Microbial Mechanisms of Pathogenicity (BE #1) Flashcards
Describe 3 cases of symbiosis.
- commensalism: one organism benefits, the other is unaffected.
- mutualism: both organisms benefit. Ex. E. coli live in the large intestine of humans. They produce Vit. K that we use to make blood clotting factors.
- parasitism: host is harmed, microbe benefits.
What benefit do we gain from E. coli in the gut?
They produce Vit K which we use to make blood clotting agents.
Define parasite
Host is harmed, microbe benefits.
Does hand washing rid the body of its normal flora?
no, reduces it
Does hand washing rid the body of transient flora?
yes
Differentiate between contamination, infection & disease.
Contamination - microbes are present
Infections - multiplication of any parasitic organism; infection does not always cause disease
Disease - disturbance in the state of health; interferes with normal function
Name internal & external body surfaces that are inhabited by normal flora.
eyes, nose, mouth, pharynx, esophagus, trachea, colon, lower urethra, vagina
What is a nosocomial infection?
hospital-acquired infection
Name a common bacterial cause of nosocomial infections.
Staphylococcus aureus
Name 3 opportunities for infection by opportunistic bacteria.
- Disrupt normal flora w/antibiotics (ex. vaginal yeast infection)
- Improper hygiene (ex. colon flora causing a UTI from improper wiping)
- Neisseria meningitides from respiratory tract, causing meningitis
Why is it import for moms to breast feed (from a microbiologist’s perspective)?
Breast milk keeps the flora of the baby’s intestinal tract at a protective level. Bifidobacterium metabolizes milk sugars into acetic and lactic acid. This keeps the pH of the intestine inhospitable to many disease-causing microbes, most importantly those causing diarrhea.
Why would a prepubertal girl be at risk for STD’s? Why would a postmenopausal woman be at risk for increased vaginal yeast infections?
They are not (yet) producing estrogen which increases the growth of lactobacilli. Lacto keeps the vagina at an acidic level, which is inhospitable to disease-causing microbes.
A place where a pathogenic microorganism is maintained between infections -
reservoirs
A healthy person who is a reservoir can be called:
a carrier
Give 3 examples of environmental reservoirs.
soil - Clostridium tetani
water - Vibrio cholera
food - Clostridium botulinum
house dust
Differentiate between an incubatory carrier & a chronic carrier.
Incubatory - a person is contagious during the early symptomless period of the disease
chronic - person who harbors a pathogen for an extended period of time w/o becoming ill
Give example of pathogen that uses soil as a reservoir. What enables it to survive?
Clostridium tetani
endospore former
Give example of pathogen that uses dust as a reservoir. How can it survive in such dry conditions?
Mycobacterium tuberculosis
waxy envelope
Pathogen that uses water as a reservoir.
Vibrio cholerae
Pathogen that uses food as a reservoir.
Clostridium botulinum
Define zoonosis and give 3 examples of diseases that use animals as reservoirs.
Human disease caused by pathogens that maintain an animal reservoir.
Rabies, Lyme disease, West Nile virus, Hantavirus
Differentiate between ID50 and LD50.
ID50 is the infection dose. The # of microbes that must enter the body to establish infection in 50% of test animals
LD50 is the lethal dose. The # of microbes that must enter the body to cause death in 50% of test animals.
Which is more pathogenic? Bacterium A = ID50 of 200. Bacterium B = ID 50 of 100
Bacterium B - takes fewer bacterial cells to establish infection.
What is the microbe that causes a specific disease?
etiologic agent
inanimate objects involved in disease transmission
fomites
Differentiate between perinatal and prenatal transmission. Give example of each.
Prenatal - infection acquired across the placenta (HIV, Listeria)
Perinatal - infection acquired when fetus passes through the birth canal (syphilis)
Ex. of disease that can be transmitted horizontally.
STD’s - gonorrhea, syphilis
Ex. of disease that can be transmitted by fecal-oral route.
Hep A
Rotavirus
Nora virus
cholera
Define parenteral & give example of disease transmitted this way.
When a biological arthropod vector introduces pathogens during a skin-penetrating bite or break in the skin.
