Overproduction of Chromosomal ampC β-Lactamase Gene Maintains Resistance to Cefazolin in Escherichia coli Isolates

Impact of extended-spectrum chromosomal AmpC (ESAC) of Escherichia coli on susceptibility to cefiderocol

The impact of chromosomally encoded wild-type or extended-spectrum (ESAC) AmpC β-lactamases of Escherichia coli on susceptibility to ceftazidime, cefepime, and cefiderocol was evaluated in different genetic backgrounds, including wild-type, PBP3-modified, and porin-deficient E. coli strains. Recombinant E. coli strains possessing the different backgrounds and producing variable ESACs were evaluated. Although ESAC enzymes conferred resistance to ceftazidime and decreased susceptibility to cefepime as expected, we showed here that cefiderocol was also a substrate of ESAC enzymes.

IMPORTANCE

We showed here that chromosomally encoded intrinsic extended-spectrum cephalosporinases of Escherichia coli may impact susceptibility not only to ceftazidime and cefepime but also to cefiderocol.

Role of RelA-synthesized (p)ppGpp and ROS-induced mutagenesis in de novo acquisition of antibiotic resistance in E. coli

The stringent response of bacteria to starvation and stress also fulfills a role in addressing the threat of antibiotics. Within this stringent response, (p)ppGpp, synthesized by RelA or SpoT, functions as a global alarmone. However, the effect of this (p)ppGpp on resistance development is poorly understood. Here, we show that knockout of relA or rpoS curtails resistance development against bactericidal antibiotics. The emergence of mutated genes associated with starvation and (p)ppGpp, among others, indicates the activation of stringent responses. The growth rate is decreased in ΔrelA-resistant strains due to the reduced ability to synthesize (p)ppGpp and the persistence of deacylated tRNA impeding protein synthesis. Sluggish cellular activity causes decreased production of reactive oxygen species (ROS), thereby reducing oxidative damage, leading to weakened DNA mismatch repair, potentially reducing the generation of mutations. These findings offer new targets for mitigating antibiotic resistance development, potentially achieved through inhibiting (p)ppGpp or ROS synthesis.

Application of phylodynamics to identify spread of antimicrobial-resistant Escherichia coli between humans and canines in an urban environment

The transmission of antimicrobial resistant bacteria in the urban environment is poorly understood. We utilized genomic sequencing and phylogenetics to characterize the transmission dynamics of antimicrobial resistant Escherichia coli (AMR-Ec) cultured from putative canine (caninep) and human feces present on urban sidewalks in San Francisco, California. We isolated a total of fifty-six AMR-Ec isolates from human (n = 20) and caninep (n = 36) fecal samples from the Tenderloin and South of Market (SoMa) neighborhoods of San Francisco. We then analyzed phenotypic and genotypic antimicrobial resistance (AMR) of the isolates, as well as clonal relationships based on cgMLST and single nucleotide polymorphisms (SNPs) of the core genomes. Using Bayesian inference, we reconstructed the transmission dynamics between humans and caninesp from multiple local outbreak clusters using the marginal structured coalescent approximation (MASCOT). Our results provide evidence for multiple sharing events of AMR-Ec between humans and caninesp. In particular, we found one instance of likely transmission from caninesp to humans as well as an additional local outbreak cluster consisting of one caninep and one human sample. Based on this analysis, it appears that non-human feces act as an important reservoir of clinically relevant AMR-Ec within the urban environment for this study population. This work showcases the utility of genomic epidemiology to reconstruct potential pathways by which antimicrobial resistance spreads.

Fatal Necrotizing Fasciitis Mediated by Escherichia coli After Parotidectomy and Neck Dissection: A Case Report and Review of the Literature

Necrotizing soft tissue infection (NSTI) is a rare, but life-threatening, complication of head and neck surgery. We present a 70-year-old male with a history of immunosuppression who presented with polymicrobial NSTI following parotidectomy and neck dissection for cutaneous squamous cell carcinoma. The objective of this report was to promote awareness for NSTI following parotidectomy and selective neck dissection and highlight the management measures that can optimize survival outcomes. We performed a database search that identified 1,025 citations, of which 5 articles described classified as craniocervical necrotizing fasciitis following major head and neck surgery. Consent was obtained from the patient for inclusion in the research study and Institutional Review Board approval was waived. Our literature review yielded 6 cases of craniocervical necrotizing fasciitis following major head and neck surgery. This NSTI, however-unlike the others previously reported-was predominantly mediated by Escherichia coli, a bacterium associated with elevated mortality rates. Despite immediate awake fiberoptic intubation, repeated surgical debridement, and empirical antibiotic therapy, he deteriorated rapidly and was withdrawn from life-support on postoperative day seven. Prophylactic antibiotics, airway management, prompt diagnosis, and surgical debridement are critical for limiting mortality in NSTI of the head and neck.