The increase of methicillin-resistant Staphylococcus aureus(MRSA) and the presence of an unusual sequence type ST49 in slaughter pigs in Switzerland

Abstract

BackgroundIn years past, methicillin-resistant S. aureus (MRSA) has been frequently detected in pigs in Europe, North America and Asia. Recent, yet sporadic studies have revealed a low occurrence of MRSA in Switzerland. In 2009, a monitoring survey of the prevalence and genetic diversity of methicillin-resistant S. aureus (MRSA) in slaughter pigs in Switzerland was conducted using methods recommended by the EU guidelines, and using a sampling strategy evenly distributed throughout the year and representative of the Swiss slaughter pig population. Monitoring should determine if the overall prevalence of MRSA in the entire country is increasing over the years and if specific multi-resistant MRSA clones are spreading over the country.ResultsIn 2009, the nasal cavities of eight out of 405 randomly selected pigs were positive for MRSA, representing a prevalence of 2.0% (95% CI 0.9-3.9). The following year, 23 out of 392 pigs were positive for MRSA [5.9% prevalence (95% CI 3.8-8.7)]. Three multilocus sequence types (ST), four spa types and two types of staphylococcal cassette chromosome mec (SCCmec) elements were detected. The most frequent genotypes were ST398 (MLST)-(spa)t034-V(SCCmec) (n = 18) and ST49-t208-V (n = 7), followed by ST398-t011-V (n = 4), ST398-t1451-V (n = 1), and ST1-t2279-IVc (n = 1). The isolates displayed resistance to ß-lactams [mecA, (31/31); blaZ, (19/31)]; tetracycline [tet(M), (31/31); tet(K), (30/31)] (n = 31); macrolides and lincosamides [erm(C) (4/31) or erm(A) (18/31)] (n = 22); tiamulin [vga(A)v (9/31) or unknown mechanism (18/31)] (n = 27); trimethoprim [dfr(G) (18/31); spectinomycin [ant(9)-Ia (19/31) or unknown mechanism (3/31)] (n = 22); streptomycin [str (19/31)]; sulphamethoxazole (7/31) and ciprofloxacin (n = 1) (mechanisms not determined).ConclusionsThis study is the first to describe the presence of MRSA ST49 in slaughter pigs, and to demonstrate a significant and nearly three-fold increase of MRSA prevalence in pigs within two years. The presence of a specific clonal lineage of MRSA from Switzerland suggests that it has been selected in Swiss pig husbandry. Effective hygiene measures should be enhanced within the entire pig production chain to suppress the spread of these pathogens into the community.

Antimicrobial Resistance of Staphylococcus aureus Strains Acquired by Pig Farmers from Pigs

“…This was in agreement with other studies conducted in Switzerland (19,27,34). We speculate that this might be due to differences in the use of antimicrobial agents in farming.…”

“…There are few reports of other pig-associated MRSA genotypes that seem rare in humans: CC9, CC1, and CC49 (2,15,27,34,40). Pig-associated ST9 S. aureus can be transmitted to humans who were in contact with pigs (26).…”

New Transposon Tn 6133 in Methicillin-Resistant Staphylococcus aureus ST398 Contains vga (E), a Novel Streptogramin A, Pleuromutilin, and Lincosamide Resistance Gene

“…While one-third of these tiamulin-resistant MRSA isolates harbored the vga(A)v gene, the remaining isolates did not contain any of the known vga genes (25). In the present study, we characterized a new streptogramin A, pleuromutilin, and lincosamide resistance gene, vga (E).…”

“…During the monitoring of methicillin-resistant Staphylococcus aureus (MRSA) in the nasal cavities of pigs at slaughterhouses in Switzerland in 2009 and 2010, 90% of the MRSA isolates were resistant to tiamulin (25). While one-third of these tiamulin-resistant MRSA isolates harbored the vga(A)v gene, the remaining isolates did not contain any of the known vga genes (25).…”

High Prevalence of tetM as Compared to tetK Amongst Methicillin-Resistant Staphylococcus aureus (MRSA) Isolates from Hospitals in Perak, Malaysia

“…A study by Schmitz et al, in 2001 reported that tetM gene was detected in 76.0% of tetracycline-resistant MRSA, which followed closely by 73.0% of tetK gene (28). Another study also showed that all the MRSA samples collected from nasal cavities in pigs were mostly tetM-positive (29). In addition, tetM gene was also detected in 92.0% of all the tetracycline-resistant MRSA strains isolated in a Spanish hospital (30).…”