Abstract
Carbapenem-resistant Klebsiella pneumoniae (CRKP) is becoming increasingly problematic due to the limited effectiveness of new antimicrobials or other factors such as treatment cost. Thus, combination therapy remains a suitable treatment option. We aimed to evaluate the in vitro bactericidal activity of various antibiotic combinations against CRKP with different carbapenemase genotypes and sequence types (STs). Thirty-seven CRKP with various STs and carbapenemases were exposed to 11 antibiotic combinations (polymyxin B or tigecycline in combination with β-lactams including aztreonam, cefepime, piperacillin/tazobactam, doripenem, meropenem, and polymyxin B with tigecycline) in static time-kill studies (TKS) using clinically achievable concentrations. Out of the 407 isolate-combination pairs, only 146 (35.8%) were bactericidal (≥3 log10CFU/mL decrease from initial inoculum). Polymyxin B in combination with doripenem, meropenem, or cefepime was the most active, each demonstrating bactericidal activity in 27, 24, and 24 out of 37 isolates, respectively. Tigecycline in combination with β-lactams was rarely bactericidal. Aside from the lower frequency of bactericidal activity in the dual-carbapenemase producers, there was no apparent difference in combination activity among the strains with other carbapenemase types. In addition, bactericidal combinations were varied even in strains with similar STs, carbapenemases, and other genomic characteristics. Our findings demonstrate that the bactericidal activity of antibiotic combinations is highly strain-specific likely owing to the complex interplay of carbapenem-resistance mechanisms, i.e., carbapenemase genotype alone cannot predict in vitro bactericidal activity. The availability of WGS information can help rationalize the activity of certain combinations. Further studies should explore the use of genomic markers with phenotypic information to predict combination activity.
Highlights
MATERIALS AND METHODSKlebsiella pneumoniae are common Gram-negative pathogens that are implicated in a variety of infections including pneumonia, bloodstream infections, and skin/soft tissue infections
Polymyxin B and tigecycline resistance were observed in nine (24.3%) and four (10.8%) isolates, respectively, of which one isolate was resistant to both polymyxin B and tigecycline (EC301)
As the understanding of the mechanisms behind the bactericidal/synergistic/additive effect of combinations remains poor, we evaluated 37 carbapenem-resistant K. pneumoniae (CRKP) isolates with differing carbapenemase genotypes against 11 two-antibiotic combinations in this study
Summary
MATERIALS AND METHODSKlebsiella pneumoniae are common Gram-negative pathogens that are implicated in a variety of infections including pneumonia, bloodstream infections, and skin/soft tissue infections. As one of the ESKAPE organisms, it possesses the ability to acquire multiple resistance mechanisms to the various drug classes and is a major contributor to nosocomial infections (Rice, 2010). Resistance to carbapenems, one of the last-line antimicrobial agents, in these bacteria has resulted in very limited treatment options for these infections. Multiple in vitro studies evaluating combination therapy in CRKP infections have been conducted with varying results (Lenhard et al, 2016). We have shown that antibiotic combinations were highly strain-specific in extensively drug-resistant NDMproducing K. pneumoniae (Lim et al, 2015), while in vitro synergy of double carbapenem combinations have been widely demonstrated, albeit primarily in KPC-producing K. pneumoniae (Bulik and Nicolau, 2011; Chua et al, 2015; Oliva et al, 2016)
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