- Volume 8, Issue 4, 1975

In or on agar media, low-density seedings of enterobacteria fail to grow in the presence of certain concentrations of ethylene diamine-di-orthohydroxyphenyl acetic acid (EDDA); on the other hand, high-density seedings not only grow but secrete iron chelators which release the iron bound by the EDDA in the medium and stimulate the growth of low-density seedings.

Plates of media containing EDDA with low-density seedings of indicator organisms were used to survey iron-chelator production in seven enterobacterial genera, including a number of virulent smooth (S) forms from which rough (R) mutants had been obtained. An examination of over 80 strains of Aeromonas, Escherichia, Klebsiella, Proteus, Pseudomonas, Salmonella and Shigella species indicated that the iron chelators from bacteria in all these genera were functionally interchangeable.

Chelator production was equally good with randomly selected avirulent and virulent strains of Klebsiella spp. and E. coli; and with the S forms and their avirulent R mutants in one pair of escherichiae, six pairs of salmonellae (4 species) and six pairs of shigellae (3 species). As determinable in vitro, the capacity to synthesise iron chelators is clearly no index of the capacity of a strain to proliferate in vivo.

Differential counts of the faecal flora of patients with ulcerative colitis showed a dysbiotic flora with a 100-fold increase of group-D streptococci and a reduction of bifidobacteria in comparison with the stable eubiotic flora of healthy subjects.

The increase in number in group-D streptococci was accompanied by an increase in variety. About four different varieties of enterococci were found in faeces from patients compared with one or two in samples from healthy subjects. The strains isolated from patients were more active in mucin breakdown, and only strains from patients were able to break down hyaluronic acid. Lactic acid could be formed from these substrates. The increased secretion of mucin in colitis and the presence of unprotected hyaluronic acid in ulcers seem to select these organisms which are probably the cause of the high lactic-acid content of the faeces in such patients.

Normal skin sites in children from a population in which streptococcal impetigo is endemic were examined for the presence of β-haemolytic streptococci by a direct agar-contact technique. Ninety-eight of 554 samples (18%) were positive for these organisms. Penicillin prophylaxis reduced the frequency of isolation of streptococci from the normal skin for a period of 3 weeks, perhaps accounting in part for the lower isolation rate in this than in earlier studies.

Numbers of streptococcal colony-forming units in positive samples were generally low, both in terms of absolute numbers isolated from the surface area sampled and in comparison with numbers of other aerobic flora recovered. The presence of streptococcal pyoderma at the time of agar contact was not necessarily associated with the presence of or with increased numbers of streptococci on samples obtained from normal skin sites. Low counts were consistently found in early summer and higher counts in some samples in late summer.

In a simultaneous comparison of paired samples taken from adjacent sites, the frequency of detection of streptococci by direct agar contact compared favourably with that obtained with a moist-swab method. The increased frequency of detection by the agar-contact method appeared to be related to an increased sensitivity for the detection of low numbers of streptococcal colony-forming units on the normal skin.

Mucoid strains of Pseudomonas aeruginosa isolated from the respiratory tract of patients with cystic fibrosis (CF), those obtained from non-CF patients, and those obtained in vitro by the action of phage, were found to be stable in their mucoid colonial form when serially subcultured on deoxycholate-citrate agar. The ability of anionic, cationic and neutral surfactants to stabilise mucus production is described. The possible importance of dipalmitoyl lecithin as a stabilising agent for mucus production in vivo is considered, with particular reference to the role of mucoid P. aeruginosa in CF disease.

Five ureaplasmas (T-mycoplasmas) of human origin and four of bovine origin were inoculated into the mammary glands of mice. The strains multiplied and neutrophils were observed in sections of infected glands. Some of the glands were macroscopically inflamed, albeit slightly, at necropsy but none of the mice showed any sign of disease during the course of the experiments. All nine ureaplasma strains produced mastitis in BSVS mice and the mammary glands of mice appear more susceptible to ureaplasmas than the udders of cows or goats. Mouse mastitis is suggested as being a suitable small animal model for studying ureaplasma infections.

A method for pyocin-sensitivity typing by means of “phage-free” preparations of pyocin is described. The method was tested on 227 isolates of P. aeruginosa, collected from 34 different foci of infection in hospitals in the British Isles and the results were compared with those for combined serological and phage typing of all strains and pyocin production of 105 of the isolates. It is concluded that pyocin-sensitivity typing is a simple and reliable method giving a high degree of discrimination, comparable to that of combined serological and phage typing, and it is suitable for use in routine hospital laboratories.

A provisional serotyping scheme for Bacillus cereus has been developed. Eighteen selected cultures of B. cereus isolated from foods and clinical specimens were used to prepare agglutinating sera against the flagellar antigen. There were no significant cross-reactions between the sera.

The sera were used to type 137 isolates of B. cereus from 34 British and Australian incidents of food poisoning associated with the consumption of cooked rice. The majority of the isolates from samples of food (56 of 84; 66.7%) and from clinical specimens (43 of 53; 81.1%) were of H-serotype 1. Types 1, 3 and 5 were isolated from foods, clinical specimens or both, obtained from 31 of the 34 episodes.

Sixty-six isolates of B. cereus were obtained from 63 samples of uncooked long-grain rice. The majority of the isolates (38 of 66; 57.6%) were untypable and types 1, 3 and 5 made up only 5 of 66 (7.5%) of the total.

The results support the theory that B. cereus may cause two distinct forms of foodborne illness. Strains from incidents of food poisoning characterised by a longer incubation period and with diarrhoea as the main symptom have provided serotypes 2, 6, 8, 9 and 10, whereas those causing the rice-associated emetic illness are usually serotypes 1, 3 or 5.

Various factors influencing the susceptibility of C3H mice to lethal infection by the phycomycete Absidia ramosa were examined. Mice 19–21 days old were exposed to graded doses of A. ramosa spores by various routes. After intravenous inoculation with doses in excess of 103 viable units, a variable proportion of mice developed lethal phycomycosis of the central nervous system within 2–8 days. The proportion of mice affected was related to the inoculum size, doses of 5 × 107 spores producing lethal infection in 90–100% of the mice. The disease was characterised by signs of involvement of the central nervous system appearing 8–12 h before death. At necropsy, fungal hyphae, frequently surrounded by infiltrations of mononuclear cells, could be demonstrated in the brain. Lesions were also often present in the kidneys; in other organs they were rare, but the presence of viable fungal spores could be detected by cultural procedures. Subcutaneous inoculation of A. ramosa spores did not produce lethal infection but intraperitoneal inoculation occasionally did so. Direct intracerebral inoculation invariably produced lethal infection even with very small doses of spores. The clinical and histopathological features of the disease were almost identical with those resulting from intravenous inoculation.

Pre-inoculation treatment with azathioprine, cyclophosphamide and antithymocyte serum did not increase susceptibility. Susceptibility was increased by injections of zymosan, aggregated γ-globulin, cortisone acetate and Fe(II) salts and by reticuloendothelial blockade. These treatments increased the proportion of mice developing lethal phycomycosis of the central nervous system, and in the case of cortisone acetate, also promoted disseminated infection.

It was concluded that the natural resistance of mice to A. ramosa infection was probably dependent upon the activity of phagocytic cells, possibly acting in conjunction with complement and other non-specific serum factors.