Phenotypic and Genotypic Detection of Biofilm Formation in Staphylococcus epidermidis Isolates from Retrieved Orthopaedic Implants and Prostheses
Noha Tharwat Abou El-Khier *
Medical Microbiology and Immunology Department, Faculty of Medicine, Mansoura University, Egypt
Samah Sabry El-Kazzaz
Medical Microbiology and Immunology Department, Faculty of Medicine, Mansoura University, Egypt
Abd Elrahman Elganainy
Orthopaedic Surgery Department, Faculty of Medicine, Mansoura University, Egypt.
*Author to whom correspondence should be addressed.
Abstract
Background: Most of orthopaedic implant and prosthesis infections are actually biofilm-correlated infections that are highly resistant to antibiotic treatment and to the host immune responses. Staphylococcus epidermidis is considered one of the principal etiologic agents of orthopedic implant infection and prosthetic joint infection (PJI). Moreover, it has strong implant-adhering ability, and its biofilm-forming ability is considered as a serious pathogenic factor. Early detection and management of biofilm-forming S. epidermidis can be one of the essential steps towards the prevention and management of orthopaedic implant and prosthesis infections.
Aim of the Study: To evaluate the biofilm developing ability of the S. epidermidis isolates originated from retrieved orthopedic implants and prostheses with the phenotypic methods of microtiter plate assay (MtP) and Congo red agar (CRA) analysis, as well as detection of icaA and icaD genes by PCR.
Materials and Methods: A total of 39 S. epidermidis isolates obtained from 100 retrieved orthopaedic implants and prostheses were subjected to the biofilm formation and detection with different methods. Isolates were identified by standard microbiological procedures. Qualitative detection of the biofilm formation by the isolates was performed by culturing bacteria on Congo red agar (CRA) plates, while the quantitative detection of biofilm production was done by MtP assay. PCR was performed for the detection of two biofilm-development related genes; icaA and icaD.
Results: By CRA method, 17 (43.6%) S. epidermidis isolates were defined as biofilm producers through their black colonies. By MtP assay, 20 isolates (51.3%) were found to be biofilm producers with different grades: 12 (30.8%) strong producers (SP), 5 (12.8%) moderate producers (MP), and 3 (7.7%) weak producers (WP). The icaA and icaD genes were detected concomitantly in 15 (38.5%) isolates. In comparison with the data of ica gene detection, CRA had a sensitivity of 93.3% and specificity of 87.5% while MtP assay represented 100% sensitivity and 79.2% specificity. There was a substantial agreement between MtP assay and the concomitant presence of icaAD genes (kappa= 0.74). It was also noticed that all the SP isolates were positive for ica genes, and perfect agreement (kappa= 0.83) was observed between SP isolates and the concomitant presence of icaAD genes (p<0.0001).
Conclusions: Both genetic and phenotypic analyses are required for optimum evaluation of the biofilm producing ability of clinical S. epidermidis isolates. Moreover, MtP assay is recommended as a general screening method for detection of biofilm from retrieved orthopaedic implants and prostheses.
Keywords: Biofilm, Staphylococcus epidermidis, orthopaedic implant, PJI, CRA, MtP, icaA/D.