Bacteria Flashcards
Two ways bacteria can survive in the phagosome?
- preventing fusion of lysosome
- inhibiting acidification of the phagolysosome (lysosomal enzymes are active at low pH)
How do polysaccharide capsules prevent phagocytosis?
binds serum factor H and accelerates the breakdown of C3b (opsonin)
Organism with unprogrammed antigenic variation?
Influenza A drifts and shifts
Organism with programmed antigenic variation?
Haemophilus influenza
How do A-B exotoxins work?
- binding subunit binds to cell membrane
- whole toxin is endocytosed
- active subunit dissociates and leaves endosome to ADP-ribosylate cellular enzymes, disrupting cell function
How do membrane active exotoxins damage cells? Three organisms that use these exotoxins?
- binds, inserts, and forms a pore
- cytoplasmic content spills out and water comes in
- death by osmotic lysis
- S. aureus, GAS, B. pertussis
What are the effects of super antigen exotoxins? Two organisms?
- toxins elaborated at site of infection go into blood stream
- bind MHC II on APC’s without processing
- results in polyclonal stimulation of T cells with massive cytokine release (IL-1, TNF, monocyte stimulation)
- S. aureus, GAS
How does hydrolytic enzyme hyaluronidase facilitate bacterial invasion of tissues?
- lyses hyaluronan to lower viscosity of ECM
How do endotoxins differ from exotoxins?
- ex’s are secreted by bacteria
- endotoxins are part of the bacterium itself
What is the common gram negative endotoxin and what does it do during sepsis?
- LPS
- Lipid A component stimulates the excessive release of IL-1 and TNF producing fever and shock
Three organisms that cause atypical acute CAP?
- mycoplasma pneumoniae
- Chlamydophila pneumonia
- Coxiella burnetii (Q fever)
Organism of Q fever?
Coxiella burnetii
Three organisms of pneumonia in neonates 0-3 months?
BIRTH CANAL ORGS
- GBS
- enteric gram negative rods
- HSV
When does Moraxella catarrhalis become a cause of pneumonia in children?
- 1-5 years
- acquires with age as a normal upper airway organism
What adults most often acquire acute CAP? 7 underlying diseases/co-morbidities that are RF”s?
- mid 50’s to late 60’s
- year round (peak in midwinter to early spring)
- COPD, CVD, neurologic disorders, DM, EtOH, IC, tobacco
5 patient types who get aspiration pneumonia? What causes damage in this type of pneumonia?
- suppressed gag and swallow reflexes: neuro impaired, tube fed, dementia, EtOH, anesthesia
- acid from stomach induces release of pro-inflamm cytokines
- neutrophils recruited to the lung mediate much of the damage seen
What organisms are seen in aspiration CAP and HAP?
- mixed cultures
- endogenous mouth flora (S. pneumonia, H. inf) in CAP
- GNR (60%, enterobacter), S. aureus (13-40%) in HAP
Why do anaerobes appear in half of aspiration pneumonia cases?
facultative aerobes in mixed culture take up all of the oxygen which allows anaerobes to come in
What is the second leading hospital acquired infection and leading cause of infection-related death in hospitalized patients?
nosocomial pneumonia - quality and safety indicator for hospitals
How does acute pneumonia present clinically?
- sudden onset of chill, fever/sweats, pleuritic chest pain, productive cough (mucopurulent)
- tachypnea, tachycardia, rales, B-like symptoms
What cultures are collected in pneumonia cases?
- 2 sets of blood cultures drawn from two sites (nearly 90% sensitive in 24 hours)
- 1 aerobic bottle and 1 anaerobic bottle for each site
- sputum culture
What two organisms can be detected with a rapid urinary antigen test? TAT?
- Strep pneumo
- Legionella
- 15 min TAT
How is an inadequate sputum specimen defined?
reject sputum sample if greater than or equal to 10 squamous epithelial cells per LPF (implies spit - not from LRT)
Uses of blood agar plate?
- non-selective
- detection of hemolysis (alpha, beta, gamma)
Selection and differential of MacConkey Agar Plate?
- selective for non-fastidious GNR
- pink colonies ferment lactose
Uses of the chocolate agar plate?
- non-selective, non-differential
- enriched medium for fastidious organisms like Haemophilus
MALDI-tof TAT?
10 min = Matrix Assisted Laser Desorption Ionization time of flight mass spec (Bruker score >2 is a good ID)
How does E-test Strip susceptibility testing work?
