- Volume 40, Issue 2, 1994

Seventy-one Escherichia coli strains isolated from diarrhoeic weaned rabbits from different areas of France were tested for the presence of DNA sequences specific for the EPEC, EHEC, DAEC and EAggEC strains and 16 of them were tested for pathogenicity in animal experiments. High pathogenicity was observed only with strains unable to ferment rhamnose. DNA from all 55 rhamnose-negative O103,O26 and rough strains hybridised with the eaeA probe. Similar hybridisation was obtained with six non-pathogenic rhamnose-positive strains belonging to serogroups O128 and O132. No hybridisation was observed with the other probes. This is the first report of the presence of eaeA sequences in genomic DNA of non-pathogenic strains.

Three hundred and nine strains of Escherichia coli isolated from infants and children with diarrhoea but not belonging to any recognised classes of diarrhoeagenic E. coli were investigated for their ability to adhere to HeLa cells in the presence of D-mannose. An enteroadherent-aggregative pattern (EAgg) was observed in 32·03%, localised adherence (LA)in 4·5%, diffuse adherence (DA) in 5·8%, and LA/DA and EAgg/LA in 1·9% and 1·2% of the isolates respectively. The results obtained with 100 control isolates were: EAgg 17%, LA 2%, DA 2%, LA/DA 2%, EAgg/LA 6% and DA/EAgg 1%. No adherence was manifested by 168 (54·36%) of 309 diarrhoeal isolates and 70% of the 100 control isolates. The results of this study showed that amongst non-enteropathogenic E. coli, strains exhibiting the EAgg pattern are significantly associated with diarrhoea (p < 0·005). Most of these strains showed a pattern of multiple drug resistance.

During the 1980s the emergence of multiple antibiotic-resistant strains of Staphylococcus aureus posed new problems for infection control worldwide, many of which still remain. In investigations of outbreaks of infection, the laboratory has a key role in identifying infected or colonised patients and staff. The rapid isolation and accurate identification of the causative organisms are essential for the implementation of appropriate control measures. Speed and accuracy in identification, by colonial morphology, is often difficult to achieve in the presence of a mixed population of commensal bacteria.

To this end, the sensitivity of three media for the isolation of methicillin-resistant S. aureus (MRSA) from simulated clinical specimens was compared. Initial colonial recognition of MRSA was enhanced on methicillin-milk agar when compared with that on other media.

The kinetics of the appearance of intestinal lesions induced by orogastric inoculation of gnotobiotic mice with a lethal strain of Clostridium difficile (VPI) that produced toxins A and B in vivo and in vitro was studied and compared with the lesions induced by non-lethal C. difficile strain 786 that produced toxins A and B in vitro but only toxin B in measurable amounts in vivo. Different portions of the intestine were removed 12, 20, 26 and 30 h after inoculation and studied by scanning electronmicroscopy. The remaining portions were homogenised for enumeration of C. difficile and quantification of toxin A by enzyme immunoassay and toxin B by cytotoxicity. The results showed that, following inoculation: (i) measurable amounts of both toxins were necessary to produce lesions; (ii) with strain VPI, the caecum and the colon were rapidly impaired and completely destroyed after 1 day, whereas the small intestine was damaged to a lesser extent; (iii) C. difficile strain 786 did not cause mucosal damage but induced mucus-like or serum-like secretion and morphological changes in the caecal enterocytes only.

Platelet aggregation is believed to be a virulence factor in infective endocarditis. Other factors may be adhesion to components of thrombotic vegetations, particularly platelets, fibronectin and fibrinogen. Two strains from the Streptococcus sanguis group (SSG) were chosen for comparative study on the basis that one aggregated both human and rat platelets and the other lacked this capacity. Both strains caused endocarditis in the rat model but the aggregating strain was found in higher numbers in the excised vegetations. The non-aggregating strain was unable to bind to human or rat platelets but could bind insoluble fibronectin, insoluble fibrinogen and platelet-fibrin clots from both sources, albeit to a lesser extent than the aggregating strain. These results suggest that whereas adhesion to, and aggregation of, platelets are not essential events in the initiation of the pathogenesis of experimental endocarditis, they may be factors contributing to virulence.

