Comps Microbiology Listing Questions

Factors influencing occurrence of infection:

Portal of Entry

Number of Organisms

Virulence of Organisms

Resistance of Host

Physiological defenses against infection:

Inflammation

Fever

Phagocytosis

Portals of entry and exit:

Skin & mucous membranes

Respiratory tract

Digestive tract

Genito-urinary tract

Placenta

Modes of Transmission of Infections:

• Direct transmission

-Physical contact

-Droplet infection (aerosol)

-Congenital

• Indirect transmission

-Food

-Milk

-Fomite

-Water

-Soil

-Vectors (Biological Vectors & Mechanical Vectors)

Mechanical defenses of the body against infection:

-Skin

-Mucus membranes

-Bony encasements

Physiological defense of the body against infection:

-Inflammation

-Fever

-Phagocytosis

Chemical defenses of the body against infection:

1. Body secretions

-Lysozymes (enzymes which damage bacterial cell walls that are found in body secretions such as tears, saliva, human milk, and mucus)

-Gastric juice

2. Antibodies

3. Interferon – (assists the immune response by inhibiting viral replication within host cells)

Naturally Acquired Immunity:

--Active – having the disease and recovering from it

--Passive – placental transfer of antibodies and/or from colostrum

Artificially Acquired Immunity:

--Active – vaccines (made from weakened microbes – measles, mumps, rubella)

--Passive – immune serums / antibodies (snake bite serums, Hepatitis A & B, immunoglobulin)

Humoral Immunity:

B cells circulation in the blood and lymph – secrete antibodies to fight off microbes.

Cell-mediated Immunity:

T-cells (T-lymphocytes) – secrete lymphokines to assist phagocytes. They fight microbes, cancers, and reject transplanted tissues.

Staphylococcus aureus:

1. skin abcesses

a. furuncle (boil)

b. carbuncle (connected group of boils)

2. food poisoning (staphylococcal enterotoxicosis) a. due to heat-stable enterotoxin

3. nosocomial infections (hospital-acquired) transmission from hospital personnel

4. toxic shock syndrome

-due to toxic shock syndrome toxin l(TSST-l)

-previously associated with use of super absorbent tampons

Portals of Entrance (skin and digestive tract)

Portal of Exit (skin)

Modes of Transmission (physical contact & vehicle (food-borne) transmission)

Streptococcus pyogenes (Group A streptococci):

1. septic sore throat (streptococcal sore throat)

2. scarlet fever [caused by strains that produce erythrogenic toxin (exotoxin)]

3. rheumatic fever

(Sequela to strep throat or scarlet fever due to cross-reacting antibodies can result in damage to valves of the heart)

4. puerperal sepsis (childbed fever)

(Infection of reproductive tract following childbirth, peritonitis and septicemia are possible)

Portals of Entry

1. respiratory tract (strep throat and scarlet fever)

2. genitor-urinary tract (puerperal sepsis)

Portals of Exit

1. respiratory tract

2. genitor-urinary tract

Modes of Transmission

1. droplet transmission (strep throat and scarlet fever)

2. physical contact (puerperal sepsis)