- Volume 14, Issue 2, 1981

The volatile substances produced and utilised by some species of Candida isolated from man, were determined in two cultural conditions by gas chromatography. It was possible to characterise Candida krusei, C. parapsilosis, C. tropicalis, C. albicans and C. guilliermondii, but more species and isolates would have to be studied for conclusive results.

Twenty-three strains of Escherichia coli with mannose-resistant and eluting (MRE) haemagglutinins with eight different patterns of substrate specificity were examined by a variety of electronmicroscope methods. In 12 strains, the presence of MRE haemagglutinins with broad-spectrum patterns 1, 3 and 4 was correlated with that of fimbriae. In 11 strains with MRE haemagglutinins with the less common patterns 6, 7 var., 8, 9 and 10, fimbriae were not found on bacteria in MRE+ cultures, indicating that the latter haemagglutinins are non-fimbrial.

An examination of 10 strains of Staphylococcus aureus for survival within abscesses developing in the peritoneal cavity of mice revealed three distinct patterns of survival. Although non-haemolytic mutants were destroyed more rapidly than were their parent strains, this difference could not be attributed to any particular haemolysin. In abscesses generated with mixtures of non-haemolytic variants and their parent strains, the former were preferentially eliminated; this suggests that the non-haemolytic variants were inherently more sensitive to the conditions within these lesions. Subsequent studies confirmed that abscess homogenates were cidal for staphylococci and that this activity resided in the insoluble fraction of the homogenates. Staphylococci added to abscess homogenates were killed, but only after a lag. This lag could be shortened or eliminated by incubating homogenates before adding the test organism. After development of a suitable assay, it was found that the cidal activity in abscess homogenates could be increased 3-20-fold by pre-incubation. Staphylococcal strains differed in their relative sensitivities to the cidal material; those strains rapidly destroyed within abscesses were the most sensitive and strains capable of better survival were more resistant. The results support the concept that the cidal material is responsible for destruction of staphylococci within such lesions.

The effects of ethyleneglycoltetra-acetic acid (EGTA) and EGTA+magnesium (MgEGTA) on the viable counts of 10 strains of Escherichia coli O6 have been studied in normal human serum (NHS), heat-inactivated serum (HIS) and in culture media with and without the addition of a β-lactam antibiotic. The addition of EGTA to NHS largely prevented bactericidal activity against serum-sensitive strains while, in contrast, it reduced the growth of a serum-resistant strain. These apparently paradoxical effects are due to the lower growth rate permitted by the reduced amount of available magnesium in the presence of EGTA.

Experiments with equimolar concentrations of EGTA and magnesium indicated that whilst MgEGTA is a reagent allowing alternative complement-pathway activity, such activity must be determined by comparison with results in HIS + MgEGTA rather than in HIS alone, classical-pathway activity being taken as the difference between the results in NHS and in NHS + MgEGTA.

By these criteria, prompt killing by serum was found to occur via the classical pathway while delayed serum bactericidal activity occurred by the alternative pathway in some strains and by the classical pathway in others.

The presence of diaminopimelic acid (m-DAP) in strains of Bacteroides melaninogenicus, B. bivius and other species as well as in unidentified strains of Bacteroides was investigated by thin-layer chromatography. Strains of B. bivius and B. disiens all contained m-DAP as did the subspecies intermedius and melaninogenicus of B. melaninogenicus. Strains of B. asaccharolyticus and similar black pigment-producing butyrate-positive isolates showed heterogeneity. Asaccharoly-tic strains were DAP negative, whereas two strains fermenting glucose were positive. Some of the non-pigmented propionate-negative and butyrate-negative unidentified strains also contained DAP. The consistent finding of m-DAP in strains of B. bivius, B. disiens, and B. melaninogenicus indicates that DAP detection might be of value in the identification of these species.