Among the 181 urinary isolates, 151 belonged to Enterobacterales. E. coli was the most common bacterial isolate [62.4% (113/181) ] followed by Klebsiella spp. [21% (38/181)], Pseudomonas aeruginosa [7.7% (14/181)], Enterobacter spp. [2.8% (5/181)], Citrobacter spp. [1.1% (2/181)] and Proteus mirabilis [0.6% (1/181)]. Among GPCs, Enterococcus faecium [2.8% (5/181)] was found commonest followed by E. faecalis [1.7% (3/181)].
AST of FP by different methods
Considering AD as a gold standard, more than 85% of isolates were observed susceptible to FP. The results of AD, DD, and E-test following CLSI and EUCAST breakpoints had been shown in the table (Table 1).
The percentage of susceptible, intermediate, and resistant isolates by AD method following CLSI breakpoints was 93.4%, 0.5%, and 6.1%, respectively. Regardless of any of the methods, isolates found more susceptible to FP following CLSI breakpoints than EUCAST breakpoint. (Table 1). Nitrofurantoin resistance was observed much higher than FP (27% against all uropathogens and as high as 50% among Klebsiella spp.) On the contrary, resistance to FP was found less than 10% in most of the resistant phenotypes i.e. MDR, XDR, PDR, ESBL, and Carbapenem-resistant GNB (CR-GNB) isolates (Table 2). Isolates of Enterococcus spp. with HLAR were observed to exhibit 25% resistance against FP. Colistin had the same MIC50 and MIC90 (0.5 µg/mL) in colistin susceptible strain. The overall MIC50 of 8 µg/mL and MIC90 of 64 µg/mL was observed in AD whereas E-test showed lower MIC50 value of 0.5 µg/mL and MIC90 of 64 µg/mL. The MIC50/90 rates of E-test in Pseudomonas aeruginosa were similar to gold standard AD, whereas difference between two methods was seen in other organisms with higher MIC90 in E-test (Tab.1).
Agreement analysis by different methods
The rates of EA, CA, mE, ME, and VME were assessed against all the organisms for DD/ E test. Applying CLSI breakpoints, EA, CA, mE, ME, and VME for E-test/DD were found 91.2%/NA, 95%/93.9%, 2.8%/1.1%, 1.8%/4.7% and 9.1%/9.1%, respectively. Using EUCAST breakpoints, CA, ME, and VME for E-test/DD were found 88.9%/80.1%, 6.3%/16.3% and 52.4%/52.4%, respectively.
Performance of the E-test for Klebsiella spp. was found good in comparison to E. coli, considering the VME result. Similar results were also observed for Enterococcus spp. Lastly, isolates of Pseudomonas aeruginosa had shown no mE, ME, or VME using CLSI breakpoints of E.coli (Table 3).
A Scatter diagram was plotted using the FP AST result of 181 isolates by E-test and DD and compared with AD result.(Fig. 1a, 1b) One hundred out of 142 isolate with MIC ≤16 mg/L by AD showed an excellent correlation with E-test. However, a poor correlation was seen between the results of the E-test and AD result for the isolates with MIC between 64-128 mg/L (Fig. 1a). Comparing the results of DD method with AD, a good categorical agreement was observed for the isolates with MIC ≤64 mg/L. Few isolates (8 out of 142) with MIC ≤ 16 mg/L by AD were classified as resistant by DD (Fig. 1b).
The correlation plot between MIC results of E-test and AD values was drawn for the comparative analysis. Pearson R2 value was found 0.6518, which indicates a good correlation between both methods.