Biofilm-forming and antimicrobial resistance traits of staphylococci isolated from goat dairy plants

Abstract

Introduction: Biofilm-associated antimicrobial resistance is of increasing importance to the maintenance and spread of foodborne pathogens in the food industry. This study aimed to investigate the ability to form biofilm and the antimicrobial resistance of staphylococci contaminating small-scale goat milk dairy plants.

Methodology: Sixty isolates were tested for antimicrobial resistance against 20 drugs by the microdilution method. Biofilm-forming traits were assessed by the microtiter plate method (MtP), Congo red agar method (CRA), and icaD gene detection by polymerase chain reaction (PCR).

Results: High antimicrobial resistance to ampicillin (60/60; 100%), penicillin G (21/60; 35%), and erythromycin (15/60; 25%) was observed, but all isolates were susceptible to amoxicillin/K-clavulanate, ceftriaxone, ciprofloxacin, gentamicin, levofloxacin, linezolid, and moxifloxacin. No resistance to oxacillin or vancomycin was seen among Staphylococcus aureus. Twenty-seven isolates (27/60; 45%) were considered to form biofilm according to MtP, and similar biofilm-producing frequencies were observed in coagulase-negative staphylococci (CoNS) (20/44; 45.4%) and S. aureus (7/16; 43.7%). The icaD gene was observed only in S. aureus isolates. There was no association between biofilm production and antimicrobial resistance. A higher frequency of biofilm-producing staphylococci was found in isolates from bulk tank milk and hand swabs. On the other hand, isolates from pasteurized milk showed lower frequency of biofilm formation.

Conclusions: Staphylococci contaminating goat dairy plants are potential biofilm producers. The results suggest no association between the ability to form biofilm and antimicrobial resistance.