Cefazolin and imipenem enhance AmpC expression and resistance in NagZ-dependent manner in Enterobacter cloacae complex

Exploring nagZ as a virulence biomarker and treatment target in Enterobacter cloacae

BACKGROUND

Enterobacter cloacae is increasingly prevalent and resistant to multiple antibiotics, making it a significant pathogen in healthcare settings with high mortality rates. However, its pathogenic mechanisms are not fully understood.

RESULTS

In this study, we explored the role of nagZ in regulating the virulence of E. cloacae and its potential as a therapeutic target. Our research showed that pathogenic strains of E. cloacae express higher levels of nagZ than colonizing strains, particularly in simulated infection environments. Deleting nagZ significantly reduced E. cloacae virulence in various infection models, including Galleria mellonella larvae, mice, and RAW264.7 cells. Moreover, nagZ knockout decreased the bacterium's ability to induce inflammatory factor levels, while complementing nagZ in knockout strains partially rescued this ability. Importantly, the absence of nagZ also enhanced the antibacterial efficacy of ceftazidime against E. cloacae.

CONCLUSIONS

These findings underscore the crucial role of nagZ in E. cloacae pathogenesis and highlight its potential as a novel therapeutic target for treating infections caused by this pathogen.

Cefepime versus carbapenems for treatment of AmpC beta-lactamase-producing Enterobacterales bloodstream infections

PURPOSE

Cefepime is recommended for treating infections caused by AmpC beta-lactamase-producing Enterobacterales (AmpC-PE), though supporting evidence is limited. Therefore, this study compared outcomes associated with cefepime versus carbapenem therapy for bloodstream infections (BSIs) caused by AmpC-PE after phenotypic exclusion of ESBL-co-producing isolates.

METHODS

This retrospective cohort study compared definite cefepime versus carbapenem treatment for AmpC-PE BSI in hospitalized patients of the University Hospital Basel, Switzerland, between 01/2015 and 07/2020. Primary outcomes included in-hospital death, renal impairment and neurologic adverse events; secondary outcomes included length of hospital stay and recurrent infection.

RESULTS

Two hundred and seventy episodes of AmpC-PE BSI were included, 162, 77 and 31 were treated with a carbapenem, cefepime and other antibiotics, respectively. Patients treated with carbapenems were more likely to be transferred to the ICU on admission and more frequently had central venous catheter as a source of infection. In uni- and multivariable analyses, primary and secondary outcomes did not differ between the two treatment groups, except for more frequent occurrence of neurological adverse events among patients treated with carbapenems and shorter length of hospital stay among survivors treated with cefepime.

CONCLUSION

After excluding isolates with phenotypic ESBL-co-production, cefepime was not associated with adverse outcomes compared to carbapenems when used to treat BSIs caused by AmpC-PE. Our study provides evidence to support the use of cefepime as a safe treatment strategy for AmpC-PE BSI, particularly in clinically stable patients without initial renal impairment or increased susceptibility to neurological adverse events.

Filling knowledge gaps related to AmpC-dependent β-lactam resistance in Enterobacter cloacae

Enterobacter cloacae starred different pioneer studies that enabled the development of a widely accepted model for the peptidoglycan metabolism-linked regulation of intrinsic class C cephalosporinases, highly conserved in different Gram-negatives. However, some mechanistic and fitness/virulence-related aspects of E. cloacae choromosomal AmpC-dependent resistance are not completely understood. The present study including knockout mutants, β-lactamase cloning, gene expression analysis, characterization of resistance phenotypes, and the Galleria mellonella infection model fills these gaps demonstrating that: (i) AmpC enzyme does not show any collateral activity impacting fitness/virulence; (ii) AmpC hyperproduction mediated by ampD inactivation does not entail any biological cost; (iii) alteration of peptidoglycan recycling alone or combined with AmpC hyperproduction causes no attenuation of E. cloacae virulence in contrast to other species; (iv) derepression of E. cloacae AmpC does not follow a stepwise dynamics linked to the sequential inactivation of AmpD amidase homologues as happens in Pseudomonas aeruginosa; (v) the enigmatic additional putative AmpC-type β-lactamase generally present in E. cloacae does not contribute to the classical cephalosporinase hyperproduction-based resistance, having a negligible impact on phenotypes even when hyperproduced from multicopy vector. This study reveals interesting particularities in the chromosomal AmpC-related behavior of E. cloacae that complete the knowledge on this top resistance mechanism.