- plastic strip embedded with a linear gradient of a single drug and planted onto a lawn of organism
- 24 hours
- used to find Mean Inhibitory Concentration of drug
What population of pathogens is tested for by routine cultures?
routine aerobic bacteria (not viruses, fungi, myco, anaerobes, fastidious orgs)
What are the best testing options for viral respiratory infectious disease?
- Influenza A/B/RSV PCR (batch tested daily during flu season)
- PCR battery with lots of viruses
Why are respiratory viral cultures not often used?
- expensive
- 21 day TAT
- not as sensitive as PCR
What is the leading cause of bacterial CAP? Where does it come from and who gets infected?
- Strep pneumoniae = pneumococcal pneumonia
- organism aspirated from flora = 5-20% carrier state
- extremes of age; >50 at greatest death risk
How does Strep pneumo pneumonia manifest?
- lobar pneumonia
- rusty/bloody sputa
What common cause of bacterial CAP is not reliably ID’d by MALDI-tof?
Strep pneumo
Hemolysis, catalase, and optochin of Strep pneumo culture? Gram stain?
- alpha, cat negative, inhibited by optochin
- dimpled colonies due to autolysin presence
- gram + diplococci (lancet shaped)
Diagnosis of Strep pneumo?
- urinary antigen
- blood cultures only + in 50%
Source and presentations of H. influenza?
- nasopharynx (20-80%)
- post-viral respiratory infections are common
- descending laryngotracheobronchitis –> lobar pneumonia
- similar to Strep pneumo
Differences in H. influenzae invasive disease worldwide vs. developed countries?
- Type b strains cause 90% of invasive disease peaking in age 2-5
- non-Hib causes most invasive disease; all ages (Hib vaccine)
Four virulence factors of Strep pneumo?
- choline binding protein (attachment, factor H)
- capsule blocks C3b
- autolysin
- pneumolysin released on bacterial death (pores in respiratory epithelium directly breaks down mucosal barrier = sepsis, directly affects phagocytes)
In addition to pili, OMP, and capsule, what determines serotypes of H. influenzae? How does it invade?
- capsular polysaccharide antigens (associated with virulence, Hib is most virulent)
- between respiratory epithelial cells
Gram stain of H. influenzae? What makes it unique?
- GNR
- PLEOMORPHIC – coccibacillary
What does H. influenza grow on?
- fastidious
- grows on chocolate in CO2 – requires both hemin and NAD (factors X and V) in RBC’s
- may be seen satelliting around beta hemolytic colonies
H. influenza catalase, oxidase, MALDI-tof?
- cat negative
- ox +
- reliable (also E test)
Common presentation of S. aureus pneumonia? What percent of pneumonias? Where is it found?
- acute lobar pneumonia with abscess formation
- 2-5%
- 10-30% skin/nares colonization
- IVDU w/ endocarditis, post-Inf A, iatrogenic infections
S. aureus gram stain? Hemolysis, catalase, and coagulase?
- gram + cocci in clusters
- beta, cat +, coag + opaque cream rapidly growing colonies
Four S. aureus surface proteins?
- clumping factor = mediates cell binding to fibrinogen
- coagulase = conversion of fibrinogen to fibrin and binding of org to fibrin
- fibronectin binding proteins
- protein A = binds Fc of IgG
Two S. aureus extracellular enzymes?
- alpha toxin = cytolytic, pore-forming toxin
- superantigen toxins = TSS
Where is Moraxella catarrhalis found? Who is colonized?
- normal flora of oropharynx
- most children > COPD (2-10%) > normal adults (1-5%)
Four presentations of Moraxella catarrhalis in children?
- otitis media
- acute sinusitis
- bronchitis
- pneumonia
Second most common cause of COPD exacerbation in older adults?
- Moraxella catarrhalis
- 2-10% colonized
- bronchitis and pneumonia
Two common co-infections of Moraxella catarrhalis?
Strep pneumo and H. inf
Two gram stain morphologies of Moraxella catarrhalis? What does it look similar to?
- GN diplococci
- GN coccobacilli
- Neisseria
Hemolysis of Moraxella? How is it distinguished from Neisseria?
- gamma
- + butyrate esterase activity (spot test)
Presentation of Legionnaire’s?
