Cultural characteristics of Yersinia enterocolitica and Yersinia pseudotuberculosis on differential media.

A study was made of the cultural characteristics of 43 strains of Yersinia enterocolitica and 49 strains of Yersinia pseudotuberculosis on media commonly used for the isolation and differentiation of enteric bacteria. Best growth of the yersinia occurred on MacConkey agar, followed by growth on SS agar; none of the strains of either species developed colonies on brilliant green agar. The Y. pseudotuberculosis strains developed only one type of colony on MacConkey, SS, EMB, Hektoen, and XLD media whereas Y. enterocolitica exhibited more than one type of colony on all of the media except MacConkey and SS agar. The 'lactose-positive' colonies of Y. enterocolitica were especially distinctive on EMB. These were quite dark, with or without a metallic sheen, and closely resembled the colonies of lactose fermenting Escherichia coli on EMB agar. Strains of both Y. enterocolitica and Y. pseudotuberculosis grew better on the differential media at 35 degrees C than at 22 degrees C but the growth of Y. pseudotuberculosis was considerably slower than that of the other species.

Agglutination with O antisera of salmonella exposed to antibiotics.

Five strains of Salmonella were grown on agar containing subinhibitory concentrations of ampicillin, gentamicin, tetracycline, or chloramphenicol, and on drug-free agar (control). Antigens were prepared by heating bacteria suspensions in saline solution at 100 C or by suspension in alcohol. Antigens were tested for agglutinability with somatic O antisera and fluorescent antibody staining. The alcohol-treated antigens prepared from organisms grown in the presence of antibiotics other than ampicillin had lower agglutination titers than did the control grown on drug-free agar. Heat-treated control antigens had lower agglutination titers than did the alcohol-treated control antigens. The agglutinability of heat-treated antigens prepared from organisms that had been exposed to antibiotics was preserved or enhanced. The agglutinated filaments produced a flocculent sediment, in contrast to the granular sediment of the controls. No significant morphologic abnormality in cell-wall structures of antibiotic-exposed cells could be detected by either electron microscopy or the fluorescent antibody staining.

Molecular relationships among the Salmonelleae.

Polynucleotide sequence relatedness studies were carried out to determine the extent of divergence present in members of the tribe Salmonelleae and between salmonellae and other enteric bacteria. Typical Salmonella were 85 to 100% related. Two groups of biochemically atypical Salmonella showed somewhat lower binding to typical salmonellae and to each other. Arizona were 70 to 80% related to salmonellae. Two groups of Arizona were detected. These groups correlated with the presence of monophasic or diphasic flagellar antigens. Salmonella and Arizona were no more related to Citrobacter than to Escherichia coli (45-55%). Relatedness of Salmonella and Arizona to other enterobacteria ranged from 20 to 40% with klebsiellae and shigellae, to 20 to 25% with erwiniae, and to less than 20% with edwardsiellae and Proteus mirabilis.

Phase variation of Andrewes in Salmonella enteritidis bioserotype paratyphi-A.

The natural occurrence of a strain of Salmonella enteritidis bioserotype Paratyphi-A is reported, in which the flagellar antigens segregated readily into normal phase 2 antigens and mixtures of normal phase 1 and phase 2 antigens, and in which phase variation of Andrewes was demonstrated with ease.

Characterization of indole-positive Proteus mirabilis.

Thirteen indole-producing, swarming strains of Proteus were identified by additional biochemical testing as being Proteus mirabilis. These strains were characterized by 40 biochemical tests and by susceptibility testing to 11 antibiotics. All produced ornithine decarboxylase and were susceptible to members of the penicillin-cephalosporin groups of antibiotics. These indole-positive strains are similar to indole-negative P. mirabilis and are distinctly different from P. vulgaris. For greatest accuracy and to insure greatest clinical relevancy, P. mirabilis and P. vulgaris should be distinguished from one another in the laboratory by performing both the indole and ornithine decarboxylase tests.

Serratia marcescens: biochemical, serological, and epidemiological characteristics and antibiotic susceptibility of strains isolated at Boston City Hospital.

The biochemical, serological, and epidemiological characteristics of 95 strains of Serratia marcescens isolated at the Boston City Hospital were examined. Several strains were shown to be endemic, and the majority of isolates were cultured from urine or respiratory secretions. Serratia species were highly resistant to polymyxin B and the cephalosporins, and various proportions were also resistant to other antibiotics including kanamycin, but all of the isolates were sensitive to gentamicin. The appearance of resistance to kanamycin and nalidixic acid among endemic strains was demonstrated. The nosocomial nature of Serratia infections, particularly those involving the urinary tract, was confirmed. Many clinical bacteriology laboratories currently fail to identify the nonpigmented strains.

Prevalence of serotypes of Salmonella.

The distribution of species and serotypes of Salmonella among 2,498 cultures which were isolated in the United States and its territories is presented. These isolates were received for examination during the 12-month period between October 1, 1966 and September 30, 1967. These and other data obtained from the Salmonella Surveillance Summaries for the past five years indicate that a relatively small number of species and serotypes of Salmonella are regularly isolated from diagnostic specimens. Of approximately 1,300 presently known Salmonella species and serotypes, 33 account for almost 90% of the isolates reported from humans and approximately 80% of the isolates from nonhuman sources. The 50 most prevalent species and serotypes account for 97% of the isolates from humans. An abbreviated antigenic schema based on these 50 species and serotypes of Salmonella, in conjunction with adequate biochemical tests, permits complete bacteriological characterization of the common Salmonella

Biochemical differentiation of the Enterobacteriaceae with the aid of lysine-iron-agar.

A procedure is described for identifying members of the family Enterobacteriaceae isolated from clinical specimens. The methods are based on primary differentiation of the various groups of bacteria by the use of Kligler Iron Agar and lysine-iron-agar. For identification of Salmonella, Shigella, and Arizona group organisms from stools, Triple Sugar Iron Agar and lysine-iron-agar are employed. The usefulness of this schema for diagnostic bacteriology laboratories is discussed. It is not intended to replace methods used in reference or research laboratories.