A quantitative in vivo assay for bacterial adherence to the urethra

Bacterial adherence to urinary tract mucosal surfaces is thought to be the initiating event in ascending urinary tract infection. To study this process, we have developed a physiologic, quantitative, in vivo assay for bacterial adherence to the urethra. The effect of local (vaginal mucosa) immunization on the adherence of E. coli to the urethra was studied. Local immunization with a formalinized E. coli vaccine significantly reduced the capacity of viable cells of the immunizing strain to adhere to the urethra. Immunization-induced decrease in bacterial adherence to urethral mucosa is in agreement with our previous observations that immunization of the vaginal mucosa decreases the adherence of E. coli to the rat bladder. These data provide further evidence of a protective effect from local immunization against ascending urinary tract infection. No obvious change in indigenous urethral flora occurred after mucosal immunization.

The effect of microbial flora, diet, and age on the tumoricidal activity of natural killer cells

This study examined the effects of diet (chemically defined vs natural-ingredient), age, and microbial flora on the tumoricidal activity of natural killer (NK) cells from the spleens of mice. Results from a 4-h 51Cr-release assay indicate the following: Germfree C3H/HeCr mice raised on a chemically defined diet had significantly greater NK cell activity than their germfree or "clean-conventional" (i.e., barrier-maintained) counterparts who were raised on a sterilized natural-ingredient diet. The NK activity of germfree mice was dramatically increased after their alimentary tract was colonized with a complex intestinal flora. Conventional mice raised under clean (barrier) conditions had significantly less NK cell activity than nonbarrier-maintained mice. Switching germfree mice from a chemically defined diet to a sterile natural-ingredient diet did not enhance NK cell activity. No significant differences in NK activity were evident with C3H/HeCr mice of different (6-10 wk vs 29-36 wk) ages. These results indicate that diet and microbial flora can modulate the NK cell activity of mice.

Enhanced immune response in the urinary tract of the rat following vaginal immunization

The immune response in the rat urinary tract was assessed by an enzyme-linked immunosorbent assay for immunoglobulins following vaginal immunization and subsequent intravesical challenge with live E. coli 06. Vaginally immunized rats showed a strong and rapid bladder immune response following intravesical challenge, in contrast to nonimmunized control rats. The immune response was localized to the urinary tract in that antibody to E. coli 06 was not detected in serum, saliva and vaginal washes from immunized rats.

Colonization of congenitally athymic, gnotobiotic mice by Candida albicans

Colony counts, scanning electron microscopy, and light microscopy were used to assess the capacity of Candida albicans to colonize (naturally) and infect the alimentary tract of adult and neonatal (athymic [nu/nu] or heterozygous [+/nu] littermates) germfree BALB/c mice. When exposed to yeast-phase C. albicans, the alimentary tract of adult germfree mice (nu/nu or +/nu) is quickly (within 24 to 48 h) colonized with yeast cells. Neither morbidity nor mortality was evident in any mice that were colonized with a pure culture of C. albicans for 6 months. Yeast cells of C. albicans predominated on mucosal surfaces in the oral cavities and vaginas of adult athymic and heterozygous mice. In both genotypes, C. albicans hyphae were observed in keratinized tissue on the dorsal posterior tongue surface and in the cardial-atrium section of the stomach. Conversely, neonatal athymic or heterozygous mice, born to germfree or C. albicans-colonized mothers, do not become heavily colonized or infected with C. albicans until 11 to 15 days after birth. Although yeast cells adhered to some mucosal surfaces in vivo, neither widespread mucocutaneous candidiasis, i.e., invasion of mucosal surfaces with C. albicans hyphae, nor overwhelming systemic candidiasis was evident in neonatal (nu/nu or +/nu) mice. Thus, even in the absence of functional T-cells and a viable bacterial flora, athymic and heterozygous littermate mice (adult or neonatal BALB/c) that are colonized with a pure culture of C. albicans manifest resistance to extensive mucocutaneous and systemic candidiasis.

