Aztreonam-avibactam may not replace ceftazidime/avibactam: the case of KPC-21 carbapenemase and penicillin-binding protein 3 with four extra amino acids

Emergence of aztreonam/avibactam and tigecycline-resistant Pseudomonas putida group Co-producing blaIMP-1, blaAFM-4 and blaOXA-1041 with a novel sequence type ST268 in Southwestern China

OBJECTIVES

The emergence of carbapenem-resistant Pseudomonas putida (CRPP) has raised public awareness. This study investigated two strains from the Pseudomonas putida group that were resistant to carbapenem, tigecycline, and aztreonam-avibactam (ATM-AVI), with a focus on their microbial and genomic characteristics.

METHODS

We assessed the antibiotic resistance profile using broth dilution, disk diffusion, and E-test methods. Efflux pump phenotype testing and real-time quantitative PCR were employed to evaluate efflux pump activity in tigecycline resistance, while polymerase chain reaction was utilized to detect common carbapenem genes. Additionally, whole-genome sequencing was performed to analyze genomic characteristics. The transferability of blaIMP-1 and blaAFM-4 was assessed through a conjugation experiment. Furthermore, growth kinetics and biofilm formation were examined using growth curves and crystal violet staining.

RESULTS

Both strains demonstrated resistance to carbapenem, tigecycline, and ATM-AVI. Notably, NMP can restore sensitivity to tigecycline. Subsequent analysis revealed that they co-produced blaIMP-1, blaAFM-4, tmexCD-toprJ, and blaOXA-1041, belonging to a novel sequence type ST268. Although they were closely related on the phylogenetic tree, they exhibited different levels of virulence. Genetic environment analysis indicated variations compared to prior studies, particularly regarding the blaIMP-1 and blaAFM-4 genes, which showed limited horizontal transferability. Moreover, it was observed that temperature exerted a specific influence on their biological factors.

CONCLUSION

We initially identified two P. putida ST268 strains co-producing blaIMP-1, blaAFM-4, blaOXA-1041, and tmexCD-toprJ. The resistance to tigecycline and ATM-AVI can be attributed to the presence of multiple drug resistance determinants. These findings underscore the significance of P. putida as a reservoir for novel antibiotic resistance genes. Therefore, it is imperative to develop alternative antibiotic therapies and establish effective monitoring of bacterial resistance.

Hijacking a small plasmid to confer high-level resistance to aztreonam-avibactam and ceftazidime-avibactam

Acquired β-lactamase-encoding genes are typically carried by large plasmids in Gram-negative bacteria, which also commonly carry multi-copy small plasmids. This study found that mobile genetic elements carrying antimicrobial resistance genes are capable of hijacking small plasmids. This study focused on aztreonam-avibactam (ATM-AVI) as this combination can be used to effectively counter almost all β-lactamases produced by bacteria, and has been recommended against carbapenem-resistant Enterobacterales. A clinical strain (085003) of carbapenem-resistant Escherichia coli was investigated, and mutants (085003R32 and 085003R512) able to grow under 32/4 and 512/4 mg/L of ATM-AVI were obtained as representatives of low- and high-level resistance, respectively, by induction. Comparative genomics showed that 085003R32 and 085003R512 had a single nucleotide mutation of β-lactamase gene blaCMY-2, encoding a novel CMY with a Thr319Ile substitution, assigned 'CMY-2R'. Cloning and enzyme kinetics were used to verify that CMY-2R conferred ATM-AVI resistance by compromising binding of AVI and subsequent protection of ATM. Mechanisms for the discrepant resistance between 085003R32 and 085003R512 were investigated. Three tandem copies of blaCMY-2R were identified on a self-transmissible IncP1 plasmid of 085003R32 due to IS1294 misrecognizing its end terIS and rolling-circle replication. 085003R512 had only a single copy of blaCMY-2R on the IncP1 plasmid, but possessed anther blaCMY-2R on an already present 4-kb small plasmid. IS1294-mediated mobilization on to this multi-copy small plasmid increased the copy number of blaCMY-2R significantly, rendering higher resistance. This study shows that bacteria can employ multiple approaches to accommodate selection pressures imposed by exposure to varied concentrations of antimicrobial agents.

In Vitro Activities of Aztreonam-Avibactam, Eravacycline, Cefoselis, and Other Comparators against Clinical Enterobacterales Isolates: a Multicenter Study in China, 2019

