control of microbial growth
DESCRIPTION
this is a series of lectures on microbiology for undergraduate medical and paramedical studentsTRANSCRIPT
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Control of Microbial Growth
Dr. Ashish Jawarkar
Pathologist
Parul Sevashram Hospital
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History
Humans vs. Microbes• infections• diseases• plagues• epidemics• pandemics
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Nursery Rhyme
Ring- a - ring of rosies
Pocketful of posies
Achoo ! Achoo !
We all fall down.
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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 Gram (-) rod
2 Vectors• Rat• Flea
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Yersinia pestis - Gram (-) bacillus
Vectors - Rat and Flea
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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
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4. Hemorrhaging occurs in lymph nodes, resulting in “black and blue” swellings or Buboes (hence the name Bubonic Plague or Black Death)
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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)
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Nursery Rhyme
Ring - a - ring of rosies,
A pocketful of posies
Achoo ! Achoo !
We all fall down.
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“ I wouldn’t touch it with a 10’ pole”
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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
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Smallpox
Variola virus
Eradicated in 1977 (Somalia)
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Methods to Control Microbial Growth 1. Physical
2. Chemical
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Terms used: Sterilization vs. Disinfection Sterilization
• destroying all forms of life
Disinfection• destroying pathogens or unwanted organisms
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Disinfectant vs. Antiseptic Disinfectant
• antimicrobial agent used on inanimate objects
Antiseptic• antimicrobial agent used on living tissue
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cidal vs. static
Bactericidal - kills bacteria Bacteristatic - inhibits bacterial growth
Fungicidal Fungistatic Algacidal Algastatic
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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
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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
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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
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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.
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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
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Filtration Removes microorganisms from solutions
that might be damaged by heat
• culture media• enzymes• vaccines• antibiotics
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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
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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
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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.
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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)
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Portals of Entry
1. Mucus Membranes
2. Skin
3. Parentarel
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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
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Common Diseases contracted via the Respiratory Tract
Common cold Flu Tuberculosis Whooping cough Pneumonia Measles Strep Throat Diphtheria
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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
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Common diseases contracted via the G.I. Tract Salmonellosis
• Salmonella sp.
Shigellosis• Shigella sp.
Cholera• Vibrio cholorea
Ulcers• Helicobacter pylori
Botulism• Clostridium botulinum
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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.
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Mucus Membranes of the Genitourinary System - STD’s
Gonorrhea
Neisseria gonorrhoeae
Syphilis
Treponema pallidum
Chlamydia
Chlamydia trachomatis
HIV
Herpes Simplex II
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Mucus Membranes
D. Conjunctiva –• mucus membranes that cover
the eyeball and lines the eyelid
Trachoma• Chlamydia trachomatis
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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
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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
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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
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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