A veterinary perspective on methicillin-resistant staphylococci

Methicillin-resistant staphylococci (MRS) and extended-spectrum beta-lactamases (ESBL)-producing Enterobacteriaceae in companion animals: nosocomial infections as one reason for the rising prevalence of these potential zoonotic pathogens in clinical samples

The ongoing change in the relationship between humans and companion animals is hallmarked by the increasing intensive care provided to companion animals in veterinary medicine, resulting in growing numbers of high-risk animal patients. The emergence of nosocomial infections in small animal clinics is one of the major drawbacks of this development, especially in terms of multidrug-resistance and potentially zoonotic pathogens. This mini-review therefore addresses recent findings regarding the increasing prevalence of multi-resistant bacterial pathogens like methicillin-resistant staphylococci (MRS), including Staphylococcus aureus (MRSA) and Staphylococcus pseudintermedius (MRSP) as well as extended-spectrum beta-lactamases (ESBL)-producing Enterobacteriaceae in companion animals. Along with the steady increase of nosocomial infection rates in veterinary clinics, particular attention has recently been drawn to the genetic background of multi-resistant strains, resulting in the identification of certain genetic lineages which frequently appear in both, human and animal samples. These sequence types (ST), included ST254, ST8 and ST22 in terms of MRSA and ST131, ST405 and ST648 for ESBL-producing E. coli. The interspecies distribution of these STs resulted in the assumption that certain extended-host spectrum genotypes (EHSG) might exist both for MRS and ESBL-producing E. coli. These initial findings underline the necessity to investigate the major molecular or functional driving forces facilitating interspecies transferability of such EHSG strains. Due to the zoonotic potential of these multi-resistant bacteria, another aspect of the changing social role of companion animals needs to be addressed: the close contact of pets with their owners, resulting in presumptive new transmission and infection routes. We therefore envision retaliatory actions like initial surveillance and monitoring programs not only in livestock, but also particularly in companion animals. Interdisciplinary approaches including human and veterinary experts should be implemented to develop reliable investigation procedures with respect to the current reality of animal owners and their pets. Additionally, consequent basic hygienic measures, prudent use of antimicrobials in companion animals and efforts regarding implementation of antibiotic stewardships should be fostered.

Gene expression profiling of dendritic cells reveals important mechanisms associated with predisposition to Staphylococcus infections

BACKGROUND

Staphylococcus aureus is a major pathogen of humans and animals and emerging antibiotic-resistant strains have further increased the concern of this health issue. Host genetics influence susceptibility to S. aureus infections, and the genes determining the outcome of infections should be identified to find alternative therapies to treatment with antibiotics. Here, we used outbred animals from a divergent selection based on susceptibility towards Staphylococcus infection to explore host immunogenetics.

METHODOLOGY/PRINCIPAL FINDINGS

We investigated how dendritic cells respond to heat-inactivated S. aureus and whether dendritic cells from animals showing different degrees of susceptibility had distinct gene expression profiles. We measured gene expression levels of in vitro S. aureus-stimulated bone marrow-derived dendritic cells at three different time points (0, 3 and 8 hrs) by using 15 k ovine Agilent microarrays. Furthermore, differential expression of a selected number of genes was confirmed by RT-qPCR. Gene signatures of stimulated DCs were obtained and showed that genes involved in the inflammatory process and T helper cell polarization were highly up-regulated upon stimulation. Moreover, a set of 204 genes were statistically differentially expressed between susceptible and resistant animals, and grouped them according to their predisposition to staphylococcal infection. Interestingly, over-expression of the C1q and Ido1 genes was observed in the resistant line and suggested a role of classical pathway of complement and early regulation of inflammation pathways, respectively. On the contrary, over expression of genes involved in the IL1R pathway was observed in susceptible animals. Furthermore, the leucocyte extravasation pathway was also found to be dominant in the susceptible line.

CONCLUSION/SIGNIFICANCE

We successfully obtained Staphylococcus aureus associated gene expression of ovine BM-DC in an 8-hour kinetics experiment. The distinct transcriptional profiles of dendritic cells obtained from resistant and susceptible animals may explain susceptibility towards S. aureus infections in a broader context.

Isolation of methicillin-resistant Staphylococcus pseudintermedius from breeding dogs

The overuse of antimicrobials can select resistant bacteria strains; staphylococci have the ability to become resistant to all beta-lactam antimicrobials and are a significant concern in human medicine and a growing issue for veterinary medicine. Because antimicrobials are sometimes incorrectly used in breeding kennels, the objective of the work was to assess the occurrence of methicillin-resistant coagulase-positive staphylococci in breeding dogs. The research was carried out in 13 kennels that were allotted to three categories according to the intensity of antimicrobial use. Vaginal and milk swabs were taken from 87 healthy bitches around parturition and also from multiple organs of 27 of their pups that died within the first 2 weeks. Standard bacteriological examinations were carried out and coagulase-positive staphylococci were identified. All the coagulase-positive staphylococci resulted to be Staphylococcus pseudintermedius. Susceptibility to oxacillin and the presence of the mecA gene were tested. Nine out of 89 strains (six isolated from the bitches' milk and three from dead puppies, all belonging to kennels characterized by an excessive use of antimicrobials) were multidrug-resistant, methicillin-resistant and mecA positive. Our results confirm that excessive use of antimicrobials entails the risk of selecting resistant staphylococci strains. Our data also indicate that the bacterial flora of healthy dogs belonging to specific populations may act as a reservoir of resistance genes.