RTI's (bacterial) Flashcards
How are RTIs normally divided?
Into lower and upper tract infections
What two types of infections are grouped into lower tract infections?
- Pneumonia (CA and nosocomial)
2. AECB/AE-COPD
What does AECB/AE-COPD stand for?
Acute exacerbations of chronic bronchitis / acute exacerbations of chronic obstructive pulmonary disease
What 3 infections are grouped into upper tract infections?
Pharyngitis
Otitis media
Sinusitis
What is the most common type of sample to obtain from someone with a lower tract infection?
Sputum
What are 7 types of specimens you can obtain to test for an RTI ?
Sputum BAL / bronchial washing Nasopharyngeal aspirates / swabs Endotracheal aspirates Sinus aspirates Tympanocentesis Throat swabs
What is the pathogen most commonly associated with all RTIs (with the exception of pharyngitis)?
Streptococcus pneumoniae
What are the 3 common (not atypical) pathogens responsible for RTIs?
- Streptococcus pneumoniae
- Haemophilus influenzae
- Moraxella catarrhalis
What are the 3 atypical pathogens commonly associated with RTIs?
- Mycoplasma pneumoniae
- Chlamydophyla pneumoniae
- Legionella pneumophila
What are the 2 major causes (pathogens/types of pathogen) for community acquired pneumonia?
- Streptococcus pneumoniae (40%)
2. Atypical pathogens (30%)
Why can you not treat CA pneumonia empirically with a a ß-lactam?
Because it won’t deal with the atypical pathogens that are the cause in 30% of cases
Define pneumonia
an inflammatory condition of the lung primarily affecting the alveoli (microscopic air sacs)
What are the three “types” of pneumonia?
CAP: community acquired
HAP: hospital acquired
VAP: ventilator associated pneumonia
What pathogens tend to be the cause of HAP and VAP?
gram negatives and anaerobes
- ex: Klebsiella, S. aureus
What are some typical signs and symptoms of pneumonia?
fever,cough (productive or dry), chest pain,shortness of breath
Why are throat swabs useless for diagnosing pneumonia?
Because 5-10 % of adults and 20-40% of children have their nasopharynx colonizes by streptococcus pneumoniae
What are the main features (atmosphere, shape, testing, susceptibilities) of Strep. pneumoniae?
- small gram positive diplococci
- alpha haemolytic
- bile soluble
- optochin sensitive
- growth often enhanced in CO2 atmosphere
- most are encapsulated
Streptococcus pneumoniae being soluble in bile and sensitive to optochin allows it to be separated from…?
other viridans group strep
What are 6 factors that can predispose someone to developing a pneumococcal infection?
- defective Ab formation
- insufficient numbers of neutrophils
- day-cares, military, prisons, shelters (close quarters)
- chronic respiratory disease (i.e. COPD)
- infancy and aging
- diabetes, alcoholism, liver disease (comorbidities)
What is the most important virulence factor for S. pneumoniae?
Capsule formation!
What two jobs does the capsule have for S. pneumoniae?
- Helping the bacteria escape from phagocytic cells
2. Help form adherence + colonization
What are 2 other virulence factors used by S. pneumoniae?
- Pneumolysin (hemolysin)
2. Secretory IgA protease
What does pneumolysin do? (3 things)
- destroys ciliated epithelial cells
- suppress oxidative burst by phagocytic cells
- activates the classical complement pathway
What two vaccines exist against pneumococcal infections?
- Pneumovax (pneumococcal vaccine)
2. PREVNAR (conjugate vaccine)
What is Penumovax preventative against? what are the drawbacks?
Effective against 23 most common capsular serotypes of invasive disease causing pathogens (getting into the blood)
- these account for 90% of infective strains
Drawbacks are that it is not very immunogenic and doesn’t offer long lasting protection because it’s a carbohydrate vaccine
- also doesn’t work for kids
What is PREVNAR effective against? What are the drawbacks?
Conjugative vaccine that can be used for kids under 2 y/o as well as adults
Drawbacks: not as wide a spectrum?
What are the 5 kinds of antibiotics that you can prescribe for an infection with Streptococcus pneumoniae? Which one can you not use empirically?
penicillins, cephalosporins, macrolides, fluoroquinolones, vancomycin
- can’t use the penicillins empirically
What 4 factors will influence the choice of antibiotic for S. pneumoniae?
- Site of infection
- Comorbidities
- Severity of illness
- Ambulatory / inpatient
What tend to be the 3 main causes of acute bronchitis?
- Viral antigens
- pollutants/allergens/smoke
- atypical pathogens
What are the 3 classifications of chronic bronchitis?
