Characterization of oxacillin-susceptible mecA-positive Staphylococcus aureus: a new type of MRSA.
Methicillin-resistant Staphylococcus aureus (MRSA) has been defined as S. aureus having the mecA gene or showing a minimum inhibitory concentration (MIC) of oxacillin higher than 4 mg/l. However, some clinical isolates are mecA-positive and oxacillin-susceptible. Therefore, we surveyed the occurrence of S. aureus having the mecA gene and an MIC of oxacillin of less than 2 mg/l (oxacillin-susceptible MRSA; OS-MRSA) in a total of 480 strains of S. aureus collected from 11 hospitals in different location in Japan isolated from 2003 through 2005. We found 6 strains matching the criteria for OS-MRSA. All 6 strains were staphylococcal cassette chromosome (SCC) mec-positive, without exception, and 4 strains showed the SCCmec type III-variant, which is unique in Japan. These OS-MRSAs were least resistant to oxacillin among the MRSAs tested and they were within the susceptible range to seven other beta-lactam antibiotics tested. Thus, OS-MRSA may become a high-resistant MRSA upon the treatment of patients with beta-lactam antibiotics. To characterize whether these OS-MRSAs were hospital-acquired or community-acquired MRSAs, we tested for the presence of the genes encoding toxins. Genes encoding hemolysin, exfoliative toxin, enterotoxin, toxic shock syndrome toxin-1, and Panton-Valentine leukocidin were found in 6, 4, 0, 0, and 0 strains, respectively. These results revealed that OS-MRSAs could be classified as a new type of MRSA that exhibits properties distinguishable from either hospital- or community-acquired MRSA. Coagulase typing of the OS-MRSAs supported the above conclusion. In this study, the occurrence of OS-MRSA at a certain frequency was noted; precautions are called for in the classification of oxacillin-resistant S. aureus and in the treatment of OS-MRSA infection.
Hososaka
Yasuko
Y
Kitasato Research Center for Anti-infection Drugs, 5-9-1 Shirokane, Minato-ku, Tokyo 108-8642, Japan. fyasuko-tky@umin.ac.jp
Hanaki
Hideaki
H
Endo
Harumi
H
Suzuki
Yumiko
Y
Nagasawa
Zenzo
Z
Otsuka
Yoshihito
Y
Nakae
Taiji
T
Sunakawa
Keisuke
K
D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001427:Bacterial Toxins / Q000235:genetics; D017714:Community-Acquired Infections / Q000235:genetics / Q000382:microbiology; D003428:Cross Infection / Q000235:genetics / Q000382:microbiology; D006801:Humans; D007564:Japan; D016106:Methicillin Resistance / Q000187:drug effects / Q000235:genetics*; D008826:Microbial Sensitivity Tests; D010068:Oxacillin / Q000494:pharmacology*; D013211:Staphylococcus aureus / Q000145:classification / Q000187:drug effects* / Q000235:genetics* / Q000302:isolation & purification; D001618:beta-Lactamases / Q000378:metabolism
D000900:Anti-Bacterial Agents; D001427:Bacterial Toxins; D001618:beta-Lactamases; D010068:Oxacillin