The Control of Microbial Growth

Physical and Chemical Control of Microbes Chapter 7 2

to destroy or reduce microbes Control of microbes Physical and chemical methods to destroy or reduce microbes in a given area 3

4

STERILIZATION All killed non-selective Microbial death Involves permanent loss of reproductive capability, even under optimum growth conditions 5 5 5

Mode of action of Microbial control agents Alteration of membrane permeability ( lipid & proteins) Damage to proteins and Nucleic acids (cellular proteins & DNA replication) 6

Physical Methods of Control Heat Filtration Radiation

Physical Methods of Control HEAT Mode of action: Denaturing proteins. 8

HEAT Mode of action: Denaturing proteins Moist heat Dry heat Denaturation of proteins Oxidation or coagulation of proteins Flaming Boiling = 100C Pasteurization less than 100C Hot air oven Autoclaving more than 100C

Physical Methods of Control HEAT Moist heat (Kills by denaturation of proteins) = boiling = pasteurization = autoclaving (Steam under pressure) Dry heat = flaming = hot air oven

Pasteurization Eliminate pathogenic microbes Lowering microbial count and prolong shelf life. without altering the flavor (HTST) High temperature at short time 140 oC for 3 second (dairy products) store several month without refrigeration 63  C for 30 minutes ordinary 72  C for 15sec HTST UHT Ultra high temperature, 11

Steam under pressure Autoclaving The higher the pressure the higher the temperature15 min at 121 C at 15 psi 12

Dry heat using higher temperatures than moist heat, can also sterilize Flaming ( oxidation) Dry ovens – 150-180oC- 2 hours (coagulate proteins & oxidation) 13

Using Heat to Control Microbes 14

Filtration Is the passage of liquid or gas through filters with pores small enough to retain bacteria Membrane filters 15

Membrane filters pores bacteria 16 16 16 16

Radiation Effect on cells varies according to its wavelength, duration and intensity. Ionizing and non ionizing radiation. Ionizing radiation: Gamma rays: x-rays & high –energy electron beams = has a high degree of penetration used to sterilize medical supplies & food products Non-ionizing radiation - little penetrating power to sterilize air, water & solid surfaces UV light which interfere with DNA replication 17

RADIATION EFFECT Oxidation of DNA effect of ionizing radiation Interferes with DNA replication 18

19

Chemical control Chemical agents that used on living tissues as antiseptics And on non living objects as disinfectants Halogens Phenolics Chlorhexidine Alcohols Hydrogen peroxide Detergents & soaps Heavy metals Aldehydes 20

21

22