Genetic characterization of methicillin-resistant Staphylococcus aureus from humans and animals within the community / 대한수의학회지

Methicillin-resistant Staphylococcus (S.) aureus (MRSA) is one of the most important nosocomial pathogens worldwide and the emergence of this strain has become a major clinical problem. In this study, we investigated the prevalence of MRSA and their genetic characteristics in 69 S. aureus isolated from humans and animals. In human isolates, higher antimicrobial resistance rates were observed against penicillin (80.6%), followed by erythromycin (11.9%) and tetracycline (9.0%). All of them were susceptible to clindamycin, enrofloxacin, novobiocin, pirlimycin, trimethoprim/sulfamethoxazole and vancomycin. The resistance patterns in animal isolates were similar to those of human isolates. Two (2.9%) MRSA strains were isolated from human (n = 1) and animal (n = 1), and these isolates were confirmed as carrying the mecA gene. One isolate originating from human was resistant to 7 drugs and the other isolate derived from animal was resistant to 11 drugs. Staphylococcal cassette chromosome mec (SCCmec) variant IIIB was identified in animal isolate but SCCmec type of an isolate from human was not exactly determined. Two MRSA isolates showed unrelated PFGE pattern between them. Our results indicated although the frequency of MRSA isolates from humans and animals was low, a continuous surveillance and monitoring should be called for to prevent the contamination and spread of MRSA in the community. To our knowledge, this is the first time that SCCmec type variant IIIB was detected from animals in Korea.

Antibiotic Resistance and Genotypic Characterization of Escherichia coli Isolated from Pig Farm Environment

The use of antibiotics, including therapeutically in human and veterinary medicine, or as prophylaxis of growth promotion in animal husbandry, ultimately exerts selective pressure favorable for the propagation of antibiotic resistant bacteria. In this study we have determined the resistance for antibiotics of E. coli from pig farm environment, and investigate genetic relatedness by random amplification of polymorphic DNA (RAPD). Six farms were randomly selected in Gyeongsanman-do and Busan provinces for collecting samples from feces, manure and underground water. A total of 88 isolates from feces, 74 isolates from manure and 1 isolate from underground water were analyzed by antibiotic resistance and RAPD. Antibiotic resistance testing was performed by disk diffusion method using 16 antibiotics. The highest percentage of antibiotic resistance of isolates from feces and manure was found to the following antibiotics; tetracycline (100% and 100%), sulfamethoxazole/trimethoprim (60.2% and 62.2%), streptomycin (50.0% and 68.9%), chloramphenicol (56.8% and 56.8%), ampicillin (50.0% and 81.1%) and cephalothin (50.0% and 51.4%). Of isolates from feces and manure, 22.7% and 20.3% showed multiple resistance to 4 and 5 antibiotics, respectively. The isolates from GE pig farm showed six RAPD patterns. A single pattern, RAPD-C, was predominat in feces isolates (50.0%) and manual isolates (46.7%), and the rest of feces isolates showed RADP-A, B and E pattern and manure isolates showed D and E pattern. One isolate from underground water showed F pattern. The appearance of multiresistant in E. coli isolates from pig farms environment is a problem of major concern of public health and RAPD may offer an useful tool of discrimination for the epidemiological investigation.

Alteration in gyrA and parC Gene Associated with Fluoroquinolone Resistance of Enterococcus spp. Isolated from Feces of Chicken

The purpose of this study was to investigate the fluoroquinolone resistance frequency of Enterococcus spp. from normal chicken feces and to analyse mutations of the gyrA and parC gene associated with fluoroquinolone resistance. Among 52 Enterococcus faecalis and 25 E. faecium isolates, 23 (44.2%) E. faecalis and 7 (28.0%) E. faecium were resistant to ciprofloxacin (CIP) by disc diffusion method. Genetic exchange in gyrA and parC gene among 2 CIP intermediate isolates and 15 CIP resistant isolates were found in the amino acid codon of Ser-83 and Asp-87, and Ser-80 and Glu-84, respectively. These mutants contained a change from Ser to Phe, Val, Tyr, Ile, Thr or Pro at codon 83 and from Glu to Gly or Leu at codon 87 in gyrA gene, and a change from Ser to Ile or Thr at codon 80 and from Glu to Asp or Lys at codon 84 in parC gene. The isolates with mutation in gyrA regardless of a mutation in parC showed high resistance (MIC > or =32 microgram/ml) to CIP, enrofloxacin, norfloxacin and ofloxacin. These results suggested that gyrA gene is the primary target for 4 fluoroquinolones resistance in Enterococcus spp.

Phage Typing of Staphylococcus intermedius Isolated from Canine Clinical Specimens

Bacteriophages were induced from staphylococcus intermedius isolates from dogs and used for a phage typing. Mitomycin C induction was performed on 60 strains of S. intermedius and all phages were reacted with the strains. Twenty-eight strains (46.7%) were found to be lysogenic. Based on host ranges, eight phages were selected. By using the eight phages, 129 strains isolated from canine clinical specimens were subjected to the phage typing at the routine test dilution (RTD) and 100xRTD. Typability of the phage set was 78.3%, yielding 40 phage patterns. The phage set was considered useful for differentiating S. intermedius strains isolated from dogs. None of 50 strains of S. aureus, 2 (3.6%) of 56 S. simulance strains, 13 (24.5%) of 53 S. chromogenes strains and 46 (28.1%) of 164 S. hyicus strains were typable by the phages at 100xRTD.

Biochemical Characteristics and Antimicrobials Susceptibility of Salmonella gallinarum Isolated in Korea

Fowl typhoid (FT) reported since 1992 in Korea is a septicemic disease of domestic birds caused by Salmonella gallinarum (S. gallinarum). The purpose of this study was to investigate the biochemical characteristics and antimicrobials susceptibility of field isolates of S. gallinarum isolated by year in Korea. A total of 258 isolates of S. gallinarum from 1995 to 2001 showed the same pattern in the majority of biochemical test such as IMViC (indole, methyl red, Voges-Proskauer and citrate utilization), carbohydrate fermentation and amino acid decarboxylation, and these results were almost in accordance with the traditional biochemical characteristics of S. gallinarum strain. When the antimicrobial susceptibility test against 258 isolates of S. gallinarum was performed by the disk diffusion method using 12 antimicrobial agents, all isolates from 1995 appeared to be susceptible to all of the antimicrobial agents tested except for tetracycline and oxytetracycline, whereas the vast majority of isolates from 2001 showed the reduced susceptibility to ampicillin (13.0%), gentamicin (43.4%), kanamycin (69.6%), enrofloxacin (6.5%), ciprofloxacin (10.9%), norfloxacin (52.5%) and ofloxacin (82. 6%). The prevalence of the prevalence of completely resisyany isolates resistant isolates to one or more drugs rapidly increased from 0% in 1995 to 93.5% in 2001. The minimal concentrations range of the majority of antimicrobial agents to inhibit 50% (MIC50s) against S. gallinarum isolates increased from 0.06 -- 8 microgram/ml in 1997 to 2 -- 256 microgram/ml in 2001. Especially, MIC50s for gentamicin and fluoroquinolones of isolates from 2001 increased over 10-fold than those of isolates from 1997. Therefore, our results indicate that sorbitol fermentation and arginine decarboxylation showed the diversity by isolates and the vast majority of isolates from 2001 showed the reduced susceptibility to antimicrobials tested.