Antibiotics growth promoters (AGP) have been used for growth promotion of chickens in poultry industry since 1950. Recently, concerns have been raised to the use of AGP in livestock due to development of antibiotic resistance in bacteria. The objective of our study is to investigate the effect of AGP in cecal microbiota of broiler chickens. Two groups (n = 30) of chickens were fed corn-soybean meal diets with (ANT) and without supplementation of Penicillin (CON) at the concentration of 55 mg/kg. At 18 d of age, ANT group had significantly (P < 0.05) higher mean body weight than CON group (668.6 vs. 570.0 g). Cecal samples of 5 randomly selected birds were pooled from each group and used for genomic DNA isolation and PCR amplification of 16S rRNA gene. 454 pyrosequencing of the amplicons resulted in 7,881 and 11,214 sequence reads for CON and ANT groups, respectively. BLAST and phylogenetic analysis using MEGAN-3 indicate that AGP supplementation in ANT group resulted in elevated proportion of phylum Firmicutes from 16.67% to 17.47% and a decreased proportion of phylum Bacteriodetes from 15.71% to 0.14% as compared with CON group. Recent studies conducted in humans, pigs and mice have shown a similar shift in gut microbiota in obese individuals as compared with lean ones, indicating that this shift could be responsible for increase in energy harvest and body weight. The results of this study suggest that the growth promoting effect of AGP supplementation in broilers may be mediated by a similar microbial process. Hence, new and alternative methods for promoting the growth of the birds need to be sought for that may alter gut microflora in a similar pattern.
