The Effect of Sub-Minimal Inhibitory Concentrations of Daptomycin and Linezolid on Biofilm Formation of Methicillin Resistant Staphylococcus aureus Isolated from Clinical Samples.

IF 2
Halil Bal, Nurten Altanlar, Sulhiye Yıldız
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Abstract

Objectives: The aim of this study was to determine the development of in vitro resistance and changes in biofilm forming abilities in methicillin-resistant Staphylococcus aureus (MRSA) isolates exposed to sub-minimal inhibitory concentrations (sub-MICs) of daptomycin and linezolid; and to investigate the presence of the methicillin resistance gene (mecA) and the biofilm-associated genes (icaA, icaD) by polymerase chain reaction.

Materials and methods: This study was carried out with thirty-two MRSA isolates. The susceptibility of the isolates to daptomycin and linezolid was investigated by the broth microdilution method, and MIC values were determined (1st MIC). After serial passages, the 2nd MIC and the 3rd MIC values were similarly detected. Before and after serial passages, the biofilm-forming abilities of MRSA isolates were examined using the microtiter plate (MTP) method.

Results: When the daptomycin and linezolid 1st MIC and 3rd MIC values of the isolates were compared, there was a 2-8 fold increase in linezolid (p<0.05) and a 4-32 fold increase in daptomycin (p<0.05). According to the MTP method, 20 (62.5%) of the 32 isolates formed biofilm at various levels, while 12 (37.5%) did not form biofilm. After the second series of passages, biofilm formation was observed in 19 (59.4%) isolates with daptomycin (p>0.05) and in 16 (50%) isolates with linezolid (p>0.05). The mecA gene was found in all isolates. Also, icaA and icaD genes were detected in 31 (96.9%) of 32 MRSA isolates.

Conclusion: MRSA isolates exposed to sub-MICs of the antibiotics daptomycin and linezolid were observed to form biofilms at varying levels or to lose their ability to form biofilms. The induction, reduction or eradication of biofilm depended on the type of antibiotic and the MRSA isolate.

达托霉素和利奈唑胺亚最低抑菌浓度对耐甲氧西林金黄色葡萄球菌生物膜形成的影响。
目的:本研究旨在确定耐甲氧西林金黄色葡萄球菌(MRSA)暴露于达托霉素和利奈唑胺亚最低抑制浓度(亚mic)下的体外耐药发展和生物膜形成能力的变化;聚合酶链反应检测甲氧西林耐药基因(mecA)和生物膜相关基因(icaA、icaD)的存在。材料与方法:采用32株MRSA分离株进行研究。采用微量肉汤稀释法考察菌株对达托霉素和利奈唑胺的敏感性,并测定MIC值(1 MIC)。连续传代后,第2 MIC和第3 MIC值检测相似。连续传代前后,采用微滴板(MTP)法检测MRSA分离株的生物膜形成能力。结果:比较达托霉素和利奈唑胺的第1 MIC和第3 MIC值,利奈唑胺增加2 ~ 8倍(p < 0.05),利奈唑胺增加16株(50%)(p < 0.05)。在所有分离株中均发现mecA基因。32株MRSA中31株(96.9%)检出icaA和icaD基因。结论:MRSA分离株暴露于抗生素达托霉素和利奈唑胺的亚mic下,可形成不同程度的生物膜或失去形成生物膜的能力。生物膜的诱导、减少或根除取决于抗生素和MRSA分离物的类型。
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