- Volume 11, Issue 1, 1978

This paper demonstrates that various degrees of mycobactin dependence exist within the M. avium group of mycobacteria and that this characteristic is not confined to M. paratuberculosis. The strains employed came from a wide range of animal species and all were virulent for chickens. Mycobactin dependence was observed in the M. avium serotypes 1, 2 and 3.

The importance of employing a medium containing mycobactin for primary isolations from tissue containing only small numbers of viable units of M. avium is emphasised. This observation may be of interest in relation to the primary isolation of other species of mycobacteria.

The antiswarming agent p-nitrophenylglycerol (PNPG) has been found invaluable for the recognition and isolation of pathogenic bacteria from specimens contaminated with swarming strains of Proteus spp. PNPG is cheap, stable and non-toxic. All strains tested grew well in its presence and produced characteristic morphology. PNPG was without effect on the results of a variety of identification tests performed directly on colonies from media containing PNPG. This permitted identification without the need for further subculture.

Empirical methods of assigning type designations to the patterns that describe the reactions of a bacterial isolate towards a reference set of indicator (or producer) strains have resulted in loss of information and have made it difficult to compare published reports.

We propose that the whole pattern sequence be considered a binary number and be translated into its decimal counterpart, which may be used as a rational, compact and meaningful type designation for reporting purposes.

The effects of hydrocortisone (HC) and methylprednisolone (MP) on the biological activities of staphylococcol α toxin were studied. Incubation of either HC or MP at concentrations of 4-8 mg per ml with purified a toxin (690 HU per ml) reduced or eliminated haemolytic activity for rabbit red cells, intraperitoneal lethality for mice, and dermonecrotic activity for rabbits. Detoxification was related to the dose of steroid, and MP was slightly more active than HC. The mechanism of detoxification apparently involves a direct molecular interaction between a toxin and steroid, and pretreatment of animals with HC or MP did not enhance their resistance to the subsequent effects of toxin.

Three capsulate pneumococcal strains of serotypes 1, 2 and 3, and one non-capsulate strain of serotype 47, were found to activate human complement by the alternative pathway to a similar extent over the concentration range examined. Nevertheless, the capsulate strains, in contrast to the non-capsulate, are known to require complement attachment for phagocytosis and it is therefore postulated that the toxic by-products released cause the wave of oedema characteristic of pneumococcal lobar pneumonia.

Polyagglutinable (PA) strains of Pseudomonas aeruginosa are agglutinated by more than one of the antisera prepared against antigenically unrelated O serogroups. They form c. 4% of strains—other than isolates from cystic-fibrosis units—submitted to us for typing. We were able to allocate 80% of PA strains to a single O serogroup by agglutination with typing sera that had been absorbed with the polyagglutinable strain SMC-247, or by co-agglutination tests with protein A-containing staphylococci coated with immunoglobulin from unabsorbed sera. Similar results were obtained by precipitation tests with crude bacterial extracts and unabsorbed sera, but these tests were less sensitive and less specific. Evidence is presented that PA antigen is a heat-stable cell constituent distinct from the O antigen. In rabbit antisera, anti-PA antibody is exclusively of the IgM class, but O antibody of both IgM and IgG classes is present.

Breast-fed infants are less susceptible to gastroenteritis than bottle-fed infants. Antibodies against rotavirus, the major pathogen of infantile gastroenteritis, were sought in human sera, colostrum and milk specimens by immuno-fluorescence. An experimental murine-rotavirus model was established by infecting the second litters of dams 4 weeks after infecting their first litters. Antibodies were absent from human and murine colostrum and milk specimens despite being present in virtually all sera, and the second mouse litters were as susceptible as the first. The inability of rotavirus to infect adult human beings and mice may prevent the formation of gut-derived antibody-secreting lymphocytes in milk, and thus prevent transmission of passive immunity. The association of bottle-feeding with rotavirus gastroenteritis appears to be the result of increased opportunity for spread of infection rather than of the absence of specific protective antibody.

Clinical details are presented of 16 patients from whom thymine-requiring (thy−) mutants of pathogenic organisms were isolated; all had been treated with co-trimoxazole. The urine of six patients infected with thy− mutants contained levels of a thymine-like compound sufficient to support their growth. This might be the result either of the breakdown of pus cells or of thymine production by living bacteria that persist in stones or scar tissue, a suggestion supported by the observation of mutant growth “in satellitism” in vitro. Since 1975 we have isolated mutants from patients who have had short courses of co-trimoxazole, in contrast to those we reported upon previously, all except one of whom had had long courses. We are now isolating thy− mutants more frequently than hitherto. Secondary mutations to a low thymine requirement may now be occurring more rapidly, thereby allowing more mutant organisms to survive. The clinical significance of infection with thy− mutants is not yet clear, but evidence is accumulating that they are pathogenic. Alternative chemotherapy is suggested for patients from whom such mutants have been isolated.