This value ranged from 0 (no growth in the presence of antibiotic) to 1 (no inhibition by antibiotic), and was used in all subsequent analyses. It is desirable to reduce the AR readings over the time course to a single value characterizing the particular isolate. Therefore, all isolates were characterized by the smallest resistance value over the time course of growth. MAPK inhibitor We tested all antibiotics at three concentrations, thereby producing three values of AR for each isolate. We presumed that the antibiotic concentration leading to the biggest variability in AR values between the isolates would be the most informative for characterizing

the resistance levels in the population. To evaluate the variability at different antibiotic concentrations, the pairwise differences in resistance values for all isolates were calculated and the values combined to give a sum total for each particular antibiotic concentration. The concentration with the biggest total was defined as the most informative and selected for further analysis. The informative concentrations were 100 μg mL-1 for ampicillin, 5 μg mL-1 for

chloramphenicol, 1 μg mL-1 for kanamycin, 0.5 μg mL-1 for norfloxacin, 5 μg mL-1 for tetracycline and 0.3 μg SBI-0206965 price mL-1 for meropenem. Distribution of resistance We analyzed the prevalence of antibiotic resistance in the eight genera that were represented by more than 20 isolates each: Aeromonas with 57 isolates (represented by 3 Operational Taxonomic Units (OTU) as defined by the 16S rRNA sequence types), Pseudomonas

217 (7 OTUs), Stenotrophomonas 73 (5 OTUs), Chryseobacterium 86 (25 OTUs), Pedobacter 61 (7 OTUs), Flavobacterium 41 (11 OTUs), Microbacterium 37 (6 OTUs) and Brevundimonas Calpain 23 (5 OTUs). The number of OTUs indicates that the actual species richness might be lower than can be estimated from the number of isolates. On the other hand, the similarity of the 16S rRNA sequences is not always a sensitive enough criterion to distinguish different species [38, 39]. In most cases, one OTU contains small number of isolates making it impossible to analyze the data at OTU level. Therefore the subsequent analyses (Figure 2) were performed at the level of genus. Still, it is Selleckchem Luminespib interesting to note that three major OTUs of Chrysobacterium had considerably different resistance patterns when compared between each other (Table 1). OTU “A”, containing 18 isolates is considerably more sensitive to ampicillin, meropenem (p value 10-5) and norfloxacin when compared to OTU “C”, containing 13 isolates. OTU “B”, containing 11 isolates was more sensitive to ampicillin, meropenem, norfloxacin and tetracycline when compared to OTU “C”. There were no significant differences between “A” and “B”. Figure 2 The average values of resistance coefficients in a specific genus as grouped by antibiotics (A) and genera (B). (A) The genera are organized by antibiotics tested.