Effects of vendor and genetic background on the composition of the fecal microbiota of inbred mice.

The commensal gut microbiota has been implicated as a determinant in several human diseases and conditions. There is mounting evidence that the gut microbiota of laboratory mice (Mus musculus) similarly modulates the phenotype of mouse models used to study human disease and development. While differing model phenotypes have been reported using mice purchased from different vendors, the composition and uniformity of the fecal microbiota in mice of various genetic backgrounds from different vendors is unclear. Using culture-independent methods and robust statistical analysis, we demonstrate significant differences in the richness and diversity of fecal microbial populations in mice purchased from two large commercial vendors. Moreover, the abundance of many operational taxonomic units, often identified to the species level, as well as several higher taxa, differed in vendor- and strain-dependent manners. Such differences were evident in the fecal microbiota of weanling mice and persisted throughout the study, to twenty-four weeks of age. These data provide the first in-depth analysis of the developmental trajectory of the fecal microbiota in mice from different vendors, and a starting point from which researchers may be able to refine animal models affected by differences in the gut microbiota and thus possibly reduce the number of animals required to perform studies with sufficient statistical power.

Gastrointestinal microbiota of wild and inbred individuals of two house mouse subspecies assessed using high-throughput parallel pyrosequencing.

The effects of gastrointestinal tract microbiota (GTM) on host physiology and health have been the subject of considerable interest in recent years. While a variety of captive bred species have been used in experiments, the extent to which GTM of captive and/or inbred individuals resembles natural composition and variation in wild populations is poorly understood. Using 454 pyrosequencing, we performed 16S rDNA GTM barcoding for 30 wild house mice (Mus musculus) and wild-derived inbred strain mice belonging to two subspecies (M. m. musculus and M. m. domesticus). Sequenced individuals were selected according to a 2 × 2 experimental design: wild (14) vs. inbred origin (16) and M. m. musculus (15) vs. M. m. domesticus (15). We compared alpha diversity (i.e. number of operational taxonomic units - OTUs), beta diversity (i.e. interindividual variability) and microbiota composition across the four groups. We found no difference between M. m. musculus and M. m. domesticus subspecies, suggesting low effect of genetic differentiation between these two subspecies on GTM structure. Both inbred and wild populations showed the same level of microbial alpha and beta diversity; however, we found strong differentiation in microbiota composition between wild and inbred populations. Relative abundance of ~ 16% of OTUs differed significantly between wild and inbred individuals. As laboratory mice represent the most abundant model for studying the effects of gut microbiota on host metabolism, immunity and neurology, we suggest that the distinctness of laboratory-kept mouse microbiota, which differs from wild mouse microbiota, needs to be considered in future biomedical research.

Identification and characterization of vancomycin-resistant Enterococcus species frequently isolated from laboratory mice.

To determine the prevalence of drug resistant bacteria colonizing laboratory mice, we isolated and characterized vancomycin-resistant Enterococcus species (VRE) from commercially available mice. A total of 24 VRE isolates were obtained from 19 of 21 mouse strains supplied by 4 commercial breeding companies. Of these, 19 isolates of E. gallinarum and 5 isolates of E. casseliflavus possessing the vanC1 and vanC2/3 genes intrinsically, exhibited intermediate resistance to vancomycin respectively. In addition, these isolates also exhibited diverse resistant patterns to erythromycin, tetracycline, and ciprofloxacin, whereas the use of antibiotics had not been undertaken in mouse strains tested in this study. Although 6 virulence-associated genes (ace, asa, cylA, efaA, esp, and gelE) and secretion of gelatinase and hemolysin were not detected in all isolates, 23 of 24 isolates including the isolates of E. casselifalvus secreted ATP into culture supernatants. Since secretion of ATP by bacteria resident in the intestinal tract modulates the local immune responses, the prevalence of ATP-secreting VRE in mice therefore needs to be considered in animal experiments that alter the gut microflora by use of antibiotics.

Seven strains of mice as potential models of bovine pasteurellosis following intranasal challenge with a bovine pneumonic strain of Pasteurella multocida A:3; comparisons of disease and pathological outcomes.

