Limits...
Longitudinal characterization of antimicrobial resistance genes in feces shed from cattle fed different subtherapeutic antibiotics.

Alexander TW, Yanke JL, Reuter T, Topp E, Read RR, Selinger BL, McAllister TA - BMC Microbiol. (2011)

Bottom Line: At day 7, the concentration of erm(X) was greatest in feces from cattle fed tylosin, compared to all other treatments.Resistance genes can persist in feces from cattle beyond 175 days with concentrations of some genes increasing with time.Management practices that accelerate DNA degradation such as frequent land application or composting of manure may reduce the extent to which bovine feces serves as a reservoir of antimicrobial resistance.

View Article: PubMed Central - HTML - PubMed

Affiliation: Agriculture and Agri-Food Canada Research Centre, Lethbridge, Alberta T1J 4B1, Canada.

ABSTRACT

Background: Environmental transmission of antimicrobial-resistant bacteria and resistance gene determinants originating from livestock is affected by their persistence in agricultural-related matrices. This study investigated the effects of administering subtherapeutic concentrations of antimicrobials to beef cattle on the abundance and persistence of resistance genes within the microbial community of fecal deposits. Cattle (three pens per treatment, 10 steers per pen) were administered chlortetracycline, chlortetracycline plus sulfamethazine, tylosin, or no antimicrobials (control). Model fecal deposits (n = 3) were prepared by mixing fresh feces from each pen into a single composite sample. Real-time PCR was used to measure concentrations of tet, sul and erm resistance genes in DNA extracted from composites over 175 days of environmental exposure in the field. The microbial communities were analyzed by quantification and denaturing gradient gel electrophoresis (DGGE) of PCR-amplified 16S-rRNA.

Results: The concentrations of 16S-rRNA in feces were similar across treatments and increased by day 56, declining thereafter. DGGE profiles of 16S-rRNA differed amongst treatments and with time, illustrating temporal shifts in microbial communities. All measured resistance gene determinants were quantifiable in feces after 175 days. Antimicrobial treatment differentially affected the abundance of certain resistance genes but generally not their persistence. In the first 56 days, concentrations of tet(B), tet(C), sul1, sul2, erm(A) tended to increase, and decline thereafter, whereas tet(M) and tet(W) gradually declined over 175 days. At day 7, the concentration of erm(X) was greatest in feces from cattle fed tylosin, compared to all other treatments.

Conclusion: The abundance of genes coding for antimicrobial resistance in bovine feces can be affected by inclusion of antibiotics in the feed. Resistance genes can persist in feces from cattle beyond 175 days with concentrations of some genes increasing with time. Management practices that accelerate DNA degradation such as frequent land application or composting of manure may reduce the extent to which bovine feces serves as a reservoir of antimicrobial resistance.

Show MeSH

Related in: MedlinePlus

Persistence of tetracycline resistance genes in cattle fecal deposits under field conditions. The treatments were (N = 3; plus standard error): Control, no antimicrobial agents added to the diets of steers from which fecal deposits originated; A44, chlortetracycline (44 ppm); AS700, chlortetracycline and sulfamethazine (each at 44 ppm); T11, tylosin (11 ppm).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC3037836&req=5

Figure 2: Persistence of tetracycline resistance genes in cattle fecal deposits under field conditions. The treatments were (N = 3; plus standard error): Control, no antimicrobial agents added to the diets of steers from which fecal deposits originated; A44, chlortetracycline (44 ppm); AS700, chlortetracycline and sulfamethazine (each at 44 ppm); T11, tylosin (11 ppm).

Mentions: The concentrations of tet(B), tet(C), tet(M) and tet(W) in fecal deposits were affected by both treatment and time of exposure (P = 0.05, Figure 2). Numbers of copies of tet(B) in A44 and AS700 fecal deposits were greater than control and T11 fecal deposits but did not differ between A44 and AS700 treatments. Compared to day 7 levels, the concentration of tet(B) increased by day 42 (P = 0.01) approximately one order of magnitude and remained greater than day 7 levels up to day 112 (P = 0.03), decreasing thereafter. Similarly, the concentration of tet(C) increased from initial amounts and was greater between days 42-70 when compared to day 7, but all other time points were not different from day 7. Treatments A44, AS700, and T11 all resulted in greater concentrations of tet(C) compared to the control fecal deposits, with AS700 having more copies than all other treatments. The control fecal deposits contained less tet(W) compared to the other treatments, but unlike tet(C), the T11 fecal deposits had the highest concentration of tet(W). After 28 days, the amount of tet(W) decreased below the concentration on day 7. Only time (P = 0.0001) affected the concentration of tet(L) in fecal deposits, which decreased from the initial concentrations on day 7, after 175 days of exposure. An interaction between treatment and time influenced the concentration of tet(M). By day 175, copies of tet(M) were less in all fecal deposits compared to those on day 7 (P = 0.05), with the exception of control samples. There were no differences in tet(M) numbers in A44, AS700 or T11 deposits, and all had greater amounts of tet(M) on day 7 as compared to control deposits. However, by day 112, the fecal deposits had similar tet(M) concentrations. Although not analyzed statistically, the concentrations of tet(M) and tet(W) were greater than other tetracycline resistance determinants.


