Assessing Clinician Utilization of Next-Generation Antibiotics Against Resistant Gram-Negative Infections in U.S. Hospitals : A Retrospective Cohort Study.

BACKGROUND: The U.S. antibiotic market failure has threatened future innovation and supply. Understanding when and why clinicians underutilize recently approved gram-negative antibiotics might help prioritize the patient in future antibiotic development and potential market entry rewards. OBJECTIVE: To determine use patterns of recently U.S. Food and Drug Administration (FDA)-approved gram-negative antibiotics (ceftazidime-avibactam, ceftolozane-tazobactam, meropenem-vaborbactam, plazomicin, eravacycline, imipenem-relebactam-cilastatin, and cefiderocol) and identify factors associated with their preferential use (over traditional generic agents) in patients with gram-negative infections due to pathogens displaying difficult-to-treat resistance (DTR; that is, resistance to all first-line antibiotics). DESIGN: Retrospective cohort. SETTING: 619 U.S. hospitals. PARTICIPANTS: Adult inpatients. MEASUREMENTS: Quarterly percentage change in antibiotic use was calculated using weighted linear regression. Machine learning selected candidate variables, and mixed models identified factors associated with new (vs. traditional) antibiotic use in DTR infections. RESULTS: Between quarter 1 of 2016 and quarter 2 of 2021, ceftolozane-tazobactam (approved 2014) and ceftazidime-avibactam (2015) predominated new antibiotic usage whereas subsequently approved gram-negative antibiotics saw relatively sluggish uptake. Among gram-negative infection hospitalizations, 0.7% (2551 [2631 episodes] of 362 142) displayed DTR pathogens. Patients were treated exclusively using traditional agents in 1091 of 2631 DTR episodes (41.5%), including "reserve" antibiotics such as polymyxins, aminoglycosides, and tigecycline in 865 of 1091 episodes (79.3%). Patients with bacteremia and chronic diseases had greater adjusted probabilities and those with do-not-resuscitate status, acute liver failure, and Acinetobacter baumannii complex and other nonpseudomonal nonfermenter pathogens had lower adjusted probabilities of receiving newer (vs. traditional) antibiotics for DTR infections, respectively. Availability of susceptibility testing for new antibiotics increased probability of usage. LIMITATION: Residual confounding. CONCLUSION: Despite FDA approval of 7 next-generation gram-negative antibiotics between 2014 and 2019, clinicians still frequently treat resistant gram-negative infections with older, generic antibiotics with suboptimal safety-efficacy profiles. Future antibiotics with innovative mechanisms targeting untapped pathogen niches, widely available susceptibility testing, and evidence demonstrating improved outcomes in resistant infections might enhance utilization. PRIMARY FUNDING SOURCE: U.S. Food and Drug Administration; NIH Intramural Research Program.

In Vitro Activity of Plazomicin Against Carbapenem Resistant Klebsiella pneumoniae Strains.

BACKGROUND: In our study, we evaluated the in vitro activities of plazomicin, amikacin, gentamicin, and tobramycin among fifty carbapenem resistant Klebsiella pneumoniae (CR-Kp) isolates. Aminoglycoside resistance genes in selected CR-Kp strains were also examined. METHODS: Minimum inhibitory concentration (MIC) of meropenem, plazomicin, tobramycin, gentamicin, and amikacin were determined by gradient test (G-test) method. In all strains carbapenemase activity was assessed by polymerase chain reaction (PCR). Aminoglycoside modifying enzyme (AME) genes in 14 CR-Kp strains that are resistant to at least one of tobramycin, gentamicin, and amikacin among fifty CR-Kp isolates, and 16S ribosomal methylase genes in 6 CR-Kp strains with plazomicin MIC ≥ 128 mg/L were investigated by PCR method. RESULTS: The most frequently detected carbapenemase enzyme in the strains in our study was OXA-48 (88%). Aminoglycoside susceptibilities of all isolates were determined; plazomicin 84%, amikacin 66%, gentamicin 50%, tobramycin 18%. The most common AME gene positivities were found, 93% (n = 13) ant(3')-I, 78% (n = 11) aac(6')-Ib, 57% (n = 8) aac(3')-IV, 42% (n = 6) aac(3')-IIa, and 29% (n = 4) aph(3')-VI. Most of the isolates examined for the presence of AME carry at least two or more AME genes. The most common 16S ribosomal methylase gene was rmtH. In our study, MIC values of ≥ 256 µg/mL were found in 6 (12%) of 50 isolates against amikacin, tobramycin, and gentamicin, including plazomicin. At least two 16S ribosomal methylase gene positivity has been shown in these 6 strains. CONCLUSIONS: In our study, increased in vitro efficacy of plazomicin was shown in CR-Kp isolates comparing to other aminoglycosides. Plazomicin is an effective treatment option against CR-Kp isolates and needs to be sup-ported by clinical studies.

