Imipenem/Relebactam Resistance in Clinical Isolates of Extensively Drug Resistant Pseudomonas aeruginosa: Inhibitor-Resistant β-Lactamases and Their Increasing Importance

Evolving resistance landscape in gram-negative pathogens: An update on β-lactam and β-lactam-inhibitor treatment combinations for carbapenem-resistant organisms

Antibiotic resistance has become a global threat as it is continuously growing due to the evolution of β-lactamases diminishing the activity of classic β-lactam (BL) antibiotics. Recent antibiotic discovery and development efforts have led to the availability of β-lactamase inhibitors (BLIs) with activity against extended-spectrum β-lactamases as well as Klebsiella pneumoniae carbapenemase (KPC)-producing carbapenem-resistant organisms (CRO). Nevertheless, there is still a lack of drugs that target metallo-β-lactamases (MBL), which hydrolyze carbapenems efficiently, and oxacillinases (OXA) often present in carbapenem-resistant Acinetobacter baumannii. This review aims to provide a snapshot of microbiology, pharmacology, and clinical data for currently available BL/BLI treatment options as well as agents in late stage development for CRO harboring various β-lactamases including MBL and OXA-enzymes.

Identification of bla OXA-23 gene in resistant Pseudomonas aeruginosa strains isolated from cows and humans in Basra province, Iraq

Background and Aim

Pseudomonas aeruginosa is an infectious agent of great importance for animals and humans. It causes serious infections that show high resistance to antibiotics. This study investigated the molecular detection of blaOXA-23 gene in antibiotic-resistant P. aeruginosa strains isolated from cows and humans.

Materials and Methods

In total, 120 samples, comprised 60 from cows (30 milk and 30 nasal discharge) and 60 from their owners (30 urine and 30 sputum), were individually collected, cultured, and tested for P. aeruginosa through molecular analysis targeting the blaOXA-23 gene. P. aeruginosa antibiotic-resistant isolates were identified by performing antibiotic susceptibility testing and detecting biofilm formation.

Results

In total, 74.17% positive P. aeruginosa isolates, including 66.67% and 81.67% for cows and humans, respectively. Subsequently, positive cow isolates were detected in 60% of milk samples and 73.33% of nasal discharge samples; while positive human isolates were detected in 76.67% of urine samples and 86.66% of sputum samples. Targeting blaOXA-23 gene, 58.43% of cultured isolates were positive for P. aeruginosa by polymerase chain reaction. Respectively, positive isolates were detected in 66.67% and 45.46% of cow milk and nasal discharges as well as in 60.87% and 61.54% of human urine and sputum. The antibiotic susceptibility test revealed that all isolates were resistant to all applied antibiotics, particularly imipenem. Results of biofilm formation revealed 67.31% total positives, including 51.43% strong, 34.285% moderate, and 14.285% weak reactions. In addition, although values of the total positive cows and humans differed insignificantly, total positives showed insignificant variation between values of milk and nasal discharges of cows as well as between urine and sputum of humans; however, significant differences were identified in the distribution of strong, moderate, and weak positivity of these samples.

Conclusion

Antibiotic overuse contributes extensively to increasing the prevalence of resistant P. aeruginosa isolates carrying the blaOXA-23 gene in both cows and humans. Furthermore, studies in other Iraqi areas are necessary to support our findings. The main limitations include that the number of tested samples is relatively low, and there is a need to use a large number of samples from different sources. Also, the current methods for detection of resistant isolates are still culture-based approaches.

Levofloxacin-induced MexS mutation triggers imipenem-relebactam resistance in a KPC-producing Pseudomonas aeruginosa

OBJECTIVES

Imipenem-relebactam (IMR), a novel β-lactam/β-lactamase inhibitor combination, is recommended for infections caused by difficult-to-treat Pseudomonas aeruginosa. This study aimed to investigate the evolution trajectory of IMR resistance under the selection of levofloxacin in P. aeruginosa.

