Prevalence and Antimicrobial Susceptibility Patterns of Salmonella from 

Beef Cows 

October 2001 

Salmonellae have been isolated from nearly all vertebrates, and infection has been associated with both animal and human 

disease. Human Salmonella infections in the United States have been estimated in the millions annually. In some of these cases, 

foods of animal origin have been implicated as the source of the pathogen. In addition to being a food-safety concern for humans, 

Salmonella can cause illness or death among cattle. There is worldwide concern that many bacteria, including Salmonella, are 

becoming resistant to antimicrobial agents. Trends in antimicrobial susceptibility patterns of Salmonella isolates are being 

monitored. 

The USDA:APHIS:VS conducted a study of health and management of cattle and calves on cow-calf operations as part of the 

National Animal Health Monitoring System's (NAHMS) Beef '97 study. This study was designed to determine the prevalence of 

Salmonella shedding in feces of beef cows on cow-calf operations throughout the U.S., and to determine antimicrobial 

susceptibility patterns for all Salmonellae isolated. A stratified random sample of cow-calf operations from the 23 major cow/calf

states1 was selected for the Beef '97 study. A total of 2,713 producers participated. 

A convenience sample of 187 operations in 21 states was selected to submit fecal samples (operations in Arkansas and Wyoming

were not tested). Fecal samples were collected between August 1997 and January 1998. Culture work was performed at the 

Richard Russell Research Center in Athens, Georgia, and the serotyping was done at the National Veterinary Services 

Laboratories in Ames, Iowa. Up to 40 fecal samples were collected from the ground on each operation, depending on herd size. 

All Salmonella isolates were serotyped. In addition, all Salmonella isolates were screened for resistance against a panel of 17 

antimicrobials2. 

A total of 5,049 fecal samples on 187 operations were cultured for Salmonella. Salmonella spp. were recovered from 21 

operations (11.2 percent). Seventy samples (1.4 percent) tested positive for Salmonella, and from these samples, 78 Salmonella 

isolates were identified. Most of the isolates (64.1 percent) were recovered from two operations (46.2 percent from one operation 

and 17.9 percent from another). Only one serotype was recovered from the majority of operations. The five most common 

serotypes of Salmonella isolated from samples were S. oranienburg, S. cerro, S. anatum, S. bredeney, and S. mbandaka (Table 

1). 

 

Herds were classified into one of five geographic regions (Figure 1). Herds also were classified into one of five herd size 

categories based on the number of beef cows reported on the date of sample collection. The herd prevalence of fecal shedding of

Table 1. The Five Most Common Salmonella Serotypes Isolated from Cattle Feces

Serotype

Number of 

Positive Isolates Percent Isolates

Number of Positive 

Operations

Percent Positive 

Operations

Oranienburg 17 21.8 3 14.3 

Cerro 17 21.8 1 4.8 

Anatum 8 10.3 2 9.5 

Bredeney 7 9 3 14.3 

Mbandaka 4 5.1 2 9.5 

Body Page 1 of 3

file://G:\CAHM\NAHMS_website_publish\beefcowcalf\beef97\Beef97_is_Salmonella.htm 7/14/2010
Salmonellae was compared by geographic region and herd size using chi-square analysis. 

Herd prevalence was related to geographic region (Table 2). The largest proportion of operations tested was positive in the 

Southcentral region followed by the Central region. More herds with 1 to 25 beef cows or 26 to 49 beef cows had positive 

samples, though prevalence by herd size was not significantly different (Table 3). Most of the isolates (87.2 percent) were 

sensitive to the entire panel of antimicrobials tested. The most common resistance identified was to Sulfamethoxazole and 

Streptomycin (11.5 percent of isolates each) followed by Tetracycline and Gentamicin (2.6 percent of isolates each). For all other 

antimicrobials, fewer than 1.5 percent of isolates were considered resistant. 

Table 2. Number of Operations with at Least One Positive Sample for Salmonella, by Region 

 

While the prevalence of Salmonella within beef cow-calf operations appears to be variable, in general it is very low. Only 1.4 

percent of samples and only 11.2 percent of the operations were cultured positive for Salmonellae. Factors that may have 

influenced the outcome of these results include the time of year samples were collected, quality and number of samples collected, 

and the presence or lack of environmental stressors affecting shedding by the cattle. A higher proportion of the herds that tested 

positive came from the Southcentral, Central, and Southeast regions, which could be related to weather conditions at the time of

sampling that were more conducive to detecting Salmonella. Determination of the full significance of the antimicrobial 

susceptibility patterns for Salmonella isolates will have to await further studies. Prudent use of all antimicrobics by producers 

and veterinarians will help ensure that these products remain effective and available. 

For more information, contact: 

Centers for Epidemiology and Animal Health 

USDA:APHIS:VS, attn. NAHMS 

2150 Centre Ave., Bldg. B, MS 2E7 

Fort Collins, CO 80526-8117 

Telephone: (970) 494-7000 

E-mail: NAHMSweb@usda.gov 

www.aphis.usda.gov/vs/ceah/ncahs

 

Region Number Operations Tested Number Positive Operations Percent Positive Operations

West 26 1 3.80 

Northcentral 37 1 2.70 

Southcentral 42 9 21.40 

Central 39 6 15.40 

Southeast 43 4 9.30 

Total 187 21 11.20 

Table 3. Number of Operations with at Least One Positive Sample for Salmonella, by Herd Size

Herd Size (Cows) Number Operations Tested Number Positive Operations Percent Positive Operations

1-25 46 7 15.20 

26-49 42 7 16.70 

50-99 41 3 7.30 

100-249 40 2 5.00 

250 or more 18 2 11.10 

Total 187 21 11.20 

Body Page 2 of 3

file://G:\CAHM\NAHMS_website_publish\beefcowcalf\beef97\Beef97_is_Salmonella.htm 7/14/2010
N300.1001 

Alabama, Arkansas, California, Colorado, Florida, Georgia, Illinois, Iowa, Kansas, Kentucky, Mississippi, Montana, Nebraska, New Mexico, Missouri, 

North Dakota, Oklahoma, Oregon, South Dakota, Texas, Tennessee, Virginia, and Wyoming. Amikacin, Amoxicillin/Clavulanic Acid, Ampicillin, Apramycin, Ceftiofur, Ceftriaxone, Cephalothin, Chloramphenicol, Ciprofloxacin, Gentamicin, 

Kanamycin, Nalidixic Acid, Streptomycin, Sulfamethoxazole, Tetracycline, Ticarcillin, and Trimethoprim/Sulfamethoxazole.

Body Page 3 of 3

file://G:\CAHM\NAHMS_website_publish\beefcowcalf\beef97\Beef97_is_Salmonella.htm 7/14/2010