Identification Procedure for Pasteurella Pneumotropica in Microbiologic Monitoring of Laboratory Animals

Genomic and pathogenic characterization of RTX toxin producing Rodentibacter sp. that is closely related to Rodentibacter haemolyticus

Rodentibacter spp. are opportunistic pathogens that are often isolated from the upper respiratory tracts of laboratory rodents. In particular, R. pneumotropicus and R. heylii require considerable caution in rodent colonies, as they cause lethal pneumonia in rodents. A new species, R. haemolyticus, has recently been classified in the genus, and a very closely related strain, Rodentibacter sp. strain JRC, has been isolated in Japan. This study focused on strain JRC by performing genomic and pathogenic analyses. Draft genome sequencing of strain JRC identified several genes coding for putative virulent proteins, including hemolysin and adhesin. Furthermore, we found a new RTX (repeats-in-structural toxin) toxin gene in the genome, which was predicted to produce a critical virulence factor (RTXIA) similar to Enterobacteriaceae. The concentrated culture supernatant containing RTX toxin (RTXIA) showed cytotoxicity toward RAW264.7 cells. Pre-incubation with anti-CD11a attenuated the cytolysis, suggesting that the concentrated culture supernatant containing RTXIA is cell surface LFA-1 mediated cytolysin. Experimental infection of strain JRC intranasally with 5 female BALB/c-Rag2^-/- mice showed 60% lethality and was not significantly different from those of R. pneumotropicus ATCC 35149^T using the log-rank test. Combined with our finding that RTXIA has an almost identical amino acid sequence (98% identity) to that of R. haemolyticus 1625/19^T, these results strongly suggest that RTXIA-producing strain JRC (and related R. haemolyticus) is pathogenic to immunodeficient rodents, and both agents should be excluded in laboratory rodent colonies.

Septic arthritis of the ankle: Do not forget Pasteurella pneumotropica

Pasteurella pneumotropica is an important bacterial pathogen in both animals and humans. Most reported Pasteurella infections in humans involve skin and soft tissues, often after an animal bite, scratch, or lick to an open wound. We report a case of septic arthritis with Pasteurella pneumotropica in a diabetic and cardiopathic patient who was the victim of a rat bite in the street, with a good evolution after medical and surgical treatment.

A new pleuromutilin candidate with potent antibacterial activity against Pasteurella multocida

This study assessed the antimicrobial activity of 14-O-[(4,6-Diaminopyrimidine-2-yl) thioacetyl] mutilin (DPTM), a novel pleuromutilin candidate with a substituted pyrimidine moiety, against Pasteurella multocida. Minimum Inhibitory Concentration (MIC), Oxford Cup assay, and time-kill experiments were used to measure the activity of DPTM against P. multocida serotype A in vitro. We observed that DPTM was potent against Pasteurella multocida serotype A with the MIC value of 0.781 μg/mL. The mean inhibition-zone diameters of DPTM (50, 25, and 12.5 μg/mL) were 29.4, 24.2 and 20.1 mm, respectively. Time-kill experiments showed that the drug caused a rapid decline in the number of bacteria compared with the initial inoculum at 4 h and killed 94.6% of the bacteria during 24 h. Furthermore, DPTM activity was also assessed in a lung infection model challenged with 4.0 × 109 CFU/mL P. multocida serotype A. The results showed that DPTM significantly reduced mortality rate and bacterial load, and alleviated the pathological changes of lung. The antibacterial effect of DPTM found in this study suggested that it was useful in the prevention or control of pneumonia caused by P. multocida.

The Likelihood of Misidentifying Rodent Pasteurellaceae by Using Results from a Single PCR Assay

The precise identification of rodent Pasteurellaceae is known to be highly challenging. An unknown strain of Pasteurellaceae appeared and rapidly spread throughout our animal facilities. Standard microbiology, combined with biochemical analysis, suggested that the bacteria strain was Rodentibacter pneumotropicus or R. heylii. We submitted samples of the unknown bacteria and known isolates of R. pneumotropicus, R. heylii, and Muribacter muris, to 2 service laboratories that provide animal health monitoring. Results of microbiology tests performed by both laboratories, species-specific PCR analysis performed by one laboratory, and independent 16S rRNA gene sequencing yielded identical identification of the unknown bacteria as Pasteurellaceae (Pasteurella spp.) and not R. pneumotropicus or R. heylii. In contrast, the similarly intended PCR assay performed by the other laboratory identified the bacteria as R. heylii. Careful evaluation of all of the results led us to conclude that the correct identification of the bacteria is Pasteurellaceae. From our experience, we recommend that a combination of several methods should be used to achieve correct identification of rodent Pasteurellaceae. Specifically, we advise that all primer sets used should be disclosed when reporting PCR test results, including in health reports provided by service laboratories and animal vendors. Careful, correct, and informative health monitoring reports are most beneficial to animal researchers and caretakers who might encounter the presence and effects of rodent Pasteurellaceae.

