title: Trends of beta-lactam antibiotic susceptibility in blood-borne methicillin-resistant Staphylococcus aureus (MRSA) and their linkage to the staphylococcal cassette chromosome mec (SCCmec) type.
abstract: We investigated trends of beta-lactam antibiotic susceptibility in a total of 218 strains of blood-borne methicillin-resistant Staphylococcus aureus (MRSA) isolated from 1978 through 2002 at a middle-size geriatric hospital in Tokyo; the strains were classified by the MRSA marker, staphylococcal cassette chromosome mec (SCCmec). The minimum growth inhibitory concentration (MIC) of cloxacillin at which 50% of the strains were inhibited (MIC50) was 2 microg/ml in the strains isolated in 1978-1984 and 32 to 64 microg/ml in the strains isolated subsequently. Similarly, the MIC50 values of cefazolin and imipenem in the 1978-1984 isolates were 16 and <or=0.25 microg/ml, respectively, and those in the strains isolated subsequently were 128 and 16 to 32 microg/ml, respectively. These results indicated that the MRSA strains isolated after 1985 had gained high-level resistance to beta-lactam antibiotics. The type of SCCmec was investigated by polymerase chain reaction (PCR). We observed an elevated frequency of type II SCCmec, from about 15% in the strains isolated in 1978-1984 to about 50% in the 1985-1989 isolates, and the frequency reached and remained at about 90% subsequently. These results imply that the high-level beta-lactam antibiotic resistance of the MRSA strains isolated after 1985 is most likely due to the increased integration of type II SCCmec.
authors.affiliation: Laboratory of Infectious Diseases, Graduate School of Infection Control Sciences, Kitasato University, 5-9-1 Shirokane, Tokyo 108-8642, Japan. p98224@st.pharm.kitasato-u.ac.jp
authors.forename: Kazunari
authors.initials: K
authors.lastname: Barada
authors.forename: Hideaki
authors.initials: H
authors.lastname: Hanaki
authors.forename: Yoshio
authors.initials: Y
authors.lastname: Yamaguchi
authors.forename: Shinsuke
authors.initials: S
authors.lastname: Ikeda
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Akama
authors.forename: Taiji
authors.initials: T
authors.lastname: Nakae
authors.forename: Takashi
authors.initials: T
authors.lastname: Inamatsu
authors.forename: Keisuke
authors.initials: K
authors.lastname: Sunakawa
mesh_terms: D016470:Bacteremia / Q000382:microbiology*; D002876:Chromosomes, Bacterial / Q000235:genetics; D024901:Drug Resistance, Multiple, Bacterial / Q000235:genetics*; D006801:Humans; D007564:Japan / Q000453:epidemiology; D016106:Methicillin Resistance / Q000235:genetics*; D012189:Retrospective Studies; D013203:Staphylococcal Infections / Q000453:epidemiology / Q000235:genetics*; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000235:genetics*