- multilobar pneumonia with headache, fever, chills, dry cough, chest pain
- males
- very high fever
- rapid progression (necrosis) with respiratory failure and shock within 3-6 days
Prognosis of Legionnaire’s? How is it acquired?
- 15-50% death rate
- environmental water resources (water features, shower heads, cooling towers)
Causative organism in Legionnaire’s?
Legionella pneumophila
What type of pathogen is Legionella pneumophila? Pathogenesis?
- facultative intracellular pathogen
- endocytic invasion and prevention of phagolysosome fusion
- extracts iron from transferrin
- inhibits oxidative killing activities of macro’s
How does Legionella cause damage to host tissues?
- facultative intracellular
- produces pore-forming toxin that lyses the monocyte releasing the bacteria and monocyte-derived enzymes that damage tissues
What makes gram stain diagnosis of Legionella difficult?
faintly staining thin GNR so it is often missed on gram stain
Why is culture of Legionella no longer standard of care? What is SOC?
- fastidious, BYCE agar only (no blood), 2-5 days to produce colonies, low sensitivity, weakly cat and ox +
- PCR of respiratory specimen is GOLD standard (serogroup 1)
- urinary antigen (serogroup 1 reliably, others inconsistently)
How does GAS Strep pyogenes pulmonary disease present in normally healthy people?
lobar pneumonia and TSS
How does strep toxic shock present?
- begins at site of any GAS infection
- starts with myalgia, fever/chills, severe pain
- progression with NVD
- ends with hypotension, shock and organ failure including renal impairment
- sepsis seen in over half
What percent of GAS produces super antigen toxin?
10%
GAS-specific binding protein? Toxin?
- M protein = binds fibrinogen, factor H, Ig
- Streptolysin O = pore-forming toxin that lyses WBC’s
Three enzymes produced by GAS?
- streptokinase = lyses fibrin
- C5a peptidase (C5a attracts phagocytes)
- Hyaluronidase - degrades ECM (dec viscosity)
How does streptolysin O cause damage?
pore-forming toxin that lyses WBC
Hemolysis, catalase, and colony morphology of GAS pyogenes?
- beta (hemolysin O and S)
- catalase neg
- small, grey colonies
Two ways to definitively ID Strep pyogenes?
- Lancefield grouping latex reagent
- MALDI-tof
Gram stain morphology of S. pyogenes?
- GPC in CHAINS
What underlying diseases are often associated with GNR pneumonias? What organism causes half of GNR pneumonias? How are the infections acquired?
- COPD, CF, neutropenia
- P. aeruginosa
- aspiration
What environments are P. aeruginosa found it?
- water/soil associated
- usual respiratory flora in 2-10% of healthy peopl
What 4 P. aeruginosa virulence factors mediate adherence to host cells?
- LPS
- pili
- alginate
- flagellum
Two exotoxins produced by P. aeruginosa? Functions?
- breakdown of respiratory epithelium
- A = inhibits eukaryotic elongation factor preventing protein synthesis and resulting in cell death
- S = acts on G proteins to disrupt the cell’s cytoskeleton, signaling pathways and induces apoptotic death?
What does P. aeruginosa exotoxin A do?
- inhibits eukaryotic EF preventing protein synthesis and resulting in cell death
What does P. aeruginosa exotoxin S do?
- acts on G proteins to disrupt cytoskeleton, signaling pathways
- induces apoptotic death
Two enzymes produced by P. aeruginosa that aid in tissue damage and dissemination?
elastase and phospholipase
How does PA in CF cause serious problems?
mucoid slime alginate production is switched on by quorum sensing mechanisms in biofilms that form in CF patients (makes culture plates slimy)
P. aeruginosa gram stain morphology?
slender GNR
Hemolysis and oxidase of P. aeruginosa?
- metallic sheen with beta
- oxidase positive
What type of pulmonary disease is associated with enterobacteriaceae?
lobar pnemonia in at-risk populations (EtOH, aspiration, hospitalized patients - aspiration and ventilation)
Where is enterobacteriaceae found in the human body?
- usual gut flora
- upper airway of hospitalized patients
Four common enterobacteriaceae?
- E. coli, Klebsiella pneumoniae, serratia marcescens, enterobacter
Three ways enterobacteriaceae cause damage?
- LPS endotoxin
- alpha hemolysin - pore-forming toxin = cell death
- cytotoxic necrotizing factors that disrupt cellular signaling
Four culture characteristics of enterobacteriaceae?
