|
ISS
820 East 20th Street
Cookeville, TN 38501 USA
931 526 1106
Bob@sproutnet.com
中文版
En espaņol
| |
Isolation of
Salmonella from alfalfa seed and demonstration of impaired growth of
heat-injured cells in seed homogenates.
Int J Food Microbiol. 2003 May 15;82(3):245-53.
Liao CH, Fett WF.
US Department of Agriculture, Agricultural Research Service, Eastern Regional
Research Center, 600 East Mermaid Lane, Wyndmoor, PA 19038, USA.
Three major foodborne outbreaks of salmonellosis in 1998 and 1999 were linked to
the consumption of raw alfalfa sprouts. In this report, an improved method is
described for isolation of Salmonella from alfalfa seed lots, which had been
implicated in these outbreaks. From each seed lot, eight samples each containing
25 g of seed were tested for the presence of Salmonella by the US FDA
Bacteriological Analytical Manual (BAM) procedure and by a modified method
applying two successive pre-enrichment steps. Depending on the seed lot, one to
four out of eight samples tested positive for Salmonella by the standard
procedure and two to seven out of eight samples tested positive by the modified
method. Thus, the use of two consecutive pre-enrichment steps led to a higher
detection rate than a single pre-enrichment step. This result indirectly
suggested that Salmonella cells on contaminated seeds might be injured and
failed to fully resuscitate in pre-enrichment broth containing seed components
during the first 24 h of incubation. Responses of heat-injured Salmonella cells
grown in buffered peptone water (BPW) and in three alfalfa seed homogenates were
investigated. For preparation of seed homogenates, 25 g of seeds were
homogenized in 200 ml of BPW using a laboratory Stomacher and subsequently held
at 37 degrees C for 24 h prior to centrifugation and filtration. While untreated
cells grew at about the same rate in BPW and in seed homogenates, heat-injured
cells (52 degrees C, 10 min) required approximately 0.5 to 4.0 h longer to
resuscitate in seed homogenates than in BPW. This result suggests that the
alfalfa seed components or fermented metabolites from native bacteria hinder the
repair and growth of heat-injured cells. This study also shows that an
additional pre-enrichment step increases the frequency of isolation of
Salmonella from naturally contaminated seeds, possibly by alleviating the toxic
effect of seed homogenates on repair or growth of injured cells.
Related Article
|
