Gp. Zhang et Ra. Holley, Development and PFGE monitoring of dominance among spoilage lactic acid bacteria from cured meats, FOOD MICROB, 16(6), 1999, pp. 633-644
Strains of lactic acid bacteria (LAB), isolated from intact vacuum-packaged
cured meats obtained at retail were subjected to single inhibitory factor
and mixed-culture dominance tests during challenge with different condition
s of pH and temperature in the presence of NaCl and NaNO2 to study reasons
for strain dominance. Bacteria were checked for bacteriocin production Both
initial pH and temperature had a significant effect on the growth of spoil
age LAB isolates in modified MRS broth. Lactobacilli generally grew better
than Lc. mesenteroides at pH 5.5. it appeared that L. curvatus and L. sakei
grew faster at elevated temperature (12 degrees C) than Lc. mesenteroides.
it was also noted that there was a similar response for strains within the
same species to the challenges of NaCl, NaNO2, pH and temperature. When pr
esent in mixed cultures, Leuconostoc strains did not grow well at 2 degrees
C and at an initial pH of 5.5 compared with lactobacilli, but performed be
tter at this low temperature as pure cultures than when mixed with lactobac
illi. At normal cured meat pH (6.0 and 6.5) and higher temperatures (6 degr
ees C and 12 degrees C), dominant bacteria always grew from the originally
larger bacterial population. When leuconostocs and lactobacilli were presen
t in equal initial numbers, leuconostocs generally did not grow as well as
lactobacilli. Lc mesenteroides grew faster than L. curvatus at 6 degrees C
but did not out-compete L. sakei at this temperature (pH greater than or eq
ual to 6.0). Pulsed field gel electrophoresis (PFGE) of Smal digested genom
ic DNA successfully distinguished all the strains under study Difficulties
associated with enumeration of LAB having similar biochemical properties we
re addressed by the development of a composite-simultaneous PFGE method for
interspecies qualification using single colonies from agar plates to gener
ate digested DNA for analysis. (C) 1999 Academic Press.