from indigenous fermented foods and human gut ... - Thapar University

4.7.4 Antagonistic activity against pathogens
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Chapter IV: Results
In the agar spot test, the indicator strains, S. aureus ATCC 9144, A. hydrophila
ATCC 35654, Y. enterolitica ATCC 9610, E. sakazakii ATCC 51329, S. flexneri 2a, S.
typhimurium ATCC 19585, L. monocytogenes ATCC 1911, E. coli 0157:H7, L.
acidophilus ATCC 4356 and L. plantarum ATCC 8014 showed weak to strong inhibition
(zone of inhibition of more than 1 mm from edge of producer colony up to 23 mm) as
listed in Table 4.16. L. acidophilus ATCC 4356 was not inhibited at all by five of the
lactobacillus strains tested but weakly inhibited by L. fermentum Lamec-29 strain. The
indicator strains belonging to the Lactobacillus genus were weakly or not inhibited
(inhibition zone of less than 2 mm) except in the case of L. monocytogenes ATCC 1911,
where as the maximum inhibition was observed in the case of E. sakazakii ATCC 51329
by L. fermentum Lamec-29.
The inhibitory activity was not due to bacteriocin production, as neutralised, cell-free
supernatant of the producer culture did not exhibit any antimicrobial activity when
compared to the effect of live cells in the agar spot test. Therefore, the inhibitory activity
observed probably depended on production and diffusion of organic acids into the medium.
Hydrogen peroxide could hypothetically also act as an inhibitory substance, but the
incubation of the plates under anaerobic conditions overrules this as a possible cause for
the observed inhibition. Production of H 2O 2 under aerobic conditions was also investigated
and it was observed that two of the L. delbrueckii strains tested (LKH-2 and LKH-3) and
one strain of L. helveticus (LKH-5) were able to produce H 2O 2 (Table 4.17)