Med Micro 1.2

Question 1

Main mechanisms of pathogenesis

Answer 1

Invasion of tissue (entry!) and production of toxins. May be one or both.

Question 2

Why is adhesion not mentioned in main mechanisms of pathogenesis?

Answer 2

It is a prerequisite for invasion. Goes without saying

Question 3

Invasiveness factors

Answer 3

Intracellular and extracellular pathogens; capsules; adaptation; extracellular enzymes

Question 4

Intracellular and extracellular pathogens

Answer 4

Few intra, cause chronic disease; extra- cause acute disease (needs to access nutrients - cause damage)

Question 5

Endogenous and exogenous antigens and their result

Answer 5

Endogenous presented to cytotoxic T cells by MHC1: show viral infection, etc. Exogenous to T helper cells by MHC2: present results of phagocytosis; T helpers make cytokines, B cells make antibodies

Question 6

Capsules

Answer 6

hydrophilic gels that inhibit phagocytosis. Usually an essential virulence factor

Question 7

Adaptation

Answer 7

microenvironments of host provide habitats for bacteria that are capable of selective tissue invasion. Not every pathogen in a region can cause an infection there.

Question 8

Extracellular enzymes

Answer 8

Help degrade host tissues

Question 9

Invasins

Answer 9

Basically a spreading factor, can’t stay in same place forever!; enzyme family, help get through tissue matrices and intercellular spaces

Question 10

Quorum sensing

Answer 10

Need a certain number of microbes. Turns on many other genes. Others can bind

Question 11

Toxins

Answer 11

Exotoxins: toxic but heat labile; Good immunogens. Endotoxins: complex lipopolysaccharide from cell wall; poorly immunogenic; released when cells lyse; heat stable, mostly in gram negative.

Question 12

Why is it important that LPS is a poor immunogen?

Answer 12

Immunogen = elicits immune response; most proteins are (except small ones). We don’t have a good response to LPS.

Question 13

Membrane-damaging exotoxins

Answer 13

Form pores in eukaryotic membranes; streptolysin from streptococcus lyse RBC, WBC, platelets; hemolysin lyses RBC (S. aureus) ; listeriolysin from Listeria helps it evade lysosomes when endocytosed.

Question 14

How is hemolysin expression regulated?

Answer 14

In response to low iron levels so it can break open RBC and gain some

Question 15

Defining entry again

Answer 15

Portals of entry are the areas where the pathogen gains access to tissues. Actual entry is invading those tissues, actually getting into the body

Question 16

A-B toxins

Answer 16

A chain inhibits some cell functions; B chain binds and helps A enter. In cholera

Question 17

Endotoxin (LPS)

Answer 17

Lipopolysaccharide or Lipid A in gram negative bacteria. Very variable in polysaccharide size even within one type of bac. Need to test for LPS even if bacteria don’t grow

Question 18

Virulence

Answer 18

combination of invasiveness and toxigenicity producing the ability to overcome host defenses and cause disease

Question 19

Testing Virulence

Answer 19

measured with LD50. lethal dose: the # of bacteria to kill half of a population

Question 20

What is the point of an LD50 study?

Answer 20

Gives level of virulence and we can look at virulence factors (mutate the bacteria and perform the test several times), which is needed for vaccine development

Question 21

Some host defences

Answer 21

Skin, mucous, innate immunity, inducible ; some are specific, others not; vary with alcohol, drugs, nutrition, genetics,

Question 22

Factors in innate immunity

Answer 22

Inflammatory response, phagocytes, antimicrobials, complement, other WBC (neutrophils), Natural killer cells

Question 23

Inducible/Adaptive response

Answer 23

Hemoral immunity (ABs from B cells), cell-mediated response

Question 24

Skin and mucous pupose

Answer 24

Mechanical factors, chemical (eg Lysosyme, sebum), microbial factors (normal microflora are competitive, release antibiotics to compete for resources)

Question 25

Phagocytic cells

Answer 25

Respond to and release cytokines when they consume pathogens. Cytokines turn on inflammation, neutrophils etc recruited. Monocytes in blood, macrophages/dendritic cells fixed in tissues.

Question 26

Responses to phagocytosis of a bacterial cell? (lots!)

Answer 26

Signal b/w 2nd and 3rd line of defense. Antigen presentation (humoral); inflammation (interstitial fluid leaks easier, enter lymph to present antigens or bacteria);

Question 27

Humoral factors - role of antibody mediated defense

Answer 27

Antitoxins. Bacteriolytic antibodies (AB plus complement - make hole in them). Opsonizing AB (coat cell surface and enhance phagocytosis - ie target for phagocytosis). Agglutinating ABs

Question 28

Cell-mediated factors

Answer 28

Cytotoxic T lymphocytes; NK cells; activate macrophages

Question 29

Communicability

Answer 29

Source (dormant or latent - carriers?); # infectious agents released from host; capability of surviving transit b/w hosts; Percent of host population susceptible

Question 30

Superinfector

Answer 30

Someone who doesn’t display symptoms but releases huge amounts of -particles

Question 31

Triangle of relationships

Answer 31

Humans, drugs, microbes. All interacting, all evolving.