Preliminary Study on the Effect of Lipid Extracted and Supplemented Persea americana (Mill) Agar as a Growth Medium for Escherichia coli

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.