Activity of minocycline against Klebsiella pneumoniae carbapenemase (KPC)-producing Enterobacteriaceae clinical isolates, with comparison to doxycycline and tigecycline

Guidelines for Antibacterial Treatment of Carbapenem-Resistant Enterobacterales Infections

This guideline aims to promote the prudent use of antibacterial agents for managing carbapenem-resistant Enterobacterales (CRE) infections in clinical practice in Korea. The general section encompasses recommendations for the management of common CRE infections and diagnostics, whereas each specific section is structured with key questions that are focused on antibacterial agents and disease-specific approaches. This guideline covers both currently available and upcoming antibacterial agents in Korea.

Fosfomycin Disk Diffusion Testing among Klebsiella pneumoniae Results in Frequent Inner Colonies and Categorical Disagreement Based on Conflicting Breakpoint Organization Recommendations

Recent studies indicate that discrete inner colonies (ICs) arise during fosfomycin disk diffusion (DD) testing. CLSI and EUCAST have contradicting recommendations on the interpretation of ICs; CLSI recommends considering them while EUCAST recommends ignoring them when interpreting DD results. We sought to compare the categorical agreement of DD and agar dilution (AD) MIC and to assess the implications of ICs interpretation on zone diameter readings. A convenience sample of 80 Klebsiella pneumoniae clinical isolates with varied phenotypic profiles collected from 3 United States locations was included. Susceptibility was determined in duplicate, using both organization recommendations and interpretations for Enterobacterales. Correlations between methods were calculated using EUCASTIV AD as the reference method. MIC values ranged from 1 to >256 μg/mL with an MIC50/90 of 32/256 μg/mL. Extrapolating EUCASToral and CLSI AD Escherichia coli breakpoints, 12.5% and 83.8% of isolates were susceptible, respectively, whereas 66.3% were susceptible by EUCASTIV AD-which applies to K. pneumoniae. CLSI DD measurements were 2 to 13 mm smaller than EUCAST measurements due to 66 (82.5%) isolates producing discrete ICs. Categorical agreement with EUCASTIV AD was greatest for CLSI AD (65.0%) and poorest for EUCASToral DD (6.3%). Isolates among this collection were frequently classified into different interpretive categories based on varying breakpoint organization recommendations. The more conservative oral breakpoints of EUCAST resulted in more isolates categorized as resistant despite frequent ICs. Differing zone diameter distributions and poor categorical agreement highlight issues of extrapolating E. coli breakpoints and methods to other Enterobacterales, and the clinical relevance of this issue warrants further investigation. IMPORTANCE Fosfomycin susceptibility testing recommendations are complex. Both the Clinical and Laboratory Standards Institute and the European Committee on Antimicrobial Susceptibility Testing (EUCAST) recognize agar dilution as the reference method, but they also support disk diffusion as an approved method for Escherichia coli. However, these two organizations have conflicting recommendations for the interpretation of inner colonies that arise during disk diffusion testing which can lead to varying zone diameters and interpretations despite isolates having identical MIC values. Using a collection of 80 Klebsiella pneumoniae isolates, we found that a large (82.5%) portion produced discrete inner colonies during disk diffusion and isolates were frequently classified into different interpretive categories. The more conservative breakpoints of EUCAST resulted in more isolates categorized as resistant despite frequent inner colonies. Differing zone diameter distributions and poor categorical agreement highlight issues of extrapolating E. coli breakpoints and methods to other Enterobacterales, and the clinical relevance of this issue warrants further investigation.

The antimicrobial peptide DGL13K is active against drug-resistant gram-negative bacteria and sub-inhibitory concentrations stimulate bacterial growth without causing resistance

Antimicrobial peptides may be alternatives to traditional antibiotics with reduced bacterial resistance. The antimicrobial peptide GL13K was derived from the salivary protein BPIFA2. This study determined the relative activity of the L-and D-enantiomers of GL13K to wild-type and drug-resistant strains of three gram-negative species and against Pseudomonas aeruginosa biofilms. DGL13K displayed in vitro activity against extended-spectrum beta-lactamase (ESBL)-producing and Klebsiella pneumoniae carbapenemase (KPC)-producing Klebsiella pneumoniae (MICs 16-32 μg/ml), MDR and XDR P. aeruginosa, and XDR Acinetobacter baumannii carrying metallo-beta-lactamases (MICs 8-32 μg/ml). P. aeruginosa showed low inherent resistance to DGL13K and the increased metabolic activity and growth caused by sub-MIC concentrations of GL13K peptides did not result in acquired bacterial resistance. Daily treatment for approximately two weeks did not increase the MIC of DGL13K or cause cross-resistance between LGL13K and DGL13K. These data suggest that DGL13K is a promising antimicrobial peptide candidate for further development.

