Comparative studies on five culture media for bacterial isolation

Abstract

The research made comparative studies on five media for bacterial isolation. This study aimed at capturing important comparative data in the various types of media for growth efficiency and specific bacteria identification in clinical microbiology. The sources of the samples were urine, nasal swabs and stool. The totality of 15 samples was plated monthly and 120 samples were studied during an eight month period. The mean bacterial load from the cultures grown over the period from each source was calculated and used for comparative growth efficacy. Dominant colonies were characterized and identified based on morphological features and biochemical tests. A 0.1 ml of 10-3 of each bacteria isolate was evaluated for growth potential in triplicate on three different special purpose media. The mean bacteria load from the triplicate cultures was calculated. Salmonella-Shigella agar (SSA); a selective medium had the highest number of bacterial colonies of 2.98 x 105 CFU/ ml followed by the enrichment medium; blood agar that had 2.96 x 105 CFU/ ml and MacConkey agar (MCA) with 2.93 x 105 CFU/ ml. Biochemical identification and characterization of four dominant isolates confirmed the presence of Staphylococcus aureus, Escherichia coli, Salmonella and Shigella. Growth potential of each medium on the bacterial isolates showed that MacConkey agar recorded the highest growth potential of 8.9 x 105 CFU/ ml for E. coli followed by Blood Agar that gave 8.8 x 105 CFU/ml for Shigella. The third highest growth potential of 8.6 x 105 CFU/ ml was recorded in nutrient agar against S. aureus. Statistically, there exists a significant difference among the mean of the five media in their support for bacteria growth at α =0.05.\r\r\tKey words: Bacterial isolation, isolates, Escherichia coli, Shigella, Blood agar.