Abstract
Poultry frequently account for the highest prevalence of extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae in livestock. To investigate the impact of direct-fed microbials (DFM) and phytobiotic feed additives on prevalence and conjugation of extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae, an animal trial was conducted. Lactobacillus agilis LA73 and Lactobacillus salivarius LS1 and two commercial phytogenic feed additives (consisting of carvacrol, cinnamaldehyde, and eugenol) were used as feed additives either alone or as a combination of DFM and phytogenic feed additive. An ESBL-producing E. coli donor and a potentially pathogenic Salmonella Typhimurium recipient were inoculated at 5 × 109 cells/mL in cecal contents from 2-week-old broilers. Conjugation frequencies were determined after 4 h aerobic co-incubation at 37 °C and corrected for the impact of the sample matrix on bacterial growth of donor and recipient. Surprisingly, indigenous Enterobacteriaceae acted as recipients instead of the anticipated Salmonella recipient. The observed increase in conjugation frequency was most obvious in the groups fed the combinations of DFM and phytogenic product, but merely up to 0.6 log units. Further, cecal samples were examined for ESBL-producing Enterobacteriaceae on five consecutive days in broilers aged 27–31 days. All samples derived from animals fed the experimental diet showed lower ESBL-prevalence than the control. It is concluded that Lactobacillus spp. and essential oils may help to reduce the prevalence of ESBL-harboring plasmids in broilers, while the effect on horizontal gene transfer is less obvious.
Highlights
Broiler chickens are the livestock with the highest prevalence of extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae in many regions of the world
The different feed additives and their combinations did not show a significant impact on Salmonella Typhimurium L1219-R32 (p = 0.183) or E. coli ESBL10682 (p = 0.317) growth (Table 3)
The initial concentration of approximately 8.7 log cfu/mL cecal content of each donor and recipient strain declined after 4 h of incubation to 7.5–7.9 log cfu/g cecal content for E. coli ESBL10682 and 7.9–8.4 log cfu Salmonella Typhimurium/g cecal content while the indigenous, SXT-resistant Enterobacteriaceae showed concentrations of 6.4–7.1 log cfu/g cecal content
Summary
Broiler chickens are the livestock with the highest prevalence of extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae in many regions of the world In this context, E. coli and Salmonella spp. are the bacteria most commonly identified as the host of bla (ESBL encoding genes) carrying plasmids [1]. Transmission of ESBL-producing bacteria between animals happens rapidly and undetected, as no specific symptoms accompany the inoculation and establishment of ESBL-producing Enterobacteriaceae in broilers. These primarily non-pathogenic bacteria can, transfer mobile genetic elements to pathogenic bacteria and thereby cause infections, which are difficult to cure [2,3,4,5]. These studies comprise commercial products and competitive exclusion cultures, no exact qualitative and quantitative specification of the containing microorganisms was provided
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