Application of Population Pharmacokinetic Modeling, Exposure-Response Analysis, and Classification and Regression Tree Analysis to Support Dosage Regimen and Therapeutic Drug Monitoring of Plazomicin in Complicated Urinary Tract Infection Patients with Renal Impairment.

In 2018, the FDA approved plazomicin for the treatment of complicated urinary tract infections (cUTI) including pyelonephritis in adult patients with limited or no alternative treatment options. The objective of this article is to provide the scientific rationales behind the recommended dosage regimen and therapeutic drug monitoring (TDM) of plazomicin in cUTI patients with renal impairment. A previous population pharmacokinetic (PK) model was used to evaluate the dosage regimen in cUTI patients with different degrees of renal impairment. The exposure-response analysis was conducted to identify the relationship between plazomicin exposure and nephrotoxicity incidence in cUTI patients with renal impairment. Classification and regression tree (CART) analysis was utilized to assess the TDM strategy. The receiver operating characteristics curve was plotted to compare two TDM thresholds in cUTI patients with renal impairment. The analyses suggested that dose reduction is necessary for cUTI patients with moderate or severe renal impairment. TDM should be implemented for cUTI patients with mild, moderate, or severe renal impairment to reduce the risk of nephrotoxicity. The trough concentration of 3 µg/mL is a reasonable TDM threshold to reduce the nephrotoxicity incidence while maintaining efficacy in cUTI patients with renal impairment. The application of population PK modeling, exposure-response analysis, and CART analysis allowed for the evaluation of a dosage regimen and TDM strategy for plazomicin in cUTI patients with renal impairment. Our study demonstrates the utility of pharmacometrics and statistical approaches to inform a dosage regimen and TDM strategy for drugs with narrow therapeutic windows.

Radiolabeling, characterization, and preclinical evaluation of plazomicin: A potential tracer for bacterial infection.

In this study, 99m Tc-plazomicin, a new radio-antibiotic complex, was prepared specifically for bacterial infection localization and monitoring. Factors affecting the labeling reaction were studied and optimized to obtain a high yield (98.8 ± 0.2%). In silico, radiochemical and physicochemical characterization and biodistribution were performed to assess the complex aptness as a radiopharmaceutical. The complex was biologically evaluated in vitro using bacteria and in vivo using different inflammation models (sterile, bacterial, and fungal). Uptake in the bacterial model was highest (7.8 ± 0.3%). Results indicated that the technetium label did not alter the antibiotic biological behavior and backed the usefulness of 99m Tc-plazomicin as a potential tracer.

Epidemiology and in vitro activity of ceftazidime-avibactam, meropenem-vaborbactam, imipenem-relebactam, eravacycline, plazomicin, and comparators against Greek carbapenemase-producing Klebsiella pneumoniae isolates.

