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
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
A convenience sample of 187 operations in 21 states was selected to submit
fecal samples (operations in
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).
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 |
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 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
|
|||
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 |
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
N300.1001