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PA Microbiology test 2


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the ability of a microorganism to cause disease
the extent of pathogenicity
contagious or communicable
diseases that are spread from an infected animal or person
disease is constantly present in a geographic area
when the occurrence of the disease exceeds the expected levels
when an epidemic of a disease become worldwide
if a disease occurs only occasionally
incubation period
the interval between infection and appearance of the first symptoms of the disease; followed by illness and then by convalescence (infectious organism can be spread to others during these stages)
individuals that have acquired sufficient immunity to the disease producing organism to prevent occurrence of symptoms; however, unable to eliminate the agent from the body
virulence factor: adhesins
responsible for adherance;
2 types: bacterial fimbriae and cell surface structures;
are not responsible for disease, their loss rendersw the organism avirulent
virulence factor: host cell invasion
organisms able to invade and grow inside host cells where they're protected from host's humoral immune system
virulence factor: antiphagocytic mechanisms
capsules, fimbriae, siderophores, toxins
most common antiphagocytic mech;
made of polysaccharide, making organism "slippery" to prevent being engulfed
i.e. pneumococci & meningococci
bind to a surface component of the phagocyte, preventing close contact necesary for phagocytosis
vertebrates have evolved different ways of retaining iron so it's available for synthesis of new cell components
(10 of them)
toxic substances excreted from bacterial cell or released after lysis of bacterium;
ie. streptococci, staphylococci
toxin: hyaluronidase
breaks down hyaluronic acid, (the intracellular glue that keeps connecgtive tissue together)
toxin: streptokinase
activates plasmin (proteolytic enz) and causes dissolution of blood clots allowing spread of streptococci
toxin: coagulase
causes coagulation of plasma producing a fibrin clot; prevents phagocytosis-produced by staphylococci
toxin: collagenase
causes breakdown of collagen and helps spread the org. - produced by clostridia
toxin: hemolysins
induce lysis of host's RBC
toxin: leukocidins
kills host's leucocytes
toxin: enterotoxins
interact w/GI system to cause diarrhea or dysentery;
2 types: ones that stimulate synthesis of cAMP causing electrolyte imbalance - Vibrio cholera, E coli, B cereus;
ones that inhibit protein synthesis killing intestinal epithelial cells - Shigella, E. coli
toxin: neutotoxins
tetanus toxin causes spastic paralysis by blocking inhibitory nerve impulses causing neurons to fire continuously; botulism causes flaccid paralysis preventing Ach release
toxin: pyrogenic
produced by group A strept and staph;
termed superAg b/c induce secretion of lg quantities of TNF-a and IL-1 inducing inflammation, shock, death
toxin: endotoxin
lipid A part of gram neg cells; results in fever, inflammation, and irreversible shock; binds to macros causing the synthesis of TNF-a & IL-1
spread of microbes by blood
if free: they're exposed to body defenses like Ab and phagocytes
if associated: the associated cell can protect them from host defenses and carry them around body
spread of rabies, HSV, and varicella-zoster virus
spread by peripheral nerves
genetic determinants of spread replication
virulence (determined by adhesion), penetration into cells, anti-phagocytic activity, production of toxins, interaction w/ immune system
constitution of the host
the ability of a microorganism to infect and cause disease in a given host
ex. malaria and sickle cell anemia
2 categories of persistent microbes
1. those that shed more / less continuously ie. EBV, hep B
2. those that shed intermittently ie. HSV typhoid bacilli, malaria parasites
4 reasons why viruses good at thwarting immune defenses
1. invasion is often silent
2. can infect cells for long periods of time without adverse effects (ie. rubella, warts, hep B, EBV)
3. establish intimate molecular relationships with infected cell (like interfering with production of interferons)
4. latency, virus genome continues to be present without producing Ag & only does when virus reactivated
hit and run infection
microbe invades, multiplies, and shed within few days, b/f immune defenses have time to react; ie. rhinoviruses, rotaviruses
Concealment of Ag
(a strategy used by parasites to evade immune sys)
1. remaining inside cell & not displaying Ag on the surface
2.colonizing privileged sites keeps microbe out of reach of circulating lymphocytes
3. microbes take up host molecules to cover their surface
4. avoid inducing immune response
types of privileged sites
skin, intestinal lumen, CNS, joints, testes, placenta, and when virus integrated it's DNA into host cell
how microbes conceal themselves by taking up host molecules
Fc receptors are displayed on surface in a useless upside down position - preventing Ab or T cells from attacking it
Antigenic Variation
to confuse the host by repeated changes in appearance
ie. African trypanosome
can occur:
1. during course of infection in individual
2. during spread of microbe through host community ie. influenza
3 types of antigenic variation
1. mutation
2. recombination
3. gene switching
antigenic variation: mutation
ie. influenza virus
mutations in genes coding for hemagglutinin & neuraminidase, causing reduced effectiveness of B & T cell memory;
antigenic drift
antigenic variation: recombination
ie. influenza A virus
recombination takes place by exchange of genetic material btw 2 different microbes;
antigenic shift
antigenic variation: gene switching
ie. African trypanosome
carries 1000 surface molecules; can switch from one gene to another causing a persistent infection on the host
allows microbe enough time to grow, spread, and shed;
an infection of the immune cells (T, B, macros, dendritic)
lasting general immunosuppression would be detrimental to microbe b/c.....
susceptibility to other infections would cause unnecessary damage to host species; (HIV at the limit)
persistent infections
represent failure of hos defenses:
1. microbe can persist in the infectious form
2. low infectivity
3. completely non-infectious form, not producing any Ag
persistent infections important b/c.....
