Characterization of Biofilm Formation Ability, Virulence Factors and Antibiotic Resistance Pattern of Staphylococcus aureus Isolates from Subclinical Bovine Mastitis

Abstract

Background Staphylococcus aureus is the common mastitis pathogen. This pathogen has the tendency to biofilm forming, and happens antibiotic resistance. ObjectivesThe aim of this study is characterization of biofilm formation ability, virulence factors and antibiotic resistance pattern of S. aureus isolates from subclinical mastitis.MethodsThe lactating dairy cows were screened for subclinical mastitis. The isolates were identified by phenotypic method and presence of the nuc gene. The biofilm forming & quantification was characterized by using a colorimetric assay. The S. aureus biofilm gene targeted by using PCR detection. The antimicrobial susceptibility of isolates was performed by using DAD method. The lowest antimicrobial agent preventing visible growth was construed by MIC50. Antibiotic susceptibility and MBECs for bacteria embedded in biofilms were determined by XTT method.ResultThe results highest resistance rate was seen against Penicillin, and the Ceftiofur and Ciprofloxacin had the lowest resistance rate. The MIC50 of Ceftiofur was founded 2 μg/ml. The results showed the 100% of the isolates were biofilm producers, and most of them formed strong biofilms. The frequency of icaAD, fnbAB and bap as virulence genes encoding biofilm was identified. The icaD and fnbB genes had the highest and lowest frequencies, respectively. The MBEC results for bacterial biofilm showed resistant to Ceftiofur in biofilm state; however, these strains were susceptible to this agent in the planktonic state.ConclusionsBiofilm formation is a significant virulence factor that, were detected at a high rate and antibiotic-resistant, and responsible for subclinical bovine mastitis that does not respond to routine treatments. Based on this results, we should look for more appropriate treatment strategies to prevent the formation or dispersion of biofilms.