Clonal outbreaks of [ Pasteurella] pneumotropica biovar Heyl in two mouse colonies

The aim of this study was to document the pathogenic role of biovar Heyl of [ Pasteurella] pneumotropica in mouse colonies. Fifty-three isolates associated with mastitis and orbital, cutaneous and vaginal abscesses as well as isolates from the nose and vagina of healthy mice were investigated. According to phenotypic characteristics and rpoB sequencing, the isolates were identified as [ P.] pneumotropica biovar Heyl. Pulsed-field gel electrophoresis (PFGE) revealed five closely related profiles separated by only one to four fragments. The outbreak strains diverged from epidemiologically unrelated strains with the same rpoB sequence type, as shown by the PFGE profiles. The investigation documented that members of biovar Heyl of [ P.] pneumotropica caused disease outbreaks in mouse colonies since the clonality indicated a primary role of [ P.] pneumotropica biovar Heyl in the infections observed.

High-Resolution Melting Curve Analysis for Identification of Pasteurellaceae Species in Experimental Animal Facilities

Pasteurellaceae are among the most prevalent bacterial pathogens isolated from mice housed in experimental animal facilities. Reliable detection and differentiation of Pasteurellaceae are essential for high-quality health monitoring. In this study, we combined a real-time PCR assay amplifying a variable region in the 16S rRNA sequence with high-resolution melting curve analysis (HRM) to identify and differentiate among the commonly isolated species Pasteurella pneumotropica biotypes “Jawetz” and “Heyl”, Actinobacillus muris, and Haemophilus influenzaemurium. We used a set of six reference strains for assay development, with the melting profiles of these strains clearly distinguishable due to DNA sequence variations in the amplicon. For evaluation, we used real-time PCR/HRM to test 25 unknown Pasteurellaceae isolates obtained from an external diagnostic laboratory and found the results to be consistent with those of partial 16S rRNA sequencing. The real-time PCR/HRM method provides a sensitive, rapid, and closed-tube approach for Pasteurellaceae species identification for health monitoring of laboratory mice.

16S ribosomal DNA sequence-based identification of bacteria in laboratory rodents: a practical approach in laboratory animal bacteriology diagnostics

Correct identification of bacteria is crucial for the management of rodent colonies. Some bacteria are difficult to identify phenotypically outside reference laboratories. In this study, we evaluated the utility of 16S ribosomal DNA (rDNA) sequencing as a means of identifying a collection of 30 isolates of rodent origin which are conventionally difficult to identify. Sequence analysis of the first approximate 720 to 880 bp of the 5'- end of 16S rDNA identified 25 isolates (83.33%) with ≥ 99% similarity to a sequence of a type strain, whereas three isolates (10%) displayed a sequence similarity ≥ 97% but <99% to the type strain sequences. These similarity scores were used to define identification to species and genus levels, respectively. Two of the 30 isolates (6.67%) displayed a sequence similarity of ≥ 95 but <97% to the reference strains and were thus allocated to a family. This technique allowed us to document the association of mice with bacteria relevant for the colonies management such as Pasteurellaceae, Bordetella hinzii or Streptococcus danieliae. In addition, human potential pathogens such as Acinetobacter spp., Ochrobactrum anthropi and Paracoccus yeei or others not yet reported in mouse bacterial species such as Leucobacter chironomi, Neisseria perflava and Pantoea dispersa were observed. In conclusion, the sequence analysis of 16S rDNA proved to be a useful diagnostic tool, with higher performance characteristics than the classical phenotypic methods, for identification of laboratory animal bacteria. For the first time this method allowed us to document the association of certain bacterial species with the laboratory mouse.

Development of a multiplex PCR assay based on the 16S-23S rRNA internal transcribed spacer for the detection and identification of rodent Pasteurellaceae

The rodents Pasteurellaceae have to be excluded from the specified pathogen free experimental animal facilities. Despite the biological and economic importance of Pasteurellaceae in relation to experimental animals just a few molecular based methods are available for their detection and identification. The aim of the present investigation was to develop a multiplex PCR assay allowing detection of all rodent Pasteurellaceae and identification of [Pasteurella] pneumotropica biotype Jawetz, [P.] pneumotropica biotype Heyl and [Actinobacillus] muris, as the most prevalent members of the group. For this, a Pasteurellaceae common forward primer located on the 16S rRNA gene was used in conjunction with four different reverse primers specific for [P.] pneumotropica biotype Jawetz, [P.] pneumotropica biotype Heyl, [A.] muris and a common reverse primer for all rodent Pasteurellaceae, all targeting the 16S-23S rRNA internal transcribed spacer sequences. The performance characteristics of the assay were tested against 125 Pasteurellaceae isolates belonging to eleven different species and including 34 strains of [P.] pneumotropica biotype Jawetz, 44 strains of [P.] pneumotropica biotype Heyl and 37 strains of [A.] muris. Additionally, eight other mouse associated bacterial species which could pose a diagnostic problem were included. The assay showed 100% sensitivity and specificity. Identification of the clinical isolates was validated by ITS profiling and when necessary by 16S rRNA gene sequencing. This multiplex PCR represents the first molecular tool able to detect and differentiate in a single assay among the Pasteurellaceae found in laboratory mouse and may become a reliable alternative to the present diagnostic methods.