1. can be reactivated
2. sometimes associated w/chronic disease
3. sometimes associated w/cancers
Common cold
rhinoviruses & coronaviruses cause >50%
most common invader of nasopharynx
transmission: aerosol or by virus-contaminated hands
possess surface molecules that bind them firmly to host cell - not washed away in secretions
Common cold
anticongestants, analgesics, resolve in 48 hrs
Pharyngitis & Tonsilitis
70% caused by viruses
sore throat due to mucosa infected or b/c inflammation in lymphoid tissues
caused by EBV
tonsils and uvula swollen and covered with white exudate; petechiae present on soft palate
bacteria responsible for pharyngitis
Streptococcus pyogenes (commonest), Corynebacterium diphtheriae, & Haemophilus influenza
Complications of S. pyogenes
1. peritonsillar abscess
2. otitis media, sinusitis
3. scarlet fever
4. rheumatic fever
5. acute glomerulonephritis
peritonsillar abscess
uncommon; 1-2 days after recovery pt develops swelling, redness, white exudate on tonsil; opening mouth is painful; muffled voice; "hot potato speech"
Scarlet fever
S. pyogenes produces erythrogenic toxin - causes rash 12-48 hrs after fever; rash has sunburn sandpaper appearance w/goose pimples; "strawberry tongue";
tx: fever dissovles in 12-24 hrs; not tx: septicemia, otits media, pneumonia, rheumatic fever, etc.
occurs in ages 4-8
Rheumatic fever
Ab formed to Ag of streptococcal cell wall that react w/sarcolemma of heart; granulomas from in heart about 2-4 wks after sore throat; leads to heart valve disease
Acute glomerulonephritis
blood in urine, edema, HTN 1-2 wks after sore throat
tx: penicillin
complication of S. pyogenes (5)
1. peritonsillar abscess
2. otitis media, sinusitis
3. scarlet fever
4. rheumatic fever
5. acute glomerulonephritis
acute otitis media
cause: Strep. pneumoniae & H. influenzae; common in infants & small kids b/c eustachian tube open more widely; fever, diarrhea, vomiting; fluid may persist for wks-months
otitis externa
infections of outer ear cause irritation and pain;
cause: S.aureus, Candida albicans, Proteus, and Ps. aeruginosa
"swimmers ear"
acute sinusitis
facial pain, pus in sinsuses; tx: ampicillin or amoxicillin
Acute epiglottis
cause: H. influenza; often in kids; difficulty breathing b/c of respiratory obstruction; extreme care when examining b/c epiglottis can be sucked into airway
Oral Candidiasis
prolonged use of broad spectrum of antibiotics allows C. albicans to grow; causes thrush; prevalent when immunity is impaired
Tx: antifungals (nystatin)
Laryngitis and Tracheitis
cause: parainfluenza, RSV, influenza; hoarseness, burning pain on breathing in/out; swelling of mucus membrane lead to croup (consists of dry cough and inspiratory stridor - crowing)
cause: corynebacterium diphtheriae; colonize in larynx, pharynx, nose; form "pseudomembrane" - becomes dark and malodorous, fatal bleeding can occur when removing it or block the airway; toxin can lead to myocarditis & cardia failure; tx: antitoxin, penicillin; prevented by DPT
Acute lower resp tract infections (6)
1. whooping cough
2. acute bronchitis
3. acute exacerbations of chronic bronchitis
4. acute bronchiolitis
5. pneumonia
6. measles
Chronic lower resp tract infections (4)
1. specific infections of TB & aspergillosis
2. lung abscesses & empyema
3. infections of cystic fibrosis
4. parasite infections
Whooping cough
cause: Bortedella pertussis (gram neg); severe disease of childhood, spread by airborne droplets; organism produces several toxins; incubation period 1-3 wks, then appears like URI followed by 1 wk of non-productive cough that is paroxysmal; complications: CNS, exhaustion, vomiting; prevention: DPT vaccine
Acute bronchitis
cause: rhinoviruses, coronaviruses; secondary infections w/ S. pyogenes & H. influenzae; cough most prominent characteristic
Acute exacerbations of chronic bronchitis
cough and excessive mucous secretion; other causes: smoking, inhalation of dust or fumes; bacteria not the initial infection but perpetuate the disease: Strep. Pneumoniae, H influenzae
tx: antibiotics
cause: mainly RSV, Mycoplasma pneumoniae; restricted to childhood; transmitted by droplets or hands; cough, rapid resp rate, cyanosis, otitis media; infection may spread to lungs
Lobar pneumonia
involvement of a specific region of lung; the exudate clots in alveoli and makes them solid;
outcome-respiratory distress
diffuse patchy infection throughout lungs;
outcome: resp distress
Interstitial pneumonia
invasion of lung interstitium; characteristic of viral infection;
outcome: resp distress
Lung abscess
