Microccus & Staphylococcus
Morphology: Cocci
Gram: Positive
Catalase: Positive
Differences between Micrococcus and Staphylococcus
| Characteristics | Micrococcus spp. | Staphylococcus spp. |
| Respiratory system | Obligate aerobe | Facultative anaerobe |
| Oxidase | Positive | Negative |
| Resistance to vibriostatic agent O/129 | S | R |
| Resistance to lysostaphin | R | S (±R) |
| Resistance to bacitracin | S | R |
| Growth in presence of furazolidone | + | - |
| % GC | 66-75 % | 30-39 % |
Tests to identify pathogenic Staphylococci
- Free coagulase test - Coagulase broth
- Clumping factor - Slidex staph kit
- Deoxyribonuclease (DNAse) test
- Thermostable DNAse test - Lachica medium
- Hemolysis test - Sheep blood agar (5 %)
Cultures
Baird-Parker Agar
Principles:
Enzymatic Digest of Casein and Beef Extract are the carbon and nitrogen sources in Baird Parker Agar. Yeast Extract supplies B-complex vitamins that stimulate bacterial growth. Glycine and Sodium Pyruvate stimulate growth of staphylococci. The selectivity of the medium is due to Lithium Chloride and a 1% Potassium Tellurite Solution, suppressing growth of organisms other than staphylococci. The differentiation of coagulase-positive staphylococci is based on Potassium Tellurite and Egg Yolk Emulsion. Staphylococci that contain lecithinase break down the Egg Yolk and cause clear zones around the colonies. An opaque zone of precipitation may form due to lipase activity. Reduction of Potassium Tellurite is a characteristic of coagulasepositive staphylococci, and causes blackening of colonies. Agar is the solidifying agent.
Results:
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| Staphylococcus aureus on Baird-Parker agar |
Coagulase-positive staphylococci produce black, shiny, convex colonies with entire margins and clear zones. Sometimes, an opaque zone of precipitation may form due to lipase activity around that clear zone. Coagulase-negative staphylococci produce poor or no growth. If growth occurs, colonies are black; clear or opaque zones are rare. The majority of other organisms are inhibited or grow poorly. If growth appears, colonies are light to brown-black, with no clear or opaque zones.
Reference: Neogen [Link]
Baird-Parker RPF (Rabbit Plasma Fibrinogen)
Champan agar
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| Staphylococcus aureus on Chapman agar |
Please, feel free to comment if there is any mistake
lecithinase activity appears as clear zone around a colony not as an opaque zone, since lecithinase breaks down lecithin into insoluble diglycerides ?
ReplyDeleteit's a confusion to me!
Sorry I took so long to get back to you. I had almost forgotten I wrote this blog a couple years ago to help me study that thing. I must say it is confused the way I wrote it. I was referring to the darker area you can see on the picture which may form due to lipase activity.
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