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Microbiology lab exercise 46- Bacteria of the respiratory tract

front 1

The respiratory tract can be divided into 2 systems name them.

back 1

upper and lower respiratory tracts

front 2

The upper respiratory tract consists of:

back 2

the nose and throat

front 3

The lower respiratory consists of:

back 3

larynx, trachea, bronchial tubes and alveoli.

front 4

The lower respiratory system is usually sterile because of the efficient functioning of the _____ ________.

back 4

ciliary escalator

front 5

The upper respiratory tract is in contact with ___________ - air _________________.

back 5

the air we breathe
air contaminated with microorganisms

front 6

The ______ is moist, warm environment allowing many ________ to establish residence.

back 6

throat
bacteria

front 7

Species of many different genera can be found residing in the throat: name them

back 7

Staphylococcus, Streptococcus, Neisseria, Haemophilus

front 8

Despite the presence of potentially pathogenic bacteria in the URS the rate of infection is minimized by ______________.

back 8

microbial antagonism

front 9

What is microbial antagonism?

back 9

Certain microorganisms of normal microbiota suppress the growth of other microorganisms through competition for nutrients and production of inhibitory substances.

front 10

_________ are predominant organisms in the throat cultures and some species are the major cause of bacterial sore throat (acute pharyngitis).

back 10

Streptococcal species

front 11

Streptococci are ___________ and catalase _________.

back 11

gram (+)
negative

front 12

Streptococcal species are identified by _______
characteristics including ________, and __________
characteristics.

back 12

biochemical
hemolytic reactions
antigenic characteristics

front 13

Hemolytic reactions are based on ___________ that are produced by streptococci while growing on blood- enriched agar.

back 13

hemolysins

front 14

Blood agar is usually made from ________.

back 14

defibrinated sheep blood (5.%), sodium chloride (0.5%)to minimize spontaneous hemolysis and nutrient agar

front 15

Three patterns of hemolysis can occur on blood agar:

back 15

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.

front 16

_____ and _____ streptococci are usually _________.

back 16

Alpha-hemolytic and gamma-hemolytic streptococci
normal microbiota

front 17

_________ streptococci are usually pathogenic.

back 17

beta-hemolytic

front 18

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?

back 18

using optochin inhibition with an optochin disk.

front 19

With optochin inhibition a zone of inhibition = to or > than ______ or larger indicated optochin sensitivity.

back 19

15mm

front 20

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.

back 20

the cell walls and the cells lyse

front 21

The streptococci can be antigenically classified into Lancefield's groups A through O by ________ in their cell walls.

back 21

antigens

front 22

Over 90% of streptococcal infections are caused by _________ group ______ ______.

back 22

beta-hemolytic
A streptococci

front 23

Beta-hemolytic group A streptococci are assigned to the species ______ _______.

back 23

S. pyogenes

front 24

S. pyogenes is sensitive to the antibiotic _______; other streptococci are resistant to _______.

back 24

bacitracin
bacitracin

front 25

Procedure for throat culture:

back 25

-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

front 26

Procedure for streptococcus:

back 26

-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.

front 27

Is blood agar selective or differential?

back 27

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".

front 28

Is the Gram stain of significant importance in identifying the organisms studied in this exercise?

back 28

no because all streptococci are gram (+) and catalase negative they are differentiated by biochemical characteristics such as hemolysis and Lancefield's characterizations

front 29

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?

back 29

catalase
(using hydrogen peroxide)