Medical microbiology is a branch of science that deals with the study of of pathogenic micro-organisms and is concern with disease, diagnosis ,prevention, control and treatment.
Diseases caused by micro-organisms
- Staphylococcus aureus
- Staphylococcus aureus are gram-positive spherical cocci approximately 1 micrometer in diameter.These cells may be arranged in singly,in pairs,shorts chains or in clusters.
- They are non-spore forming, non-motile.They may be capsulated or non-capsulated.
- Under influence of some chemicals the cocci form may change into L-forms.
2. Cultural characters
- Staphylococcus aureus may readily grow in ordinary media.It can grow on Nutrient agar, MacConkey’s agar.
- It grow on temperature range of 10° C to 42° C and optimum temperature for its growth is 37° C
- Optimum pH is 7.3-7.6.
- They may be aerobic or facultative anaerobic in nature.
- The colonies are 2-4 mm in diameter,circular in shapes ,convex and shiny .
- These organisms are golden yellow pigment producing organism.These pigment production occurs in aerobic cultures at optimum pH at 22°C.
- Most of the strains of Staphylococcus aureus show heamolytic activity on blood agar.
- The Staphylococcus aureus show pink coloured colony due to lactose fermentation on MacConkey’s agar.
3. Biochemical characters
- Staphylococcus aureus is able to ferment number of sugars by producing acid but no gas.
- Fermentation of mannitol is useful character for diagnosis of Staphylococcus aureus it produces acid and no gas in mannitol sugar fermentation.
- This organism shows catalase, urea hydrolysis, gelatin liquification,MR and VP, phosphatase and co-agulase test positive.
- It can reduce nitrates to nitrites.
- It shows indole test negative.
- Most of the Staphylococcus strains are lipolytic in nature.
- Staphylococcus is a non-spore forming resistant bacteria with a viability of 3-6 months.
- It can be isolated from dried pus.
- It is a heat resistant bacterial and can grow at temperature of about 44°C to 45° C .
- It can also tolerate high salt concentration up to 10% to 15% of NaCl.
- Staphylococcus can get inhibited with 1% phenol for 15 minutes and 1 % mercuric perichloride for 10 minutes.
- Staphylococcus is penicillin resistant bacteria.
- It can be inhibited at temperature of about 80° C for one hour.
5. Pathogenecity and virulence
- Diseases produced by Staphylococcus are of two types that are infection and intoxication.
- In infection the Staphylococci get attach to damage skin or tissue and multiply and after multiplication it overcome the host defense mechanism and cause tissue damage.
- In intoxication the disease occurs by toxin production by organism or by host.
6. Staphylococcus disease
- It is the most common bacterial infection.
- Common Staphylococcus infections.
- Respiratory infection.
- Skin and soft tissue infection.
- Central nervous system infection.
- Musculosketal and urinary tract infection.
7. Laboratory diagnosis
- The sample is collected from the infected area of skin, pus from lesion, sputum sample form respiratory infection.
- In case of food poisoning suspected food sample is collected.
- Gram nature and motility is observed.
- The organism is plated on blood agar and observed for heamolysis.
- Staphylococcus are inoculated on selective media like Robertson’s cooked medium.
- Co-agulase test is carried out as it is co-agulase positive.
- Antibiotic sensitivity test should be carried out for proper treatment.
- Staphylococcus is resistant to some antibiotic so antibiotic sensitivity test should be performed and appropriate antibiotic should be choosen.
- If the strain are sensitive to benzyl than penicillin is the most effective antibiotic.
- Vancomycin is effective drug in dangerous infection.