METHODS

Antimicrobial susceptibility testing, complete genome sequencing and gene manipulation experiments were performed. Quantitative reverse transcription PCR for specific genes and porin levels were detected. Evolution trajectory was simulated in vitro by induction assay.

RESULTS

P. aeruginosa HS347 and HS355 were isolated from abdominal drainage of two neighbouring patients (S and Z) undergoing surgery of colon carcinoma in Shanghai, China, with the latter patient having received levofloxacin. They were closely related ST16 strains, and both carried blaKPC-2 plasmids highly similar to those of P. aeruginosa endemic clones from Zhejiang province, where patient Z had received enteroscopy before this admission. Acquisition of resistance was observed for both IMR and fluoroquinolones in HS355, likely prompted by treatment with levofloxacin. The T274I substitution in MexS (putative oxidoreductase), upregulated efflux pump operon mexEF-oprN and decreased production of porin OprD leading to cross-resistance to fluoroquinolones and IMR, which was also verified by in vitro mutant selection under levofloxacin selection.

CONCLUSIONS

The emergence of a rare blaKPC-2-plasmid-bearing ST16 clone implies the horizonal spread and inter-regional dissemination of a high-risk plasmid-clone combination, representing a public health challenge. Levofloxacin exposure can select for mexS inactivating mutation, which in turn leads to IMR resistance phenotype, implicating the role of an unrelated, widely used antimicrobial agent in insidiously triggering the development of cross resistance to a latest β-lactam/β-lactamase inhibitor combination.

Assessing the in vivo impact of novel β-lactamase inhibitors on the efficacy of their partner β-lactams against serine carbapenemase-producing Pseudomonas aeruginosa using human-simulated exposures

OBJECTIVES

To evaluate the efficacy of human-simulated regimens (HSRs) of ceftazidime, ceftazidime/avibactam, imipenem, imipenem/relebactam, meropenem and meropenem/vaborbactam in a murine thigh infection model against serine carbapenemase-producing Pseudomonas aeruginosa.

METHODS

Nine P. aeruginosa clinical isolates harbouring GES-5 (n = 1), GES-20 (n = 1), GES-5/20 (n = 1), GES-19, GES-20 (n = 3) and KPC (n = 3) were evaluated. Six mice were administered HSRs of ceftazidime 2 g q8h (2 h infusion), ceftazidime/avibactam 2.5 g q8h (2 h infusion), meropenem 2 g q8h (3 h infusion), imipenem 0.5 g q6h (0.5 h infusion), imipenem/relebactam 1.25 g q6h (0.5 h infusion) and meropenem/vaborbactam 4 g q8h (3 h infusion). Change in bacterial burden relative to baseline and the percent of isolates meeting the 1 log10 kill endpoint were assessed.

RESULTS

The addition of avibactam to ceftazidime increased the percentage of isolates meeting 1 log10 kill from 33% to 100% of GES- or KPC-harbouring isolates. Imipenem/relebactam HSR produced ≥1 log10 of kill against 83% and 100% of GES- and KPC-harbouring isolates, respectively, while imipenem alone failed to reach 1 log10 kill for any isolates. Vaborbactam resulted in variable restoration of meropenem activity as 1 log10 kill was achieved in only 33% and 66% of GES- and KPC-harbouring isolates, respectively, compared with no isolates for meropenem alone.

CONCLUSIONS

Ceftazidime/avibactam and imipenem/relebactam were active against 100% and 89% of KPC- or GES-harbouring isolates tested in vivo. The activity of meropenem/vaborbactam was variable, suggesting this may be an inferior treatment option in this setting. Further studies to evaluate clinical outcomes in GES- and KPC-producing P. aeruginosa are warranted given their increasing prevalence worldwide.

Reviewing novel treatment options for carbapenem-resistant Enterobacterales

INTRODUCTION

Carbapenem resistant Enterobacterales (CRE) are a major threat to global health and hospital-onset CRE infections have risen during the COVID-19 pandemic. Novel antimicrobials are now available for the treatment of CRE infections. There remains an urgent need for new antimicrobials for CRE, especially for those producing metallo-β-lactamases.

