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J. Anim. Sci. 2005. 83:E44-E47
© 2005 American Society of Animal Science

Use of competitive exclusion to control enterotoxigenic strains of Escherichia coli in weaned pigs1,2,3

R. B. Harvey4, R. C. Anderson, K. J. Genovese, T. R. Callaway and D. J. Nisbet

Food and Feed Safety Research Unit, Southern Plains Agricultural Research Center, ARS, USDA, College Station, TX 77845


   Abstract
Top
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 Implications
 Literature Cited
 
Mortality and morbidity associated with Escherichia coli cause economic losses to the swine industry. Enterotoxigenic strains of E. coli affecting nursery-age pigs have become more difficult to treat because of increased antibiotic resistance, and alternatives to antibiotics are currently being sought. Our laboratory developed a defined culture of commensal bacteria of porcine gastrointestinal tract origin, maintained it in continuous-flow culture for 3 yr, and designated it as RPCF. Laboratory studies have shown that RPCF-treated pigs had decreased mortality and bacterial shedding compared with controls when challenged with enterotoxigenic strains of E. coli. The objective of the present study was to evaluate the practicality, safety, and efficacy of RPCF to protect nursery-age pigs in commercial swine operations from field challenge by enterotoxigenic strains of E. coli. In field studies involving six geographically separated farms with a history of high mortality from K-88 and F-18 strains of E. coli, piglets were administered RPCF within 24 h of birth and monitored throughout the nursery period. A total of 21,467 piglets were treated with RPCF, and a similar number of piglets on the same farms served as untreated controls. On five of six farms, mortality in RPCF-treated pigs decreased by an average of 2.6% compared with untreated pigs. Differences in mortality were not observed in RPCF-treated pigs compared with controls on one Minnesota farm. When projected to an annual basis, the economic benefits from decreased medication costs and mortality averaged $24,663 per farm. These studies suggest that under commercial conditions, RPCF tended to control disease induced by enterotoxigenic E. coli, and that RPCF may be a viable alternative to the use of antibiotics.

Key Words: Competitive Exclusion • Enterotoxigenic Escherichia coli • Field Trials • Swine


   Introduction
Top
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 Implications
 Literature Cited
 
Enterotoxigenic strains of Escherichia coli are considered the most important cause of neonatal and post-weaning diarrhea in pigs in the United States, and E. coli-related problems were rated as the first and third most important diseases in suckling and weaned pigs, respectively (USDA, 2002Go). Morbidity, loss of productivity, and mortality from E. coli cost swine producers millions of dollars annually. Colibacillosis induced by E. coli has become increasingly difficult to treat because of the build-up of antibiotic resistance by many strains of these bacteria; hence, nonantibiotic intervention methods for these organisms are a high priority. One such solution would be the use of competitive exclusion (CE) cultures. Our laboratory has developed a porcine-origin, defined, continuous-flow, CE culture of commensal bacteria designated RPCF. The culture has been patented (Nisbet et al., 1999Go). In laboratory studies, RPCF protected piglets from challenge with enterotoxigenic strains of E. coli (Genovese et al., 2000Go, 2001Go), and we questioned whether similar protection could be reproduced in commercial swine nursery operations. The objective of the present study was to evaluate, under field conditions, the practicality, safety, and efficacy of RPCF to prevent or decrease disease induced by enterotoxigenic E. coli in nursery-age pigs.


   Materials and Methods
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 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 Implications
 Literature Cited
 
Five nursery farms and one wean-to-finish farm in six geographically separate locations with a history of K-88 or F-18 E. coli disease were selected for field trials. Piglets from 11 different sow units were orally administered 108 cfu (2.0 mL) of RPCF within 24 h of birth, and on weaning, were shipped to nursery barns. Barns were filled with only RPCF-treated piglets. The RPCF-treated pigs were monitored throughout the nursery period, and their performance was compared with a similar number of untreated pigs from the same farm. Except for Farm E, control pigs were made up of "historic" controls and the performance and mortality data, and the cost of medication of these controls were calculated from equivalent numbers of pigs during the previous 6 mo. On Farm E, there were "contemporary" side-by-side controls. Measurements included mortality and weaning weights in the farrowing barns, and ADG, feed efficiency, mortality and culls, and medication costs in the nurseries. A total of 37,276 piglets were included in these trials; 21,467 were treated with RPCF, and 15,809 served as untreated controls. The breakout of piglet numbers and the general geographic location per farm are shown in Table 1Go. Trials were conducted from August 2002 to February 2004.


