General Microbial Pathogenesis Flashcards
Normal human body harbors ____x more microbial cells than human cells.
10x
Most skin infections are initiated by what type of injury to epidermis?
Mechanical
What organism can cause superficial infections of instact stratum corneum, hair, and nails?
Certain fungi - dermatophytes
What organism can cross unbroken skin? How?
Larvae of Schistosoma - releases enzymes that dissolve adhesive proteins that hold keratinocytes together
What local defenses does the GI tract have?
- Acidic gastric secretions, - viscous layer of mucus covers gut protecting surface epithelium
- pancreatic enzymes and bile detergents
What non-enveloped virus is resistant to inactivation by acid, bile, and pancreatic enzymes?
Norovirus
What organisms have acid-resistant outer coats?
Intestinal helminthes, protozoa, and Shigella
What are mechanisms pathogens use to establish symptomatic GI disease?
- Adhesion and local proliferation - multiply in overlying mucous
- Adhesion and mucosal invasion - cause ulceration, inflamm, hemorrhage
What defense mechanisms does respiratory tract have against pathogens?
- Mucociliary blanket that lines respiratory tract
- Alveolar macrophages
What does influenza have that allows it to bind surface of epithelial cells in respiratory tract?
Hemagglutinins that bind sialic acid
What is superinfection?
Infection by organisms like S pneumoniae and S aureus as a result of viral damage to respiratory epithelium
What pathogens release toxins that enhance their ability to establish infection by impairing ciliary activity?
H influenzae, M pneumoniae, B pertussis
What defense mechanisms does urogenital tract have?
- 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
What must urinary tract pathogens be able to do to cause infection? What is most common urinary tract pathogen?
Gain access via urethra and adhere to urothelium.
E. coli
What is transfer of infectious agents from mother to fetus called?
Vertical transmission
What infection during the first trimester can lead to heart malformations, mental retardation, cataracts, or deafness?
Rubella
T or F. Infection can spread to child postnatally through maternal milk.
True - HIV, Hep B, cytomegalovirus
What are mechanisms organisms use to invade tissues and spread to distant sites? What does S. aureus do to allow it to spread?
- Lymphatics
- Bloodstream
- Peripheral nerves along axons
- S. aureus secretes hyaluronidase to degrade ECM between host and cells
What are exit mechanisms microbes use to transmit from one host to next?
Skin shedding, coughing, sneezing, urine and feces, sexual contact, insect vectors
What viral epidemics are carried by fecal-oral route?
Hep A and E, poliovirus, rotavirus
What bacterial epidemics are carried by fecal-oral route?
V cholerae, Shigella, C jejuni, Salmonella
What pathogens have sophisticated genetic mechanisms that allow them to periodically switch their major surface proteins?
Spirochetes and trypanosomes
What do epithelial cells and some leukocytes produce that are toxic to microbes?
Cationic antimicrobial peptides like defensins and cathelicidins
What mechanisms do pathogens use to evade the immune system?
- 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
