Insight into Antibiotic Synergy Combinations for Eliminating Colistin Heteroresistant Klebsiella pneumoniae

Abstract

Colistin heteroresistance has been identified in several bacterial species, including Escherichia coli and Klebsiella pneumoniae, and may underlie antibiotic therapy failures since it most often goes undetected by conventional antimicrobial susceptibility tests. This study utilizes population analysis profiling (PAP) and time–kill assay for the detection of heteroresistance in K. pneumoniae and for evaluating the association between in vitro regrowth and heteroresistance. The mechanisms of colistin resistance and the ability of combination therapies to suppress resistance selection were also analysed. In total, 3 (18%) of the 16 colistin-susceptible strains (MIC ≤ 2 mg/L) were confirmed to be heteroresistant to colistin by PAP assay. In contrast to the colistin-susceptible control strains, all three heteroresistant strains showed regrowth when exposed to colistin after 24 h following a rapid bactericidal action. Colistin resistance in all the resistant subpopulations was due to the disruption of the mgrB gene by various insertion elements such as ISKpn14 of the IS1 family and IS903B of the IS5 family. Colistin combined with carbapenems (imipenem, meropenem), aminoglycosides (amikacin, gentamicin) or tigecycline was found to elicit in vitro synergistic effects against these colistin heteroresistant strains. Our experimental results showcase the potential of combination therapies for treatment of K. pneumoniae infections associated with colistin heteroresistance.

Assessment of Colistin Heteroresistance among Multidrug-Resistant Klebsiella pneumoniae Isolated from Intensive Care Patients in Europe

“…Isolates AN1505CP2 and IT0244CP were previously already determined to be CHR [ 16 ]. In this study, these findings were confirmed with both isolates fulfilling C1, and colonies from each plate were sequenced (data not published).…”

“…An isolate was classified as susceptible (MIC ≤ 2 mg/L) or resistant (MIC > 2 mg/L) based on the epidemiological cut-off (ECOFF) values provided by EUCAST [ 15 ]. Two CS strains, Escherichia coli ATCC 25922 (MIC: 0.25–2 mg/L) and P. aeruginosa ATCC 27853 (MIC: 0.5–4 mg/L), and two CR strains, K. pneumoniae 08400 (MIC: 64 mg/L) and E. coli NCTC 13846 mcr-1 positive (MIC: 4 mg/L), were used as controls [ 16 ].…”

“…The number of colonies were counted after 24 h of aerobic incubation of the plates at 37 °C, and a graph of the log 10 CFU/mL was plotted against the increasing colistin concentrations. One CS strain, E. coli ATCC 25922 (MIC: 0.25–2 mg/L), one CR strain, K. pneumoniae 08400 (MIC: 64 mg/L), and two CHR strains, K. pneumoniae ATCC 13883 (MIC: 1 mg/L) and K. pneumoniae IT0244CP (MIC: 0.5 mg/L), were used as quality controls [ 16 ].…”