21st European Congress of Clinical Microbiology and Infectious Diseases

Antibiotic resistance profiles and molecular epidemiological characteristics of Staphylococcus aureus isolates in Changsha, south China

Abstract number: R2376

Zou M., Zhou R., Fan X., Hu F., Liu W., Wu W., Li X.

Objectives: Increasing prevalence of Staphylococcus aureus, particularly methicillin-resistant S. aureus (MRSA) has been reported in China. The aim of the present study is to investigate the drug resistance characteristic, the genetic background and the molecular epidemiological characteristic of S. aureus in Changsha, south China.

Methods: Between December 2006 and December 2008, a total of 293 clinical isolates of S. aureus were collected from 11 representative hospitals in Changsha and then identified by Vitek-2 system. All the isolates were verified as S. aureus and MRSA by PCR amplification of femA and mecA gene respectively. K-B disk method was used to test drug sensitivity of S. aureus to 23 commonly used antibiotics. Chromogenic cephalosporin spot test was applied to detect b-lactamase. Pulsed-field gel electrophoresis (PFGE) was performed for genotypic and homologous analysis of 115 isolates randomly selected from the original 293 clinical S. aureus isolates.

Results: Among the 293 strains, 273 (93.2%) were b-lactamase test positive. Resistant rates to penicillin and ampicillin were the highest (both 96.6%). All the isolates were susceptible to tecoplanin, vancomycin and linezolid. All the stains exhibited 93 antimicrobial-resistant profiles to the 23 antibiotics tested. The PX1 type included 47 (16.0%) strains and the PX2 type included 35 (11.9%) strains, which accounted 28.0% (82/293) of all, were the primary epidemic antimicrobial-resistant profiles. 190 (64.8%) were MRSA and 103 (35.2%) were MSSA. The resistant rates of MRSA to 18 antibiotics were higher than MSSA (P < 0.05). The MIC range of OXA and FOX was 0.125 mg/ml–>256 mg/ml and 2 mg/ml–>256 mg/ml respectively. Both of their MIC₅₀ and MIC₉₀ were 256 mg/ml. Of all the 115 clinical S. aureus isolates, 39 PFGE types were demonstrated. PFGE type A with the incidence of 48.7% (56/115), from 8 hospitals (8/11), was the predominant genotype. 55 (55/56) strains with PFGE type A were MRSA. The next was PFGE type L with the incidence of 4.3% (5/115). PFGE type A included 13 subtypes from A1 to A13, and the subtype A1 is the predominant type and epidemic clone with the incidence of 22.6% (26/115).

Conclusion:S. aureus in Changsha is multiple resistant to commonly used antimicrobial agents and has a high resistant rate to methicillin. PFGE type A outbreak at clinical isolates of S. aureus occurred in Changsha and A1 subtype is the predominant epidemic clone.