Abstract
Integrons are genetic elements that capture and express antimicrobial resistance genes within arrays, facilitating horizontal spread of multiple drug resistance in a range of bacterial species. The aim of this study was to estimate prevalence for class 1, 2, and 3 integrons in Scottish cattle and examine whether spatial, seasonal or herd management factors influenced integron herd status. We used fecal samples collected from 108 Scottish cattle herds in a national, cross-sectional survey between 2014 and 2015, and screened fecal DNA extracts by multiplex PCR for the integrase genes intI1, intI2, and intI3. Herd-level prevalence was estimated [95% confidence interval (CI)] for intI1 as 76.9% (67.8–84.0%) and intI2 as 82.4% (73.9–88.6%). We did not detect intI3 in any of the herd samples tested. A regional effect was observed for intI1, highest in the North East (OR 11.5, 95% CI: 1.0–130.9, P = 0.05) and South East (OR 8.7, 95% CI: 1.1–20.9, P = 0.04), lowest in the Highlands. A generalized linear mixed model was used to test for potential associations between herd status and cattle management, soil type and regional livestock density variables. Within the final multivariable model, factors associated with herd positivity for intI1 included spring season of the year (OR 6.3, 95% CI: 1.1–36.4, P = 0.04) and watering cattle from a natural spring source (OR 4.4, 95% CI: 1.3–14.8, P = 0.017), and cattle being housed at the time of sampling for intI2 (OR 75.0, 95% CI: 10.4–540.5, P < 0.001). This study provides baseline estimates for integron prevalence in Scottish cattle and identifies factors that may be associated with carriage that warrant future investigation.
Highlights
Antimicrobial resistance (AMR) is a serious global health problem that prevents the effective treatment of bacterial infections in humans and animals worldwide and requires a One Health approach [1, 2]
The overall number of herds included in the study and the number of samples taken per herd were based on a previous sampling framework for estimating E. coli O157 prevalence in Scotland, designed to estimate prevalence with a sensitivity of 90% and confidence of 96% for an expected herd prevalence level of 20.5% [37]
The observed prevalence for intI1 and intI2 in the study herds was examined by Animal Health District (AHD) to investigate possible geographical variation across Scotland (Figure 1)
Summary
Antimicrobial resistance (AMR) is a serious global health problem that prevents the effective treatment of bacterial infections in humans and animals worldwide and requires a One Health approach [1, 2]. Antimicrobial resistance genes (ARG) are disseminated through two main routes, the vertical transmission of chromosomally encoded resistance genes to daughter cells and the horizontal transfer of genes between bacterial cells facilitated by mobile genetic elements, such as plasmids, transposons, and phage DNA [5]. Integrons are genetic elements that function as gene capture and expression systems, integrating single or multiple gene cassettes at the attI recombination site by means of the integrase, intI, gene [6, 7]. There are several classes of integron found in many bacterial species worldwide, from diverse human, animal and environmental origins, only classes 1 to 3 are thought to be of clinical relevance within human healthcare or livestock settings [9]
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