BMSC207 Lecture Notes - Lecture 7: Cytokine, Deoxyribonuclease, Hyaluronidase
Bacteriology
-
gram positive
Objectives:
Clinically important gram
-
positive cocci and bacilli
•
Microbiological characteristics
•
Associated diseases
•
Laboratory detection•
Staph○
Strep○
Listeria
Enterococcus○
Corynebacterium○
bacillus○
Important bacteria:•
Gram stains for gram positive bacteria:
Summary of biochemical tests to distinguish bacteria:
•
Catalase test:
Identify organisms that produce the enzyme, catalase
•
○
Catalase detoxifies hydrogen peroxide by breaking it down into water and oxygen
•
The bubbles resulting from the production of oxygen gas indicates a catalase positive
•
Staphylococcus spp. and the Micrococcus spp. are catal ase positive
○
Streptococcus and Enterococcus spp. are catalase negative
○
The sample on the right shows a catalse positive test
•
Coagulase test:
Coagulase is an enzyme that clots blood plasma
•
Test is performed on catalase positive (gram +) species to distinguish coagul ase positive
Staphylococcus aureus
•
Coagulase is a
virulence factor
of Staph. Aureus
•
The formation of clot around an infection caused by this bacterium protects it from
phagocytosi s by the immune system
•
This test differentiates Staphylococcus aureus from other coagulase negative
species
•
Motility test:
Capable of swimming away from a stab mark
○
Differential medium is used to determine whether an organism is equipped with flagella
•
The results of motility agar are often difficult to interpret
•
Are motile
○
Generally, if the entire tube is turbid, this indicates bacteria have moved away from the
mark
•
The one of the left is somewhat clear
○
The organi sms in the two tubes pictured on the right are motile (turbid)
•
Where the stab mark is clearly visible and the rest of the tube is not turbid (non
-
motile
organism suspected)
•
Mannitol salt agar:
This medium both selective and differential•
E.g. Staphylococcus species plate on the left in the picture below
○
MSA will select for organisms which can live in areas of high salt concentration
•
In contrast, Streptococcus species, whose growth is selected against by this high salt
(plate on the right in the picture below) do not grow
•
The differential ingredient in MSA is the sugar mannitol
•
Bacteria capable of using mannitol will produce aci dic by
-
products from fermentation
lower pH) and cause the pH indicator, phenol red, to turn yellow
•
taphylococcus aureus is capable of fermenting mannitol (left side of left plate) while
Staphylococcus epidermidis is not (right side of left plate)
•
Blood agar plate (BAP) - test for haemolytic activity:
BAP are a complex differential medium that contains 5% sheep RBC
•
BAP tests the ability of bacteria to produce haemolysins, enzymes that damage/lyse RBC
•
The degree of haemolysis by these haemolysins helps to differentiate members of the
genera Staphylococcus, Streptococcus and Enterococcus
•
β
-
haemolysis is complete haemolysi s:
•
Lecture 4
-
22/8/16
Monday, 22 August 2016
9:56 AM
Lectures Page 1
Document Summary
Catalase detoxifies hydrogen peroxide by breaki ng it down into water and oxygen. The bubbles resulting from the production of oxygen gas indi cates a catalase positive. The sample on the right shows a catal se positive test. Staphylococcus spp. and the micrococcus spp. are catal ase positive. Coagulase is an enzyme that clots blood plasma. Test is performed on catal ase positive (gram +) species to distinguish coagul ase positive. The formation of clot around an infection caused by this bacterium protects it from phagocytosis by the immune system. This test differentiates staphylococcus aureus from other coagulase negative species. Differential medium is used to determine whether an organism is equipped with flagell a. Capable of swimming away from a stab mark. The results of motility agar are often difficult to interpret. Generally, if the entire tube is turbid, this indicates bacteria have moved away from the mark.
