Emergence of SCCmec type IV as the most common type of methicillin-resistant Staphylococcus aureus in a university hospital.
BACKGROUND
The epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) has dramatically changed over the last decade by the emergence of community-associated MRSA (CA-MRSA). Recent studies indicate that these strains have already spread to hospitals. To evaluate if SCCmec type IV and Panton-Valentine leukocidin (PVL) are unambiguous markers of CA-MRSA, we analyzed 77 sporadic MRSA strains isolated, in our low MRSA incidence university hospital, from inpatients between 2000 and 2004.


METHODS
MRSA strains were analyzed by staphylococcal cassette chromosome mmecec (SCCmec) typing, PCR for PVL genes and pulsed-field gel electrophoresis (PFGE). MRSA was classified in HA-MRSA or CA-MRSA according to Centers for Disease Control and Prevention (CDC) criteria. Antimicrobial susceptibility testing was performed using microbroth dilution method following CLSI recommendations.


RESULTS
Among 77 sporadic single-patient strains, SCCmec types I-IV and four subtypes were identified. Type IV/IVA was most common (42.9%).The distribution of SCCmec types changed over the years. Type IV/IVA strains increased from 33.3% in 2000 to 57.9% in 2004. Type IV strains were resistant to ciprofloxacin in 81.8%, and in 9.1% to tobramycin while type IVA strains were 100% resistant to both antimicrobials. In contrast, non-type IV/IVA strains were resistant to ciprofloxacin in 86.4%, and in 75.0% to tobramycin. Only one strain was PVL positive and harbored SCCmec type III variant. By PFGE analysis, the 33 SCCmec type IV/IVA strains comprised 12 distinct genotypes. 36.4% of 11 CA-MRSA and 43.9% of 66 HA-MRSA harbored SCCmec type IV/IVA.


CONCLUSIONS
Type IV/IVA has become the most common SCCmec type in inpatients of our university hospital. The SCCmec type IV/IVA is present in both CA-MRSA and HA-MRSA limiting its use as a marker for CA-MRSA.
Strandén
A M
AM
Infection Control and Hospital Epidemiology, University Hospital Basel, Basel, Switzerland.
Frei
R
R
Adler
H
H
Flückiger
U
U
Widmer
A F
AF
D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001426:Bacterial Proteins / Q000235:genetics; D001427:Bacterial Toxins / Q000235:genetics; D016000:Cluster Analysis; D017714:Community-Acquired Infections / Q000382:microbiology*; D016172:DNA Fingerprinting; D004269:DNA, Bacterial / Q000235:genetics*; D024881:Drug Resistance, Bacterial; D016521:Electrophoresis, Gel, Pulsed-Field; D005098:Exotoxins / Q000235:genetics; D005838:Genotype; D006785:Hospitals, University; D006801:Humans; D007297:Inpatients; D007956:Leukocidins / Q000235:genetics; D055624:Methicillin-Resistant Staphylococcus aureus / Q000145:classification* / Q000235:genetics / Q000302:isolation & purification*; D008826:Microbial Sensitivity Tests; D013203:Staphylococcal Infections / Q000382:microbiology*; D037521:Virulence Factors / Q000235:genetics
D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D001427:Bacterial Toxins; D004269:DNA, Bacterial; D005098:Exotoxins; D007956:Leukocidins; C078284:Panton-Valentine leukocidin; D037521:Virulence Factors