Coproduction of KPC-18 and VIM-1 Carbapenemases by Enterobacter cloacae: Implications for Newer β-Lactam-β-Lactamase Inhibitor Combinations

The Revival of Aztreonam in Combination with Avibactam against Metallo-β-Lactamase-Producing Gram-Negatives: A Systematic Review of In Vitro Studies and Clinical Cases

Infections caused by metallo-β-lactamase (MBL)-producing Enterobacterales and Pseudomonas are increasingly reported worldwide and are usually associated with high mortality rates (>30%). Neither standard therapy nor consensus for the management of these infections exist. Aztreonam, an old β-lactam antibiotic, is not hydrolyzed by MBLs. However, since many MBL-producing strains co-produce enzymes that could hydrolyze aztreonam (e.g., AmpC, ESBL), a robust β-lactamase inhibitor such as avibactam could be given as a partner drug. We performed a systematic review including 35 in vitro and 18 in vivo studies on the combination aztreonam + avibactam for infections sustained by MBL-producing Gram-negatives. In vitro data on 2209 Gram-negatives were available, showing the high antimicrobial activity of aztreonam (MIC ≤ 4 mg/L when combined with avibactam) in 80% of MBL-producing Enterobacterales, 85% of Stenotrophomonas and 6% of MBL-producing Pseudomonas. Clinical data were available for 94 patients: 83% of them had bloodstream infections. Clinical resolution within 30 days was reported in 80% of infected patients. Analyzing only patients with bloodstream infections (64 patients), death occurred in 19% of patients treated with aztreonam + ceftazidime/avibactam. The combination aztreonam + avibactam appears to be a promising option against MBL-producing bacteria (especially Enterobacterales, much less for Pseudomonas) while waiting for new antimicrobials.

Multispecies Outbreak of Verona Integron-Encoded Metallo-ß-Lactamase-Producing Multidrug Resistant Bacteria Driven by a Promiscuous Incompatibility Group A/C2 Plasmid

BACKGROUND

Antibiotic resistance is often spread through bacterial populations via conjugative plasmids. However, plasmid transfer is not well recognized in clinical settings because of technical limitations, and health care-associated infections are usually caused by clonal transmission of a single pathogen. In 2015, multiple species of carbapenem-resistant Enterobacteriaceae (CRE), all producing a rare carbapenemase, were identified among patients in an intensive care unit. This observation suggested a large, previously unrecognized plasmid transmission chain and prompted our investigation.

METHODS

Electronic medical record reviews, infection control observations, and environmental sampling completed the epidemiologic outbreak investigation. A laboratory analysis, conducted on patient and environmental isolates, included long-read whole-genome sequencing to fully elucidate plasmid DNA structures. Bioinformatics analyses were applied to infer plasmid transmission chains and results were subsequently confirmed using plasmid conjugation experiments.

RESULTS

We identified 14 Verona integron-encoded metallo-ß-lactamase (VIM)-producing CRE in 12 patients, and 1 additional isolate was obtained from a patient room sink drain. Whole-genome sequencing identified the horizontal transfer of blaVIM-1, a rare carbapenem resistance mechanism in the United States, via a promiscuous incompatibility group A/C2 plasmid that spread among 5 bacterial species isolated from patients and the environment.

CONCLUSIONS

This investigation represents the largest known outbreak of VIM-producing CRE in the United States to date, which comprises numerous bacterial species and strains. We present evidence of in-hospital plasmid transmission, as well as environmental contamination. Our findings demonstrate the potential for 2 types of hospital-acquired infection outbreaks: those due to clonal expansion and those due to the spread of conjugative plasmids encoding antibiotic resistance across species.

Recognizing and Overcoming Resistance to New Beta-Lactam/Beta-Lactamase Inhibitor Combinations

PURPOSE OF REVIEW

To describe the mechanisms and clinical relevance of emergent resistance to three recently introduced beta-lactamase inhibitor combinations (BLICs) active against resistant Gram-negative organisms: ceftolozane-tazobactam, ceftazidime-avibactam, and meropenem-vaborbactam.

