Antibiotic use in animal agriculture: what have we learned and where are we going?
ABSTRACT Antibiotics are enormously important for the humane and efficient production of food animals. These benefits are somewhat offset by the human and animal health antibiotic resistance risks posed by their use in animals. This article provides an overview of what we have learned about antibiotic resistance as an issue in animal agriculture and where that knowledge could lead us in the future. To preserve the effectiveness of antibiotics, more action is needed to ensure their prudent use, particularly in the case of antibiotic growth promoters and antibiotics deemed critically important for human and animal health.
Article: Molecular ecology of macrolide-lincosamide-streptogramin B methylases in waste lagoons and subsurface waters associated with swine production.[show abstract] [hide abstract]
ABSTRACT: RNA methylase genes are common antibiotic resistance determinants for multiple drugs of the macrolide, lincosamide, and streptogramin B (MLS(B)) families. We used molecular methods to investigate the diversity, distribution, and abundance of MLS(B) methylases in waste lagoons and groundwater wells at two swine farms with a history of tylosin (a macrolide antibiotic structurally related to erythromycin) and tetracycline usage. Phylogenetic analysis guided primer design for quantification of MLS(B) resistance genes found in tylosin-producing Streptomyces (tlr(B), tlr(D)) and commensal/pathogenic bacteria (erm(A), erm(B), erm(C), erm(F), erm(G), erm(Q)). The near absence of tlr genes at these sites suggested a lack of native antibiotic-producing organisms. The gene combination erm(ABCF) was found in all lagoon samples analyzed. These four genes were also detected with high frequency in wells previously found to be contaminated by lagoon leakage. A weak correlation was found between the distribution of erm genes and previously reported patterns of tetracycline resistance determinants, suggesting that dissemination of these genes into the environment is not necessarily linked. Considerations of gene origins in history (i.e., phylogeny) and gene distributions in the landscape provide a useful "molecular ecology" framework for studying environmental spread of antibiotic resistance.Microbial Ecology 11/2009; 59(3):487-98. · 2.91 Impact Factor
Article: Field experience with two different vaccination strategies aiming to control infections with Actinobacillus pleuropneumoniae in a fattening pig herd.[show abstract] [hide abstract]
ABSTRACT: The prevalence of pleurisies recorded at slaughter is increasing in Sweden, and acute outbreaks of actinobacillosis that require antimicrobial treatments have become more frequent. As an increased use of antimicrobials may result in the development of antimicrobial resistance it is essential to develop alternative measures to control the disease. Vaccinations present an appealing alternative to antimicrobial treatments. The aim of this work was to evaluate the potential of two different vaccination strategies in a specialized fattening herd affected by actinobacillosis. The study was conducted in a specialized fattening herd employing age segregated rearing in eight units. The herd suffered from infections caused by Actinobacillus pleuropneumoniae serotype 2, confirmed by necropsy and serology. The study included 54 batches of pigs grouped into five periods. Batches of pigs of the second period were vaccinated against actinobacillosis twice, and pigs in the fourth period were vaccinated three times. Batches of pigs of the first, third and fifth period were not vaccinated. Concentrations of serum antibodies to A. pleuropneumoniae and serum amyloid A (SAA) were analysed and production data were recorded. Despite vaccinating, medical treatments were required to reduce the impact of the disease. The mean incidence of individual treatments for respiratory diseases during the rearing period ranged from 0 to 4.7 +/- 1.8%, and was greatest during the triple vaccination period (period IV; p < 0.05 when compared to other groups). A large proportion of the vaccinated pigs seroconverted to A. pleuropneumoniae serotype 2 in the absence of a SAA-response. The prevalence of pleuritis decreased from 25.4 +/- 6.5% in the first period to 5.0 +/- 3.7% in the fifth period (p < 0.001). The vaccine did not effectively prevent clinical expression of A. pleuropneumoniae infections, but seroconversion to A. pleuropneumoniae in the absence of a SAA-response in a large number pigs indicated that the vaccine had activated the immune system. Further, the prevalence of pleuritis decreased with time. This indicates that vaccinations together with intensified medical treatments of affected pigs could be useful in reducing the impact of A. pleuropneumoniae serotype 2 infections.Acta Veterinaria Scandinavica 03/2010; 52:23. · 1.00 Impact Factor
Article: Distribution and characterization of ampicillin- and tetracycline-resistant Escherichia coli from feedlot cattle fed subtherapeutic antimicrobials.[show abstract] [hide abstract]
ABSTRACT: Feedlot cattle in North America are routinely fed subtherapeutic levels of antimicrobials to prevent disease and improve the efficiency of growth. This practice has been shown to promote antimicrobial resistance (AMR) in subpopulations of intestinal microflora including Escherichia coli. To date, studies of AMR in feedlot production settings have rarely employed selective isolation, therefore yielding too few AMR isolates to enable characterization of the emergence and nature of AMR in E. coli as an indicator bacterium. E. coli isolates (n = 531) were recovered from 140 cattle that were housed (10 animals/pen) in 14 pens and received no dietary antimicrobials (control--5 pens, CON), or were intermittently administered subtherapeutic levels of chlortetracycline (5 pens-T), chlortetracycline + sulfamethazine (4 pens-TS), or virginiamycin (5 pens-V) for two separate periods over a 9-month feeding period. Phenotype and genotype of the isolates were determined by susceptibility testing and pulsed field gel electrophoresis and distribution of characterized isolates among housed cattle reported. It was hypothesized that the feeding of subtherapeutic antibiotics would increase the isolation of distinct genotypes of AMR E. coli from cattle. Overall, patterns of antimicrobial resistance expressed by E. coli isolates did not change among diet groups (CON vs. antibiotic treatments), however; isolates obtained on selective plates (i.e., M(A),M(T)), exhibited multi-resistance to sulfamethoxazole and chloramphenicol more frequently when obtained from TS-fed steers than from other treatments. Antibiograms and PFGE patterns suggested that AMR E. coli were readily transferred among steers within pens. Most M(T) isolates possessed the tet(B) efflux gene (58.2, 53.5, 40.8, and 50.6% of isolates from CON, T, TS, and V steers, respectively) whereas among the M(A) (ampicillin-resistant) isolates, the tem1-like determinant was predominant (occurring in 50, 66.7, 80.3, and 100% of isolates from CON, T, TS, and V steers, respectively). Factors other than, or in addition to subtherapeutic administration of antibiotics influence the establishment and transmission of AMR E. coli among feedlot cattle.BMC Microbiology 01/2011; 11:78. · 3.04 Impact Factor