Although you cannot see them without
a microscope, microscopic
organisms are living inside your nasal and throat passages. While many of
these bacteria are harmless, some can cause illness if they penetrate the
bodies natural defenses.
Some examples of these bacteria are Streptococcus, Neisseria, Haemophilus, and Micrococcus. Some of the pathogenic species include
Staphylococcus aureus,
Corynebacterium diphtheriae, Streptococcus pneumoniae, and Haemophilus influenzae. Before the discovery of antibiotics, many people died from
bacterial infections of the pathogenic strains of Staphylococcus
and Streptococcus. Here is a diagram of
some infections caused by these bacteria: 
Some examples of these bacteria are Streptococcus, Neisseria, Haemophilus, and Micrococcus. Some of the pathogenic species include
Staphylococcus aureus,
Corynebacterium diphtheriae, Streptococcus pneumoniae, and Haemophilus influenzae. Before the discovery of antibiotics, many people died from
bacterial infections of the pathogenic strains of Staphylococcus
and Streptococcus. Here is a diagram of
some infections caused by these bacteria: 
| Characteristics of
Staphylococcus and Micrococcus |
| Gram +
cocci |
| Catalase
+ |
| Aerobic |
| Can grow in high NaCl
environment |
| Pathogenic- S. aureus Nonpathogenic- S. epidermidis |
Two major types of Staphylococcus
Staphylococcus epidermidis -- Non-pathogenic( no pigment)
Staphylococcus aureus -- Pathogenic( yellowish pigment)
Because of of Staphylococcus aureus' pathogenic nature, techniques have been developed to distiguish it from other non-pathogenic gram-positive cocci shaper bacteria based on its tolerance for high slat concentrations and its ability to ferment mannitol, coagulate plasma, liquify gelatin, and produce a yellow pigment. The first step in this process of isolating S. aureus is to innoculate a throat or nasal swab on Blood agar. Staphylococcus aureus will grow as yellowish colonies that produce beta hemolysis.
Image taken from Applications in General Microbiology, A Laboratory Manual; Kerr/McHale; 6th edition;copyright 2003; pg.333
Staph No. 110 is a selective media that utilizes S. aureus' tolerancefor high concentrations and allows for the determination of mannitol fermentation, pigment production, and gelatin liquification. Any colonies that appear yellow or orange on this media should be transfered to brain heart infusion broth to be tested for coagulase activity. If clotting develops, then the organism tested positive for coagulase activity( a good indication that the organism is pathogenic).
To test for mannitol fermentaion, add Brom cresol purple indicator to the area where te colony was picked. Any change in color denotes a positive test result. Finally, flood the plate with saturated ammonium sulfate and incubate it at 37 degrees C for 10 minutes. A zone of clearance around the area where the colonies where picked indicates a positive test result for gelatinase activity.
Image taken from Applications in General Microbiology, A Laboratory Manual; Kerr/McHale; 6th edition;copyright 2003; pg.334
| Characteristics
of Streptococcus |
| Gram + cocci (chain)ci |
| Aerobic |
| Characterized by hemolysis |
| Pathogenic- S. pyogenes Non-pathogenic- S. salivarius, S. lactis |
Because the flora of the throat contain several gram-positive bacteria, some of which are pathogenic and some not, it is important to develop tests to distinguish between the two. One way to distinguish between pathogenic Streptococcus and non-pathogenic Staphylococcus is to view their hemolytic reactions on Blood Agar. Streptococcus found in the throat is characterized by its different hemolysis reactions, or its Lancefield group.
Image taken from Brock Biology of Microorganisms, 9th ed. Madigan/Martinko/Parker. Copyright 2000; pg. 506