Pharmacodynamics of colistin resistance in carbapenemase-producing Klebsiella pneumoniae: the double-edged sword of heteroresistance and adaptive resistance.

Introduction. The presence of heteroresistant subpopulations and the development of resistance during drug exposure (adaptive resistance) limits colistin's efficacy against carbapenemase-producing Klebsiella pneumoniae (CP-Kp) isolates.Hypothesis/Gap statement. The pharmacokinetic/pharmacodynamic (PK/PD) characteristics of both types of colistin resistance against CP-Kp are unknown.Aim. We therefore studied the PK/PD characteristics of colistin resistance in an in vitro PK/PD model simulating clinical colistin exposures.Methods. Two K. pneumoniae clinical isolates, one non-CP-Kp and one CP-Kp, with colistin MICs of 0.5-1 mg l-1 at a final inoculum of 107 c.f.u. ml-1 were used in an in vitro PK/PD dialysis/diffusion closed model simulating 4.5 MU q12h and 3 MU q8h clinical dosing regimens. Heteroresistant (HRS, bacteria with stable high-level resistance present before drug exposure) and adaptive resistant (ARS, bacteria with reversible low-level resistance emerging after drug exposure) subpopulations were measured and optimal PK/PD targets for reducing both ARS and HRS were determined. Cumulative fractional response (CFR) was calculated with Monte Carlo simulation for 9 MU q24h, 4.5 MU q12h and 3 MU q8h clinical dosing regimens.Results. A 2-5 log10c.f.u. ml-1 decrease of the total bacterial population was observed within the first 2 h of exposure, followed by regrowth at 12 h. Colistin exposure was positively and negatively correlated with HRS and ARS 24-0 h c.f.u. ml-1 changes, respectively. An optimal PK/PD (~0.5log10 increase) target of 35 fAUC/MIC (the ratio of the area under the unbound concentration-time curve to the MIC) was found for reducing both HRS and ARS of high-level resistance (MIC >16 mg l-1). The 4.5 MU q12h regimen had slightly higher CFR (74 %) compared to the other dosing regimens.Conclusions. High colistin exposures reduced high-level adaptive resistance at the expense of selection of heteroresistant subpopulations.

In vitro comparative activity of the new beta-lactamase inhibitor taniborbactam with cefepime or meropenem against Klebsiella pneumoniae and cefepime against Pseudomonas aeruginosa metallo-beta-lactamase-producing clinical isolates.

Metallo-beta-lactamase (MBL)-producing Gram-negative bacteria are increasing worldwide and very few agents are active against these pathogens. Taniborbactam (formerly VNRX-5133) is a newly developed bicyclic boronate beta-lactamase inhibitor that directly inhibits all four Ambler classes of beta-lactamases. In the present study the in vitro activity of cefepime or meropenem combined with taniborbactam against 100 Klebsiella pneumoniae and cefepime combined with taniborbactam against 100 Pseudomonas aeruginosa molecularly characterized MBL-producing strains were investigated using ISO standard broth microdilution assays and compared with a panel of antimicrobial agents that are used in clinical practice (amikacin, aztreonam, ciprofloxacin, levofloxacin, gentamicin, piperacillin/tazobactam, imipenem, tigecycline, ceftolozane-tazobactam, cefepime-tazobactam, meropenem-vaborbactam, ceftazidime-avibactam). For K. pneumoniae isolates, the MIC90 values were ≥64 mg/L for all drugs except cefepime-taniborbactam (16 mg/L; 87% inhibited at ≤8/4 mg/L), meropenem-taniborbactam (4 mg/L; 94% inhibited at ≤8/4 mg/L) and tigecycline (8 mg/L), with high levels of resistance (≥65%) found for all approved comparator antimicrobials tested. For P. aeruginosa, the MIC90 values were ≥64 mg/L for all drugs except aztreonam (32 mg/L), cefepime-taniborbactam (32 mg/L; 88% inhibited at ≤16/4 mg/L) and ciprofloxacin (32 mg/L), with high levels of resistance (≥73%) for all approved drugs except aztreonam (27%). Taniborbactam reduced cefepime and meropenem MICs by a median 5 and 7 two-fold dilutions to ≤8 mg/L in 87% and 94% of MBL-producing K. pneumoniae isolates, and cefepime MICs by a median 5 two-fold dilutions to ≤16 mg/L in 86% of MBL-producing P. aeruginosa, respectively. The combinations cefepime-taniborbactam and meropenem-taniborbactam are promising alternative treatment options for infections by MBL-producing isolates.

Activity of vancomycin, linezolid, and daptomycin against staphylococci and enterococci isolated in 5 Greek hospitals during a 5-year period (2008-2012).

The tendency of vancomycin, linezolid, and daptomycin MICs was investigated among 6920 staphylococci and enterococci during a 5-year period. Antimicrobial consumption was determined. Decrease of vancomycin MIC was detected associated with reduction in consumption. Linezolid and daptomycin remained active. An upward trend of linezolid MIC for methicillin-resistant staphylococci was observed.