Systemic candidosis in silica-treated athymic and euthymic mice

Intravenous silica injections were used to assess the role of macrophages in the resistance of BALB/c nude and euthymic mice to systemic candidosis. CFU of Candida albicans in the kidneys, livers, and spleens of saline- or silica-treated mice were enumerated at various times after inoculation with 10(4) viable yeast cells. The number of C. albicans organisms recovered from the kidneys of silica-treated euthymic mice was similar to the number recovered from saline-treated controls during the first 3 days of infection; however, at every assay period thereafter, the number of organisms recovered from the kidneys of silica-treated mice was dramatically reduced (100- to 1,000-fold). Conversely, silica-treated nude mice were no more susceptible to systemic candidosis than were saline-injected nude mice. Silica treatment did not alter the ability of treated or control mice to clear C. albicans from the liver and spleen. These results demonstrate that macrophages play an important role in susceptibility to Candida infections.

Clostridium tetani growth and toxin production in the intestines of germfree rats

Germfree rats were challenged orally and intrarectally with spores of Clostridium tetani. Although C. tetani spores remained viable in the intestinal tract, they were unable to germinate. Germfree rats were then challenged orally with vegetative cells of C. tetani. Vegetative cells were able to colonize the intestinal tract, replicate, and produce toxin. Tetanus antitoxin, but no tetanus toxin, was detected in the sera of monoassociated rats.

The thymus dependency of acquired resistance to Trichophyton mentagrophytes dermatophytosis in rats

Congenitally athymic "nude" (RNU/RNU) rats and euthymic (+/RNU) rats were cutaneously inoculated with Trichophyton mentagrophytes. Dermatophytosis, as evidenced by erythema and scaling, was observed in both athymic and euthymic rats by day 7 postinfection. Macroscopic lesions in +/RNU rats became intensely erythematous (climax days 10-14), were limited in spread and alopecia (days 16-20), and healed with hair regrowth by day 35. In nude rats, however, erythema peaked early (days 8-10) and a persistent, mild erythema and scaling spread over the animals' backs. Viable T. mentagrophytes was cultured from the skin of all infected nude rats for the duration of each experiment (90 days), while +/RNU rats became culture-negative by day 35. Following clearance of primary lesions, +/RNU rats manifest a delayed-type hypersensitivity skin test response to soluble trichophytin and an accelerated cutaneous inflammation and enhanced resistance to reinfection. Although T. mentagrophytes primarily invaded the keratinized layers of the epidermis in both nude and +/RNU rats, hyphae and arthrospores were also observed within the nucleated layers of the internal root sheath of hair follicles. Our observations are consistent with the hypothesis that thymus-dependent cell-mediated immunity is required to limit cutaneous spread and terminate cutaneous T. mentagrophytes infection. This acquired immunity against T. mentagrophytes in +/RNU rats was characterized histologically by: (1) an intense inflammatory migration of lymphocytes, monocytes, and macrophages into the epidermis, dermis, and follicular epithelium; (2) hyperplasia of the epidermis and follicular epithelium; and (3) elimination of arthrospores and hyphae from T. mentagrophytes-infected skin.

The influence of a gastrointestinal microflora on natural killer cell activity

These studies demonstrate that the natural cytotoxicity of BALB/c mouse spleen cells for 51Cr-labeled YAC-1 cells can be significantly enhanced by microorganisms in the alimentary tract. Spleen cells from germfree BALB/c mice, euthymic, athymic, or non-nude background (+/+), had natural cell-mediated cytotoxicity for YAC-1 cells. Intestinal colonization with a few (flora-defined) or many (complex flora-conventionalized) microorganisms significantly enhanced natural cell-mediated cytotoxicity of athymic and euthymic mice over their germfree counterparts. Conversely, colonization of the alimentary tract of athymic and euthymic germfree mice with a pure culture of Candida albicans or colonization with Candida and a Bacillus sp. did not enhance natural cell-mediated cytotoxic activity over germfree levels. Spleen cells from germfree athymic mice were significantly more cytotoxic than spleen cells from germfree BALB/c mice that did not carry the nude gene (ie, +/+). In the germfree or gnotobiotic state, no difference in natural killer cell activity was evident between athymic (nu/nu) and heterozygous (+/nu) littermate mice; however, athymic (nu/nu) flora-defined or conventionalized mouse spleen cells were significantly more cytotoxic for YAC-1 cells than splenocytes from flora-defined or conventionalized heterozygous (+/nu) littermates. Spleen cells from BALB/c mice that were athymic (nu/nu) and colonized with a complex microbial flora (ie, conventionalized) had the highest percentage of cytotoxicity, at three different effector to target ratios, for YAC-1 cells. These studies indicate that the intestinal microflora can alter murine natural cell-mediated cytotoxicity.

