Microbiology, 2021

308 8 • Microbial Metabolism
as determining the strain’s Gram morphology, an appropriate test strip that contains 10 to 20 different
biochemical tests for differentiating strains within that microbial group can be used. Currently, the various API
strips can be used to quickly and easily identify more than 600 species of bacteria, both aerobic and anaerobic,
and approximately 100 different types of yeasts. Based on the colors of the reactions when metabolic end
products are present, due to the presence of pH indicators, a metabolic profile is created from the results
(Figure 8.18). Microbiologists can then compare the sample’s profile to the database to identify the specific
microbe.
Figure 8.18
The API 20NE test strip is used to identify specific strains of gram-negative bacteria outside the Enterobacteriaceae. Here is
an API 20NE test strip result for Photobacterium damselae ssp. piscicida.
Clinical Focus
Part 2
Many of Hannah’s symptoms are consistent with several different infections, including influenza and
pneumonia. However, her sluggish reflexes along with her light sensitivity and stiff neck suggest some
possible involvement of the central nervous system, perhaps indicating meningitis. Meningitis is an
infection of the cerebrospinal fluid (CSF) around the brain and spinal cord that causes inflammation of the
meninges, the protective layers covering the brain. Meningitis can be caused by viruses, bacteria, or fungi.
Although all forms of meningitis are serious, bacterial meningitis is particularly serious. Bacterial
meningitis may be caused by several different bacteria, but the bacterium Neisseria meningitidis, a gramnegative,
bean-shaped diplococcus, is a common cause and leads to death within 1 to 2 days in 5% to 10%
of patients.
Given the potential seriousness of Hannah’s conditions, her physician advised her parents to take her to
the hospital in the Gambian capital of Banjul and there have her tested and treated for possible meningitis.
After a 3-hour drive to the hospital, Hannah was immediately admitted. Physicians took a blood sample
and performed a lumbar puncture to test her CSF. They also immediately started her on a course of the
antibiotic ceftriaxone, the drug of choice for treatment of meningitis caused by N. meningitidis, without
waiting for laboratory test results.
• How might biochemical testing be used to confirm the identity of N. meningitidis?
• Why did Hannah’s doctors decide to administer antibiotics without waiting for the test results?
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8.5 Catabolism of Lipids and Proteins
Learning Objectives
By the end of this section, you will be able to:
• Describe how lipids are catabolized
• Describe how lipid catabolism can be used to identify microbes
• Describe how proteins are catabolized
• Describe how protein catabolism can be used to identify bacteria
Previous sections have discussed the catabolism of glucose, which provides energy to living cells, as well as
how polysaccharides like glycogen, starch, and cellulose are degraded to glucose monomers. But microbes
consume more than just carbohydrates for food. In fact, the microbial world is known for its ability to degrade
a wide range of molecules, both naturally occurring and those made by human processes, for use as carbon
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