25 1 4 0 5 0 25 2 4 0 25- No mechanisms of resistance identified

25 1 4 0.5 0.25 2 4 0.25- No mechanisms of resistance identified 7 (0) 4 2 4-8b 4 2 8 4 16 XY+, MBL 7 (6) >32 >32 8 256 >32 >256 >256 >32 XY+ 7 (5) 16 8/16b 32 8/256b >32 256 2/>256b 0.5/>32b ABM+, XY+ 5 (2) 0.25/8b 0.25/2b 16 8 4 256 2- >256c 32 ABM+, XY+, MBL 4 (3) >32 >32 8 256 >32 >256 >256 >32 ABM+ 3 (2) 0.5-16b 1 16 2-8c 4 4-32c 1-8c 0.25-8c XY+, GES-1 3 (2) 8- >32c 8- >32c 8 128 >32 >256 256 16 ABM+, XY+, AmpC+ 2 (2) 16/>32b >32 8/32b 32/64b Tubastatin A cost 16/32b 4/64b 1/8b

2/4b ABM+, GES-5 1 (1) >32 32 8 32 >32 128 128 32 ABM+, CTX-M2 1 (1) 4 1 >32 2 >32 128 256 16 XY+, AmpC+, MBL 2 (2) 32/>32b >32 16/>32b 128/>256b >32 >256 >256 >32 MBL 2 (2) >32 >32 8 256 >32 >256 >256 32 AmpC+ 3 (2) 1-8 2-16c 4-32c 16-256c 16 4 2 0.5-32c OprD- 12 (12) ≤0.25 1-2 8 2 2 8 2 0.25 MER, meropenem; IPM, imipenem; ATM, aztreonam; CAZ, ceftazidime; FEP, cefepime; AMK, amikacin; GEN, gentamicin; CIP, ciprofloxacin. a, Modal MIC is defined as the antimicrobial MICs that were more frequently observed at each association of resistance mechanisms. b, two modal MICs observed; c MIC range when no modal MIC was observed. The gene expression analysis showed that 50.8% (n = 30) and 27.1% (n = 16) of P. aeruginosa clinical isolates demonstrated increased

mexY (from 2.2- to 41.0-fold) and mexB (from 2.1- to 10.0-fold) transcription CX-6258 in vivo mRNA levels, respectively, compared to those of PAO1. In addition, 11 P. aeruginosa isolates (18.6%) showed overexpression of both mexB and mexY efflux genes. Overexpression of MexCD-OprJ and MexEF-OprN were not Decitabine concentration observed

among the clinical isolates of P. aeruginosa evaluated in this study. Overall, 69.5% and 11.9% of P. aeruginosa clinical isolates studied showed decreased oprD expression (from 0.1- to 0.7-fold compared to PAO1), and overexpression of ampC (from 14- to 402-fold compared to PAO1), respectively. None of the investigated resistance determinants was identified in 11.8% of clinical isolates (n = 7, Table 2). Among the isolates overexpressing the mexY efflux gene, 86.7% were not susceptible to amikacin, gentamicin and ciprofloxacin. Cefepime non-susceptibility was observed in 80% of isolates overexpressing mexY. Of those, 79.2% also presented reduced oprD transcription, 54.2% were MBL-producers, 12.5% produced the ESBL GES-1, and 16.7% showed increased ampC transcriptional P505-15 order levels (data not shown). Among the cefepime non-susceptible isolates that did not show mexY overexpression, 33.3% produced SPM-1, 33.3% overexpressed ampC, 16.7% produced the ESBL CTX-M-2, and 16.7% produced GES-5, an ESBL with carbapenemase activity. Meropenem non-susceptibility was observed among 62.5% of isolates overexpressing mexB (from 2.1- to 5.5-fold higher than PAO1).

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