Biology Class 4: Bacteria and Human Interaction

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Questions and Answers

What is the size range of bacteria?

0.1-100 μm

1-10 mm

10-100 μm

0.1-10 μm (correct)

Who disproved the theory of spontaneous generation?

Louis Pasteur (correct)

Robert Koch

Antonie van Leeuwenhoek

Ferdinand Cohn

What is the purpose of Koch's postulates?

To classify microorganisms into different types

To identify the characteristics of bacteria

To study the history of microbiology

To determine the pathogenicity of microorganisms (correct)

What type of microorganisms live on dead or decaying organic matter?

Saprophytes Signup and view all the answers

What is the term for microorganisms that live on a living host and derive nutrition from the host?

Parasites Signup and view all the answers

What is the term for harmless microbes that live on a living host as normal flora?

Commensals Signup and view all the answers

What is the term for microorganisms capable of causing disease?

Pathogens Signup and view all the answers

Who developed the technique of pasteurization?

Louis Pasteur Signup and view all the answers

What is the function of coagulase produced by Staphylococcus aureus?

Accelerating the formation of a fibrin clot Signup and view all the answers

Which type of bacteria does not possess endotoxins?

Gram-positive bacteria Signup and view all the answers

What is the effect of endotoxins on the body?

It causes fever, shock, and other generalized symptoms Signup and view all the answers

What is the result of the activation of the alternative pathway of the complement cascade?

Inflammation and tissue damage Signup and view all the answers

What is the result of bradykinin release and increased vascular permeability?

Hypotension, shock, and reduced perfusion of major organs Signup and view all the answers

What is the result of generalized activation of the coagulation system?

Disseminated intravascular coagulation and thrombosis Signup and view all the answers

What is the characteristic of exotoxins?

They are polypeptides whose genes are frequently located on plasmids or lysogenic bacterial viruses Signup and view all the answers

What is the effect of leukocidins?

They destroy both neutrophilic leukocytes and macrophages Signup and view all the answers

What is the effect of the heat-labile toxin of E. coli on the mucosal cells of the small intestine?

Increase in the concentration of cAMP Signup and view all the answers

What is the function of the heat-labile toxin of E. coli in the gut?

Mediate the synthesis of cAMP Signup and view all the answers

What is the effect of the heat-stable toxin of E. coli?

Stimulate guanylate cyclase Signup and view all the answers

What is the function of the α-toxin produced by C. welchii?

Hydrolyse lecithin Signup and view all the answers

What is the common characteristic of the toxins produced by C. welchii?

They destroy cells and connective tissue Signup and view all the answers

What is the effect of the heat-labile toxin of E. coli on the gut?

Fluid and electrolyte loss Signup and view all the answers

What is the mode of action of the heat-stable toxin of E. coli?

Stimulation of guanylate cyclase Signup and view all the answers

Which of the following toxins has a similar mode of action to the heat-labile toxin of E. coli?

Enterotoxins produced by V. cholerae and Bacillus cereus Signup and view all the answers

Why are there few normal flora present in the upper part of the small intestine?

Because bile kills them Signup and view all the answers

What percentage of normal flora in the large intestine are anaerobic Bacteroides spp.?

99% Signup and view all the answers

Which of the following is a determinant of virulence of microorganisms?

Infecting dose Signup and view all the answers

What is the primary function of fimbriae or pili in bacteria?

To facilitate adhesion to host cells Signup and view all the answers

What is the function of the capsule produced by certain bacteria?

To prevent phagocytosis by preventing the adhesion of phagocytes to the bacteria Signup and view all the answers

Which of the following enzymes is involved in the degradation of intercellular substances, allowing easy spread of bacteria through tissues?

Collagenase Signup and view all the answers

Which of the following bacteria produces a protein that binds to IgG and prevents the activation of complement?

Staphylococcus aureus Signup and view all the answers

What is the term for the self-produced matrix of extracellular polymeric substance that embeds bacteria in a biofilm?

Glycocalyx Signup and view all the answers

What proportion of the microbial world do opportunistic pathogens represent?

A small proportion Signup and view all the answers

What do some normal flora produce to protect against invading pathogens?

Substances that kill pathogens Signup and view all the answers

What is a function of normal flora in newborns?

To stimulate the development of the immune system Signup and view all the answers

What nutrient do normal flora in the gut provide?

Vitamin K Signup and view all the answers

What can happen when normal flora are displaced from their normal site in the body?

Bloodstream infections Signup and view all the answers

What can happen when potential pathogens gain a competitive advantage?

