Dynamic observation and antibiotic susceptibility analysis of biofilm of Staphylococcus aureus isolated from clinical specimens / 中华检验医学杂志

ABSTRACT

Objective To analyze the correlation between antibiotic susceptibility andbiofilm formation of Staphylococcus aureus. Methods According to Standardized Operational Guidance for Clinical Microbiological Testing, fifty-eight non-repetitive pathogenic Staphylococcus aureus isolates were collected from blood, urine, sputum and purulent secretions of inpatients in the Laboratory Department of the First Affiliated Hospital of Guangxi Medical University in January 2018. The antibiotics susceptibility of strains was characterized by disk diffusion method and VITEK-2.96-hole culture. The biofilm formation ability was detected bythe crystal violet assay and Congo redplate methods.The in vitro dynamic forming process of S.aureus′sbiofilm was analyzed by crystal violet staining combined with bacterial culture in 96 wells.Besides, the rate differences of drug resistance between biofilm producers and non-producers was performed by Chi-square test. The diameter of bacteriostasis zone of biofilm producers and non-producers was compared by t test. The drug resistance among strains with different biofilm formation ability was analyzed withnonparametric rank sum test. Results The positive ratio of biofilm producing S. aureus was higher in MRSA (68.42％) than in MSSA(20.00％)(χ2=12.304,P=0.001. Antibiotic resistance rates of biofilm producers were higher than non-producers.The resistance rates of biofilm positive strains to oxacillin and clindamycin were 73.33％ and 53.33％, respectively. The antibiotic resistance of the strain was higher along with the biofilm forming ability was increasing. (χ2=9.099, P=0.008). Depths of the S. aureus′s biofilm on the 96-well plates increased significantly over time and reached biofilm maturation after 72 hours′ incubation. Light microscopic observation revealed that the mature biofilm was compact and growing with many layers. Conclusions For the clinical isolates of S. aureus, the antibiotic resistance of biofilm producers is significantly higher than non-producers. Strains with stronger biofilm forming ability had higher antibiotics resistance. Depths of the S. aureus′s biofilm on the 96-well plates increased significantly over time and reached biofilm maturation after 72 hours′incubation.