الفهرس 
Staphylococci
PathogenesisOnly 14 pages are availabe for public view
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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.