ARS | Publication request: Antimicrobial Susceptibility and Factors Affecting the Shedding of E. Coli O157:h7 and Salmonella in Dairy Cattle

Submitted to: Letters in Applied Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 26, 2003
Publication Date: November 15, 2003
Citation: FITZGERALD, A.C., EDRINGTON, T.S., LOOPER, M.L., CALLAWAY, T.R., ELDER, R.O., GENOVESE, K.J., BISCHOFF, K.M., THOMAS, J.D., ANDERSON, R.C., NISBET, D.J. ANTIMICROBIAL SUSCEPTIBILITY AND FACTORS AFFECTING THE SHEDDING OF E. COLI O157:H7 AND SALMONELLA IN DAIRY CATTLE. LETTERS IN APPLIED MICROBIOLOGY. 2003. V. 37. P. 392-398.

Interpretive Summary: Dairy cattle may contain the bacteria E. coli and Salmonella that can make people sick. Drugs used to treat people made sick by these bacteria may not always work because the bacteria are resistant to them. The purpose of the present study was to determine if certain kinds of stress in dairy cattle increases fecal shedding of bacteria. We also examined the ability of several antibiotic drugs to kill Salmonella and E. coli from dairy cattle. Results showed that stress can affect fecal shedding of these bacteria and that some drugs are not effective against these bacteria. However, these drugs are the kind used by veterinarians, not the drugs used in humans that were able to kill the Salmonella and E. coli.

Technical Abstract: Factors affecting fecal shedding of the foodborne pathogens E. coli O157:H7 and Salmonella in dairy cattle were evaluated. Fecal samples were obtained in replicate from lactating (LAC; n = 60) and non-lactating (NLAC; n = 60) Holstein cattle to determine influence of time of day (morning vs late afternoon), parity, lactation status (LAC vs NLAC), and stage of lactation [less than or equal to 60 or >60 days in milk (DIM)] on shedding of E. coli O157:H7 and Salmonella. Overall, the incidence of E. coli O157:H7 and Salmonella shedding was 56 and 53%, respectively. While some differences were found between the AM and PM sampling times, no consistent patterns of pathogen shedding were detected. Lactating cows shed more (P < 0.01) E. coli O157:H7 than NLAC cows (43 vs 32%, respectively). Multiparous LAC cows tended to shed more (P = 0.06) Salmonella than primiparous LAC cows (39 vs 27%, respectively). Parity did not influence (P > 0.10) bacterial shedding in NLAC cows. Cows less than or equal to 60 DIM shed more (P < 0.05) Salmonella than cows >60 DIM. The most prevalent Salmonella serotypes were Senftenberg (18%), Newport (17%) and Anatum (15%) of a total of 17 different serotypes isolated, with several cows shedding multiple Salmonella serotypes within a day. Examination of antimicrobial susceptibility found 79% of the Salmonella isolates were resistant to at least one of seven antibiotics. Escherichia coli O157:H7 isolates were resistant to 12 different antibiotics with resistance to nine or more antibiotics observed in five isolates.