Antimicrobial resistance profiles and clonal diversity of Staphylococcus epidermidis isolates from pig farms, slaughterhouses, and retail pork.

Livestock-associated coagulase-negative staphylococci (CoNS), such as Staphylococcus (S.) epidermidis, have emerged as a significant reservoir of antimicrobial resistance (AMR). In the current study, the AMR profiles and genetic diversity of S. epidermidis isolates obtained from pig farms, slaughterhouses, and retail pork were analyzed. A total of 89 S. epidermidis isolates, comprising 22 methicillin-resistant (MRSE) and 67 methicillin-susceptible S. epidermidis (MSSE) isolates, were assessed to determine (i) the clonal lineages of the isolates [multilocus sequence (MLST), agr, and staphylococcal cassette chromosome mec (SCCmec) types], (ii) the profiles of AMR phenotypes, and (iii) the carriage of genetic factors associated with major AMR phenotypes and zinc chloride resistance. Two dominant clonal lineages of S. epidermidis, ST100 and ST570, were observed on pig farms, especially in healthy pigs. In addition, potential transmission of pig-associated ST100 MRSE-SCCmec V and ST100 MSSE to farm workers was identified. The high prevalence of ST100 and ST570 isolates in pig farms was associated with high levels of AMR and zinc chloride resistance. In relation to resistance phenotypes, higher carriage rates of resistance genes, such as ß-lactams (mecA), phenicols (fexA), and tetracyclines [tet(K), tet(L), tet(S), tet(M), and tet(O)], were identified in pig farm-associated isolates. Furthermore, cfr-mediated linezolid resistance was detected in 14 MSSE isolates from pig farms. This study is the first to provide important insights into the clonal structures and AMR profiles of S. epidermidis isolates collected from healthy pigs, carcass/pork samples, and human workers in Korea.

Occurrence and Characteristics of Methicillin-Resistant and -Susceptible Staphylococcus aureus Isolated from the Beef Production Chain in Korea.

The emergence and persistence of methicillin-susceptible Staphylococcus aureus (MSSA) and methicillin-resistant S. aureus (MRSA) in livestock animals have been reported as a potential risk factor for transmission to humans. In this study, we investigated the nationwide prevalence and characteristics of MRSA and MSSA in the Korean beef production system, including retail markets, slaughterhouses, and cattle farms. From a total of 1,285 samples, only 5 MRSA strains were isolated: from a farmer (1 ST72 MRSA), a carcass sample from a slaughterhouse (1 ST72 MRSA), and beef cattle (3 ST5 MRSA). In addition, 11 MSSA strains were isolated from beef cattle (n=3), humans (1 farmer, 1 slaughterhouse worker, and 4 retail market workers), and carcass samples (n=1) and slaughterhouse environment (n=1). Although the prevalence of MRSA and MSSA in beef cattle was much lower than that reported in pigs, 5/5 MRSA and 2/11 MSSA strains displayed multiple drug resistance (MDR) phenotypes. Unlike the swine-associated MRSA, no correlation was found between tetracycline/zinc resistance and MDR phenotype. However, MRSA strains had an identical set of staphylococcal enterotoxins and exhibited enhanced levels of resistance to antimicrobial peptides (PMAP-36 and LL-37) compared to the MSSA strains. In conclusion, continued and systemic surveillance of livestock, meat products, and humans in close contact with livestock/meat products is necessary to prevent the transmission of MRSA and MSSA to humans.

Livestock-associated methicillin-resistant Staphylococcus aureus in Korea: antimicrobial resistance and molecular characteristics of LA-MRSA strains isolated from pigs, pig farmers, and farm environment.

The emergence of livestock-associated (LA)-methicillin-resistant Staphylococcus aureus (MRSA) in livestock animal has become a significant zoonotic concern. In the present study, we investigated nationwide prevalence of LA-MRSA across pork production chain including pig farms, slaughterhouses, and retail markets. A total of 40 MRSA strains were isolated during the investigation and the overall prevalence of MRSA was 3.4% (n = 37), 0.6% (n = 2), and 0.4% (n = 1) in pig farms, slaughterhouses, and retail markets, respectively. Multilocus sequence typing analyses revealed that the 2 most significant clonal lineages in pork production chain in Korea were ST398 (n = 25) and ST541 (n = 6). All of the 40 MRSA isolates were further characterized to investigate key genotypic and phenotypic correlates associated with the emergence and spread of clonal complex 398 (CC398; ST398, and ST541) LA-MRSA. Although the prevalence of swine-associated MRSA was still relatively low and mostly restricted to pig farms, multidrug-resistant CC398 LA-MRSA isolates with new spa types (t18102 and t18103) were identified as a major clonal lineage. The CC398 LA-MRSA strains tended to exhibit increased levels of multiple drug resistance (MDR) phenotype compared with non-CC398 MRSA strains. Of note, in comparison with non-CC398 MRSA isolates, CC398 LA-MRSA isolates exhibited significantly enhanced tetracycline (TET) and zinc resistance. These findings suggested that co-selection pressure associated with MDR phenotype, especially TET resistance, and zinc resistance may have played a significant role in the emergence and persistence of CC398 LA-MRSA in pig farms in Korea.

Prevalence and characteristics of livestock-associated methicillin-susceptible Staphylococcus aureus in the pork production chain in Korea.

The emergence and prevalence of methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-susceptible S. aureus (MSSA) in livestock animals have become a worldwide public health concern. While the prevalence and genetic profiles of MRSA strains in pigs and pork meat have been actively studied, livestock-associated MSSA strains have only been characterized in a few small-scale studies. In this investigation, we assessed the nationwide prevalence of MSSA in the Korean pig production chain, including pig farms, slaughterhouses, and retail markets. Among the 41 MSSA strains, the predominant clonal lineages were sequence type (ST) 398 (n = 15, 37%) and ST5 (n = 13, 32%). Although the overall prevalence of MSSA (2.58%) was low and mostly restricted to pig farms, ST398 MSSA strains showed higher level of multidrug resistance phenotype versus non-ST398 MSSA strains. In addition to the MDR phenotype, all of the ST398 MSSA strains exhibited resistance to tetracycline as they harbored the tet(K), tet(L), and/or tet(M) genes. However, ST398 MSSA strains did not exhibit increased resistance to zinc compared with the non-ST398 strains. This study is the first to provide evidence of ST398 MSSA emergence in livestock animals in Korea. Further studies are necessary to elucidate the potential of ST398 MSSA strains for human transmission. Our findings suggest that the MDR phenotype and high levels of tetracycline resistance may have played an important role in the emergence and prevalence of ST398 MSSA in pig farms in Korea.