The microflora of pus samples aspirated from 50 acute dento-alveolar abscesses was examined. A total of 143 bacterial strains was isolated, consisting predominantly of Prevotella spp., α-haemolytic Streptococcus spp., Peptostreptococcus spp. and Eubacterium spp. An unclassified asaccharolytic Eubacterium taxon was encountered in 17 (34%) of the abscesses. This taxon was found to have a positive association with Fusobacterium spp. and a negative association with α-haemolytic Streptococcus spp.

The relationship between Streptococcus constellatus, one of the species of the “Streptococcus milleri group” and Prevotella intermedia was studied in a model of pneumonia in mice and in vitro to elucidate mechanisms of pathogenicity in “S. milleri group”-associated pulmonary infection. Acute pneumonia with or without empyema and lung abscess in mice with mixed infection resulted in 60% mortality rate, but there was only 10% mortality and mild pneumonia in each separate infection. Bacterial clearance of organisms, especially S. constellatus, in mixed infection was delayed. Enhancement of growth of S. constellatus was demonstrated when cultured with P. intermedia; growth was also stimulated by a culture filtrate of P. intermedia which also inhibited bactericidal activity of human neutrophils. In an examination of infectivity and bacterial clearance of S. constellatus with P. intermedia culture filtrate in vivo, there was 20% mortality and delayed clearance of S. constellatus, although the infection was not as severe as that produced by the combination of both organisms. These results suggest that P. intermedia may act with S. constellatus in the production of pulmonaryinfections by stimulating its growth and suppressing bactericidal activity of the host.

The induction of heat-shock proteins has been postulated to play a role not only in thermo-adaptation, but also in phase transition of the dimorphic fungi. In this study, we used yeast and mycelial forms of the thermally dimorphic fungus Paracoccidioides brasiliensis to evaluate the effect of temperature on the induction of the heat-shock response. We also evaluated protein synthesis by P. brasiliensis caused by exposure to low pH and H2O2. Analysis of protein synthesis by SDS-PAGE disclosed that P. brasiliensis mycelia increased synthesis of all major constitutive proteins when stressed at 37°C and increased synthesis of three non-constitutive proteins of 134, 82 and 28 kDa at 40°C. Yeasts incubated at 40°C showed decreased synthesis of five constitutive proteins (136, 98, 62, 57 and 54 kDa) and the appearance of three new proteins (134, 82 and 28 kDa). There was a decrease in the synthesis of all major constitutive proteins except for three proteins of 141, 136 and 16 kDa when yeast cells were incubated at 25°C. When stressed by low pH and H2O2, P. brasiliensis yeast increased synthesis of one (134 kDa) and five (134, 104, 82, 52 and 40 kDa) non-constitutive proteins, respectively. P. brasiliensis mycelia and yeast forms disclosed the same profile of protein synthesis when stressed at temperatures that trigger phase transition (37°C for mycelia; 25°C for yeast). The same profile of protein synthesis by both forms occurred when the fungi were incubated at 40°C and was similar to that of yeast cells stressed by low pH or H2O2, but different from the patterns produced by mycelia incubated at 37°C or yeast at 25°C. These results suggest that synthesis of stress proteins by P. brasiliensis mycelia and yeast forms at 40°C, low pH or exposed to H2O2 was associated with adaptation to hostile environments. In contrast, the overall increased and decreased synthesis of major constitutive proteins by mycelia and yeast forms at 37°C and 25°C was associated with phase transition. It is unlikely that the heat-shock proteins produced in these experiments are important in the maintenance of the morphology of yeast or mycelia at their usual temperatures of growth.

Both smooth transparent (SmT) and smooth domed-opaque (SmD) colonial variants were obtained from a strain of Mycobacterium avium isolated from a patient with AIDS. The two variants showed similar biochemical characteristics but SmT bacteria proliferated better than SmD bacteria inside human macrophages and were much less capable than the SmD variant of inducing the release of IL-1β, IL-6, TNF-α, GM-CSF and G-CSF, after incubation for either 3 or 6 days. As cytokines are important extracellular signals for immune cells, the lack of induction observed in SmT-infected macrophages may be one of the pathogenic mechanisms of M. avium.

