GENOTYPIC CHARACTERIZATION AND BIOFILM FORMATION OF FOOD-RELATED STAPHYLOCOCCUS AUREUS STRAINS

Staphylococcus aureus (S.aureus) is one of the well known pathogens that can live in a wide variety of environments. Several genotypes of S.aureus that differ in their pathogenicity were identified. The genotype B (GTB) is known for its high contagiousness and virulence potential compared with other genotype (Hummerjohann, et al., 2014). Biofilm production in diverse S.aureus subtypes have been reported (Thiran et al., 2015). The aim of this study was to measure the biofilm formation of different food-related S.aureus genotypes. The experiment was conducted on 10 S.aureus food-related strains. Gene amplification of the lukEB, sea and sed and the genotyping by RS-PCR, based on PCR amplification of the 16S–23S rRNA intergenic spacer region, were performed (Graber et al., 2008). Biofilm assays were carried out on polystyrene and stainless steel at 37°C (Di Ciccio et al., 2015). All results were expressed as “Biofilm Production Index” (BPI). Biofilm was compared with reference strains (S.aureus ATCC 35556, S.aureus ATCC 12600, and S.epidermidis ATCC 12228) for each isolate. All isolates were defined into different categories on the basis of their BPIs values. The cutoff point for the biofilm production was the BPI value obtained by negative control on polystyrene and stainless steel. S.aureus strains showing ability to produce biofilms were classified as weak (BPINC ≤ S.aureus BPIs < BPI12600), moderate (BPI12600 ≤ S.aureus BPIs < BPIPC) or strong (S.aureus BPIs ≥ BPIPC). Among S.aureus strains, 10/10 were positive for lukEB and 1/10 was positive for sea. All S.aureus strains were negative for sed. Eight different genotypes were found. All S.aureus strains were negative for GTB. At 37°C, 9/10 of S.aureus strains were biofilm producer in at least one tested surface. A total of 6/10 of S.aureus strains were biofilm producer on polystyrene whereas 9/10 were biofilm producer on stainless steel. Moreover, 6/10 of S. aureus strains were biofilm producers on both selected surfaces. In details, 3/10 strains formed strong biofilms, 2/10 moderate biofilms and 1/10 formed weak biofilms on polystyrene whereas 9/10 strains formed weak biofilms on stainless steel. Further studies are needed to evaluate the biofilm formation of genetically different subtypes of S.aureus strains.