C.difficile grows in the gut Signup and view all the answers

What can occur in immunocompromised individuals?

Normal flora overgrow and become pathogenic Signup and view all the answers

Which of the following is NOT a site where normal flora can be found?

Liver Signup and view all the answers

Study Notes

Bacteria and Human Interaction

Bacteria are the smallest (0.1-10 μm) independently living cells with a cytoplasmic membrane surrounded by a cell wall.
They divide by binary fission and can be grown in artificial culture, often in less than 1 day.
Archaea are prokaryotic, but differ in the chemical structure of their cell walls and other features.

History of Bacteria

Louis Pasteur (1822-1895) disproved the theory of spontaneous generation and developed vaccines, such as anthrax.
Robert Koch (1843-1910) developed Koch's postulates, which include:
- The microorganism must be re-isolated from the inoculated, diseased experimental host and identified as being identical to the original specific causative agent.

Types of Microorganisms

Saprophytes: free-living microbes that live on dead or decaying organic matter, usually found in soil and water.
Parasites: microbes that live on a living host, derive nutrition from the host, and cause harm to the host.
Commensals: harmless microbes that harbor on a living host as normal flora, without causing injury.
Pathogens: microbes capable of causing disease, representing a small proportion of the microbial world.
Opportunistic pathogens: microbes capable of causing disease only in immunocompromized individuals.

Beneficial Functions of Normal Flora

Protects organs and systems from invading pathogens.
Stimulates development of immune system in newborns.
Provides important nutrients, such as Vitamin K, for digestion and absorption.

Harmful Effects of Normal Flora

Displacement from normal site of the body can lead to bloodstream infections.
Diminished populations of harmless competitors can lead to overgrowth of potential pathogens.
Normal flora can become pathogenic in immunocompromized individuals.

Where Can We Find Normal Flora?

Skin
Eyes and Ears
Respiratory Tract
Oral Cavity (Mouth)
Gastro-intestinal Tract
Urogenital Tract

Normal Flora in the Oral Cavity

Includes both aerobic and anaerobic bacteria, such as Streptococcus mutans, S. aureus, and S. epidermidis.
Also includes yeasts, molds, protozoa, and viruses.
Poor dental hygiene can lead to bacterial growth and dental caries.

Normal Flora in the Gastrointestinal Tract

Stomach: few bacteria present due to gastric enzymes and acidic pH.
Small intestine: few normal flora present in the upper part, more in the lower part.
Large intestine: has the most bacteria, with 99% being anaerobic, such as Bacteroides spp.

Determinants of Virulence of Microorganisms

Transmissibility
Adhesion
Invasiveness
Toxigenicity
Enzymes
Plasmids
Bacteriophages
Infecting dose
Route of infection

Virulence Factors of Microorganisms

Fimbriae or pili: important adhesions present in some bacteria.
Biofilm formation: a mechanism for strong adherence to structures, such as catheters, prosthetic implants, and heart valves.
Capsule: prevents phagocytosis of bacteria by preventing phagocytes from adhering to them.
Cell wall proteins: help in invasion, such as Protein A of Staphylococcus aureus.
Collagenase and hyaluronidase: degrade intercellular substances, allowing easy spread of bacteria through tissues.
Coagulase: accelerates the formation of a fibrin clot, protecting the organism from phagocytosis.
Leukocidins: destroy neutrophilic leukocytes and macrophages.
Toxigenicity: ability to produce toxic substances, including endotoxins and exotoxins.

Endotoxins

Cell wall lipopolysaccharides of Gram-negative bacteria.
Not actively released from the cell.
Cause fever, shock, and other generalized symptoms.
Effects include:
- Fever due to release of endogenous pyrogens.
- Hypotension, shock, and reduced perfusion of major organs.
- Activation of the alternative pathway of the complement cascade.
- Generalized activation of the coagulation system.
- Increased phagocytic activity of macrophages and polyclonal B cell activation.
- Increased antibody production.

Exotoxins

Polypeptides whose genes are frequently located on plasmids or lysogenic bacterial viruses.
Both Gram-positive and Gram-negative bacteria secrete exotoxins.
Enterotoxins: act on the gut mucosa, causing gastrointestinal disturbances.
Heat-labile and heat-stable toxins: both cause fluid and electrolyte loss into the gut lumen.
Miscellaneous exotoxins: produced by C. welchii and other species of clostridia, causing gas gangrene.

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Description

This quiz covers the basics of bacteria, their characteristics, and their interaction with humans. Understand the structure, growth, and history of bacteria with this quiz.