Molecular diversity and prevalence of Helicobacter, Bartonella and Streptococcus in Mus musculus from sub-Antarctic Marion Island in relation to host diversity

The house mouse (Mus musculus) was introduced to Marion Island by sealers in the early 1800’s and was found abundantly over the entire Island as early as 1818. Despite the abundance of this rodent, little information is known about the invasive house mouse from Marion Island with regards to its genetics and infectious disease potential. Therefore, this study aimed to determine the genetic diversity of the house mouse Mus musculus on Marion Island, as well as the prevalence of three zoonotic bacterial disease agents viz. Bartonella, Helicobacter and Streptococcus.

To determine the genetic diversity of Mus musculus from Marion Island a sub population of 91 mice was used for mitochondrial DNA sequence analysis. Sequencing the mitochondrial control region resulted in 539 bp homologous gene segment, comprising of five haplotypes that varied in abundance and geographical distribution. The most abundant haplotypes were haplotype 1 and haplotype 2, with haplotype 1 being found across all sample localities and haplotype 2 being found throughout the northern part of the island. The determination of disease transmission through urine contamination was explored by molecularly screening the kidneys of the house mice for Streptococcus genome presence. A low Streptococcus prevalence of 7.4% was recovered. In order to validate the potential novel Streptococcus species reported previously, four culturing attempts were undertaken. Any bacterial growth recovered from the culture attempts were screened using a universal 16S primer set to identify the bacteria to genus level and where possible classify them to species level. Subsequent sequencing of PCR positive samples revealed 8/9 samples to be novel and having the highest nucleotide sequence identity match (96%) to S. constellatus, while the remaining positive PCR sample grouped most closely to S. parasanguinis with 99% sequence similarity.

To determine Helicobacter prevalence, DNA was extracted from the gastrointestinal (GI) tracts as well as the livers of the mice and used as template for 16S rRNA lineage-specific amplification. The overall Helicobacter infection rate was 12.4%, with different infection rates being observed in the GI tracts (10.7%) and in the livers (2.5%). Two species were recovered viz. H. typhlonius and H. hepaticus, with the remaining five samples appearing to contain novel Helicobacter species. Lastly, the presence of Bartonella was evaluated by targeting the livers of the mice and screening them with primers targeting the citrate synthase (gltA) gene. All 171 samples screened were negative, corresponding to an overall prevalence of 0%. These results contrast markedly with the generally high levels of prevalence reported for other murid rodent species. In conclusion, Mus musculus from Marion Island harbour at least two genera with known zoonotic potential. However, the extent and severity of potential disease transmission risk that these invasive rodents pose to native vertebrates is not known and requires further investigation. Future studies should focus on a wider range of zoonotic bacteria and also take into consideration the potential effect of seasonality on disease transmission.