Investigating the OXA Variants of ESKAPE Pathogens

Genomic analyses of Bacteroides fragilis: subdivisions I and II represent distinct species

Introduction. Bacteroides fragilis is a Gram-negative anaerobe that is a member of the human gastrointestinal microbiota and is frequently found as an extra-intestinal opportunistic pathogen. B. fragilis comprises two distinct groups - divisions I and II - characterized by the presence/absence of genes [cepA and ccrA (cfiA), respectively] that confer resistance to β-lactam antibiotics by either serine or metallo-β-lactamase production. No large-scale analyses of publicly available B. fragilis sequence data have been undertaken, and the resistome of the species remains poorly defined.Hypothesis/Gap Statement. Reclassification of divisions I and II B. fragilis as two distinct species has been proposed but additional evidence is required.Aims. To investigate the genomic diversity of GenBank B. fragilis genomes and establish the prevalence of division I and II strains among publicly available B. fragilis genomes, and to generate further evidence to demonstrate that B. fragilis division I and II strains represent distinct genomospecies.Methodology. High-quality (n=377) genomes listed as B. fragilis in GenBank were included in pangenome and functional analyses. Genome data were also subject to resistome profiling using The Comprehensive Antibiotic Resistance Database.Results. Average nucleotide identity and phylogenetic analyses showed B. fragilis divisions I and II represent distinct species: B. fragilis sensu stricto (n=275 genomes) and B. fragilis A (n=102 genomes; Genome Taxonomy Database designation), respectively. Exploration of the pangenome of B. fragilis sensu stricto and B. fragilis A revealed separation of the two species at the core and accessory gene levels.Conclusion. The findings indicate that B. fragilis A, previously referred to as division II B. fragilis, is an individual species and distinct from B. fragilis sensu stricto. The B. fragilis pangenome analysis supported previous genomic, phylogenetic and resistome screening analyses collectively reinforcing that divisions I and II are two separate species. In addition, it was confirmed that differences in the accessory genes of B. fragilis divisions I and II are primarily associated with carbohydrate metabolism and suggest that differences other than antimicrobial resistance could also be used to distinguish between these two species.

Acinetobacter baumannii from Samples of Commercially Reared Turkeys: Genomic Relationships, Antimicrobial and Biocide Susceptibility

Acinetobacter baumannii is especially known as a cause of nosocomial infections worldwide. It shows intrinsic and acquired resistances to numerous antimicrobial agents, which can render the treatment difficult. In contrast to the situation in human medicine, there are only few studies focusing on A. baumannii among livestock. In this study, we have examined 643 samples from turkeys reared for meat production, including 250 environmental and 393 diagnostic samples, for the presence of A. baumannii. In total, 99 isolates were identified, confirmed to species level via MALDI-TOF-MS and characterised with pulsed-field gel electrophoresis. Antimicrobial and biocide susceptibility was tested by broth microdilution methods. Based on the results, 26 representative isolates were selected and subjected to whole-genome sequencing (WGS). In general, A. baumannii was detected at a very low prevalence, except for a high prevalence of 79.7% in chick-box-papers (n = 118) of one-day-old turkey chicks. The distributions of the minimal inhibitory concentration values were unimodal for the four biocides and for most of the antimicrobial agents tested. WGS revealed 16 Pasteur and 18 Oxford sequence types, including new ones. Core genome MLST highlighted the diversity of most isolates. In conclusion, the isolates detected were highly diverse and still susceptible to many antimicrobial agents.

Comparative genomic analysis of plasmids harboring bla OXA-48-like genes in Klebsiella pneumoniae

