L17: Intro to Microbio

Question 1

Normal flora (microbiota)

Answer 1

Tend to be commensal or mutual symbionts adapted to the special conditions found in various body locations. Normal flora tend to avoid injuring the host, and are often beneficial to the host.

Question 2

Virulence

Answer 2

The ability of a microorganism to cause disease

Question 3

Virulence factor

Answer 3

Factors (e.g. toxins) produced by organisms that enable it to infect, cause disease, and/or kill the host

Question 4

Virus

Answer 4

Smallest infectious particle (0.03- 0.3 µm). Viruses are obligate intracellular pathogens; they require a host cell for replication.

Question 5

Bacterium

Answer 5

Simple, unicellular, prokaryotes with no nuclear membrane, mitochondria, Golgi bodies or endoplasmic reticulum that reproduce by asexual division. 0.1- 10 µm.

Question 6

Fungus

Answer 6

More complex cellular structure, eukaryotic organism with well-defined nucleus, mitochondria, Golgi bodies and endoplasmic reticulum. Fungi exist as unicellular yeast or in filamentous forms (mold). Fungi replicate sexually and asexually. 4- 10 µm.

Question 7

Parasite

Answer 7

The most complex microbes. Eukaryotes that exist as single cellular (Leishmania) or multicellular (Shistosome). Wide range in size.

Question 8

Differences between eukaryotes and prokaryotes

Answer 8

• -Lack nucleus
• -Typically have single, double-stranded, circular DNA chromosome
• -Haploid
• -Smaller ribosome (70S)
• -Mesh-like peptidoglycan cell wall

Question 9

How can we detect bacteria in clinical samples?

Answer 9

• -Microscopy
• -Detection of bacterial antigens or nucleic acids
• -Culture
• -Detection of antibody response to bacteria (serology)

Question 10

Microscopy

Answer 10

Looking at bacteria under a microscope to view morphology and Gram stain

Question 11

Detection of bacterial antigens

Answer 11

Can be found in patient specimens; examples are H-antigen (flagella), K-antigen (capsule), O-antigen (LPS)

Question 12

Detection of bacterial nucleic acids

Answer 12

PCR, sequencing

Question 13

Culture

Answer 13

Using media, four types include:

1. Enriched nonselective
2. Selective
3. Differential
4. Specialized

Question 14

How do we classify bacteria?

Answer 14

• -Visible features (size, shape, Gram stain)
• -Nutrition (media, aerobic vs. anaerobic)
• -End products
• -Surface molecules

Question 15

General cytology of bacteria

Answer 15

• -Contain chromosome, mRNA, ribosomes, proteins, and metabolites in cytoplasm
• -Membrane is a lipid bilayer
• -Have a cell wall made of peptidoglycan
• -Have appendages such as pili or flagella
• -Capsule covers outside

Question 16

Difference between Gram + and - cell walls

Answer 16

Gram + = layer of peptidoglycan covering outside with a plasma membrane underneath
Gram - = outer membrane surrounds a peptidoglycan layer with periplasmic space underneath and a cell membrane underneath that

Question 17

General characteristics of peptidoglycan

Answer 17

• -Linear chain of alternating sugars (NAG and NAM) that are crosslinked by B-1,4 linkages
• -Provides essential protection for bacteria
• -Determines shape of bacteria
• -Good drug target because it’s found uniquely on bacteria

Question 18

How does peptidoglycan affect our immune system (basic level)?

Answer 18

Proinflammatory; fixes complement, binds pattern recognition receptors and triggers TNF production; can be degraded by lysozyme found in tears and mucus

Question 19

2 major components of Gram + envelope

Answer 19

1. Peptidoglycan (any layers with extensive crosslinking)

2. Teichoic acid (along with LTA promotes attachment to other bacteria and host cells)

Question 20

Basic elements of Gram - envelope

Answer 20

• -Greatly reduced peptidoglycan, which is located within periplasmic space
• -Surrounded by porin- and LPS-rich outer membrane that maintains structure and makes a permeability barrier

Question 21

Lipopolysaccharide (LPS, endotoxin)

Answer 21

Comprised of 3 subunits:

1. Lipid A – responsible for endotoxin activity of LPS (anchored into OM by fatty acids)
2. Core polysaccharide – required for bacterial structure and viability (branched polysaccharide of 9-12 sugars)
3. O antigen – long polysaccharide with much variation (not in Neisseria)

Question 22

Acid-fast stain

Answer 22

Bacteria stain red by carbol fuchsin, destain by acid alcohol, then methylene blue used to counterstain – acid-fast organisms stay red/pink

Question 23

Acid-fast bacterial structure

Answer 23

Similar to Gram + – LAM, arabinogalactans, and mycolic acid (waxy); grow VERY slowly (ex. mycobacteria)

Question 24

Pili/fimbrae

Answer 24

Composed of protein subunits pilin which form tube with hollow core, hair-like and grow on both Gram +/-

Question 25

2 types of pili

Answer 25

1. Common (attachment to epithelial cells)

2. Sex (only one per cell, involved in gene transfer)

Question 26

Flagella (H-antigen)

Answer 26

Rotating helical structures anchored to plasma membrane responsible for locomotion; important virulence factor for bacteria

Question 27

Capsule (K-antigen)

Answer 27

Loose polysaccharide/protein layer surrounding Gram +/- bacteria that is hydrophillic and protects against immune system (antiphagocytic); important virulence factor

Question 28

Biofilm

Answer 28

An organized community of microbial cells that has a capsule/slime layer over the entire population

Question 29

Gram staining process

Answer 29

• -Crystal violet of Gram stain is precipitated by Gram iodine and is trapped in the thick peptidoglycan layer in gram-positive bacteria
• -The decolorizer disperses the gram-negative outer membrane and washes the crystal violet from the thin layer of peptidoglycan.
• -Gram-negative bacteria are visualized by the red counterstain.

Question 30

Endospores

Answer 30

• -Only occur with Gram+ bacteria
• -Dehydrated, multishelled structures that are basically bacteria that are dormant
• -Contain a complete copy of the chromosome and a high concentration of calcium bound to dipicolinic acid