- Volume 17, Issue 1, 1984

A McCoy cell line persistently infected with Mycoplasma orale was examined by light microscopy and electronmicroscopy after specific labelling with a direct immunoperoxidase conjugate. Mycoplasmas were readily detected in monolayer cultures in bright-field conditions and these were related to labelled organisms observed by electronmicroscopy in thin sections of similar cells. The specificity of the conjugate for M. orale was demonstrated by blocking with unconjugated antiserum, and by its inability to detect M. bovirhinis. Non-specific background labelling was consistently absent.

Results of the examination of urine specimens with evidence of acute urinary tract infections from children aged 16 years and under in general practice were analysed during a period of 16 months. Infections were much commoner in girls than in boys, with Escherichia coli most frequently involved in both groups. Urinary tract infections caused by Proteus strains were predominantly associated with boys. Infections in girls showed a higher incidence at 3, 6 and 16 years of age. Possible reasons for these sex- and age-associated patterns of infection are discussed. It is suggested than an important factor in the prevention of urinary tract infections in young girls is proper supervision of school lavatories. The report illustrates how much useful information can be obtained from the analysis of diagnostic results based on a simple but thorough laboratory approach.

The activities of azlocillin and ticarcillin against Pseudomonas aeruginosa were compared by estimating minimum inhibitory and bactericidal concentrations (MIC and MBC) in liquid and solid media, and by constructing killing curves from sequential viable counts. In MIC studies, azlocillin was about three times more active than ticarcillin in solid medium (agar dilution test) and in liquid media (tube and microdilution tests). When the MBC was measured, however, results varied according to the technique used. On agar and in microdilution tests, both azlocillin and ticarcillin were bactericidal, the MBC being 1.3-3 MIC. In the tube test, the MBC for ticarcillin was again about 3 MIC, but azlocillin appeared not to be bactericidal (MBC < 1 mg/ml). However, sequential viable counts of four clinical isolates showed that at 4 MIC both antibiotics reduced viable counts by a factor of 104 in 8 h. Our results stress the importance of methodology when assessing the antibacterial activity of an antibiotic.

Chemoattractive properties of Neisseria gonorrhoeae were studied by measuring leukocyte migration in agarose gel. Human serum albumin (0.5%) was present in the gel and normal human serum was excluded from all components of the assay. Viable cell populations and lysates of colonial types F62T1, F62T2 and F62T3 induced migration of polymorphonuclear leukocytes. Chemotactic activity of the lysate was not altered by heating at 100°C for 10 min and was retained in the 12 100 g supernatant fraction of the heated lysate. Fractionation of the supernate by Sephadex G-100 chromatography showed that the chemotactic activity was associated primarily with an absorbance peak at 280 nm of relatively low mol. wt. The chemotactic activity of this fraction was lost after dialysis and the peak was no longer present in the Sephadex G-100 elution profile of the dialysed supernate. The gonococcal leukotaxins were sensitive to digestion by trypsin, pronase and amyloglucosidase, but insensitive to treatment with RNAase, DNAase or lipase at pH 5.7-7.1.

The prevalence of different types of diarrhoea-producing Escherichia coli among 240 patients with acute diarrhoea in hospital was investigated. The 25 patients (10.4% of the total) from whose faeces we isolated enteropathogenic E. coli (EPEC) were all < 5 years old but the 29 (12.1%) from whom we isolated enterotoxigenic E. coli (ETEC) were of various ages, most of them > 12 years old. No enteroinvasive E. coli (EIEC) strains were isolated. ETEC strains that produced heat-labile toxin (LT) were encountered more often than those that produced either heat-stable toxin (ST) alone or both LT and ST. The ETEC isolates were distributed among eight different serotypes, the commonest being O148:H28 (38%). Correlations between enterotoxin production, serotype pattern and possession of colonisation factor antigens I and II were observed.

