Are animals a source of Stenotrophomonas maltophilia in human infections? Contributions of a nationwide molecular study

Stenotrophomonas maltophilia (Sm) is an archetypal environmental opportunistic bacterium responsible for health care-associated infections. The role of animals in human Sm infections is unknown. This study aims to reveal the genetic and phylogenetic relationships between pathogenic strains of Sm, both animal and human, and identify a putative role for animals as a reservoir in human infection. We phenotypically and genotypically characterized 61 Sm strains responsible for animal infections (mainly respiratory tract infections in horses) from a French nationwide veterinary laboratory network. We tested antimicrobial susceptibility and performed MLST and genogrouping using the concatenation of the seven housekeeping genes from the original MLST scheme. Excluding the eight untypeable strains owing to the lack of gene amplification, only 10 out of the 53 strains yielded a known ST (ST5, ST39, ST162, ST8, ST27, ST126, ST131). The genogroup distribution highlighted not only genogroups (genogroups 5 and 9) comprised exclusively of animal strains but also genogroups shared by human and animal strains. Interestingly, these shared genogroups were primarily groups 2 and 6, which have previously been identified as the two most frequent genogroups among human-pathogenic Sm strains, especially among respiratory pathogens. The antimicrobial susceptibility testing underlined the presence of acquired resistance: 18.8 and 7.5% of the tested isolates were resistant to the sulfonamide-trimethoprim combination and ciprofloxacin, respectively. Animal strains of Sm shared phylogenetic traits with some of the most successful human strains. The exact relationships between the human and animal strains, and the genetic support of these common traits, need to be determined.