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C. P. Nix, D. Miller, H. W. Flynn, Jr.; Assessment of Biofilm Formation as a Predictive Factor for Antibiotic Resistance Among Coagulase-Negative Staphylococcus Isolates From Patients With Endophthalmitis. Invest. Ophthalmol. Vis. Sci. 2007;48(13):744.
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The most common organism causing post cataract extraction endophthalmitis is coagulase-negative Staphylococcus(CoNS). In patients with intraocular lenses or other biomaterials, the ability to produce biofilm in vivo has been associated with increased pathogenesis and poorer visual outcomes. The current study was initiated to determine if a relationship exists between in vitro antibiotic resistance patterns and biofilm formation among CoNS isolates recovered from patients with endophthalmitis.
A microbiological database was used to select culture positive cases of CoNS (N=21) diagnosed at the Bascom Palmer Eye Institute between January 1, 2006 and September 30, 2006. The Christensen Qualitative Tube Method (CQTM) was employed to measure biofilm formation. Isolates were grown in trypticase soy broth and subsequently stained with crystal violet for biofilm production. Stained biofilms were eluded and the resultant color intensity measured. Isolates were scored as absent, mild, moderate, or strong biofilm producers. In vitro antibiotic susceptibilities using the Vitek Automated System and/or E tests were recorded for vancomycin, gentamicin, gatifloxacin, moxifloxacin, and methicillin/oxacillin. Methicillin/oxacillin resistance was used as a marker for cerfuroxime resistance.
Of the 21 isolates, 19 (90.5%) of the CoNS isolates demonstrated biofilm formation. The amount of detected biofilm varied: absent, 9.5%; mild, 38.1%; moderate, 38.1%; strong, 14.3%. In vitro susceptibilities measured as the percentage of CoNS isolates sensitive, in descending order, were as follows: vancomycin, 100%; gentamicin, 95.2%; gatifloxacin, 57.1%; moxifloxacin, 57.1%; and methicillin/oxacillin, 42.9%. Cefuroxime resistance among our most recent samples of CoNS endophthalmitis was 42.9%. Sixty-two percent of the isolates were resistant to at least one of the above antibiotics; of these, 62% were resistant of ≥3 of the drugs. The biofilm scores showed no significant association with antibiotic resistance (p = 0.4 - 0.6, 95% CI).
Although a majority of the CoNS isolates produced biofilm in the current study, there appears to be no statistically significant relationship between antibiotic resistance and the presence or extent of biofilm formation.
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