- Volume 35, Issue 4, 1991

Gram-negative spiral organisms, currently referred to as Helicobacter pylori, are associated with primary gastritis and duodenal ulceration. The organisms colonise gastric mucus and adhere to epithelial cells of inflamed antra. To further examine the binding of H. pylori to human gastric epithelial cells, we developed and characterised an in-vitro bacterial adherence assay. Scanning electronmicroscopy suggested that spiral-shaped bacteria were adherent to the surface of KATO-III cells which were derived from a human gastric adenocarcinoma. Transmission electronmicroscopy confirmed the attachment of H. pylori to these epithelial cells in tissue culture. Some bacteria were adherent to intact microvilli, others were closely adherent to the plasma membrane in regions where microvilli were effaced. In studies with radiolabelled H. pylori, adherence to epithelial cells in tissue culture contrasted with minimal binding of bacteria to polystyrene wells alone. Incubation of bacteria with gastric cells at 4° significantly reduced adherence of H. pylori. We conclude that adherence of H. pylori to gastric epithelial cells in tissue culture involved “attachment and effacement mechanisms”. This assay could serve as a suitable in-vitro model for the study of the bacterial adhesins and host receptors which mediate attachment of H. pylori to gastric epithelial cell surfaces.

Immunoblotting of urine from 21 patients of both sexes and of wide age range who had a Proteus mirabilis urinary tract infection (UTI) showed that 14 (64%) specimens contained immunoglobulin A (IgA). In nine (64%) of these the IgA heavy chain had been degraded to fragments of a size identical to those formed when purified IgA was degraded by pure P. mirabilis protease. Urine from patients with clinical evidence of upper UTI contained fragmented IgA and in some of these urine samples P. mirabilis protease activity was detectable. Urine infected with a non-proteolytic strain contained only intact IgA. It is concluded that P. mirabilis IgA protease is produced and is active during infections of the urinary tract.

Xanthomonas maltophilia produces two inducible β-lactamases, L1 and L2, and resists the antimicrobial activity of β-lactam antibiotics, including carbapenems. L1 is a zinc-metaloenzyme with carbapenemase activity; L2 is an unusual cephalosporinase. Mutant strains with high-and low-level constitutive expression of these enzymes were derived from three reference strains of X. maltophilia. With a single exception, the mutant strains had altered expression of both enzymes, indicating that these β-lactamases share regulatory components. The exception was a mutant strain that had low-level constitutive (basal) expression of L1 enzyme but remained inducible for L2. A parent strain with low-level β-lactamase inducibility was more susceptible to penicillins, cephalosporins and carbapenems than were those in which higher levels of enzyme activity were inducible. Mutations that caused high-level constitutive β-lactamase expression increased resistance to penicillins and newer cephalosporins. β-Lactamase basal mutant strains, including the one that remained inducible for L2 enzyme, were more susceptible than inducible strains to these drugs. Organisms with inducible or high-level constitutive β-lactamase expression were equally resistant to meropenem and imipenem but basal mutant strains, including the one that remained inducible for L2 enzyme, were more susceptible to meropenem than imipenem. Minimal inhibitory concentrations of meropenem, penicillins and cephalosporins, but not imipenem, were greater on Mueller Hinton agar than on IsoSensitest or Diagnostic Sensitivity Test agars. This behaviour was independent of β-lactamase inducibility, and may reflect permeability differences between cells grown on different media.

The complete sequence of the type VI dihydrofolate reductase (DHFR) gene from plasmid pUK672 was determined. The structural gene coded for a polypeptide of 157 amino acids which had a deduced mol. wt of 17 424. Comparison with amino-acid sequences of the type I, type V and Escherichia coli K12 chromosomal DHFRs showed that there was 63%, 61% and 31% homology respectively. Putative RNA polymerase and ribosomal binding sites were identified proximal to the initiation codon and a feature consistent with transcription termination was present distal to the coding region. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis showed that the enzyme had a subunit mol. wt of 17 500.

