Is there a relationship between biofilm forming-capacity and antibiotic resistance in Staphylococcus spp.? In vitro results

Biofilm-production facilitates the survival of Staphylococcus spp. both in harsh environmental conditions, and provides protection against in vivo and in protecting against various environmental noxa. The possible relationship between the antibiotic-resistant phenotype and biofilm-forming capacity has raised considerable interest in various bacterial species. In the present study, the interdependence between biofilm-forming capacity and the antibiotic-resistant phenotype in 299 environmental Staphylococcus spp. (S. aureus n=143, non-aureus staphylococci [NAS] n=156) was determined. Antimicrobial susceptibility testing and detection of methicillin-resistance (MR) was performed. Biofilm-forming capacity was assessed using Congo Red agar (CRA) plates and a crystal violet micro-titer-plate-based (CV-MTP) method. MR was identified in 46.9% of S. aureus and 53.8% of NAS isolates (p>0.05). Among the commonly-used antimicrobials, resistance was highest for clindamycin (57.9%), erythromycin (52.2%) and trimethoprim-sulfamethoxazole (51.1%). Based on the CRA plates, biofilm was produced by 30.8% of S. aureus and 44.9% of NAS, while based on the CV-MTP method, 51.7% of S. aureus and 62.8% of NAS were identified as strong biofilm-biofilm producers. (mean OD₅₇₀ values: S. aureus: 0.779±0.471 vs. NAS: 1.053±0.551; p<0.001). No significant differences in biofilm-formation were shown observed on the basis of MR (susceptible: 0.824 ± 0.325 vs. resistant: 0.896 ± 0.367; p=0.101). On the other hand, significant differences in biofilm-formation were identified based on rifampicin susceptibility (S: 0.784 ± 0.281 vs. R: 1.239 ± 0.286; p=0.011). The association of the antibiotic-resistant phenotype and biofilm-formation is still inconclusive, due to the heterogeneity of the results in the presently available studies, however, the understanding of these mechanisms in Staphylococcus spp. is crucial to appropriately address the therapy and eradication of these pathogens.