Streptococcus canis genomic epidemiology reveals the potential for zoonotic transfer.

Streptococcus canis, a multi-host pathogen commonly isolated from dogs and cats, has been occasionally reported in severe cases of human infection. To address the gap in knowledge on its virulence and host tropism, we investigated S. canis genomic epidemiology and report the results of this analysis for the first time. We analysed 59 S. canis whole genome sequences originating from a variety of host species, comprising 39 newly sequenced isolates from UK sources, along with all (n=20) publicly available genomes. Antimicrobial resistance (AMR) phenotype was determined for all 39 available isolates. Genomes were screened for determinants of resistance and virulence. We created a core SNP phylogeny and compared strain clustering to multi-locus sequence typing (MLST) and S. canis M-like protein (SCM) typing. We investigated the dataset for signals of host adaptation using phylogenetic analysis, accessory genome clustering and pan-genome-wide association study analysis. A total of 23 % (9/39) of isolates exhibited phenotypic resistance to lincosamides, macrolides and/or tetracyclines. This was complemented by the identification of AMR-encoding genes in all genomes: tetracycline (tetO 14 %, 8/59; and tetM 7 %, 4/59) and lincosamide/macrolide (ermB, 7 %, 4/59). AMR was more common in human (36 %, 4/11) compared to companion animal (18 %, 5/28) isolates. We identified 19 virulence gene homologues, 14 of which were present in all strains analysed. In an S. canis strain isolated from a dog with otitis externa we identified a homologue of S. pyogenes superantigen SMEZ. The MLST and SCM typing schemes were found to be incapable of accurately representing core SNP-based genomic diversity of the S. canis population. No evidence of host adaptation was detected, suggesting the potential for inter-species transmission, including zoonotic transfer.

Streptococcus canis, the underdog of the genus.

Streptococcus canis is a multi-host pathogen that causes disease of varying severity in a wide range of mammals, including humans. Dogs and cats appear to be the primary hosts and may play a role in transmitting infection to humans. The broader epidemiology of S. canis, however, is still poorly understood, as are its virulence mechanisms, antimicrobial resistance (AMR) and population structure. In this review we gather existing knowledge on S. canis, describing its epidemiology in animals and humans and present information on virulence factors, classification schemes and AMR prevalence. We describe the main ecological niches of S. canis in companion animals, discuss potential risk factors for infection in humans and propose a multi-host transmission cycle. We show that current knowledge on S. canis virulence determinants is limited and sometimes contradictory. We illustrate the different typing systems proposed to classify S. canis. We also report the range of known AMR phenotypes and the emergence of new mechanisms of resistance. Finally, we discuss the zoonotic potential of S. canis, highlighting the need for further evidence in this area. Streptococcus canis may be regarded as a neglected pathogen of one health concern. Further research is needed for its better understanding and effective control.

Complete Genome Sequences of Three Invasive Strains of Streptococcus pyogenes Subtype emm5.23 Isolated in Scotland.

Streptococcus pyogenes emm5.23 is uncommon; however, it has recently been involved in a relatively high proportion of cases of invasive disease in Scotland. Here, we report the complete genome sequences of three emm5.23 isolates, which may be used as a reference for investigating the virulence and epidemiology of this strain.

The duration of antibiotic treatment is associated with carriage of toxigenic and non-toxigenic strains of Clostridioides difficile in dogs.

Clostridioides difficile is a leading cause of human antibiotic-associated diarrhoeal disease globally. Zoonotic reservoirs of infection are increasingly suspected to play a role in the emergence of this disease in the community and dogs are considered as one potential source. Here we use a canine case-control study at a referral veterinary hospital in Scotland to assess: i) the risk factors associated with carriage of C. difficile by dogs, ii) whether carriage of C. difficile is associated with clinical disease in dogs and iii) the similarity of strains isolated from dogs with local human clinical surveillance. The overall prevalence of C. difficile carriage in dogs was 18.7% (95% CI 14.8-23.2%, n = 61/327) of which 34% (n = 21/61) were toxigenic strains. We found risk factors related to prior antibiotic treatment were significantly associated with C. difficile carriage by dogs. However, the presence of toxigenic strains of C. difficile in a canine faecal sample was not associated with diarrhoeal disease in dogs. Active toxin was infrequently detected in canine faecal samples carrying toxigenic strains (2/11 samples). Both dogs in which active toxin was detected had no clinical evidence of gastrointestinal disease. Among the ten toxigenic ribotypes of C. difficile detected in dogs in this study, six of these (012, 014, 020, 026, 078, 106) were ribotypes commonly associated with human clinical disease in Scotland, while nontoxigenic isolates largely belonged to 010 and 039 ribotypes. Whilst C. difficile does not appear commonly associated with diarrhoeal disease in dogs, antibiotic treatment increases carriage of this bacteria including toxigenic strains commonly found in human clinical disease.