- Volume 34, Issue 1, 1991

The adherence of six non-mucoid and three mucoid strains of Pseudomonas aeruginosa to polyvinyl chloride (PVC), polyurethane (PU) and siliconised latex (SL) was evaluated by a radiometric method and scanning electronmicroscopy. Initially greater numbers of mucoid than non-mucoid strains adhered to all three materials. Hydrophobic non-mucoid strains adhered more efficiently than hydrophilic strains. Numbers of adherent non-mucoid P. aeruginosa cells increased with time, reaching a peak, which was different for each strain, at 1–4h for PU, 4 h–2 days for SL and 2–3 days for PVC; thereafter a gradual decrease was observed, maximal and final values of adherence being higher with PVC and SL than with PU. Adherence of mucoid strains increased with time in 3–5 days, until a stready state was reached. We conclude that although non-mucoid strains of P. aeruginosa initially colonise plastic surfaces better than mucoid strains, mucoid strains also persist on these surfaces.

The virulence of 74 Listeria monocytogenes isolates from clinical cases and food products and of 11 isolates of other Listeria species was tested in mice immunocompromised with carrageenan. Isolates of species other than L. monocytogenes were not lethal to such mice. All 29 clinical isolates of L. monocytogenes (serotypes 1/2a, 1/2b, 4b) and 33 of 42 isolates of various serotypes isolated mainly from dairy products killed all test mice (100% lethality) at an inoculum of 104 cfu/mouse. All lethal strains of L. monocytogenes were haemolytic and possessed the 58-Kda band specific for listeriolysin O as demonstrated by SDS-PAGE immunoblotting. The nine avirulent strains of L. monocytogenes had detectable haemolytic activity, but in six of them this activity was significantly weaker than in virulent strains and the 58-Kda band was not detected. The other three avirulent strains were highly haemolytic and possessed the 58-Kda band, which suggests that other factor(s) could be involved in the virulence of L. monocytogenes.

Ciprofloxacin, unlike nalidixic acid, can kill Escherichia coli cells in the absence of synthesis of protein of RNA. Hence, chloramphenicol or rifampicin do not abolish the bactericidal activity of ciprofloxacin against wild-type E. coli. Protein and RNA synthesis were not required for the bactericidal activity of ciprofloxacin against nalB, nalC and nalD mutants of E. coli. However, the addition of chloramphenicol or rifampicin abolished the bactericidal activity of ciprofloxacin against a nalA mutant in nutrient broth. It is concluded that the ability of ciprofloxacin to kill E. coli in the absence of protein or RNA synthesis involves the A subunit of DNA gyrase.

The auxotype, serogroup and antimicrobial susceptibility of 977 clinical isolates of Neisseria gonorrhoeae obtained at St Thomas’ Hospital, London, during 1989 were determined; 23 isolates from 15 patients were resistant to 4-quinolones. Twelve of the patients acquired their infection in the UK and these strains were generally sensitive to other antimicrobial agents; strains from 10 patients were of serogroup IB-6. Three patients acquired their strains outside the UK and these isolates were multi-resistant and of different serogroups.

A rapid micro-agglutination test (RMAT) for the detection of antibody to Legionella pneumophila serogroup 5 is described. It was found to be both sensitive and specific when compared with the indirect immunofluorescence test. Evaluation of 89 paired sera from patients with respiratory symptoms showed that the incidence of L. pneumophila serogroup 5 respiratory infection in East Anglia is low: only one case was found in this study. The RMAT would be easy to perform as a screening test in a routine serological laboratory.

