DETECTION OF SOME VIRULENCE FACTORS IN STAPHYLOCOCCUS EPIDERMIDIS ISOLATED FROM CLINICAL SPECIMENS IN IRAQ.

Abstract

        Staphylococcus epidermidis is a member of the coagulase-negative staphylococci, and considered the most commensal bacterium that is abundant in the human skin and mucous membrane. It is also the most nosocomial prevalent pathogen. Staphylococcus epidermidis can cause different clinical infection when the skin is breaching.  The most common clinical infection in hospitals belongs to Staphylococcus epidermidis, which associated with life-threatening infections. This is due to the antibiotic-resistant phenotype and the formation of biofilm, which is considered one of their virulence factors, especially on indwelling medical devices and at surgical sites. This study was conducted to determine the virulence factors of Staphylococcus epidermidis (S. epidermidis) that were isolated from different clinical samples. The clinical samples were collected from blood, wound, nasal, and acne swabs, CSF and medical devices (heart valves and dialysis catheters), during the period from December 2022 to August 2023. 120 clinical samples were collected from Baghdad Teaching Hospital and Ghazi Al-hariri Hospital. The isolated samples were cultured in specific and differential culture media, and the Vitek- 2 system was used to confirm the presence of Staphylococcus epidermidis. The results confirmed that only 73 isolates were positive for Staphylococcus epidermidis. All isolates were screened for biofilm formation, antibiotic sensitivity tests (AST), molecular studies, and tests for detection of virulence factors such as lipase, gelatinase, protease, and DNase. The lethal dose (LD₅₀) showed the effect of commensal Staphylococcus epidermidis on mice, and the bacterial virulence appeared with highly sensitive quantification. The present study showed that Staphylococcus epidermidis was a strong biofilm producer in about 36 isolates (49.32), 27 (36.99%) of isolates were considered moderate for biofilm production, and 10 (13.70%) of isolates were weak or non-biofilm producers. The isolates appeared to be resistance to methicillin and other antibiotics, so they were considered multi-drug-resistance pathogens. The molecular study confirmed that all isolates possessed mecA genes and lacked ermA genes. The mice that were injected with the bacterial suspension showed pathological changes in the internal organs, with picture including skin dermatitis. These results proved that Staphylococcus epidermidis is a life threatening pathogen to the humans and animals.

Keywords: differential culture media; AST; virulence factors; molecular study; LD₅₀.