Bacteriology

General Characteristics of Bacteria

1. Unicellular

2. Prokaryotic

3. Smallest free-living organisms

4. Some are spore-forming and considered the hardiest microorganisms

Structural Components

1. Cell wall - superficial layer above the cell membrane

2. Cell membrane

3. Nucleoid - bacterial chromosome; single circular piece of DNA

4. Plasmid - extra-chromosomal DNA

5. Capsule - protective layer superficial to the cell wall

6. Flagella - used for locomotion

7. Pili - used for attachment and genetic exchange

Classification According to General Morphology

1. Cocci

2. Bacilli

3. Spirochete

4. Spirilla

Classification According to Cell-Wall Structure

1. Gram - Positive

2. Gram - Negative

3. Acid - Fast

4. Cell Wall Deficient

IMPORTANT FACTORS THAT AID IN VIRULENCE

1. Endotoxin

• Cell wall component that acts as a toxin

2. Exotoxins

• Toxic substances that are secreted by bacterial cells

• Produced by both gram-negative and gram-positive bacteria

3. Invasiveness

• Some bacteria are able to enter deep into tissues by disrupting cell membranes and tissue matrix

4. Genetic Recombination

• Bacteria are able to accomplish horizontal exchange of genes. This way, virulence genes can be transferred between different species.

• Transformation

Uptake and incorporation of naked DNA into a bacterial cell

• Transduction

Transfer of bacterial genes by a bacteriophage (virus-infected bacterium)

• Conjugation

Transfer of genetic material from a donor bacterial strain to a recipient strain

• Antibiotic Resistance

• A natural consequence of drug exposure and results from the use and overuse of antimicrobial agents

COMMON LABORATORY PROCEDURES IN BACTERIOLOGY

1.  Gram Staining

A microscopic exam that divides bacteria into four major groups:

1. Gram-positive cocci 

(Purple circles)

2. Gram-negative cocci

(Red circles)

3. Gram-positive bacilli

(Purple chain like)

4. Gram-negative bacilli

(Red chain like)

2. Acid-Fast Staining tuberculosis.

A microscopic exam used to detect acid-fast bacteria such as Mycobacterium Tuberculosis.

3.  Culture

Specimens are inoculated onto artificial (agar) media and incubated to allow the growth of bacteria. The bacteria are then identified through biochemical tests.

4. Susceptibility Tests

Bacteria are tested against antibiotics to determine which antibiotic is most effective for therapy.