Interestingly, tetracycline resistance was the most abundant class of virulence subsystems within the swine fecal metagenome, which may be explained by the fact that this antibiotic class was used in the diet supplied to the animals associated with this study. This antibiotic class is reported as comprising nearly half of the total amount of antibiotics used in commercial swine operations [20]. Resistance to fluoroquinolones was also well represented in the swine fecal metagenome, and may be explained by the increase of its non-therapeutic use within pig feed. While
early studies indicated there was a low risk of fluoroquinolone resistance, recent studies are showing the use of Selleck AZD2014 fluoroquinolones is among the most important factors associated with Foretinib finding resistant E. coli and Campylobacter in animal operations PF-6463922 supplier [21]. Interestingly, there was no history of fluoroquinolone use
on the swine farm from which these samples were collected. Fluoroquinolone resistance has been found on farms with no history of fluoroquinolone use, suggesting that resistant organisms, such as Campylobacter have the ability to spread between pig farms. Genes with high sequence similarity to methicillin-resistant Staphylococcus subsystem were also retrieved in this study. This finding is important considering MRSA carriage has been elevated in swine and exposed farmers and veterinarians [22], suggesting Metformin purchase that MRSA infection is a significant risk in swine farm resident and worker cohorts. More than 12% of virulence subsystems identified in the pig fecal metagenome were classified as multi-drug resistance mechanisms, suggesting the pig gut could be a hot-spot for multiple-antibiotic resistant bacteria. One subsystem, the MexA-MexB-OprM multiple drug efflux pump was found exclusively in the swine fecal metagenome. This antibiotic resistance mechanism
has been detected only in Pseudomonas aeruginosa strains known to carry resistance in cystic fibrosis patients [23] and has not been previously described in distal gut environments. Additionally, more than 10% of virulence-associated sequences were assigned to yet-to-be-described virulence subsystems, suggesting that unknown virulence mechanisms are at work within the distal gut. Altogether, the high abundance of metagenomic sequences assigned to known and unknown antibiotic resistance subsystems suggests that functional metagenomics is an adequate tool for assessing the prevalence of antibiotic resistance within high cell density environments. Pair-wise comparisons of each gut metagenome (MG-RAST SEED database) with the swine gut revealed 15 SEED subsystems that were significantly different in abundance for the swine fecal metagenome (Figure 6 and Additional File 1, Fig. S12).