Study On The Antibacterial Agents Resistance And Homology Of Staphylococcus Haemolyticus

Coagulase-negative staphylococci (CNS) have long been regarded as apathogenic, commensals in the human skin and mucous membrane. The increasing use of invasive technologies and foreign materials has brought that the incidence of infection caused by CNS has increased gradually in recent years. CNS account for one-fourth of nosocomial blood stream infections. Staphylococcus haemolyticus is known to be frequently isolated from patients. At the same time, the isolating rate of methicillin-resistant Staphylococcus haemolyticus (MRSH) is over 80% and higher than that of other CNS. Only glycopeptide antibiotics is considered as one drug valid for treating such infections caused by MRSH till now. The expanded use of these antibiotics has resulted in emergence of Staphylococcus haemolyticus resistant to glycopeptide antibiotics. So it is necessary to surveil the use of glycopeptide antibiotics. If the epidemic of multiresistant Staphylococcus haemolyticus can not be controlled, the mortality rate will range from 18.8%-57%. It is very important to discover the epidemic of MRSH in earlier period.In this study, 133 strains of Staphylococcus haemolyticus were collected fromclinical specimens of our hospital from Apr. 2002 to Apr. 2003, including 39 strains isolated from outpatients and 94 strains isolated from inpatients. Minimal inhibitory concentrations (MICs) of 16 antimicrobial agents against 133 strains of Staphylococcus haemolyticus were determined by the broth microdilution method. MecA genes of these strains were detected by polymerase chain reaction (PCR). Compared with the results of the susceptibility test, these discrepant strains were analyzed by inhibition and induction tests. Pulsed-field gel electrophoresis (PFGE) was used to type the chromosome DNA of 90 strains of MRSH.The results showed that there were no isolates resistant to linezolid, vancomycin, norvancomycin and only 6.0% of strains resistant to teicoplanin. The resistant rates to amikacin, isepamicin, minocycline, rifapin, flomoxef were lower than 20%, while the ones to penicillin G and oxacillin were higher than 90%. The resistant rates against the antibacterial agents except minocycline of the strains isolated from inpatients were higher than that from outpatients. The positive rate of mecA genes in all strains was 90.23%. The PCR product confirmed by cloning and sequencing was specific product of the mecA gene. MICs of oxacillin against two isolates, which mecA genes were positive and MICs of oxacillin were lower than 0.25g/ml, were higher than 0.5g/ml after inducing test. MICs of oxacillin against three strains, which mecA genes were negative and MICs of oxacillin were higer than 0.5g/ml, decreased more than 8 times after inhibition test. 25 different PFGE patterns (A~Y) were found among 90 MRSH strains, most of MRSH were PFGE type A (36 strains). Type Al was epidemic from Apr. 2002 to Aug. 2002 and Dec. 2002 toMar. 2003. Type A3 was epidemic from Oct. 2002 to Mar. 2003 and in Aug. 2002. The epidemic strains were spread over wards and different patients. 6 of 12 strains isolated from blood were from patiens with bacteriemia. The 6 strains belonged to type A by PFGE.The above results have shown:1. It was noted that staphylococcus haemolyticus was resistant to majority of the antibacterial agents and the susceptibility to the glycopeptide antibiotics also declined.2. It is more reliable to judge whether it is MRSH according to the detection of mecA gene.3. It is more probable that the strains with the similar homology cause bacteriemia.4. MRSH has become an important pathogen of nosocomial infection. MRSH caused several epidemics outbreak in our hospital and infection by multiple pathways. It is meaningful to strengthen the sterilization and insulation for controlling the epidemic of MRSH.