BACKGROUND: The increase in carbapenem-resistant Klebsiella pneumoniae (CRKP) infections is of great concern because of limited treatment options. New antimicrobials were recently approved for clinical therapy. This study evaluated the epidemiology of carbapenemase-producing K. pneumoniae isolates collected at a Greek university hospital during 2017-2020, and their susceptibilities to ceftazidime-avibactam (CAZ/AVI), meropenem-vaborbactam (M/V), imipenem-relebactam (I/R), eravacycline, plazomicin, and comparators. METHODS: Minimum inhibitory concentrations (MICs) were evaluated by Etest. Only colistin MICs were determined by the broth microdilution method. Carbapenemase genes were detected by PCR. Selected isolates were typed by multilocus sequence typing (MLST). RESULTS: A total of 266 carbapenemase-producing K. pneumoniae strains were isolated during the 4-year study period. Among them, KPC was the most prevalent (75.6%), followed by NDM (11.7%), VIM (5.6%), and OXA-48 (4.1%). KPC-producing isolates belonged mainly to ST258 and NDM producers belonged to ST11, whereas OXA-48- and VIM producers were polyclonal. Susceptibility to tigecycline, fosfomycin, and colistin was 80.5%, 83.8%, and 65.8%, respectively. Of the novel agents tested, plazomicin was the most active inhibiting 94% of the isolates at ≤ 1.5 µg/ml. CAZ/AVI and M/V inhibited all KPC producers and I/R 98.5% of them. All OXA-48 producers were susceptible to CAZ/AVI and plazomicin. The novel ß-lactam/ß-lactamase inhibitors (BLBLIs) tested were inactive against MBL-positive isolates, while eravacycline inhibited 61.3% and 66.7% of the NDM and VIM producers, respectively. CONCLUSIONS: KPC remains the predominant carbapenemase among K. pneumoniae, followed by NDM. Novel BLBLIs, eravacycline, and plazomicin are promising agents for combating infections by carbapenemase-producing K. pneumoniae. However, the emergence of resistance to these agents highlights the need for continuous surveillance and application of enhanced antimicrobial stewardship.

Multicenter Clinical Evaluation of ETEST Plazomicin (PLZ) for Susceptibility Testing of Enterobacterales.

Plazomicin (PLZ), brand name ZEMDRI (Cipla Therapeutics), is a novel aminoglycoside antibiotic approved by the U.S. Food and Drug Administration (FDA) for treatment of complicated urinary tract infections including pyelonephritis. ETEST® is a gradient diffusion method that represents an alternative to the more laborious broth micro-dilution (BMD) method for performing antimicrobial susceptibility testing (AST). A multi-center evaluation of the performance of the new ETEST PLZ (bioMérieux) was conducted in comparison with BMD following FDA and International Standards Organization (ISO) recommendations using FDA-defined breakpoints. Clinical isolates of Enterobacterales (n = 598) were included. Fifty-three isolates were resistant to PLZ according to BMD. Overall, the ETEST PLZ demonstrated 99.0% essential agreement (EA), 92.8% category agreement (CA), 1.9% very major errors (VME), 0% major errors (ME), and 7.0% minor errors (mE) with both clinical and challenge isolates of Enterobacterales. The VME was found for a single Serratia marcescens strain. Individual species demonstrated EA rates ≥ 90%. In conclusion, we report that ETEST PLZ represents an accurate tool for performing PLZ AST of Enterobacterales.

Comparison of in vitro activities of plazomicin and other aminoglycosides against clinical isolates of Klebsiella pneumoniae and Escherichia coli.

OBJECTIVES: To compare the in vitro activity of plazomicin and two older aminoglycosides (gentamicin and amikacin) against 180 isolates of Escherichia coli and Klebsiella pneumoniae, including subsets of 60 non-ESBL-producing, 60 ESBL-producing and 60 carbapenem-resistant (46 carrying blaOXA-48, 11 carrying blaNDM and 3 carrying blaOXA-48 and blaNDM) strains. METHODS: MICs of plazomicin, gentamicin and amikacin were determined by a gradient diffusion method. Gentamicin and amikacin MICs were interpreted according to CLSI criteria and EUCAST breakpoint tables. Plazomicin MICs were interpreted using FDA-defined breakpoints. RESULTS: All non-ESBL-producing and ESBL-producing isolates were susceptible to plazomicin. The plazomicin susceptibility rate (71.7%) in carbapenem-resistant isolates was significantly higher than those observed for gentamicin (45%) and amikacin (56.7% and 51.7% according to CLSI and EUCAST breakpoints, respectively). Gentamicin, amikacin and plazomicin susceptibility rates (35.6% for gentamicin; 44.4% and 37.8% for amikacin according to CLSI and EUCAST breakpoints, respectively; 64.4% for plazomicin) in carbapenem-resistant K. pneumoniae were significantly lower than those observed for carbapenem-resistant E. coli isolates (73.3% for gentamicin; 93.3% for amikacin and plazomicin). Gentamicin, amikacin and plazomicin susceptibility rates for blaNDM-positive isolates were lower than those observed for blaOXA-48-positive isolates, but differences were not statistically significant. Among the isolates that were non-susceptible to both gentamicin and amikacin, the plazomicin susceptibility rate was less than 30%. CONCLUSIONS: Although plazomicin showed excellent in vitro activity against carbapenem-susceptible isolates, the plazomicin resistance rate increased to 35.6% among carbapenem-resistant K. pneumoniae and further increased to 45.5% among blaNDM-positive isolates.

