Detection of intercellular adhesion icaAD genes in Staphylococcus aureus and coagulase-negative staphylococci and their role in biofilm production

Abstract

Objectives This study aimed to investigate the resistance patterns of nosocomial and community-acquired Staphylococcus aureus and coagulase-negative staphylococci (CoNS) and screen methicillin-resistant and vancomycin-resistant isolates by phenotypic and genotypic methods. It also aimed to determine the biofilm-forming capacity and detect icaA and icaD genes responsible for polysaccharide intercellular adhesion synthesis and analyze the association between the biofilm-forming capacity of staphylococcal isolates and their multidrug resistance patterns. Background Biofilms have dramatically increased resistance to antibiotics. The genes and products of ica locus [icaR (regulatory) and icaADBC (biosynthetic) genes] have been demonstrated to be necessary for biofilm formation and virulence. Materials and methods The study was carried out on specimens collected from Menoufia University Hospitals. Isolation, identification, and antimicrobial susceptibility of staphylococcal isolates were carried out using standardized microbiological methods. Phenotypic biofilm detection was carried out by microtiter plate adherence assay, the Congo red agar method, and the modified Congo red agar method. All clinical isolates (CIs) of S. aureus and CoNS demonstrating reduced susceptibility to methicillin and vancomycin and showing the ability to form biofilm were tested for the presence of methicillin-resistant gene (mecA), vancomycin-resistant genotypes (vanA and vanB), and biofilm-producing genes (icaA and icaD) by means of multiplex PCR. Results About 82.4% of S. aureus isolates were methicillin-resistant S. aureus, whereas only 76.5% of them were positive for the mecA gene. VanA-positive gene was detected in 10.3% of S. aureus isolates. Regarding CoNS isolates, 76.9% were negative for the mecA gene and 78.8% were methicillin-resistant coagulase-negative staphylococci. About 10% were positive for the vanA genes in CoNS isolates. Biofilm formation was detected in 45.6 and 41.2% of S. aureus and in 76.9 and 55.8% of CoNS isolates, as detected by microtiter plate and Congo red agar, respectively. Ica genes were detected in 38.2% of S. aureus CIs and in 63.5% of CoNS CIs. Conclusion The biofilm-forming ability of staphylococcal isolates correlated with clinical significance and drug resistance. Biofilm-forming ability in the absence of icaA and icaD genes highlights the importance of further genetic investigations of ica- independent biofilm formation mechanisms.