08 microbial control physical means

8/18/2019 08 Microbial Control Physical Means

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Microbial Control -

Physical MeansNestor T. Hilvano, M.D., M.P.H.


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Learning Objectives

You should be able to:1. Contrast sterilization, disinfection, antisepsis, sanitization, and pasteurization .

. Co!pare the effects of "#static" versus "#cidal" controla$ents on !icrobial $ro%th.

&. Define !icrobial death rate, and describe its si$nificancein !icrobial control.

'. Describe ho% anti!icrobial a$ents act a$ainst cellboundaries, proteins, and nucleic acids.

(. )dentif* the three !ost#resistant $roups of !icrobes, ande+plain %h* the* are resistant to !an* anti!icrobiala$ents.

. Describe t*pes of ph*sical !ethods of !icrobial controland discuss their advanta$es and disadvanta$es.


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Microbial Control- ntisepsis / reduction in nu!ber of !icroor$anis!s and

viruses on livin$ tissue0 e+: alcohol, iodine- Disinfection / destruction of !ost !icroor$anis!s and

viruses on non#livin$ tissue0 e+: alcohol, phenol- Pasteurization / use of heat to destro* patho$en0 e+:

pasteurized !il and fruit 2uice- 3anitation / re!oval of patho$ens fro! ob2ects to !eet

public health standards0 e+: %ashin$ table %ares inrestaurants

- 3terilization / destruction of all !icroor$anis!s andviruses in or on an ob2ect0 b* autoclave, incineration, oreth*lene o+ide $as0 e+: preparin$ culture !edia


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Microbial Death Rates

- Microbial death / per!anent loss ofreproductive abilit*

- MDR is constant over time for an* !icrobesunder a particular set of conditions

- 4+ in $raph: 5678!in.0 re9uires 5 !ins. toachieve sterilization


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Physical Methods of Microbial Control

1. Heat / !oist0 dr*. o% te!perature / refri$eration0 freezin$

&. ;iltration'. Desiccation(.


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Heat

- Heat / oldest and co!!on !eans- Ther!al death point #lo%est te!p. that ills

all cells in16 !ins.- Ther!al death ti!e / !ini!u! ti!e

re9uired to ill all or$anis!s at $iven te!p.=e+: .( !ins>

- Deci!al reduction ti!e =D> # ti!e re9uired

to ill 567of or$anis!s0 useful in foodprocessin$ to eli!inate endospores of C.botulinu!


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Moist HeatMoist Heat / used to disinfect, sanitize, sterilize, ?

pasteurize:1.@oilin$ / ve$etative bacteria ? fun$i, trophozoitesof protozoas,and !ost viruses in 16 !ins.

. utoclave / uses stea! heat under pressure =1 1AC, 1( psi at 1( !ins.> to sterilize che!icalsand ob2ects.&.Pasteurization / heatin$ food8bevera$es to ill

patho$ens and control spoila$e or$anis!s.


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Dry Heat

- Dr* Heat / at hi$her te!p. for lon$erti!es:

1.


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Refrigeration and Freezing

- Befri$eration bet%een 6AC and AC, halts$ro%th of !ost patho$ens

- 3lo% ;reezin$ belo% 6AC , inhibits

!icrobial !etabolis!0 but !an* ve$etitivebacterial cells, bacterial endospores, andviruses can survive for *ears


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Desiccation Lyo!hilization

- Desiccation / dr*in$ to preserve foods0inhibits $ro%th because !etabolis!re9uires li9uid %ater

- *ophilization / freeze#dr*in$0 preserve!icrobes and other cells for !an* *ears0freeze culture in li9uid nitro$en or frozen

C< , then re!ove %ater via a vacuu!


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Filtration Osmotic Press"re- ;iltration / passa$e of air or li9uid

throu$h !aterial that traps and re!oves!icrobes0 6.& E! for


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Radiation1. )onizin$ radiation / %avelen$ths shorter than 1

n!0 electron bea!s, $a!!a ra*s, F#ra*s 0effects leadin$ to denaturation =destro* DN >0!edical8lab e9uip!ent sterilization

. Nonionizin$ radiation / %avelen$ths lon$erthan 1 n!0 G li$ht, visible li$ht, infrared li$ht,radio %aves 0 G causes p*ri!idine di!ers%hich ills cells0 sterilization of surfaces and of

transparent fluids and $ases&. Micro%aves / heat ills !icrobes0 Trichinella

spiralis in por resist heatin$


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Home#or$ 1. Define ter!s: sterilization, disinfection, antisepsis,

sanitation, bacteriostatic, and bactericidal.. Co!pare !oist heat and dr* heat !ethod of !icrobial

control and discuss advanta$es and disadvanta$es.&. Co!pare uses8advanta$es of !icrobial control of

desiccation and l*ophilization0 and filtration andos!otic pressure.'. Co!pare ionizin$ and non#ionizin$ radiation.(. Ihat is !icrobial death rateJ Deci!al reduction ti!eJ

08 microbial control physical means

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