The gram-negative bacterium Pasteurella multocida causes pneumonic and systemic pasteurellosis in bovids for which vaccines are either unavailable or inadequate. The work assessed whether an intranasal P. multocida challenge in mice might provide a model of infection for future vaccine development work. Clinical, pathological and biochemical responses were compared in seven strains of mice challenged with a virulent bovine pneumonic isolate of P. multocida A:3. Six mouse strains (Porton, CD-1, BALB/c, VM, C57BL/10 and C57BL/6) developed clinical signs of pneumonic disease and variable pneumonic lesions 41-70 h post-infection. In contrast, mouse strain RIII became septicaemic within 36 h post-infection. Concentrations of plasma acute phase proteins and serum lipopolysaccharide increased in all mice after infection, and the main or interaction effect of mouse strain and infection status was statistically significant (P<0.05). Responses in C57BL/10 mice showed close similarity to bovine pneumonic and in RIII mice to bovine systemic pasteurellosis.

Inflammation-associated enterotypes, host genotype, cage and inter-individual effects drive gut microbiota variation in common laboratory mice.

BACKGROUND: Murine models are a crucial component of gut microbiome research. Unfortunately, a multitude of genetic backgrounds and experimental setups, together with inter-individual variation, complicates cross-study comparisons and a global understanding of the mouse microbiota landscape. Here, we investigate the variability of the healthy mouse microbiota of five common lab mouse strains using 16S rDNA pyrosequencing. RESULTS: We find initial evidence for richness-driven, strain-independent murine enterotypes that show a striking resemblance to those in human, and which associate with calprotectin levels, a marker for intestinal inflammation. After enterotype stratification, we find that genetic, caging and inter-individual variation contribute on average 19%, 31.7% and 45.5%, respectively, to the variance in the murine gut microbiota composition. Genetic distance correlates positively to microbiota distance, so that genetically similar strains have more similar microbiota than genetically distant ones. Specific mouse strains are enriched for specific operational taxonomic units and taxonomic groups, while the 'cage effect' can occur across mouse strain boundaries and is mainly driven by Helicobacter infections. CONCLUSIONS: The detection of enterotypes suggests a common ecological cause, possibly low-grade inflammation that might drive differences among gut microbiota composition in mammals. Furthermore, the observed environmental and genetic effects have important consequences for experimental design in mouse microbiome research.

Differences in health status affect susceptibility and mapping of genetic loci for atherosclerosis (fatty streak) in inbred mice.

OBJECTIVE: We observed differences in atherosclerosis susceptibility in mouse inbred strains over the years as the health status of our animal rooms increased. Therefore, we investigated the effect of animal room health status on atherosclerosis susceptibility in different strains. As these data can also be used for genome-wide association mapping, we performed a mapping study and compared our results with previously found quantitative trait loci for atherosclerosis in mouse and humans. METHODS AND RESULTS: Males and females from 48 inbred strains were housed in 2 animal rooms with different health status and given an atherogenic diet. We compared atherosclerosis susceptibility between animal rooms and between sexes and found that susceptibility is dependent on both health status and sex. Subsequently, the data were used for associations with loci on the mouse genome using 63 222 single nucleotide polymorphism. Three loci in males and 4 loci in females were identified using the data from the low-health status room. No significant associations were identified using the data from the high-health status room. CONCLUSIONS: Health status influences susceptibility to atherosclerosis and suggests that microbiological pressure plays an important role in the development of atherosclerosis in many strains. As we were only able to map susceptibility loci using the data from the lower health status room, we argue that susceptibility under these conditions is determined by a few key loci, whereas in the higher health status room different mechanisms might play a role in the differences in atherosclerosis susceptibility between strains and we did not have enough power to map the loci that are involved.

Eradication of Helicobacter spp. by using medicated diet in mice deficient in functional natural killer cells and complement factor D.

