Abstract:
In the process of improving Persea americana (Mill.) Agar (PAA)
as a growth medium for Escherichia coli, six reformulations of PAA were
evaluated in this study. These are Supplemented PAA (SPAA), Lipidextracted
SPAA, Glucose-enhanced SPAA, Glucose-enhanced Lipidextracted
SPAA, Sucrose-enhanced SPAA and Sucrose-enhanced Lipidextracted
SPAA. Using the nutritional requirement of bacteria as cited by
Brooks et al. (1998), the following modifications in the media formulation
of PAA were made to create SPAA: adjustment of Persea americana
extract concentration to 20 g/L, and the addition of 5.9 g NaNOs, 0.166 g
MgSO, and 0.186 g KH, PO, per liter medium. pH was determined to be
~7. A portion of SPAA was subjected to lipid extraction. In an effort to
improve cellular morphology, glucose or sucrose was added to separate
preparations of SPAA and Lipid-extracted SPAA. Evaluation of the
medium efficiency was based on population density, cultural
characteristics and cellular morphology using Nutrient Agar (BBL) as a
reference medium. Broth cultures of Escherichia coli with an estimated
population density of ~10° cfu/ml were plated on Nutrient Agar (NA) and
the six reformulations of PAA. The population density was evaluated
using the Miles and Mizra Method after incubation for 24 hours at 37 °C.
Comparison of the resulting values showed that the population density of
E. coli in NA and Lipid-extracted SPAA are equal. Also, population
densities in the other five media were comparable to that of NA, that is, all
values fell under the same exponential power of approximately 10° cfu/ml.
Cultural characteristics of E. coli in all reformulations were similar to that
of NA. The only notable difference is that colonies in the six reformulated
media were smaller (1.0 to 1.4 mm) than those in NA (1.5 mm).
Microscopic observation of Gram-stained bacterial smears showed that
cells grown in the six reformulations were larger (3.6 to 7.3 micrometers)
than those in NA (3.3 micrometers). Individual cells grown in the
glucose- and sucrose-enhanced media showed the formation of septated
fusiform cells. Of the six reformulations, Lipid-extracted SPAA poses an
improved alternative medium for the growth of E. coli.