Aztreonam-avibactam, eravacycline, and cefoselis are three novel antimicrobial agents for the treatment of serious infections caused by Gram-negative bacteria. We evaluated the in vitro activities of the above-mentioned three antimicrobial agents against clinical Enterobacterales isolates. A total of 1,202 Enterobacterales isolates, including 10 genera or species, were collected from 26 hospitals that cover seven regions of China. The susceptibilities of the 30 antimicrobial agents were interpreted based on the combination of U.S. Food and Drug Administration and Clinical and Laboratory Standards Institute guidelines. The results indicated that all Enterobacterales isolates showed high susceptibility to aztreonam-avibactam (98.25%), eravacycline (85.69%), and cefoselis (62.73%). The first two antimicrobial agents also demonstrated potent activities against multidrug-resistant and carbapenem-resistant Enterobacterales independent of antimicrobial resistance mechanisms. The rates of susceptibility to aztreonam-avibactam, eravacycline, and cefoselis were lowest in Morganella spp. (84.42%), Proteus spp. (33.65%), and Escherichia coli (40.14%), respectively. In general, the lower rates of susceptibility to eravacycline and cefoselis were in the older inpatient group. The strains isolated from urinary tract exhibited the lowest rate of susceptibility (78.97%) to eravacycline, and the lowest rate of susceptibility (45.83%) to cefoselis was observed in nervous system specimens. The strains isolated from intensive care unit (ICU) wards showed significantly reduced susceptibility to cefoselis compared with those isolated from non-ICU wards. The MIC values of aztreonam-avibactam and ceftazidime-avibactam have poor consistency (weighted kappa = 0.243), as did eravacycline and tigecycline (weighted kappa = 0.478). Cefoselis and cefepime showed highly similar activities against Enterobacterales (weighted kappa = 0.801). Our results support the clinical development of aztreonam-avibactam, eravacycline, and cefoselis to treat infections caused by Enterobacterales. IMPORTANCE Infections caused by multidrug-resistant (MDR) Enterobacterales, especially carbapenem-resistant Enterobacterales (CRE), have been a challenging clinical problem due to the limited therapeutic options. Therefore, the need to develop novel antimicrobial agents and evaluate their activities against Enterobacterales in vitro is urgent. Our results show that the novel antimicrobial agents aztreonam-avibactam and eravacycline retain activities against MDR and CRE isolates, including carbapenemase producers and non-carbapenemase producers. Further analysis combined with clinical information on the strains tested revealed that no significant differences were observed in susceptibility rates of strains with different demographic parameters to aztreonam-avibactam. Age, specimen source, and department were associated with the susceptibility of strains to eravacycline and cefoselis (P ≤ 0.01). Compared with ceftazidime-avibactam, aztreonam-avibactam has its advantages and limitations against Enterobacterales. The potent activity of eravacycline against Enterobacterales was higher than that of tigecycline. Cefoselis and cefepime showed a highly consistent activity against Enterobacterales.

Novel Antimicrobial Agents for Gram-Negative Pathogens

Gram-negative bacterial resistance to antimicrobials has had an exponential increase at a global level during the last decades and represent an everyday challenge, especially for the hospital practice of our era. Concerted efforts from the researchers and the industry have recently provided several novel promising antimicrobials, resilient to various bacterial resistance mechanisms. There are new antimicrobials that became commercially available during the last five years, namely, cefiderocol, imipenem-cilastatin-relebactam, eravacycline, omadacycline, and plazomicin. Furthermore, other agents are in advanced development, having reached phase 3 clinical trials, namely, aztreonam-avibactam, cefepime-enmetazobactam, cefepime-taniborbactam, cefepime-zidebactam, sulopenem, tebipenem, and benapenem. In this present review, we critically discuss the characteristics of the above-mentioned antimicrobials, their pharmacokinetic/pharmacodynamic properties and the current clinical data.

Resistance to aztreonam-avibactam due to CTX-M-15 in the presence of penicillin-binding protein 3 with extra amino acids in Escherichia coli

Aztreonam-avibactam is a promising combination to treat carbapenem-resistant Enterobacterales including coverage for metallo-β-lactamases. Escherichia coli strains resistant to aztreonam-avibactam have emerged but resistance mechanisms remain to be elucidated. We performed a study to investigate the mechanism for aztreonam-avibactam in a carbapenem-resistant Escherichia coli clinical strain. This strain was resistant to aztreonam-avibactam (aztreonam MIC, 16 mg/L in the presence of 4 mg/L avibactam). Whole genome sequencing revealed that the strain carried metallo-β-lactamase gene bla_NDM-4 and the extended-spectrum β-lactamase (ESBL) gene bla_CTX-M-15 and had a YRIK four amino acid insertion in penicillin-binding protein 3 (PBP3). bla_CTX-M-15 was cloned into pET-28a(+), followed by the transformation, with the gene, of E. coli strain 035125∆pCMY42 possessing the YRIK insertion in PBP3 and strain BL21 with the wildtype PBP3. bla_CTX-M-14, another common ESBL gene, and bla_CTX-M-199, a hybrid of bla_CTX-M-14 and bla_CTX-M-15 were also individually cloned into both E. coli strains for comparison. Aztreonam-avibactam resistance was only observed in the E. coli strains with the YRIK insertion in PBP3 that produced CTX-M-15 or its hybrid enzyme CTX-M-199. Checkerboard titration assays were performed to determine the synergistic effects between aztreonam-avibactam and ceftazidime or meropenem. Doubling avibactam concentration in vitro reversed aztreonam-avibactam resistance, while the combination of aztreonam-avibactam and ceftazidime or meropenem did not. In conclusion, CTX-M enzymes with activity against aztreonam, (e.g., CTX-M-15 and CTX-M-199), can confer resistance in the combination of PBP3 with YRIK insertions in metallo-β-lactamase-producing carbapenem-resistant E. coli. Doubling the concentration of avibactam may overcome such resistance.