Hep C
tetanus
HIV
Pathogens attach to specific types of target cells by means of protein molecules called:
adhesins
Adhesins are generally found on
capsules or pili
Bacteria that can invade deeper tissues are called:
invasive
Name 2 groups of bacteria that are intracellular pathogens:
Rickettisias
Chlamydias
How are Rickettsia bacteria transmitted?
- Rocky Mtn Spotted Fever & typhus
- arthropod vectors
List the 4 major ways that bacteria cause disease.
- Exotoxin production
- Endotoxin production
- Exoenzyme production
- Stimulation of the body’s defenses
Exotoxins
- produced by G(+) AND G(-) bacteria
- Proteins
- minute amounts can be deadly
- heat sensitive
- specific for cells they effect
- can be neutralized w/antibodies (antitoxins)
- causes food poisoning (food borne intoxication)
- produce toxoids from them
- includes tetanus, Shigella toxin, botulinum, E. coli toxin
Endotoxins
- produced by only G(-)
- lipolysaccharides
- heat stable
- nonspecific for cells they effect
- don’t stimulate immune system to produce antibodies
- effects include fever, shock, diarrhea
- antibodies can increase effects
- released into environment when bacterial cells die
Toxoid is
- a type of exotoxin
- attenuated (weakened) toxin
- they’ve lost their disease causing properties
Tetanus toxin
- A neurotoxin
- inhibits release of inhibitory neurotransmitters so that opposing muscles contract at same time-causing rigid paralysis
Botulinum toxin
- a neurotoxin
- inhibits nerve impulse to muscle; causes flacid paralysis
Diptheria toxin
- a neurotoxin
- Corynebacterium diphtheria - inhibits protein syntesis; gene for exotoxin is found on lysogenized prophages
Strep toxin
- a erythrogenic toxin
- Streptococcus pyogenes - damages capillaries under the skin & produces a red rash (Scarlatina / Scarlet fever)
Vibrio toxin
- an enterotoxin
- Vibrio cholerae - binds to plasma membranes of epithelial cells in small intestine
- leads to severe diarrhea & vomiting
Staphylococcal toxin
- an enterotoxin
- Staphyloccocus aureus - staph food poisoning
Shigella toxin
- an enterotoxin
- Shigella dysenteriae - bloody diarrhea
Differentiate between the 2 types of food borne illness (food poisoning).
Infection - bacteria are ingested in the food, multiply in body, producing toxin. Onset takes longer than intoxication
Intoxication - bacteria grow in the good, producing toxin in the food. Onset of illness is quick b/c toxin is already present.
Classify each as due to infection or intoxication: Eschericia coli Salmonella typhimurium Shigella dysenteriae Staphylococcus aureus Clostridium botulinum
E. coli - infection Salmonella typhimurium - infection Shigella dysenteriae - infection Staphylococcus aureus - intoxication Clostridium botulinum - intoxication
Exoenzymes
produced & then released by bacteria
coagulase
- triggers blood clotting mechanism, allowing bacteria protection from immune defenses
- allows bacteria to hide & multiply in clots
Ex. Staphylococcus aureus
streptokinase
- dissolves blood clots so bacteria can spread to other tissues
- allows bacteria to invade other tissues
Ex. Streptococcus
protease
- destroys proteins (ex. antibodies)
- disables the immune response
Ex. Neisseria gonorrhoeae
hyaluronidase
- breaks down glue (hyaluronic acid) that holds cells together in tissue
- helps bacteria to invade deeper tissues
Ex. Streptococcus
catalase
- breaks down toxic hydrogen peroxide into water & oxygen (bubbles).
- H2O2 -> H2O + O2
Ex. Staphylococcus
hemolysins
Alpha-hemolysin: partially breaks down hemoglobin leaving a greenish halo around colonies (Streptococcus pneumonia)
Beta-hemolysin: completely breaks down hemoglobin leaving a clear ring around colonies (Streptococcus progenies & Staphylococcus aureus)
Gamma hemolytic: no hemolysis occurs
leukocidins
- produced by streptococci & staphylococci
- damage or destroy certain kinds of leukocytes
- some diseases may result in a decrease in # of wbc (leucopenia) (Staphylococcus)
How does Streptococcus pneumonia cause disease?
