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Comparison of microplate,
agar drop and well diffusion plate methods for evaluating
hemolytic activity of Listeria monocytogenes
M. L. Vaca Ruiz*, P. G. Silva and A.
L. Laciar
Area
Microbiología. Facultad de Química, Bioquímica y Farmacia.
Universidad Nacional de San Luis. Chacabuco y Pedernera.
5700 San Luis. Argentina.
*Corresponding author. E-mail:
mlvaca@unsl.edu.ar.
Tel: + 54
02652 423789.
Accepted
27 May, 2009 |
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Hemolytic activity is an important characteristic for the
differentiation of
Listeria
monocytogenes
from apathogenic Listeria species within of
conventional laboratory practices. We compared the efficacy
of the agar
well
diffusion method with respect to two previously described
methods such as the agar drop and microplate methods in
quantifying hemolysis of L. monocytogenes cultures.
The hemolytic activities of 13 strains of L.
monocytogenes were tested. Two culture media (Mueller
Hinton blood agar and Mueller Hinton blood agar supplemented
with 0.2% activated charcoal and 1 mmol/L CaCl2)
were evaluated, using the
agar drop
and well diffusion methods as plating procedure. The agar
well diffusion method was the best plating procedure for
detecting the hemolysis of all strains studied after 24 and
48 h of incubation (p < 0.01).
In addition, this plating procedure showed a greater
sensitivity compared to microplate method at a read time of
6 h, giving positive reactions with all strains at an
inoculum of 108 cfu/ml. The supplementation of
charcoal on blood agar had a positive effect only when the
plates were incubated after 48 h (p < 0.01). The results
indicate that the agar well diffusion method can detect and
quantify L. monocytogenes
hemolytic activity faster and with higher sensitivity than
the other two methods here studied.
Key
words:
Listeria monocytogenes, hemolytic activity,
microplate, agar drop and well diffusion methods |