From Sept. 1986 to Jan. 1989, a hospital-based study was conducted on 736 children, under 5 years of age, with acute respiratory infection. Nasopharyngeal secretions were examined for viruses by culture and by immunofluorescence. Viruses were detected in 22% of specimens: respiratory syncytial (5%), parainfluenza (5%), influenza A (4%), influenza B (2%), adenovirus (3%), measles (3%). The highest rates of detection were with patients diagnosed clinically as pneumonia or upper respiratory tract infection. The case fatality rate was very high (43%) in children with measles virus infection.

A direct immunofluorescence (IF) method was compared with traditional culture methods for the detection of Actinomyces israelii in endocervical and intra-uterine-device (IUD) smears from 124 IUD wearers. Of 11 specimens that gave positive results by IF, only one was positive by culture. Of the 10 patients with positive IF specimens, three (30%) had signs and symptoms suggestive of pelvic infection and no other pathogen was detected. Direct IF of cervical smears offers a simple, relatively cheap method to screen IUD wearers for A. israelii. Clinical management of such cases is discussed.

The reactivity of four different monoclonal antibodies (MAbs) with populations of Bacteroides fragilis NCTC 9343, enriched by density gradient centrifugation for a large capsule, small capsule and electron-dense layer (EDL) only visible by electronmicroscopy, was examined. The MAbs reacted strongly with polysaccharides present in both the large capsule- and EDL-enriched populations but not in the small capsule-enriched populations. The pattern of labelling was determined by immunoblotting, immunofluorescence and immuno-electronmicroscopy, and flow cytometry. The MAbs labelled cell membrane-associated epitopes in the large capsule- and EDL-enriched populations and cell-free material in the EDL population. By immunoblotting, ladders of repeating polysaccharide subunits were evident in the EDL population but not in the large capsule population. The proportion of cells labelled within each population was determined by flow cytometry. The reactivity of another MAb with the small capsule population was confirmed by flow cytometry. A qualitative indication of epitope expression was obtained by examination of the flow cytometric profiles. Differential expression of the same saccharide epitope was observed both between and within structurally distinct B. fragilis populations. The MAbs were species-specific and cross-reacted with several recent clinical isolates. These polysaccharides may be relevant to the virulence of B. fragilis.

A semi-quantitative bacteriological method was used to study faecal flora in 42 patients with Crohn’s disease, 37 with ulcerative colitis and 21 healthy controls. Faecal homogenates were plated on primary isolation plates by a technique that allowed the growth of various microbial isolates to be assessed on a visual 1 + -5 + score. This method was first calibrated against a standard quantitative bacteriological technique, which confirmed the reliability and reproducibility of the results obtained by the simpler method. Patients with clinically active Crohn’s disease (22) had significantly higher total aerobe scores than patients with quiescent disease (20) (p 0.006) or ulcerative colitis (p 0.04) or normal controls (p 0.02). The scores of Escherichia coli were parallel to those of total aerobes. Lactobacillus and bifidobacteria scores were significantly reduced in patients with Crohn’s disease compared to those with ulcerative colitis and controls. The anaerobic flora in both Crohn’s disease and ulcerative colitis was indistinguishable from that of controls. Bacteroides vulgatus and B. fragilis were the predominant bacteroides in all groups. Patients with ulcerative colitis, regardless of disease activity, harboured faecal flora that did not differ from that of normal controls. The abnormal faecal flora in Crohn’s disease did not correlate with established clinical and laboratory indicators of disease activity.

Using a set of sera for which full chlamydial micro-immunofluorescence results suggested a clear diagnosis, we have evaluated the Chlamydia Spot-IF test (bioMerieux), which allows a comparison of titres to Chlamydia trachomatis and C. psittaci antigens. A modification of the test in which the antigen slides were pre-treated with a monoclonal antibody to chlamydial lipopolysaccharide, improved its ability to differentiate infections with C. trachomatis from those with C. psittaci or C. pneumoniae.

A Kemble Robotic sample processor was programmed to perform routine serological tests for microbiology. Accuracy of dispensed volumes was assessed and precision of dilutions was compared with manual methods. An appraisal of time taken to perform complement-fixation and enzyme-linked immunosorbent assays by manual and automated methods was undertaken. Labour requirements were reduced when processing large numbers of samples and the reproducibility of more demanding tests was improved by the greater accuracy of the robotic manipulations.