7th Lab

CHEMICAL AND PHYSICAL EFFECTS ON

BACTERIAL GROWTH

• Phenol

• Halogens (Chlorine, iodine, bromine)

• Alcohols (e.g.. isopropyl alcohol)

• Heavy metals (Ag, Hg, Cu, Zn)

• Surface active agents (soaps & detergents)

• Quaternary Ammonium Cmpds(quats)

• Aldehydes (e.g.. glutaraldehyde)

• Heat: Moist vs. Dry

• Autoclaving, pasteurization

• Filtration

• Cold

• Desiccation & high osmotic

pressure

• Radiation (UV, gamma rays)

WHAT FACTORS LIMIT MICROBIAL GROWTH

Physical Control Methods Chemical Control Methods

Factors that influence effectiveness

Number of microbes

Conc.and kind of agents used

Time exposure

Microbial characteristics

METHODS OF CONTROL

ChemicalAntimicrobial agents

Chemical depends on circumstances and degree of control

require

PhysicalHeat (Temperature)

Radiation

Filtration

PHYSICAL CONTROLS:

HEAT

Dry Heat Sterilization kills by oxidation

Dry Heat Sterilization Kills by oxidation

Flaming

Incineration

Hot-air sterilization

Dry Heat

• Moist heat

denatures

proteins

• Autoclave:

Steam under

pressure

• 15 min at 121oC

at 15 psi

AUTOCLAVING PHYSICAL CONTROLS

Escherichia colisubtilisBacillusTemperature

60 mins30 mins60 mins30 mins

5C

RT

37 C

55 C

70 C

90C

PASTEURIZATIONPHYSICAL CONTROLS

63oC for 30 minutes

72oC for 15 seconds

140oC for 1 second

Pasteurization reduces spoilage organisms and pathogens

http://www.mun.ca/biology/scarr/Thymine-

Thymine_Dimers.html

Radiation UV Physical Controls

RadiationPhysical Controls

Ionizing radiation (X rays, gamma rays, electron

beams)

• Ionizing water and other molecules to form

radicals that disrupts proteins and DNA

• surgical supplies, plastic syringes

Nonionizing radiation UV

DNA damage (260 nm Thymine dimers)

Time

1 second

5 second

10 second

30 second

45 second

50 second

60 second

Led on

• Micrococcus luteus

RADIATION

DesiccationVery variable effect on microbes, many can survive extended times (months), some endospore for centuries, others die in minutesUsed usually for hospital & nursing home microbiology, Osmotic PressureHigh salt or sugar content (hypertonic conditions)

Other Physical Controls

15% NaCl10%NaCl5%NaCl

Salt

concentration

Figure : The growth of Escherichia coli and Staphylococcus aureus in Nacl concentrations of 5%,10%,15% respectively

Filtration

For heat sensitive solutions/liquids

Cellulose esters or plastic polymers (pore

size from 0.01-0.45 µm)

Used for :

Culture media

Laboratory reagents

Pharmaceutical products

Culture mediaLaboratory reagentsPharmaceutical

products