The aim of this study was to investigate the prevalence of antimicrobial resistance in Escherichia coli isolated from pigs and their farmhouse environment in Korea. A total of 585 E. coli were isolated in this study during 2006 2007: 426 isolates from 492 pigs and 159 isolates from 312 farmhouse environment samples from 16 different pig farms. The most frequently observed resistance in pig fecal samples was antimicrobials such as tetracycline, streptomycin, and ampicillin. However, resistance to cephalosproins, β-lactam / β-lactam inhibitor combination, and colistin was low. We found an inverse relationship between prevalence of resistant E. coli and animal age. Resistance rate and multi-drug resistance (MDR) was greater in young pigs (piglet and nursery) than for those from adult pigs (grower-finish and sow). Resistance of E. coli from farm environment such as floor, Iron partition, and ventilation was similar with those from pig fecal samples. Farm environment contaminated with MDR bacteria might be a possible source of infections to pigs. Thus, to control and reduce the antimicrobial resistance in pigs, we must also pay attention to the environment.

During January-November 2012, a total of 2,041 quarter milk samples were collected from dairy cattle of 82 dairy farms nationwide. About 42% (870/2,041) of the samples that had somatic cell counts (SCC) of ≥ 200,000 cells/ml were subjected to microbiological examination. No bacteria was isolated from 95 of 870 (10.9%) samples. Among 1,237 bacteria isolated from the rest 775 samples, 1,085 were identified with VITEK: more than half (52.1%, 645/1,237) of the isolates were gram negative bacillus. Gram positive cocci including Staphylococcus accounted for 35% of the isolates and almost none of gram positive bacilli isolated. Excluding Coagulase-negative Staphylococcus (CNS), the most frequently isolated bacterial species was Escherichia coli (11.2%, 138/1, 237), followed by Klebsiella pneumoniae (8.1%,100/1,237), Staphylococcus aureus (7.1%, 88/1, 237), Enterobacter cloacae (6.0%, 74/1, 237), and Serratia marcescens (3.5%, 43/1, 237). The most common resistance of S. aureus was to penicillin (77.4%) and ampicillin (73.0%), while no resistance was observed against gentamicin and cephalothin. Although CNS presented resistance to all antimicrobials tested but the most prevalent resistance was to penicillin (35.6%) and ampicillin (37.0%). The pattern of antimicrobial resistance observed in CNS was similar to that of S. aureus, but the rates were much lower than those of S. aureus. E. coli also showed resistance to all the antimicrobials tested, although the rates were not very high. The highest resistance of E. coli was to cephalothin (39.4%) and ampicillin (36.2%), while most of the strains (98.0%) showed sensitivity to amikacin. The results of this study provide information on current situation of bovine mastitis in Korea.

To determine current rate of antimicrobial resistance, a total of 236 isolates from milk samples of dairy cattle with mastitis in Korea during 2010-2011 were examined against 12 antimicrobials using disc diffusion method: 67 Staphylococcus aureus, 74 coagulase-negative Staphylococcus spp. (CNS), and 95 Escherichia coli isolates. The isolates examined in this study were submitted by Local Veterinary Service Laboratories located in 13 provinces and metropolitan cities nationwide. The highest rates of resistance among S. aureus isolates were against ampicillin (56.7%) and penicillin (56.7%), followed by kanamycin (11.9%). All S. aureus isolates were sensitive to lincomycin, amikacin, and cephalothin. Only one isolate showed resistance to tetracycline and oxacillin, respectively. Less than 10% of the S. aureus isolates presented resistance to erythromycin, neomycin, and gentamicin. Among CNS isolates, the most frequently observed resistance was to lincomycin (44.5%), followed by penicillin (28.3%), ampicillin (18.9%), tetracycline (17.5%), kanamycin (13.5%), and erythromycin (9.4%). All or most of the CNS isolates were sensitive to cephalothin, amikacin, neomycin, and gentamicin. The highest rate of resistance among E. coli isolates was against tetracycline (26.3%), followed by streptomycin (21%), neomycin (15%), kanamycin (12.6%), and gentamicin (10.5%). Amikacin was the only antimicrobial to which no E. coli isolates showed resistance. Around 10% of the S. aureus isolates and 15% of the CNS isolates showed resistance against three or more antimicrobials simultaneously, while more than 30% of the E. coli isolates did.

