Microbiology lab exercise 46- Bacteria of the respiratory tract
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The respiratory tract can be divided into 2 systems name them.
upper and lower respiratory tracts
The upper respiratory tract consists of:
the nose and throat
The lower respiratory consists of:
larynx, trachea, bronchial tubes and alveoli.
The lower respiratory system is usually sterile because of the efficient functioning of the _____ ________.
The upper respiratory tract is in contact with ___________ - air _________________.
the air we breathe
air contaminated with microorganisms
The ______ is moist, warm environment allowing many ________ to establish residence.
Species of many different genera can be found residing in the throat: name them
Staphylococcus, Streptococcus, Neisseria, Haemophilus
Despite the presence of potentially pathogenic bacteria in the URS the rate of infection is minimized by ______________.
What is microbial antagonism?
Certain microorganisms of normal microbiota suppress the growth of other microorganisms through competition for nutrients and production of inhibitory substances.
_________ are predominant organisms in the throat cultures and some species are the major cause of bacterial sore throat (acute pharyngitis).
Streptococci are ___________ and catalase _________.
Streptococcal species are identified by _______
characteristics including ________, and __________
Hemolytic reactions are based on ___________ that are produced by streptococci while growing on blood- enriched agar.
Blood agar is usually made from ________.
defibrinated sheep blood (5.%), sodium chloride (0.5%)to minimize spontaneous hemolysis and nutrient agar
Three patterns of hemolysis can occur on blood agar:
1. Alphahemolysis- Green, cloudy zone around the colony. Partial destruction of the RBCs is due to bacteria-produced by hydrogen peroxide.
2. Beta-hemolysis: complete hemolysis, giving a clear zone with a clean edge around the colony
3. Gamma-hemolysis: No hemolysis and no change in the blood agar around the colony.
_____ and _____ streptococci are usually _________.
Alpha-hemolytic and gamma-hemolytic streptococci
_________ streptococci are usually pathogenic.
S. pneumoniae is a causative agent of pneumonia and cannot be differentiated from other alpha-hemolytic streptococci on blood agar. How do they identify it?
using optochin inhibition with an optochin disk.
With optochin inhibition a zone of inhibition = to or > than ______ or larger indicated optochin sensitivity.
Bile solubility is also used to distinguish S. pneumoniae from other hemolytic streptococci. The addition of bile salts activates an enzyme that destroys _________ and the cells ______- colonies will disappear after the addition of bile salts. The other alpha-hemolytic streptococci do not have this enzyme.
the cell walls and the cells lyse
The streptococci can be antigenically classified into Lancefield's groups A through O by ________ in their cell walls.
Over 90% of streptococcal infections are caused by _________ group ______ ______.
Beta-hemolytic group A streptococci are assigned to the species ______ _______.
S. pyogenes is sensitive to the antibiotic _______; other streptococci are resistant to _______.
Procedure for throat culture:
-swab throat with sterile swab on the golden arches
-after obtaining the culture swab 1/2 of the blood agar plate
-streak the remainder of the plate with an inoculating loop
-incubate the plate inverted at 35*C for 24 hours
Procedure for streptococcus:
-inoculate each 1/2 of blood red agar plate one side with S. pyogenes and other with S. pneumoniae
-dip forceps in alcohol and burn off the alcohol
-using the forceps place and press a bacitracin disk and an optochin disk on each 1/2
-space the disks so that the zones of inhibition may be observed
-incubate plates at 35*C for 24 hours
Second phases are gram stains of each
suspension of each into nutrient broth
add a few drops of bile salts
observe the tubes after 15 mins for lysis of the cells.
Is blood agar selective or differential?
Blood agar is considered differential because it is used to distinguish pathogenic bacteria based on the effect of bacterial enzymes known as hemolysins which lyse red blood cells. Blood agar is mainly used clinically to detect the presence of Streptococcus pyogenes, the human pathogen which causes "strep throat".
Is the Gram stain of significant importance in identifying the organisms studied in this exercise?
no because all streptococci are gram (+) and catalase negative they are differentiated by biochemical characteristics such as hemolysis and Lancefield's characterizations
You have isolated gram-positive cocci from a throat culture that you cannot identify as staphylococci or streptococci. A test for one enzyme can be used to distinguish these bacteria quickly. What is the enzyme?
(using hydrogen peroxide)