When it multiplies in the lungs, phagocytes come to combat it. Since the bacteria is protected by a capsule, it’s hard to phagocytize, so more & more white blood cells come to help. Dead bacteria & phagocytes accumulate in the lungs making gas exchange hard and breathing difficult.
Describe 3 mechanisms by which viruses cause disease.
- Lytic cycle - results in lysis of cells
- Lysogenic cycle (insertion of provirus in a host’s chromosome) –
- functional changes - ex. stop hormone production
- unregulated mitosis - cells divide out of control (HPV) - Cell fusion - adjacent cells fuse to form syncytia (RSV, measles)
How do viruses interfere with the “switch” that supposed to turn off mitosis?
They insert a provirus in a host’s chromosome.
Ex. HPV, Hepatitis B & C, Epstein Barr Virus (Burkitt’s Lymphoma)
Give an example of a virus that causes adjacent cells to fuse, forming a syncytium.
RSV [respiratory syncytial virus] causes bronchiolitis
List 3 bacterial mechanisms that help bacteria evade host defenses?
- protection agains phagocytosis ( capsules, surface proteins/M proteins, living inside the wbc)
- antigenic variation - some microbes mutate & change their surface antigens
- production of exoenzymes
Name a bacterial species that can survive a phagocyte’s enzymes & live inside the phagocyte.
Mycobacterium tuberculosis
Mycobacterium leprae
List 4 exoenzymes that help bacteria to evade host defenses.
- coagulase
- streptokinase
- protease
- leukocidins
Describe antigenic variation & give a bacterial & viral example
- some microbes mutate & change their surface antigens
Ex. Neisseria gonorrhoeae, HIV, cold virus, influenza virus
How does HIV evade host defenses?
HIV attacks the immune system white blood cells (T lymphocytes & macrophages)
How does an envelope help viruses to evade host defenses?
- Envelopes help to mask them (actually part of the host cell it took when it budded)
- Makes it easier for virus to enter the cell (fusion w/the plasma membrane & then virus gets dumped into cytoplasm)
ID normal portal of entry & exit:
Bordetella pertussis
respiratory droplets
ID normal portal of entry & exit:
gonorrhea
mucosa of genital tract for both
ID normal portal of entry & exit:
herpes
mucosa of genital tract for both
ID normal portal of entry & exit:
HIV
mucosa of genital tract for both
blood/body fluids (parenteral)
ID normal portal of entry & exit:
Vibrio cholerae
fecal-oral
ID normal portal of entry & exit:
hepatitis B
mucosa of genital tract
blood/body fluids (parenteral)
ID normal portal of entry & exit:
hepatitis A
fecal-oral
ID normal portal of entry & exit:
Plasmodium (protistan)
parenteral (mosquito bite)
ID normal portal of entry & exit:
Clostridium tetani
parenteral - entry through break in skin - dirty wound
exit - endospores living in digestive tract of livestock - their manure contaminates the soil
ID normal portal of entry & exit:
Mycobacterium tuberculosis
respiratory system for both
ID normal portal of entry & exit:
influenza
respiratory system for both
ID normal portal of entry & exit:
cold virus
respiratory system for both
acute
develops quickly; runs its course quickly (cold, flu, food poisoning)
chronic
- develops more slowly,
- is usually less severe;
- persists for a long period of time (Hep B & C, mono)
Latent
- has periods of inactivity
- herpes, shingles, HIV
Local infection
confined to a specific area
systemic infection
- generalized infection;
- affects most of body
septicemia
- pathogens are present and multiply in blood
primary infection
initial infection in a previously healthy person
secondary infection
follows a primary infection (sinus infection following a cold)
superinfection
secondary infection that results from the destruction of normal microflora and often follows the use of broad-spectrum antibiotics
mixed infection
caused by several species of organisms present at the same time
communicable
disease spread from one host to another (flu)
noncommunicable
disease not spread from one host to another (tetanus)
contagious
disease that spreads easily from one host to another (chicken pox)
How does Corynebacteium diphtheria produce toxins?
its prophage has the code for toxin. If the bacterium is not infected with a virus, it doesn’t (can’t) make toxin.