Pseudomembranous colitis in Clostridium difficile-monoassociated rats

Germfree rats were monoassociated with either a toxin-producing strain of Clostridium difficile (Tox+) or a variant of this strain (ToxR) which produced much less toxin (1/10,000) in vivo and in vitro. Monoassociation of germfree rats with C. difficile Tox+ resulted in mortality (17%) and in pathology to the small and large intestines, livers, and lungs. Cecal filtrates from the Tox+-monoassociated rats were cytotoxic for tissue culture cells. The cytotoxicity of cecal filtrates could be blocked by sera from Tox+-monoassociated rats. Monoassociation of rats with C. difficile ToxR resulted in no deaths or pathology, and much less toxin was detected in the cecal filtrates of these animals than in those of rats colonized with the Tox+ strain. This gnotobiotic model may be useful for investigating the etiology, prophylaxis, therapy, and exacerbation of C. difficile-induced pseudomembranous colitis.

Vaginal immunization against urinary tract infection

In an attempt to lessen susceptibility to induced urinary tract infections, rats were immunized by a non-traumatic, non-parenteral, intra-vaginal route. Up to 8 weeks following vaginal immunization against Escherichia coli O6, there was decreased adherence of viable E. coli O6 to the rats' bladder epithelium. Scanning electron microscopy of the urothelium revealed that immunized rats had less epithelial swelling, exfoliation, and surface mucin disruption than non-immunized control animals. Immunized animals also cleared an induced E. coli O6 infection from the kidneys and bladder faster than control animals. Vaginal immunization may offer a new approach to prophylaxis and treatment of ascending urinary tract infections.

Origin of excess urinary nitrate in the rat

The ability of intestinal microorganisms to N-oxidize nitrogenous compounds to nitrite or nitrate was evaluated both in vivo and in vitro. Nitrate balance studies with germ-free and conventional rats indicated that the host and not the microbial flora is responsible for excess urinary nitrate. In vitro studies showed that most intestinal microorganisms are not able to N-oxidize nitrogenous compounds to nitrite. Although the metabolic pathway for endogenous nitrate formation remains unknown, the capacity of the rats to N-oxidize acetohydroxamate and hydroxylamine to nitrate indicates that such compounds could be intermediates in nitrate synthesis.

Resolution of induced urinary tract infection: an animal model to assess bladder immunization

The resolution of an Escherichia coli urinary tract infection in the bladder and kidneys of control and immunized rats was used to assess their resistance to experimentally induced infection. Prior intravesical immunization of rats with formalin killed E. coli 06 resulted in faster resolution of an infection that had been induced with viable E. coli 06 than was observed in nonimmunized controls. The faster resolution of infection after immunization correlates with our previous findings of decreased adherence of bacteria to urothelium of immunized rats and supports the hypothesis that local immune responses in the urinary tract may play a role in resistance to recurrent urinary tract infections.

Lysosomal enzyme activity in pulmonary alveolar macrophages from conventional, germfree, monoassociated, and conventionalized rats

Pulmonary alveolar macrophages (PAM) were harvested from conventional (CONV), germfree (GF), conventionalized, and monoassociated (MA) rats. Germfree rats had significantly fewer PAM than did their CONV, conventionalized or MA counterparts. The bronchopulmonary wash from the CONV and conventionalized rats contained higher lysosomal specific activity for beta-glucuronidase and cathepsin D than did similar washes from GF rats. Cellular and subcellular PAM fractions from GF rats also showed decreased enzyme activity in comparison with similar fractions from the PAM or CONV rats. Colonization of GF rats with one (MA) or more bacterial species (conventionalized) increased the beta-glucuronidase and cathepsin D activity of their PAM as well as total PAM. These data suggest that the intestinal flora not only enhances PAM proliferation but also is associated with an increase in their lysosomal enzyme activity.

