Activity of Antimicrobial Combinations against KPC-2-Producing Klebsiella pneumoniae in a Rat Model and Time-Kill Assay

Abstract

f This study evaluated the efficacy of tigecycline (TIG), polymyxin B (PMB), and meropenem (MER) in 80 rats challenged with Klebsiella pneumoniae carbapenemase (KPC)-producing K. pneumoniae infection. A time-kill assay was performed with the same strain. Triple therapy and PMB؉TIG were synergistic, promoted 100% survival, and produced negative peritoneal cultures, while MER؉TIG showed lower survival and higher culture positivity than other regimens (P ‫؍‬ 0.018) and was antagonistic. In vivo and in vitro studies showed that combined regimens, except MER؉TIG, were more effective than monotherapies for this KPC-producing strain. Infections due to Klebsiella pneumoniae carbapenemase (KPC)-producing Enterobacteriaceae are associated with therapeutic failure and increased mortality (1-5). It has been suggested that antibiotic combination might be a better alternative compared to monotherapy for treatment of KPC-producing isolates (4-9); however, further investigation on this therapeutic strategy is required (10, 11).In the present study, we evaluated the efficacy of regimes for a KPC-producing K. pneumoniae strain in an experimental model of systemic infection and in a time-kill assay (TKA).A KPC-producing K. pneumoniae strain, coded RM-1209, was isolated from a patient's blood and identified by Vitek 2 (bioMérieux, Craponne, France) in 2012. Antibiotic MICs were determined by agar dilution and interpreted according to CLSI and EUCAST for tigecycline (TIG) (12, 13). The strain presented MICs of Ͼ32 mg/liter, 1 mg/liter, and 0.5 mg/liter for meropenem (MER), tigecycline, and polymyxin B (PMB), respectively. Detection of the bla KPC gene was performed with BigDye v1.1 Sequencing kits (Applied Biosystems, Foster City, CA, USA), and KPC-2 was confirmed at databases queried by NCBI BLAST (6).The study was approved by the ethical committee, according to the Protocol for the Protection and Welfare of Animals (European Union). The animal model has been previously described (13). In brief, male and female immunocompetent Wistar rats weighing between 190 and 300 g were randomized into each treatment group. Absence of immunosuppression demanded administration of highly concentrated inoculums with 1.5 ϫ 10 10 CFU/ml. This solution, when diluted 1:20 presents an absorbance of 0.546 at 625 nm wavelength on spectrophotometry (corresponding to tube 50 of nephelometric scale). Seven groups of 10 rats were treated with the following regimens: MER, TIG, PMB, MERϩPMB, MERϩTIG, PMBϩTIG, or PMBϩMERϩTIG. Ten rats were untreated (control group). The sample size (80 rats) was calculated using the formula n ϭ z2PQ/d2 based on the expected proportion of deaths (50%) and 8% standard error with an 80% statistical power.Animals were injected with a 0.7-ml intraperitoneal aliquot of 1.5 ϫ 10 10 CFU/ml KPC-producing K. pneumoniae inoculum in the log growth state (14). After infection, rats received antimicrobials intraperitoneally, TIG (Tygacil) at 7 mg/kg of body weight every 12 h (15, 16), PMB (polymyxin B) at 2 mg/kg every 12 h (17, 18), or MER ...

Polymyxin B in Combination with Rifampin and Meropenem against Polymyxin B-Resistant KPC-Producing Klebsiella pneumoniae

“…This is in agreement with data from other in vitro studies that evaluated PB s KPC-producing K. pneumoniae isolates and detected synergy between polymyxin B and meropenem (21,28). The combination of polymyxin B and meropenem has also been shown to significantly reduce mortality in infected rats compared to either agent as monotherapy (29).…”

Global Dissemination of Carbapenemase-Producing Klebsiella pneumoniae: Epidemiology, Genetic Context, Treatment Options, and Detection Methods

“…The synergistic combination of colistin and rifampin was also effective in the treatment of colistin-resistant KPC-producing K. pneumoniae by slowing the selection of heteroresistant subpopulations during colistin therapy ( Tascini et al, 2013 ). However, several reports have shown that combination therapy was not superior to monotherapy ( de Oliveira et al, 2015 ; Toledo et al, 2015 ). Thus, extensive studies will be required to assess the effectiveness of combination therapy.…”

The “Old” and the “New” Antibiotics for MDR Gram-Negative Pathogens: For Whom, When, and How

“…Before the advent of the new antimicrobials listed in the next section, possible companions were limited to colistin and meropenem (25, 69, 76). Tigecycline-colistin or -polymyxin B combinations have shown in vitro and in vivo synergy in animal model studies with KPC-2 (77–81). Real life data on colistin-tigecycline combination were captured in the INCREMENT retrospective cohort, in which high-risk patients with CRE-BSI on tigecycline-containing combinations (79 patients) had lower mortality compared with those who received colistin monotherapy (27).…”