Question

1. Which microbial growth control methods (physical and chemical) kill by these mechanisms?

Denaturation of proteins	Damage to nucleic acids	Damage to cell membrane

Answer 1

Microbial Growth

Microbial organisams are responsible for causing life threatening infections.They cause various type of diseases and contamination of materials. Inorder to prevent these infection, reduce death and prevent spoiling of food and other materials it became important to find ways to control these microbial organisams.

Growth control: can be by means of  killing, denaturing or reducing number to a certain extent that they will be no longer able to cause disease. Bacteria as well as their spores have to be eliminated to achieve a complete growth control.

Sterilization	Living microbes as well as spored are destroyed
Disinfection	Destroying living microbes not necesserly the spores
Sanitizaton	Reducing the number of microbes to a low level they are incapable of causing any damage
Antisepsis	Those applied to living tissues.
Bacteriostatic	Agent inhibiting growth of bacteria

Principles of growth control

• Denaturation of protein : Changing the 3D structure of protein
• Damage to nucleic acid
• Damage to cell membrane
• Coagulation of protein : Changing the state of protein.
• Inhibition of metabolisam

Methods used

1. Physical
2. Chemical

Physical Method killing microorganisam by Denaturation of protein are

1. Temperature : Organisam needs an optimal temerature for their growth and reproduction, increase in temperature can cause cidal effect hence heating used to control micro organisams. Methods using denaturation of protein as working principle are

i)Moist Heat :

• able to penetrate the cell ,
• most effective method
• Two methods employed are autoclave and boiling

Method	Temperature	Efficiency
Autoclaving	1210c , 15 psi pressure 30minutes	Kills organisams as well as spores
Boiling	boiling water at 1000C 10 minutes to 30 minutes	Kills live organisam not necessarly the spores
Pasteurization	Flash method : 71.60c for 15 s Holding method 62.90C for 30 min	Used to kill pathogen or increase the shelf life of milk

ii)Dry Heat : causes denaturation of protein and alteration in cell membrane.

Method	Temperature	Efficiency
Hot air oven	1700 C for 2 hours	Kills microorganisam and spore

iii) Pressure

iv) Radiation: Three types of radiation used to kill microbes, they causes distruction of nucleic acid or mutation in the genetic material. Disadvatages of using radiation are they can be harmful for humans.

• Ionising radiation
• Ultraviolet radiation
• Microwave radiation

Chemical Method

Disinfectans

• Causes the lysis of plasma membrane and denaturation of protein

Compounds	Function	Efficiency
Phenol	once used widely to clean hospitals not commonly used now because it can cause irritation	Kills microbes not necesserly spores
Alcohol	Used on intact skin for disinfection before and after any procedure.	Kills microbes not necesserly spores
Aldehyde	used for disinfection of medical equipments Less irritation	Kills microbes
Halogens	used as disinfectant and also in purification of water	intermediate efficiency