General Microbial Pathogenesis

Question 1

Normal human body harbors ____x more microbial cells than human cells.

Answer 1

10x

Question 2

Most skin infections are initiated by what type of injury to epidermis?

Answer 2

Mechanical

Question 3

What organism can cause superficial infections of instact stratum corneum, hair, and nails?

Answer 3

Certain fungi - dermatophytes

Question 4

What organism can cross unbroken skin? How?

Answer 4

Larvae of Schistosoma - releases enzymes that dissolve adhesive proteins that hold keratinocytes together

Question 5

What local defenses does the GI tract have?

Answer 5

• Acidic gastric secretions, - viscous layer of mucus covers gut protecting surface epithelium
• pancreatic enzymes and bile detergents

Question 6

What non-enveloped virus is resistant to inactivation by acid, bile, and pancreatic enzymes?

Answer 6

Norovirus

Question 7

What organisms have acid-resistant outer coats?

Answer 7

Intestinal helminthes, protozoa, and Shigella

Question 8

What are mechanisms pathogens use to establish symptomatic GI disease?

Answer 8

1. Adhesion and local proliferation - multiply in overlying mucous
2. Adhesion and mucosal invasion - cause ulceration, inflamm, hemorrhage

Question 9

What defense mechanisms does respiratory tract have against pathogens?

Answer 9

• Mucociliary blanket that lines respiratory tract

- Alveolar macrophages

Question 10

What does influenza have that allows it to bind surface of epithelial cells in respiratory tract?

Answer 10

Hemagglutinins that bind sialic acid

Question 11

What is superinfection?

Answer 11

Infection by organisms like S pneumoniae and S aureus as a result of viral damage to respiratory epithelium

Question 12

What pathogens release toxins that enhance their ability to establish infection by impairing ciliary activity?

Answer 12

H influenzae, M pneumoniae, B pertussis

Question 13

What defense mechanisms does urogenital tract have?

Answer 13

• Regular emptying during micturition
• Vagina: Lactobacilli - creates low pH environment to suppress growth of pathogens
• Uterine cervix covered by squamous mucosa that is resistant to infection

Question 14

What must urinary tract pathogens be able to do to cause infection? What is most common urinary tract pathogen?

Answer 14

Gain access via urethra and adhere to urothelium.

E. coli

Question 15

What is transfer of infectious agents from mother to fetus called?

Answer 15

Vertical transmission

Question 16

What infection during the first trimester can lead to heart malformations, mental retardation, cataracts, or deafness?

Answer 16

Rubella

Question 17

T or F. Infection can spread to child postnatally through maternal milk.

Answer 17

True - HIV, Hep B, cytomegalovirus

Question 18

What are mechanisms organisms use to invade tissues and spread to distant sites? What does S. aureus do to allow it to spread?

Answer 18

• Lymphatics
• Bloodstream
• Peripheral nerves along axons
• S. aureus secretes hyaluronidase to degrade ECM between host and cells

Question 19

What are exit mechanisms microbes use to transmit from one host to next?

Answer 19

Skin shedding, coughing, sneezing, urine and feces, sexual contact, insect vectors

Question 20

What viral epidemics are carried by fecal-oral route?

Answer 20

Hep A and E, poliovirus, rotavirus

Question 21

What bacterial epidemics are carried by fecal-oral route?

Answer 21

V cholerae, Shigella, C jejuni, Salmonella

Question 22

What pathogens have sophisticated genetic mechanisms that allow them to periodically switch their major surface proteins?

Answer 22

Spirochetes and trypanosomes

Question 23

What do epithelial cells and some leukocytes produce that are toxic to microbes?

Answer 23

Cationic antimicrobial peptides like defensins and cathelicidins

Question 24

What mechanisms do pathogens use to evade the immune system?

Answer 24

• Antigenic variation
• complex genomes that allow for recombination
• resistance to antimicrobial peptides
• resistance to killing by phagocytes
• evasion of apoptosis
• manipulation of host cell metabolism

Question 25

What do the following organisms do to evade phagocytosis:

• E coli
• S Aureus

Answer 25

• E coli: special carbohydrate capsule with sialic acid that does not bind C3b
• S aureus: expresses protein A which binds Fc portion of Abs

Question 26

How do some viruses prevent apoptosis of host cell?

Answer 26

Produce soluble homologues of IFNalpha/beta/gamma receptors that function as decoys and inhibit actions of secreted interferons