Prospective case-cohort study of intestinal colonization with enterococci that produce extracellular superoxide and the risk for colorectal adenomas or cancer.

OBJECTIVE: The aim of this study was to determine whether intestinal colonization with enterococci that produce extracellular superoxide (O2*-), a free radical implicated in the development of colorectal cancer, is associated with these lesions or their precursors. METHODS: A prospective case-cohort study was performed by isolating enterococci from stools of consecutive patients undergoing colonoscopy who had no prior history of colonoscopy or colorectal cancer. A food frequency questionnaire was also administered to control for dietary factors known to affect the risk for these lesions. RESULTS: Among 159 evaluable participants were 77 with no precancerous or cancerous pathology, 61 with adenomas <2 cm, 10 with adenomas > or =2 cm, and 11 with cancer. Regression analyses found no associations for those subjects with adenomas of any size or with cancer and colonization with O2*--producing enterococci, any nutrient, or age. For those patients with large adenomas > or = 2 cm or cancer, however, significant associations were noted for age (OR 1.94 per decade, 95% CI 1.2-3.5), beta-carotene (OR 0.44 per 500 microg/1000 kcal/day, 95% CI 0.2-0.8), vitamin A (OR 3.20 per 500 microg/1000 kcal/day, 95% CI 1.2-8.9), and vitamin E (OR 0.09 per 10 mg/ 1000 kcal/day, 95% CI 0.006-0.9), but not colonization with O2*--producing enterococci. Second stools collected 1 yr later, however, often contained dissimilar enterococcal flora, undermining an important study assumption. CONCLUSIONS: Significant associations were found for those with large adenomas or cancer (but not small adenomas), with age, and with foods enriched for vitamin A, vitamin E, and beta-carotene. An association between colonization with O2*--producing enterococci and colorectal adenomas or cancer, however, could not be ascertained, possibly because intestinal enterococcal flora changes over time, leaving a potentially cohesive hypothesis of colon cancer and risk factors as yet unanswered.

Enterococcus faecalis cytolysin without effect on the intestinal growth of susceptible enterococci in mice.

A murine model was developed to determine whether the Enterococcus faecalis cytolysin, through its bacteriolytic action on gram-positive bacteria, could promote intestinal overgrowth of cytolytic strains. Sets of E. faecalis strains with varying cytolytic production and susceptibility to cytolytic activity were mixed 1:1 and allowed to compete in vitro in broth or in vivo after orogastric administration in mice pretreated with antibiotics. In general, cytolytic strains outgrew, by as much as 2000-fold, competing cytolysin-susceptible or -hypersusceptible strains in vitro. In contrast, no growth advantage was observed in vivo, despite similar transient colonization of the murine intestinal tract by both cytolytic and cytolysin-susceptible strains. These data suggest that cytolysin plays little role in promoting intestinal overgrowth of enterococci through bacteriolytic activity.

Gastric colonization with Candida albicans.

We adapted a rat model of gastrointestinal candidiasis for studies of in vivo gastric colonization with Candida albicans. Whereas normal rats cleared a single intragastric inoculum of 5 x 10(6) C. albicans from the stomach within 4 hours, rats pretreated with chloramphenicol and gentamicin achieved stable gastric colonization for at least 5 days after administration of this inoculum. We next used this model to study host modifications hypothesized to alter gastric colonization. A first group received dilute HCl 4 hr before yeast inoculation, to induce acute superficial gastric erosions; another group was treated with glucocorticosteroid beginning 12 days before yeast inoculation; and another group received famotidine therapy beginning 3 days before yeast inoculation, to neutralize gastric acidity. Recovery of yeasts from stomachs was significantly different from the control group only in rats treated with steroids; greater colonization was found in the rats so treated. In a final group of experiments, we attempted to inhibit in vivo gastric colonization with yeasts by preincubation of yeasts in vitro with a polyclonal antiserum raised in rabbits against heat-killed C. albicans. We were not able to demonstrate inhibition of gastric colonization by preincubation with this antiserum in this model system.

Cryptosporidiosis in adult and neonatal mice with severe combined immunodeficiency.

