Correlation between biofilm formation and antibacterial resistance pattern among coagulase negative Staphylococcus.

Abstract

I dentification of coagulase negative Staphylococcus species (CNS) involved in mastitis and providing information about pathogenicity and antimicrobial resistance are essential to developing efficient strategies to control mastitis caused by the CNS. A total of 100 raw milk samples from mastitic cows were collected aseptically from different private dairy cow farms at Alexandria Governorate. All samples were subjected to bacteriological isolation of the CNS. All isolates were identified biochemically and confirmed by Vitek compact system . The CNS strains were tested for their haemolytic activity. Biofilm formation and antimicrobial resistance were investigated. The haemolytic and biofilm forming isolates were further identified by 16S rRNA gene sequences. Antimicrobial resistance genes assayed by PCR. The obtained results revealed the isolation of 16 CNS isolates, with a percentage of 16%. Species identification of CNS isolates by Vitek compact system revealed S. epidermidis, S. chromogenes, S. warneri, S. saprophyticus, S. simulans, S. haemolyticus and S. xylosus (4, 3, 3, 2, 2, 1, and 1 isolate) respectively. All S.warneri and S. haemolyticus isolates showed haemolytic activity , while the other isolates were non-haemolytic. Four isolates that showed haemolytic activity were investigated for biofilm formation ability, which revealed that all isolates were biofilm formers to a different degrees. Identification on the basis of 16S rRNA of haemolytic and biofilm forming isolates revealed the presence of an amplicon gene of 412 bp. The results of in vitro antimicrobial susceptibility testing of haemolytic and biofilm forming CNS isolates against 11 antimicrobial agents showed high resistance against ampicillin, followed by amoxicillin-clavulanic acid , cefotaxime, gentamicin, deoxycycline HCL, and tertacycline. Meanwhile, they were highly sensitive to vancomycin, followed by ciprofloxacin, clindamycinand sulfamethoxazole-trimethoprim. The results of genotypic detection of blaZ and mecA resistance genes and the icaD biofilm coding gene using PCR showed that they were detected in 2 isolates (50%), 3 isolates (75%), and 3 isolates (75%) of the tested four haemolytic and biofilm forming isolates ( 3 S.warneri and 1 S. haemolyticus ) respectively.