M4 Upper Respiratory Tract Infections Flashcards
What areas of the body does the upper respiratory tract include?
The nose, pharynx, and larynx.
What is pharyngitis?
Pharyngitis - Inflammation of the pharynx, hypopharynx, uvula, and tonsils.
Note: Slide 3 includes lots of URT infections like Rhinitis, Rhino-sinusitis or sinusitis, Nasopharyngitis (rhino-pharyngitis or the common cold), Epiglottitis (supraglottitis), Laryngitis, Laryngotracheitis and Tracheitis but we are focusing on pharyngitis.
What factors for defense do some virulent strains of Gr. A Strep posses?
Virulent strains possess a variety of factors for defense,
1. Adherence and
2. Invasion (M protein- hyaluronic acid- streptolysins O & S- hyaluronidase)
What do some Gr. A Strep strains possess that cause systemic illness?
Exotoxins
Some strains possess exotoxins that can progress from pharyngitis → systemic illness (scarlet fever, systemic shock syndrome)
What are the complications that can be from a Strep. Gr. A infection?
-Acute Glomerulonephritis (IgG & other antibodies involved collect in glomeruli in kidneys (hematuria, proteinuria, RBC casts)
-Acute Rheumatic fever (after strep throat, antibodies involved heart, joints, skin, brain). More common in children 5-15. Damages heart valves.
- Scarlet fever from exotoxins
- Acute pharyngitis
How many typical normal flora can you name (for >50% of the people)?
Viridans streptococci
Neisseria sp., Moraxella spp.
Corynebacteria
Bacteroides
Anaerobic cocci (Veillonella)
Fusiform bacteria
Candida albicans
Streptococcus mutans
Haemophilus influenzae
What are some occasional surprising residents of the URT (these people would then be carriers of these bacteria)?
Streptococcus pyogenes
Streptococcus pneumoniae
Neisseria meningitidis
What are some uncommon residents that <1% of people have?
Corynebacterium diphtheriae
Klebsiella pneumoniae
And esp. after antibiotic treatment
- Pseudomonas
- E. coli
- Candida albicans
What are the transport/storage requirements for throat swabs for routine pharyngitis?
Routine pharyngitis
1. Throat swab normally received in transport media
2. stable for 4 hrs at room temperature
3. refrigerate up to 24 hours
How should throat swabs received for direct antigen detection be received?
Swabs received for “Direct Antigen Detection” should be dry
Do you need to culture if your swab direct antigen test for Gr. A Strep is positive?
Highly specific (if +, no need for culture)
What happens if your direct antigen test for Gr. A Strep is negative?
Not so highly sensitive (If neg–>culture).
Note: Direct Antigen test: swab against Antibodies for Strep A (only!).
What plate do you plant throat swab specimens? Incubation?
Planting: BA plate in CO2 (in theory: ideally anaerobic).
Some Labs add a Bacitracin disk (TAXOS A) or use media with it, why?
Strep A is susceptible to bacitracin, then you can see this halo (zone of inhibition’s) that will tell you it is GAS. But if the organism is in low amounts then it is hard to tell if it is R or S. In rare cases it can inhibit Strep A. So not a common practice any more.
Some labs make cuts in the agar, why?
Some labs make cuts in the agar, to allow for the streptolysins to show they are beta-hem.
Do we need a direct smear for URT specimens?
A direct smear does not help to differentiate the Streptococcus species, so we do not do the direct smears (i.e. smear directly from the patient sample).
Note: She mentioned an exception to this in class.
What are we looking for on our BA plate for throat swabs?
Culture:
Looking for beta-hem colonies:
Strep Group A (pyogenes), C & G (dysgalactiae)
Arcanobacterium haemolyticus (rare): GPB!
What tests are done if we find Beta-hem colonies?
Gram stain
Catalase
PYR
–> enough for Group A
Lancefield typing: if PYR neg or to confirm “A”
How do you report typically for URT infections?
Quantitation: 1+, 2+, 3+, 4+ (lab manual)
Then it will be either:
- Beta-haemolytic Strep Gr A or Streptococcus pyogenes
- Beta-haemolytic Strep Gr C (or G).
- No beta-haemolytic strepto- coccus isolated
Why are AST tests not routinely done on throat swabs? Exception?
