Studies On Detecting And Multiple Antibiotics Resistance Of Methicillin-resistant Staphylococcus Aureus

Objective To evaluate clinical application values of four methods that cefoxitin disk diffusion,oxacillin disk diffusion appending 2%salt in MHA,oxacillin-salt agar and penicillin binding protein 2a(PBP2a) latex agglutination test for detecting Methicillin-resistant Staphylococcus aureus(MRSA) in order to offer simple and accurate detecting MRSA methods in clinical microbiology laboratory;To study the situation of MRSA resistant to multiple antimicrobial agents in the local area in order to provide evidence for exploring resistant mechanism of MRSA and choosing antimicrobial agents to therapy MRSA in clinic.Methods Accroding to the Clinical and Laboratory Standards Institute 2006 standard, 100 strains Staphylococcus aureus(SA) provided by the surveillance center for bacterial resistance of Anhui Province in 2005 collected frow each surveillance units were tested by cefoxitin disk diffusion,oxacillin disk diffusion appending 2%salt in MHA,oxacillin-salt agar and PBP2a latex agglutination respectively with the polymerase chain reaction(PCR) as the gold standard method for detecting MRSA;51 stains MRSA were determinedβ-lactamase with penicillinase acid determining method,erythromycin(ERY) disk,clindamycin(DA) disk,Erythromycin inducible clindamycin resistance(D-test),4 kind fluoroquinolones(FQs) antimicrobial agents disks(Ofloxacin,Norfloxacin,Levofloxacin,Gatifloxacin) and Vancomycin(VAN) disk. Results The sensitivities and specificities of cefoxitin disk diffusion,oxacillin disk diffusion appending 2%salt in MHA,oxacillin-salt agar and PBP2a latex agglutination test for detecting MRSA were 96.3%(26/27) and 100.0%(73/73),77.8%(21/27) and 100.0%(73/73),92.6%(25/27) and 94.5%(69/73),100.0%(27/27) and 100.0%(73/73),respectively;2 strains MRSA grown on the oxacillin-salt agar in 48 hours but not grown in 24 hours.The sensitivity of oxacillin-salt agar was 100.0%(27/27) in 48 hours,but specificity decreased to 89.0%(65/73);There was significant difference between oxacillin disk diffusion appending 2%salt in MHA and PCR for detecting MRSA(P＜0.05)while there were no significant difference between cefoxitin disk diffusion,oxacillin-salt agar,PBP2a latex agglutination test(P＞0.05) and PCR for detecting MRSA;MRSA isolated rate in SA strains collected frow the surveillance center for bacterial resistance of Anhui Province in 2005 was 27.0%(27/100);The range of inhibition zone diameters of cefoxitin disk in 51 stains MRSA was 6-20mm.β-lactamase production rate was 84.3%(43/51).The resistance rate to ERY,DA,FQs,VAN were 98.0%(50/51),86.3%(44/51),88.2%(45/51),0.0% (0/51),respectively.3 strains MRSA demonstrated erythromycin inducible clindamycin resistance.Inducible resistance rate was 50.0%(3/6).Conclusions The study suggested that cefoxitin disk diffusion,oxacillin disk diffusion appending 2%salt in MHA,oxacillin-salt agar and PBP2a latex agglutination can detect MRSA reliably. PBP2a latex agglutination can confirm MRSA insteading of PCR.Both the cefoxitin disk diffusion and oxacillin-salt agar have high application value for detecting MRSA in clinical microbiology laboratory.Two methods can combine to detect MRSA accurately; MRSA were resistant to multiple antibiotics.Erythromycin inducible clindamycin resistance rate was high in MRSA strains.D-test should be used to determine for MRSA in routine.There was a negative correlation between resistance level of MRSA and inhibition zone diameter of cefoxitin disk.Vancomycin associated with fluoroquinolones antibiotics could been adopted in low level MRSA infections according to antimicrobial susceptibility testing results.