Bacteriology

Question 1

What characteristics of bacteria are major targets for antibacterial medications?

Answer 1

They have 70S ribosomes (Eukaryotes have 80S) and their peptidoglycan cell walls are unique

Question 2

What structure helps bacteria avoid phagocytosis and why?

Answer 2

Encapsulated bacteria are harder to absorb because the largely negative charge of the capsule tends to repel macrophages

Question 3

What shapes can be used to describe bacteria?

Answer 3

Bacillus = Rod shaped; they can be regular, fusiform (with tapered ends) or filamentous (thread like)
Cocci = spherical
Coccobaccilus= intermediate btwn bacillus and coccus
Spirillus= curved
Spirochete = long and spiral shaped

Question 4

What is the generalized process for Gram staining?

Answer 4

Cells are bathed in a violet stain and iodine. The dyes are then rinsed from the culture. A counterstain of safranin follows. Gram positive cells will be violet; Gram negative will be pink

Question 5

What are the two main exceptions to Gram staining?

Answer 5

Spirochetes stain poorly in general; mycobacteria require a different staining procedure called acid-fast

Question 6

Classify the following bacteria:

B. cereus

Answer 6

Gram positive bacillus with obligate aerobicity

Question 7

Classify the following bacteria:

C. tetani

Answer 7

Gram positive bacillus

Question 8

Classify the following bacteria:

E. coli

Answer 8

Gram negative bacillus; facultative anaerobe

Question 9

Classify the following bacteria:
S. aureus
Comment on its metabolic properties

Answer 9

Gram positive coccus; positive for catalase and coagulase; facultative anaerobe

Question 10

Classify the following bacteria:

S. pyogenes

Answer 10

Gram positive coccus; aerotolerant anaerobe

Question 11

Classify the following bacteria:

S. pneumoniae

Answer 11

Gram positive coccus

Question 12

Classify the following bacteria:
N. meningitidis
Comment on its metabolic properties

Answer 12

Gram negative coccus; can use glucose or maltose but not sucrose; microaerophile

Question 13

Classify the following bacteria:

V. cholerae

Answer 13

Gream negative spirillus

Question 14

Classify the following bacteria:

T. pallidum

Answer 14

Spirochete

Question 15

What are the four main mechanisms by which bacteria can express pathogenicity?

Answer 15

1) exotoxins from mobile DNA that often have enzymatic activity (e.g. tetanus and diphtheria)
2) May invade host cell but fail to invade cells
3) Both 1 and 2
4) may be intracellularly pathogenic (mycobacteria)

Question 16

What are the generalized layers of Gram positive cells?

Answer 16

1) Typical phospholipid bilayer
2) Peptidoglycan layer with n-acetyl glucosamine and n-acteyl muramic acid cross linkages
3) Negatively charge capsule to repel cells or mimic host antigens. Most are polysaccharides except B. anthracis which uses poly-D-glutamic acid

Question 17

How are layers of the bacterial cell wall connected to each other?

Answer 17

Techoic acid and lipotechoic acid

Question 18

How are peptidoglycan crosslinkages constructed?

Answer 18

Muramic acid has a chain of D and L amino acids bound to it; a D-ala member will create a peptide cross linkage with an L-lys on another amino acid chain

Question 19

How can muramic acid be adjusted to promote inflammation? In what geni do they exist?

Answer 19

If bacteria acetylate their acids, they become O-acetylated, which the host organism usually struggles to degrade; exists in streptococci and neisseria

Question 20

How can bacteria anchor onto host surfaces?

Answer 20

An adhesion protein can emerge from their capsule; most commonly, this is M protein

Question 21

What are fimbrae in Gram positive cells and what are their purposes?

Answer 21

They are protrusions of proteins and techoic acids from the capsule that help in adhesion, combating phagocytosis, and promoting nutrient uptake.

Question 22

What are flagellae in Gram positive cells, how can they appear, and what is the major exception to the presence of flagellae in this category of cells?

