Resistance Of Staphylococcus Aureus And The Effect Of ε-PL On Its Biofilm Formation

Staphylococcus aureus(S.aureus)has becoming increasingly prominent in drug resistance and pathogenicity,resulting in a great challenge to clinical anti-infective therapy.The formation of biofilm,which could induce drug resistance of bacteria and disturb the immune system indentification and killing mechanism,is one of main triggers to bring about persistent infection for patients.Herein,we focused on intervening clinical isolated Staphylococcus aureus by ε-poly-L-lysine(ε-PL)and investigating the effects of ε-PL on the growth of Staphylococcus aureus and the formation of biofilm.It is our purpose to clarify the hospital Staphylococcus aureus resistant characteristics and provide a theoretical basis for developing new anti-infective drugs.Objective To understand the resistance characteristics of Staphylococcus aureus in a hospital and to evaluate the clinical value of MALDI-TOF MS in the identification of clinical isolates.And to investigate the biofilm phenotype of Staphylococcus aureus and explore the effect of ε-PL on the formation of Staphylococcus aureus biofilms.Methods Clinical isolates were collected between September 2016 and September 2017,which were identified as Staphylococcus aureus according to conventional identification methods such as colony morphology and biochemical reactions.Furthermore,the strains were confirmed by MALDI-TOF MS.The Kirby-Bauer method was used to perform drug susceptibility testing,which was analyzed by WHONET 5.6 software.100 clinical isolates of Staphylococcus aureus were collected.Phenotypic characterizations of biofilm were conducted using Congo red agar(CRA)and the detections of icaA/icaD gene distribution were performed by polymerase chain reaction(PCR).The Constant Broth Dilution was performed to determine the minimum inhibitory concentration(MIC)of ε-PL on Staphylococcus aureus strains.Microplate reader Absorbance Spectrophotometric.Observation of the Growth Curve of ATCC25923 and USA 300 and crystal violet dyeing method was used to detect the biofilm formation.Scanning electron microscopy(SEM)was conducted to observe the effect of ε-PL on biofilm formationResults After clinical identification and MALDI-TOF MS confirmation,a total number of 417 strains of Staphylococcus aureus were isolated.The specimens were mainly derived from wound swab,and the main source of the department is burns.Except vancomycin and linezolid,Staphylococcus aureus exhibited different degrees of resistance to other commonly used antimicrobial agents.417 strains of Staphylococcus aureus were composed by 238 MRSA strains(57.1%)and 179 MSSA strains(42.9%).Besides the sulfamethoxazole-trimethoprim,linezolid,vancomycin and quinuptine/darfupin,the remaining groups of antibacterial drug resistance differences in groups were statistically significant(P<0.05).Among the 100 Staphylococcus aureus clinical isolates,79 isolates were positive for biofilm formation with a positive rate of 79.0%(79/100),including 41 strains of MRSA and 38 strains of MSSA.The detection rates of icaA and icaD genes were both 78.0%.The icaA/icaD gene positive rates of biofilm-positive and biofilm-nagtive Staphylococcus aureus strains were 94.9% and 14.3%,respectively.The MIC of the ε-PL on Staphylococcus aureus strains was 31.25mg/mL.With the increase the ε-PL concentration,the inhibitory effect on the growth of ATCC25923 and USA 300 was gradually enhanced.1/2 MIC ε-PL can significantly suppress the biofilm formation.Conclusion MALDI-TOF MS can identify Staphylococcus aureus quickly and accurately.Staphylococcus aureus is mainly derived from burns,who can easily catch wounds and respiratory tract infections.The resistance of Staphylococcus aureus to common antibiotics is serious and the resistance rates of MRSA are generally higher than that of MSSA.The icaA/icaD gene is closely related to the formation of Staphylococcus aureus biofilm.As a safe and efficient natural preservative,ε-PL could significantly inhibit the growth of Staphylococcus aureus bacteria and biofilm formation.