BACTERIOLOGY

Manu Aravind

STAPHYLOCOCCUS

Staphylococcus is a genus of Gram-positive bacteria. Under the microscope, they appear round (cocci),non motile arranged in groups and form in grape-like clusters. Staphylococcus can cause a wide variety of diseases in humans and animals through either toxin production or penetration. Staphylococcal toxins are a common cause of food poisoning.

CLASSIFICATION

On the basis of pigment production mainly 3 types.

Staphylococcus aureus ( produces golden yellow colonies)

Staphylococcus albus ( produces white colonies )

Staphylococcus citerus ( produces lemon yellow colonies )

CLASSIFICATION

On the basis of pathogenecity

Pathogenic species - Staphylococcus aureus

Non pathogenic species – Staphylococcus epidermidis

RESISTANCE :

It is the more resistant among non-sporing organisms.

It withstands 600C for 30 min It resist 1% phenol for 15 min Mercury perchloride (1%) kills it in 10

min Crystal violet and brilliant green are

lethal for it Staphylococci are resistant to penicillin.

 STREPTOCOCCUS

They are gram positive cocci arranged in chains , non motile and non sporing. The require media enriched with blood , serum or ascetic fluid for their growth. They are important human pathogens causing pathogenic infection with a characteristic tendency to spread.

CLASSIFICATION

Morphological

classification

Long chains – Pathogenic

Short chains - Non pathogenic

Based on cultural

character

Anaerobe

Aerobes

CLASSIFICATION

Aerobes – the aerobic streptococci are further classified on the basis of haemolytic property on blood agar plates.

Alpha haemolytic - produces a zone of greenish discoloration around the colony.

Beta haemolytic – produces sharply defined , clear , colourless zone of haemolysis.

RESISTANCE :

o it is easily destroyed by heat @ 560 C for 80 min.

It can survive in dust for several weeks if protected from sunlight

It is resistant to crystal violet.

PNEUMOCOCCUS

They are gram positive diplococcic and are capsulated. Pneumococci primary occur in human throat and are the most common cause of pneumonia. They require enriched medium with blood , serum or ascetic fluid for their growth.

MORPHOLOGY

It is typically small and slightly elongated with one end broad and other end pointed (flame shaped ). It occurs in pairs. It is capsulated , capsules enclosing both pair. It is non motile and non sporing.

RESISTANCE :

It is readily destroyed by heat 520C for 15 min., in 1 hr by phenol , potassium permanganate and other antiseptics.

CULTURAL CHARACTERISTICS

It requires serum or whole blood for growth. It grows best at 370C and at PH7.6. it is aerobic. growth is improved by providing them 5 to 10% CO2.

BACILLUS

They are rode shaped sporogenous. classified into two groups.

Aerobic bacillus Anerobic basillus

Aerobic bacillus They are gram positive , non motile ,

spore bearing bacillus occurring in chains.

Eg. Bacillus anthrax

BACILLUS ANTHRAX

It is non motile , non acid fast , gram positive bacilli. They may be arranged singly or in short chains. The entire chain may be surrounded by capsule. Spores are formed in soil only in presence of oxygen and not in animal body. It remains in parasitic form in cattle and sheep. Infection in man is the result of accidental contact with the infected animals.

CULTURAL CHARACTERISTICS

It is aerobic growing at optimum temperature of 370C. The optimum temperature for spore formation is 25- 300C. growth may occur in ordinary medium.

RESISTANCE

Vegetative form is killed within 30 min @ 560C. Anthrax spores remains viable for years in dry state. Dry heat @400C requires 3 hrs and steam5-20 min for sterilization. They survive in 5% phenol for weeks. They are killed in 4% potassium permanganate and destroyed in 2% formaldehyde, they are susceptible to penicillin , sulphonamide , erythromycin , streptomycin , tetracycline and chloramphenicol.

Route of infection in man.

There are mainly 3 routes of infection.

Through skin Pulmonary anthrax Intestinal anthrax

CLOSTRIDIUM

They are gram positive , anaerobic , spore forming , spindle shaped highly pleomorphic bacilli. Spores are wider than the bacillary body. The genus containing bacteria will cause diseases mainly like tetanus, food poisoning etc.

Cultural characteristics.

It is an anaerobe and grows only in absence of oxygen. The optimum temperature required is 370C and pH 7.4. it grows fairly well in ordinary media

RESISTANCE

Spores of clostridium tetani withstand boiling for 15-90 min. autoclaving @1210C for 20 min kills spores.. spores otherwise can survive in soil for yrs. Iodine (1% aqueous solution) and H2O2 kills spores within a few min.