Microbial Control Lab 4

Selective and Differential Media We have completed Isolation of bacteria using steak plate and spread plate This is a good beginning, but now we must determine more about the bacteria using: Selective Media and Differential Media

Selective and Differential Media Selective Media – chemicals added that allow certain bacteria to grow and inhibit others. Differential Media – Allows all bacteria to grow but has chemicals to cause a change in appearance of certain bacteria.

Selective and Differential Media Media can be selective, differential or both The 3 media we will use today in Exercises 1-3 are BOTH selective and differential

Selective and Differential Media Exercise 1 – Manitol Salt Agar (MSA) –Manitol – carbohydrate (differential) –Sodium Chloride – salt (selective) –Phenol Red – pH indicator Only pathogenic forms of S. aureus can ferment manitol which produces acid and therefore causes the pH indicator to turn yellow Only staphylococci bacteria can live in salt MSA is Selective for all staphylococci and differential for S. aureus

Selective and Differential Media Exercise 2 - Eosin Methylene Blue Agar (EMB) –Lactose – carbohydrate (differential) –Sucrose – carbohydrate (differential) –Eosin Y – Dye (selective) –Methylene Blue – Dye (selective) Dye inhibits growth of Gram + Bacteria Selective for Gram – bacteria and is Differential for fecal coliform bacteria by how actively it ferments the carbohydrate (fecal coliform will have a green metalic sheen)

Selective and Differential Media Exercise 3 – Mac Conkey Agar –Lactose – carbohydrate (differential) –Bile salts – salt (selective) –Neutral Red – pH indicator –Crystal Violet – Dye (selective) Bile salts and dye inhibit Gram + bacteria Selective for Gram – bacteria and Differential for gram – especially enterbacteriaceae because they can ferment lactose and create acid causeing pH indicator to turn red

Microbial Control Exercise 4 – Kirby bauer Antibiotic Sensitivity Sensitive – if a bacteria is sensitive to an antibiotic, the antibiotic will inhibit or slow growth of that bacteria and will have a “zone of inhibition” (an area of no bacteria growth) around the antibiotic.

Microbial Control Exercise 4 – Kirby bauer Antibiotic Sensitivity – (cont) Resistant – if a bacteria is resistant to an antibiotic, then the presence of the antibiotic will have no affect on the growth of the bacteria

Microbial Control Exercise 5 - Effectiveness of Disinfectants We will use paper disks soaked in various disinfectants to determine the effectiveness of those products Make sure to use a disk soaked in sterile water placed in center of agar plate for our control group

Microbial Control Exercise 6 – Effect of pH pH scale ranges fro 0 – 14 pH 7 is neutral Below 7 is acidic Above 7 is basic Each number is 10 times more than the one before it

Microbial Control Exercise 6 – Effect of pH (cont) We want to determine the optimum pH for each bacteria Below pH 5.5 – Acidophiles pH 5.5 – 8.5 – Neutrophiles Above pH Alkaphiles

Microbial Control Exercise 7 – Effect of Temperature We want to determine the optimum temperature for bacteria Cardinal Temperatures for a bacteria are their optimum temperature, minimum temperature and maximum temperature

Microbial Control Exercise 7 – Effect of Temperature (cont) Below 20° C – psychorphiles Freezing to 30 ° C - psychrotrophs 15 ° - 45 ° C – mesophiles –Usually bacteria in human body are mesophiles Above 40 ° C – thermophiles 65 ° – 110 ° C – Extreme thermophiles