A commercial 4-drug diet has shown promise in eradicating Helicobacter spp. from rodents; however, its effectiveness in immunocompromised mice is unknown. This study evaluated the efficacy of this treatment in eradicating Helicobacter spp. from mice deficient in functional natural killer cells (Cd1(-/-)) or complement factor D (Df(-/-)). Cd1(-/-) mice naturally infected with H. hepaticus with or without H. rodentium were fed either control or medicated diet for 8 wk followed by 4 wk on control diet. Fecal samples were PCR-evaluated for Helicobacter spp. before mice began treatment and then every 2 wk thereafter for 12 wk. The same experimental design was repeated for eighteen 9- to 21-wk-old Df(-/-) mice naturally infected with H. bilis with or without H. rodentium. All Df(-/-) mice and 8- to 21-wk-old Cd1(-/-) mice ceased shedding Helicobacter spp. after 2 wk of treatment and remained negative throughout the study. In contrast, the Cd1(-/-) mice that were 24 wk or older shed Helicobacter spp. for the first 8 wk but tested negative at 10 and 12 wk. All treated animals had enlarged ceca and gained less weight than control untreated mice, and 6 of 7 treated Cd1(-/-) male mice developed mild portal fibrosis. These findings show that within 2 wk of treatment, the 4-drug diet eradicated H. hepaticus and H. rodentium from young Cd1(-/-) mice and H. bilis and H. rodentium from Df(-/-) mice, but eradication of established infections in Cd1(-/-) mice required 8 wk of treatment.

Evaluation of a commercial colorimetric fecal dipstick assay for the detection of Helicobacter hepaticus infections in laboratory mice.

Mice used in biomedical research typically are tested for the presence of Helicobacter spp., including Helicobacter hepaticus. Here we evaluated the ability of a commercially available colorimetric Helicobacter dipstick assay to detect H. hepaticus in experimentally and naturally infected mice, with use of a Helicobacter PCR assay as the 'gold standard' test. None of the fecal samples from experimentally infected A/JCr mice (n = 12) tested positive for Helicobacter by the colorimetric dipstick test. In naturally infected A/JCr and C57BL/6 mice, 11% (1 of 9) and 30% (3 of 10) of fecal samples, respectively, tested positive for Helicobacter by the colorimetric dipstick assay. In these 3 groups of H. hepaticus-infected mice, statistically fewer mice tested positive by the colorimetric dipstick test than by PCR. The colorimetric Helicobacter dipstick assay had an overall diagnostic sensitivity of 13%, diagnostic specificity of 94%, and analytical sensitivity of 10(8) H. hepaticus cfu/mL. As currently formulated, the colorimetric dipstick assay had high specificity but lacked sensitivity for detecting H. hepaticus infections in 2 strains of mice commonly used in research, thereby limiting its utility as a diagnostic screening test for H. hepaticus infections in research mice.

Infection of different strains of mice with Lawsonia intracellularis derived from rabbit or porcine proliferative enteropathy.

This report describes intestinal lesions in five strains of mice infected orally with Lawsonia intracellularis-infected tissue homogenates from rabbits or pigs (RLI and PLI). BALB/cA, C3H/HeJ, C57BL/6J and ICR mice were susceptible to infection with RLI, whereas only C3H/HeJ, C57BL/6J and ICR strains were susceptible to PLI. In susceptible mice, crypt epithelial hyperplasia occurred in association with an inflammatory reaction, as in proliferative enteropathy (PE) in other species. The intestinal changes in the infected mice varied from mild to severe. Unlike rabbit or porcine PE, in which the changes are confined to the ileum, the lesions in mice were located in the caecum. Immunolabelling of L. intracellularis antigen was abundant in early infection when the epithelial hyperplasia was mild or absent. When the hyperplasia had become severe, however, immunolabelling was weak. For this reason, it is suggested that transitory infection of the epithelium induces epithelial hyperplasia. Genetic differences between mouse strains appeared to play an important role in the response to L. intracellularis infection. Moreover, the susceptibility of BALB/cA mice to RLI but not to PLI suggests that there are significant biological differences between L. intracellularis isolates from rabbit PE and porcine PE.

Spontaneous exocrine pancreas hypoplasia in specific pathogen-free C3HeB/FeJ and 101/H mouse pups causes steatorrhea and runting.

