Page 107 - MNU microbiology theoritical 2025

General Microbiology & Immunology (PM 401) Second level Semester 4 2024/2025

6. Urination: flushes microbes outside the urethra

7. Tears: The flushing action of tears helps prevent infection of the eyes

B. Chemical barrier

1. Low pH inhibits microbial growth

●Skin- pH 5.5 ●Gastric acid- pH 1-3 ●Vagina pH 4.4

2. Lysozyme enzyme that degrades peptidoglycan, is found in tears, saliva, and in

mucus, is also found within the body, in phagocytic cells, blood

3. Sebum secreted by sebaceous glands: unsaturated fatty acid provides a

protective film on the skin and inhibits microbial growth

C. Biological barrier (Normal microbiota)

• Normal microbiota help protect the body by

competing with potential pathogens

• Various activities of normal microbiota make it hard

for pathogens to compete

– Consumption of nutrients makes them unavailable to

pathogens

– Create an environment unfavorable to other microorganisms by changing pH

Second Line of Defense of innate immunity

General Microbiology & Immunology (PM 401) theoretical handbook Page 96