- Simple
- Complicated
- Complicated + risks
What 2 pathogens tend to be the cause of Simple chronic bronchitis?
H. influenzae and S. pneumoniae
What types of pathogens (4) tend to be the cause of more complicated/risky chronic bronchitis?
- Enterobacteriaceae
- Pseudomonas spp
- Gram-negatives
- Resistant organisms
What is COPD? (acronym and definition). What types of diseases does it include
Chronic obstructive pulmonary disease
umbrella term used to describe progressive lung diseases including emphysema, chronic bronchitis, refractory (non-reversible) asthma, and some forms of bronchiectasis.
What is a common characteristic of all COPD?
increasing breathlessness due to narrowing of the bronchiole tree
- hard to breathe in, even harder to breathe out
Which pathogen is the most common cause of AE-COPD?
Haemophilus infleunzae
What are 4 ‘facts’ about H. influenzae (growth, morphology, requirements..)
- small gram negative bacilli
- requires X and V factors for growth
- will grow on “chocolate” agar with 5% CO2
- may be encapsulated
Why is the infectious encapsulated form of H. infleunzae not an issue currently? What did it used to cause?
Because of the effectiveness of the Hib vaccine against the type b form of H. influenzae
Used to cause meningitis (kids) and acute epiglottitis (kids and adults)
what does H. influenzae cause most now? In what form?
majority of mucosal disease due to non-encapsulated strains
What are the other two members of Haemophilus spp that you need to be able to differentiate between?
H. parainfluenzae, Aggregatibacter aphrophilus
How can you differentiate between H. influenzae, H. parainfluenzae, A. aphrophilus? What 3 tests?
Test if they are X, or V factor dependent as well as the catalase test
H. influenzae: positive for all 3
H. parainfluenzae: negative for X factor, positive for V factor and catalase (can be +/-)
A. aphrophilus: negative for all tests
What is X factor
Porphyrin which is essentially heme
What is V factor?
NAD
Why is H. influenzae X factos dependent?
They do not excrete porpho-bilinogen and porphyrins because of deficiencies in the hemin biosynthetic pathway
How can you test for X factor dependence (porphyrin test). How do you know if you have H. influenzae or not?
Heavy suspension in amino-levulinic acid, incubated 4 hr illuminated with UV light and examined for red fluorescence
Positive test = Fluorescence under UV = indicates enzymatic conversion of amino-levulinic acid to porphyrins and therefore X-factor independence = not H. influenzae
What is the best approach to treating an infection with H. influenzae? what kinds of drugs are they resistant to?
- Want to test for ß-lactamase activity (present in 18%) with a nitrocephin disk test
- If no ß-lactamase produced, you can treat with amoxicillin
- If there is a ß-lactamase produced, treat with amoxicillin clavulanate
- can also treat with 2nd / 3rd generation cephalosporins, newer macrolides (ok), and fluroquinolones (not in kids)
What % of H. influenzae infections have altered PBPs?
~1%
What is the morphology of Moraxella catarrhalis?
small gram negative cocco-bacilli
What 3 infections is M. catarrhalis associated with?
otitis media, sinusitis, AECB
What is the approximate carriage rate of M. catarrhalis?
about 50 %
What % of M. catarrhalis stains are resistant to ß-lactams? why?
about 90% produce a ß-lactamase
What is M. catarrhalis predictably susceptible to?
Most oral antibiotics with the exception of ampicillin / amoxicillin
- susceptible to TMP/SMX?
What 2 tests is M. catarrhalis positive for?
DNase +, asacchrolytic
What type of bacteria is Legionella pneumophila? Where does it live?
Intracellular gram negative bacilli
Where does Legionella penumophila tend to be found?
widespread in the environment, found in the soil, water, taps, and showers
Why is Legionella sometimes missed on a gram stain
because it stains very faintly
What type of agar does Legionella require for growth? Why? what other condition makes growth favourable?
Buffer charcoal, yeast extract with the addition of L-cysteine (BYCE)
- Need blood or charcoal to mop up toxins or it won’t grow
stimulated by 5% CO2
What are 2 other growth features of Legionella (ie movement and sugar…)
Motile and asaccharolytic
What is the best (of 4 possible) diagnostic lab tests to detect Legionella? Which is the worst?
- Urine sample (for antigen detection)
- Culture
the worst is DFA testing but serology is also useless unless the disease presentation is acute
Is susceptibility testing done for Legionella typically? Why?
No because you can get in vitro macrolide resistance but it works fine clinically
What two drugs are Legionella predictably susceptible to?
- Fluoroquinolones
2. Macrolides
What are 3 morphological and genomic features of mycoplasma?