Livingstone was the third most common salmonella serotype isolated from cases of human salmonellosis in the Tayside region of Scotland in 1989–1991; latterly, it spread to Grampian region. The significant upsurge of Livingstone in these two Scottish regions was not matched by similar increases in its frequency of isolation from human cases of salmonellosis in other regions of Scotland or elsewhere in the UK. Although Salmonella Livingstone is usually associated in the UK with incidents of infection among poultry flocks, our detailed investigations found no clear evidence that poultry, eggs or poultry-related products were responsible for this outbreak. Most cases occurred in the summer months from July to September and many of the patients required hospital treatment. Other than one outbreak among geriatric patients in a long-stay hospital in north Tayside, most of the cases were sporadic. The extent of the outbreak, covering 3 years, was recognised mainly because Livingstone was previously an uncommon serotype in Tayside. There were few Livingstone isolations from non-human sources in Scotland in these same years. Possible sources of infection and predisposing factors among patients are discussed. Livingstone was not isolated in Scotland in 1992.

Livingstone was the third most common salmonella serotype isolated from cases of human salmonellosis in the Tayside region of Scotland in 1989–1991; latterly, it spread to Grampian region. The significant upsurge of Livingstone in these two Scottish regions was not matched by similar increases in its frequency of isolation from human cases of salmonellosis in other regions of Scotland or elsewhere in the UK. Although Salmonella Livingstone is usually associated in the UK with incidents of infection among poultry flocks, our detailed investigations found no clear evidence that poultry, eggs or poultry-related products were responsible for this outbreak. Most cases occurred in the summer months from July to September and many of the patients required hospital treatment. Other than one outbreak among geriatric patients in a long-stay hospital in north Tayside, most of the cases were sporadic. The extent of the outbreak, covering 3 years, was recognised mainly because Livingstone was previously an uncommon serotype in Tayside. There were few Livingstone isolations from non-human sources in Scotland in these same years. Possible sources of infection and predisposing factors among patients are discussed. Livingstone was not isolated in Scotland in 1992.

The applicability of polymerase chain reaction (PCR)-mediated DNA typing, with primers complementary to dispersed repetitive DNA sequences and arbitrarily chosen DNA motifs, to study the epidemiology of campylobacter infection was evaluated. With a single PCR reaction and simple gel electrophoresis, strain-specific DNA banding patterns were observed for Campylobacter jejuni and C. upsaliensis. DNA from multiple strains isolated during an outbreak of C. jejuni meningitis generated identical banding patterns and could be distinguished from randomly isolated strains. Strains from a community outbreak of C. upsaliensis, that were all identical by conventional typing methods, could be divided into two genetically different groups. This report illustrates that PCR fingerprinting can be successfully applied in epidemiological investigations of campylobacter infections.

Acanthamoeba spp. are free-living predators that selectively feed on bacteria. Adherence of the bacterial food source to the trophozoite membrane is followed by internalisation and digestion. Through co-cultivation of A. castellanii and A. polyphaga, individually, with Xanthomonas maltophilia, Escherichia coli, Staphylococcus epidermidis and Pseudomonas aeruginosa (despite the amoebicidal properties of the latter organism), specificity with regard to the preferred bacterial substrate was judged. X. maltophilia and P. aeruginosa adhered almost immediately forming a multilayered mantle of bacilli around trophozoites of both species of amoebae. E. coli adhered to fewer trophozoites and in smaller numbers. X. maltophilia was readily internalised after co-cultivation for 8 h, whereas P. aeruginosa, E. coli and S. epidermidis were not internalised even after co-cultivation for 24 h. These data suggest that the suitability of a bacterial food source for the Acanthamoeba spp. studied is associated not only with the proclivity with which the bacterial species binds to the trophozoite surface, but also with the rate of its internalisation.