Bacterial Taxonomy & Morphology

Question 1

What are the 3 types of pathogens that bacterial can be considered as?

Answer 1

1. FRANK PATHOGENS: capable of causing disease in any host; always a pathogen when isolated
2. OPPORTUNISTIC PATHOGENS: capable of causing disease given the opportunity, but often a commensal relationship and part of the normal host flora and can cause disease in normally sterile tissues**
3. NON-PATHOGENS (may cause disease in immunocompromised individuals)

Question 2

What is the general rule of thumb for disease?

Answer 2

D = N x V/R

N = number of organisms
V = virulence
R = resistance (innate and adaptive immunity) of host

Question 3

What are the 3 kingdoms of taxonomy? How where they developed?

Answer 3

1. EUKARYA
2. BACTERIA
3. ARCHAEA

based on the sequences of rRNA

Question 4

What are the main goals of bacterial classification?

Answer 4

speed up the identification process and identify bacteria using a limited number of characteristics

Question 5

Bacterial nomenclature involves the use of…

Answer 5

a binomial system to assign a genus and species
(Salmonella cholerasuis)

Question 6

What are the main characteristics that bacterial identification is normally based on?

Answer 6

morphological, biochemical, and serological traits
nucleic acid profile (DNA/RNA)

Question 7

Bacterial morphology examples:

Answer 7

Question 8

What are the 2 major morphologies that opportunistically dangerous bacteria take on?

Answer 8

strept- and staph-

Question 9

What structures of bacteria are we most concerned with?

Answer 9

those on the outer surface that the host will come into contact with - fimbrae, flagella, capsule

Question 10

What are bacterial spores?

Answer 10

small oval or spherical structures that are very resistant to high temperatures, radiation, desiccation, and chemical agents
contain some genetic material from original bacteria and help maintain life in times of stress or adverse conditions/environments where they will remain latent until times are favorable

Question 11

How can spores be differentiated microscopically?

Answer 11

they do not stain

Question 12

What is the difference between Gram positive and Gram negative bacterial? How do they stain?

Answer 12

GRAM + bacteria have a thick peptidoglycan cell wall; appear blue/violet

GRAM - bacterial have a thin peptidoglycan wall and have a lipid-rich outer membrane; appear red

Question 13

What is the general 6 step Gram stain procedure?

Answer 13

1. make a thin smear from a pure culture on a slide and heat-fix
2. cover smear with crystal violet; let stand and rinse
3. cover smear with Gram’s iodine (mordant); let stand and rinse
4. hold slide at an angle and rinse with alcohol or alcohol-acetone until blue runs off; rinse
5. cover smear with safranin; let stand and rinse
6. blot sample dry and examine under oil immersion at 100x

Question 14

Gram positive vs Gram negative cell walls:

Answer 14

+ = thick
- = thin

Question 15

How is the peptidoglycan network arranged?

Answer 15

2 interchanging N-acetyl-D-glucosamine (G) and N-acetyl-D-muranic acid (M) backbones are held together via amino acid-amino acid covalent bonds

Question 16

How do antibiotics like penicillin and enzymes like lysozyme affect the peptidoglycan networks of bacteria?

Answer 16

penicillin targets and disrupts transpeptidase, which creates the AA-AA bonds

lysozyme targets and degrades the bonds between G and M in the backbone

• both result in the breakdown of the entire network, leaving the bacterium vulnerable

Question 17

What makes the cell wall of acid-fast bacteria unique? What are 3 common types of this kind of bacteria?

Answer 17

the presence of mycolic acid, that is linked to muranic acid via phosphodiester bonds and arabinogalactans by glycolipid bonds

Corynebacterium, Nocardia, Mycobacterium

Question 18

What is the significance of acid-fast bacteria in an identification sense?

Answer 18

mycolic acid imparts resistance to acid discoloration, making it look extremely red when observing after carbol fuscin staining

Question 19

Gram positive vs. Gram negative vs acid fast cell walls:

Answer 19

Question 20

What is the non-peptidoglycan component is found on the outermost layer of Gram negative bacterial cell walls? How does it tend to induce an immune response?

Answer 20

lipopolysaccharide (LPS)
it is an endotoxin that can bind the CD14/TLR4/MD2 receptor complex, which promotes the secretion of pro-inflammatory cytokines in many cells types (mostly macrophages)

Question 21

What are the 3 major structures that make up the LPS found on Gram negative bacteria? Which one is important in immune responses?

Answer 21

lipid A
core glycolipid - inner and outer
O-specific polysaccharide chain - highly immunogenic and can be used for genetic testing of the bacteria (O antigens)

Question 22

What are flagella? What antigen on this structure is recognized by host antibodies?

Answer 22

filamentous appendages composed of flagellin monomers (and sometimes glycosylated proteins) that allow for motility

H antigens

Question 23

What is glycocalyx? What is its purpose? What antigen on this structure is recognized by host antibodies?

Answer 23

the capsule, or slime layer, that is composed of carbohyrates/glycoproteins

not necessary for growth, but inhibits phagocytosis and antibiotic uptake

K antigens (in German = “kapsule”)

Question 24

What are pili? What are their purpose?

Answer 24

filamentous appendages composed of pilin monomers that allow for adhesion (fimbriae) and transfer of DNA between a donor and recipient (sex pili)

Question 25

What is the average range in bacteria size?

Answer 25

0.5 - 2 microns