Multi-resistant strains from three UK centres, previously identified as Burkholderia (formerly Pseudomonas) cepacia, and associated with morbidity, mortality and transmission among patients with cystic fibrosis have been further characterised. Biochemical tests and fatty acid analyses indicate these strains to possess some characteristics atypical of B. cepacia but bearing close resemblance to Burkholderia gladioli, an organism previously regarded solely as a plant pathogen and a hindrance to the identification of B. cepacia. In contrast to the majority of reference strains, all multi-resistant clinical isolates possessed rough lipopolysaccharide which may be a major factor responsible for their increased antibiotic resistance and virulence. In view of the potential clinical and social problems in CF patients posed by these multi-resistant strains, it would seem prudent to consider the isolation of either B. cepacia or B. gladioli as of equal significance.

Two independent surveys have been conducted to determine the prevalent bacterial species and beta-lactamase types present in clinical populations of gram-negative, ampicillin-resistant isolates. A total of 208 isolates (112 from Nottingham Hospital and 96 from Charing Cross Hospital), all of which had been collected from out-patients suffering from urinary tract infections, were investigated. The incidence of ampicillin-resistant isolates (minimum inhibitory concentrations, 8 micrograms/ml) was 24.1% and 18.8% within the Nottingham and Charing Cross samples, respectively. The surveys gave similar results within the ampicillin-resistant samples. Escherichia coli was the prevalent bacterial species (52.9%), followed by Klebseilla pneumoniae (30.3%). The majority of isolates, at least 54.8% and possibly as high as 74.5%, owed their principal beta-lactamase activity to enzymes mediated by R-plasmids. The most prevalent beta-lactamases were TEM-1 (53.3%), SHV-1 (30.9%), and OXA-1 (11.5%). Positive associations were found between E. coli and TEM-1 or OXA-1 and between K. pneumoniae and SHV-1.

The incidence and mechanisms of ampicillin resistance (MIC greater than 1 mg/l) were investigated in 105 clinical isolates of Haemophilus influenzae collected in Edinburgh during 1983/4. Fifteen (14.3%) ampicillin-resistant strains were identified and these were non-serotypable and comprised six biotypes. Isoelectric focusing and beta-lactamase-inhibition studies demonstrated that production of the TEM-1 beta-lactamase was the principal mechanism of resistance in nine (60%) strains. Radiolabelling revealed that one beta-lactamase-positive strain also had an unusual penicillin-binding protein (PBP) profit. No beta-lactamase activity was detected in the other six (40%) ampicillin-resistant strains. Two beta-lactamase-negative ampicillin-resistant strains had atypical PBP profiles. SDS-PAGE analysis showed that four beta-lactamase-negative ampicillin-resistant strains, including one with altered PBPs, exhibited outer membrane protein profiles which differed from those of sensitive strains of the same biotype. The ampicillin-resistance mechanism of the remaining strain could not be determined. Thus, several resistance mechanisms, either acting individually or in combination, are implicated in ampicillin resistance in H. influenzae.

The variation in penicillin titre within populations of cultures of Aspergillus nidulans derived from untreated conidia and from conidia treated with ethyl methanesulphonate (EMS), near-ultraviolet light in the presence of 8-methoxypsoralen (8MOP) or N-methyl-N'-nitro-N-nitrosoguanidine (NTG), each at several dose levels, was determined. Both mutagentreated and untreated populations showed a continuous distribution of pencillin titres. The population mean titre of the mutagenized populations was decreased and the range of titres was increased relative to those of the control populations. No differences between sister cultures could be detected in three untreated populations, but nine out of ten populations derived from mutagenized conidia showed significant variation for penicillin titre. In general the magnitude of this induced variation increased with increasing dosage of the mutagen. Comparisons at fixed survival levels indicate that 8MOP mutagenesis is less effective for the induction of variation in penicillin titre than EMS or NTG mutagenesis. A statistical procedure was adopted to classify the survivors as unchanged cultures ('0'), titre-increasing mutants ('+') or titre-decreasing mutants ("-"). The frequency of both '+' and '-' mutants increased following mutagenesis, with NTG being the most active of the three mutagens. Over all treatments, these two mutant classes were recovered with equal frequency. The frequency of "+" mutants was largely independent of mutagen dose, within the ranges used, and moderate treatments (around 10% survival) gave as high or higher frequencies than more extreme doses. All three mutagens, and in particular NTG, produced morphological mutants. These contained an increased frequency of titre-decreasing mutants, but increases in titre appeared to be independent of changes in colony morphology. Estimates based on the observed frequencies of penicillin titre mutants suggest that several hundred genes are potentially capable of affecting this continuous variable.

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