Beneficial Microbes, June 2012; 3(2): 137-144 Wageningen Academic Publisher s ISSN 1876-2833 print, ISSN 1876-2891 online, DOI 10.3920/BM2011.0058 137 1. Introduction Horizontal gene transfer of determinants for antibiotic resistance, pathogenicity, and other operational features (e.g. those involved in housekeeping) between microorganisms is a common phenomenon in diverse ecosystems, such as the natural environment and the animal gut (Jain et al., 1999). Environmental variables such as temperature, the availability and type of nutrients, and other factors such as the rate of transduction mediated by viruses, or conjugation between donor and recipient partners in complex bacterial communities, can all influence the uptake of exogenous naked DNA via transformation. The misuse and intense use of antimicrobial drugs in modern animal husbandry is a strong selective force that drives the development of multi-drug resistant populations of microorganisms, Transfer of antibiotic resistance determinants between lactobacilli isolates from the gastrointestinal tract of chicken F. Vieira de Souza 1 , R. Roque 1 , J.L. Silva Moreira 1 , M. Resende de Souza 3 , J.R. Nicoli 2 , E. Neumann 2 and Á. Cantini Nunes 1 1 Universidade Federal de Minas Gerais, Departamento de Biologia Geral, Campus Pampulha, Av. Antônio Carlos, 6627, 31270-901 Belo Horizonte, MG, Brazil; 2 Universidade Federal de Minas Gerais, Instituto de Ciências Biológicas, Departamento de Microbiologia, Campus Pampulha, Av. Antônio Carlos, 6627, 31270-901 Belo Horizonte, MG, Brazil; 3 Universidade Federal de Minas Gerais, Escola de Veterinária, Departamento de Inspeção e Tecnologia de Produtos de Origem Animal, Campus Pampulha, Av. Antônio Carlos, 6627, 30123-970 Belo Horizonte, MG, Brazil; cantini@icb.ufmg.br Received: 22 December 2011 / Accepted: 1 March 2012 © 2012 Wageningen Academic Publishers Abstract The aim of this study was to assess the potential horizontal transfer of genetic traits for antibiotic resistance between lactobacilli isolated from the chicken gut, both in vitro and in vivo. Thirty-seven Lactobacillus spp. strains isolated from the gizzard, small and large intestines and caeca of free-range broiler chickens showed multi-drug resistance as assessed by disc diffusion assays. The minimum inhibitory concentration (MIC) for vancomycin, tetracycline, erythromycin and chloramphenicol was determined in De Man, Rogosa and Sharpe broth in a microplate assay. Almost all the lactobacilli isolates were resistant to vancomycin (except strains belonging to the Lactobacillus acidophilus group) and to tetracycline (MIC≥128 µg/ml). Only five strains were resistant to erythromycin, and six to chloramphenicol. The transfer rate in filter mating experiments performed using L. acidophilus strain 4M14E (Em R ), Lactobacillus vaginalis strain 5M14E (Cm R ), Lactobacillus salivarius strain 5C14C (Em R ), and the 4G14L and 3C14C strains of Lactobacillus reuteri (Cm R ) showed a frequency of approximately 1×10 4 cfu/ml of double- resistant transconjugants for the different combinations. The exception was the L. salivarius 5C14C (Em R ) and L. vaginalis 5M14E (Cm R ) mating combination, which produced no transconjugants. In vivo experiments performed in gnotobiotic mice by mating L. acidophilus 4M14E (Em R ) with L. reuteri 3C14C (Cm R ), L. reuteri 4G14L (Cm R ) or L. vaginalis 5M14E (Cm R ) resulted in transconjugants at 3.95±0.29, 3.16±0.33, and 4.55±1.52 log 10 cfu/g of faeces, respectively. Taken together, these data suggest that genetic exchange may occur between native bacterial strains within the gastrointestinal tract of chickens, which might maintain a dynamic gene pool conferring antibiotic resistance upon indigenous microbiota components, even in the absence of the pathogens. This possibility must be taken into account as a complementary criterion when lactobacilli are screened for probiotic use. Keywords: horizontal gene transfer, Lactobacillus, gut, chicken, antibiotic resistance http://www.wageningenacademic.com/doi/pdf/10.3920/BM2011.0058 - Tuesday, November 28, 2017 1:27:40 PM - Göteborgs Universitet IP Address:130.241.16.16