IDMM Week 2 PBL Flashcards
List the etiologic agents for pneumonia (bacterial)
- Step. pneumoniae
- Haemophilus influenzae
- Moraxella catarrhalis
- Klebsiella pneumoniae
- Chlamydia pneumoniae
- Mycoplasma pneumoniae
- Legionella pneumoniae
Transmission of step. pneumo
person to person
Strep. pneumo disease in humans
- Typical pneumonia–rusty-colored sputum, fever, chest pain, SOB, abrupt onset, invasive with lobar extension
other diseases include: meningitis, sepsis, otitis media in kids, sinusitis
Strep. pneumo virulence mechanism
- capsule–resists phagocytosis but is antigenic (encapsulated organism)
- toxins–secretes many toxins including pneumolysin (binds to cholesterol in host-cell membrane)
colonized in oropharynx
What is the most common cause of pneumonia?
Strep. pneumoniae
Describe strep. pneumoniae:
- gram stain
- aerobic or anaerobic?
- catalase?
- other
- Gram + cocci
- facultatively anaerobic
- catalase +
- alpha-hemolytic, requires host for survival, activates complement–>inflammation
* *IgA protease
* *Teichoic acid: mimics human protein so may not be recognized as foreign–> DIC
Describe haemophilus influenzae
Gram - rod
facultative anaerobe
reservoir in humans only (blood loving)
What type of pneumonia is associated with H. influenzae?
ASPIRATION pneumonia
TYPICAL pneumonia
transmission of H. influenzae
- respiratory
- (opportunistic infections when have influenza viral infection)
H. Influenzae disease in humans
- *encapsulated**
- HiB is most common cause of MENINGITIS in infants
- acute epiglottitis
- septic arthritis (infants)
- sepsis (asplenic patients)
- TYPICAL pneumonia
- *nonencapsulated**
- otitis media
- sinusitis
What are the symptoms of typical pneumonia
cough chest pain fever dyspnea productive (even bloody) sputum increased WBC
H. influenzae virulence mechanism
- Capsule: 6 types (b is most virulent)
- attachment pili
- IgA protease
- LPS
- binds to sialic acid
Describe characteristics of moraxella catarrhalis
- gram - rods
- oxidase -
- aerobic
- needs host for survival
Type of pneumonia seen with M. catarrhalis
Aspiration pneumonia (Typical_
Transmission of M. catarrhalis
respiratory
Disease in humans: M. catarrhalis
-Typical pneumonia (aspiration)
especially in elderly and those with COPD
-otitis media
-sinusitis, bronchitis
M. Catarrhalis virulence factors
- thin CAPSULE
- virulent strains are serum resistant
- beta-lactamase producing strain hemagglutinates RBCs
Klebsiella pneumoniae characteristics
- enteric
- gram - rods
- lactose fermenter
- non motile
type of pneumonia seen with K. pneumoniae
typical/aspiration pneumonia
K. pneumoniae transmission
water borne
GI tract
K. pneumoniae disease in humans
Typical pneumonia (aspiration) with signs of lung necrosis and BLOODY SPUTUM, especially in alcoholics and IC --nosocomial UTIs and sepsis as well
K. pneumoniae virulence factors
- CAPSULE: phagocytosis resistant
- LPS
- serum resistant
Chlamydia pneumoniae characteristics
-gram indifferent intracellular pathogen
-OBLIGATE intracellular bacteria
(steals ATP from host with ATP/ADP translocator)
Chlamydia pneumoniae transmission
- respiratory
- human to human
Chlamydia pneumoniae disease in humans
ATYPICAL pneumonia, especially in young adults
- strongly associated with atherosclerosis
- arthritis
Describe the symptoms of atypical pneumonia
differs from typical in that it is:
- dry
- no fever
- “not as sick”
- DECREASED WBC
Chlamydia pneumoniae virulence factors
- “elementary body” (EB) infects cells–converts to “initial body” (IB)
- IB can reproduce (uses ATP from host)–IB transforms back into EB–>leaves and infects other cells
- attaches to columnar epithelial cells
- binds to sialic acid
Mycoplasma pneumoniae transmission
respiratory (droplet)
human, enviro and animal carries
characteristics of M. pneumoniae
- NO CELL WALL
- amorphous shape
- needs host for survival
- needs CHOLESTEROL in membrane
- facultative anaerobe
M. pneumoniae disease in humans
- “walking pneumonia”/Atypycal pneumonia—fever with dry, nonproductive couch, chills common
- tracheobronchitis
- sputum–monnuclear cells, fewer PNMs than bact pneumo
Legionella pneumonia characteristics
- gram - bacilli
- anaerobia
- facultative intracellulat parasite–inside alveolar macrophages
Leigionella pneumonia transmission
humans and natural WATER environment
AC systems!!
