this is a series of lectures on microbiology for undergraduate medical and paramedical students

1. Control of Microbial Growth
Dr. Ashish Jawarkar
Pathologist
Parul Sevashram Hospital

2. History
Humans vs. Microbes
•
•
•
•
•
infections
diseases
plagues
epidemics
pandemics

3. Nursery Rhyme
Ring- a - ring of rosies
Pocketful of posies
Achoo ! Achoo !
We all fall down.

4. Bubonic Plague or the Black Death
Epidemic swept thru Europe in the Middle
Ages (13th and 14th centuries)
40 million people were killed
• About 1/3 of the population of the continent
Etiological agent:
• Yersinia pestis
2 Vectors
• Rat
• Flea
Gram (-) rod

5. Yersinia pestis - Gram (-) bacillus
Vectors - Rat and Flea

6. Bubonic Plague Infection
1. Flea bite with Yersinia pestis
2. Bacteria multiply in the bloodstream
• Bacteremia
3. Bacteria localize in lymph nodes,
especially axillary and groin areas

7. 4. Hemorrhaging occurs in lymph nodes, resulting in
“black and blue” swellings or Buboes (hence the name
Bubonic Plague or Black Death)

8. Bubonic Plague Infection
5. If untreated, about 50 % Mortality Rate
6. If bacteria spread to the lungs, it becomes
Pneumonic Plague and is now highly
contagious (Almost a 99 % Mortality Rate)

9. Nursery Rhyme
Ring - a - ring of rosies,
A pocketful of posies
Achoo ! Achoo !
We all fall down.

10. “ I wouldn’t touch it with a 10’ pole”

11. Humans vs. Microbes
1. Most of History, microbes have been
winning the battle
2. In the last 100 yrs or so the battle has
swung in our favor
• Why?
• Because of our increasing knowledge of how to
Control Microbial Growth

12. Smallpox
Variola virus
Eradicated in 1977 (Somalia)

13. Methods to Control Microbial
Growth
1. Physical
2. Chemical

14. Terms used:
Sterilization vs. Disinfection
Sterilization
• destroying all forms of life
Disinfection
• destroying pathogens or unwanted organisms

15. Disinfectant vs. Antiseptic
Disinfectant
• antimicrobial agent used on inanimate objects
Antiseptic
• antimicrobial agent used on living tissue

16. cidal
vs. static
Bactericidal - kills bacteria
Bacteristatic - inhibits bacterial growth
Fungicidal
Fungistatic
Algacidal
Algastatic

17. Factors that effect Antimicrobial
Activity
1. Temp
2. Time
3. Concentration of Antimicrobial agent
4. Type of Microbe
5. Activity of Microbe
6. Presence of organic matter

18. Physical Methods of Microbial Control
1. Heat
• works by denaturing enzymes and proteins
A. Thermal Death Point (TDP)
• lowest temp. at which all microorganism in a
liquid culture are killed in 10 minutes
B. Thermal Death Time (TDT)
• minimum length of time in which all
microorganisms in a liquid culture are killed at
a given temperature

19. Moist Heat
1. Boiling Water
• kills vegetative bacterial cells, Fungi and many
viruses
• not effective for endospores and some viruses
• Hepititis (20 min)
• Some spores may survive boiling water for up
to 20 hrs

20. Moist Heat
2. Autoclave (Steam under pressure)
• preferred method of sterilization
• Water boils at 100 C
• Increasing the pressure raises the Temp.
• 15 lbs./ per sq. inch (psi) ------> 121 C
•
121 C for 15 min.

21. Dry Heat
1. Direct Flaming
• Inoculating Loop and Needle 100% effective
2. Incineration
• disposable wastes (paper cups, bags, dressings)
3. Hot Air Sterilization
• Oven ( 170 C for 2 hours)
• used on substances that would be damaged by
moist heat sterilization
• gauzes, dressings or powders

22. Filtration
Removes microorganisms from solutions
that might be damaged by heat
•
•
•
•
culture media
enzymes
vaccines
antibiotics

23. Radiation
1. Ionizing Radiation
• gamma rays & x-rays
• penetrates most substances
Used on substances that could be damaged
by heat
•
•
•
•
plastic petri dishes
plastic syringes
catheters
surgical gloves

24. Radiation
2. Non-Ionizing Radiation
• UV Light
• does not penetrate plastic, glass or proteinaceous
matter
Used to reduce microbial populations
• hospital rooms
• nurseries
• operating rooms
Thymine Dimers

25. Pasteurization
Disinfection - not sterilization (removes
unwanted organisms)
Mycobacterium tuberculosis
63 C for 30 minutes
72 C for 15 seconds (HTST)
Thermodurics
• able to survive high temps.

26. Methods used to control Microbial Growth
1. Heat
• Moist Heat
• Boiling Water
• Steam Heat (Autoclave)
• Dry Heat
• Direct Flaming
• Incineration
• Hot Air Sterilization (Oven)
2. Filtration
3. Radiation
• Ionizing Radiation
• Non-Ionizing Radiation
4. Pasteurization (Heat)

27. Portals of Entry
1. Mucus Membranes
2. Skin
3. Parentarel

28. 1. Mucus Membranes
A. Respiratory Tract
• microbes inhaled into
mouth or nose in
droplets of moisture or
dust particles
• Easiest and most
frequently traveled
portal of entry

29. Common Diseases contracted via
the Respiratory Tract
Common cold
Flu
Tuberculosis
Whooping cough
Pneumonia
Measles
Strep Throat
Diphtheria

30. Mucus Membranes
B. Gastrointestinal Tract
• microbes gain entrance thru
contaminated food & water
or fingers & hands
• most microbes that enter the
G.I. Tract are destroyed by
HCL & enzymes of stomach
or bile & enzymes of small
intestine

31. Common diseases contracted via
the G.I. Tract
Salmonellosis
• Salmonella sp.
Shigellosis
• Shigella sp.
Cholera
• Vibrio cholorea
Ulcers
• Helicobacter pylori
Botulism
• Clostridium botulinum

32. Fecal - Oral Diseases
These pathogens enter the G.I. Tract at one
end and exit at the other end.
Spread by contaminated hands & fingers or
contaminated food & water
Poor personal hygiene.

33. Mucus Membranes of the Genitourinary System - STD’s
Gonorrhea
Neisseria gonorrhoeae
Syphilis
Treponema pallidum
Chlamydia
Chlamydia trachomatis
HIV
Herpes Simplex II

34. Mucus Membranes
D. Conjunctiva –
•
mucus membranes that cover
the eyeball and lines the eyelid
Trachoma
• Chlamydia trachomatis

35. 2nd Portal of Entry: Skin
Skin - the largest organ of the body. When
unbroken is an effective barrier for most
microorganisms.
Some microbes can gain entrance thru
openings in the skin: hair follicles and
sweat glands

36. 3rd Portal of Entry: Parentarel
Microorganisms are deposited into the
tissues below the skin or mucus membranes
Punctures
injections
bites
scratches
surgery
splitting of skin due to swelling or dryness

37. Preferred Portal of Entry
Just because a pathogen enters your body it
does not mean it’s going to cause disease.
pathogens - preferred portal of entry

38. Preferred Portal of Entry
Streptococcus pneumoniae
• if inhaled can cause pneumonia
• if enters the G.I. Tract, no disease
Salmonella typhi
• if enters the G.I. Tract can cause Typhoid Fever
• if on skin, no disease