Microbiology for Health Sciences: Exam 1 Study Guide

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Introduction to Microbes

General Characteristics of Microbial Groups

Microbes are diverse organisms that include bacteria, archaea, protists, fungi, molds, and protozoa. Understanding their characteristics is fundamental to microbiology.

Eubacteria (Bacteria): Prokaryotic, unicellular, possess peptidoglycan cell walls, reproduce by binary fission.
Archaea (Archaebacteria): Prokaryotic, lack peptidoglycan, often found in extreme environments.
Protists: Eukaryotic, mostly unicellular, include protozoa and algae.
Fungi: Eukaryotic, can be unicellular (yeasts) or multicellular (molds), cell walls contain chitin.
Mold: Multicellular fungi, form hyphae.
Protozoa: Unicellular eukaryotes, often motile, lack cell walls.
Prokaryotes: Cells without a nucleus (bacteria and archaea).
Eukaryotes: Cells with a nucleus (protists, fungi, plants, animals).

Example: Escherichia coli is a common eubacterium found in the human gut.

History of Microbiology

Abiogenesis and Experiments Disproving It

Abiogenesis is the idea that life can arise spontaneously from non-living matter. Key experiments disproved this concept.

Redi's Experiment: Used meat in jars to show that maggots only appeared when flies could access the meat, disproving spontaneous generation for larger organisms.
Pasteur's S-shaped Flask Experiment: Demonstrated that microbes in the air, not spontaneous generation, caused contamination. The S-shaped flask prevented airborne microbes from reaching the broth.

Significance: These experiments established that life arises from existing life (biogenesis).

Contributions of Key Scientists

Pasteur: Developed pasteurization, proposed the germ theory of disease.
Koch: Formulated Koch's postulates, proving the germ theory of disease.
Semmelweis: Advocated handwashing to prevent disease transmission.
Hooke: First described cells using a microscope.
Lister: Introduced antiseptic techniques in surgery.

Koch's Postulates

Microorganism must be found in all cases of the disease.
It must be isolated and grown in pure culture.
The cultured microorganism must cause disease when introduced into a healthy host.
It must be re-isolated from the experimentally infected host.

Application: Koch's postulates are still used to identify causative agents of diseases.

Basic Tools in Microbiology

Microscopy

Microscopes are essential for observing microbes. The choice of microscope depends on the size and detail required.

Bright Field (Compound Light) Microscope: Suitable for most bacteria and cells.
Electron Microscope: Used for viruses and ultrastructural details.

Key Terms: Contrast and resolution are critical for clear imaging. Oil immersion lens increases resolution for small specimens.

Morphology and Arrangement

Cocci: Spherical bacteria.
Bacilli: Rod-shaped bacteria.
Diplococci: Pairs of cocci.
Streptococci: Chains of cocci.
Tetrads: Groups of four cocci.
Sarcina: Cubical packets of cocci.
Spirochetes: Spiral-shaped bacteria.

Staining Techniques

Staining enhances visibility and differentiation of microbes.

Smear Preparation and Fixation: Involves spreading microbes on a slide and heat fixing to kill and adhere them.
Simple Stain: Uses one dye to highlight cells.
Differential Stain: Distinguishes between types of bacteria (e.g., Gram stain).
Special Stain: Targets specific structures (e.g., capsule, flagella).

Gram Stain: Differentiates bacteria into Gram-positive (purple) and Gram-negative (pink) based on cell wall structure.

Taxonomy and Identification of Bacteria

Binomial Nomenclature

Scientific names consist of genus and species. The genus is capitalized; the species is lowercase and both are italicized.

Example: Staphylococcus aureus

Classification Tools

rRNA Gene Sequencing: Used to classify bacteria; developed by Carl Woese and Fox.
Domains: Woese's system includes Domain Archaea, Domain Bacteria, and Domain Eukarya.
Biochemical Testing: Identifies metabolic capabilities.
Serological Testing: Uses antibodies to detect specific microbes.
Gram Staining: Differentiates cell wall types.
Dichotomous Key: Stepwise tool for identification based on characteristics.

