Characterization of porin expression in Klebsiella pneumoniae carbapenemase

23 We characterized carbapenem resistance mechanisms among 12 Klebsiella 24 pneumoniae carbapenemase-producing K. pneumoniae (KPC-Kp) clinical isolates, and 25 evaluated their effects on the activity of 2and 3-drug combinations of colistin, 26 doripenem and ertapenem. All isolates were resistant to ertapenem and doripenem; 27 75% (9/12) were resistant to colistin. Isolates belonged to ST258 clonal group, and 28 harbored blaKPC-2, blaSHV-12, and blaTEM-1. By time-kills, doripenem (8 μg/ml) and 29 ertapenem (2 μg/ml) were inactive against 92% (11/12) and 100% (12/12) of isolates, 30 respectively. Colistin (2.5 μg/ml) exerted bactericidal effects (range: 0.39-2.5 log10) 31 against 78% (7/9) of colistin-resistant isolates. Colistin-ertapenem, colistin-doripenem 32 and colistin-doripenem-ertapenem exhibited synergy against 42% (5/12), 50% (6/12) 33 and 67% (8/12) of isolates, respectively. Expression of ompK35 and ompK36 porins 34 correlated with each other (R = 0.80). Levels of porin expression did not correlate with 35 colistin-doripenem or colistin–ertapenem synergy. However, synergy with colistin36 doripenem-ertapenem was more likely against isolates with high porin expression than 37 low expression (100% (8/8) vs 0% (0/4); p=0.002). Moreover, bactericidal activity (area 38 under the bacterial killing curve) against isolates with high porin expression was greater 39 for colistin-doripenem-ertapenem than colistin-doripenem or colistin-ertapenem 40 (p≤0.049). In conclusion, colistin-carbapenem combinations may provide optimal 41 activity against KPC-Kp, including colistin-resistant isolates. Screening for porin 42 expression may identify isolates that are most likely to respond to a triple combination of 43 colistin-doripenem-ertapenem. In the future, molecular characterization of KPC-Kp 44 isolates may be a practical tool for identifying effective combination regimens. 45 46 on July 0, 2017 by gest httpaac.asm .rg/ D ow nladed fom