RECENT FINDINGS

Despite their recent introduction into practice, clinical reports of resistance to BLICs among typically susceptible organisms have already emerged, in some cases associated with therapeutic failure. The resistance mechanisms vary by agent, including mutations in beta-lactamase active sites, upregulation of efflux pumps, and alterations in the structure or expression of porin channels. These changes may confer cross-resistance or, rarely, increased susceptibility to related agents. Clinicians need to be aware of the potential for initial or emergent resistance to BLICs and ensure appropriate antimicrobial susceptibility testing is performed. Dose optimization and novel combinations of agents may play a role in preventing and managing resistance. Recently approved BLICs have provided important new therapeutic options against resistant Gram-negative organisms, but are already coming up against emergent resistance. Awareness of the potential for resistance, early detection, and dose optimization may be important in preserving the utility of these agents.

Further Spread of a blaKPC-Harboring Untypeable Plasmid in Enterobacteriaceae in China

The wide spread of Klebsiella pneumoniae carbapenemase (KPC)-producing Enterobacteriaceae is great threat to public health in China. Plasmids are among the major factors mediating bla_KPC gene dissemination. A total of 156 carbapenem-resistant Enterobacteriaceae (CRE) isolates were identified in a tertiary hospital in China. Six KPC-producing isolates, namely, E. coli (n = 2), E. asburiae (n = 1), C. freundii (n = 1), C. portucalensis (n = 1), and C. koseri (n = 1), tested positive for the pCKPC18-1-like untypeable plasmid, which was described recently in C. freundii. All 6 plasmids could be easily transferred into E. coli by chemical transformation or conjugation and were confirmed by sequencing to harbor bla_KPC-2. Multilocus PCRs and EcoRI-RFLP revealed that the 6 untypeable plasmids belonged to 2 isoforms. High-throughput sequencing of representative plasmids (pCP40 and pEC86) led to the identification of 2 plasmids that shared the common backbone genes repA, DnaJ, StpA, and yafB, which were characteristic of the untypeable plasmid, and had similar bla_KPC-2 genetic contexts of the Tn3-Tn4401 chimera. Nucleotide comparison revealed high sequence identity of the 2 plasmids with previously reported bla_KPC-2-carrying untypeable plasmids. In particular, the pCP40 plasmid from C. portucalensis and the pHS062105-3 plasmid from K. pneumoniae differed by only 20 single-nucleotide polymorphisms (SNPs). To the best of our knowledge, this is the first report of a bla_KPC-harboring untypeable plasmid spread into E. coli, E. asburiae, and C. koseri strains in China.

High-Stringency Evaluation of the Automated BD Phoenix CPO Detect and Rapidec Carba NP Tests for Detection and Classification of Carbapenemases

There is an urgent need for rapid, accurate detection and classification of carbapenemases. The current study evaluated the automated BD Phoenix CPO Detect and the manual bioMérieux Rapidec Carba NP tests for meeting these needs. Both tests were challenged with 294 isolates of Enterobacteriaceae spp., Pseudomonas aeruginosa, and Acinetobacter baumannii chosen to provide extreme diagnostic difficulty. Carbapenemases such as KPC, NMC-A, IMI, SME, NDM, SPM, IMP, VIM, and OXA-23, 40, 48, 58, 72, 181, and 232 were produced by 243 isolates and 51 carbapenemase-negative isolates included porin mutants and producers of extended-spectrum β-lactamases (ESBLs), AmpCs, K1, and broad-spectrum β-lactamases. Both tests exhibited high sensitivity of carbapenemase detection (>97%). Due to the highly challenging carbapenemase-negative isolates, specificities were lower than typical for evaluations involving mostly routine clinical isolates. BD Phoenix CPO Detect was 68.6% specific and Rapidec Carba NP was 60.8% to 78.4% specific, depending on how borderline results were interpreted. Only BD Phoenix CPO Detect classified carbapenemases. It correctly classified 85.0% of class A, 72.4% of class B, and 88.6% of class D carbapenemases. Importantly with respect to empirical therapy with new β-lactamase inhibitor combinations such as ceftazidime/avibactam, no class B carbapenemases were misclassified as class A carbapenemases. Both tests offer advantages. Used alone, without initial susceptibility tests, Rapidec Carba NP can provide positive results for some isolates after only 10 to 30 min incubation. BD Phoenix CPO Detect provides novel advantages such as automated carbapenemase detection, inclusion in susceptibility panels to eliminate delays and subjectivity in initiating carbapenemase tests, and classification of most carbapenemases.

