Characteristics of Aerococcus viridans isolated from porcine fetuses in Korean farms.

Swine abortion caused by viruses as well as bacteria has caused many economic losses in domestic farms over the years; however, bacterial abortion has not yet been studied in Korea. Several bacterial species were isolated from aborted fetuses (n = 103) for which the cause of death was not viral abortion. Among them, we focused on Aerococcus viridans, which had the highest positive rate within three provinces (Gangwon, Jeonnam and Gyeongnam). A total of 16 isolates were identified as A. viridans by matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS), and 13 were characterized by both antibiotic resistance and 16S rRNA gene analysis. Based on antibiotic susceptibility testing result, eight antimicrobials could not effectively eliminate the present isolation (more than 40% of isolates can resist these antibiotics), while all except two strains were susceptible to trimethoprim/sulfamethoxazole. Molecular analysis indicated genetic variation among these strains. This study is the first report detecting A. viridans from aborted fetuses in Korean domestic farms.

In vitro activities of antimicrobials against six important species of gram-negative bacteria isolated from raw milk samples in Korea.

Gram-negative bacteria (GNB) with multidrug resistance pose a serious threat to public health. They are environmental pathogens frequently isolated from raw milk and mastitis in dairy cattle. This study was to examine the in vitro antimicrobial activities against 225 isolates belonging to six important species of GNB from mastitic raw milk samples of dairy herds in the Republic of Korea: Acinetobacter baumannii (n = 17), Citrobacter freundii (n = 19), Enterobacter cloacae (n = 54), Klebsiella pneumoniae (n = 55), Pseudomonas aeruginosa (n = 45), and Serratia marcescens (n = 35). In general, amikacin, gentamicin, and piperacillin exhibited strong antimicrobial activities against all bacterial species tested, whereas rifampin, cephalothin, cefazolin, and ampicillin were ineffective against most of the bacterial species tested. Wide differences were observed in the patterns of resistance among the bacterial species; in particular, resistance to kanamycin, streptomycin, tetracycline, and chloramphenicol was highly variable among the strains belonging to different bacterial species. Almost half of the GNB isolates (45.3%, 102/225) were resistant to 5 or more of 12 antimicrobial agents tested: P. aeruginosa (86.6%, 39/45) showed the highest resistance rate, followed by S. marcescens (65.7%, 23/35). This study indicates that multiple antimicrobial resistances are prevalent among GNB isolates from mastitic milk samples of dairy cattle in the Republic of Korea.

Antimicrobial resistance of streptococci isolated from mastitic bovine milk samples in Korea.

The aim of this study was to determine the antimicrobial resistance of streptococci isolated from mastitic bovine milk samples. A total of 178 isolates belonging to 6 different Streptococcus species were examined: S. uberis (n = 99), S. bovis (n = 30), S. oralis (n = 24), S. salivarius (n = 13), S. intermedius (n = 7), and S. agalactiae (n = 5). Only 8.9% (16/178) of the isolates were susceptible to all antimicrobial agents tested in this study, and S. agalactiae and S. intermedius isolates were all resistant to at least 1 antimicrobial agent tested. Overall, the most frequently observed resistance was to tetracycline (61.2%), followed by lincomycin (43.2%), gentamycin (35.3%), oxacillin (34.3%), and erythromycin (28.6%). Cephalothin and penicillin were the only antimicrobial agents to which most of the streptococci (>or=92%) were susceptible. Wide differences in the prevalence of resistance are apparent among the individual species: S. salivarius displayed exceptionally high resistance to cephalothin (23.0%) and oxacillin (76.9%) and S. agalactiae (20%) and S. intermedius (14.2%) to penicillin. Streptococcus salivarius and S. agalactiae were all susceptible to erythromycin, but others showed various rates of resistance ranging from 12.5% to 42.8%. Resistance to 3 or more of 7 antimicrobial agents was observed in all species (37.6%, 67/178).