Under specific pathogen-free conditions, 1.3% to 1.8% of litters born in our inbred 101/H and C3HeB/FeJ mouse colonies had pups with steatorrhea and runting. Clinically affected male and female pups were first identified when they were from 14 to 25 d old. Unaffected littermates were healthy and were weaned successfully. Postmortem findings in 8 clinically affected mice included a small, poorly differentiated exocrine pancreas comprising cytokeratin-negative duct-like structures but lacking recognizable acinar cells with their normal carboxypeptidase B-positive zymogen granules. Endocrine pancreas islets were unremarkable and contained insulin-positive beta cells and glucagon-positive alpha cells. There was mild inflammation of the hindgut but no evidence of intestinal pathogens or marked inflammation or necrosis of pancreas, either alone or as part of a multisystemic inflammatory condition. Sera from pups in 4 affected litters did not contain antibodies to reovirus 3, mouse coronavirus, rotavirus, or mouse adenovirus 2. Furthermore, 4 sets of parental mice and sentinel mice from the facility were negative for 13 viruses, bacteria, and parasites. C3HeB/FeJ and 101/H inbred strains may be genetically predisposed because the steatorrhea and runting was absent in 13 other mouse strains and subspecies bred in the specific pathogen-free facility. This condition resembles exocrine pancreas hypoplasia, but the inheritance is complex. A wider implication is that runting coupled with steatorrhea are phenotypic criteria to suspect pancreatic disease that could be used in the context of a mouse N-ethyl-N-nitrosourea-mutagenesis program to identify potential mutants with defects in pancreas development.

A specific polymerase chain reaction based on the gyrB gene sequence and subsequent restriction fragment length polymorphism analysis of Pasteurella pneumotropica isolates from laboratory mice.

For a molecular identification and typing tool, we developed a specific polymerase chain reaction (PCR) based on the gyrB gene sequence and a subsequent restriction fragment length polymorphism (RFLP) analysis using the products amplified from the specific PCR to facilitate discrimination of biotypes of Pasteurella pneumotropica from laboratory mice. Appropriate PCR products, a 1039-basepair fragment for biotype Jawetz and a 1033-basepair fragment for biotype Heyl, were amplified by use of the primers CZO-1 and NJO-2 from all 105 P. pneumotropica isolates tested and the 2 reference strains but not from other bacterial species tested. MspI digestion of PCR-generated products showed 3 RFLP patterns among the 105 isolates, and these patterns correlated with the biotype of the isolate (RFLP pattern 1, biotype Jawetz; RFLP pattern 2, biotype Heyl; and RFLP pattern 3, biotype Jawetz with Beta-hemolytic activity). Our procedure identifies and biotypes isolates of P. pneumotropica from laboratory mice, using simple PCR and enzymatic restriction techniques. Therefore, this procedure is useful as a rapid identification and biotyping tool for isolates of P. pneumotropica from laboratory mice.

Strain differences influence murine pulmonary responses to Stachybotrys chartarum.

When the fungus Stachybotrys chartarum is inhaled, its mycotoxins may cause lung injury and inflammation. The severity of human responses to S. chartarum in both occupational and home settings varies widely. To explore these differences, we intratracheally instilled C3H/HeJ, BALB/c, and C57BL/6J mice with S. chartarum spores suspended in saline. One day later, the mice were humanely killed, bronchoalveolar lavage (BAL) was performed, and biochemical and cellular indicators of lung injury and inflammation were measured. BALB/c mice showed the highest myeloperoxidase activity, albumin and hemoglobin levels, and neutrophil numbers in their BAL among the three strains. BALB/c was the only strain to show significant increases in keratinocyte-derived cytokine (KC), monocyte chemotactic protein (MCP)-1, MCP-3, macrophage inflammatory protein (MIP)-1alpha, MIP-1beta, MIP-1gamma, MIP-2, RANTES, IL-1alpha, IL-1beta, IL-3, IL-6, IL-18, leukemia inhibitory factor, macrophage colony-stimulating factor, and TNF-alpha. A model of allergen-induced airway inflammation was examined to assess whether underlying allergic inflammation might contribute to increased susceptibility to S. chartarum-induced pulmonary inflammation and injury. Surprisingly, in BALB/c mice, ovalbumin-induced airway inflammation produced a protective effect against some S. chartarum-induced pulmonary responses. This is the first report of mammalian strain differences affecting responses to S. chartarum. These responses differ from those reported for LPS and other fungi. Analogous underlying genetic differences may contribute to the wide range of sensitivity to Stachybotrys among humans.

