Download Lecture 2 – Week 7 Control of Microbial Growth

LAB 7: RESPIRATORY SYSTEM
RESPIRATORY SYSTEM: UPPER AND LOWER
THE RESPIRATORY SYSTEM
Host Defense Mechanisms
Anatomical characteristics/mechanisms to prevent/fight infection:
– nasal hairs
– antibacterial enzymes (lysozyme)
– convoluted passages
– cilia and mucous lining of the trachea
– mucous linings of the nasal turbinates
– reflexes --coughing, sneezing, swallowing
– Normal flora of nasopharynx and presence of normal flora
NORMAL MICROBIOTA OF THE
RESPIRATORY SYSTEM
• UPPER respiratory tract :
– Coagulase – negative staphylococci
– Neisseria (Gram – negative cocci)
– Corynebacterium spp. (Diphtheroids) (Gram – positive rods)
– Anaerobic bacteria
– Pathogens in low numbers (colonization vs. pathogenic) (S. aureus,
Gram-negative rods (Enteric/Pseudomonas spp.)
• LOWER respiratory tract (trachea, bronchi, and bronchioles) is virtually
free of microorganisms, mainly because of the efficient cleansing action of the
ciliated epithelium
RESPIRATORY TRACT INFECTIONS
Bronchitis
Pharyngitis
Pneumonia
Epiglottitis
Sinusitis
PATHOGENS OF THE UPPER
RESPIRATORY TRACT
THROAT:
•Streptococcus pyrogenes (Group A strep)
•Viruses
SINUS:
•Moraxella catarrhalis (Gram – negative cocci)
•Gram – negative rods
•Staphylococcus aureus
•Viruses
PATHOGENS OF THE LOWER
RESPIRATORY TRACT
• Streptococcus pneumoniae
• Hemophilus influenzae
• Staphylococcus aureus
• Moraxella catarrhalis (Gram – negative
cocci)
• Gram – negative rods (Klebsiella sp.,
Enterobacter sp., Serratia sp., E. coli,
Pseudomonas sp.)
• Fungi (Cryptococcus neoformans)
• Viruses
The Respiratory System:
Collecting Specimens & Diagnosis
• Upper respiratory tract: Mucus membrane (throat, sinus) is wiped with
a special collection swab.
– Culture for isolation, identification
and susceptibility testing of pathogens
• Lower respiratory tract: Sputum and or bronchial specimens are
collected into a sterile container.
– Gram stain for white blood cells and microorganism and to check
for the quality of the specimen
– Culture for isolation, identification and
susceptibility testing of pathogens.
MEDIA
Sheep Blood agar:
•Enriched (contains 5% sheep blood with
tryptic soy agar base)
•Differential (used to detect hemolysis of
microorganisms)
•Microorganisms produce toxins called
hemolysins that can break down red blood
cells causing a visual change in the media
IDENTIFICATION
• DIFFERENTIATION OF
STAPHYLOCOCCI AND
STREPTOCOCCI
– GRAM STAIN
– CATALASE
– HEMOLYSIS ON SHEEP BLOOD AGAR
GRAM STAIN
• STAPHYLOCOCCUS
GRAM POSITIVE COCCI IN PAIRS AND
CLUSTERS
• STREPTOCOCCUS
GRAM POSITIVE COCCI IN PAIRS AND
CHAINS
CATALASE TEST
Streptococci are
Gram-positive,
catalase negative (no
bubbles)
Staphylococci are
Gram-positive,
catalase positive
(bubbles)
Blood Agar - Hemolysins
• Alpha-hemolysis – causes partial lysis of RBCs and
breakdown of hemoglobin which leads to a green color
change in the agar.
• Beta-hemolysis – causes complete lysis of RBCs and
breakdown of hemoglobin which leads to a colorless
clearing in the agar.
• Gamma-hemolysis – an organism that does not cause
hemolysis.
SHEEP BLOOD AGAR
BLOOD AGAR LAB PROCEDURE
BLOOD AGAR LAB PROCEDURE
Blood Agar Lab Procedure: RESULTS
GROUP A STREP (S. pyrogenes) –
(causative agent of ‘Strep throat’)
Bacitracin (A) disk test
Group A beta strep is
sensitive to bacitracin
(zone of inhibition)
Other beta streps are
resistant to bacitracin
(no zone of inhibition)
Streptococcus pneumoniae
• S. pneumoniae is an alpha
streptococci that is
susceptible to the
optochin disk (zone of
inhibition)
• Most common cause of
CAP
• Other alpha streptococci
are resistant to optochin
(no zone of inhibition)
Streptococcus pneumoniae
• S. pneumoniae
• Catalase negative
• Gram – positive cocci in
LANCET PAIRS
• Frequently
encapsulated
DICHOTOMOUS KEY FOR IDENTIFICATION OF STAPHYLOCOCCI AND
STREPTOCOCCI
GRAM POSITIVECOCCI IN PAIRS,
CHAINS OR CLUSTERS
CATALASE NEGATIVE
= STREPTOCOCCI
CATALASE TEST
CATALASE POSITIVE=
STAPHYLOCOCCI
HEMOLYSIS
ALPHA HEMOLYSIS – Optochin disk sensitive = S.
pneumoniae
BETA HEMOLYSIS – Bacitracin disk sensitive = S.
pyrogenes (Beta hemolytic strep Group A)
GAMMA
HEMOLYSIS
STAPHYLOCOCCI VS. STREPTOCOCCI
PAIRS AND
CHAINS
GRAM POSITIVE COCCI
PAIRS AND
CLUSTERS
NEGATIVE
CATALASE
POSITIVE
HEMOLYSIS
ALPHA
BETA
GAMMA
POSITIVE
S. aureus
MSA PLATE
NEGATIVE
Coagulase negative
Staphylococci