at a restricted number of sites occurred, leading to cell lysis. In the presence of erythromycin, a few morphologically normal cells were present but no spheroplasts or minicells were observed. Viable counts demonstrated that ampicillin killed the bacteria faster than erythromycin. Regrowth did not occur in the continued presence of either antibiotic, but after their removal regrowth was observed.

Prednisolone, given orally or intraperitoneally before challenge, protected mice against the lethal effect of a crude cell extract of Bordetella pertussis containing heat-labile toxin (HLT) as the major toxic component. Prednisolone did not diminish the lethal toxicity of heated B. pertussis cell suspensions containing pertussis toxin and endotoxin but devoid of HLT. This suggests that the protective effect of the steroid was directed against the HLT. When live bacteria were injected intraperitoneally, prednisolone showed a protective effect against the initial toxaemia. By day 7, however, the protection was no longer evident and the steroid promoted the survival of the organisms within the peritoneal cavity. These findings are discussed in the light of reports of the beneficial effects of corticosteroids in the treatment of whooping cough and in relation to a possible role for HLT in the pathogenesis of the disease.