Legionella pneumoiae disease in humans
- PONTIAC fever: in healthy hosts, allergy like reaction; self limiting within one week
- Legionnaires disease: starts with non-respiratory and progresses to respiratory (es in 50 yo males and smokers)
- Atypical pneumonia
Legionella pneumoniae virulence factors
- inhibits phagolysosomal fusion after being eated alive by macrophages
- CAPSULE
- motile
- hemolysin
Which causes of pneumonia are atypical?
Chlamydia/mycoplasma/leigionella pneumo
Describe facultative intracellular growth in primary TB
- inhaled bacteria causes local infiltration of neutrophil and macrophages–no acquired immunity
- SULFATIDES (virulence factor) prevent phagosomes from fusing to lysosomes and thus allows phagocytosed bacteria to replicated in the macrophage
- bacteria travel through the lymphatics and blood to spread to distant sites
What is the virulence factor that allows primary TB to replicate in the macrophage
sulfatides
Describe the role of cell mediated immunity in primary TB infection
- some macrophages are able to cause destruction of phagocytosed bacteria and present antigens to helper T cells to establish acquired immunity
- sensitized T cells enter the circulation in search of bacteria: LYMPHOKINES, which serve to attract and activate macrophages, are released upon antigen encounter
- activated macrophages destroy the bacteria, but also cause local destruction and damage to lung tissue–CASEOUS NECROSIS (granular creamy cheese)
- sites of caseous necrosis are surrounded by macrophages, fibroblasts and collagens and frequently calcify–bacteria are essentially “walled off” but remain viable
Is primary TB usually symptomatic or asymptomatic
asymptomatic
In which populations does symptomatic primary TB occur
often occurs in children, the elderly or the immunocompromised
What are overt symptoms of primary TB
large CASEOUS GRANULOMAS developed in the lungs or other organs
in the lungs, the caseous material eventually liquifies, is extruded out via the bronchi and leaves behind cavitary lesions
How is TB spread
via aerosolized droplets which land in areas of the lung that receive the highest air flow–middle and lower zones
What is another name for a TB granuloma
tubercle
What are calcified TB tubercles called
Ghon foci
What is a Ghon complex
a Ghon focus accompanied by a perihilar lymph node calcified granulomas
What leads to reactivation TB (secondary TB)
depression of the immune systm–infection can occur in any of the organ systems seeded during primary infection
List possible sites of TB reactivation
- pulmonary TB
- pleural and pericardial infection
- lymph node involvement
- kidney
- skeletal
- joints
- CNS
- miliary TB (disseminated—like a shotgun blast)
How does reactivation TB present clinically
chronic low grade fever night sweats weight loss productive cough hemoptysis
Where does TB get its historical name “consumption”
from the weight loss associated with reactivation TB
Where is the most likely site of TB reactivation
Upper Right lobe of Lung due to higher O2 concentration
What is the risk of reactivation in all people? in HIV+?
10 % in all people for lifetime; in HIV + its 10% per year
What is the basis for the tuberculin skin test?
requires a T cell mediated delayed type hypersensitivity reaction–becomes positive approximately 2-10 weeks post-infection
What is the procedure for a tuberculin skin test
inject tuberculin under the skin–if a red welt with diameter of 10 mm or more forms around the injection site within 72 hours, the patient MAY have been previously exposed to TB
Does a positive tuberculin skin test mean the person has active disease?
No. A positive test could mean:
- the patient was previously exposed to TB
- exposed to a related bacteria
- previously vaccinated with the BCG vaccine
- the patient has latent (not active) disease
- the patient has active disease
Does a negative tuberculin skin test rule out active disease?
No–some patients may simply have fewer T cells to respond to the injected antigen
Should a definitive diagnosis of TB rely on the tuberculin skin test?
No
How useful is the BDG vaccine?
around 50%
used in developing countries but not in Canada
What tests may be performed in the investigation of pneumonia?
- CXR: not able to diagnose specific organism with radio patterns
- Gram stain and culture of sputum
- antigen tests: 2 commercially available tests for pneumococcal and certain Legionella Ags; rapid test for influenza; direct fluorescent antibody test for influenza and RSV
- PCR: available for L. pneumophila and mycobacteria
- Serology
- Blood cultures: not used rigorously anymore for hospitalized patients with CAP
What tests may be ordered in the diagnosis of TB?
- PPD skin test: reveals if person has been INFECTED with M. mycobacterium tuberculosis
- Quantiferon-TB: bloos test that measured IFN gamma levels produced in whole blood in response to addition of specific TB antigens; specific for M. tuberculosis, not positive in people with BDG vaccine
- CXR: pick up isolated granuloma, Ghon focus, Ghon complex, old scarring in upper lobes, or active TB pneumonia
- Sputum acid fast stain and culture: when acid fast stain or culture is positive you have an active pulmonary infection
What is the mechanism of the PPD skin test for TB
- after induction of cell mediated immunity against M. TB, any additional exposure will result in localized delayed type hypersensitivity reaction
- inject intradermally purified protein derivative (PPD) which contains antigenic particles from killed M. TV–if positive, results in localized skin welling and redness
- macrophages in skin take up antigen, carry it to T cells, T cells move to skin site, release cytokines to activate macrophages
