The aim of this study was to determine the presence and persistence of methicillin-resistant Staphylococcus aureus (MRSA) in milk, farm environment, and farmers on 22 dairy cattle farms in Korea during 2008-2009. Genetic relatedness among the MRSA isolates was also investigated. Of 1146 samples examined, 35 of 559 (6.3%) quarter milk samples from 371 cows, four of 86 (4.7%) hand and nose samples from 43 farmers, and 6 of 501 (1.2%) farm environment samples were MRSA positive. Except for three isolates, all MRSA were classified into ST72-spa t324-SCCmec IV with PVL negative, the most predominant clonal type among community-associated MRSA in South Korea. All 35 MRSA-positive milk samples from 19 cows were obtained from a single farm (Farm G) out of 22 (4.5%) farms tested. The farm G was revisited 1 year later and milk samples were collected for examination of MRSA again. Two of six previous MRSA-positive cattle that had been kept on the farm still harbored MRSA genetically identical to MRSA strains, which were isolated from the same farm a year ago. The results of this study provide the evidence of transmission of MRSA among cattle, farm environment, and farmers and also long-term persistence of MRSA in animals.
Resistance to antimicrobials was measured in 73 isolates of Campylobacter
jejuni (C. jejuni) and 121 isolates of Campylobacter
coli (C. coli) from chicken and swine feces and carcasses in
Korea. Both bacterial species showed the highest resistance to (fluoro) quinolones
(ciprofloxacin and nalidixic acid) out of the nine antimicrobials tested. Erythromycin
resistance was much higher in C. coli (19.0%, 23/121) than in C.
jejuni (6.8%, 5/73). The mutation in the 23S rRNA gene was primarily
responsible for macrolide resistance in Campylobacter isolates. Several
amino acid substitutions in the L4 and L22 ribosomal proteins may play a role in the
mechanism of resistance, but the role requires further evaluation. A total of eight
virulence genes were detected in 28 erythromycin-resistant Campylobacter
isolates. All C. jejuni isolates carried more than four such genes, while
C. coli isolates carried fewer than three such genes. The high rate of
resistance highlights the need to employ more prudent use of critically important
antimicrobials, such as fluoroquinolones and macrolides, in swine and poultry production,
and to more carefully monitor antimicrobial resistance in Campylobacter
isolates in food animals.
To investigate apramycin resistance in humans in Korea, a total of 138 human Escherichia coli strains confirmed as gentamicin-resistant were collected from Korean Culture Collection Antimicrobial-Resistant Microbes. Apramycin resistance (minimum inhibitory concentrations ≥1,024 μg/ml) was observed in 16 (11.6%) of the 138 gentamicin-resistant E. coli (GREC) strains. Among the seven different kinds of aminoglycoside resistance genes tested, only four kinds were detected in the apramycin-resistant GREC strains: aac (3)-II, aac (3)-III, aac (3)-IV, and armA. The aac (3)-IV gene was found in all apramycin-resistant GREC strains, whereas aac(3)-II, aac(3)-III, and armA genes were detected in 8 (50.0%), 6 (37.5%), and 1 (6.3%) GREC strains resistant to apramycin, respectively. Of 16 apramycin-resistant GREC strains, transfer of apramycin resistance was observed in seven (43.8%), and co-transfer of resistance to other antimicrobials along with apramycin resistance was also found in four strains (25.0%) by broth mating. The results of this study suggest that more prudential use of apramycin in animals is needed.
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