الفهرس | Only 14 pages are availabe for public view |
Abstract Biofilms are communities of microorganisms which are embedded within a matrix of extracellular polymeric material. Biofilm helps the bacteria to form stable communities of protection rather than live as free planktonic cells. Biofilm is a serious threat for the patient, as it may cause therapeutic failure with regular antibacterial therapy and also evade the host immune system. High antimicrobial concentrations are required to inactivate organisms growing in biofilms and resistance may often increases thousand folds. Biofilm formation is commonly regulated by quorum sensing mechanisms. Availability of nutrients, chemotaxis, and surface adhesion influence biofilm formation in microorganisms. Among the risk factors which increase susceptibility to biofilm formation; indwelling medical devices as intravascular catheters, prior hospitalization and prior antibiotic use and prior MRSA colonization. Mechanism of biofilm formation is either PIA dependent or PIA independent. Where, PIA dependent biofilm formation is mediated by ica gene, while PIA independent is mediated by Adhesive proteins, Poly-gamma-glutamic acid and extracellular DNA. Coagulase negative Staphylococci have higher capability of biofilm production than S. aureus. Also, CONS are associated with increased antimicrobial therapeutic failure.Hence CONS cannot be neglected if isolated from the nosocomial infection samples. There are different approaches applied for the detection of biofilm formation, however, it is evident, that a method allowing a complete analysis of biofilm does not exist. Methods of detection of biofilm formation are either phenotypic or genotypic. Phenotypic methods include Staining based methods, Metabolic activity assays, Culture based methods and Microscopy based methods, While genotypic methods depend on detection of ica gene. In our study, 150 staphylococcal isolates were obtained from specimens from patients from different departments of Ain Shams University. The isolates were subjected to identification according to morphology by Gram stain, cultural characters and biochemical reactions. CONS species were identified using automated identification system (Vitek 2, bioMérieux, France). All staphylococcal isolates were tested for antibiotic susceptibility performed by Kirby Bauer disc diffusion method. All staphylococcal isolates were tested for biofilm production by three phenotypic methods; TCP, TM and CRA. Tissue culture plate method detected total positive biofilm production in 111 out of 150 isolates (74%), Strong biofilm production in 65 (43.3%) isolates of staphylococci. Moderate biofilm production was detected in 46 (30.7%) isolates of staphylococci whereas 39 (26%) isolates were biofilm nonproducers. The results of our study revealed that according to TCP S. aureus was the most common biofilm producing organism where 53.1% of S. aureus isolates and 46.8% of CONS were biofilm producers. Biofilm production in CONS species was highest in S. hemolyticus (57.7%), followed by S. epidermidis (21.2%) and S. hominis (19.2%). Maximum biofilm producing staphylococci were isolated from Blood cultures (82.6%) followed by those isolated from urine and body fluids (80%). Only 59.1% of staphylococci isolated from sputum samples were biofilm producers. Tube method detected total positive biofilm production in 64 out of 150 isolates (42.7%). Strong biofilm production was detected in 11 Staphylococci and 53 showed moderate biofilm production whereas 86 (57.3%) isolates were biofilm nonproducers. Congo red agar method detected only 2 MRCONS as biofilm producers. Comparing biofilm production by TM and TCP: TM is considered a highly significant test P value (<0.001), while, comparing biofilm production by CRA and TCP: CRA is considered a non-significant test P value (<0.579). With respect to TCP method which is considered as gold standard, TM was 51.4% sensitive and 82.1% specific, while, CRA was 0.9% sensitive and 97.4% specific. Biofilm production was higher in Methicillin sensitive than Methicillin resistant Staphylococcal isolates. Where, biofilm production was detected by TCP method in 73.3% of MRS versus 78.9% of MSS. Biofilm production is furthurly classified into 75% among MRSA, 80% among MSSA 71.4% among MRCONS, and 77.8% among MSCONS. Antimicrobial susceptibility testing was done to all specimens. All biofilm producing staphylococci were fully susceptible to Vancomycin, 96.4% susceptible to Linezolid and resistant to Cefoxitin, Levofloxacin, Gentamycin, Doxycycline, Clindamycin and Erythromycin as compared to non-biofilm producing strains. |