- Impact of Tetracycline on the Human Intestinal Microbiome and Antimicrobial Resistance
- Plasmids from Salmonella Can Contribute to Their Antimicrobial Resistance and Potential Virulence
Antimicrobial-Resistance Research
Impact of Tetracycline on the Human Intestinal Microbiome and Antimicrobial Resistance
Scientists from NCTR and CVM have shown—using in vitro batch cultures of bacteria-laden fecal slurries derived from humans—that tetracycline, an antibiotic, at low-residue concentrations following acute and chronic exposure could affect the human intestinal-microbiome composition and the antimicrobial-resistance gene profile. There are two microbiological endpoints that are measured based on national regulatory guidelines: 1) microbial composition changes that could cause colonization barrier disruption and 2) selection/emergence of resistance after antibiotic exposure. The use of antibiotics in food-producing animals may result in residues of these drugs in meat, milk, and eggs. Dietary exposure to antimicrobial agents in food may lower the gastrointestinal-colonization barrier to allow the emergence of resistant bacteria in the human intestinal microbiome.
Scientists from NCTR and CVM have shown—using in vitro batch cultures of bacteria-laden fecal slurries derived from humans—that tetracycline, an antibiotic, at low-residue concentrations following acute and chronic exposure could affect the human intestinal-microbiome composition and the antimicrobial-resistance gene profile. There are two microbiological endpoints that are measured based on national regulatory guidelines: 1) microbial composition changes that could cause colonization barrier disruption and 2) selection/emergence of resistance after antibiotic exposure. The use of antibiotics in food-producing animals may result in residues of these drugs in meat, milk, and eggs. Dietary exposure to antimicrobial agents in food may lower the gastrointestinal-colonization barrier to allow the emergence of resistant bacteria in the human intestinal microbiome.
Changes in the bacterial community after tetracycline exposure were variable due to inter-individual differences in the intestinal microbiome composition. Among the 23 tetracycline-resistance genes screened, four genes were common in both tetracycline-dosed and non-dosed fecal samples. A slight increase in antibiotic-resistance genes appeared to be related to the tetracycline treatment. Despite the inherent variability of the intestinal microbiota among and within individuals, this pilot study—using high-throughput sequencing, quantitative PCR, and bioinformatic analysis—has contributed to the knowledge base. It has helped assess the safety of veterinary antimicrobial-drug residues in food, their impact on the human intestinal microbiome, and the potential for antimicrobial resistance. A manuscript describing the study is available online at Anaerobe.
For more information, contact Carl Cerniglia, Ph.D., Director, Division of Microbiology or Youngbeom Ahn, Ph.D., Division of Microbiology, FDA/NCTR.
Plasmids from Salmonella Can Contribute to their Antimicrobial Resistance and Potential VirulenceScientists from NCTR, the University of Arkansas at Fayetteville, and the University of Arkansas at Pine Bluff found that many plasmids carry genes for bacterial toxins that may give bacterial strains (that carry the plasmids) a competitive advantage in shared environments. Antimicrobial resistance and virulence properties in Salmonellacan be encoded on plasmids—non-chromosomal DNA elements that replicate independently of the bacterial chromosome—that can carry and spread antimicrobial resistance and pathogenicity-associated genes in bacteria. In this study, scientists evaluated 92 Salmonella enterica strains (known to carry a class of plasmids termed "incompatibility group I1 plasmids") for their susceptibility to nine different antimicrobial agents and ability to produce bacterial colicin toxins. Approximately 90 percent of the strains were resistant to at least one antimicrobial, and more than 50 percent were resistant to five or more antimicrobials. Over half of the strains also produced colicin toxins that inhibited the growth of another bacterial strain.
Plasmids from Salmonella Can Contribute to their Antimicrobial Resistance and Potential VirulenceScientists from NCTR, the University of Arkansas at Fayetteville, and the University of Arkansas at Pine Bluff found that many plasmids carry genes for bacterial toxins that may give bacterial strains (that carry the plasmids) a competitive advantage in shared environments. Antimicrobial resistance and virulence properties in Salmonellacan be encoded on plasmids—non-chromosomal DNA elements that replicate independently of the bacterial chromosome—that can carry and spread antimicrobial resistance and pathogenicity-associated genes in bacteria. In this study, scientists evaluated 92 Salmonella enterica strains (known to carry a class of plasmids termed "incompatibility group I1 plasmids") for their susceptibility to nine different antimicrobial agents and ability to produce bacterial colicin toxins. Approximately 90 percent of the strains were resistant to at least one antimicrobial, and more than 50 percent were resistant to five or more antimicrobials. Over half of the strains also produced colicin toxins that inhibited the growth of another bacterial strain.
These research findings confirmed the importance of plasmids as vehicles for the spread of antimicrobial resistance and bacterial toxins among bacterial pathogens and help the research community better understand this public-health challenge that has limited the effectiveness of antimicrobials to prevent and treat infections. A manuscript describing the study can be found in Foodborne Pathogens and Diseases.
For more information, contact Steven Foley, Ph.D., Deputy Director, Division of Microbiology, FDA/NCTR.
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