c, d Isolates positive and negative

for exopolysaccharide rope production, respectively. Distribution of MIC by species, isolate, and ropy phenotype Resistance to the 17 antimicrobial compounds and hop-compounds was determined, and the antimicrobial compounds to which resistant isolates of Pediococcus were found are given in Additional file 1. For the majority of the 29 isolates tested, a moderate degree of susceptibility was shown to each of the antibiotics and a MIC value could be determined. However, for two of the antibiotics (i.e., Vancomycin and Ciprofloxacin), the majority of isolates (72% learn more and 52%, respectively) grew in the presence of the antibiotic at all concentrations tested. Additionally, 48% of isolates were hop-resistant. When Pediococcus claussenii and Pediococcus parvulus were assessed on the basis of ropy (i.e., exopolysaccharide-producing) phenotype, there was no significant difference found among the MICs for each antibiotic [Additional files 1 and 2]. Analysis of antimicrobial resistance according see more to Pediococcus species demonstrated that just over half of the antibiotics (9/17) had significantly different MICs for different species (Table 2 and Additional files 1 and 2). The non-parametric Kruskal-Wallis H-test was used to test for equality in population medians. This test is an extension of the

Mann-Whitney U-test which is designed to examine whether two samples of observations come from the same distribution. Unfortunately, post-hoc analyses to determine which of the six species had significantly different MICs for each antibiotic was not possible due to the low number of isolates per Orotidine 5′-phosphate decarboxylase species. However, when P. claussenii isolates were compared to isolates of the other species combined, P. claussenii had significantly lower MICs (Mann-Whitney U-test, p < 0.05) for all antimicrobial compounds tested, except for Erythromycin, Clindamycin, Daptomycin, and Vancomycin (data not shown). Table 2 Antimicrobial compounds having significantly different MICs among the six Pediococcus species. Antimicrobial compound p-valuea Ampicillin < 0.02 Ceftriaxone

< 0.02 Ciprofloxacin < 0.02 Daptomycin < 0.02 Gatifloxacin < 0.01 Gentamicin < 0.05 Levofloxacin < 0.01 Penicillin < 0.02 Synercid < 0.05 a p-value corresponds to the H-test statistic as derived from the non-parametric Kruskal-Wallis H-test which tests for equality in population medians where there are three or more groups. Distribution of MIC by presence of genes associated with beer-spoilage and/or hop-resistance Whether any of the beer-spoilage and/or hop resistance-correlated genes ABC2, bsrA, bsrB, hitA, horA, and horC were associated with any of the antimicrobial MICs was determined [Additional file 2]. Of these six genes, hitA, horC, and ABC2, did not occur with sufficient frequency to be analyzed statistically.