Biofilm formation and presence of icaAD gene in clinical isolates of staphylococci
In view of the significant negative impact of biofilm mediated infection on patient health and the necessity of a reliable phenotypic method for detecting biofilm producers, this study aimed to determine biofilm producing ability and presence of icaAD gene in clinical staphylococcal isolates as well as to assess the reliability of two phenotypic methods used for detection of biofilm. A total of 50 staphylococcal strains were isolated from 124 clinical specimen (94 intravascular catheters and 30 blood samples) collected from in-patients at Pediatric Hospital of Ain Shams University. Two phenotypic methods were used for detection of biofilm production; qualitative Congo red agar (CRA) and quantitative Microtiter plate (MTP). PCR was used to determine the presence of icaAD gene. Biofilm production was detected in 23(46%) isolates by CRA and MTP, however, both methods correlated only in 10(20%) of isolates. The icaAD gene was detected in 16(32%) staphylococcal isolates. Correlating phenotypic methods with icaAD gene detection, only 8(50%) of the icaAD positive staphylococci were positive by MTP, while 5(31%) were positive by CRA method. Unexpectedly, 15(30%) and 18 (36%) of the isolates were icaAD negative while MTP and CRA positive, respectively. In conclusion, despite the presence of icaAD gene, it does not always correlate with in vitro biofilm formation. The biofilm-forming ability of some isolates in absence of icaAD gene highlights the importance of further genetic investigations of ica independent biofilm formation mechanisms. Comparing phenotypic methods, MTP remains a better tool for biofilm screening.
Keywords: Staphylococci; Biofilm; Congo red agar; Microtiter plate; icaAD gene