Predicting and preventing antimicrobial resistance utilizing pharmacodynamics: part II Gram-negative bacteria

Emergence of Resistance in Klebsiella aerogenes to Piperacillin-Tazobactam and Ceftriaxone

We examined the effects of piperacillin-tazobactam (TZP) concentration and bacterial inoculum on in vitro killing and the emergence of resistance in Klebsiella aerogenes The MICs for 15 clinical respiratory isolates were determined by broth microdilution for TZP and by Etest for ceftriaxone (CRO) and cefepime (FEP). The presence of resistance in TZP-susceptible isolates (n = 10) was determined by serial passes over increasing concentrations of TZP-containing and CRO-containing agar plates. Isolates with growth on TZP 16/4-μg/ml and CRO 8-μg/ml plates (n = 5) were tested in high-inoculum (HI; 7.0 log10 CFU/ml) and low-inoculum (LI; 5.0 log10 CFU/ml) time-kill studies. Antibiotic concentrations were selected to approximate TZP 3.375 g every 8 h (q8h) via a 4-h prolonged-infusion free peak concentration (40 μg/ml [TZP40]), peak epithelial lining fluid (ELF) concentrations, and average AUC0-24 values for TZP (20 μg/ml [TZP20] and 10 μg/ml [TZP10], respectively), the ELF FEP concentration (14 μg/ml), and the average AUC0-24 CRO concentration (6 μg/ml). For HI, FEP exposure significantly reduced 24-h inocula against all comparators (P ≤ 0.05) with a reduction of 4.93 ± 0.64 log10 CFU/ml. Exposure to TZP40, TZP20, and TZP10 reduced inocula by 0.81 ± 0.43, 0.21 ± 0.18, and 0.05 ± 0.16 log10 CFU/ml, respectively. CRO-exposed isolates demonstrated an increase of 0.42 ± 0.39 log10 CFU/ml compared to the starting inocula, with four of five CRO-exposed isolates demonstrating TZP-nonsusceptibility. At LI after 24 h of exposure to TZP20 and TZP10, the starting inoculum decreased by averages of 2.24 ± 1.98 and 2.91 ± 0.50 log10 CFU/ml, respectively. TZP demonstrated significant inoculum-dependent killing, warranting dose optimization studies.

Some Suggestions from PK/PD Principles to Contain Resistance in the Clinical Setting-Focus on ICU Patients and Gram-Negative Strains

The containment of the phenomenon of resistance towards antimicrobials is a priority, especially in preserving molecules acting against Gram-negative pathogens, which represent the isolates more frequently found in the fragile population of patients admitted to Intensive Care Units. Antimicrobial therapy aims to prevent resistance through several actions, which are collectively known as “antimicrobial stewardship”, to be taken together, including the application of pharmacokinetic/pharmacodynamic (PK/PD) principles. PK/PD application has been shown to prevent the emergence of resistance in numerous experimental studies, although a straight translation to the clinical setting is not possible. Individualized antibiotic dosing and duration should be pursued in all patients, and even more especially when treating intensive care unit (ICU) septic patients in whom optimal exposure is both difficult to achieve and necessary. In this review, we report on the available data that support the application of PK/PD parameters to contain the development of resistance and we give some practical suggestions that can help to translate the benefit of PK/PD application to the bedside.

In Vitro and In Vivo Characterization of Tebipenem, an Oral Carbapenem

The continued evolution of bacterial resistance to the β-lactam class of antibiotics has necessitated countermeasures to ensure continued effectiveness in the treatment of infections caused by bacterial pathogens. One relatively successful approach has been the development of new β-lactam analogs with advantages over prior compounds in this class. The carbapenems are an example of such β-lactam analogs possessing improved stability against β-lactamase enzymes and, therefore, a wider spectrum of activity. However, all carbapenems currently marketed for adult patients are intravenous agents, and there is an unmet need for an oral agent to treat patients that otherwise do not require hospitalization. Tebipenem pivoxil hydrobromide (tebipenem-PI-HBr or SPR994) is an orally available prodrug of tebipenem, a carbapenem with activity versus multidrug-resistant (MDR) Gram-negative pathogens, including quinolone-resistant and extended-spectrum-β-lactamase-producing Enterobacterales Tebipenem-PI-HBr is currently in development for the treatment of complicated urinary tract infections (cUTI). Microbiological data are presented here that demonstrate equivalency of tebipenem with intravenous carbapenems such as meropenem and support its use in infections in which the potency and spectrum of a carbapenem are desired. The results from standard in vitro microbiology assays as well as efficacy in several in vivo mouse infection models suggest that tebipenem-PI-HBr could be a valuable oral agent available to physicians for the treatment of infections, particularly those caused by antibiotic-resistant Gram-negative pathogens.