Killing of Listeria monocytogens by conventional and germfree rat sera

Serum from both germfree and conventional rats, but not plasma or plasma serum, killed Listeria monocytogenes in vitro by a calcium-dependent mechanism that was independent of either complement or lysozyme and was not inhibited by the addition of iron. The listericidin was purified by passing either rat serum or platelet lysate through a nitrocellulose filter (0.2 micrometer) and eluting the activity from the filter with 0.02 N HCl. The partially purified listericidin was heat stable (56 degrees C for 30 min), removed by absorption with zymosan or bentonite, sensitive to treatment with trypsin or pronase, and inhibited by the addition of citrate (0.045 M), suggesting that the serum listericidin is a cationic protein. The development of serum listericidal activity, which could be important in the innate resistance of rats to L. monocytogenes, was dependent on both age and microbial status. Although some discrepancies exist between the serum listericidin and previous descriptions of serum beta-lysin, we believe that the rat serum listericidin is a similar cationic protein.

Evaluation of nitrate synthesis by intestinal microorganisms in vivo

The nitrate balance of germfree and conventional rats was assessed to determine whether the intestinal flora produces nitrate in vivo. The results indicate that there can be excess nitrate in the urine of germfree as well as conventional rats. This nitrate is apparently of host origin, and the presence of intestinal flora decreases the output of nitrate in urine.

Interaction of rat platelets with Listeria monocytogenes

Listeria monocytogenes induced aggregation of rat platelets in vitro and stimulated the nonlytic release of [3H]serotonin. Listeria-induced platelet aggregation and serotonin release required the presence of intact Listeria, was maximal at a 1:1 Listeria/platelet ratio, required a plasma cofactor, and was not inhibited by indomethacin, acetylsalicylic acid, or apyrase. Aggregation either of platelets in platelet-rich plasma with adenosine diphosphate or of washed platelets with thrombin resulted in the release of a listericidin from the platelets; however, direct interaction of L. monocytogenes with platelet-rich plasma did not kill Listeria. The ability of rats to clear an intravenous challenge of L. monocytogenes (0.005 50% lethal dose), as determined by the recovery of viable L. monocytogenes from the spleen and liver, was unaffected by prior treatment with antiplatelet serum.

Pathogenesis of Listeria monocytogenes for gnotobiotic rats

Listeria monocytogenes colonized the gastrointestinal tract of adult germfree rats (10(10) to 10(11)/g, dry weight) within 24 h after oral exposure. Between 3 and 14 days after monoassociation, L. monocytogenes caused a self-limiting pseudomembranous colitis, bacteremia, and infection of the spleen and liver. Monoassociation of rats with Listeria for 8 weeks stimulated 32- and 4-fold increases in serum immunoglobulin A (IgA) and IgG, respectively, whereas serum IgM decreased 2-fold. The normal microbial flora was inhibitory to Listeria colonization, since L. monocytogenes was cleared from the gastrointestinal tract of formerly monoassociated rats within 20 days after conventionalization and did not colonize the gastrointestinal tract of conventional rats after intragastric instillation of 10(8) viable L. monocytogenes. Listeria-monoassociated rats delivered large litters of healthy pups whose gastrointestinal tracts were slowly colonized with L. monocytogenes. between 3 and 60 days of age, Listeria-monoassociated rat pups exhibited eight- and fourfold increases in serum IgG and IgM, respectively; however, serum IgA was elevated (16-fold) only at 9 to 15 days of age. Adult Listeria-monoassociated rats had acquired cellular resistance to intravenous challenge with L. monocytogenes. Prolonged monoassociation of L. monocytogenes in rats attenuated its virulence for conventional rats.