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Stenotrophomonas maltophilia, an opportunistic pathogen usually connected with healthcare-associated infections, is an environmental bacterium. Intrinsic resistance to multiple antibiotics, with different virulence determinants in the last decade classified this bacterium in the group of global multiple drug resistant (MDR) organism. S. maltophilia clinical isolates, were collected from tertiary care pediatric hospital in Belgrade, Serbia to investigate influence of different factors on biofilm formation, kinetics of biofilm formation for strong biofilm producers and effect of trimethoprim-sulfamethoxazole (TMP/SMX) on formed biofilm. Most of the isolates (89.8%) were able to form a biofilm. Analysis of biofilm formation in different growth conditions showed that changing of temeperature and pH had the stronggest effect on biofilm formation almost equally in group of cystic fibrosis (CF) and non-CF strains. TMP/SMX in concentration of 50 μg/ml reduced completely 24 h old biofilms while concentration of 25 μg/ml effects formed biofilms in a strain dependent manner. Among strains able to form strong biofilm CF isolates formed biofilm slower than non-CF isolates, while shaking conditions did not affect biofilm formation. Swimming motility was detected in both CF and non-CF isolates, however more motile strain formed stronger biofilms. This study suggests that temperature, pH and TMP/SMX had the strongest influence on biofilm formation in analyzed collection of S. maltophilia. A positive correlation between motility and strength of formed biofilm was demonstrated.

The prevalence of quinolone resistance was studied in Salmonella enterica serotype Enteritidis isolates collected during 2005-2010 in Southern Bačka County, Serbia. A total of 878 clinical isolates were examined, among which 19 (2.2%) nalidixic acid (NAL)-resistant S. Enteritidis were detected by selection on agar plates containing 64 mg/L NAL. Antimicrobial susceptibility of the isolates was tested by the agar dilution method. According to Clinical and Laboratory Standards Institute (CLSI) breakpoints, ciprofloxacin (CIP) resistance was not present in the strains. Multiple drug resistance was rare, and resistance to NAL was most often present as a single resistance property. All but one NAL-resistant S. Enteritidis showed reduced susceptibility to CIP [i.e. minimum inhibitory concentration (MIC)≥0.125 mg/L]. This isolate of human origin had a CIP MIC of 0.064 mg/L and DNA sequencing revealed that it contained an Asp87Gly gyrA mutation. Most of the remaining isolates had MICs for NAL and CIP of 256 mg/L and 0.256 mg/L, respectively. Mutations in the Asp87 codon resulted in substitutions to Asn in most of the isolates, but Asp87Gly and Ser83Phe exchanges were also detected. No mutations were present in the gyrB, parC or parE genes. Although CIP resistance was absent, reduced susceptibility characterised by mutations in gyrA was apparent among S. Enteritidis isolates from Serbia., (Copyright © 2012 Elsevier B.V. and the International Society of Chemotherapy. All rights reserved.)