Occurrence of Helicobacter species other than H. hepaticus in laboratory mice and rats in Sweden.

The aim of this study was to determine which Helicobacter species other than H. hepaticus colonize laboratory mice and rats in Sweden. We analyzed 63 intestinal samples from mice and 42 intestinal samples from rats by partial 16S rDNA sequence analysis. Previously these samples had been found positive for Helicobacter species but negative for H. hepaticus in a polymerase chain reaction screening assay at the National Veterinary Institute in Sweden. H. ganmani, H. typhlonius, H. rodentium, an uncharacterized Helicobacter species ('hamster B'), and a possibly novel species were detected in mice. The possibly novel species was most closely related to H. apodemus strain YMRC 000216 (98.3% sequence similarity). Two different Helicobacter species were detected in rats: H. ganmani and H. rodentium. H. ganmani colonization of rats has not previously been reported.

Characteristic intestinal microflora of specific pathogen-free mice bred in two different colonies and their influence on postnatal murine immunocyte profiles.

Cecal microflora of BALB/c mice originating from two different SPF-breeding colonies were compared. The analysis of cultivable bacteria in the ceca showed significantly higher numbers of total bacteria in BALB/cCrSlc (SLC mice) than in BALB/cA Jcl (JCL mice) (p<0.05), which were mainly based on higher numbers and occurrence of Peptococaceae. Bifidobacteria were detected only in SLC mice. Feeding an oligosaccharide, raffinose, to the mice also induced different shifts in the composition of cecal microflora and the concentration of cecal organic acids. In the second experiment, hysterectomy-derived (HD) SLC mice were fostered to SPF lactating SLC mothers, or SPF lactating JCL mice, together with the mother's own natural birth (NB) pups in each isolator. HD mice fostered to SLC-mothers showed significantly higher percentages of T-cell receptor alphabeta cells expressing a CD8alpha homodimer (p<0.05) and a CD8alphabeta heterodimer (p<0.001) in the intraepithelial lymphocytes (IEL) compared with HD mice fostered to JCL-mothers. IEL profiles of HD mice corresponded well to those of NB mice that were breast-fed by the same mothers. Differences in the ratio of B220(+)cells to Thy1.2(+)cells in the splenocytes were also observed as a trend between both HD mice fostered to SLC or JCL mothers (p=0.06). These results suggest that postnatal colonization of various characteristic intestinal microflora derived from SPF-breeding colonies results in differences in development of lymphocyte populations in the intestinal and systemic organs of mice.

Health surveillance of specific pathogen-free and conventionally-housed mice and rats in Korea.

The present study contains information about proper microbiological monitoring of laboratory animals' health and the standardization of microbiological monitoring methods in Korea. Microbiological quality control for laboratory animals, composed of biosecurity and health surveillance, is essential to guard against research complications and public health dangers that have been associated with adventitious infections. In this study, one hundred and twenty-two mice and ninety rats from laboratory animal breeding companies and one animal facility of the national universities in Korea were monitored in 2000-2003. Histopathologically, thickening of the alveolar walls and lymphocytic infiltration around the bronchioles were observed in mice and rats from microbiologically contaminated facilities. Cryptosporidial oocysts were observed in the gastric pits of only conventionally-housed mice and rats. Helicobacter spp. infection was also detected in 1 of 24 feces DNA samples in mice and 9 of 40 feces DNA samples in rats by PCR in 2003, but they were not Helicobacter hepaticus. This paper describes bacteriological, parasitological, and virological examinations of the animals.

High prevalence of Helicobacter Species detected in laboratory mouse strains by multiplex PCR-denaturing gradient gel electrophoresis and pyrosequencing.

