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Growth Dynamics of Salmonella enterica Strains on Alfalfa Sprouts and in Waste
Seed Irrigation Water.
Appl Environ Microbiol 2003 Jan;69(1):548-53
Howard MB, Hutcheson SW.
Department of Cell Biology and Molecular Genetics, University of Maryland,
College Park, Maryland 20742.
Alfalfa sprouts and other seed sprouts have been implicated in numerous
outbreaks of salmonellosis. The source of these epidemics appears to have been
low-level contamination of seeds by Salmonella bacteria that developed into
clinically significant populations during the seed germination process. To test
the possibility that Salmonella enterica strains carry host range determinants
that allow them to grow on alfalfa, strains isolated from alfalfa or other
sources were surveyed for their ability to grow on germinating alfalfa seeds. An
S. enterica serovar Cubana strain originally isolated from contaminated alfalfa
sprouts multiplied most rapidly during the initial 24 h of the seed germination
process. Germinating alfalfa seeds supported the multiplication of S. enterica
cells prior to the emergence of the root radicle at 72 h. Thereafter, much lower
rates of multiplication were apparent. The ability of S. enterica to grow on
germinating alfalfa seeds was independent of the serovar, isolation source, or
virulence of the strain. Isolates obtained from alfalfa attained population
levels similar to those observed for strains isolated from contaminated meat
products or stools. Each of the strains could be detected in the waste
irrigation water, with populations being strongly correlated with those detected
on the germinating alfalfa seeds. The S. enterica strains were capable of
utilizing the waste irrigation water as a sole carbon and nitrogen source. S.
enterica strains thus appear to grow saprophytically on soluble organics
released from seeds during early phases of germination. The ability to detect S.
enterica in the waste irrigation water early in the germination process
indicates that this method may be used as a simple way to monitor the
contamination of sprouts during commercial operations.
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