pt. V (Chapter 4: Microbial Growth and Its Control)

Controlling Microbe Growth

disinfection

treatment of an object or surface to maek it safe to handle, directly targeting pathogens (might not eliminate all microbes). Requires a disinfectant

methods of microbial growth control: physical

1. heat

2. radiation

3. filtration

decimal reduction time (D)

measure of the effectiveness of heat as a sterilizer that is quantified by the tiem required for a 10-fold reduction in the viability of microbial populaiton at a given temp. represented logarithmically

moist heat v. dry heat

moist has better penitrative power and inhibits growth/kills cells more quickly

thermal death time

time it takes to kill all cells at a given temp

autoclave

sealed heating device that uses steam under pressure to kill microbes. killing heat resistant endospore requires temps hifher than the bp of water at 1 atm

pasteurization

uses heat to significantly reduce (not eliminate) the microbes from a liquid (i.e. milk). at the sstanderdized times and temps, all pathofens are eliminated and microbs are reduced → longer shelf life

slash pasteurization

heat source rates temp of liquid for a breif time where the liquid is then rapidly cooled

ultrahigh-temperature (UHT) pasteurization

of milk, requires head treatment at 135 degrees C for 1-2 sec. sterilizes to a degree where milk can be stored at room temp for long periods of time

UV radiation

between 220 and 300 nm and is absorbed by DNA, can cause mutations that lead to death of the exposed organism

germicidal UV light

light that can disinfect surfaces and air but has low penetrating power; can onlly reach surfaces or air

roentgen

unit of ionizing radiation with the standard for sterilization being the absorbed radiation dose mesured in rads (p202)

ionizing radition source

x-rays or ⁶⁰Co or ¹³⁷Cs (both can produces x-rays and gamma rays

troubles with radial sterilization

smaller things are harder to sterilize/kill (i.e. easier < Harder; vegitative<endospores; bacteria<viruses; multicellular<microbes)

filter filtration

the use of filter with average size 0.2 um (not for viruses) or in the lab, 0.45 um and 0.2 um

depth filer

fibrous sheet made from an array of overlapping paper of glass fibers that traps particals in that network

HEPA filter

high-efficiency particulat air filter that generally can remoce 0.3 um particles from airdtreem with >99.% accuracy

membrane filters

most common filters used for liquid sterilization in lab. made of high tnsile strength polymers with many tiny pores. liquid is force pumped throught the filtration apparatus into a sterile collection vessel

nucleopore filter

made from thin polycarbonate film treated with radiation then etched to yeild highly uniform holes. sued to isolate specimen for scanning electron microscopy

antimicrobial agent

chemical routeinly used to control microbial growth (natural or synthetic) that kills or inhibits the growth of microorganisms

microcidal agents

ones that kill microbes. the micro prefix can be changed to indicate what type of microbe is killed (i.e. bactericidal, fungicidal, viricidal)

microstatic agents

ones that only inhibit growth (i.e bacteriostatic, fungistatic, viristatic)

-lytic

cell lysing (same rules for naming)

minimum inhibitory concetration (MIC)

smallest amount of an agent needed to inhibit the growth of a test organism.

can be tested by inoculating a series of test tubes with different dilutions of the agent (liquid)

or

known amounts of antimicrobial agent are added to filter-paper discs and discs are arranged on the surface of a uniformly incoulated agar plate. zone of growth inhibition is a fucntion of several things, including overall effectiveness

chemical sterilants

destroy ALL microbes, including endospores. Used when heat or radition are impractical or impossible to use. It is a cold sterilization using gases (thylene oxide, aldehydes-formaldehyde or glutaraldehyde)

disinfectants

chemicals that kill microbes but not nessisarally endospores (generally on surfaces)

sanitizers

less harsh that disinfectants and reduce microbial numbers but do not sterilize

antiseptics or germicides

chemicals that kill or inhibit growth of microbs but mostly notoxic to animals and can be applied to living tissue (hand washing and wound care)