Image one	CONTROL OF MICROBIAL GROWTH, PHYSICAL MEANS ©David B. Fankhauser, Ph.D., Professor of Biology and Chemistry University of Cincinnati Clermont College, Batavia OH 45103	Image Two
legend for image one	This page has been accessed  times since 18 July 2007. rvsd 23 July '97, 17 July 2000, 29 January 2002, 15 July 02, 21 July 03, 14Apr06, 18July07	legend for image two

TF&C,2nd, p 182-, TFC 7^th: 184-193, Black: p 150-155, 339-348, Bauman 2^nd, pp262-276

Contrast            sterilization:     all life forms destroyed

(p 263)              disinfection:     all pathogens destroyed

                          sanitize:            microbe population reduced to safe level

PATTERN OF DEATH: (P 263)          numbers decline logarithmically, aim to half life:

                                                                 the higher the starting number the longer to sterilize

TARGETS: MECHANISMS BY WHICH CONTROL AGENTS WORK (P 264)

             Alter membrane:         quaternary ammonium salts, EtOH, etc.

             Damage protein:         Heat, cold, heavy metals, halogens, etc. Anything altering 3D form (p)

             Damage DNA:             UV, radioactivity

Relative susceptibility to antimicrobials:              enveloped viruses

(p 265)                                                                  Gram positive bacteria

                                                                              Non enveloped viruses

                                                                              Fungi

                                                                              Gram negative bacteria Pseudomonads highly resistant.

                                                                              Active protozoa

                                                                              Protozoan cysts

                                                                              Mycobacteria

                                                                              Bacterial endospores

CONDITIONS INFLUENCING MICROBIAL CONTROL:

             Temperature:                 disinfectants work better in warmth

             Physiological state:        log phase most sensitive

             Environment:                Low pH, large amounts of organic material inhibits (feces etc.)

EVALUATION:          Semilog plot of population vs time of exposure

PHENOL COEFFICIENT      (p. 266) first used by Lister, still standard: ratio of antibacterial activ.

                                       test against S. aureus, S typhimurium, and P. aeruginosa,

PHYSICAL TECHNIQUES

TEMPERATURE

        HEAT dry                          high heat kills by oxidation

                          incineration                  flaming, burns up

                          hot air sterilization      used for glass ware: 170 C/2 hr poor heat conductance

                     moist                       heat disrupts H bonds. Moist heat (100 C) kills vegetative forms of bacteria, many viruses and fungi in 10 min. (not spores or some viruses)

                      Autoclave              water boils at 121 C 1 ATM (15lbs) usually for 15 minutes (p 268)

                     Pasteurization        Classic was 63 C/30 min (Does not kill thermoduric organisms ) (p 270)

                                                      High-temp, Short (HTST) now used: 72 C,15 sec

        LOW TEMP:                      bacteriostatic (except for psychrophiles)

                                                      Slow freezing more effective: xyls formed

FILTRATION  heat sens materials: filter thru unglazed porcelain. Now membrane filters: 0.45 um. (P 272)

DESICCATION:                     also generally bacteriostatic: Neisseria dies in 2 hrs, Mycobacterium viable for mo.

OSMOTIC PRESSURE:        plasmolysis is bacteriostatic to bacteriocidal. Yeast and mold resistant

ACID pH                                 Alters folding of protein. Vaginal health, pickles, various foods.

RADIATION:                          Ionizing: hydroxyl radicals kill bacteria: used on disposable supplies & pharmac.

                     UV:                      thymine dimers, most effective at 260 nm germicidal lamps, penetrate poorly

                     Sunlight:              short UV filtered out, but singlet 0₂ kills