AREAS COVERED

This article discusses previously published research supporting currently available novel antimicrobials for the treatment of CRE infections. Newer compounds currently being evaluated in clinical trials are covered. A literature search was conducted in PubMed over all available dates for relevant published papers and conference abstracts with the search terms, 'CRE,' 'carbapenem-resistant Enterobacterales,' 'β-lactam-β-lactamase inhibitor,' 'KPC,' 'NDM,' 'metallo-β-lactamase,' 'ceftazidime-avibactam,' 'meropenem-vaborbactam,' 'imipenem-cilastatin-relebactam,' 'cefiderocol,' 'eravacycline,' 'plazomicin,' 'taniborbactam,' 'zidebactam,' and 'nacubactam.'

EXPERT OPINION

Novel antimicrobials for CRE infections have been developed, most notably the β-lactam-β-lactamase inhibitor combinations, though treatment options for infections with metallo-β-lactamase producing Enterobacterales remain few and have limitations. Development of antibiotics with activity against metallo-β-lactamase producing Enterobacterales is eagerly awaited, and there are promising new compounds in clinical trials. Finally, more clinical research is needed to optimize and individualize treatment approaches, which will help guide antimicrobial stewardship initiatives aimed at reducing the spread of CRE and development of further resistance.

Efficacy and safety of novel carbapenem-β-lactamase inhibitor combinations: imipenem-cilastatin/relebactam results from randomized controlled trials

Background

Gram-negative bacteria is a global public health problem. Treatment options include novel beta-lactamase inhibitors.

Objectives

The objective of this study was to collect information on the efficacy and safety of novel β-lactamase inhibitor combinations such as imipenem-cilastatin/relebactam (IMI/REL).

Methods

In order to comprehensively evaluate the clinical, microbiological, and adverse events outcomes, a meta-analysis was conducted on clinical trials comparing novel β-lactamase inhibitor combinations with existing comparator therapies.

Results

Four studies comprising 948 patients were included in the analysis. IMI/REL therapy demonstrated similar clinical responses to comparators across various treatment visits, including discontinuation of intravenously administered therapy visits [DCIV, RR = 1.00 (0.88, 1.12)], early follow-up visits [EFU, RR = 1.00 (0.89, 1.14)], late follow-up visits [LFU, RR = 1.00 (0.88, 1.13)]. Moreover, no significant difference in the microbiologic response of MITT patients was observed between IMI/REL and comparators across DCIV [RR = 0.99 (0.89, 1.11)], EFU [RR = 1.01 (0.95, 1.07)], and LFU visits [RR = 1.00 (90.94, 1.07)]. In terms of safety, therapy with IMI/REL and comparators exhibited similar risks of at least one adverse event (AE), drug-related AEs, and discontinuation due to AEs. The incidence of serious AEs (SAEs) was significantly lower in the IMI/REL group compared to the comparison groups. The predominant AEs were gastrointestinal disorders, with no significant difference observed between the IMI/REL group and comparators.

Conclusion

The clinical and microbiologic response to IMI/REL in the treatment of bacterial infection was comparable to that of the comparator. Furthermore, the incidence of AEs and the tolerability of IMI/REL were similar among the comparators. Based on these findings, IMI/REL can be considered as a viable alternative treatment option.

Transcending the challenge of evolving resistance mechanisms in Pseudomonas aeruginosa through β-lactam-enhancer-mechanism-based cefepime/zidebactam

Compared to other genera of Gram-negative pathogens, Pseudomonas is adept in acquiring complex non-enzymatic and enzymatic resistance mechanisms thus remaining a challenge to even novel antibiotics including recently developed β-lactam and β-lactamase inhibitor combinations. This study shows that the novel β-lactam enhancer approach enables cefepime/zidebactam to overcome both non-enzymatic and enzymatic resistance mechanisms associated with a challenging panel of P. aeruginosa. This study highlights that the β-lactam enhancer mechanism is a promising alternative to the conventional β-lactam/β-lactamase inhibitor approach in combating ever-evolving MDR P. aeruginosa.

