Interspecies transfer of plasmid-borne gentamicin resistance between Staphylococcus isolated from domestic dogs to Staphylococcus aureus.

As preconized by the One Health concept, the intimate relationship between pets and owners is a common source for the trade of microorganisms with zoonotic potential, and with them, antimicrobial resistance genes. In this work, we evaluated the presence of antimicrobial resistance genes, that are usually within mobile genetic elements, in a laboratory collection of 79 canine Staphylococcus strains, mostly Staphylococcus pseudintermedius and Staphylococcus coagulans. Resistance to tetracycline was observed in 34% of the strains, followed by resistance to erythromycin (21%) and gentamicin (19%). These phenotypes were partially correlated with the presence of the tetracycline resistance genes tet(M) and tet(K) in 64% and 44% of all strains, respectively; erythromycin resistance genes erm(A) and erm(C) in 53% and 23%; and gentamicin resistance gene aac(6')-aph(2″) in 26% of the strains. At least 45% of the strains harbored high- and/or low-molecular weight plasmids, whose transfer may be facilitated by their widespread biofilm-forming capacity, and absence of restrictive CRISPR systems. We selected eight plasmid-bearing and multidrug resistant strains, which were submitted to plasmid curing by stress with SDS. No strain lost resistance during stressing cultivation but, by conjugation experiments, the S. pseudintermedius strain 27 transferred its plasmid-borne resistance to gentamicin, conferred by the aac(6')-aph(2″) gene, to Staphylococcus aureus. The frequent empirical use of gentamicin to treat skin and ear infections in domestic dogs is likely to select resistant strains. Also, as demonstrated by our study, these strains can serve as gene reservoirs for human pathogens, such as S. aureus.

Staphylococcus nepalensis, a commensal of the oral microbiota of domestic cats, is a reservoir of transferrable antimicrobial resistance.

Staphylococcus nepalensis is a commensal bacterium from the oral microbiota of domestic cats, with a still obscure clinical importance. In this work, we analysed the ability of feline strains of S. nepalensis to transfer antimicrobial resistance genes to Staphylococcus aureus isolated from humans through plasmids. To this end, we first analysed all publicly available genomes from cat staphylococci using computational methods to build a pan-resistome. Genes that encode resistance to erythromycin, gentamicin, mupirocin and tetracycline, common to human and cat staphylococci and previously described to be located in mobile genetic elements, were chosen for the next analyses. We studied 15 strains of S. nepalensis, which were shown to be genetically different by GTG5-PCR. As observed by disc diffusion, resistance to tetracycline was widespread (80 %), followed by resistance to erythromycin (40 %), gentamicin (27 %) and mupirocin (7 %). The strains were positive for several antimicrobial resistance genes and more than half of them harboured plasmids. The loss of plasmids and resistance genes in some strains were induced by stress with SDS. Through conjugation experiments, we observed that these plasmids can be transferred to S. aureus, thus increasing its potential to resist drug therapy. Our findings show that S. nepalensis, an underestimated inhabitant of the cat microbiota, can be a reservoir of antimicrobial resistance genes for S. aureus and, like many other staphylococci, be an overlooked and silent threat to their animal hosts and humans living with them.

CRISPR-Cas Systems Features and the Gene-Reservoir Role of Coagulase-Negative Staphylococci.

The claimed role of gene reservoir of coagulase-negative staphylococci (CoNS) could be contradicted by estimates that CRISPR/Cas systems are found in the genomes of 40-50% of bacteria, as these systems interfere with plasmid uptake in staphylococci. To further correlate this role with presence of CRISPR, we analyzed, by computational methods, 122 genomes from 15 species of CoNS. Only 15% of them harbored CRISPR/Cas systems, and this proportion was much lower for S. epidermidis and S. haemolyticus, the CoNS most frequently associated with opportunistic infections in humans. These systems are of type II or III, and at least two of them are located within SCCmec, a mobile genetic element of Staphylococcus bacterial species. An analysis of the spacers of these CRISPRs, which come from exogenous origin, allowed us to track the transference of the SCCmec, which was exchanged between different strains, species and hosts. Some of the spacers are derived from plasmids described in Staphylococcus species that are different from those in which the CRISPR are found, evidencing the attempt (and failure) of plasmid transference between them. Based on the polymorphisms of the cas1 gene in CRISPRs of types II and III, we developed a multiplex polymerase chain reaction (PCR) suitable to screen and type CRISPR systems in CoNS. The PCR was tested in 59 S. haemolyticus strains, of which only two contained a type III cas1. This gene was shown to be expressed in the exponential growth, stationary phase and during biofilm formation. The low abundance of CRISPRs in CoNS is in accordance with their role as gene reservoirs, but when present, their spacers sequence evidence and give an insight on the dynamics of horizontal genetic transfer among staphylococci.