CTX-M [a major type of extended-spectrum beta-lactamase (ESBL)] producing Escherichia coli are increasingly involved in human infections worldwide. The aim of this study was to investigate potential reservoirs for such strains: soils, cattle, and farm environment. The prevalence of bla_CTX-M genes was determined directly from soil DNA extracts obtained from 120 sites in Burgundy (France) using real-time PCR. bla_CTX-M targets were found in 20% of the DNA extracts tested. Samples of cattle feces (n = 271) were collected from 182 farms in Burgundy. Thirteen ESBL-producing isolates were obtained from 12 farms and further characterized for the presence of bla genes. Of the 13 strains, five and eight strains carried bla_TEM-71 genes and bla_CTX-M-1 genes respectively. Ten strains of CTX-M-1 producing E. coli were isolated from cultivated and pasture soils as well as from composted manure within two of these farms. The genotypic analysis revealed that environmental and animal strains were clonally related. Our study confirms the occurrence of CTX-M producing E. coli in cattle and reports for the first time the occurrence of such strains in cultivated soils. The environmental competence of such strains has to be determined and might explain their long term survival since CTX-M isolates were recovered from a soil that was last amended with manure 1 year before sampling.

SUMMARY: Achromobacter spp. are emerging opportunistic Gram-negative rods responsible for diverse nosocomial or community-acquired infections. We describe, for the first time, the distribution of Achromobacter spp., defined by nrdA gene sequencing, and their antimicrobial susceptibility in a variety of non-respiratory samples recovered from hospitalized patients from 2010 to 2015. Of the 63 isolates studied, A. xylosoxidans was the most prevalent (41 isolates), and with the exception of A. insuavis (four isolates), the remaining 10 species identified were represented by one or two isolates only. All isolates were uniformly susceptible to piperacillin and piperacillin-tazobactam and 97% to meropenem, but 76% showed resistance to ciprofloxacin. This study confirms the diversity of Achromobacter spp. in non-cystic fibrosis (CF) isolates and the predominance of A. xylosoxidans, as previously reported for CF sputum isolates. There was no apparent link between the clinical site of infection and the species of Achromobacter.

AxyXY-OprZ is an RND-type efflux system that confers innate aminoglycoside resistance to Achromobacter spp. We investigated here a putative TetR family transcriptional regulator encoded by the axyZ gene located upstream of axyXY-oprZ . An in-frame axyZ gene deletion assay led to increased MICs of antibiotic substrates of the efflux system, including aminoglycosides, cefepime, fluoroquinolones, tetracyclines, and erythromycin, indicating that the product of axyZ negatively regulates expression of axyXY-oprZ . Moreover, we identified an amino acid substitution at position 29 of AxyZ (V29G) in a clinical Achromobacter strain that occurred during the course of chronic respiratory tract colonization in a cystic fibrosis (CF) patient. This substitution, also detected in three other strains exposed in vitro to tobramycin, led to an increase in the axyY transcription level (5- to 17-fold) together with an increase in antibiotic resistance level. This overproduction of AxyXY-OprZ is the first description of antibiotic resistance acquisition due to modification of a chromosomally encoded mechanism in Achromobacter and might have an impact on the management of infected CF patients. Indeed, tobramycin is widely used for aerosol therapy within this population, and we have demonstrated that it easily selects mutants with increased MICs of not only aminoglycosides but also fluoroquinolones, cefepime, and tetracyclines.