Plazomicin for the treatment of multidrug-resistant Klebsiella bacteraemia in a patient with underlying chronic kidney disease and acute renal failure requiring renal replacement therapy.

A 75-year-old man presented with shortness of breath and somnolence and was found to have urosepsis. Blood and urine cultures subsequently grew multidrug-resistant (MDR) Klebsiella pneumoniae (Kp) with the New Delhi metallo-ß-lactamase gene. The patient was treated successfully with plazomicin and meropenem/vaborbactam combination therapy. The course was complicated by acute kidney injury temporarily requiring haemodialysis, gastrointestinal bleed requiring multiple transfusions and hospital readmission with blood cultures again positive with MDR Kp. Plazomicin drug levels were persistently high during treatment, suggesting that therapeutic drug monitoring may be needed to safely use this drug in patients with severe renal dysfunction. This case marks the first use of plazomicin for bacteraemia in the literature outside of a clinical trial and demonstrates its safe and effective use in a patient with advanced renal disease, and provides important insights about dosing and therapeutic drug monitoring considerations in this patient population.

New Antibiotics for Multidrug-Resistant Bacterial Strains: Latest Research Developments and Future Perspectives.

The present work aims to examine the worrying problem of antibiotic resistance and the emergence of multidrug-resistant bacterial strains, which have now become really common in hospitals and risk hindering the global control of infectious diseases. After a careful examination of these phenomena and multiple mechanisms that make certain bacteria resistant to specific antibiotics that were originally effective in the treatment of infections caused by the same pathogens, possible strategies to stem antibiotic resistance are analyzed. This paper, therefore, focuses on the most promising new chemical compounds in the current pipeline active against multidrug-resistant organisms that are innovative compared to traditional antibiotics: Firstly, the main antibacterial agents in clinical development (Phase III) from 2017 to 2020 are listed (with special attention on the treatment of infections caused by the pathogens Neisseria gonorrhoeae, including multidrug-resistant isolates, and Clostridium difficile), and then the paper moves on to the new agents of pharmacological interest that have been approved during the same period. They include tetracycline derivatives (eravacycline), fourth generation fluoroquinolones (delafloxacin), new combinations between one ß-lactam and one ß-lactamase inhibitor (meropenem and vaborbactam), siderophore cephalosporins (cefiderocol), new aminoglycosides (plazomicin), and agents in development for treating drug-resistant TB (pretomanid). It concludes with the advantages that can result from the use of these compounds, also mentioning other approaches, still poorly developed, for combating antibiotic resistance: Nanoparticles delivery systems for antibiotics.

Structural and phylogenetic analyses of resistance to next-generation aminoglycosides conferred by AAC(2') enzymes.

Plazomicin is currently the only next-generation aminoglycoside approved for clinical use that has the potential of evading the effects of widespread enzymatic resistance factors. However, plazomicin is still susceptible to the action of the resistance enzyme AAC(2')-Ia from Providencia stuartii. As the clinical use of plazomicin begins to increase, the spread of resistance factors will undoubtedly accelerate, rendering this aminoglycoside increasingly obsolete. Understanding resistance to plazomicin is an important step to ensure this aminoglycoside remains a viable treatment option for the foreseeable future. Here, we present three crystal structures of AAC(2')-Ia from P. stuartii, two in complex with acetylated aminoglycosides tobramycin and netilmicin, and one in complex with a non-substrate aminoglycoside, amikacin. Together, with our previously reported AAC(2')-Ia-acetylated plazomicin complex, these structures outline AAC(2')-Ia's specificity for a wide range of aminoglycosides. Additionally, our survey of AAC(2')-I homologues highlights the conservation of residues predicted to be involved in aminoglycoside binding, and identifies the presence of plasmid-encoded enzymes in environmental strains that confer resistance to the latest next-generation aminoglycoside. These results forecast the likely spread of plazomicin resistance and highlight the urgency for advancements in next-generation aminoglycoside design.

