THE factors affecting strains of Escherichia coli carried in the bowel of man are poorly understood. Some workers have found the coliform population of the bowel to be relatively stable (Sears, Brownlee and Uchiyama, 1950), but others have shown that the faecal coliform flora may change (Cooke, Ewins and Shooter, 1969; Wiedmann and Knothe, 1969) and this, in one instance, has been related to the ingestion of large numbers of E. coli in food . It has also been postulated that these strains of E. coli may be of animal origin, and may reach the prepared food by cross-contamination in the kitchen .It is not known whether all strains of ingested E. coli will establish themselves in the bowel, what numbers if ingested will be detectable in the faeces, and whether strains from different sources or of different serotype or colicine type behave differently. The experiments reported here were performed in an attempt to answer these questions. MATERIALS AND METHODSVolunteers. These were one man and two women who were members of the laboratory staff. They were aged 33-37 yr, and had no known abnormality of the gastro-intestinal tract. They were not receiving antibiotics and were eating a normal mixed diet. The food eaten by these volunteers was not examined for the presence of coliform bacteria.E. coli strains for ingestion. Twelve strains of E. coli, some of human and some of animal origin, were ingested. The sources, serotype, antibiotic sensitivity, colicinogenicity, and colicine sensitivity of the strains are shown in table I.The human strains were isolates from normal faeces of patients in a medical ward. The four animal strains were faecal isolates from healthy animals.Except on two occasions, the strains were rendered resistant to streptomycin or nalidixic acid in the laboratory before they were ingested. From a 5-hr broth culture of the test strain 0.5 ml was added to 200 ml of cold milk which was drunk in the late afternoon, 3-4 hr after the last meal. The numbers of organisms ingested, determined by surface-viable counts on blood agar, ranged from 105 to 108 except that on one occasion 1011 freeze-dried organisms were ingested. Examination of faeces. Specimens of faeces were examined on at least three occasions before ingestion of E. coli, and on three occasions after its disappearance. In each experiment, every specimen of faeces passed was examined.Specimens were examined as soon as they were passed or were stored for up to 24 hr at
SYNOPSISThe incorporation of trimethoprim into existing selective media using either saponin-lysed blood agar or chocolate agar as the base is suggested for the routine isolation of the gonococcus. The principal advantage over other selective media is the inhibition ofProteus mirabilis and other commensal organisms as a consequence of which multiple swabs can be plated out onto a single selective plate irrespective of source, while the recovery rate of the gonococcus from these specimens is increased. The relative merits of both basic media are briefly discussed.The isolation of N. gonorrhoeae on selective media is still hampered by their failure to suppress the growth of some commensal organisms, notably Proteus mirabilis, spreading members of which overgrow other organisms and render isolation of the gonococcus impossible. Also, if multiple swabs are inoculated onto a single plate, one colony of this organism will spread and invalidate all results. The incorporation of first ristocetin and polymyxin (Thayer and Martin, 1964), and, more recently, vancomycin, sodiumcolistimethate, and nystatin (Martin, Billings, Hackney, and Thayer, 1967) incorporated into the VCN medium of Thayer and Martin. The lowest amount of trimethoprim which would inhibit the growth of 10 spreading strains of Pr. mirabilis was 1-5 ,tg/ml. Six times this amount did not affect the recovery of N. gonorrhoeae and 3 ,ug/ml was selected as the amount which would safely inhibit Pr. mirabilis while not affecting the gonococcus. Vancomycin was then omitted from the above mixture but had to be reintroduced as certain commensals, notably staphylococci, were insufficiently suppressed.A comparison was made in the first part of the study of the isolation rates of N. gonorrhoeae on plain chocolate agar, the VCN medium and the VCN medium with trimethoprim 3,ug/ml. In the latter medium the vancomycin was increased fronP 3,ug/ml to 5,ug/ml, a previous experiment showing this concentration to be more effective against Gram-positive cocci without reducing the yield of gonococci. A similar study was made in the second part but using saponin-lysed blood agar as the basal medium. Vancomycin was used at a concentration of 3,ug/ml as in the original Thayer and Martin medium, but in the trimethoprimcontaining medium nystatin was replaced by an
Summary A 23 year old woman died within six hours of admission from acute disseminated intravascular coagulation. Fusobacterium necrophorum, a Gram negative anaerobic organism, was isolated as a single pathogen from the blood cultures. This association has not previously been reported.
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