الفهرس 
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Abstract
Biofilm is a highly structured community characterized by cells irreversibly attached to interface and to each other and embedded in a water-rich matrix of extracellular polymeric substances. Once formed, these biofilms render the cells less accessible to the defense system of the host and more resistant to antibiotics. Formation of biofilms is a major virulence factor of staphylococci. A number of S. aureus infections are associated with the formation of biofilms. Also, S. epidermidis is an excellent biofilm former, and most S. epidermidis infections involve biofilms. Febrile neutropenia is one of the most concerning complications of cancer chemotherapy. The duration of neutropenia also contributes significantly to the risk of serious infections. The most common bacterial etiologic agent isolated from blood cultures in most centers was reported to be coagulase-negative staphylococci. The aim of this study is to define the main causative organisms of bacteremia in febrile neutropenic cancer patients, to study the prevalence of biofilm forming capability of staphylococci in blood isolates of these patients and to determine the antimicrobial susceptibility of these isolates. In the present study, blood cultures were done to 155 febrile neutropenic cancer patients and staphylococcal strains were identified and subjectd to testing antimicrobial susceptibilities to different antimicrobial agents. Biofilm formation by staphylococci was tested by congo red agar test, microtitre plate test and by detection of icaA gene using PCR procedure. Detection of biofilm by scanning electron microscope was done for some cases. In our study, bacteremia in febrile neutropenic cancer patients represented 33%. Bacterial strains isolated from blood cultures from those patients had the following distribution: 21.5 % were gram negative organisms, 78.5% % were gram positive. The gram positive cocci were distributed as follows: 33% were S. aureus, 45.1% S. epidermidis. Biofilm formation were 23.6% strains in S. aureus and 30.4% in S. epidermidis when tested by CRA and were 35.3% of S. aureus and 43.5 % strains of S. epidermidis when tested by MTP. Detection of icaA gene by PCR revealed that 17.7% of S. aureus strains and 21.7% of S.epidermidis were icaA gene positive. Comparing biofilm formation by the two phenotypic methods (CRA test and MTP) and icaA gene carriage, our study showed that there was better agreement between the presence of the icaA gene and CRA (66% in S.aureus and 80% in S. epidermidis) compared to the results obtained for icaA gene carriage in relation to MTP method (25% in S.aureus and 40% in S.epidermidis). Most strains that form biofilm were found to be more resistant to most antibiotics than other strains that does not form biofilm. In conclusion, we can see that biofilm formation led to increased antibiotic resistance and that CRA test can be used for screening of biofilm in clinical microbiology laboratory as its results agreed more with the presence of icaA gene.