Hence, cefazolin may be Peptide 17 cell line readily inactivated by the respective lactamases produced by these isolates. All other isolates showed fluorescence profiles similar

to #2. Although, ideally #2 should not exhibit fluorescence change over time, a slight increase was noted (Figure 2). A range of mean ±3X standard deviation observed for #2 (β-LEAF only reaction) would give 99.7% confidence intervals for values by Gaussian statistics. The upper limit of this range, i.e. mean + 3X standard deviation was set up as a cut-off value (Figure 2). Isolates showing cleavage rates within this cut-off, that is, low/negligible increase in fluorescence of β-LEAF with time similar to non-producer #2, were designated as AZD6244 mouse non-producers of β-lactamase. Also as negligible differences between the cleavage rates of β-LEAF and β-LEAF + cefazolin reactions were observed, cefazolin was predicted to be

active to treat infections caused by these bacteria. Isolates that showed cleavage rate of β-LEAF alone higher than the cut-off included those observed to cleave β-LEAF efficiently (#6, #18, #19 and #20), as well as some isolates showing marginal differences from #2, such as #22. These could be low producers. As the difference JNJ-64619178 in cleavage rates in the absence and presence of cefazolin was minimal in these marginal cases, cefazolin was predicted as active. The results of the β-LEAF assay for all isolates are summarized in Table 2

(column 2 and column 6). Table 2 Comparison of different methods of β-lactamase detection and cefazolin antibiotic susceptibility/activity determination S. aureus isolate # β-LACTAMSE GENOTYPE (‘blaZ’ PCR) β-LACTAMASE PHENOTYPE CEFAZOLIN SUSCEPTIBILITY/ACTIVITY     β-LEAF assay* Nitrocefin disk test Zone edge test Disk diffusion Antibiotic activity – β-LEAF assay**   ‘+’ = positive PCR   Uniform orange color = ‘+’ (positive) Sharp zone edge = ‘+’ (positive) S = susceptible LA = less active   $: contained stop codon or deletion       (!) = sharp zone edge A = active 1 + + + + S (!) LA 2 – - – - S A 3 + – - – S A 4 – - – - S A 5 + – - – S A 6 + + + + S (!) LA 7 + – - – S A 8 + – - – S A 9 + – - – S A 10 +$ – - – S A 11 + – - – S A 12 + – - – S A 13 + – - – S A 14 + – - – S A 15 + – - – S A 16 +$ – - – S A 17 +$ – - – S A 18 + + + Bumetanide + S (!) LA 19 + + + + S (!) LA 20 + + + + S (!) LA 21 – - – - S A 22 + (Weak) + – - S A 23 – - – - S A 24 Unknown – - – S A 25 – - – - S A 26 + – - – S A 27 + – - – S A   Col. 1 Col. 2 Col. 3 Col. 4 Col. 5 Col. 6 $Special comment – blaZ contained Stop codon or deletion (so non-functional) (Robert L. Skov, unpublished results). *Classification into positive and negative is based on proposed cut-off depicted in Figure 2 (upper limit of mean ± 3X Std. deviation for strain #2, β-LEAF probe reaction) to demarcate β-lactamase production.