Adult female mice were given drinking water containing tobramycin 0.05 mg/ml for a week. After a further day without antibiotic they were inoculated intragastrically with one of three strains of Campylobacter jejuni. Colonisation of the gastrointestinal tract was judged by culturing faecal pellets. Tobramycin-treated mice differed from untreated animals in that many more of them discharged infected pellets, and their pellets contained 5-> 300 times more campylobacters. Colonisation could be prevented by inoculating the tobramycin-treated animals intragastrically, 24 h before the administration of C. jejuni, with a bacterial suspension prepared from normal faecal pellets. Coliforms, lactobacilli, the two in combination, and anaerobes grown from faecal pellets were not effective in preventing colonisation. Most of the C. jejuni were found in the large intestine of the tobramycin-fed mice. The persistence of colonisation of six dams nursing C. jejuni-infected offspring ranged from 10 to at least 29 weeks.

The virulence of 93 clinical isolates of Klebsiella was compared in a mouse model by subcutaneous injection. Skin pathogenicity was measured by estimating the number of viable bacteria in the lesions 24 h after infection with a dose of 107 bacteria. Strains of serotypes K1-6 were compared with strains of serotypes higher than K6. All K1 and K5, and some K2 and K4 strains were more virulent for mice than strains with a serotype higher than K6. The K3 strains were significantly less virulent than the strains with a serotype higher than K6. The bacteriological findings were confirmed by histological examination with some strains. No differences in virulence were observed between strains of the same serotype isolated from patients with cystitis or from those with pyelonephritis, nor between strains of the same serotype isolated from the blood of patients with septicaemia or from other sites. The mouse model has been found satisfactory for observing differences in virulence between Klebsiella isolates.

Antibiotic multiresistant isolates of Staphylococcus aureus from outbreaks of nosocomial infection throughout Australia were found to possess essentially similar patterns of antibiotic resistance. Plasmid DNA profiles from these isolates exhibited a common pattern of large plasmids, of (15–22) × 106 mol. wt, associated with resistance to gentamicin, kanamycin and tobramycin, plasmids of 3 × 106 mol. wt, mediating resistance to chloramphenicol, and cryptic plasmids of 1 × 106 mol. wt. Restriction endonuclease digestion confirmed the presence of related plasmids in isolates from all the hospitals that were surveyed. The homogeneity of these organisms suggests the dissemination of a multiresistant, plasmid-bearing strain of S. aureus, or its derivatives, among geographically-separated hospitals in Australia.

Twelve selected strains of Bordetella pertussis were compared quantitatively for their ability to produce heat-labile toxin (HLT); all proved to be active producers, with only a three-fold range between the highest and the lowest. Bordet-Gengou agar, charcoal agar, modified Hornibrook medium and Stainer and Schölte (12G) medium differed little in their ability to support toxin production by three B. pertussis strains. However, cells grown on the solid media for 24 h were slightly more toxic than their counterparts grown for 72 h whereas in the liquid media the opposite was true. The concentration of iron in the medium did not influence HLT production, but high concentrations of nicotinic acid significantly reduced the HLT content of the cells. Crude preparations of toxin underwent only a 10% loss of toxicity per annum at—20°C and were stable for up to 2 weeks at 4°C. At 37°C, toxicity was lost within a few days. The toxin was partially purified by a series of mild procedures and had a mol. wt by gel filtration of 89 000 ±10%. HLT was toxoided by treatment with formaldehyde to give a product which was immunogenic in rabbits but not in mice. Because anti-HLT could be absorbed out of the rabbit antisera by treatment with intact B. pertussis, it was concluded that some of the HLT in the bacteria is surface-exposed even though the main part may have a cytoplasmic location.

Antibodies specific for rubella virion polypeptide, VPI, secreted by clones of hybridoma cells or produced in rabbits in response to specific antigenic stimulation, located determinants for haemagglutination inhibiting (HI) and neutralising (Nt) antibodies on this envelope component.