- smallest free living bacteria
- small genome size
- lack a cell wall
What are 2 growth condition preferences/requirements for mycoplasma?
Facultative anaerobes and require complex media for growth
Which two diseases is Mycoplasma pneumoniae often the cause of? what %?
- 70-80% of tracheobronchitis cases
2. 20-30% of pneumonia cases
What is a common symptom of M. pneumoniae caused tracheobronchitis?
prolonged post infectious cough
What is a common symptom of M. pneumoniae caused pneumonia?
mild disease but long duration
What are 2 atypical pathogens that cause RTIs ?
- Mycoplasma pneumoniae
2. Chlamydophyla pneumoniae
What drugs (3) are the atypical pathogens typically susceptible to?
- doxycycline
- macrolides
- fluoroquinolones
What type of bacteria is Bordella pertussis?
small gram negative cocco-bacilli
What type of growth conditions does B. pertussis require? What is the name of the media?
- strict anaerobe
- media containing charcoal, blood, or starch
- Bordet-Gengou(BG) or RL medium
What are the 3 stages of disease progression of pertussis? Which is the most contagious stage?
- Catarrhal stage (highly contagious)
- Paroxysmal stage
- Convalescent stage
What is the general incubation period for pertussis?
7-10 days (can range from 4-21)
How long does the catarrhal stage of infection last? what are the symptoms?
1-2 weeks
Sneezing, runny nose, mild cough, low grade fever
- fairly non-specific resp. tract infection
How long does the paroxysmal stage of infection last? what are the symptoms?
1-6 weeks
paroxysmal cough, inspiratory whoop, posttussive vomiting, cyanosis, exhaustion leukocytosis, lymphocytosis
How long does the convalescent stage of infection last? what are the symptoms?
2-3 weeks
Symptoms should be clearing unless the patient acquires a secondary infection
What is the best sample collection method to use to diagnose a respiratory tract infection? What tests should be done after this? what is the best course of antibiotics to put a patient on?
- Naso-pharyngeal specimens (either by swab or aspirate)
- PCR is test of choice (can also culture on Bordet-Genou agar)
- Macrolides are the best choice antibiotics
What are the stats on S. pyogenes? (type of bacteria, what tests is it positive for, grouping, hemolysis…)
- gram positive, catalase -ve, β-haemolytic
- Lancefield Group A
- Pyr +, Taxo A (bacitracin) S
What 2 drugs are commonly used to treat bacterial pharyngitis caused by S. pyogenes?
Penicillin/Amoxicillin
Why do we treat S. pyogenes?
Not to resolve symptoms but to:
- reduce risk of transmission
- reduce risk of post-strep complications
what are two complications that can arise after an infection with S. pyogenes?
- Rheumatic heart disease
2. Post streptococcal glomerulonephritis
What is a test that can be used to diagnose S. pyogenes? what population is is not used for and why?
Rapid Group A Ag test
Not used for people 16+ because you’re more likely to get a false positive
What bacteria causes pharyngitis in teens/YA between 16-24 that also presents with a rash and occasionally more invasive disease?
Arcanobacterium hemolyticum
If you’re going to treat Arcanobacterium hemolyticum, what should you use?
Macrolide is the first choice
- may respond poorly to penicillin
What culture conditions are required for Arcanobacterium hemolyticum?
Best on rabbit blood with CO2 for 48 hours
What is the hemolysis patten for Arcanobacterium hemolyticum ?
weakly ß-hemolytic
do we treat bacterial pharyngitis empirically? why or why not?
No because you aren’t trying to ameliorate symptoms, just prevent spread and complications
An otherwise healthy, non-smoking 41 yr male presents to your office complaining of pleuritic chest pain and SOB.
He is mildly febrile and crackles are heard on exam. Chest x-ray confirms the diagnosis of CAP
How would you manage this patient? - Specimens? Antibiotics?
No need for a sample
treat empirically with a macrolide
12 year old female presents to your office complaining of a sore throat. She is febrile, has evidence of cervical lymphadenopathy.
How would you manage this patient?-Specimens / tests, antibiotics?
Take a swab and treat with antibiotic if you get a positive result (that its not viral…)
78 year old female presents to the ER complaining of SOB and increased sputum production and purulence. She is afebrile.
Her history indicates she was treated for some unspecified respiratory tract infection 2 months ago with ciprofloxacin (fluoroquinolone)
How would you manage this patient? - Specimens? Antibiotics?
What does she have?
want to take a sample (because she’s been treated recently)
Also want to treat empirically but not with cipro
likely has AE-COPD
- don’t always see fever with bronchitis
