630 Modern Food Microbiology
in feces, through which other birds become contaminated. Among the methods that may be employed
to reduce or eliminate intestinal carriage is competitive exclusion (the Nurmi concept).
Under natural conditions where salmonellae exist when eggs hatch, young chicks develop a gastrointestinal tract flora that consists of these organisms and campylobacters, in addition to a variety
of nonpathogens. Once the pathogens are established, they may remain and be shed in droppings
during the entire lifetime of the bird. Competitive exclusion is a phenomenon whereby feces from
salmonellae-free birds, or a mixed fecal culture of bacteria, are given to young chicks so that they
will colonize the same intestinal sites that salmonellae employ and, thus, exclude the subsequent
attachment of salmonellae or other enteropathogens. This concept was advanced in the 1970s and
has been studied and found to be workable by a number of investigators relative to salmonellae
exclusion.
The enteropathogen-free biota may be administered orally to newly hatched chicks through drinking
water or by spray inoculation in the hatchery. Protection is established within a few hours and generally
persists throughout the life of the fowl or as long as the biota remains undisturbed. Older birds can
be treated by first administering antibacterial agents to eliminate enteropathogens, and they are then
administered the competitive exclusion biota. Only viable cells are effective, and both aerobic and
anaerobic components of the gut flora seem to be required. The crop and ceca appear to be the major
adherence sites, with the ceca being higher in germ-free chickens. In one study, the protective flora
remained attached to cecal walls after four successive washings.
52 Partial protection was achieved in
0.5–1.0 hour, but full protection required 6–8 hours after treatment of 1-day-old chicks.
50 In a review
of the microbiology of competitive exclusion of Salmonella in poultry, the use of undefined cultures
afford more protection than the use of defined cultures, especially under laboratory conditions.
51
Field trials in several European countries have shown the success of the competitive exclusion
treatment in preventing or reducing the entry of salmonellae in broilers and adult breeder birds.
39 In
chicks pretreated with a cecal culture and later challenged with a Salmonella sp., the latter failed to
multiply in the ceca over a 48-hour period, whereas in untreated control birds, more than 10
6 /g of
salmonellae were colonized in the ceca.
27
The gist of competitive exclusion is that salmonellae and the native gut biota compete for the same
adherence sites on gut walls. The precise nature of the bacterial adhesins is not entirely clear, although
fimbriae, flagella, and pili have been suggested. In regard to the attachment of salmonellae to poultry
skin, these bacterial cell structures were found not to be critical.
36 Extracellular polysaccharides of a
glycocalyx nature may be involved, and if so, treatment of young chicks with this material may be as
effective as the use of live cultures. Although the competitive exclusion treatment seems quite feasible
for large hatcheries, its practicality for small producers seems less likely.
The sugar mannose is a receptor in the intestinal tract to which bacterial pathogens such as salmonellae bind. Since the yeast strain Saccharomyces cerevisiae var. boulardii contains mannose in its outer
wall, some have suggested that the feeding of this yeast to susceptible poults should reduce the attachment of salmonellae. In essence, the yeast cell wall material would outcompete the gastrointestinal
tract for the pathogens.
The possible use of probiotic cultures to exclude some Gram-negative pathogens from the gut biota
has been investigated by several groups. When a 3-strain mixture of probiotic bacteria (competitive
exclusion of E. coli strains) was used on weaned calves and challenged with E. coli serotypes 0111:NM,
026:H11, and 0157:H7, the probiotic-treated calves showed a significant reduction in the shedding
of two of the three pathogens but not E. coli serotype 026:H11.
55 In another study, a mixed culture
of Lactobacillus crispatus and Clostridium lactatifermentans cultured under cecal growth conditions
inhibited the growth of S. Enteritidis.
