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Appl. Environ. Microbiol., 09 1995, 3268-3273, Vol 61, No. 9
M Rocelle, S Clavero and LR Beuchat
The efficacy of tryptic soy agar (TSA), modified sorbitol MacConkey agar
(MSMA), modified eosin methylene blue (MEMB) agar, and modified SD- 39
(MSD) agar in recovering a five-strain mixture of enterohemorrhagic
Escherichia coli O157:H7 and five non-O157 strains of E. coli heated in
tryptic soy broth at 52, 54, or 56 degrees C for 10, 20, and 30 min was
determined. Nonselective TSA supported the highest recovery of heated
cells. Significantly (P < or = 0.05) lower recovery of heat-stressed
cells was observed on MSMA than on TSA, MEMB agar, or MSD agar. The
suitability of MEMB agar or MSD agar for recovery of E. coli O157:H7 from
heated or frozen (-20 degrees C) low- or high-fat ground beef was
determined. Recovery of E. coli O157:H7 from heated ground beef was
significantly (P < or = 0.05) higher on TSA than on MEMB agar, which in
turn supported higher recovery than MSD agar did; MSMA was inferior.
Recovery from frozen ground beef was also higher on MEMB and MSD agars than
on MSMA. Higher populations were generally recovered from high-fat beef
than from low-fat beef, but the relative performance of the recovery media
was the same. The inability of MSMA to recover stressed cells of E. coli
O157:H7 underscores the need to develop a better selective medium for
enumerating E. coli O157:H7.
Copyright © 1995, American Society for Microbiology
Suitability of selective plating media for recovering heat- or freeze- stressed Escherichia coli O157:H7 from tryptic soy broth and ground beef
Department of Food Science and Technology, University of Georgia, Griffin 30223-1797, USA.
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