Activity of plazomicin against carbapenem-intermediate or -resistant Escherichia coli isolates from the United States and international sites in relation to clonal background, resistance genes, co-resistance, and region.

BACKGROUND: Emerging carbapenem resistance in Escherichia coli, including sequence type 131 (ST131), threatens therapeutic efficacy. Plazomicin (PLZ), a semisynthetic aminoglycoside approved by the FDA in 2018, overcomes the most common aminoglycoside resistance mechanisms and maintains activity against many carbapenem-intermediate or -resistant (CIR) E. coli strains. OBJECTIVES: To assess plazomicin susceptibility among CIR E. coli in relation to region and multiple bacterial characteristics. METHODS: We determined broth microdilution MICs for plazomicin and 11 comparators against 343 CIR clinical E. coli isolates, then compared susceptibility results by bacterial characteristics and region. The collection comprised 203 US isolates (2002-17) and 141 isolates from 17 countries in Europe, Latin America, and the Asia-West Pacific region (2003-17). Isolates were characterized for phylogenetic group, resistance-associated sequence types (STs) and subsets thereof, and relevant ß-lactamase-encoding genes. RESULTS: Plazomicin exhibited the highest percentage susceptible (89%) after tigecycline (99%). The percentage susceptible to plazomicin varied significantly by phylogroup (63%, group B1; versus >93%, others) and ST131 subclone (92%, H30Rx; versus 87%-89%, H30R1 and non-H30), but not ST. It also varied by resistance genotype [higher with Klebsiella pneumoniae carbapenemase (KPC), lower with metallo-ß-lactamases], global region [highest for Latin America (94%), lowest for Asia-West Pacific (69%)], and US region (80%, South, versus 96%-100%, others). Although reduced susceptibility to comparators often predicted reduced susceptibility to plazomicin, even among comparator-intermediate or -resistant isolates the plazomicin-susceptible fraction was ≥77%, except for amikacin (53%). CONCLUSIONS: The likely utility of plazomicin against CIR E. coli is high overall, but varies with region and multiple bacterial characteristics.

Structural basis for plazomicin antibiotic action and resistance.

The approval of plazomicin broadened the clinical library of aminoglycosides available for use against emerging bacterial pathogens. Contrarily to other aminoglycosides, resistance to plazomicin is limited; still, instances of resistance have been reported in clinical settings. Here, we present structural insights into the mechanism of plazomicin action and the mechanisms of clinical resistance. The structural data reveal that plazomicin exclusively binds to the 16S ribosomal A site, where it likely interferes with the fidelity of mRNA translation. The unique extensions to the core aminoglycoside scaffold incorporated into the structure of plazomicin do not interfere with ribosome binding, which is analogously seen in the binding of this antibiotic to the AAC(2')-Ia resistance enzyme. The data provides a structural rationale for resistance conferred by drug acetylation and ribosome methylation, i.e., the two mechanisms of resistance observed clinically. Finally, the crystal structures of plazomicin in complex with both its target and the clinically relevant resistance factor provide a roadmap for next-generation drug development that aims to ameliorate the impact of antibiotic resistance.

Advances in novel antibiotics to treat multidrug-resistant gram-negative bacterial infections.

Antimicrobial resistance is a growing threat to public health and an increasingly common problem for acute care physicians to confront. Several novel antibiotics have been approved in the past decade to combat these infections; however, physicians may be unfamiliar with how to appropriately utilize them. The purpose of this review is to evaluate novel antibiotics active against resistant gram-negative bacteria and highlight clinical information regarding their use in the acute care setting. This review focuses on novel antibiotics useful in the treatment of infections caused by resistant gram-negative organisms that may be seen in the acute care setting. These novel antibiotics include ceftolozane/tazobactam, ceftazidime/avibactam, meropenem/vaborbactam, imipenem/cilistatin/relebactam, cefiderocol, plazomicin, eravacycline, and omadacycline. Acute care physicians should be familiar with these novel antibiotics so they can utilize them appropriately.