Emerging Treatment Options for Multi-Drug-Resistant Bacterial Infections

Antimicrobial resistance (AMR) remains one of the top public health issues of global concern. Among the most important strategies for AMR control there is the correct and appropriate use of antibiotics, including those available for the treatment of AMR pathogens. In this article, after briefly reviewing the most important and clinically relevant multi-drug-resistant bacteria and their main resistance mechanisms, we describe the emerging antimicrobial options for both MDR Gram-positive cocci and Gram-negative bacilli, including recently marketed agents, molecules just approved or under evaluation and rediscovered older antibiotics that have regained importance due to their antimicrobial spectrum. Specifically, emerging options for Gram-positive cocci we reviewed include ceftaroline, ceftobiprole, tedizolid, dalbavancin, and fosfomycin. Emerging treatment options for Gram-negative bacilli we considered comprise ceftolozane-tazobactam, ceftazidime-avibactam, meropenem-vaborbactam, imipenem-relebactam, aztreonam-avibactam, minocycline, fosfomycin, eravacycline, plazomicin, and cefiderocol. An exciting scenario is opening today with the long awaited growing availability of novel molecules for the treatment of AMR bacteria. Knowledge of mechanisms of action and resistance patterns allows physicians to increasingly drive antimicrobial treatment towards a precision medicine approach. Strict adherence to antimicrobial stewardship practices will allow us to preserve the emerging antimicrobials for our future.

Mechanisms of Antibiotic Resistance in Important Gram-Positive and Gram-Negative Pathogens and Novel Antibiotic Solutions

Multidrug-resistant bacteria have on overwhelming impact on human health, as they cause over 670,000 infections and 33,000 deaths annually in the European Union alone. Of these, the vast majority of infections and deaths are caused by only a handful of species-multi-drug resistant Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, Enterococcus spp., Acinetobacter spp. and Klebsiella pneumoniae. These pathogens employ a multitude of antibiotic resistance mechanisms, such as the production of antibiotic deactivating enzymes, changes in antibiotic targets, or a reduction of intracellular antibiotic concentration, which render them insusceptible to multiple antibiotics. The purpose of this review is to summarize in a clinical manner the resistance mechanisms of each of these 6 pathogens, as well as the mechanisms of recently developed antibiotics designed to overcome them. Through a basic understanding of the mechanisms of antibiotic resistance, the clinician can better comprehend and predict resistance patterns even to antibiotics not reported on the antibiogram and can subsequently select the most appropriate antibiotic for the pathogen in question.