Salmonellosis constitutes an important public health problem in both developing and developed countries, including Korea. The aims of present study were to investigate the serovar and antimicrobial resistance of Salmonella isolated from food animals and animal products in slaughterhouses and farms. A total of 323 Salmonella were isolated from food animals (n=277) and meats (n=46) during 2010. Of the isolates, 21 different serovars were identified. The predominant serovars were S. Rissen (35%) and S. Montevideo (24.3) in healthy pigs, while S. Enteritidis (25.5%) in healthy chicken. S. Typhimurium (88.8%) was predominant in disease pigs, while S. Gallinarum (29.2%) and S. Montevideo (26.9%) were in diseased chickens. Among meat samples, S. Typhimurium (57.1%) was the most common serovar in pork but S. Enteritidis (38.7%) and S. Montevideo(32.3%) were in chikcen meats. Analysis of antimicrobial resistance patterns revealed that 20.7% of the isolates were sensitive to all the 15 drugs tested. The isolates were frequently resistant to nalidixic acid (47.7%), tetracycline (38.4%), streptomycin (33.7%), and ampicillin (32.8%). The resistance to quinolone and 3rd generation cephalosporins was higher in chicken and chicken meat isolates. Of the 323 isolates, 174 (53.9%) were resistant to one or more CLSI subclass, and 117 (36.2%) showed multiple-resistance. Our findings showed that multiple resistant Salmonella organism are widespread in animals and animal products in Korea. To prevent the transmission or exposure for consumers of antimicrobial resistant Salmonella, policies and guidelines aiming at prudential use of critical antimicrobials for humans are needed.

Campylobacterosis is the most common food borne bacterial disease in many countries. Food animals and animal products are considered to be the reservoir of the Campylobacter species. The aim of this study was to investigate the antimicrobial resistance of Campylobacter spp. from food animals and raw meats in slaughterhouses. A total of 90 Campylobacter jejuni (C. jejuni) and 127 Campylobacter coli (C. coli) were isolated, for which antimicrobial susceptibility was examined using broth dilution method. Resistance to macrolide antimicrobials was higher among C. coli isolates than among C. jejuni. Among both C. jejuni and C. coli isolates, the most frequently observed resistance was to nalidixic acid, ciprofloxacin, and tetracycline. No erythromycin resistance was observed among C. jejuni isolates from cattle, pig and beef. However, 28.3% (n=13) and 25% (n=3) of C. coli isolates from pigs and pork showed resistance to erythromycin, respectively. The predominant profile of multiple resistance among C. jejuni and C. coli isolates was ciprofloxacin/tetracycline/nalidixic acid resistance (46.7%) and ciprofloxacin/nalidixic acid resistance (31.5%), respectively. This finding has important implication for food safety and public health.

Staphylococcus aureus is an important food-borne pathogen, which is present on the skin and mucosa of animals. Some of the S. aureus strains are causative agent of food poisoning syndrome. The aim of this study was to investigate the antimicrobial resistance of S. aureus isolates from raw meats in slaughterhouses during 2010. From 17,874 raw meat samples tested, a total of 190 S. aureus were isolated, for which antimicrobial susceptibility to 17 agents was examined using broth dilution method. Among isolates from beef, chicken and pork, 20 (51.3%), 20 (24.7%) and 9 (12.9%) were sensitive to all antimicrobials tested, respectively. Isolates from pork and chicken meats showed much higher resistance, compared to isolates from beef. Penicillin resistance was the most frequent among isolates from beef (35.3%) and pork (75.7%), while tetracycline resistance was among those from chicken meats (48.1%). A total of 3 methicillin resistant S. aureus (MRSA) were detected from beef (5.1%, 2/39) and pork (1.4%, 1/70). Although the prevalence of MRSA was low, the presence of antimicrobial resistant S. aureus such as MRSA suggests that further investigation and strict surveillance on MRSA and antimicrobial resistance are needed.

A total of 222 udder-half milk samples of lactating goats were collected from two herds in Korea during 2008 and all samples were subjected to bacteriological examination. Somatic cell counts (SCC) were also determined for all samples except for 13 (5.9%), which were collected from halves of udders with clinical mastitis. A total of 85 bacteria were isolated from 82 (36.9%) of 222 milk samples tested. Staphylococci were the predominant pathogens, accounting for almost 70% of the isolates: Coagulase negative staphylococci (CNS) and S. aureus constituted 55% (47/85) and 14.1% (12/85), respectively. Among 209 samples tested for SCC, bacteria were isolated from 36 of 115 (31.3%) samples with SCC of <1×106 cells/㎖ and 38 of 94 (40.4%) samples that had SCC of ≥1×106 cells/㎖, respectively. All S. aureus were detected from samples with SCC of ≥1×106 cells/㎖, while 25 of 47 (61.0%) CNS were isolated from milk samples with SCC of <1×106 cells/㎖. Mean SCC of milk samples that harbored S. aureus and CNS was 4,787×103 cells/㎖ and >1×106 cells/㎖, respectively. All S. aureus and CNS isolates were susceptible to all antimicrobials tested except for penicillin, to which 2 (16.6%) S. aureus and 12 (25.5%) CNS isolates showed resistance.

One hundred one enterococcal isolates from feces of livestock animals in Korea were screened for the presence of bacteriocins. Sixteen of 41 (39%) E. faecalis and 4 of 56 (7.1%) E. faecium isolates showed antimicrobial activity against at least one indicator strain. Only 4 of 20 the enterococcal isolates showing antimicrobial activity possessed at least one bacteriocin gene. While entA and entB were detected in three isolates as a pair of genotype, entQ, bac31, and AS-48 were not found in the enterococcal isolates. In almost all isolates, a correlation between genotype and phenotype of these determinants was not always observed.