Methicillin-resistant Staphylococcus pseudintermedius among dogs in the description of novel SCCmec variants.

The presence and genetic characteristics of methicillin-resistant Staphylococcus pseudintermedius (MRSP) in Sri Lanka was investigated to add additional insight into global spread, emergence and evolution of MRSP. A total of 234 samples from dogs visiting veterinary clinics were cultured for staphylococci and the genomes of the MRSP isolates were sequenced, to identify resistance genes, the multilocus sequence types (MLST) and spa types. From a questionnaire the history of antimicrobial treatment and patient information was obtained. S. pseudintermedius was isolated from 116/229 samples, eight of these were MRSP. Six MRSP CC45 isolates contained a pseudo-SCC element ΨSCCmec57395. Two isolates belonging to ST429 (CC761) and ST121 (CC121) contained novel variants of the SCCmec Type V(T) element. The elements were designated SCCmecV(T)SL/066, that carried additional transposon-related genes, and SCCmecV(T)SL/154 that carried a type III restriction-modification system, a type 7 ccr gene complex, and a cadA coding sequence. Thirty-seven percent of the dogs received antimicrobial treatment at the time of sampling of which four dogs were MRSP-positive. The proportion of MRSP among S. pseudintermedius is low compared to other countries, despite the fact that in Sri Lanka antimicrobials for treatment of dogs are available over the counter. Important is the finding of novel type V(T) SCCmec elements, which further underlines the high recombination frequency of SCC elements. The ΨSCCmec57395 was found in isolates of CC45, which is the only sequence type of MRSP known to contain this pseudo-cassette.

Livestock-associated MRSA in household members of pig farmers: transmission and dynamics of carriage, a prospective cohort study.

This prospective cohort study describes carriage of livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) in household members from 49 farrowing pig farms in the Netherlands (2010-2011). Of 171 household members, 4% were persistent MRSA nasal carriers, and the MRSA prevalence on any given sampling moment was 10% (range 7-11%). Working in the stables (of which 98% was MRSA-positive, prevalence ratio (PR) = 2.11 per 10 hours), working with sows (PR=1.97), and living with an MRSA-positive pig farmer (PR=4.63) were significant determinants for MRSA carriage. Significant protective factors were carriage of methicillin-susceptible Staphylococcus aureus (MSSA) (PR=0.50), and wearing a facemask when working in the stables (37% decreased prevalence). All MRSA strains during the study period were known livestock-associated types. The bacteriophage φ3 was not found in household members. Transmission from pigs and the environment appeared to be important determinants; human-to-human transmission could not sufficiently be differentiated. Wearing a facemask when working in the stables and carriage of MSSA are potential interventional targets.

Dynamics of MRSA carriage in veal calves: a longitudinal field study.

Colonization of Methicillin-Resistant Staphylococcus aureus (MRSA) in food producing animals has public health implications, but intervention targets have not yet been identified. In this field study occurrence and dynamics of MRSA in veal calves were investigated longitudinally on three farms. Determinants generally associated with MRSA carriage, such as environmental exposure and antimicrobial use, were explored. In addition, the reliability and reproducibility of MRSA detection in nasal samples from veal calves were investigated as well as the additional value of rectal samples to establish MRSA status of an individual animal. On these three farms, MRSA prevalence and MRSA air loads in stables rapidly increased during the production cycle, especially after releasing calves from their individual houses, but not simultaneously with or directly after treatment with antimicrobials. These observations constitute the hypothesis that antimicrobial use may not necessarily be the only condition for MRSA transmission in veal calves, but indicate that other factors may contribute to transmission as well. MRSA in calves was present both nasally and rectally. The reproducibility and repeatability of the nasal samples were moderate. The results of this study give a better understanding of the dynamics of MRSA in a field situation.

In vitro antimicrobial activity of miconazole and polymyxin B against canine meticillin-resistant Staphylococcus aureus and meticillin-resistant Staphylococcus pseudintermedius isolates.

BACKGROUND: Meticillin-resistant Staphylococcus aureus (MRSA) and meticillin-resistant Staphylococcus pseudintermedius (MRSP) infections are increasingly reported in dogs, and these bacteria may be isolated from ear infections. HYPOTHESIS/OBJECTIVES: The main aim of the present study was to investigate the in vitro antimicrobial activity of miconazole, polymyxin B and a combination of both against 24 canine MRSA and 50 canine MRSP isolates. The minimal inhibitory concentration (MIC) values of 12 other antimicrobial agents were also determined. METHODS: All MIC values were determined according to a broth microdilution assay. RESULTS: Acquired resistance was found to all tested agents, except for linezolid, miconazole and polymyxin B. The MIC values for miconazole and polymyxin B against MRSA were in the range of 4-8 and 8-64 µg/mL, respectively, while the MIC values for miconazole and polymyxin B against MRSP were in the range of 1-2 and 0.25-4 µg/mL, respectively. Using a combination of miconazole and polymyxin B, there was no evidence for enhanced in vitro activity of the combination (i.e. synergy) of both products. Nevertheless, MIC(90) values of the combination of these antimicrobial agents and of a commercial product containing both agents were at least 1000 times lower than the concentration present in the commercial product. CONCLUSIONS AND CLINICAL IMPORTANCE: These results indicate that the topical use of a combination of miconazole and polymyxin B in a 43.5:1 ratio may have potential for the treatment of MRSA-mediated and MRSP-associated otitis externa in dogs.