Cryptosporidium parvum causes protracted diarrhoea in immunodeficient hosts. To characterize the role that T and B lymphocytes play in the eradication of the parasite from the intestinal mucosa, the course of infection in mice with severe combined immunodeficiency (SCID) was studied. Twenty-nine SCID and 26 BALB/c adult mice received 10(6) oocysts intragastrically. The course of infection in the two strains was similar until 2 months after inoculation, when moderate numbers of organisms were identified in the villous and crypt mucosa of the ileum and proximal colon of SCID mice. Three months after inoculation, SCID mice developed wasting and progressive intestinal and biliary tract disease. At 5 months, mortality of 72 and 0 per cent, respectively, was observed in the SCID and BALB/c mice. Twenty-four SCID and 26 BALB/c neonatal mice were also inoculated with C. parvum. Cryptosporidiosis occurred in SCID and BALB/c mice within 2 weeks of inoculation. Subsequently, BALB/c, but not SCID mice, eradicated the parasite from their intestinal mucosa. SCID mice developed progressively severe cryptosporidiosis which killed all animals within 7 weeks. Responses mediated by B or T cells, or both, appeared to play a role in eradicating C. parvum from the intestinal mucosa, since SCID mice were more severely affected than BALB/c mice. The different course of infection in adult and neonatal SCID mice indicated that other age-related factors also played a role in containing C. parvum infection.

Gastrointestinal candidiasis in a murine model of severe combined immunodeficiency syndrome.

A murine model of severe combined immunodeficiency syndrome (scid mice) affords an opportunity to study the interaction of Candida albicans with a host lacking functional B- and T-cell mechanisms. We have previously reported no significant difference in yeast recovery after intravenous challenge of BALB/c mice and scid mice with C. albicans (S. Mahanty, R.A. Greenfield, W.A. Joyce, and P.W. Kincade, Infect. Immun. 56:3162-3166, 1988). In this study, we evaluate the course of gastrointestinal candidiasis after a single oral challenge with C. albicans. BALB/c and scid mice received H2O containing 10(6) C. albicans per ml for 16 h. Half the mice of each strain continuously received H2O containing 1 mg of tetracycline per ml. Stool samples were cultured for yeast twice weekly until they were negative three consecutive times or positive for 8 weeks. Mice were then sacrificed for quantitative cultures of liver, spleen, and kidneys. At eight weeks postinoculation, 2 of 13 BALB/c mice, 0 of 14 BALB/c mice receiving tetracycline, 6 of 12 scid mice, and 8 of 13 scid mice receiving tetracycline had positive stool cultures (P less than 0.05, likelihood ratio chi-square). Quantitative recovery of yeasts from stools was also higher in the scid mice. Cultures of liver, spleen, and kidneys wer negative in all BALB/c mice and essentially all negative in scid mice; a single colony was isolated from the kidney of one scid mouse and the liver of another scid mouse. We conclude that B cells and/or T cells and their products are important in gastrointestinal colonization with C. albicans but that even in their absence, dissemination of infection from the gastrointestinal tract does not consistently occur. Thus, other aspects of host defense must be critical in containing gastrointestinal Candida colonization.

Inoculation candidiasis in a murine model of severe combined immunodeficiency syndrome.

To further elucidate the importance of T- and B-lymphocyte-mediated responses in host defense against systemic infection with Candida albicans, we studied this infection in a murine model of severe combined immunodeficiency (SCID). The course of inoculation candidiasis in these mice, which lack functional T and B lymphocytes, was compared with that in immunologically normal BALB/c mice. Mice were inoculated intravenously with 10(5) yeast cells. Quantitative cultures of liver, spleen, and kidneys were performed with necropsy specimens obtained 1, 3, 7, 10, 14, and 21 days after this intravenous inoculation. The differences in the time courses of recovery of organisms from liver and spleen specimens were not significantly different in the SCID mice compared with the BALB/c mice. The recovery of C. albicans from the kidneys was significantly lower in the SCID mice, indicating less persistence of the organism in the kidneys of the SCID mice than in those of the BALB/c mice. These data indicate that defense mechanisms other than T- and B-lymphocyte-mediated mechanisms are primarily responsible for host defense against inoculation candidiasis.