The genus Enterobacter is a member of the ESKAPE group, which contains the major resistant bacterial pathogens. First described in 1960, this group member has proven to be more complex as a result of the exponential evolution of phenotypic and genotypic methods. Today, 22 species belong to the Enterobacter genus. These species are described in the environment and have been reported as opportunistic pathogens in plants, animals, and humans. The pathogenicity/virulence of this bacterium remains rather unclear due to the limited amount of work performed to date in this field. In contrast, its resistance against antibacterial agents has been extensively studied. In the face of antibiotic treatment, it is able to manage different mechanisms of resistance via various local and global regulator genes and the modulation of the expression of different proteins, including enzymes (β-lactamases, etc.) or membrane transporters, such as porins and efflux pumps. During various hospital outbreaks, the Enterobacter aerogenes and E. cloacae complex exhibited a multidrug-resistant phenotype, which has stimulated questions about the role of cascade regulation in the emergence of these well-adapted clones.

https://hal-amu.archives-ouvertes.fr/hal-02735917/document

Enterobacter spp.: Update on Taxonomy, Clinical Aspects, and Emerging Antimicrobial Resistance

Cefepime is a broad-spectrum cephalosporin with enhanced coverage against Gram-positive and Gram-negative bacteria. We did a systematic review of randomised trials that compared cefepime with another beta-lactam antibiotic, alone or with the addition of a non-beta-lactam antibiotic to both study groups. We searched Central, PubMed, Embase, Lilacs, new US Food and Drug Administration drug applications, conference proceedings, and references of the included studies. Two reviewers independently did the search and data extraction. 57 trials were included. All-cause mortality-the primary outcome-was higher with cefepime than other beta-lactams (risk ratio [RR] 1.26 [95% CI 1.08-1.49]). Sensitivity analyses by the trials' methodological quality revealed higher RRs for trials reporting adequate allocation-sequence generation (1.52 [1.20-1.92]) and allocation concealment (1.36 [1.09-1.70]). Baseline risk factors for mortality were similar. No significant differences between groups in treatment failure, superinfection, or adverse events were found. This Review provides evidence and offers possible explanations for increased mortality among patients treated with cefepime in randomised trials.

/pdf/efficacy-and-safety-of-cefepime-a-systematic-review-and-meta-87izpw509w.pdf

Efficacy and safety of cefepime: a systematic review and meta-analysis

Mutation-dependent overproduction of intrinsic β-lactamase AmpC is considered the main cause of resistance of clinical strains of Pseudomonas aeruginosa to antipseudomonal penicillins and cephalosporins. Analysis of 31 AmpC-overproducing clinical isolates exhibiting a greater resistance to ceftazidime than to piperacillin-tazobactam revealed the presence of 17 mutations in the β-lactamase, combined with various polymorphic amino acid substitutions. When overexpressed in AmpC-deficient P. aeruginosa 4098, the genes coding for 20/23 of these AmpC variants were found to confer a higher (2-fold to >64-fold) resistance to ceftazidime and ceftolozane-tazobactam than did the gene from reference strain PAO1. The mutations had variable effects on the MICs of ticarcillin, piperacillin-tazobactam, aztreonam, and cefepime. Depending on their location in the AmpC structure and their impact on β-lactam MICs, they could be assigned to 4 distinct groups. Most of the mutations affecting the omega loop, the R2 domain, and the C-terminal end of the protein were shared with extended-spectrum AmpCs (ESACs) from other Gram-negative species. Interestingly, two new mutations (F121L and P154L) were predicted to enlarge the substrate binding pocket by disrupting the stacking between residues F121 and P154. We also found that the reported ESACs emerged locally in a variety of clones, some of which are epidemic and did not require hypermutability. Taken together, our results show that P. aeruginosa is able to adapt to efficacious β-lactams, including the newer cephalosporin ceftolozane, through a variety of mutations affecting its intrinsic β-lactamase, AmpC. Data suggest that the rates of ESAC-producing mutants are ≥1.5% in the clinical setting.