Prokaryotic and Eukaryotic Cell Structure

Comparison of Cell Types

Prokaryotic and eukaryotic cells differ in structure and complexity.

Prokaryotes: No nucleus, nucleoid region, cell wall (often peptidoglycan), simple organelles.
Eukaryotes: Nucleus, membrane-bound organelles, complex structure.

Cell Envelope Differences

Gram-positive: Thick peptidoglycan layer, no outer membrane.
Gram-negative: Thin peptidoglycan, outer membrane with lipopolysaccharide (LPS).

Key Structures and Functions

Nucleus: Contains genetic material (eukaryotes).
Nucleoid: Region with DNA (prokaryotes).
Cell Membrane: Controls entry/exit of substances.
Cell Wall: Provides structure and protection.
Peptidoglycan: Main component of bacterial cell walls.
Glycocalyx: Protective layer; includes slime layer and capsule.
Flagella: Motility structures; made of flagellin.
Pili/Fimbriae: Attachment and conjugation structures.
Cilia: Motility in eukaryotes.
Ribosomes: Protein synthesis; size differs between prokaryotes and eukaryotes.
Endospores: Resistant structures formed by some bacteria.

Transport Mechanisms

Passive Transport: Includes simple and facilitated diffusion.
Active Transport: Requires energy to move substances against gradients.

Example: Bacillus species form endospores to survive harsh conditions.

Microbial Nutrition and Growth

Microbial Feeding and Energy Acquisition

Microbes obtain energy and nutrients through various modes.

Photoautotrophs: Use light and CO2 for energy and carbon.
Photoheterotrophs: Use light for energy, organic compounds for carbon.
Chemoautotrophs: Use inorganic chemicals for energy, CO2 for carbon.
Chemoheterotrophs: Use organic compounds for energy and carbon.

Types of Media

Selective Medium: Favors growth of specific microbes.
Differential Medium: Distinguishes microbes based on reactions.
Transport Medium: Maintains viability during transport.
Cell/Animal Cultures: Used for microbes that require living cells.

Physical Requirements for Growth

Temperature: Psychrophiles (cold), Mesophiles (moderate), Thermophiles (hot), Hyperthermophiles (very hot).
pH: Acidophiles (acidic), Alkalinophiles (alkaline), Neutrophiles (neutral).
Oxygen: Strict aerobes (require O2), Strict anaerobes (cannot tolerate O2), Facultative anaerobes (can use O2 or not), Aerotolerant anaerobes (tolerate O2), Microaerophiles (require low O2).
Salt: Halophiles (require high salt), Facultative halophiles (tolerate salt).

Example: Halobacterium is a halophile found in salty environments.

Growth Curve of Bacteria

Bacterial populations grow in distinct phases:

Lag Phase: Adaptation, no growth.
Log Phase: Exponential growth.
Stationary Phase: Growth rate equals death rate.
Death Phase: Decline in population.

Physical Requirements: Anaerobic jars and thioglycolate broths are used to grow anaerobic bacteria.

Summary Table: Microbial Growth Requirements

Requirement	Type	Description
Temperature	Psychrophile	Grows at low temperatures (0-20°C)
Temperature	Mesophile	Grows at moderate temperatures (20-45°C)
Temperature	Thermophile	Grows at high temperatures (45-80°C)
Temperature	Hyperthermophile	Grows at very high temperatures (>80°C)
pH	Acidophile	Prefers acidic environments (pH < 5)
pH	Alkalinophile	Prefers alkaline environments (pH > 9)
pH	Neutrophile	Prefers neutral pH (pH 6-8)
Oxygen	Strict aerobe	Requires oxygen
Oxygen	Strict anaerobe	Cannot tolerate oxygen
Oxygen	Facultative anaerobe	Can grow with or without oxygen
Oxygen	Aerotolerant anaerobe	Tolerates oxygen, does not use it
Oxygen	Microaerophile	Requires low oxygen
Salt	Halophile	Requires high salt concentration
Salt	Facultative halophile	Tolerates high salt

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