Answer 22

Made of flagelllin polymers that help with propulsion; they can be peritrichous (meaning flagella surround the organism) or polar (on the ends). Pathogenic cocci tend not to have them

Question 23

What are spores, what are they made of, and what genuses participate in their creation?

Answer 23

Inert structures that help the organism weather acrid or adverse conditions that can return to a vegetative state in ideal environmental circumstances. Made of dipicolinic acid (from lysine) and calcium. Found in bacillus and clostridium

Question 24

What are the generalized layers of Gram negative cells?

Answer 24

Layer 1= typical plasma membrane
Layer 2= Thin, poorly linked layer of peptidoglycans
Layer 3=Phospholipid bilayers with lipopolysaccharides
Layer 4= Capsule

Question 25

What is the term for the space between layers one and three in a Gram negative cell and what is found there?

Answer 25

Periplasm; molecules with a molecular weight of less than 800 cannot escape this space

Question 26

What are porins in Gram negative cells?

Answer 26

Trimers of proteins in portions of the cell membranes that permit transmission of virulence factors

Question 27

What are pili in Gram negative cells?

Answer 27

Made of pilin proteins that can attach to a host or to other bacteria for sexual reproduction

Question 28

What are the indications of an infection by N. meningitidis?

Answer 28

Sudden onset of high fever, stiff neck, vomiting, profound hypotension and petichiae advancing to purpura

Question 29

What are the predominant symptoms affiliated with purpura fulminans?

Answer 29

Disease is also called Waterhouse-Friderichsen syndrome; involves severe bleeding in the adrenal glands which leads to organ failure and adrenocortical insufficiency (hyperkalemia and hyponatremia). Noted by profound purpura in the patient’s skin

Question 30

What are the components of lipopolysaccharide?

Answer 30

O side chain sugars that contain antigenic specificities, a core polysaccharide made of unusual sugars like KDO and heptose, and lipid A, which is the main toxic component.

Question 31

Which bacterial antigens are most potent in generating toxic shock?

Answer 31

From Gram negative: LPS
From Gram positive: Peptidoglycan and lipotechoic acid
From streptococci and staph aureus: Superantigen

Question 32

Through what Toll like receptors do toxic antigens promote inflammatory and pyrogenic cytokine production?

Answer 32

Peptidoglycans use 2/6 and 1/2 dimers
LPS uses 4/4 dimers
Superantigen forms MHC/TCR complexes that activate immune responses to poor antigen selections.

Question 33

What are the four possible growth patterns for bacterial colonies and at what stage is a population’s toxicity highest?

Answer 33

Lag phase= bacteria collect enzymes that promote growth
Log phase = rapid multiplication with low doubling times
–end of log phase is period at which bacteria sense a quorum and emit signals to promote endotoxins
Stationary phase = population growth stops as metabolites exhausted
Death phase = metabolic byproducts are toxic to the population; obligate fermenters especially deal with this

Question 34

How are the following metabolic criteria defined and what enzymes are present in the first four?

1) Obligate aerobes
2) Facultative anaerobes
3) Aerotolerant anaerobes
4) Obligate anaerobes
5) Microaerobes

Answer 34

1) Require O2 for growth, have SOD and catalase
2) May grow in or out of the presence of O2, have SOD and catalase
3) May grow in the presence of O2, but only conduct fermentation; have SOD but NOT catalase
4) Cannot grow in the presence of O2; have no SOD nor catalase
5) Use O2 for growth but prefer limited quantities

Question 35

What stages of bacterial replication and translation are targetable by antibiotics and what classes conduct these actions?

Answer 35

1) Bacteriological DNA gyrase (quinolones like cipro and ofloxacin)
2) Transcription factors (rifampin)
3) Unique ribosome structure
30S subunit–>erythromycin, clinda, chloramphenicol
50S subunit–>gentamycin, tobrex, tetracyclines, mupirocin