Virulence of a spaP mutant of Streptococcus mutans in a gnotobiotic rat model.
(1/1204)
Streptococcus mutans, the principal etiologic agent of dental caries in humans, possesses a variety of virulence traits that enable it to establish itself in the oral cavity and initiate disease. A 185-kDa cell surface-localized protein known variously as antigen I/II, antigen B, PAc, and P1 has been postulated to be a virulence factor in S. mutans. We showed previously that P1 expression is necessary for in vitro adherence of S. mutans to salivary agglutinin-coated hydroxyapatite as well as for fluid-phase aggregation. Since adherence of the organism is a necessary first step toward colonization of the tooth surface, we sought to determine what effect deletion of the gene for P1, spaP, has on the colonization and subsequent cariogenicity of this organism in vivo. Germ-free Fischer rats fed a diet containing 5% sucrose were infected with either S. mutans NG8 or an NG8-derived spaP mutant strain, PC3370, which had been constructed by allelic exchange mutagenesis. At 1-week intervals for 6 weeks after infection, total organisms recovered from mandibles were enumerated. At week 6, caries lesions also were scored. A significantly lower number of enamel and dentinal carious lesions was observed for the mutant-infected rats, although there was no difference between parent and mutant in the number of organisms recovered from teeth through 6 weeks postinfection. Coinfection of animals with both parent and mutant strains resulted in an increasing predominance of the mutant strain being recovered over time, suggesting that P1 is not a necessary prerequisite for colonization. These data do, however, suggest a role for P1 in the virulence of S. mutans, as reflected by a decrease in the cariogenicity of bacteria lacking this surface protein. (+info)
Production of germfree mice by embryo transfer.
(2/1204)
We applied the embryo transfer technique to germfree (GF) mouse production. Embryos harvested from superovulated mice were transferred aseptically, in a sterile environment, to the uterus of GF recipient females which had been mated with vasectomized GF males. One of the recipients became pregnant and delivered offspring. Sterility tests confirmed that the vasectomized males, newborns, recipient female mice, embryo-containing culture media, and the inside of the vinyl film isolator were germfree. These results suggest that the embryo transfer technique can be successfully applied to the production of GF mice. (+info)
Experimental enteropathy in athymic and euthymic rats: synergistic role of lipopolysaccharide and indomethacin.
(3/1204)
The aim of this study was to investigate the immunologic and microbiological bases of indomethacin enteropathy. Athymic nude and euthymic specific pathogen-free (SPF) rats were reared under conventional or SPF conditions. In each group, indomethacin was given intrarectally for 2 days. Indomethacin enteropathy was evaluated using a previously described ulcer index and tissue myeloperoxidase activity. Both euthymic and athymic nude rats developed intestinal ulcers to the same degree under conventional conditions but no or minimal ulcer under SPF conditions. Pretreatment of conventional rats with intragastric kanamycin sulfate, an aminoglycoside antibiotic, attenuated indomethacin enteropathy in a dose-dependent fashion. Interestingly, when lipopolysaccharide was injected intraperitoneally in kanamycin-pretreated rats, it fully restored enteropathy in these rats in a dose-dependent manner. We confirmed that kanamycin decreased the number of gram-negative bacteria and endotoxin concentration of the small intestine in a dose-dependent fashion. These results indicate that indomethacin enteropathy is bacteria dependent and does not require a T cell function. Synergy between indomethacin and bacterial lipopolysaccharide may play a major role in this enteropathy. (+info)
In situ hybridization for the detection and localization of swine Chlamydia trachomatis.
(4/1204)
Gnotobiotic piglets were inoculated intralaryngeally with swine Chlamydia trachomatis strain R33 or orally with swine C. trachmatis strain R27. Archived formalin-fixed, paraffin-embedded tissues from piglets euthanatized 4-7 days postinoculation were examined by in situ hybridization for C. trachomatis nucleic acid using a nonradioactive digoxigenin-labeled DNA probes that targeted specific ribosomal RNA or omp1 mRNA molecules of the swine C. trachomatis strains. Positive hybridization signals were detected in bronchial epithelial cells, bronchiolar epithelial cells, pneumocytes, alveolar and interstitial macrophages, and jejunal and ileal enterocytes. Chlamydia-infected cells had a strong signal that was confined to the intracytoplasmic inclusions. Positive hybridization signals were not detected in tissue sections from an uninfected control piglet or in C. psittaci-infected sheep placenta. The morphology of host cells was preserved despite the relatively high temperature required in parts of the incubation procedure. The data indicate that in situ hybridization can be used to detect swine C. trachomatis in formalin-fixed, paraffin-embedded tissue specimens. (+info)
Gas supersaturation in the cecal wall of mice due to bacterial CO2 production.
