Physical methods to control microbial growth (part2)

 

Physical methods to control microbial growth (part2)

Physical methods to control microbial growth (part2)

3: Dry heat

It Kills by oxidation effects.

Direct Flaming:

Direct flaming is used to sterilize needles and inoculating loops. Heat the metal till it has a red glow.

Hot Air Sterilization:

Put the objects in an oven. Two hours at 170oC for sterilization are required. Dry heat is transfers heat less effectively than moist heat, to a cool body.

4: Filtration

 Microbes’ removal by passing the liquid or gas through a screen like material which contain small pores. Filtration is used to sterilize heat sensitive materials like antibiotics, vaccines, enzymes, and some culture media.

High Efficiency Particulate Air Filters (HEPA):

It is used in operating rooms and burn units to get rid of bacteria from air.

Membrane Filters:

They have uniform pore size. They are used in industry and research. Different sizes are present:

0.22 and 0.45um Pores:

These are used to filter majority of bacteria. They don’t retain mycoplasmas, spirochetes, and viruses.

0.01 um Pores: Retain some large proteins and all viruses.

5: Low temperature

Effect depends on microorganism and treatment applied.

Refrigeration:

Temperatures from 0 to 7 oC. Bacteriostatic effect. Slow down metabolic rate of most microorganisms so they cannot reproduce or produce toxins.

Freezing: Temperatures below 0oC.

Slow Freezing: it is more harmful because cell structure is disrupted by ice crystals disrupt. Over a third of vegetative bacteria may remain alive for 1 year. Majority of parasites are killed by a few days of freezing.

6: Desiccation

Microbes cannot grow or reproduce in the absence of water, but some can remain viable for years. They start growing again when water becomes available. Susceptibility to desiccation differ widely:

Neisseria gonorrhea: remain alive for only about one hour.

Mycobacterium tuberculosis: can survive several months.

Viruses are resistant to desiccation to some extend. Clostridium spp. and Bacillus spp. may remain alive for decades.