Recipient Organization
UNIVERSITY OF CALIFORNIA, DAVIS
410 MRAK HALL
DAVIS,CA 95616-8671
Performing Department
Population Health & Reproduction
Non Technical Summary
Antimicrobial resistance (AMR) surveillance is important to monitor, evaluate and estimate the potential transfer of AMR from livestock into human pathogens. According to the latest National Antimicrobial Resistance Monitoring System (NARMS) report released by the U.S. Food and Drug Administration (FDA), one concern has been the increase in multidrug resistant (MDR) Salmonella Dublin isolates (a bovine-adapted serotype) which have also displayed high levels of resistance to important cephalosporins drugs like ceftriaxone. Another drug for which monitoring resistance is of extreme importance in Salmonella is the quinolone class (e.g., ciprofloxacin); drugs in this class are critically important for treating severe Salmonella infections in human adults. In recent years, a shift has been observed on resistance genomic factors that results in cephalosporin and fluoroquinolone resistance in gram-negative bacteria from fecal samples from dairy cattle. This includes an increase in Escherichia coli strains carrying blaCTX-M, as well as Salmonella carrying plasmid-mediated quinolone resistance (PMQR) that result in reduced susceptibility to ciprofloxacin.The objective of this project is to screen Salmonella isolates for resistance genetic elements that confer resistance to two of the most important drug classes for use in veterinary and human medicine: beta-lactams (with a focus on cephalosporin drugs) and fluoroquinolones. Isolates being screened were obtained from dairy cattle admitted in the Veterinary Medical Teaching Hospital (VMTH) at UC Davis (Davis, CA).
Animal Health Component
20%
Research Effort Categories
Basic
80%
Applied
20%
Developmental
0%
Goals / Objectives
This project objectives are: 1) screen Salmonella for beta-lactam resistance genes, focusing on genes linked to resistance to cephalosporin drugs; 2) screen Salmonella for quinolone resistance genes; 3) evaluate temporal distribution of genetic elements linked with AMR to these two drug classes, generating information to evaluate temporal-spatial spread, as well as inter-serotype spread of AMR genes.
Project Methods
Study Design: Salmonella isolates obtained from fecal samples submitted from cattle to the Veterinary Medical Teaching Hospital (VMTH) at UC Davis (Davis, CA) for a 16-year interval (2002 to 2017) will be selected for the study. Salmonella isolates are expected to be originating from fecal samples of 1) cattle that exhibited clinical signs of salmonellosis and from 2) the VMTH Infectious Disease Control program, submitted from animals that not necessarily displaying clinical signs of salmonellosis. Information to be collected from the record database for Salmonella isolates (e.g. location (county) of farm of origin, age of animals, breed, and production status) will be limited to that allowable by VMTH, assuring that individual identity of clients is preserved. Original client identifiers will not be collected to protect client identity and other confidential information. We expect to have more than 240 isolates representing over 9,000 fecal samples from cattle submitted for Salmonella culture.Screening for AMR genes using PCR: DNA extraction will be conducted using previously described methods1. Salmonella isolates with phenotypic resistance to cephalosporin drugs or fluoroquinolones drugs will be selected for screening using multiplex PCR. Primers will focus on genes known to confer resistance to beta-lactam drugs, especially cephalosporin drugs (e.g., ceftiofur and ceftriaxone), as well as genes related with resistance to quinolone drugs. Specific beta-lactam resistance genes to be screened include blaTEM variants, blaCMY variants and blaCTX-M variants, whereas for quinolone, only plasmid-mediated quinolone resistance determinants (PMQR) will be screened, and include qnrB, qnrS, oqx(A), oqx(B), and aac(6')-Ib. Methodology and primers will be based on previously described protocols5-9.Statistical Analysis: Variables of interest to be included in the analysis will be AMR genetic components as the dependent variable and age, production status, location (county) of farm of origin, breed, and year and month when samples were collected will be considered as independent variables. For each AMR genetic component tested, temporal trends in the prevalence of this genetic component for the last 16 years will be evaluated. Important confounders (e.g. Salmonella serotype) will be evaluated for temporal trends in prevalence using multivariate regression models. Spatio-temporal clusters distribution of Salmonella isolates over the last 16 years will be conducted at the county level if, assuring regional aggregates of clients occurs in a matter that assures identity protection. For all statistical analyses, P value < 0.05 will be considered significant.