Molecular characterization of Streptococcus agalactiae from vaginal colonization and neonatal infections: a 4-year multicenter study in Greece.

A multicenter collection comprising of 171 Streptococcus agalactiae isolates from pregnant women recovered between 2007 and 2010 and 46 from unmatched neonates with invasive infections was subjected to antimicrobial susceptibility testing and genetic characterization. High rates of erythromycin resistance (20.47%) were observed only in isolates from pregnant women. ST1 was dominant in the vaginal colonization, whereas the hypervirulent ST-17 clone was detected in 67.39% of neonatal infections.

Molecular detection and identification of enteroviruses in children admitted to a university hospital in Greece.

Although enteroviral infections occur frequently during childhood, the circulation of particular serotypes has never been studied in Greece. The objectives of the present report were molecular detection and identification of human enteroviruses in children admitted with nonspecific febrile illness or meningitis to a university hospital during a 22-month period. A one-step Real-Time RT-PCR protocol was used for rapid enterovirus detection in genetic material extracted directly from clinical samples, and a sensitive reverse transcription-semi-nested PCR targeting part of the VP1-coding region was used for genotypic identification of the different serotypes. Twenty-one enterovirus strains were detected and identified in 20 stool samples, one cerebrospinal fluid (CSF) sample, one whole blood sample and one throat swab from 21 out of 134 febrile patients (15.7%). Ten strains belonged to Human Enterovirus Species B (HEV-B) (six serotypes) and eleven to HEV-A (four serotypes). Most of the strains were closely associated with virulent strains circulating in Europe and elsewhere. Detection of the emerging pathogen enterovirus 71 for a first time in Greece was particularly important.

An outbreak of infection due to beta-Lactamase Klebsiella pneumoniae Carbapenemase 2-producing K. pneumoniae in a Greek University Hospital: molecular characterization, epidemiology, and outcomes.

BACKGROUND: We describe the emergence and spread of Klebsiella pneumoniae carbapenemase 2 (KPC-2)-producing K. pneumoniae at a Greek University hospital. METHODS: Isolates with a carbapenem minimum inhibitory concentration >1 microg/mL and a negative EDTA-imipenem disk synergy test result were submitted to boronic acid disk test and to polymerase chain reaction (PCR) for KPC gene and sequencing. Records from patients who had KPC-2-producing K. pneumoniae isolated were retrospectively reviewed. Clinical isolates were submitted to molecular typing using pulsed-field gel electrophoresis, and the beta-lactamase content was studied using isoelectric focusing and PCR. RESULTS: From January 2007 through December 2008, 50 patients (34 in the intensive care unit [ICU]) were colonized (n = 32) or infected (n = 18) by KPC-2-producing K. pneumoniae. Increasing prevalence of KPC-2-producing K. pneumoniae coincided with decreasing prevalence of metallo-beta lactamase-producing isolates in our ICU. Multidrug resistance characterized the studied isolates, with colistin, gentamicin, and fosfomycin being the most active agents. Besides KPC-2, clinical isolates encoded TEM-1-like, SHV-11, SHV-12, CTX-M-15, and LEN-19 enzymes. Four different clonal types were detected; the predominant one comprised 41 single patient isolates (82%). Sporadic multiclonal cases of KPC-2-producing K. pneumoniae infection were identified from September 2007 through May 2008. The outbreak strain was introduced in February 2008 and disseminated rapidly by cross-transmission; 38 patients (76%) were identified after August 2008. Fourteen cases of bacteremia, 2 surgical site infections, 2 lower respiratory tract infections (1 bacteremic), and 1 urinary tract infection were identified. Most patients received a colistin-containing combination treatment. Crude mortality was 58.8% among ICU patients and 37.5% among non-ICU patients, but attributable mortality was 22.2% and 33.3%, respectively. CONCLUSIONS: The emergence of KPC-2-producing K. pneumoniae in Greek hospitals creates an important challenge for clinicians and hospital epidemiologists, because it is added to the already high burden of antimicrobial resistance.

Novel GES/IBC extended-spectrum beta-lactamase variants with carbapenemase activity in clinical enterobacteria.

Two clinical isolates, an Escherichia coli and a Klebsiella pneumoniae, with decreased susceptibility to carbapenems were studied. This phenotype was associated with production of novel GES/IBC variant beta-lactamases, designated GES-3 (from E. coli) and GES-4 (from K. pneumoniae), exhibiting carbapenemase activity. Both enzymes possessed Ser at Ambler's position 170 instead of Gly found in the beta-lactamases GES-1 and IBC-1 that lack carbapenemase activity. Additionally, position 104 in GES-4 was occupied by a Lys as in IBC-1. bla(GES-3) and bla(GES-4) occurred as gene cassettes in the variable regions of class 1 integrons carried by plasmids. The structure of the GES-4-encoding integron was similar to that of previously described IBC-1 integrons. The GES-3-encoding integron was, most likely, truncated at the 3' conserved segment.