The ability of motile strains of the Ogawa and Inaba serotypes of classical Vibrio cholerae and of the El Tor biotypes to kill suckling mice after oral challenge with 108 colony-forming units (representing at least 100 to 1,000 minimal lethal doses) was compared to that of nonmotile derivatives of the same strains. Loss of motility, in each case, resulted in a marked reduction in virulence. The mortality (at 36 h) caused by 10 of the 13 nonmotile strains was 32% or less, whereas the motile wild-type strains resulted in nearly 100% deaths. The reduced virulence of the nonmotile strains was associated with reduced capacity to adsorb to the surface of segments of mouse intestine. The mutants were tested for alterations in enterotoxin production and surface properties. The results suggest that motility may contribute to virulence by increasing the chance for association of the vibrios with the intestinal mucosa.

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Mice immunized with purified whole-cell ribonucleic acid (RNA), RNA from the bacterial “particulate” fraction, and ribosome-associated RNA obtained from Salmonella typhimurium were found to be resistant to subsequent challenge infection with virulent salmonellae. Chemically, the immunogenic nucleic acid fractions contained from 1 to 3% “contaminant” material defined (based on the mean of 19 different preparations) as protein (0.24%), deoxyribonucleic acid (0.43%), methyl pentose (0.64%), hexose (1.58%), and undefined carbohydrate (0.76%). Heptoses and lipoidal material were not detectable in any of the immunogenic preparations examined. Physically, the nucleic acid preparations, after analytical ultracentrifugation, exhibited three boundaries similar to those reported elsewhere in comparable systems: 4 to 5 S , 16 S , and 23 S . An evaluation of the immunity induced by the ribosome-associated RNA established that the immune response was (i) comparable to that induced 15 days postimmunization with live salmonellae and by ribosomal vaccines, but greater at 30 days postimmunization than that in mice immunized with attenuated salmonellae; (ii) dependent on the quantity of immunogen administered; (iii) dependent on the size of the infective inocula; (iv) inhibited at 15 but not at 30 days postimmunization when the immunogenic nucleic acid preparations were incorporated into Freund's incomplete adjuvant, (v) reduced or lost by dialysis in relatively high or low immunizing doses, respectively; and (vi) unaffected by enzymatic treatment of the preparations with trypsin, deoxyribonuclease, Pronase plus pancreatic ribonuclease, or pancreatic ribonuclease alone. The possible mode of action of ribosome-associated RNA in inducing an immune response to subsequent challenge infection with the homologous organism is discussed.

Systemic and gastrointestinal infection can be established in infant mice after intragastric challenge with Candida albicans. Differences in virulence of the six strains tested were noted. As early as 3 h after infection, some but not all livers, spleens, and kidneys contained C. albicans, but the peak number of colonyforming units in these organs was seen at 6 h. The early colonization of the organs could not be attributed to aspiration of the inoculum since about 90% of lungs and livers tested yielded no colony-forming units at 10 to 15 min postinfection. In animals with systemic infections, lungs, livers, kidneys, and spleens showed similar numbers of colony-forming units within the organs during the first 6 h postinfection, and then the number declined progressively up to 72 h. The gastrointestinal tract was colonized throughout a 20-day period of study. Counts made at intervals beyond day 1 yielded between 105 and 106 colony-forming units in the stomach, ileum, and cecum. Preparatory techniques for scanning electron microscopy preserved the yeast, intestinal mucus layer, and epithelial surface and made it possible to visualize the association between the pathogen and host tissues within the digestive tract. Generalized systemic infections produced by Candida albicans have increased in importance

Three human isolates of Campylobacterjejuni were grown in a biphasic culture medium with and without the addition of a synthetic chelator to induce iron limitation. Cells grown in low-iron medium exhibited slower growth rates and altered cellular morphology. Increased numbers of longer, more filamentous forms were seen in Gram-stained smears. Three proteins, with apparent MrS of 82,000, 76,000, and 74,000, were consistently present in the outer membrane of cells grown in low-iron medium. At least one of these proteins (76,000 to 74,000) was exposed on the cell surface. A bioassay was used to look for the production of siderophores by these and other strains of C. jejuni. Seven of 26 strains tested produced detectable amounts of siderophores. Growing strains at 42°C failed to suppress siderophore synthesis or to alter the outer membrane protein profiles of iron-starved cells. The ability of three strains to utilize exogenously supplied siderophores for growth in low-iron medium was also examined. All three strains were able to utilize enterochelin and ferrichrome, but none utilized aerobactin, rhodotorulic acid, or desferrioxamine B. The effect of iron on the virulence of C. jejuni for 11-day-old chicken embryos inoculated via the chorioallantoic membrane was also determined.

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Infant mice 8 days of age were infected orally with virulent, motile, classical or El Tor strains of Vibrio cholerae and with nonmotile mutants of low virulence derived from the same strains. At intervals of 8 and 12 h postinfection, frozen thin sections of the ileum were prepared, stained with fluorescein isothiocyanate-labeled rabbit anti-vibrio antibody, and examined with the fluorescence microscope. The motile organisms were present in larger numbers, especially at 12 h, and had penetrated the intervillous spaces and crypts of Lieberkuhn more completely than nonmotile vibrios. Dilution counts were made on various regions of the intestines of infant mice challenged orally 12 h previously with either motile or nonmotile strains of V. cholerae. Greater numbers of organisms were found, especially in the upper intestinal regions, when motile organisms were used. Low numbers of vibrios, limited mostly to the lumen, were seen in the ileum of infant mice infected with motile organisms when the infants were the offspring of mothers that had been immunized with crude flagellar vaccine or a vesicular preparation derived from the vibrio cell surface. The distribution of vibrios in this case was similar to that found in infected infants of unvaccinated mothers challenged with nonmotile organisms. Motility appears to enable the bacteria to better populate the upper regions of the intestinal tract and to avoid the washing effects of secretions and peristalsis. Antibacterial immunity may function, at least in part, by making it impossible for motile vibrios to accomplish this widespread distribution within the ileum.