Reversal Of Multidrug Resistance And Inhibition Of Virulence By Sertraline Against Staphylococcus Aureus

Staphylococcus aureus(S.aureus)is an important foodborne pathogen that can cause lifethreatening infections in severe cases.With the wide use of antibiotics,the multi-drug resistance S.aureus strains keep emerging,which cause a serious threat to food safety,human and animal health.In this study,the multi-drug resistance S.aureus isolated from the swine farm and clinic were used to study the antibiotic resistance type and drug resistance degree by K-B paper method and double dilution method.The drug resistance genes as well as a multidrug efflux pump gene norA in S.aureus were detected by PCR,including ?-lactams,tetracyclines,lincosamides,macrolides,and aminoglycoside antibiotics.The antibacterial and bactericidal effects of sertraline alone or in combination with antibiotics on S.aureus were measured by in vitro growth activity test.The effect of sertraline on the biofilm formation ability of S.aureus was studied by crystal violet staining.The methanol extraction method was used for exploring the effect of sertraline on the ability of staphyloxanthin formation.Finally,the effect of sertraline on the transcription levels of related drug resistance genes and virulence genes was measured by real-time quantitative PCR(RT-qPCR).Correlation analysis was performed on the experimental results using statistical methods.The details were as follows:a)Five S.aureus strains isolated from the swine farm were resistant to at least seven antibiotics,including ?-lactams,tetracyclines,lincosamides,macrolides and aminoglycoside antibiotics.The minimum inhibitory concentration(MIC)far exceeded the CLSI drug sensitivity standard,and the MIC values of clindamycin and clarithromycin were as high as 1024 ?g/mL,indicating that the S.aureus strains isolated from the swine farm were highly resistant.There were no significant difference between S.aureus isolates because the MIC value of sertraline was 16 ?g/mL.The resistance genes(ermB,tetK,tetL,aac(6')/aph(2'')and aadE)and a multidrug efflux pump gene norA were detected in the S.aureus strains isolated from the swine farm,and the ?-lactam resistance gene mecA was detected in the methicillinresistant strain USA300 isolated from the clinic.b)Sertraline had a combined antibacterial effect with clindamycin,ciprofloxacin and tetracycline,and the combined drug indices were below 1.000.One of the strains,the combined drug index of sertraline and tetracycline was 0.375,indicating synergistic bacteriostatic effect.The growth curve showed that sertraline did not affect the growth activity of S.aureus substantially at low concentration(1 ?g/mL);When the sertraline and tetracycline were at the concentration of 1/2 MIC,there was a bactericidal effect for S.aureus.In the effect of low concentration sertraline,the transcription levels of norA and mecA genes were down-regulated.c)In the effect of sertraline,the biofilm formation ability of four S.aureus strains was reduced in some extent,where the USA400 and Newman strains were reduced significant and the OD value was reduced at least 35%.The strain Newman was at a biofilm-free status when the concentration of sertraline was 1/2 MIC,indicating the remarkable inhibitory effect of sertraline.With the increasing concentration of sertraline,the content of staphyloxanthin in the bacteriocin-producing strain Newman was decreased.The content of staphyloxanthin was decreased by more than 70% at 1/2 MIC,which had the same level with the nonstaphyloxanthin strains.Sertraline also had a significant effect on the transcriptional level of virulence genes.When the concentration of sertraline was 0.2 ?g/mL,the expression levels of seven virulence genes(hla,hlb,coa,sbi,spa,lukF,brnQ)were significantly reduced in the strains USA300 and Newman(p < 0.001).