Corynebacterium Diphtheriae Disease

Corynebacterium Diphtheriae Disease

Corynebacterium diphtheriae is a causative agent of diphtheria.It is upper respiratory tract illness and it is a contageous disease.

1. Morphology

  • It is a Gram positive, non-motile, non spore forming bacteria.
  • Corynebacteria is non- capsulated slender rod.
  • It shows club shaped swelling and hence called as Corynebacteria.
  • Its size ranges from 3-6 μm in lenght and 0.6-0.8 μm in width.
  • These cells posses metachromatic granules.
  • Mode of multiplication is by binary fission.

2. Cultural characters

  • Corynebacterium can grow easily on ordinary media.
  • It growth is enhanced by addition of blood or serum in the media.
  • It grows in a temperature range of 15° C-40° C and optimum temperature for its growth is 36° C.
  • Neutral pH is optimum for its growth.
  • Corynebacteria diphtheriae may be aerobic or facultative anaerobic in nature.
  • They are fast growing organism.

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Infection and its Types in Microbiology

Infection and its Types in Microbiology


  • Infection is a condition of host in which parasite lives, multiplies in the host body.
  • Infection normally occurs when a parasite is very active and it suppresses the host defense mechanism.
  • Depending upon the nature of host, parasite and the persistence of the disease the infection is divided into following types.

1. Chronic infection

  • Chronic infection is a long lasting infection.
  • Examples :- Diabetes, Cancer, Sickle cell anemia, Autoimmune diseases etc .

2. Acute infection

  • It is a disease that spreads rapidly in short period of time.
  • Example:- Common cold, Chicken pox, Pneumonia etc.

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Diseases and its Types in Microbiology

Diseases and its Types in Microbiology


  • The disease is an abnormal condition an uneasy state of the body.
  • The human body is constantly exposed to micro-organism sometime these micro-organisms are so active that they enter the host body, multiply and result in a disease.
  • Diseases are mainly of four types as shown below.


1. Epidemic

  • In an epidemic, an infectious disease spreads rapidly and a large population is affected 
  • The outbreak of disease is above the expected level.
  • Epidemic disease is of two types as shown below.

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Basics of Medical Microbiology

Basics of Medical Microbiology

Medical microbiology deals with studying the relationship between host and parasite and understanding the causative agent of disease.

In our daily life, human beings are constantly exposed to micro-organisms.
The interaction between human and micro-organisms may be useful or harmful interaction.
Parasitism can be explained a condition in which microbial population is benefited and the host is harmed.

Some important concepts in medical microbiology

1. Infection

  • In infection, a pathogen enters in a host body, lives and multiply in the host.
  • Generally, infection is caused due to the failure of host defence mechanism.
  • Due to the failure of host defence mechanism the microbial cells leads to infection.

2. Disease

  • The disease is a result of infection
  • When a disease is established the normal functioning of host body is disturbed and this disturbance results in signs and symptoms.
  • These pathogens not only multiply in the host but also releases some byproducts.
  • These byproducts may be toxic or non-toxic to host.

3.   Etiological agent

  • The etiological agent may be the causative agent of a disease
  • It may be an opportunistic pathogen

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Neisseria Gonorrhoeae Disease

Neisseria Gonorrhoeae Disease

Neisseria gonorrhoeae (Gonococci)

Neisseria gonorrhoeae
Neisseria gonorrhoeae

Neisseria gonorrhoeae is a venereal disease

1. Morphological characters

  • They are gram negative,non-sporeforming diplococci with concave adjacent side.
  • It appear like a shape of a kidney.
  • It contains pili that provide adhesion to mucosal surface and inhibit phagocytosis.

2. Cultural characters

  • These gonococci cells grow aerobically as well as anaerobically.
  • These organism can grow on selective media like Chocolate agar, Mueller-Hinton and Thayer Martin medium.
  • The optimum temperature for its growth is 36° C and it reguires a pH range of 7.2 to 7.6.
  • After incubation the colonies appear small, convex and translucent.

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Disease caused by Neisseria meningitidis

 Neisseria meningitidis.


  • It is a gram negative, non-motile cocci arranged in pairs called as diplococci.
  • Neisseria are aerobic, non-sporulating, oxidase positive cocci.
  • Neisseria meningitidis causes cerebrospinal fever that is Meningococcal meningitis.
Neisseria meningitidis
Neisseria meningitidis

1. Morphological characters

  • They are gram negative,spherical shape cocci with flattened adjacent side.
  • Its size ranges from 0.6-0.8 micrometer.
  • Its size,shape and staining properties changes as the incubation period increases.
  • Fresh culture cells are capsulated and as the culture becomes old its capsule disappears.

2. Cultural characters

  • Meningococci requires enriched media for its growth.
  • The growth media should be enriched with blood or serum.
  • Selective media like blood agar, chocolate agar, Mueller-Hinton starch casein agar are commonly used.
  • The optimum temperature required for its growth is 36°C and optimum pH is 7.5-7.6
  • The colonies are small in size bluish grey coloured and convex in elevation.

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Disease caused by Streptococcus pneumoniae

Disease caused by Streptococcus pneumoniae

The Streptococcus pneumoniae is gram-positive lancet shape bacteria. It may be diplococcus or streptococcus. Pneumococcus is non-motile, non-spore forming capsulated bacteria. They may be aerobic or facultative anaerobic in nature. They are a normal inhabitant of human respiratory tract Pneumococcus bacteria may be an important cause of pneumonia, otitis, sinusitis, bronchitis, meningitis and other infection like arthritis, conjunctivitis and suppurative lesions.

Streptococcus pneumoniae
Streptococcus pneumoniae

1. Morphology

  • Pneumococci are lancet shape with one end broad or rounded and other end pointed
  • If they occur in pair called as diplococci.
  • They are smaller than 1 micrometre in size.
  • The capsule enclose each pair of cells. These capsules can be made visible by using capsule staining method.
  • These cells are readily stained by gram staining procedure.

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Medical Microbiology

Medical Microbiology

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
    Staphylococcus aureus

1. Morophology

  • 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  colonies on blood agar showing zone of heamolysis.
Staphylococcus aureus colonies on blood agar showing zone of heamolysis.
  • 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.

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