Omadacycline: A Novel Oral and Intravenous Aminomethylcycline Antibiotic Agent

Omadacycline is a novel aminomethylcycline antibiotic developed as a once-daily, intravenous and oral treatment for acute bacterial skin and skin structure infection (ABSSSI) and community-acquired bacterial pneumonia (CABP). Omadacycline, a derivative of minocycline, has a chemical structure similar to tigecycline with an alkylaminomethyl group replacing the glycylamido group at the C-9 position of the D-ring of the tetracycline core. Similar to other tetracyclines, omadacycline inhibits bacterial protein synthesis by binding to the 30S ribosomal subunit. Omadacycline possesses broad-spectrum antibacterial activity against Gram-positive and Gram-negative aerobic, anaerobic, and atypical bacteria. Omadacycline remains active against bacterial isolates possessing common tetracycline resistance mechanisms such as efflux pumps (e.g., TetK) and ribosomal protection proteins (e.g., TetM) as well as in the presence of resistance mechanisms to other antibiotic classes. The pharmacokinetics of omadacycline are best described by a linear, three-compartment model following a zero-order intravenous infusion or first-order oral administration with transit compartments to account for delayed absorption. Omadacycline has a volume of distribution (V_d) ranging from 190 to 204 L, a terminal elimination half-life (t_½) of 13.5-17.1 h, total clearance (CL_T) of 8.8-10.6 L/h, and protein binding of 21.3% in healthy subjects. Oral bioavailability of omadacycline is estimated to be 34.5%. A single oral dose of 300 mg (bioequivalent to 100 mg IV) of omadacycline administered to fasted subjects achieved a maximum plasma concentration (C_max) of 0.5-0.6 mg/L and an area under the plasma concentration-time curve from 0 to infinity (AUC_0-∞) of 9.6-11.9 mg h/L. The free plasma area under concentration-time curve divided by the minimum inhibitory concentration (i.e., fAUC_24h/MIC), has been established as the pharmacodynamic parameter predictive of omadacycline antibacterial efficacy. Several animal models including neutropenic murine lung infection, thigh infection, and intraperitoneal challenge model have documented the in vivo antibacterial efficacy of omadacycline. A phase II clinical trial on complicated skin and skin structure infection (cSSSI) and three phase III clinical trials on ABSSSI and CABP demonstrated the safety and efficacy of omadacycline. The phase III trials, OASIS-1 (ABSSSI), OASIS-2 (ABSSSI), and OPTIC (CABP), established non-inferiority of omadacycline to linezolid (OASIS-1, OASIS-2) and moxifloxacin (OPTIC), respectively. Omadacycline is currently approved by the FDA for use in treatment of ABSSSI and CABP. Phase II clinical trials involving patients with acute cystitis and acute pyelonephritis are in progress. Mild, transient gastrointestinal events are the predominant adverse effects associated with use of omadacycline. Based on clinical trial data to date, the adverse effect profile of omadacycline is similar to studied comparators, linezolid and moxifloxacin. Unlike tigecycline and eravacycline, omadacycline has an oral formulation that allows for step-down therapy from the intravenous formulation, potentially facilitating earlier hospital discharge, outpatient therapy, and cost savings. Omadacycline has a potential role as part of an antimicrobial stewardship program in the treatment of patients with infections caused by antibiotic-resistant and multidrug-resistant Gram-positive [including methicillin-resistant Staphylococcus aureus (MRSA)] and Gram-negative pathogens.

KPC-producing Klebsiella pneumoniae bloodstream isolates from Brazilian hospitals: What (still) remains active?

OBJECTIVES

This study assessed susceptibility to polymyxin B (PMB) and alternative antimicrobials, with focus on aminoglycosides and tigecycline, according to different breakpoints in KPC-producing Klebsiella pneumoniae (KPC-Kp) bloodstream isolates from Brazilian hospitals.

METHODS

Bloodstream K. pneumoniae isolates non-susceptible to any of the three carbapenems (meropenem, imipenem or ertapenem) from four Brazilian tertiary-care hospitals were selected. Antimicrobial susceptibility was determined and interpreted according to distinct breakpoints. Twenty-nine PMB-resistant KPC-Kp isolates were selected for molecular typing.

RESULTS

A total of 158 KPC-Kp were analysed. MIC_50/90 values for PMB were 0.25/16mg/L; 40 isolates (25.3%) were resistant to PMB. MIC_50/90 values for meropenem were 32/≥256mg/L; no isolates were susceptible to meropenem according to CLSI, but 10 isolates were intermediate using EUCAST breakpoints (1, MIC=4mg/L; 9, MIC=8mg/L). MIC_50/90 values for tigecycline were 2/8mg/L; 53 (33.5%) and 94 (59.5%) isolates were susceptible according to EUCAST and FDA breakpoints, respectively. MIC_50/90 values were 32/≥64mg/L for amikacin and ≥16/≥16mg/L for gentamicin; 48 (30.4%), 28 (17.7%) and 16 (10.1%) were susceptible to amikacin according to CLSI, EUCAST and USCAST, respectively, but susceptibility rates to gentamicin were <7.0%. Eighteen distinct clonal profiles were identified among 29 PMB-resistant isolates by DNA macrorestriction. Most clones belonged to CC11.

CONCLUSION

Elevated rates of PMB-resistant KPC-Kp bloodstream infections were found in four Brazilian hospitals, mostly of polyclonal origin. Alternative antimicrobials with the highest in vitro activity were tigecycline and amikacin, although susceptibility rates significantly decreased using criteria with stricter breakpoints (e.g. EUCAST, USCAST).