- rapid growing facultative anaerobes
- ferment Glc
- reduce nitrate to nitrite
- oxidase negative
Gram stain morphology of enterobacteriaceae?
- GNR
- some are encapsulated and some may chain
Why is it important to do aerobic and anaerobic blood cultures for enterobacteriaceae?
anaerobic bottles will be positive 12 or more hours earlier than aerobic bottles in facultative anaerobes
Which Burkholderia species is associated with worse outcomes in CF?
cenocepacia
What is cepacia syndrome? Who is it seen in?
- severe progressive respiratory failure and sepsis in CF patients
- associated with higher mortality and decrease in pulmonary function following infection
What are two virulence factors of B. cepacia?
- cable pilus - mediates binding to respiratory mucus and epithelial cells
- BCESM = epidemic strain marker associated with increased virulence in patients with CF
What virulence factor of B. cepacia is associated with increased virulence in CF patients?
B. cepacia epidemic strain marker
Gram stain morphology of B. cepacia?
GNR
Media, oxidase, and catalase of B. cepacia?
- selective OFPBL media that starts off producing yellow colonies that turn media green
- ox +
- cat +
How does atypical pneumonia caused by Mycoplasma pneumonia present?
- mild tracheobronchitis
- sore throat, fever, malaise, headache, cough w/ scanty sputum, few/scattered rales
- CXR unilateral scattered areas of pneumonia
What is the disease course of mycoplasma pneumonia? How many patients are asymptomatic?
- protracted with conversion from upper to lower respiratory symptoms over a 10 day period, may persist for several weeks
- 1/3 are asymptomatic
Who gets mycoplasma pneumonia? When?
- children and adolescents 5-15 years, but may be sen in older patients
- severity increases with age
- 10% of CAP
- epidemics in enclosed populations
- year round occurrence with increased cases in late summer/fall
What makes M. pneumonia detection difficult?
no cell wall so it’s hard to detect immunologically (no targets) - also NO gram stain
How does M. pneumonia affect mucosa?
desquamation
What is the virulence strategy of M. pneumonia?
- bind and hid
- adhesion via cytadhesin P1 interacting with sialic acids on the bronchial cell surface
- interferes with ciliary action
What is the gold standard for diagnosis of M. pneumonia?
PCR - difficult to grow, requires cholesterol, ferments Glc, liquid culture make take 4 weeks, binds guinea pig RBC
Pulmonary presentations of Chlamydophila pneumonia?
- sore throat, cough that may persist for weeks/months, sinusitis
- majority of cases are asymptomatic or mildly symptomatic
Why is serology useless in Chlamydophila pneumonia?
- > 50% of adults have positive serologies
- conversion takes weeks and there is cross reactivity with other chlamydia
Which atypical pneumonia organism is associated with 10% of CAP and 5% of bronchitis?
Chlamydophila pneumoniae
What kind of organism is Chlamydophila pneumonia?
- obligate intracellular PARASITE
- infectious phase is elementary body (spore) and replication occurs via conversion to reticulate body followed by host cell lysis
Gold standard of Chlamydophila pneumonia Dx?
PCR
Three stages of Bordetella pertussis infection?
- catarrhal
- paroxysmal
- convalescent
What is the most infectious B. pertussis stage and how does it present?
Catarrhal - profuse, mucoid rhinorrhea, fever, anorexia, and sneezing for 1-2 weeks = BAD COLD
What is the lab finding associated with the paroxysmal stage of B. pertussis?
HUGE LYMPHOCYTOSIS
How does the paroxysmal stage of B. pertussis present?
- persistent paroxysmal cough up to 50 times daily for 2-4 weeks
- cough caused by inspiratory whoop and vomiting
Who is the most vulnerable population in B. pertussis infection?
70% death rate in children <1 year of age
How does disease present in vaccinated patients?
incomplete vaccination and waning immunity produces variable disease
How does B. pertussis cause most of its damage?
TOXINS
Three toxins from B. pertussis?
- A-B toxin that ADP-ribosylates a G protein that prevents inactivation of adenylate cyclase –> lymphocytosis, insulinemia, histamine sensitization
- pore-forming adenylate cyclase
- tracheal cytotoxin that causes direct toxicity to ciliated cellls
Gram stain morphology of B. pertussis?
tiny, GN coccobacillus (like Haemophilus) - fastidious, slow growth
Gold standard for B. pertussis diagnosis?
PCR
