Quantification of theBla_CMY-2in Feces from Beef Feedlot Cattle Administered Three Different Doses of Ceftiofur in a Longitudinal Controlled Field Trial

Abstract

The objective of this longitudinal controlled trial was to quantitatively compare carriage of a gene encoding for ceftiofur-resistance (bla(CMY-2)), standardized to a reference gene (16SrRNA), among total community DNA extracted from fecal samples collected from cattle treated with three different dose regimens of ceftiofur crystalline-free acid (CCFA) versus those untreated (controls). Sixty-one steers were assigned to three treatment regimens and housed in six pens. In each pen, five steers were treated and five were controls (one of the pens had six controls). CCFA administration was as follows: two-thirds dose treatment (4.4 mg/kg, on day 0), single-dose treatment (6.6 mg/kg, on day 0), and three-dose treatment (6.6 mg/kg, on days 0, 6, and 13). Fecal samples were collected on days 0, 3, 7, 10, 14, 18, 21, and 28. The gene copy numbers/gram of feces for bla(CMY-2) and 16SrRNA were determined in total community DNA samples using quantitative real-time PCR. The relationships between the quantities of standardized bla(CMY-2), nonstandardized bla(CMY-2), and nonstandardized 16SrRNA, and the explanatory variables (treatment, time, and treatment x time) were assessed using repeated measures mixed models. There were significant differences in each of the three models with respect to each explanatory variable. Overall, while steers administered three doses and two-thirds dose of CCFA had significantly higher quantities of nonstandardized bla(CMY-2) than controls, the standardized values were lower. The administration of CCFA in feedlot cattle may provide selection pressure favoring higher levels of bla(CMY-2) carriage, but this may also lead to concurrent reductions in the total bacterial population (as reflected by lowered 16SrRNA) during the treatment period.

Influence of Therapeutic Ceftiofur Treatments of Feedlot Cattle on Fecal and Hide Prevalences of Commensal Escherichia coli Resistant to Expanded-Spectrum Cephalosporins, and Molecular Characterization of Resistant Isolates

“…TIO injection is known to transiently increase the fecal concentrations of ESC r E. coli and bla CMY-2 in individual cattle before returning to levels observed prior to TIO injection (20)(21)(22). During the December 2009, March 2010, May 2010, and June 2010 sample periods, fecal prevalences of ESC r E. coli for IDSϩTIO or OtherϩTIO cattle were not significantly higher (P Ն 0.05) than the corresponding herd fecal prevalences (see Tables S1 and S2 in the supplemental material).…”

“…These antibiotic resistance genes may be transmitted to human commensal and pathogenic bacteria, either by E. coli or when horizontally transferred to food-borne pathogenic bacteria, such as S. enterica (5,37,38). Therefore, fecal samples are typically examined to assess ESC r E. coli or bla CMY-2 presence in cattle environments (20)(21)(22)(23)(24)39). Hide samples were cultured for ESC r E. coli, since hides have been demonstrated to harbor E. coli strains of fecal origin, including E. coli O157:H7 (40,41).…”

“…The critical importance of ESC to human medicine along with concerns that agricultural use of TIO may contribute to the occurrence of human ESC r infections factored into the European Food Safety Authority recommendations to severely restrict or eliminate TIO use in animal agriculture (19). Injection with TIO has been demonstrated to transiently increase the fecal concentrations of ESC r E. coli and bla CMY-2 in individual treated cattle (20)(21)(22). The long-term impact of therapeutic TIO injection of cattle on herd prevalence of ESC r E. coli is unclear since only two studies have correlated TIO use (in dairy cattle herds sampled once or twice) to ESC susceptibilities of commensal E. coli.…”

Effect of cefovecin on the fecal flora of healthy dogs

“…Ceftiofur crystalline-free acid-treated cattle also had increased levels of fecal bla CMY-2 carriage (Alali et al, 2009). The bla CMY-2 gene encodes cephalosporin resistance via AmpC β-lactamase and has been identified among commensal and pathogenic bacteria within the GI flora of humans and animals (Forward et al, 2004;Alali et al, 2009).…”

“…The bla CMY-2 gene encodes cephalosporin resistance via AmpC β-lactamase and has been identified among commensal and pathogenic bacteria within the GI flora of humans and animals (Forward et al, 2004;Alali et al, 2009). In vitro conjugation studies have documented plasmid transfer of the bla CMY-2 gene within and between fecal genera, specifically E. coli and Salmonella spp.…”