Phage Typing Learning Objectives 1. Explain the purpose of phage typing. 2. Describe the phage typing method. 3. Explain what is occurring when plaques form in a bacterial lawn. 4. If both T4 and ΦX174 use LPS as their bacterial receptor, explain why wild-type phage T4 produces plaques, while wild-type ΦX174 does not infect E. coli K-12. Identification of Unknowns 1. Why is a streak plate important for a bacterial unknown analysis? What is an additional early analysis step? 2. Describe the Enterobacteriaceae and their major characteristics. 3. Describe the test series/battery typically used to distinguish between members of the Enterobacteriaceae. 4. Explain what the symbols (+) and (-) indicate regarding the outcome of various biochemical tests. 1. Identify the 3 groups of soil organisms isolated in the soil microbial count. Explain how these groups were separated for analysis. 2. Identify the major antibiotic-producing genera found in the soil, and, for each, identify the above group to which it belongs. 3. Explain why dilutions are necessary for microbial counts. 4. Starting with a culture containing 106 cells/ml, describe in detail how to set up a serial dilution scheme to result in a countable plate. 5. Evaluate and interpret the results of a plate count, including selecting the appropriate plate for counting, and calculating the original cell density (OCD). 6. Identify three bacterial pathogens transmitted through fecal contamination of water. 7. Explain the difference between coliform and non-coliform bacteria. Identify the coliform organisms used as indicator species for fecal contamination of water. 8. Describe in detail the technique commonly used to assess the presence of fecal coliforms in water. Specify what constitutes a countable plate. 9. Identify the selective medium used to enumerate fecal coliforms and the basis for its selectivity. Describe the appearance of coliforms on this medium. 10. Given a countable plate, calculate the coliform CFU per 100 mL. Specify the coliform count of potable water.

Snyder test

A test to determine the susceptibility of bacteria to sucrose fermentation, primarily targeting Streptococcus mutans.

Specificity of the Snyder test

It specifically targets Streptococcus mutans due to its unique ability to rapidly ferment sucrose and lower pH.

How the Snyder test works

The Snyder test involves inoculating a medium with the bacteria and monitoring pH changes; a positive result is indicated by a drop in pH, usually below 4.8.

Purpose of the Kirby-Bauer procedure

To evaluate the antibiotic susceptibility of bacteria through a disk-diffusion method.

Standardization of the Kirby-Bauer protocol

Standardization ensures consistent test results by using specific criteria for inoculum size, incubation time, and temperature.

Minimum Inhibitory Concentration (MIC)

The lowest concentration of an antibiotic that inhibits the growth of a bacterium; relevant to the K-B assay as it helps determine the efficacy of antibiotics.

Factors affecting zone of inhibition size

Factors include the diffusion rate of the antibiotic through the agar, bacterial growth rate, and the antibiotic's potency.

Bactericidal vs. Bacteriostatic

Bactericidal antibiotics kill bacteria, while bacteriostatic antibiotics inhibit their growth; testing for regrowth after removing the antibiotic can help distinguish between the two.