control of microbial growth

why is it important to control microbial growth ?

prevent food spoilage, infection, biofouling, contamination of medical equipment and ensure accurate lab identification

what are the four categories of microbes based on temperature preference ?

psychrophiles, mesophiles, thermophiles, extreme thermophiles

optimal temp for psychrophiles

0 - 20°C

optimal temp for mesophiles

12 - 45

optimal temp for thermophiles

40 - 80 hot springs

optimal temp for extreme thermophiles

65 - 113 deep sea hydrothermal vents

at what temp do most human pathogens grow best at ?

37°C (mesophiles)

what are acidophiles and where are they found ?

microbes that thrive in pH 0 - 5

found in volcanic soils and acid springs

what pH range do neutrophiles prefer ?

5 - 8

what kind of environment do alkalophiles thrive in ?

soda lakes and alkaline soils pH 9 - 11

what is pH ?

measure of conc. of H+ (hydrogen ions)

pH of ammonia ?

11 - basic

pH of sulphuric acid ?

1 - acidic

acidophile example

helicobacter pylori in stomach

obligate aerobes

microbes that require oxygen for aerobic respiration

obligate anaerobes

microbes that cannot survive in oxygen

rely on fermentation or anaerobic respiration

facultative anaerobe

can switch between aerobic and anaerobic respiration

aerotolerant

survive in oxygen but do not use it - rely on fermentation

do not change O2 conc. of solution

microaerophiles

require lower (than atmospheric) levels of oxygen for survival

osmotolerant

grows over wide range of osmotic conditions

halophile

requires high salt conc. to grow

xerophile

grows in extremely dry environments

the skin is rich in what ?

salt

what is decimal reduction time (D value) ?

time required to reduce viable population by factor of 10 (time to kill 90%) under defined conditions

what does thermal death time measure ?

time needed to kill all microbes at certain temperature

what does autoclaving do and how ?

uses moist heat under pressure to kill all microbes and endospores

15 - 20 mins

autoclave tape turns what colour when heated ?

black

what is pasteurisation ?

high temperature treatment for short time to kill pathogens, not all microbes

which pathogens does pasteurisation target ?

Mycobacterium tuberculosis, Coxiella burnetti, Salmonella, E. coli

what type of radiation breaks hydrogen bonds in DNA ?

non-ionising radiation like UV light

ionising radiation

x-ray and gamma

what does ionising radiation (e.g. gamma rays) do to DNA ?

destroys hydrogen and phosphodiester bonds in DNA

what is bacteriophage therapy ?

use of viruses that infect and kill specific bacteria

what are biofilms ?

microbial communities embedded in a self produced matrix (EPS) on surfaces

how does maggot therapy help in microbial control ?

maggots secrete proteolytic enzymes and antibacterial molecules that prevent infection and clean wounds

sterilisation

destruction/removal of all microorganisms

disinfection

destruction of microorganisms (pathogens) on surface

disinfectant

antimicrobial agent used on non living surface

antisepsis

destruction/inhibition of microorganisms in/on living tissue

preservation

prevention of multiplication of microorganisms in natural or formulated products eg. food

sanitation

removal of microorganisms from objects / environments to acceptable level

meets public health standards

antibiotics

severely toxic agents that kill/inhibit microorganisms

in what ways can different major antibiotic families disrupt cells ?

cell wall

DNA / RNA synthesis

plasma membrane

ribosomes

metabolic pathways

what are the 3 types of antibiotic actions ?

• bacteriostatic: inhibits growth, cells remain alive

• bacteriocidal: kills microbes, cells remain intact

• bacteriolytic: kills and lyses cells, reducing total cell count

what factors affect chemical control agents ?

conc., exposure time, pH, presence of organic matter, microbial load

common antiseptics

alcohol (60-85%)

chlorhexidine

ammonium compounds

iodine

hydrogen peroxide

hydrogen peroxide is effective against

anaerobic bacteria

iodine is an effective antiseptic against

bacteria, viruses, fungi

common disinfectants

phenolics

quaternary ammonium compounds

aldehydes

halogens

common sterilising agents

formaldehyde

hydrogen peroxide

ethylene oxide

peroxyacetic acid