Abstract
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.
Highlights
In Microtiter plate (MTP) method, biofilm production was detected in 23 (46%) of the 50 staphylococcal isolates with different intensities; 13 (26%) isolates were strong producers, 6 (12%) isolates were moderate and 4 (8%) isolates were weak biofilm producers, whereas 27 (54%) were non biofilm producers
By Congo red agar (CRA) method, 23 (46%) were positive for biofilm; CRA method showed little correlation with MTP assay where only 10 (20%) of the isolates were positive by both the MTP and CRA methods (Table 2)
As regards staphylococci isolated from intravascular catheters, 14 (56%) were biofilm producers by CRA while 8 (32%) were positive by MTP
Summary
Biofilm-mediated infections in the hospital environment have a significant negative impact on patient health and place an enormous burden on the resources of the health services [1]. Staphylococcus aureus (SA) together with Staphylococcus epidermidis are a common cause of biofilm-mediated lifethreatening infections associated with intravenous catheters, artificial heart valves, and prosthetic joints [2]. The ability of nosocomial pathogens to form biofilms is of significant clinical interest, as biofilm formation makes the organisms more resistant to antibiotics and host defenses [2,3] and influences the subsequent outcome of an infection [4]. Development of biofilm is considered to be a two step process; first, the bacteria adhere to a surface mediated by a capsular antigen, namely capsulare polysaccharide/adhesin (PS/ A), second, the bacteria multiply to form a multilayered biofilm, associated with production of polysaccharide intercellular adhesin (PIA) which mediates cell to cell adhesion [7]
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