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  		Table 1. Effects of a defined culture of commensal bacteria of porcine gastrointestinal tract origin (RPCF) on mortality and medication costs due to E. coli
 

   Results
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 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 Implications
 Literature Cited
 
Five out of the six farms had decreased mortality and medication costs in RPCF-treated pigs compared with the untreated control pigs (Table 1Go). The enterotoxigenic strain on Farms A through D was F-18, and on Farms E and F, it was K-88. Differences in mortality between RPCF-treated and untreated pigs were not evident on Farm F. On Farms A, B, C, D, and E, mortality and culls in RPCF-treated pigs decreased by 6.16, 0.79, 0.85, 4.8, and 0.6% respectively, compared with untreated pigs. Farms A, B, C, E, and F were nursery operations, and measurements were taken at close out (approximately 9 wk after placement). Farm D was a wean-to-finish operation, and unlike nursery operations in which pigs stay in the barn for approximately 6 wk, these pigs remained in the barn from weaning until 180 d of age. In that type of barn, regularly scheduled performance measurements usually are not made, and because mortality associated with enterotoxigenic E. coli usually peaks by 4 to 6 wk after placement, we arbitrarily collected mortality data on Farm D at 4 wk after placement. We further combined mortality and culls (for all causes) in the present field trials because an increase in the number of culls was perceived as an objective measure of morbidity. Mortality alone (excluding culls) did not exceed 1.5% in any of the RPCF-treated groups during these trials (data not shown). There were no observable ill effects in neonatal piglets following RPCF administration, and there were no consistent differences on the basis of treatment in farrowing barn mortality, weaning weights, ADG, or feed efficiency on any of the farms (data not shown).

Historic controls were used in these trials because 1) all the farms had enterotoxigenic E. coli diagnosed on the farm and had experienced high mortality during the previous 6 mo; 2) many of the sow units did not have the capabilities or the capacity to generate equal numbers of contemporary controls; and 3) in some studies in which contemporary controls were used, E. coli-induced mortality in the controls was so high that producers began medicating sick pigs and were reluctant to continue with contemporary controls (our studies had no indemnity payments for mortality in control pigs).

When projected to an annual basis, the cost benefits from decreased medication and decreased mortality/ morbidity were $85,725 on Farm A, $11,570 on Farm B, $16,740 on Farm C, $7,280 on Farm D, $2,000 on Farm E, and no benefit on Farm F. Projected cost benefits for mortality were calculated as follows: mortality differences x annual number of pigs produced x $50.00 per pig = annual value (Farms A, B, and C had an annual production of 27,000 each; Farm D had an annual production of 2,600; Farm E had an annual production of 5,000; and Farm F had an annual production of 19,000). For medication calculations, medication cost differences x number of pigs produced annually = annual value. On the basis of these economic benefits and our knowledge of laboratory production costs, the authors estimate that if made commercially available, RPCF would likely be priced at $0.50 to $1.00 per dose; however, this is only an estimate and a variety of factors could change these figures before marketing.


   Discussion
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
Implications
 Literature Cited
 
Enterotoxigenic strains of E. coli are considered the most important cause of neonatal and postweaning diarrhea in pigs in the United States. Traditionally, antibiotics have been the treatment of choice. Most field isolates of enterotoxigenic E. coli have become resistant to currently available antibiotics, and in the future, antibiotic use in animal production could be severely restricted; therefore, new intervention strategies must be developed to overcome this disease-causing bacterium. One such intervention is CE.

Theoretically, CE cultures colonize the neonatal intestinal tract with beneficial/commensal bacteria that comprise the normal flora of healthy adult animals, thereby decreasing the window of opportunity for pathogens to colonize the gastrointestinal tract. Natural microbial populations in the gastrointestinal tract display antipathogenic capabilities, and this has been described as "bacterial antagonism" (Freter et al., 1983Go), "bacterial interference" (Dubos, 1963Go), and "competitive exclusion" (Lloyd et al., 1977Go). Nurmi and Rantala (1973)Go first demonstrated the effectiveness of this concept when they administered a preparation of gut bacteria from adult chickens to chicks and observed a dramatic reduction in Salmonella colonization.

Poultry CE cultures have been used extensively outside the United States for Salmonella control (Stavric, 1992Go; Stavric and D’Auost, 1993; Bielke et al., 2003Go), whereas CE treatment in the United States has been limited. The key factor in this difference is that the U.S. FDA regulates CE products and requires all CE cultures to have a defined bacterial composition. Virtually all the poultry CE products outside the United States are undefined mixtures. Our laboratory developed a defined CE culture for poultry (Preempt) that, when administered to newly hatched chicks, decreased Salmonella colonization and shedding (Nisbet et al., 1996Go, 1998Go).

Swine and cattle CE products have not progressed as far as those for poultry. Probiotics and CE cultures have been used in cattle as a strategy to eliminate or decrease Salmonella and E. coli O157:H7 (Brashers et al., 2003aGo,bGo; Zhao et al., 1998Go, 2003Go). Early work by Underdahl et al. (1982)Go and Ushe and Nagy (1985)Go showed that cultures of Streptococcus (Enterococcus) faecium were able to decrease colonization and diarrhea associated with enterotoxigenic E. coli in pigs. Later, Fedorka-Cray et al. (1999)Go and Anderson et al. (1999)Go demonstrated that undefined, pig-derived, CE cultures decreased Salmonella in swine. With in vitro studies, RPCF prevented colonization by Salmonella typhimurium, S. choleraesuis, E. coli F18, and E. coli O157:H7 (Harvey et al., 2002Go). In laboratory challenge studies with enterotoxigenic E. coli, mortality, colonization, and bacterial shedding were decreased in RPCF-treated pigs compared with controls (Genovese et al., 2000Go; 2001Go). The RPCF contains, but is not limited to, Enterococcus faecalis, Streptococcus bovis, Clostridium clostridiforme, C. symbiosurn, C. ramosum, Bacterioides fragilis, B. distasonis, B. vulgatus, B. uniformis, and B. caccae.