The aim of this study was to determine the incidence of amoxycillin and erythromycin resistance in oral streptococci in patients at risk from infective endocarditis. Samples of gingival crevicular flora were taken from 65 patients at the site of dental treatment, prior to the prophylactic administration of amoxycillin (54 patients) or erythromycin (11 patients). Samples were also taken from 65 dental patients who were not considered to be at risk from infective endocarditis. No isolate had a minimum inhibitory concentration (MIC) of amoxycillin > 24 mg/L. However, erythromycin-resistant oral streptococci with MIC values > 3μ5 mg/L were isolated from 22% of patients receiving amoxycillin prophylaxis, 9% of patients receiving amoxycillin prophylaxis, 9% of patients given erythromycin prophylaxis and 9% of patients not at risk from infective endocarditis. The antibiotic-resistant streptococci comprised mainly Streptococcus sanguis biotype II, although S. sanguis biotype I, S. mitis and S. salivarius were also frequently recovered.

The polymerase chain reaction was used to detect HSV-1 DNA in genomic DNA extracted from peripheral blood leucocytes, in patients with Behcet’s syndrome (BS), patients with recurrent oral ulcers and normal healthy controls. A 211-bp HSV-1 DNA fragment was found in a significant number of patients with BS (p <0.02). Serum anti-HSV-1 antibodies were also found in a higher proportion of patients with BS (p <0.02) than in healthy controls. However, virus-specific DNA was not detected in biopsy samples taken from oral ulcers in patients with BS.

An assay has been developed for Bordetella pertussis heat-labile toxin (HLT) based on morphological alterations in certain human embryonic lung (HEL) cell lines. Eighteen cell lines from human and other sources were tested but only two, MRC-5 and HELu2, were responsive to HLT. Confluent monolayers of the cells contracted within 24 h of exposure to the toxin, but without loss of viability during incubation for a further 3 days. The effect of HLT was quantitated by scoring the extent of morphological change, and by the decrease in Giemsa staining of the cell monolayers, as measured on an ELISA plate reader. This cell culture assay for HLT was more sensitive than lethality titration in mice but the dose-response curve had a lower slope. The specificity of the response was established by comparing unheated HLT with HLT heated at 56°C, and with extracts from transposon-insertion mutants of B. pertussis which were deficient in HLT. Purified preparations of pertussis toxin and B. pertussis lipopolysaccharide gave no morphological response even at high doses.

The ability of 19 strains of Bacteroides fragilis to adhere to buccal epithelial cells (BEC) and to the human intestinal cell line HT-29 Clone 19A, and to agglutinate rabbit erythrocytes was compared. Adhesion to BEC was poor compared with that to the cell line. Adhesion to the latter was high for 21% of the strains, moderate for 37% and poor for 42%. Only 53% of the strains agglutinated rabbit red blood cells and only strain A459 did so strongly. Haemagglutination and adhesion of B. fragilis strain A459 were inhibited by sodium periodate, but not by proteases, heat or carbohydrates. These properties were not affected by protease which removed surface appendages. Periodate treatment did not remove the fimbriae or ruthenium red-staining layer, although the capsule was lost. This suggests that carbohydrate residues on the cell surface, possibly forming part of the capsule, are involved in adhesion and haemagglutination by this strain.

The generation of smooth aromatic-dependent Salmonella serotype Bovismorbificans (Group C2, O6, 8) from a smooth wild-type parent strain by transduction with phage P1, and conjugation with Salmonella serotype Typhimurium carrying F′-8gal is described. The smooth aromatic-dependent S. serotype Bovismorbificans was non-lethal for mice at an oral challenge dose of 2 × 109 cfu (equivalent to 200 LD50 of the parent, wild-type strain). The safety of the auxotrophic mutant was further substantiated by comparing its multiplication kinetics in vivo with that of its virulent parent organisms. Mice immunised with live, smooth aromatic-dependent S serotype Bovismorbificans by either the oral or intraperitoneal (i.p.) route were protected against oral challenge with virulent S serotype Bovismorbificans; the degree of protection was significantly better (p<0.05) at a challenge dose of 100 or 200 LD50 in mice receiving two rather than one vaccination. In contrast, mice immunised with three doses of the formalin-killed virulent, parent organisms by the i.p. route were not protected, in spite of high antibody titres. Only those mice immunised with the live, smooth aromatic-dependent S serotype Bovismorbificans i.p. developed significant (p<0.01–0.05) delayed-type hypersensitivity.