Lacticin NK34 is a small nisin-like bacteriocin present in the supernatants of an isolate of Lactococcus lactis from jeotgal, a salted and fermented Korean food made with seafood such as shrimp, oysters, and fish. Recently, we demonstrated that a partially purified NK34 is highly effective against various Staphylococcus species in a murine infection model. In this study, the two major bacterial pathogens associated with bovine mastitis, Streptococcus aureus and S. agalactiae, were evaluated for their susceptibility to NK34 in vitro using a standard teat-dip assay as well as in vivo using mastitic cows infected with one of these pathogenic strains. The experimental analyses showed a significant decrease (up to 98 times) in the bacterial numbers between the NK34-treated and -untreated teats. Moreover, a dramatic reduction in somatic cell counts was observed at 3 days post-treatment with 10 ml of NK34 administered directly into the mastitic cows. Neither S. aureus nor S. agalactiae were recovered. Taken together, these results imply that lacticin NK34 is an alternative antimicrobial substitute for the treatment of bovine mastitis, caused especially by either S. aureus or S. agalactiae.

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.

This paper describes the epidemiological characteristics of bovine tuberculosis in Korea during January 2000 to September 2004, when the incidence of bovine tuberculosis increased markedly: a total of 1,054 herds (4,197 cattle) were confirmed to be infected with Mycobacterium bovis during this period. Based on the record of epidemiological investigation, introduction of purchased cattle (22.9%, 125/545) into a farm was the most frequent transmission route of M. bovis infection. On 31.7% (335/1,054) of the infected farms, recurrent infection occurred more than once before the disease has been eradicated completely. The highest rate of recurrence was detected around 70 days after the initial test of the infected herd, which seems to be related to current regulation on the test of animals that cohabited with those previously diagnosed with infection in farms, rather than to the characteristic of the disease. Although the current eradication program has been effective in controlling the disease in dairy cattle in Korea, control measures more specific to beef cattle may be needed because infection rate in beef cattle continues to increase in recent years.

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.

To control mastitis in dairy cattle, National Mastitis Control Program (NMCP) has been conducted in Korea since early 2000s. Nevertheless, mastitis still remains one of the most important disease in dairy cattle in Korea as other countries worldwide. Under the NMCP, a total of 343,090 lactating cows nationwide were tested for mastitis during 2004～June 2010 based on California Mastitis Test (CMT), and 7.8% (26,782/343,090) and 13.8% (47,335/343,090) of the cows tested were infected with clinical and subclinical mastitis, respectively. Relative frequency of 2,058 bacteria isolated from bovine milk samples with somatic cell count of ≥200,000 cells/㎖ during 2006～2010 were analyzed. The most frequently isolated bacteria were Staphylococcus spp. including Staphylococcus aureus, accounting for over 50% of the total number of isolates. The highest frequency was observed for coagulase-negative staphylococci (CNS), followed by Gram negative bacteria (GNB), S. aureus, Streptococcus spp., and Enterococcus spp. Based on the results of recent studies in Korea, the majority of pathogens isolated from subclinical mastitis in dairy cattle in Korea are environmental minor pathogens. Therefore, more attention should be paid to control of environmental pathogens such as CNS, GNB, and Streptococcus uberis in dairy farms in Korea.

For the screening of Brucella antibodies in pig, 2,140 pig serum samples were collected from six slaughter house in Korea between 2006 and 2007. The Rose Bengal test (RBT) and serum agglutination test (SAT) were used for initial screening for specific antibodies to Brucella, and competitive enzyme-linked immunosorbent assay (C-ELISA) was used for confirmation of presence of serum antibody for Brucella. Overall, 575 (26.9%) samples resulted in seropositive in RBT. In SAT, 50 (2.3%) and 10 (0.5%) samples showed suspicious positive and positive reaction, respectively, however, all sera tested in this study showed a negative reaction in C-ELISA. SAT and C-ELISA might be applicable as a tool for screening of swine brucellosis.

Lysine is the first essential amino acid for optimal nutrient quality in rice grain. For the narrow genetic diversities of lysine contents in rice, somaclonal variation was the source of mutation in our breeding program. Biochemical selection was conducted using 1 mM S-(2-aminoethyl) cysteine followed by two passages of 5 mM lysine plus threonine in the callus subculture medium. The lysine contents in endosperm of all progenies recovered from the biochemical selection were higher than those of their donor cultivar 'Hwayeongbyeo'. These elevated lysine levels of mutants were successfully transmitted to M4 generation. The lysine contents in endosperm varied 3.85 to 4.80% compare to their donor cultivar 'Hwayeongbyeo' was 3.85%. Three of high-lysine germplasms, Lys-l, Lys-2 and Lys-7 were selected by biochemical selection and rapid screening methods. DNA analysis showed that a new insertion of Tos 17 which mapped to rice chromosome 11 on the high-lysine mutant, Lys-2.