Survival of Staphylococcus aureus with different characteristics (antibiotic susceptibility, presence ica of gene, and colony morphology) in biofilms on stainless steel

This study was conducted to evaluate the effects of factors such as antibiotic susceptibility, presence of the ica gene, and colony morphology on the survival of Staphylococcus aureus in biofilm on a stainless steel surface at 43% and 68% relative humidity. Among the 19 S. aureus strains examined, 3 were negative for the ica gene, and cultivation in a Congo-red broth showed a 100% correlation between the change in broth color to yellow or red and the absence of the ica gene. Correlation between survival and resistance to several antibiotics was evaluated; groups resistant to penicillin and ampicillin showed high survival on stainless steel at 43% and 68% relative humidity. However, there was no significant difference in survival between ica-positive and ica-negative strains or between strains showing different colony shapes on soft agar. Based on these results, the resistance to some antibiotics such as penicillin and ampicillin may be correlated with the survival of S. aureus biofilms on stainless steel surfaces. Practical applications Various cell characteristics of S. aureus and the relationship between cell characteristics and survival in biofilms were evaluated. Colony morphology and the ica gene were not correlated with survival under dry conditions. However, the susceptibility to ampicillin and penicillin was correlated with survival. This study contributes to the understanding of the mechanism of survivals of S. aureus in biofilm under dry conditions.