Bacterial Growth And Controlling Bacterial Growth

Based upon your results, is your bacteria sample a strict aerobe, strict anaerobe, facultative anaerobe, or microaerophile? Why? – Look at your results from OF Glucose and OF Glucose with oil test.

How important is it to add the Kovac’s Reagent in the Indole Utilization test? What is responsible for the color change observed in a positive test? –You can read more about this test in the Test Media Reference in VUMIE2012. Click the M? button.

Did the bacteria grow in the tryptone or malonate media? Why or why not? – Remember, you can tell if they grew if culture was turbid (cloudy).

For the media used in this portion of the experiment, are the media complex or synthetic? Are the media selective, differential, both, or neither? Identify the carbon and nitrogen source for each medium. – Read more about what these terms mean starting on page 178 in your book right below Figure 6.11. Look up each media with the M? button. Remember, nutrient broth is a complex media, mineral salts is a defined media.

How many possible bacteria were remaining after conducting these biochemical tests?

Using the information in the Identification matrix, what additional tests might help you to identify the bacteria in your case study? –Look at the View Identification Matrix under the View menu. What tests would you perform? Look for ones that have a mix of + and – because they would help distinguish between organisms.

Discussion & Conclusion
Include the answers to the following questions:

Salt is one of the oldest food preservatives. How does salt control microbial growth and reduce spoilage? Which two media include elevated concentrations of NaCl? Would bacteria that have the ability to grow in these two media be more likely to cause food spoilage? Why or why not?

Bile salts are natural products of the digestive system that prevent growth of many bacteria. How do bile salts exert antimicrobial activity? What is the concentration of bile salts in bile esculin agar? Why might some bacteria be able to grow on this medium?

Nitrate is often used as a preservative in cured meats to prevent anaerobic growth of spoilage bacteria. Why would the inclusion of nitrate inhibit anaerobic growth?

Potassium cyanide (KCN) is a potent poison. How might some bacteria be able to grow on media containing potassium cyanide?