Results
Of the 80 CRPA isolates, 24 (30.00%) were extensively drug-resistant (XDR) and 56 (70.00%) were non-XDR. Resistance rates to imipenem and meropenem were 83.70% and 68.70% respectively, and no isolate was susceptible to either agent. Overall resistance rates to aztreonam, piperacillin/tazobactam, levofloxacin, ceftazidime, cefepime, amikacin, and tobramycin were 37.50%, 30.00%, 26.30%, 25.00%, 21.30%, 12.50%, and 6.30% respectively. The expected oprD amplicon failed to amplify in 55 isolates (68.75%). mCIM was positive in 23 isolates (28.75%), with 95.0% agreement with PCR-detected carbapenemase gene carriage (Cohen's κ 0.871, 95% CI 0.748-0.994). Detection rates for blaKPC, blaNDM, blaVIM, and blaIMP were 10.00%, 6.25%, 5.00%, and 2.50% respectively; neither blaOXA-10 nor blaOXA-48 was detected. qacEΔ1-sul1, merA, tehA, and oqxA were detected in 36.25%, 16.25%, 7.50%, and 2.50% of isolates respectively, whereas aceI and emrE were not detected. For ethanol the MIC50 and MIC90 were 75% (v/v) in both groups; for the chlorine-containing disinfectant and povidone-iodine the MIC50/MIC90 were 512/1024 mg/L in both groups, and neither MICs nor MBCs differed between groups. Benzalkonium bromide MICs ranged from 32 to 256 mg/L in XDR and 16 to 256 mg/L in non-XDR isolates, and MBCs from 64 to 512 and 64 to 256 mg/L respectively; the MIC difference was the primary outcome and remained significant after Holm correction (adjusted P < 0.001), whereas the MBC difference did not survive correction when considered alongside the other disinfectant endpoints (Benjamini-Hochberg q=0.144). qacEΔ1-sul1 was more frequent among XDR isolates in unadjusted analysis (58.3% versus 26.8%; OR 3.83, 95% CI 1.40-10.45; unadjusted P = 0.011) but did not retain significance after correction within the eight-test gene family (q = 0.088). Resistance to aztreonam and meropenem was nominally more frequent among qacEΔ1-sul1-positive isolates (55.20% versus 27.50% and 86.2% versus 58.80%) but neither association survived correction (q=0.072 for both; Holm-adjusted P = 0.111 and 0.100). Direct comparison of benzalkonium bromide endpoints by qacEΔ1-sul1 status showed no difference (median MIC 64 mg/L in both groups, P = 0.097; median MBC 128 mg/L in both groups, P = 0.697).
