title: The effect of chlortetracycline on faecal microbial populations in growing swine.
abstract: The effect of antimicrobial use on the gastrointestinal microbiota of food animals is of increasing concern as bacteria accumulate resistance to multiple antimicrobials. Only a small fraction of the gastrointestinal microbiome is culturable, complicating characterisation of the swine gastrointestinal ecosystem. The objective of this study was to determine the effect of a growth promotion dose (50g/ton) of chlortetracycline on the phylogenetic diversity of bacteria from swine faeces using a culture-independent method. Four freshly weaned pigs were provided a grower ration of primarily corn (63.7%) and soybean meal (25.2%) for 21 days; on Day 21 for 4 weeks the diet of two pigs was medicated with 50g/ton chlortetracycline. Faecal material was collected from each pig on Days 0, 14, 23, 28, 35, 42 and 49 for 454-pyrosequencing of the 16S rRNA gene. UniFrac analysis of pyrosequencing data showed no significant difference in bacterial diversity based on diet and among pigs (P>0.05) fed the low-level dose of chlortetracycline. The most abundant phyla in both treatment groups were Firmicutes, Bacteroidetes, Proteobacteria and Spirochaetes. Higher concentrations of chlortetracycline (e.g. 200g/ton or 400g/ton) may be required to observe a shift in the gastrointestinal flora in swine faeces compared with the low-level dose in this study. Studies of broader scope are needed to understand thoroughly how growth-promoting antimicrobials influence the gut microflora and benefit food animal growth efficiency.
authors.affiliation: US Department of Agriculture, Agricultural Research Service (USDA/ARS), Southern Plains Agricultural Research Center, 2881 F&B Road, College Station, TX 77845, USA. Electronic address: toni.poole@ars.usda.gov.
authors.forename: T L
authors.initials: TL
authors.lastname: Poole
authors.affiliation: Texas A&M University, College of Veterinary Medicine, G.I. Laboratory, College Station, TX 77845, USA.
authors.forename: J S
authors.initials: JS
authors.lastname: Suchodolski
authors.affiliation: US Department of Agriculture, Agricultural Research Service (USDA/ARS), Southern Plains Agricultural Research Center, 2881 F&B Road, College Station, TX 77845, USA.
authors.forename: T R
authors.initials: TR
authors.lastname: Callaway
authors.affiliation: Department of Food and Animal Sciences, Texas Tech University, Lubbock, Texas 79409, USA.
authors.forename: R L
authors.initials: RL
authors.lastname: Farrow
authors.affiliation: International Center for Food Industry Excellence, Department of Animal and Food Sciences, Texas Tech University, Lubbock, Texas 79409, USA.
authors.forename: G H
authors.initials: GH
authors.lastname: Loneragan
authors.affiliation: US Department of Agriculture, Agricultural Research Service (USDA/ARS), Southern Plains Agricultural Research Center, 2881 F&B Road, College Station, TX 77845, USA.
authors.forename: D J
authors.initials: DJ
authors.lastname: Nisbet
keywords: Faecal microbial diversity; Growth promotion; Pyrosequencing; Swine