Mutations in β-Lactamase AmpC Increase Resistance of Pseudomonas aeruginosa Isolates to Antipseudomonal Cephalosporins

Cefepime is a new aminothiazolylacetamido cephalosporin with a wider spectrum and greater potency than many currently available cephalosporins. It appears that these characteristics result from multiple properties of the molecule. In contrast to older cephalosporins, cefepime more rapidly penetrates the gram-negative cell, targets multiple essential penicillin-binding proteins, and escapes the effects of many beta-lactamases due to the enzymes' low affinity for the drug. The latter characteristic is most apparent in studies of Bush group 1 beta-lactamases. Derepression of this class of beta-lactamases has less effect on the in vitro activity of cefepime than on that of other cephalosporins. The results of clinical trials should now be carefully analyzed to determine whether these advantages carry over into the clinical arena.

Cefepime: the next generation?

Enterobacter cloacae CHE, a clinical strain with overproduced cephalosporinase was found to be highly resistant to the new cephalosporins, cefepime and cefpirome (MICs≥128 μg ml−1). The strain was isolated from a child previously treated with cefepime. The catalytic efficiency of the purified enzyme with the third-generation cephalosporins, cefepime and cefpirome, was 10 times higher than that with the E. cloacae P99 enzyme. This was mostly due to a decrease in Km for these β-lactams. The clinical isolate produced large amounts of the cephalosporinase because introduction of the ampD gene decreased ampC expression and partially restored the wild-type phenotype. Indeed, MICs of cefepime and cefpirome remained 10 times higher than those for a stable derepressed clinical isolate (OUDhyp) transformed with an ampD gene. Sequencing of the ampC gene showed that 18 nucleotides had been deleted, corresponding to the six amino acids SKVALA (residues 289–294). According to the crystal structure of P99 β-lactamase, this deletion was located in the H-10 helix. The ampR-ampC genes from the clinical isolates CHE and OUDhyp were cloned and expressed in Escherichia coli JM101. The MICs of cefpirome and cefepime of E. coli harboring ampC and ampR genes from CHE were 100–200 times higher than those of E. coli harboring ampC and ampR genes from OUDhyp. This suggests that the deletion, confirmed by sequencing of the ampC gene, is involved in resistance to cefepime and cefpirome. However, the high level of resistance to cefepime and cefpirome observed in the E. cloacae clinical isolate was due to a combination of hyperproduction of the AmpC β-lactamase and structural modification of the enzyme. This is the first example of an AmpC variant conferring resistance to cefepime and cefpirome, isolated as a clinical strain.

Extension of resistance to cefepime and cefpirome associated to a six amino acid deletion in the H-10 helix of the cephalosporinase of an Enterobacter cloacae clinical isolate.

One hundred clinical isolates resistant to ceftazidime and/or cefotaxime were examined for susceptibility to cefepime. The most frequently encountered ceftazidime-cefotaxime-resistant strains belonged to the genera Enterobacter, Pseudomonas, and Citrobacter. Among these strains, 92% were resistant to cefoperazone, 91% were resistant to cefotaxime, 84% were resistant to ceftazidime, and 6% were resistant to cefepime. Of the members of the family Enterobacteriaceae, 57% were resistant to ceftriaxone. The six strains resistant to cefepime were all Pseudomonas aeruginosa and were resistant to both cefotaxime and ceftazidime. Cefepime-resistant P. aeruginosa strains had exceptionally high levels of beta-lactamase activity, higher than the levels found in strains resistant to ceftazidime but susceptible to cefepime. The beta-lactamases from the cefepime-resistant strains were type I (Richmond-Sykes), were constitutively produced, and did not have increased affinity or hydrolytic activity for cefepime. Thus, cefepime was active against most gram-negative bacteria which have developed resistance to the broad-spectrum cephalosporins, and resistance to cefepime in P. aeruginosa appears to be associated with higher beta-lactamase levels than in cefepime-susceptible strains.

Activity of cefepime against ceftazidime- and cefotaxime-resistant gram-negative bacteria and its relationship to beta-lactamase levels.

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Activity of cefepime against ceftazidime- and cefotaxime-resistant gram-negative bacteria and its relationship to beta-lactamase levels.

Advancement and Challenges in Municipal Landfill Leachate Treatment–The Path Forward!