Comparative activity of plazomicin against extended-spectrum cephalosporin-resistant Escherichia coli clinical isolates (2012-2017) in relation to phylogenetic background, sequence type 131 subclones, blaCTX-M genotype, and resistance to comparator agents.

Extended-spectrum cephalosporin-resistant Escherichia coli (ESCREC) are a growing threat. Leading ESCREC lineages include sequence type ST131, especially its (blaCTX-M-15-associated) H30Rx subclone and (blaCTX-M-27-associated) C1-M27 subset within the H30R1 subclone. The comparative activity against such strains of alternative antimicrobial agents, including the recently developed aminoglycoside plazomicin, is undefined, so was investigated here. We assessed plazomicin and 11 comparators for activity against 216 well-characterized ESCREC isolates (Minnesota, 2012-2017) and then compared broth microdilution MICs with phylogenetic and clonal background, beta-lactamase genotype (blaCTX-M; group 1 and 9 variants), and co-resistance. Percent susceptible was > 99% for plazomicin, meropenem, imipenem, and tigecycline; 96-98% for amikacin and ertapenem; and ≤ 75% for the remaining comparators. For most comparators, MICs varied significantly in relation to multiple bacterial characteristics, in agent-specific patterns. By contrast, for plazomicin, the only bacterial characteristic significantly associated with MICs was ST131 subclone: plazomicin MICs were lowest among O16 ST131 isolates and highest among ST131-H30R1 C1-M27 subclone isolates. Additionally, plazomicin MICs varied significantly in relation to resistance vs. susceptibility to comparator agents only for amikacin and levofloxacin. For most study agents, antimicrobial activity against ESCREC varied extensively in relation to multiple bacterial characteristics, including clonal background, whereas for plazomicin, it varied only by ST131 subclone (C1-M27 isolates least susceptible, O16 isolates most susceptible). These findings support plazomicin as a reliable alternative for treating ESCREC infections and urge continued attention to the C1-M27 ST131 subclone.

In vitro activity of plazomicin against quinolone-resistant gram-negative bacteria isolated from catheter-associated urinary tract infections.

Quinolone resistance among uropathogens is an increasing concern. Plazomicin is a new aminoglycoside that shows promising results against resistant bacteria. However, no study has yet tested its effect specifically on quinolone-resistant organisms. This study aimed to evaluate the in vitro activity of plazomicin and comparator drugs against quinolone-resistant Gram-negative isolates of catheter-associated urinary tract infections (CAUTI). Plazomicin demonstrated high inhibiting activity against Enterobacteriaceae isolates (95.9% at MIC≤ 2 mg/L), with MIC50/90 was 1/2 mg/L. High MICs values were detected against non-Enterobacteriaceae isolates (MIC50/90, 4/32 mg/L). Plazomicin had susceptibility rate of 97.2% against Enterobacteriaceae isolates carrying aminoglycosides modifying enzymes (AME) genes, while other aminoglycosides, amikacin and gentamicin showed reduced activity (32.4% and 25.4%, respectively). In conclusion, plazomicin showed potent in vitro activity against quinolone-resistant Enterobacteriaceae causing CAUTI, regardless of the AME pattern.

Vertical and horizontal dissemination of an IncC plasmid harbouring rmtB 16S rRNA methylase gene, conferring resistance to plazomicin, among invasive ST258 and ST16 KPC-producing Klebsiella pneumoniae.

OBJECTIVES: Carbapenem resistance in Klebsiella pneumoniae is a major clinical challenge. Aminoglycosides remain an important asset in the current therapeutic arsenal to treat these infections. We examined aminoglycoside resistance phenotypes and genomics in a collection of 100 invasive KPC-producing K. pneumoniae isolates sequentially collected in a Brazilian tertiary hospital between 2014 and 2016. METHODS: Aminoglycoside susceptibility testing was performed. We used a combined long-read (MinION) and short-read (Illumina) whole-genome sequencing strategy to provide a genomic picture of aminoglycoside resistance genes, with particular emphasis on 16S rRNA methyltransferases and related plasmids. RESULTS: 68% of the strains were resistant to gentamicin and 42% to amikacin, with 35% resistant to both of these commonly used aminoglycosides. We identified the 16S rRNA methyltransferase gene rmtB in 30% of these isolates: 97% (29/30) belonged to sequence type 258 (ST258) and a single isolate to the emergent ST16 clone. In ST258 and ST16 the rmtB gene was located on large IncC plasmids of 177 kb and 174 kb, respectively, highly similar to a plasmid previously identified in Proteus mirabilis in the same hospital. Moreover, 99% of the isolates remained susceptible to the veterinary-approved drug apramycin, currently under clinical development for human medicine. CONCLUSION: Such findings in geographically and temporally related isolates suggest a combination of vertical clonal spread as well as horizontal interspecies and intraspecies plasmid transfer. This broad rmtB dissemination in an endemic setting for KPC-producing clones is worrisome since it provides resistance to most clinically available aminoglycosides, including the novel aminoglycoside-modifying enzyme-resistant plazomicin.

