Liu Zhen-Zhen, Xiong Ya-Li, Fan Xin-Jian, Gao Yan-Yu, Yu Ru-Jia
Center of Infectious Diseases, West China Hospital, Sichuan University, Chengdu 610041, China.
Sichuan Da Xue Xue Bao Yi Xue Ban. 2011 Sep;42(5):661-5.
To investigate the correlation between the phenotype and expression level of femB of Staphylococcus aureus (MRSA), to discuss the mechanism of different phenotypes in methicillin-resistant Staphylococcus aureus.
The minimal inhibitory concentrations (MICs) of oxacillin against 71 clinical isolates of Staphylococcus aureus were determined by agar dilution method according to NCCLS. The production of beta-lactamase was identified by Cefinase paper strip method. The isolation rate of beta-lactamase-producing strains was counted and the correlation between the resistance phenotype and isolation rate of beta-lactamase was analysed by statistics. Real time fluorescent quantitative PCR was used to quantify the mRNA expression of femB of non-beta-lactamase-producing strains.
The resistance rate of 71 Staphylococcus aureus to oxacillin was 66.20% (47/71), the isolation rate of beta-lactamase-producing MSSA strains was 58.3%,and that of strains of high- and low-level resistance to oxacillin were 63.15% and 55.56%. The standard curve was performed by series dilution of the heterogeneous resistant strain BB270, and the amount of femB-specific mRNA in strain BB270 was set to be 1. The calculated femB amounts in MSSA strains were from 0.4830-3.3636, while the amounts were from 0.4204-3.3636 in low-level MRSA strains, and 0.0718-16.0000 in high-level MRSA strains. There were no difference in the level of femB among MSSA, high-level MRSA and low-level MRSA.
The expression level of femB may not be related to the resistance of non-beta-lactamase-producting Staphylococcus aureus to methicillin.
研究金黄色葡萄球菌（MRSA）femB的表型与表达水平之间的相关性，探讨耐甲氧西林金黄色葡萄球菌不同表型的机制。
采用琼脂稀释法，依据NCCLS测定71株临床分离金黄色葡萄球菌对苯唑西林的最低抑菌浓度（MIC）。采用头孢硝噻吩纸片法鉴定β-内酰胺酶的产生情况。统计产β-内酰胺酶菌株的分离率，并对耐药表型与β-内酰胺酶分离率之间的相关性进行统计学分析。采用实时荧光定量PCR对不产β-内酰胺酶菌株的femB的mRNA表达进行定量分析。
71株金黄色葡萄球菌对苯唑西林的耐药率为66.20%（47/71），产β-内酰胺酶的MSSA菌株分离率为58.3%，对苯唑西林高、低水平耐药菌株的分离率分别为63.15%和55.56%。通过对异质性耐药菌株BB270进行系列稀释绘制标准曲线，将菌株BB270中femB特异性mRNA量设定为1。计算得出MSSA菌株中femB量为0.4830 - 3.3636，低水平MRSA菌株中femB量为0.4204 - 3.3636，高水平MRSA菌株中femB量为0.0718 - 16.0000。MSSA、高水平MRSA和低水平MRSA之间femB水平无差异。
femB的表达水平可能与不产β-内酰胺酶的金黄色葡萄球菌对甲氧西林的耐药性无关。