Longitudinal characterization of antimicrobial resistance genes in feces shed from cattle fed different subtherapeutic antibiotics.

Alexander TW, Yanke JL, Reuter T, Topp E, Read RR, Selinger BL, McAllister TA - BMC Microbiol. (2011)

Persistence of tetracycline resistance genes in cattle fecal deposits under field conditions. The treatments were (N = 3; plus standard error): Control, no antimicrobial agents added to the diets of steers from which fecal deposits originated; A44, chlortetracycline (44 ppm); AS700, chlortetracycline and sulfamethazine (each at 44 ppm); T11, tylosin (11 ppm).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3037836&req=5

Figure 2: Persistence of tetracycline resistance genes in cattle fecal deposits under field conditions. The treatments were (N = 3; plus standard error): Control, no antimicrobial agents added to the diets of steers from which fecal deposits originated; A44, chlortetracycline (44 ppm); AS700, chlortetracycline and sulfamethazine (each at 44 ppm); T11, tylosin (11 ppm).
Mentions: The concentrations of tet(B), tet(C), tet(M) and tet(W) in fecal deposits were affected by both treatment and time of exposure (P = 0.05, Figure 2). Numbers of copies of tet(B) in A44 and AS700 fecal deposits were greater than control and T11 fecal deposits but did not differ between A44 and AS700 treatments. Compared to day 7 levels, the concentration of tet(B) increased by day 42 (P = 0.01) approximately one order of magnitude and remained greater than day 7 levels up to day 112 (P = 0.03), decreasing thereafter. Similarly, the concentration of tet(C) increased from initial amounts and was greater between days 42-70 when compared to day 7, but all other time points were not different from day 7. Treatments A44, AS700, and T11 all resulted in greater concentrations of tet(C) compared to the control fecal deposits, with AS700 having more copies than all other treatments. The control fecal deposits contained less tet(W) compared to the other treatments, but unlike tet(C), the T11 fecal deposits had the highest concentration of tet(W). After 28 days, the amount of tet(W) decreased below the concentration on day 7. Only time (P = 0.0001) affected the concentration of tet(L) in fecal deposits, which decreased from the initial concentrations on day 7, after 175 days of exposure. An interaction between treatment and time influenced the concentration of tet(M). By day 175, copies of tet(M) were less in all fecal deposits compared to those on day 7 (P = 0.05), with the exception of control samples. There were no differences in tet(M) numbers in A44, AS700 or T11 deposits, and all had greater amounts of tet(M) on day 7 as compared to control deposits. However, by day 112, the fecal deposits had similar tet(M) concentrations. Although not analyzed statistically, the concentrations of tet(M) and tet(W) were greater than other tetracycline resistance determinants.

Bottom Line: At day 7, the concentration of erm(X) was greatest in feces from cattle fed tylosin, compared to all other treatments.Resistance genes can persist in feces from cattle beyond 175 days with concentrations of some genes increasing with time.Management practices that accelerate DNA degradation such as frequent land application or composting of manure may reduce the extent to which bovine feces serves as a reservoir of antimicrobial resistance.

View Article: PubMed Central - HTML - PubMed

Affiliation: Agriculture and Agri-Food Canada Research Centre, Lethbridge, Alberta T1J 4B1, Canada.

ABSTRACT

Background: Environmental transmission of antimicrobial-resistant bacteria and resistance gene determinants originating from livestock is affected by their persistence in agricultural-related matrices. This study investigated the effects of administering subtherapeutic concentrations of antimicrobials to beef cattle on the abundance and persistence of resistance genes within the microbial community of fecal deposits. Cattle (three pens per treatment, 10 steers per pen) were administered chlortetracycline, chlortetracycline plus sulfamethazine, tylosin, or no antimicrobials (control). Model fecal deposits (n = 3) were prepared by mixing fresh feces from each pen into a single composite sample. Real-time PCR was used to measure concentrations of tet, sul and erm resistance genes in DNA extracted from composites over 175 days of environmental exposure in the field. The microbial communities were analyzed by quantification and denaturing gradient gel electrophoresis (DGGE) of PCR-amplified 16S-rRNA.

Results: The concentrations of 16S-rRNA in feces were similar across treatments and increased by day 56, declining thereafter. DGGE profiles of 16S-rRNA differed amongst treatments and with time, illustrating temporal shifts in microbial communities. All measured resistance gene determinants were quantifiable in feces after 175 days. Antimicrobial treatment differentially affected the abundance of certain resistance genes but generally not their persistence. In the first 56 days, concentrations of tet(B), tet(C), sul1, sul2, erm(A) tended to increase, and decline thereafter, whereas tet(M) and tet(W) gradually declined over 175 days. At day 7, the concentration of erm(X) was greatest in feces from cattle fed tylosin, compared to all other treatments.

Conclusion: The abundance of genes coding for antimicrobial resistance in bovine feces can be affected by inclusion of antibiotics in the feed. Resistance genes can persist in feces from cattle beyond 175 days with concentrations of some genes increasing with time. Management practices that accelerate DNA degradation such as frequent land application or composting of manure may reduce the extent to which bovine feces serves as a reservoir of antimicrobial resistance.

Show MeSH
Related in: MedlinePlus