The emergence and spread of carbapenem-resistant Klebsiella pneumoniae (CRKP) is a serious medical problem worldwide. Acquired OXA-48-like carbapenemases encoded by plasmids are important causes of carbapenem resistance in K. pneumoniae. To explore the links between plasmids and bla _OXA-48-like genes in K. pneumoniae, we systematically analyzed the variants of bla _OXA-48-like plasmid replicon types, phylogenetic patterns, geographic distribution, conjugative transfer regions, and the genetic environments surrounding bla _OXA-48-like of 191 bla _OXA-48-like-harboring plasmids, which were identified from 4451 plasmids of K. pneumoniae downloaded from GenBank. Our results showed that seven different variants of bla _OXA-48-like genes were identified from the 191 bla _OXA-48-like-harboring plasmids in K. pneumoniae, with bla _OXA-48, bla _OXA-232, and bla _OXA-181 being highly prevalent. In K. pneumoniae, bla _OXA-48 was mainly carried by the composite transposon Tn1999.2 located on IncL/M-type conjugative plasmids, which were mainly geographically distributed in Switzerland, Germany, and China. In K. pneumoniae, the bla_OXA-232 gene was mainly carried by 6.1-kb ColKP3-type mobilizable plasmids, which were mainly isolated in India. In K. pneumoniae, bla _OXA-181 was mainly carried by a group of 50-kb ColKP3-IncX3 hybrid conjugative plasmids and a group of small ColKP3-type mobilizable plasmids with lengths of 5.9-9.3 kb, the former was sporadically discovered in China, South Korea, India, and Czech Republic, while the latter was almost all isolated in India. In addition, five bla _OXA-245-harboring 65.9-kb IncL plasmids of K. pneumoniae isolated in Spain were found to have the genetic context of bla _OXA-245 more complicated than that of bla _OXA-48-harboring IncL/M-type plasmids, with two copies of IS1R inserted both upstream and downstream of bla _OXA-245-lysR. These findings enhance our understanding of the genetic diversity of bla _OXA-48-like-harboring plasmids in K. pneumoniae.

A review on the mechanistic details of OXA enzymes of ESKAPE pathogens

The production of β-lactamases is a prevalent mechanism that poses serious pressure on the control of bacterial resistance. Furthermore, the unavoidable and alarming increase in the transmission of bacteria producing extended-spectrum β-lactamases complicates treatment alternatives with existing drugs and/or approaches. Class D β-lactamases, designated as OXA enzymes, are characterized by their activity specifically towards oxacillins. They are widely distributed among the ESKAPE bugs that are associated with antibiotic resistance and life-threatening hospital infections. The inadequacy of current β-lactamase inhibitors for conventional treatments of 'OXA' mediated infections confirms the necessity of new approaches. Here, the focus is on the mechanistic details of OXA-10, OXA-23, and OXA-48, commonly found in highly virulent and antibiotic-resistant pathogens Acinetobacter baumannii, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Enterobacter spp. to describe their similarities and differences. Furthermore, this review contains a specific emphasis on structural and computational perspectives, which will be valuable to guide efforts in the design/discovery of a common single-molecule drug against ESKAPE pathogens.

Efficacy and In Vitro Activity of Novel Antibiotics for Infections With Carbapenem-Resistant Gram-Negative Pathogens

Infections by Gram-negative multi-drug resistant (MDR) bacterial species are difficult to treat using available antibiotics. Overuse of carbapenems has contributed to widespread resistance to these antibiotics; as a result, carbapenem-resistant Enterobacterales (CRE), A. baumannii (CRAB), and P. aeruginosa (CRPA) have become common causes of healthcare-associated infections. Carbapenems, tigecycline, and colistin are the last resource antibiotics currently used; however, multiple reports of resistance to these antimicrobial agents have been documented worldwide. Recently, new antibiotics have been evaluated against Gram-negatives, including plazomicin (a new aminoglycoside) to treat CRE infection, eravacycline (a novel tetracycline) with in vitro activity against CRAB, and cefiderocol (a synthetic conjugate) for the treatment of nosocomial pneumonia by carbapenem-non-susceptible Gram-negative isolates. Furthermore, combinations of known β-lactams with recently developed β-lactam inhibitors, such as ceftazidime-avibactam, ceftolozane-tazobactam, ceftazidime-tazobactam, and meropenem-vaborbactam, has been suggested for the treatment of infections by extended-spectrum β-lactamases, carbapenemases, and AmpC producer bacteria. Nonetheless, they are not active against all carbapenemases, and there are reports of resistance to these combinations in clinical isolates.This review summarizes and discusses the in vitro and clinical evidence of the recently approved antibiotics, β-lactam inhibitors, and those in advanced phases of development for treating MDR infections caused by Gram-negative multi-drug resistant (MDR) bacterial species.