(5/1204)
PCO2 in the lumen and serosa of cecum and jejunum was measured in mice. The anesthetic used was a fentanyl-fluanisone-midazolam mixture. PCO2 was recorded in vivo and postmortem. PCO2 was 409 +/- 32 Torr (55 +/- 4 kPa) in the cecal lumen and 199 +/- 22 Torr (27 +/- 3 kPa) on the serosa in normal mice. Irrigation of the cecum resulted in serosal and luminal PCO2 levels of 65-75 Torr. Cecal PCO2 was significantly lower in germ-free mice (65 +/- 5 Torr). Cecal PCO2 increased significantly after introduction of normal bacterial flora into germ-free mice. Introduction of bacterial monocultures into germ-free mice had no effect. After the deaths of the mice, cecal PCO2 increased rapidly in normal mice. The intestinal bacteria produced the majority of the cecal PCO2, and the use of tonometry in intestinal segments with a high bacterial activity should be interpreted with caution. We propose that serosal PCO2 levels >150-190 Torr (20-25 kPa) in the cecum of mice with a normal circulation may represent a state of gas supersaturation in the cecal wall. (+info)
Estimation of growth rates of Escherichia coli BJ4 in streptomycin-treated and previously germfree mice by in situ rRNA hybridization.
(6/1204)
The growth physiology of Escherichia coli during colonization of the intestinal tract was studied with four animal models: the streptomycin-treated mouse carrying a reduced microflora, the monoassociated mouse with no other microflora than the introduced strain, the conventionalized streptomycin-treated mouse, and the conventionalized monoassociated mouse harboring a full microflora. A 23S rRNA fluorescent oligonucleotide probe was used for hybridization to whole E. coli cells fixed directly after being taken from the animals, and the respective growth rates of E. coli BJ4 in the four animal models were estimated by correlating the cellular concentrations of ribosomes with the growth rate of the strain. The growth rates thus estimated from the ribosomal content of E. coli BJ4 in vivo did not differ in the streptomycin-treated and the monoassociated mice. After conventionalization there was a slight decrease of the bacterial growth rates in both animal models. (+info)
Quantitative analysis of cytokine gene expression in the liver.
(7/1204)
The relative levels of cytokine gene expression in the liver were analysed, focusing on IL-2, IL-4, IL-5, IL-6 and IFN-gamma compared to those in the spleen and Peyer's patch by using the reverse transcriptase polymerase chain reaction (RT-PCR). The levels of expression of cytokines in the liver mononuclear cells (MNC). especially that of IL-6, were significantly higher than in other organs when mice were reared under specific pathogen-free (SPF) or conventional conditions. Both the spleen and Peyer's patch MNC expressed little of any of the cytokines, except for IL-4 in Peyer's patch MNC. The liver MNC produced significant amounts of IL-6 in the culture supernatant upon concanavalin A stimulation. These findings suggest that the liver is a potent IL-6-producing organ, which may relate to B cell differentiation, liver regeneration and the induction of acute phase proteins. (+info)
Isolation of small viruses resembling astroviruses and caliciviruses from acute enteritis of calves.
(8/1204)
Small round viruses (SRV) were isolated from the faeces of diarrhoeic calves from three farms. All three SRV preparations caused diarrhoea experimentally in gnotobiotic calves. Each preparation contained viral particles of two morphological types, "astrovirus-like" and "calicivirus-like", and from one preparation the two particle types were separated from each other. The calicivirus-like agent ("Newbury agent") was 33 nm in diameter, and caused diarrhoea in gnotobiotic calves with villous atrophy and D-xylose malabsorption. This virus did not infect cell cultures. The astrovirus-like agent did not cause diarrhoea in two gnotobiotic calves; however, it infected cell cultures (primary calf kidney) and the infected cells immunofluoresced with convalescent gnotobiotic-calf antiserum. The astrovirus-like agents in the three preparations were antigenically related. Experiments in calves showed that there was a degree of cross-protection between the three SRV preparations, as judged by the presence or absence of diarrhoea, but that at least three unrelated pathogens were present. (+info)