cause: aspiration of respiratory or gastric secretions as result of altered consciousness; ill for 2 wks producing lg amts of foul-smelling sputum;
Tx: anti-anaerobic drug (metronidazole)
most common cause of death of elderly
Bacterial pneumonia
cause: Strep. pneumoniae; tx: penicillin;
primary atypical pneumonias
when penicillin was given and pneumonias failed to respond; caused by: M. pneumoniae, Chalmydia psittaci, Legionella pneumophilia, coxiella burnetti
Bacterial pneumonia dx
symptoms: chest pain, cough, SOB, difficulty and pain on breathing;
chest radiograph and sputum for diagnosis;
tx: penicillin, ampicillin
prevention: immunization
viral pneumonia
1. parainfluenza viruses - cause croup & pneumonia in kids <5
2. adenovirus - only a few cause pneumonia
3. influenza virus - cause endemic, epidemic, pandemic influenza
Influenza viruses
3 types - A,B,C
A - causes epidemics and occ pandemics (bird resorvoir)
B - only causes epidemics
C - no epidemics, onlyminor resp illness
Antigenic drift
small mutations constantly occurring in hemagglutinin (H) & neuraminidase (N)
Antigenic shift
only occurs w/ Influenza A; a sudden major change in H & N Ag due to recombination btw different 2 strains; can lead to a pandemic
transmission, symptoms, tx, prevention
droplet inhalation; chills, malaise, fever, muscle aches, runny nose, cough; usually recover after 1 wk; most common during coldest months; amantidine inhibits A replication if given first 2 days; vaccine
symptoms, tx, prevention, complications
major cause of death in childhood in developing countries; fever, runny nose, conjuctivitis, cough, rash; end result - pneumonia & otitis media; no antiviral tx, Antibiotics given for complciations; vaccine (MMR); encephalitis
cause, transmission, prevalent with, tx
Mycobacterium tuberculosis; inhalation in aerosols and dust; prevalent with poverty, malnutrition, poor housing; primarily a disease of the lungs, but may spread;
tx: combo of 3 drugs - isoniazid, rifampicin, ethambutol - given for 6 months
TB primary infection
organisms engulfed by macros, cell mediated response detected 4-6 wks after infection; development of granulomas (tubercles); tubercles may heal spontaneously and persist for a lifetime in healthy individual;
primary TB
mild and asymptomatic, 90% doens't proceed further; 10% -develop fatigue, wt loss, weakness, fever, chronic cough ans sputum with blood, death
allergic bronchopulomonary aspergillosis
allergic response to Aspergillus Ag; more frequently in pt with asthma
occurrs in patients with preexisting lung cavities or pulmonary disorders
disseminated disease
fungus invades lungs of immunocompromised
Cystic fibrosis
most common lethal inherited disease among caucasians; characterized by pancreatic insufficiency, abn sweat electrolyte concentrations, production of very viscid bronchial secretions; Pseudomonas auruginosa colonizes lungs of pt aged 15-20; lung damage occurs by immunologic response to the organism, organism is cause of death
Pleural effusion & empyema
occurs in 50% pt with pneumonia, infection spreads to pleural space and get purulent exudate (empyema)
Tx: drainage of pus, expansion of lung
parasitic infections of lower resp tract
nematodes - migrate through lungs as move to sm intestine:
schistosome larvae - cause mild resp symptoms
Echinococcus granulosus - larvae of tapeworm cause resp distress
Chlamydia trachomatis (types D-K)
cause inclusion conjuctivitis; occurs through fingers or in newborn through birth canal - purulent conjuctivitis
Chlamydia trachomatis (types A-C)
transmission: contact, flies, fingers, towels;
major cause of blindness worldwide
result of chronic repeated infection that leads to scarring of cornea
tx: topical antibiotic tetracycline and doxycycline; prevented by improving hygiene
3 bacteria that cause conjuctivitis
Strep. pneumoniae, H. influnaze, Leptospira
haemophilus aegyptius
the common conjuctivitis (pink eye); mild or severe, swelling, of eyelids, photophobia, mucopurulent discharge; Tx: topical application of tetracycline
conjuctivitis by Nesseria gonorrhea
through infected birth canal; prevented by applying erythromycin shortly after birth
conjuctival infections transmitted by...
blood or nervous system
Toxoplasma gondii
can cause chorioretinitis leading to blindness; occurs by swallowing oocycts released by infected cats or by eating meat containing cysts
parasitic worm infections
Echinococcus granulosis (larvae tapeworm) enter the eye forming cysts causing mechanical damage; more common by larvae of nematode Toxocara canis - occurs in dogs; can enter any organ in human causing inflammation

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