- Volume 46, Issue 6, 1997

A medium (PAM: Providencia alcalifaciens medium) is described that enables the presence of the enteropathogen P. alcalifaciens in faeces to be detected with ease and simplicity. This organism is probably the only oxidase-negative organism likely to be present in tetrathionate broth cultures of faeces that is unable to ferment the mannitol, xylose or galactose present in the medium. Thus the red colonies of P. alcalifaciens appeared quite distinct from the lemon-yellow acid-forming colonies of all the other bacteria that ferment one or more of these sugars. Extensive tests showed the medium to be both highly specific and sensitive in detecting P. alcalifaciens. Two additional media are described that enable the identity of presumptive P. alcalifaciens isolates to be confirmed unequivocally and with ease.

As part of an epidemiological study of tuberculosis in Australia, 84 isolates of Mycobacterium tuberculosis from patients were analysed by pulsed-field gel electrophoresis (PFGE). The isolates were genetically heterogeneous, with 66 different DNA banding patterns obtained following digestion of genomic DNA with Dra1 and 53 patterns with Xba1. When the results were compared with those previously obtained in restriction fragment length polymorphism analysis (RFLP), in 87% of cases the results with Dra1 were consistent with those obtained with insertion sequence IS6110 as a probe in RFLP. However, PFGE was able to differentiate four of eight isolates which were identical with IS6110 typing. The high polymorphism amongst strains and the high average age of the patients (51 years) suggested that most organisms were cultured from patients who had reactivation of existing infections. Isolates with identical DNA patterns were found in different states of Australia, but no one strain predominated in any area. This suggests that tuberculosis has been introduced into Australia from various sources.

One hundred and twenty-three breakthrough bacteraemias (BB) were defined during a 5-year period in a National Cancer Centre, among 9986 admissions and a total of 979 bacteraemic episodes analysed. Of 123 bacteraemias in 103 patients, 77 were polymicrobial and 116 of the 323 organisms isolated were resistant to currently administered antimicrobial agents. Sixty-seven of the bacteraemic episodes were catheter-associated, as confirmed by the isolation of the same organisms from both blood and catheter tip. The strains isolated most frequently were coagulase-negative staphylococci (30.5%), corynebacteria (10%), Pseudomonas aeruginosa (10%), Enterococcus faecalis (9%) and viridans streptococci (8.5%). Gram-positive aerobes accounted for two-thirds of all micro-organisms isolated during breakthrough bacteraemic and fungaemic episodes. Polymicrobial episodes were associated more frequently with vascular catheters and neutropenia, and had a less favourable outcome than monomicrobial infections. Relapse was associated more frequently with catheter-related episodes, but the overall mortality rate was similar and independent of catheter insertion. Breakthrough bacteraemic and fungaemic episodes were associated more frequently with acute leukaemia. Catheter removal, as an independent variable, and modification of antimicrobial therapy were essential for better outcome.

A massive accumulation of neutrophils, mainly due to enhanced interleukin-8 (IL-8) levels, is believed to contribute to the deleterious effects of Pseudomonas aeruginosa lung infection, e.g., in cystic fibrosis (CF). Antibodies to phospholipase C, an exoenzyme of P. aeruginosa, are detected early and at high levels in CF patients. However, P. aeruginosa produces at least two types of phospholipase C (PLC), one haemolytic (PLC-H) and the other non-haemolytic (PLC-N), both with mol. wts of c. 77 kDa. Experiments were performed to evaluate the potential contribution of P. aeruginosa PLC to neutrophil accumulation during infection. Therefore, P. aeruginosa PLC-H and PLC-N were compared with regard to IL-8 generation from human monocytes. Purified PLC-H as well as culture supernates (mol. wt > 50 kDa) of a P. aeruginosa strain capable of producing both PLC-H and PLC-N, and mutant strains deficient in the production of one or other phospholipase, or both, were examined. Purified PLC-H (only at low concentrations up to 1 unit/4 × 105monocytes), induced a dose-dependent increase in IL-8 release and IL-8-specific mRNA expression over that of unstimulated cells (at 4-, 12- and 24-h incubation times). Higher concentrations of PLC-H led to a decrease in IL-8 release and IL-8-specific mRNA expression. These findings were confirmed by the results obtained with the supernates of cultures of mutant strains of P. aeruginosa PAO1 that produced either a PLC-H or PLC-N or neither. Stimulation and inhibition of IL-8 release and mRNA expression were associated with a culture supernate fraction of mol. wt > 50 kDa and containing PLC-H. These results contribute to the understanding of the role of both P. aeruginosa PLC in IL-8 generation during their interaction with human monocytes.

The detection of Mycobacterium tuberculosis DNA in peripheral blood mononuclear cells (PBMC) by PCR and non-isotopic hybridisation assay was evaluated for the laboratory diagnosis of pulmonary M. tuberculosis infection. The PCR technique was based on the presence of IS6110, a DNA sequence specific for M. tuberculosis, and performed on PBMC from 30 patients belonging to the fifth group of the American Thoracic Society (ATS) classification of tuberculosis. The identification of amplification products was confirmed after electrophoresis by hybridisation with a non-isotopic probe in a DNA enzyme immunoassay (DEIA). Of the 30 blood samples studied by the PCR-DEIA technique, 26 gave positive results and four gave negative results. Blood samples from 30 subjects in a control group were negative by this technique. The data suggest that PCR-DEIA of blood may provide a sensitive, specific and useful means of diagnosing mycobacterial infection.