Retrospective Screening and Analysis of mcr-1 and bla NDM in Gram-Negative Bacteria in China, 2010-2019

Currently, Gram-negative bacteria have developed multidrug and broad-spectrum drug resistance, and the numbers of species and strains carrying mcr or bla_NDM genes are increasing. In this study, mcr-1 and bla_NDM distribution of 12,858 Gram-negative bacteria isolated from wildlife, patients, livestock, poultry and environment in 14 provinces of China from 2010 to 2019 and the antibiotics resistance in regard to polymyxins (polymyxin B and colistin) and carbapenems of positive strains were investigated. A total of 70 strains of 10 species carried the mcr-1 gene, positive rates of patients, livestock and poultry, and environmental strains were 0.62% (36/5,828), 4.07% (29/712), 5.43% (5/92), respectively. Six strains of 3 species carrying the bla_NDM gene all came from patients 0.10% (6/5,828). Two new mcr-1 gene variants (GenBank: MK965883, MK965884) were identified, one of which contains premature stop codon. The drug susceptibility results showed that all mcr-1 carriers were sensitive to carbapenems, among which, 66 strains were resistant and 4 were sensitive to polymyxins. The strains with the bla_NDM gene had different degrees of resistance to carbapenems and were sensitive to polymyxins. The findings that species carrying mcr-1 or bla_NDM genes were limited and mostly normal flora of opportunistic or low pathogenic organisms indicated that transfer of mcr-1 and bla_NDM genes between bacteria was relatively limited in China. The none detection among wildlife compared with other sources supports the speculation that the emergence of and increase in polymyxins and carbapenem-resistant strains was mainly related to the selective pressure of antibiotics.

Amplification of Antimicrobial Resistance in Gut Flora of Patients Treated with Ceftriaxone

Although antibacterial therapy has an impact on human intestinal flora and the emergence of resistant bacteria, its role in the amplification of antimicrobial resistance and the quantitative exposure-effect relationship is not clear. An observational prospective study was conducted to determine whether and how ceftriaxone exposure is related to amplification of resistance in non-intensive care unit (non-ICU) patients. Serial stool samples from 122 extended-spectrum β-lactamase-positive (ESBL⁺) hospitalized patients were analyzed by quantitative real-time PCR to quantify the resistant gene bla_CTX-M Drug exposure was calculated for each patient by using a population pharmacokinetic model. Multi- and univariate regression and classification regression tree (CART) analyses were used to explore relationships between measures of exposure and amplification of bla_CTX-M genes. Amplification of bla_CTX-M was observed in 0% (0/11) of patients with no treatment and 33% (20/61) of patients treated with ceftriaxone. Stepwise regression analysis showed a significant association between amplification of bla_CTX-M and the plasma area under the concentration-time curve from 0 to 24 h for the unbound fraction of the drug (fAUC_0-24), the maximum concentration of drug in serum for the unbound fraction of the drug (fC_max), and the duration of ceftriaxone therapy. Using CART analysis, amplification of bla_CTX-M was observed in 11/16 (69%) patients treated for >14 days and in 9/40 (23%) patients treated for ≤14 days (P = 0.0019). In the latter group, amplification was observed in 5/7 (71%) patients with an fAUC_0-24 of ≥222 mg · h/liter and in 4/33 (12%) patients with lower drug exposures (P = 0.0033). A similar association was found for an fC_max of ≥30 mg/liter (63% versus 13%, P = 0.0079). A significant association was found between the amplification of bla_CTX-M resistance genes and exposure to ceftriaxone. Both duration of treatment and degree of ceftriaxone exposure have a significant impact on the amplification of resistance genes. (The project described in this paper has been registered at ClinicalTrials.gov under identifier NCT01208519.).