Antibiofilm Activity of Zinc Sulfate Against Staphylococcus aureus Isolates from Clinical and Retail Meat Sources in Baghdad, Iraq

Biofilm formation was investigated among 60 Staphylococcus aureus isolates obtained from both retail meat and clinical samples in Baghdad, Iraq. These isolates were divided into 75% (45/60) clinical isolates and 25% (15/60) meat-derived isolates. Biofilm formation among all isolates was evaluated using the microtiter plate assay, while the presence of the biofilm-associated genes icaA, icaB, icaC, and icaD was determined by polymerase chain reaction (PCR). The antibacterial activity of zinc sulfate was assessed using the broth microdilution method to determine the minimum inhibitory concentration (MIC). Subsequently, sub-inhibitory concentrations (sub-MICs) of zinc sulfate were applied to evaluate its antibiofilm activity against the tested isolates. This study showed that 38 (63.3%) isolates were able to form biofilm and were divided into 2 (3.3%) strong biofilm producers, 8 (13.3%) moderate, 28 (46.7%) weak producers. The most prevalent gene detected in tested isolates was icaB gene (96.7%), followed by icaA (93.3%), icaC (83.3%), and icaD (71.7%). Furthermore, the prevalence of icaD gene was significantly different between clinical 29 (64.4%) and meat isolates 14 (93.3 %) (p=0.046). For testing zinc sulfate antibiofilm activity, zinc sulfate MIC was determined at 64 µg/mL for all isolates by testing concertation ranged from 1024 to 2 µg/mL and a sub-MIC concentration of 32 µg/mL was used for the following experiment. It was shown that Zinc significantly reduced biofilm formation at p≤0.05. After treatment with zinc sulfate, 2 (3.3%) strong biofilm producers isolates were decreased to 0 (0%) strong biofilm producers, weak and moderate biofilm producers decreased to 11.7% and 3.3% and the number of non-biofilm-producing isolates increased from 36.7% to 85.0%. From these study findings, we concluded that zinc sulfate can reduce the biofilm formation ability in S. aureus isolates included in this study from clinical and raw meat sources have a promising antibiofilm application in meat-processing and clinical environments to reduce biofilm-associated persistence and contamination.