Distribution of genes encoding 16S rRNA methyltransferase in plazomicin-nonsusceptible carbapenemase-producing Enterobacterales in Brazil.

BACKGROUND: The presence of 16S rRNA methyltranferases (16S-RMTases) in carbapenemase-producing Enterobacterales (CPE) is a major concern because it inactivates all clinical use of aminoglycosides, including plazomicin. The aim of this study is to investigate the prevalence of 16S-RMTases in CPE nonsusceptible to plazomicin collected in different Brazilian hospitals. METHODS: All isolates with plazomicin MIC ≥ 4 µg/mL (n = 67) were screened for the presence of 16S-RMTases by sequencing. RESULTS: 54 (80.6%) isolates encoded 16S-RMTase genes (41 rmtB1, 7 armA, 3 rmtD2, 1 rmtD1 and 2 rmtC). Among 41 samples rmtB1 positive, 40 co-harbored blaKPC-2 and 1 blaOXA-48 gene. Of the seven isolates harboring armA gene, 6 were New Delhi Metallo-beta-lactamase (NDM)-producer. rmtD was only found in isolates Klebsiella pneumoniae Carbapenemase (KPC)-producers, one in Serratia marcescens with rmtD2, not reported in Brazil. CONCLUSION: The co-existence of 16S-RMTase and CPE is worrisome because of limited treatment options and the endemic characteristic of (KPC) and NDM in Brazil.

Expected plazomicin susceptibility in India based on the prevailing aminoglycoside resistance mechanisms in Gram-negative organisms derived from whole-genome sequencing.

Background: Aminoglycoside resistance is a growing challenge, and it is commonly mediated by the aminoglycoside-modifying enzymes (AMEs), followed by 16S rRNA methyl transferase. Plazomicin, a novel aminoglycoside agent approved by the Food and Drug Administration for complicated urinary tract infections is proven to overcome resistance mediated by AMEs but not due to 16S rRNA methyl transferase (16SRMTases). We undertook this study to predict the efficacy of plazomicin in India based on the antimicrobial resistance profile derived from whole-genome sequencing (WGS). Methodology: A total of 386 clinical isolates of Escherichia coli, Klebsiella pneumoniae and Acinetobacter baumannii subjected to WGS were screened for aminoglycoside-resistance mechanisms such as AMEs and 16SRMTases and its association with carbapenemases. Results: AMEs was present in all E. coli, A. baumannii and in 90% of K. pneumoniae. In addition, up to 47% of E. coli and 38% of K. pneumoniae co-carried 16SRMTases with AMEs genes. However, A. baumannii showed 87% of isolates co-harbouring 16SRMTase. bla NDM, bla Oxa-48-like and bla Oxa-23-like were the most predominant carbapenemases in E. coli, K. pneumoniae and A. baumannii, respectively. Notably, 48% of NDM-producing E. coli and 35% of Oxa-48-like producing K. pneumoniae were identified to co-harbour AMEs + RMTAses, where plazomicin may not be useful. Conclusion: Overall, 53%, 62% and 14% of carbapenemase-producing E. coli, K. pneumoniae and A. baumannii harbours only AMEs, indicating the role of plazomicin use. Plazomicin can be used both for ESBLs as "carbapenem-sparing agent" and carbapenemase producers as "colistin-sparing agent." For optimal use, it is essential to know the molecular epidemiology of resistance in a given geographical region where plazomicin empirical therapy is considered.