Bacterial Pathogenicity Factors – Bacteriology – Medical Microbiology

Infection by a pathogen depends upon some factors :
(a) Tissues Preference: Some pathogens prefer particular tissues of the host body as site of infection. For example malarial parasites prefer human blood cells at certain stage of their life cycle. Some pathogens prefer lungs tissue, others prefer kidney, intestine, skin etc.

(b) Hypersensitivity: Some organs or tissues become highly sensitive to infection.

(c) Virulence: Some germs have mild infectivity and in case of some others the infectivity is very high. They spread rapidly in our body and cause serious illness.

(d) Infective dosage: Pathogenicity depends upon the amount of. germs entering Into our body. When a heavy dose of pathogen enters in our body due to long exposure to a particular type of germ the chance of development of the diseases is higher than in case of one in which only a few germs have entered.

(e) Point of entry: Germ may enter into our body through different organs but specific disease will develop only vhen the specific germs enter through specific organ. For example, the organisms causing cholera, dysentery, typhoid etc. must enter through alimentary canal and in case of tuberculosis, pneumonia etc. the pathogens must enter through respiratory passage.

(f) Resistance of the body to infection: A healthy body can resist the invading pathogens which are not too virulent. Exposure of our body to extreme. environment weaken our systems which facilitate invading germs to establish quickly.
(g) Immunity: Natural defence mechanism play important role in preventing development of diseases.This aspect has been discussed earlier.

(h) Communicability: Pathogens which can escape easily and survive outside the body of the host for longer period have more chance of coming in contact with susceptible host. For example, the pathogens of typhoid, cholera etc. escape through the faecal matter, the pathogens of tuberculosis escape easily through sputum. These pathogens can survive for long time in the faecal matters, sputum etc. .

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