AST: Not done routinely as all BHS are susceptible to Penicillin (drug of choice).
If patient is allergic, AST is done following CLSI (Erythromycin, Clindamycin, D-test, etc. on MH-blood in CO2)
What comment do you put for AST in the pos throat swab report?
“S. pyogenes is intrinsically susceptible to Penicillin. If patient is allergic please contact the Lab @….”
Do you report normal flora for throat swab?
DO NOT report any of the normal flora organisms by name, or even Normal Flora.
Note: See slide 10 for interpretation and reporting flow chart.
What URT infection does Bordetella pertussis cause?
Whooping cough
What are the two virulence factors that Bordetella pertussis have?
Virulent strains possess two factors:
- FHA (filamentous hemagglutinin) –> adherence
- Cytotoxin (PTx) –> invasion
How is diagnosis typically done for Bordetella pertussis?
Testing typically done with PCR.
What kind of specimen and transport medium is used for the micro lab for Bordetella pertussis?
Nasopharyngeal swab
1. Calcium alginate for culture
2. Dacron for molecular
3. Charcoal Transport media
increases recovery
(Regan-Lowe)
What are the special culturing requirements for Bordetella pertussis?
- Organisms need increased moisture
- Culture require specialized media such as Reagan Lowe
a) cephalexin suppress normal flora
b) charcoal absorb toxic metabolites
What rare small g+b can be confused with beta-hem Strep?
What test can be used with it?
Arcanobacterium haemolyticum
grows poorly on tellurite media
confused with beta hemolytic Streptococcus
Reverse CAMP test - pos
Catalase - neg
What range of disease can Corynebacterium diphtheriae cause?
- Mild forms adhere to pharynx
causing pharyngitis - Highly virulent strains produce exotoxins leading pseudomembrane formation and serious complications
Only toxigenic strains are severe
What does Corynebacterium diphtheriae appear like on blood agar?
BA – gray to white non-hemolytic colonies up to 2 mm in size after 18-24 hours in 5% CO2 at 35oC (except C. diphtheria var mitis –βhaem)
What media is more successful for culturing Corynebacterium diphtheriae?
A selective/differential media: Tinsdale agar
What tests are performed on suspected Corynebacterium diphtheriae?
suspect colonies are gram stained
Biochemicals
- produces acid from glucose and maltose
- urease neg
What are the four biotypes of Corynebacterium diphtheriae?
Four biotypes:
1. intermedius,
2. gravis,
3. mitis,
4. belfanti
What are some (three) of the ingredients of Tinsdale Agar and what do they do?
Tinsdale Agar
1. potassium tellurite is a selective agent
Black colonies form due to the presence of tellurite reductase.
2. cysteine and sodium thiosulphate are H2S indicators.
If colonies are surrounded by a brown halo indicates cysteinase activity.
What test is used to look only for the Corynebacterium diphtheriae toxin?
ELEK toxin Assay
Describe the ELEK toxin assay test for Corynebacterium diphtheriae toxin?
- Paper strip or disk saturated
with diphtheria antitoxin is placed in molten agar at 55oC, and allowed to sink to the bottom of the plate. - The agar is allowed to solidify by cooling to room temperature.
- Streaks of unknown test organisms are placed at a right angle to the strip.
- Development of an agar precipitin line within 1-2 days of incubation at 35C is a positive result for diphtheria toxin.
What URT infection does Candida spp. cause?
Thrush
Is Candida spp. normally in the upper respiratory tract?
Yes, infection is a result of overgrowth at site, can be problematic for infants, elderly patients, immunocompromised (HIV, diabetes, cancer, transplants).
Can Neisseria gonorrhoeae
cause an upper respiratory tract infection?
Yes
What media and incubation should be used for suspected Neisseria gonorrhoeae pathogen?
- Modified Thayer-Martin (selective media) should be used, by request
- Incubate in CO2, minimum 48 hours and ID appropriately
What is the most common cause of URT infections?
S.pyogenes
Is S. pneumoniae in a carrier state in the URT?
Yes
What virulent factor is associated with serious diphtherial infection?
Exotoxin production
Which of the following organisms would not grow from a routine throat culture?
a. C. diphtheriae
b. Beta Strep Group C
c. N. gonorrhoeae
d. Candida spp
c. N. gonorrhoeae
