21st European Congress of Clinical Microbiology and Infectious Diseases (ECCMID)
27th International Congress of Chemotherapy (ICC)
07.05.2011 - 10.05.2011 Milan, Italy
Phenotypical and genetical analysis of biofilm formation by coagulase negative
staphylococci
I. Liduma*, T. Tracevska, U. Bers, A. Zilevica (Riga, LV)
Coagulase-negative staphylococci (CoNS) are major nosocomial pathogens. The most important property of CoNS is
their ability to form biofilm on the surfaces of foreign bodies introduced (implanted) into the organism. The
accumulative phase of biofilm formation is linked to the production of polysaccharide intercellular adhesin (PIA), which
is synthesized by icaADBC-encoded proteins.The accumulation associated protein (AAP) encoded by aap is
important genetic determinant of slime production.
The purpose of this study was to investigate strains of CoNS using phenotypical and genotypical methods.
Methods: 49 clinical group specimens of CoNS were isolated from surgical wounds(10), blood culture(18) and
intravenous catheters (21). A control group of 12 CoNS specimens from nose epithelium of healthy people was
included. Appearance of icaA and aap genes was tested by PCR. The Congo Red agar screening phenotypical
method was evaluated for rapid and accurate detection of slime production by coagulase negative staphylococci. The
microtiter plate assay described by Christensen et al. with modifications was used in parallel.
Results. Both genes icaA and aap positive were detected in 9 (50%) of 18 blood samples, 2 (20%) of 10 surgical
wound samples, 6 (28,6%) of 21 catheter samples. In control group(12) only one of CoNS isolate was positive for aap
gene. Congo Red agar (1% glucose) demonstrated that correlation between icaA, aap and specific phenotypical
appearance was only in 8 (13,1%) of 61 CoNS samples. In this study, the ability of biofilm formation was evaluated in
31 samples using microtiter plate (96-well cell+ plate). Positive biofilm formation was detected in 8 (53,3%) of 15
central venous catheter and peripheral venous catheter samples, and in 5 (31,2%) of 16 blood samples.
Conclusions: The data indicate that icaA and aap genes along with phenotypical analysis (microtiter plate) are reliable
methods for biofilm detection in coagulase negative staphylococci. The Congo Red agar (1% glucose) screening
could not be recommended for analysis of biofilm forming CoNS, due to high rate of heterogeneity of results.