The Drug-resistance Of Staphylococcus Aureus Induced By Linezolid In Vitro

Infections caused by multi-drug resistant are spreading around the world, infection rate and mortality rate is increasing year by year, it is a serious threat to human health, especially methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococci (VRE). According to the bacterial resistance surveillance data of China (CHINET), the proportion of MRSA were maintained at more than50%in recent years. Widespread use of antibiotics and appearance of multi-drug resistance isolates makes cure MRSA infection more difficult and complex, it has became a global public health problem.Linezolid was the first oxazolidinone approved by the US Food and Drug Administration (FDA), and is still the only compound released for clinical use in this class currently. The unique chemical structure and antibacterial mechanism brings hope for the fight against all kinds of refractory drug-resistant. Linezolid showed strong antibacterial activity to most of gram-positive bacteria, such as MRSA, VRE and multi-drug resistant Streptococcus pneumoniae, etc. However, confirmed resistance to linezolid has been detected in several countries soon after it used clinically. Therefore, it is of great significance to study the linezolid-resistance Staphylococcus for guiding clinicians use linezolid rationally.Objectives:To induce resistance of linezolid in S.aureus in vitro, preliminary study on mechanism of the drug resistance. Observation and compare the fitness of S.aureus before and after induction, and the changes of susceptibility against other antibiotics.Methods:S.aureus were sampled from blood, sputum, excreta, drainage fluid, pus, etc, from a teaching hospital in Tianjin. S.aureus was identified by both API biochemical test series and latex agglutination test. mecA gene was detected by polymerase chain reaction (PCR).9strains (5MSSA and4MRSA) with low susceptibility to linezolid were selected to be as testing strains and ATCC25923as reference strain. Linezolid-resistance of9S. aureus isolates and1reference strain were induced in vitro. Domain V region of the23S rRNA gene was amplified and sequenced. To compare the fitness of S.aureus, and the susceptibility against other antibiotics.Results:Resistance to linezolid was successfully induced in9of10strains. Sa10got the highest MIC values (128mg/L), ATCC25923(Sal) after induction MIC values were also increased16-fold (64mg/L), the MIC values of Sa8was lowest (8mg/L), the rest of S. aureus MIC values were16mg/L. Point mutation was identified in23S rRNA gene in5linezolid-resistant strains:ATCC25923(S1, A2531T)、S3(A2289G)、S5(A2289G)、S9(C2691T、A2289G)、S10(C2474A、 A2289G), and the2289point mutation was detected in4testing strains. The linezolid-resistant S. aureus grew much slower than the susceptible parent, and definite changes in the susceptibility were demonstrated.Conclusions:S.aureus resistance to linezolid can be induced in vitro, and may be associated with the point mutation of the domain V region of the23S rRNA gene. The fitness cost observed in the linezolid-resistant strains.