Antimicrobial resistance profiles of vancomycin-resistant Enterococcus species isolated from laboratory mice.

Isolates of 24 enterococci, 5 Enterococcus casseliflavus and 19 Enterococcus gallinarum, possessing vanC genes and showing low-level resistance to vancomycin were obtained from mice from commercial mouse breeding companies. Since some of these isolates showed resistance to other antibiotics, the purpose of this study was to clarify the resistant profiles of these isolates. One E. casseliflavus isolate showed resistance to erythromycin with a minimal inhibitory concentration (MIC) of 8 µg/mL and also showed apparent resistance to fluoroquinolones with an MIC of 32 µg/mL for ciprofloxacin. The MICs of 2 other fluoroquinolone-resistant E. casseliflavus and E. gallinarum isolates were 3 and 6 µg/mL, respectively. These 3 resistant isolates showed an absence of macrolide- and fluoroquinolone-resistant genes, including amino acid substitutions in the quinolone resistance determining regions of DNA gyrase and topoisomerase IV. Resistance to tetracycline was detected in 2 E. gallinarum isolates that were highly resistant, exhibiting MICs of 48 and 64 µg/mL and possessing tet(O) genes. The results indicate that antibiotic-resistant enterococci are being maintained in some laboratory mouse strains that have never been treated with an antibiotic.

Difference of two new LCMV strains in lethality and viral genome load in tissues.

More than 30 strains of lymphocytic choriomeningitis virus (LCMV) have been isolated from mice, hamsters and humans in the United States, Europe and Japan. Experimentally infected mice exhibit different clinical signs and lethality depending on a combination of LCMV epitope peptides and host major histocompatibility complex (MHC) class I molecules. This study examined the pathogenicity, clinical signs and lethality, of two new LCMV strains (BRC and OQ28) using three inbred mouse strains with different genetic backgrounds having different H-2D haplotypes. Strain OQ28 (OQ28) infected mice exhibited clinical signs and lethality, whereas strain BRC (BRC) infected mice showed no clinical signs of infection. The viral genome load in tissues of C57BL/6 mice infected with two strains was determined using one-step real time RT-PCR. In C57BL/6 mice, higher levels of OQ28 viral genome load were detected in all tissues rather than were present in BRC infected mice. The viral genome load in lungs of both virus strains remained higher levels than in other tissues at 28 days post infection. Comparing sequences of the three LCMV epitope peptide regions revealed one non-conservative amino acid substitution codon in OQ28 and two amino acid differences in BRC. These results suggest that the varied pathogenicity and viral genome load of LCMV strains are not based only on differences in the host MHC class I molecule.

Helicobacter sp. MIT 01-6451 infection during fetal and neonatal life in laboratory mice.

Helicobacter sp. MIT 01-6451 has been detected in SPF mice kept in Japan. To characterize strain MIT 01-6451, its infection route during fetal and neonatal life and effects on pregnancy were investigated using immunocompetent and immunodeficient mouse strains (BALB/c, C57BL/6, and SCID). MIT 01-6451 was detected in the uterus, vagina, and mammary glands of 50% of infected SCID mice, whereas these tissues were all negative in immunocompetent mice. No fetal infections with MIT 01-6451 were detected at 16-18 days after pregnancy in any mouse strain. In newborn mice, MIT 01-6451 was detected in intestinal tissue of C57BL/6 and SCID mice at 9-11 days after birth, but not in BALB/c mice. The IgA and IgG titers to MIT 01-6451 in sera of C57BL/6 female mice were significantly lower than those of BALB/c mice. Although no significant differences in the number of newborns per litter were observed between MIT 01-6451-infected and MIT 01-6451-free dams, the birth rate was lower in infected SCID mice than in control SCID mice. The present results indicated that MIT 01-6451 infects newborn mice after birth rather than by vertical transmission to the fetus via the placenta and that MIT 01-6451 infection shows opportunistically negative effects on the birth rate. In addition, the maternal immune response may affect infection of newborn mice with MIT 01-6451 through breast milk.

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.

Genome sequence of a pathogenic isolate of monkey B virus (species Macacine herpesvirus 1).

The only genome sequence for monkey B virus (BV; species Macacine herpesvirus 1) is that of an attenuated vaccine strain originally isolated from a rhesus monkey (BVrh). Here we report the genome sequence of a virulent BV strain isolated from a cynomolgus macaque (BVcy). The overall genome organization is the same, although sequence differences exist. The greatest sequence divergence is located in non-coding areas of the long and short repeat regions. Like BVrh, BVcy has duplicated Ori elements and lacks an ORF corresponding to the γ34.5 gene of herpes simplex virus. Nine of ten miRNAs and the majority of ORFs are conserved between BVrh and BVcy. The most divergent genes are several membrane-associated proteins and those encoding immediate early proteins.

Prevalence of an unidentified Helicobacter species in laboratory mice and its distribution in the hepatobiliary system and gastrointestinal tract.

An unidentified Helicobacter species, strain MIT 01-6451, was frequently detected in mice obtained from domestic commercial and academic institutions in Japan. To partially characterize this strain, its distributions in the gastrointestinal tract and hepatobiliary system of mice were investigated. In gastrointestinal tissues, this strain was detected in all cecum, colon, and feces samples tested, whereas fewer mice were positive in the ileum, jejunum, and duodenum. Interestingly, strain MIT 01-6451 was also detected in most stomach samples and in 33% of gallbladder samples. One mouse was found to be infected with multiple Helicobacter species. Fourteen copies of 16S rRNA genes were cloned from the tissues of this mouse. One had the highest level of sequence homology with H. canadensis, while 13 had the highest level of homology with the H. ganmani type strain or strain MIT 01-6451. Twelve of these 13 16S rRNA genes were mosaic sequences, being partially derived from H. ganmani and strain MIT 01-6451. These results suggest that H. ganmani and Helicobacter sp. MIT 01-6451 are prevalent in specific-pathogen-free mouse colonies in Japan and that lateral gene transfer probably occurs among Helicobacter species during coinfection.

Genomic analysis and pathogenic characteristics of lymphocytic choriomeningitis virus strains isolated in Japan.

Lymphocytic choriomeningitis virus (LCMV) is a zoonotic pathogen of which mice are the natural reservoir. Different strains and clones of LCMV show different pathogenicity in mice. Here we determined the complete genomic sequences of 3 LCMV strains (OQ28 and BRC which were isolated from mice in Japan and WE(ngs) which was derived from strain WE). Strains OQ28 and BRC showed high sequence homology with other LCMV strains. Although phylogenetic analyses placed these 2 Japanese strains in different subclusters, they belonged to same cluster of LCMV isolates. WE(ngs) and WE had many sequence substitutions between them but fell into same subcluster. The pathogenicity of the 3 new LCMV isolates was examined by inoculating ICR mice with 10² and 104 TCID50 of virus. ICR mice infected with OQ28 or WE(ngs) exhibited severe clinical signs, and some of the infected mice died. In contrast, all ICR mice infected with BRC showed no clinical signs and survived infection. Virus was detected in the blood, organs, or both of most of the surviving ICR mice inoculated with either OQ28 or WE(ngs). However, virus was below the level of detection in all ICR mice surviving infection with strain BRC. Therefore, LCMV strains OQ28 and BRC were genetically classified in the same cluster of LCMV strains but exhibited very different pathogenicity.