57 When ca. 10
9 cells/chicken of a chicken isolate of Enterococcus
faecium was orally administered to 30-hour-old broiler chicks followed by a challenge with 10
5 cells
in feces, through which other birds become contaminated. Among the methods that may be employed
to reduce or eliminate intestinal carriage is competitive exclusion (the Nurmi concept).
Under natural conditions where salmonellae exist when eggs hatch, young chicks develop a gastrointestinal tract flora that consists of these organisms and campylobacters, in addition to a variety
of nonpathogens. Once the pathogens are established, they may remain and be shed in droppings
during the entire lifetime of the bird. Competitive exclusion is a phenomenon whereby feces from
salmonellae-free birds, or a mixed fecal culture of bacteria, are given to young chicks so that they
will colonize the same intestinal sites that salmonellae employ and, thus, exclude the subsequent
attachment of salmonellae or other enteropathogens. This concept was advanced in the 1970s and
has been studied and found to be workable by a number of investigators relative to salmonellae
exclusion.
The enteropathogen-free biota may be administered orally to newly hatched chicks through drinking
water or by spray inoculation in the hatchery. Protection is established within a few hours and generally
persists throughout the life of the fowl or as long as the biota remains undisturbed. Older birds can
be treated by first administering antibacterial agents to eliminate enteropathogens, and they are then
administered the competitive exclusion biota. Only viable cells are effective, and both aerobic and
anaerobic components of the gut flora seem to be required. The crop and ceca appear to be the major
adherence sites, with the ceca being higher in germ-free chickens. In one study, the protective flora
remained attached to cecal walls after four successive washings.
52 Partial protection was achieved in
0.5–1.0 hour, but full protection required 6–8 hours after treatment of 1-day-old chicks.
50 In a review
of the microbiology of competitive exclusion of Salmonella in poultry, the use of undefined cultures
afford more protection than the use of defined cultures, especially under laboratory conditions.
51
Field trials in several European countries have shown the success of the competitive exclusion
treatment in preventing or reducing the entry of salmonellae in broilers and adult breeder birds.
39 In
chicks pretreated with a cecal culture and later challenged with a Salmonella sp., the latter failed to
multiply in the ceca over a 48-hour period, whereas in untreated control birds, more than 10
6 /g of
salmonellae were colonized in the ceca.
27
The gist of competitive exclusion is that salmonellae and the native gut biota compete for the same
adherence sites on gut walls. The precise nature of the bacterial adhesins is not entirely clear, although
fimbriae, flagella, and pili have been suggested. In regard to the attachment of salmonellae to poultry
skin, these bacterial cell structures were found not to be critical.
36 Extracellular polysaccharides of a
glycocalyx nature may be involved, and if so, treatment of young chicks with this material may be as
effective as the use of live cultures. Although the competitive exclusion treatment seems quite feasible
for large hatcheries, its practicality for small producers seems less likely.
The sugar mannose is a receptor in the intestinal tract to which bacterial pathogens such as salmonellae bind. Since the yeast strain Saccharomyces cerevisiae var. boulardii contains mannose in its outer
wall, some have suggested that the feeding of this yeast to susceptible poults should reduce the attachment of salmonellae. In essence, the yeast cell wall material would outcompete the gastrointestinal
tract for the pathogens.
The possible use of probiotic cultures to exclude some Gram-negative pathogens from the gut biota
has been investigated by several groups. When a 3-strain mixture of probiotic bacteria (competitive
exclusion of E. coli strains) was used on weaned calves and challenged with E. coli serotypes 0111:NM,
026:H11, and 0157:H7, the probiotic-treated calves showed a significant reduction in the shedding
of two of the three pathogens but not E. coli serotype 026:H11.
55 In another study, a mixed culture
of Lactobacillus crispatus and Clostridium lactatifermentans cultured under cecal growth conditions
inhibited the growth of S. Enteritidis.
57 When ca. 10
9 cells/chicken of a chicken isolate of Enterococcus
faecium was orally administered to 30-hour-old broiler chicks followed by a challenge with 10
5 cells