Control of Microbial Growth

Dr. Ashish Jawarkar

Pathologist

Parul Sevashram Hospital

History

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

Nursery Rhyme

Ring- a - ring of rosies

Pocketful of posies

Achoo ! Achoo !

We all fall down.

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

Yersinia pestis - Gram (-) bacillus

Vectors - Rat and Flea

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

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

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)

Nursery Rhyme

Ring - a - ring of rosies,

A pocketful of posies

Achoo ! Achoo !

We all fall down.

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

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

Smallpox

Variola virus

Eradicated in 1977 (Somalia)

Methods to Control Microbial Growth 1. Physical

2. Chemical

Terms used: Sterilization vs. Disinfection Sterilization

• destroying all forms of life

Disinfection• destroying pathogens or unwanted organisms

Disinfectant vs. Antiseptic Disinfectant

• antimicrobial agent used on inanimate objects

Antiseptic• antimicrobial agent used on living tissue

cidal vs. static

Bactericidal - kills bacteria Bacteristatic - inhibits bacterial growth

Fungicidal Fungistatic Algacidal Algastatic

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

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

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

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.

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

Filtration Removes microorganisms from solutions

that might be damaged by heat

• culture media• enzymes• vaccines• antibiotics

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

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

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.

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)

Portals of Entry

1. Mucus Membranes

2. Skin

3. Parentarel

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

Common Diseases contracted via the Respiratory Tract

Common cold Flu Tuberculosis Whooping cough Pneumonia Measles Strep Throat Diphtheria

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

Common diseases contracted via the G.I. Tract Salmonellosis

• Salmonella sp.

Shigellosis• Shigella sp.

Cholera• Vibrio cholorea

Ulcers• Helicobacter pylori

Botulism• Clostridium botulinum

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.

Mucus Membranes of the Genitourinary System - STD’s

Gonorrhea

Neisseria gonorrhoeae

Syphilis

Treponema pallidum

Chlamydia

Chlamydia trachomatis

HIV

Herpes Simplex II

Mucus Membranes

D. Conjunctiva –• mucus membranes that cover

the eyeball and lines the eyelid

Trachoma• Chlamydia trachomatis

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

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

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

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