Complete Sequence of pCY-CTX, a Plasmid Carrying a Phage-Like Region and an ISEcp1-Mediated Tn2 Element from Enterobacter cloacae

A plasmid pCY-CTX carrying a phage-like backbone from an extensively drug-resistant Enterobacter cloacae strain Guangzhou-ECL001 (previously known as CY01) was identified in this study. By Illumina MiSeq 2 × 250-bp paired-end sequencing, de novo assembly, and PCR, full sequence of pCY-CTX was obtained. Plasmid pCY-CTX was a circular plasmid with a length of 116,700 bp, harboring 136 putative open reading frames with the average G + C content of 50.8%. The backbone of pCY-CTX showed high identity to previously reported phage-like plasmid pHCM2 and phage SSU5. In addition, pCY-CTX contained a distinctive ISEcp1-mediated Tn2 region with two resistance genes bla_TEM-1 and bla_CTX-M-3. Transposition unit "ISEcp1- bla_CTX-M-3- orf477" was inserted into the Tn2 structure, dividing Tn2 into two parts. This represents the first identification of a plasmid carrying a phage-like backbone and a distinctive ISEcp1-mediated Tn2 region within bla_TEM-1 and bla_CTX-M-3 in clinical E. cloacae. The finding of phage-like regions located in plasmids provides a new perspective in gene transfer associated with antimicrobial resistance.

Chromosomal 16S Ribosomal RNA Methyltransferase RmtE1 in Escherichia coli Sequence Type 448

We identified rmtE1, an uncommon 16S ribosomal methyltransferase gene, in an aminoglycoside- and cephalosporin-resistant Escherichia coli sequence type 448 clinical strain co-harboring bla_CMY-2. Long-read sequencing revealed insertion of a 101,257-bp fragment carrying both resistance genes to the chromosome. Our findings underscore E. coli sequence type 448 as a potential high-risk multidrug-resistant clone.

Ceftazidime-avibactam (CTZ-AVI) as a treatment for hospitalized adult patients with complicated intra-abdominal infections

Avibactam, a novel β-lactamase inhibitor, has recently been co-formulated with ceftazidime and approved for use in patients with complicated intra-abdominal and urinary tract infections, where no better treatment alternative exists. The basis for its FDA approval has been the extensive clinical experience with ceftazidime and the demonstration in vitro and in animal models that the addition of avibactam reverses resistance to ceftazidime in extended-spectrum β-lactamase and some carbapenemase-producing Enterobacteriaceae. Early clinical data are promising, with efficacy demonstrated in patients with complicated intra-abdominal and urinary tract infections. This review will summarize the in vitro, animal and clinical data available on this agent to date.

The rapid spread of carbapenem-resistant Enterobacteriaceae

Carbapenems, our one-time silver bullet for multidrug resistant bacterial infections, are now threatened by widespread dissemination of carbapenem-resistant Enterobacteriaceae (CRE). Successful expansion of Enterobacteriaceae clonal groups and frequent horizontal gene transfer of carbapenemase expressing plasmids are causing increasing carbapenem resistance. Recent advances in genetic and phenotypic detection facilitate global surveillance of CRE diversity and prevalence. In particular, whole genome sequencing enabled efficient tracking, annotation, and study of genetic elements colocalized with carbapenemase genes on chromosomes and on plasmids. Improved characterization helps detail the co-occurrence of other antibiotic resistance genes in CRE isolates and helps identify pan-drug resistance mechanisms. The novel β-lactamase inhibitor, avibactam, combined with ceftazidime or aztreonam, is a promising CRE treatment compared to current colistin or tigecycline regimens. To halt increasing CRE-associated morbidity and mortality, we must continue quality, cooperative monitoring and urgently investigate novel treatments.