Rodent models have been developed to study the pathogenesis of diseases caused by Helicobacter pylori, as well as by other gastric and intestinal Helicobacter spp., but some murine enteric Helicobacter spp. cause hepatobiliary and intestinal tract diseases in specific inbred strains of laboratory mice. To identify these murine Helicobacter spp., we developed an assay based on PCR-denaturing gradient gel electrophoresis and pyrosequencing. Nine strains of mice, maintained in four conventional laboratory animal houses, were assessed for Helicobacter sp. carriage. Tissue samples from the liver, stomach, and small intestine, as well as feces and blood, were collected; and all specimens (n = 210) were screened by a Helicobacter genus-specific PCR. Positive samples were identified to the species level by multiplex denaturing gradient gel electrophoresis, pyrosequencing, and a H. ganmani-specific PCR assay. Histologic examination of 30 tissue samples from 18 animals was performed. All mice of eight of the nine strains tested were Helicobacter genus positive; H. bilis, H. hepaticus, H. typhlonius, H. ganmani, H. rodentium, and a Helicobacter sp. flexispira-like organism were identified. Helicobacter DNA was common in fecal (86%) and gastric tissue (55%) specimens, whereas samples of liver tissue (21%), small intestine tissue (17%), and blood (14%) were less commonly positive. Several mouse strains were colonized with more than one Helicobacter spp. Most tissue specimens analyzed showed no signs of inflammation; however, in one strain of mice, hepatitis was diagnosed in livers positive for H. hepaticus, and in another strain, gastric colonization by H. typhlonius was associated with gastritis. The diagnostic setup developed was efficient at identifying most murine Helicobacter spp.

Differences in mouse strain influence leukocyte and immunoglobulin phenotype response to Porphyromonas gingivalis.

This study examined the nature of the infiltrating cells in Porphyromonas gingivalis-induced lesions and immunoglobulins in the serum samples of BALB/c (H-2d), C57BL6 (H-2b), DBA/2J (H-2d) and CBA/CaH (H-2k) mice. Mice were immunized intraperitoneally with P. gingivalis outer membrane antigens or sham-immunized with phosphate-buffered saline followed by subcutaneous challenge with live organisms 1 week after the final immunization. The resulting skin abscesses were excised 7 days later, cryostat sections cut and an immunoperoxidase method used to detect the presence of CD4+ and CD8+ T-cell subsets, CD14+ macrophages and CD19+ B cells. Peroxidase positive neutrophils and IgG1- and IgG2a-producing plasma cells were also identified. Anti P. gingivalis IgG1 and IgG2a subclass antibodies were determined in serum obtained by cardiac puncture. Very few CD8+ T cells and CD19+ B cells were found in any of the lesions. The percentages of CD4+ cells, CD14+ cells and neutrophils were similar in lesions of immunized BALB/c and C57BL6 mice, with a trend towards a higher percentage of CD14+ cells in sham-immunized mice. The percentage of CD14+ cells was higher than that of CD4+ cells in immunized compared with sham-immunized DBA/2J mice. The percentages of CD4+ and CD14+ cells predominated in immunized CBA/CaH mice and CD4+ cells in sham-immunized CBA/CaH mice. The percentage of neutrophils in immunized CBA/CaH mice was significantly lower than that of CD14+ cells and CD4+ cells in sham-immunized mice. IgG1+ plasma cells were more dominant than IgG2a+ cells in immunized BALB/c, C57BL6 and DBA/2J mice, whereas IgG2a+ plasma cells were more obvious in sham-immunized mice. IgG2a+ plasma cells were predominant in immunized and sham-immunized CBA/CaH mice. In the serum, specific anti-P. gingivalis IgG2a antibody levels (Th1 response) were higher than IgG1 levels (Th2 response) in sham-immunized CBA/CaH and DBA/2J mice. In immunized BALB/c mice, IgG2a levels were lower than IgG1 levels, while IgG2a levels were higher in immunized C57BL6 mice. In conclusion, this study has shown differences in the proportion of infiltrating leukocytes and in the subclasses of immunoglobulin produced locally and systemically in response to P. gingivalis in different strains of mice, suggesting a degree of genetic control over the response to P. gingivalis.

