Molecular epidemiological characterization of Staphylococcus aureus isolates originating from food poisoning outbreaks that occurred in Tokyo, Japan.

Staphylococcal food poisoning (SFP), one of the commonest food-borne diseases, results from the ingestion of one or more staphylococcal enterotoxins (SEs) produced in foods by Staphylococcus aureus. In the present study, 203 S. aureus strains originating from 83 outbreaks that had occurred in Tokyo were examined for their coagulase type and genotype of SEs to analyze their molecular epidemiological characteristics. The representative subsets of the 83 S. aureus isolates were analyzed by multilocus sequence typing (MLST) and S. aureus pathogenicity island (SaPI) scanning. The isolates were integrated into eight specific clonal complexes (CC) s; CC81, CC8, CC6, CC5, CC508, CC59, CC20 and CC30. The profiles of the coagulase type, SE/SEl genotype and the suspected type of enterotoxin-encoding mobile genetic element (MGE) indicated a correlation with each CC. SaPI scanning showed fixed regularity between the distributions of genomic islands, including SaPIs, and the phylogenetic lineage based on MLST. These results indicate that the S. aureus isolates, which classified into eight CCs, have distinguishable properties concerning specific coagulase type, enterotoxin genotype and MGE type. Strains of S. aureus harboring these particular elements possess the potential to cause SFP.

Pattern of Methicillin-resistant Staphylococcus aureus in Dental and Medical Environments

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the most prevalent pathogens in hospitals. To investigate cross contamination by this bacterium in both dental and medical settings, the pathogens that cause acute pyogenic infection and one of the major microbes responsible for nosocomial infection were isolated from health care providers, nurses and patients. We used VITEK II to measure drug sensitivity, and we further performed biochemical testing, coagulase serotype testing and pulse-field gel electrophoresis (PFGE) for isolated MRSA colonies. The isolation rate of Staphylococcus aureus from nasal swabs was 75.0% from dental health care providers and 18.8% from the medical health care providers. A total of 10 MRSA strains were isolated from 40 health care providers and 2 patients and the prevalent coagulase serotype from patients and health care providers was VII. The antimicrobial drug resistance and partial PFGE types of the isolated MRSA strains showed a similar pattern. These results suggest that MRSA may be one of the principal causes of nosocomial infection in dental and medical hospitals.

Genotype, Coagulase Type and Antimicrobial Susceptibility of Methicillin-Resistant Staphylococcus aureus Isolated from Dermatology Patients and Healthy Individuals in Korea

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the most prevalent dermatology pathogens in hospitals and increasingly recognized in communities. We determined PFGE pattern of SmaI-restricted genomic DNA, coagulase type, and antimicrobial susceptibility of MRSA isolated in 2008 from dermatology inpatients and healthy hospital employees in A Hospital and from primary school children in Iksan city, Korea. Overall, the isolation rate of MRSA was 3.8% from the 788 normal persons: 4.9% from hospital employees and 1.1% from primary school children. MRSA was isolated in six of 13 (46.2%) family members of four school children with MRSA. The most prevalent coagulase serotype was II from patients and V from healthy individuals. Ten of twenty and six of twenty MRSA isolates from patients and from healthy personnel, respectively, had identical PFGE patterns, suggesting that these are originated from identical clones. Against MRSA from patients, only vancomycin was the most active (MIC range or =90% to amikacin, clindamycin, ciprofloxacin, erythromycin, fusidic acid, gentamicin and tetracycline. In conclusion, the MRSA carriage rates of healthy hospital workers were relatively high, 2.3~7.7%, depending on groups. Family members of a few primary school children with MRSA showed a high carriage rate, suggesting that intrafamily transmission occurred. MRSAs isolated from dermatology inpatients were relatively more resistant to various antimicrobial agents, including mupirocin, but all isolates were susceptibility to vancomycin.

Why do antimicrobial agents become ineffectual?

Antibiotic resistance has evolved over the past 50 years from a merely microbiological curiosity to a serious medical problem in hospitals all over the world. Resistance has been reported in almost all species of gram-positive and -negative bacteria to various classes of antibiotics including recently developed ones. Bacteria acquire resistance by reducing permeability and intracellular accumulation, by alteration of targets of antibiotic action, and by enzymatic modification of antibiotics. Inappropriate use of an antibiotic selects resistant strains much more frequently. Once resistant bacteria has emerged, the resistance can be transferred to other bacteria by various mechanisms, resulting in multiresistant strains. MRSA is one of the typical multiresistant nosocomial pathogens. A study of the PFGE pattern of endonuclease-digested chromosomal DNA showed that MRSA of a few clones were disseminated among newborns in the NICU of a Japanese hospital. In this regard, it is important to choose appropriate antibiotics and then after some time, to change to other classes to reduce the selection of resistant strains. Since the development of epoch-making new antibiotics is not expected in the near future, it has become very important to use existing antibiotics prudently based on mechanisms of antibiotic action and bacterial resistance. Control of nosocomial infection is also very important to reduce further spread of resistant bacteria.