Chapter 2 Study Guide

Ch. 2: The Chemistry of Microbiology

Introduction

This chapter explores the fundamental chemical principles that underlie microbiology, including the structure and function of atoms, molecules, and macromolecules, as well as their relevance to microbial life and disease. Case studies and vocabulary exercises are included to reinforce understanding of these concepts in real-world microbiological contexts.

Case Study: Raw Oysters and Antacids – A Deadly Mix?

Overview

• Context: Examines the relationship between stomach acidity, antacid use, and susceptibility to foodborne bacterial infections, particularly Vibrio vulnificus.

• Key Point: Stomach acid acts as a barrier to many pathogens. Reducing acidity (e.g., with antacids) can increase infection risk.

Key Questions and Explanations

1. Will antacids raise or lower the pH of the stomach? Antacids raise the pH of the stomach, making it less acidic and more favorable for bacteria to survive.

2. Other than refraining from antacids, what can people do to reduce their risk of infection? Cook oysters and other seafood thoroughly to kill bacteria. Avoid raw or undercooked seafood, especially if immunocompromised.

3. Name 2 other bacteria found in food and known to cause foodborne illness. Escherichia coli (E. coli) and Salmonella are common foodborne pathogens.

4. Example: A person who ate raw oysters while taking antacids developed a severe infection with V. vulnificus.

Case Study: Diarrhea Illness (Giardia)

Overview

• Context: Outbreak of diarrhea in children after exposure to contaminated ditch water. Giardia identified as the causative agent.

• Key Point: Giardia is a protozoan parasite that causes gastrointestinal illness, often transmitted via contaminated water.

Key Questions and Explanations

1. What organisms might Dr. Thompson have given for controlling severe diarrhea? Supportive care (rehydration), antiprotozoal medications such as metronidazole.

2. Describe the microbe Giardia. Giardia intestinalis is a flagellated protozoan that causes giardiasis, a diarrheal disease. It has a cyst form (infective) and a trophozoite form (active in the intestine).

3. How is this microbe transmitted to humans? Primarily through ingestion of cysts in contaminated water or food; can also occur via person-to-person contact.

4. What groups of persons are at greater risk for this infection? Children, immunocompromised individuals, travelers, and those in areas with poor sanitation.

5. How is this infection treated? Supportive care and antiprotozoal medications.

6. How might this microbe have gotten into the irrigation water supply? Contamination from animal or human feces entering the water system.

7. Why is Giardia’s ability to form cysts important in causing disease? Cysts are resistant to environmental stresses and allow the parasite to survive outside the host until ingested.

Vocabulary and Key Chemical Concepts

Overview

Understanding the vocabulary of chemistry is essential for mastering microbiology. The following table summarizes key terms, their definitions, and examples relevant to microbial life.

Vocab Term	Definition/Synonym	Example/Use in a Sentence
Atom	Smallest unit of matter	Helium atom is a single unit of helium element.
Element	Pure substance consisting of one type of atom	Oxygen is an element essential for respiration.
Isotope	Atoms with same number of protons, different number of neutrons	Carbon-12 and Carbon-14 are isotopes of carbon.
Covalent bond	Molecular bond where atoms share electrons	Water molecules are held together by covalent bonds.
Ionic bond	Bond formed by transfer of electrons and attraction between charges	Table salt (NaCl) is formed by an ionic bond between sodium and chloride.
Hydrogen bond	Weak bond between hydrogen and electronegative atom (e.g., oxygen)	Hydrogen bonds hold the two strands of DNA together.
Dehydration synthesis	Chemical reaction joining molecules by removing water	Proteins are formed by dehydration synthesis of amino acids.
Hydrolysis	Breaking down molecules by adding water	Digestion of starch involves hydrolysis.
Acid	Substance that releases hydrogen ions (H+) in solution	Stomach acid helps kill ingested microbes.
Polysaccharide	Complex carbohydrate made of many monosaccharides	Starch is a polysaccharide used for energy storage in plants.
Protein	Macromolecule composed of amino acids	Enzymes are proteins that catalyze biochemical reactions.
Unsaturated fatty acid	Fatty acid with one or more double bonds; usually liquid at room temperature	Olive oil contains unsaturated fatty acids.

Key Chemical Equations

• Dehydration Synthesis: $\text{Monomer}_1 + \text{Monomer}_2 \rightarrow \text{Polymer} + H_2O$

• Hydrolysis: $\text{Polymer} + H_2O \rightarrow \text{Monomer}_1 + \text{Monomer}_2$

Summary Table: Types of Chemical Bonds

Bond Type	Description	Example
Covalent	Atoms share electrons	H2O (water)
Ionic	Transfer of electrons, attraction between ions	NaCl (table salt)
Hydrogen	Weak attraction between hydrogen and electronegative atom	DNA double helix

Additional Info

• Understanding chemical principles is essential for grasping microbial metabolism, genetics, and pathogenesis.

• Case studies illustrate the real-world impact of chemical concepts in microbiology, such as the effect of pH on infection risk and the role of waterborne parasites.