Cdc24, the GDP-GTP exchange factor for Cdc42, is required for invasive hyphal growth of Candida albicans.

Candida albicans, the most common human fungal pathogen, is particularly problematic for immunocompromised individuals. The reversible transition of this fungal pathogen to a filamentous form that invades host tissue is important for its virulence. Although different signaling pathways such as a mitogen-activated protein kinase and a protein kinase A cascade are critical for this morphological transition, the function of polarity establishment proteins in this process has not been determined. We examined the role of four different polarity establishment proteins in C. albicans invasive growth and virulence by using strains in which one copy of each gene was deleted and the other copy expressed behind the regulatable promoter MET3. Strikingly, mutants with ectopic expression of either the Rho G-protein Cdc42 or its exchange factor Cdc24 are unable to form invasive hyphal filaments and germ tubes in response to serum or elevated temperature and yet grow normally as a budding yeast. Furthermore, these mutants are avirulent in a mouse model for systemic infection. This function of the Cdc42 GTPase module is not simply a general feature of polarity establishment proteins. Mutants with ectopic expression of the SH3 domain containing protein Bem1 or the Ras-like G-protein Bud1 can grow in an invasive fashion and are virulent in mice, albeit with reduced efficiency. These results indicate that a specific regulation of Cdc24/Cdc42 activity is required for invasive hyphal growth and suggest that these proteins are required for pathogenicity of C. albicans.

Differential susceptibility to hepatic inflammation and proliferation in AXB recombinant inbred mice chronically infected with Helicobacter hepaticus.

Helicobacter hepaticus is a naturally occurring pathogen of mice and has been used to develop models of chronic hepatitis, liver cancer, and, more recently, inflammatory bowel disease, in selected mouse strains. A/JCr mice are particularly susceptible to H. hepaticus-induced hepatitis and subsequent development of liver neoplasms, whereas C57BL/6 mice are resistant. In this study, we inoculated nine AXB recombinant inbred (RI) mouse strains, derived from A/J and C57BL/6 mice, with H. hepaticus to determine the genetic basis of resistance to Helicobacter-induced liver disease. Mice were surveyed 14 months after inoculation by culture and PCR for H. hepaticus colonization of the liver and cecum, and microscopic morphometric evaluations of the liver were performed to quantify and correlate the severity of inflammation, apoptosis, and proliferation. Analysis of variance of hepatic inflammation demonstrated significant variation among the RI strains (P < 0.0001), and the strain distribution pattern suggested a multigenic basis of disease resistance. Quantitative trait analysis using linear regression suggested possible linkage to loci on mouse chromosome 19. Hepatocellular and biliary epithelial apoptosis and proliferation indices, including proliferation of oval cells, were markedly increased and correlated with severity of inflammation. Prevalence of hepatic neoplasia was also increased in susceptible RI strains. These findings demonstrate a genetic basis for susceptibility to Helicobacter-induced disease and provide insight into its pathogenesis.

Primary Campylobacter jejuni infection in different mice strains.

Campylobacter jejuni is one of the most frequent causes of diarrhoea in man. Extra-intestinal manifestations may also occur, particularly in immunocompromised individuals. However, because of the lack of appropriate animal models the pathophysiology and immunological response of the host to C. jejuni infection are still poorly understood. In our laboratory an experimental infection of adult BALB/c, C57BL/6 and DBA/2 mice has been established. After intraperitoneal injection of 0.5-1x10(9) cfu of C. jejuni none of the infected mice showed clinical symptoms of illness, but bacterial spreading and tissue invasion were achieved. We have concentrated our studies on the duration of primary infection, recovery of bacteria from livers and spleens of infected animals and pathohistological changes of these organs. Our results showed differences in the course of systemic infection among the tested mice strains. BALB/c mice were most sensitive, resulting in the most pronounced pathohistological changes in the examined organs. The duration of the primary liver infection was the longest in BALB/c mice while the duration of the splenic infection also differed among the tested mice strains. Nevertheless, the experimental model used in this study can be efficiently used in further analysis of the pathogenesis of this bacterial infection. However, the strain differences should be taken into account depending on the parameters to be followed.