Specific detection and identification of [Actinobacillus] muris by PCR using primers targeting the 16S-23S rRNA internal transcribed spacer regions

[Actinobacillus] muris represents along with [Pasteurella] pneumotropica the most prevalent Pasteurellaceae species isolated from the laboratory mouse. Despite the biological and economic importance of Pasteurellaceae in relation to experimental animals, no molecular based methods for the identification of [A.] muris are available. The aim of the present investigation was to develop a PCR method allowing detection and identification of [A.] muris. In this assay, a Pasteurellaceae common forward primer based on a conserved region of the 16S rRNA gene was used in conjunction with two different reverse primers specific for [A.] muris, targeting the 16S-23S internal transcribed spacer sequences. The specificity of the assay was tested against 78 reference and clinical isolates of Pasteurellaceae, including 37 strains of [A.] muris. In addition, eight other mice associated bacterial species which could pose a diagnostic problem were included. The assay showed 100% sensitivity and 97.95% specificity. Identification of the clinical isolates was validated by ITS profiling and when necessary by 16S rRNA sequencing. This multiplex PCR represents the first molecular tool able to detect [A.] muris and may become a reliable alternative to the present diagnostic methods.

Biochemical characterization and phylogenetic analysis based on 16S rRNA sequences for V-factor dependent members of Pasteurellaceae derived from laboratory rats

Phylogenetic analysis based on 16S rRNA sequences with sequence data of some bacterial species of Pasteurellaceae related to rodents deposited in GenBank was performed along with biochemical characterization for the 20 strains of V-factor dependent members of Pasteurellaceae derived from laboratory rats to obtain basic information and to investigate the taxonomic positions. The results of biochemical tests for all strains were identical except for three tests, the ornithine decarboxylase test, and fermentation tests of D(+) mannose and D(+) xylose. The biochemical properties of 8 of 20 strains that showed negative results for the fermentation test of D(+) xylose agreed with those of Haemophilus parainfluenzae complex. By phylogenetic analysis, the strains were divided into two clusters that agreed with the results of the fermentation test of xylose (group I: negative reaction for xylose, group II: positive reaction for xylose). The clusters were independent of other bacterial species of Pasteurellaceae tested. The sequences of the strains in group I showed 99.7-99.8% similarity and the strains in group II showed 99.3-99.7% similarity. None of the strains in group I had a close relation with Haemophilus parainfluenzae by phylogenetic analysis, although they showed the same biochemical properties. In conclusion, the strains had characteristic biochemical properties and formed two independent groups within the "rodent cluster" of Pasteurellaceae that differed in the results of the fermentation test of xylose. Therefore, they seemed to be hitherto undescribed taxa in Pasteurellaceae.

Microbiological contamination of laboratory mice and rats in Korea from 1999 to 2003

To survey the microbiological contamination of laboratory mice and rats in Korea during a 5-year period, we monitored animals housed in mouse and rat facilities with either barrier or conventional systems. At barrier and conventional mouse facilities, the most important pathogen identified was mouse hepatitis virus (MHV), while Mycoplasma pulmonis was the most important pathogen at conventional rat facilities. Interestingly, hantavirus was recovered from both barrier and conventional mouse facilities. The most common protozoon identified was Tritrichomonas muris in mouse facilities and Entamoeba muris in rat facilities. In addition, we found that the microbiological contamination of mice and rats in conventional facilities was severe. These results suggest that conventional facilities should be renovated and monitored regularly to decrease microbiological contamination. We also propose that hantavirus should be monitored in Korea as an important mouse pathogen.

Phylogenetic Analysis of Isolates of Pasteurella pneumotropica from Laboratory Animals Based on the gyrB Gene Sequence

Phylogenetic analysis using the gyrB sequence was performed to investigate the genetic relevance among 49 isolates of P. pneumotropica. In the phylogeny, the isolates were clearly classified into three groups as follows: group A for the isolates of biotype Jawetz derived from mice, group B for the isolates of biotype Jawetz derived from rats, and group C for the isolates of biotype Heyl. These results suggest that the gyrB sequence of P. pneumotropica differs between the isolates of two biotypes, and also between the isolates derived from mice and rats in the biotype Jawetz.