In the present study, it was evident that RPCF effectively decreased the majority of losses associated with F-18 and K-88 strains of E. coli in weanling pigs. Although the RPCF was administered at birth, it continued to protect pigs throughout the 6-wk nursery period. Theoretically, RPCF protects against E. coli by stimulation of the immune system, competition for attachment sites in the intestinal tract, production of chemicals (bacteriocins) that are toxic to E. coli, and competition for nutrients with E. coli (Callaway et al., 2003Go). One key factor has to be the stimulation of the immune system. When germ-free piglets were administered this CE culture at birth, by 6 wk of age, their serum immunoglobulin concentrations were 20- to 100-fold higher than those of noncolonized control piglets (Butler et al., 2000Go).

Decreased disease on Farms A through E is similar to the results seen in laboratory studies, in which RPCF decreased colonization, shedding, and mortality in piglets from a 987p challenge strain of E. coli (Genovese et al., 2000Go; 2001Go). It is unknown why pigs on Farm F were not protected by RPCF in the nursery from E. coli disease. Anecdotally, the attending veterinarian on Farm F reported that for 6 mo before field trials, suckling piglets in farrowing barns had experienced diarrhea and mortality from rotavirus infections. Following administration of RPCF, clinical signs of rotavirus disappeared.

The results from these field trials show that RPCF tended to decrease mortality, morbidity, and medication costs associated with certain strains of E. coli. Although this intervention method is not a "silver bullet," it is possible that when used with other management tools, it might lessen the effects of enterotoxigenic E. coli, and present results suggest that RPCF may be a viable alternative to antibiotics to prevent or decrease the disease induced by enterotoxigenic E. coli.


   Implications
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 Implications
Literature Cited
 
Escherichia coli can cause disease and death in young pigs, particularly nursery-age pigs. A promising new procedure to reduce disease-causing E. coli involves the use of bacterial cultures called RPCF. The RPCF bacteria are "good bacteria" that help in digestion, keep the intestinal tract healthy, and prevent disease-causing bacteria from gaining a foothold in the intestinal tract. In field trials involving 37,276 pigs, we determined that RPCF could decrease E. coli disease in nursery-age pigs. Decreased mortality and medication costs in the RPCF-treated groups produced an average yearly cost savings of $24,563 per farm. Thus, results from this study indicate that RPCF is effective in decreasing disease associated with E. coli and that RPCF might be a viable alternative to antibiotics for the future.


   Footnotes
 
1 These studies were funded by a grant (NPB #02-196) from the Natl. Pork Board, Des Moines, IA. Back

2 Proprietary or brand names are necessary to report factually on available data; however, the USDA neither guarantees nor warrants the standard of the product, and the use of the name by the USDA implies no approval of the product, or exclusion of others that may be suitable. Back

3 Presented at the ASAS Symposium: Alternatives to Antibiotic Use, St. Louis, MO, July 28, 2004. Back

4 Correspondence: 2881 F&B Rd. (phone: 979-260-9259; fax: 979-260-9332; e-mail: Harvey{at}ffsru.tamu.edu).

Received for publication July 8, 2004. Accepted for publication January 14, 2005.


   Literature Cited
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 Implications
 Literature Cited
 


Anderson, R. C., L. H. Stanker, C. R. Young, S. A. Buckley, K. J. Genovese, R. B. Harvey, J. R. DeLoach, N. K. Keith, and D. J. Nisbet. 1999. Effect of competitive exclusion treatment on colonization of early-weaned pigs by Salmonella serovar Choleraesuis. Swine Health Prod. 7:155–160.

Bielke, L. R., A. L. Elwood, D. J. Donoghue, A. M. Donoghue, L. A. Newberry, N. K. Neighbors, and B. M. Hargis. 2003. Approach for selection of individual enteric bacteria for competitive exclusion in turkey poults. Poult. Sci. 82:1378–1382.[Abstract/Free Full Text]

Brashers, M. M., M. L. Galyean, G. H. Loneragan, J. E. Mann, and K. Killinger-Mann. 2003a. Prevalence of Escherichia coli O157:H7 and performance by beef feedlot cattle given Lactobacillus direct-fed microbials. J. Food Prot. 66:748–754.[Medline]

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Harvey, R. B., R. E. Droleskey, M. E. Hume, R. C. Anderson, K. J. Genovese, K. Andrews, and D. J. Nisbet. 2002. In vitro inhibition of Salmonella enterica serovars Choleraesuis and Typhimurium, Escherichia coli F-18, and Escherichia coli O157:H7 by a porcine continuous-flow competitive exclusion culture. Curr. Microbiol. 45:226–229.[Medline]

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