bla KPC-2 overexpression and bla GES-5 carriage as major imipenem/relebactam resistance mechanisms in Pseudomonas aeruginosa high-risk clones ST463 and ST235, respectively, in China

Pseudomonas aeruginosa high-risk clones pose severe threats to public health. Here, we characterize the imipenem/relebactam (IR) resistance mechanisms in P. aeruginosa high-risk clones sequence type 235 (ST235) and ST463 in China. Minimum inhibitory concentrations (MICs) were determined, and Illumina short-read sequencing was performed for 1,168 clinical carbapenem-resistant P. aeruginosa (CRPA) isolates. The gene copy number and expression level were analyzed by Illumina sequencing depth and reverse transcription-quantitative PCR, respectively. Resistance conferred by bla GES-5 was evaluated by cloning experiments. ST463 and ST235 accounted for 9.8% (115/1,168) and 4.5% (53/1,168) of total isolates, respectively, and showed high frequencies of extensively drug-resistant and difficult-to-treat resistant phenotypes. The overall IR-resistant rate in CRPA was 21.0% (245/1,168). However, the IR resistance rate was 81.7% (94/115) in ST463-PA and 52.8% (28/53) in ST235-PA. Of the ST463 isolates, 92.2% (106/115) were Klebsiella pneumoniae carbapenemase-producing P. aeruginosa (KPC-PA), and all 94 IR-resistant ST463-PA produced KPC-2. Compared to IR-susceptible ST463 KPC-2-PA, IR-resistant ST463 KPC-2-PA exhibited significantly higher bla KPC-2 copy numbers and expression levels. In ST463 KPC-2-PA, 16 mg/L relebactam resulted in additional fourfold reductions in imipenem MIC50/90 values compared to 4 mg/L relebactam. In ST235, 1.9% (1/53) carried bla IMP carbapenemase and 54.7% (29/53) carried bla GES carbapenemase. Other than the IMP producer, all 27 IR-resistant ST235-PA produced GES-5. Cloning experiments revealed that imipenem resistance in bla GES-5-carrying PAO1 transformants was generally unaffected by relebactam. In conclusion, IR-resistant CRPA isolates in China were mainly distributed in P. aeruginosa high-risk clones ST463 and ST235. The major underlying IR resistance mechanisms were bla KPC-2 overexpression and bla GES-5 carriage.

Potentials of organic tellurium-containing compound AS101 to overcome carbapenemase-producing Escherichia coli

BACKGROUND

The issue of carbapenem-resistant Escherichia coli was aggravated yearly. The previous studies reported the varied but critical epidemiology of carbapenem-resistant E. coli among which the carbapenemase-producing strains were regarded as one of the most notorious issues. AS101, an organic tellurium-containing compound undergoing clinical trials, was revealed with antibacterial activities. However, little is known about the antibacterial effect of AS101 against carbapenemase-producing E. coli (CPEC).

MATERIALS AND METHODS

The minimum inhibitory concentration (MIC) of AS101 against the 15 isolates was examined using a broth microdilution method. The scanning electron microscopy, pharmaceutical manipulations, reactive oxygen species level, and DNA fragmentation assay were carried out to investigate the antibacterial mechanism. The sepsis mouse model was employed to assess the in vivo treatment effect.

RESULTS

The blaNDM (33.3%) was revealed as the dominant carbapenemase gene among the 15 CPEC isolates, followed by the blaKPC gene (26.7%). The MICs of AS101 against the 15 isolates ranged from 0.5 to 32 μg/ml, and 99.9% of bacterial eradication was observed at 8 h, 4 h, and 2 h for 1×, 2×, and 4 × MIC, respectively. The mechanistic investigations suggest that AS101 would enter the bacterial cell, and induce ROS generation, leading to DNA fragmentation. The in vivo study exhibited that AS101 possessed a steady treatment effect in a sepsis mouse model, with an up to 83.3% of survival rate.

CONCLUSION

The in vitro activities, mechanisms, and in vivo study of AS101 against CPEC were unveiled. Our finding provided further evidence for the antibiotic development of AS101.