The broth dilution test you did not this test in class can b

The broth dilution test (you did not this test in class) can be used to determine the effectiveness of disinfection. In this test, serial dilutions of the disinfectant were set up in the wells of a microliter plate. Equal amounts of broth culture of Staphylococcus aurous were added to each well. Alter incubation, the wells were examined for bacterial growth. Wells with no growth were sub-cultured in nutrient broth without the disinfectant. Results were recorded as (+) for growth and (-) for no growth. With data below answer the following questions. What is the minimum bactericidal concentration of each disinfectant? What is the minimum bacteriostatic concentration? Which disinfectant is more effective against Staphylococcus aurous? Which disinfectant is more effective against Salmonella enteric? Which disinfectant is more effective against Bacillus anthraces?

Solution

Note - If a no-growth sample shows growth in the absence of disinfectant, it is bacteriostatic, rather than being bactericidal.

a) Minimum bactericidal concentration - A - 1:80 (dilutions below this is bacteriostatic, just inhibits growth, does not kill), B - 1:160.

b) Minimum bacteriostatic concentration (just good enough to stop the growth) - A - 1:100, B - 1:170

c) Both the Minimum bactericidal concentration and Minimum bacteriostatic concentration are higher for B, which means that it is active even at higher dilutions than A. Thus, B is more potent.

d, e) data insufficient