Microbial Growth

Unit 8034Unit 8034

Culture microorganisms and Culture microorganisms and control microbial growthcontrol microbial growth

By Elysia Butler By Elysia Butler

Nutritional RequirementsNutritional Requirements

All living organisms require nutrients All living organisms require nutrients to grow. to grow.

Microorganisms get their nutrients in Microorganisms get their nutrients in the form of chemical elements which the form of chemical elements which exist in nature as either organic or exist in nature as either organic or inorganic compounds.inorganic compounds.

NutrientsNutrients

Carbon – Used in the creation of Carbon – Used in the creation of proteins, carbohydrates and lipids.proteins, carbohydrates and lipids.

Nitrogen – Utilised in amino acids, Nitrogen – Utilised in amino acids, which make up proteins.which make up proteins.

Hydrogen and Oxygen – Generally Hydrogen and Oxygen – Generally make up the organic compounds that make up the organic compounds that are ingested or absorbed.are ingested or absorbed.

NutrientsNutrients

Sulphur – Important with regards to Sulphur – Important with regards to amino acids.amino acids.

Phosphorus – Important with regards Phosphorus – Important with regards to adenosine triphosphate and to adenosine triphosphate and nucleic acids.nucleic acids.

Other elements are also required for Other elements are also required for the nutrition of microorganisms but the nutrition of microorganisms but in smaller quantities.in smaller quantities.

Hetero / Auto - trophsHetero / Auto - trophs

Heterotrophs - Obtain the majority of Heterotrophs - Obtain the majority of their carbon as organic compounds their carbon as organic compounds by either directly absorbing it by either directly absorbing it through the environment or by through the environment or by ingesting other heterotrophs or ingesting other heterotrophs or autotrophs.autotrophs.

Autotrophs -Obtain their carbon Autotrophs -Obtain their carbon source as inorganic elements source as inorganic elements through the environment.through the environment.

Chemo / Photo - trophsChemo / Photo - trophs

Chemotrophs – Obtain their energy Chemotrophs – Obtain their energy from chemical compounds.from chemical compounds.

Phototrophs – Obtain the majority of Phototrophs – Obtain the majority of their energy from a light source.their energy from a light source.

Some organisms cant be classified Some organisms cant be classified solely as a chemotroph or a solely as a chemotroph or a phototroph as they have the ability to phototroph as they have the ability to adapt to the surrounds eg adapt to the surrounds eg R. rubrumR. rubrum

Selective MediaSelective Media

Encourage growth of specific types of Encourage growth of specific types of microorganismsmicroorganisms

Inhibits growth of specific Inhibits growth of specific microorganismsmicroorganisms

Sometimes used for both of the Sometimes used for both of the above purposes.above purposes.

Differential MediaDifferential Media

Can grow more than one type of Can grow more than one type of microorganismmicroorganism

Can compare one type to anotherCan compare one type to another Varying appearance of Varying appearance of

microorganisms on the mediamicroorganisms on the media For example one type may react with For example one type may react with

the media and turn blue while the media and turn blue while another type may appear purpleanother type may appear purple

Differential ExampleDifferential Example

To the right is a To the right is a photograph of photograph of different bacterium different bacterium grown on differential grown on differential mediamedia

E. coliE. coli - blue - blue E. aerogenesE. aerogenes - purple - purple P.aeruginosaP.aeruginosa - yellow - yellow

Limiting Microbial Growth Limiting Microbial Growth PhysicallyPhysically

Microbial growth can be limited by Microbial growth can be limited by altering one or all of the following to altering one or all of the following to a level that the organism will not a level that the organism will not thrive in;thrive in;

TemperatureTemperature pHpH Gaseous AtmosphereGaseous Atmosphere Osmotic PressureOsmotic Pressure

TemperatureTemperature

Psychrophiles – organisms that grow Psychrophiles – organisms that grow best between 15C – 20Cbest between 15C – 20C

Mesophiles – organisms that grow Mesophiles – organisms that grow best between 25C – 40Cbest between 25C – 40C

Thermophiles – organisms that grow Thermophiles – organisms that grow best between 25C – 40Cbest between 25C – 40C

Above - Microorganisms can be classified based on the temperature at which they thrive

Gaseous AtmosphereGaseous Atmosphere

Aerobic – Typically require oxygen at Aerobic – Typically require oxygen at levels of 21% levels of 21%

Anaerobic – Don’t require oxygen Anaerobic – Don’t require oxygen Faculative – Can grow both Faculative – Can grow both

aerobically and anaerobicallyaerobically and anaerobically Microaerophilic – Typically require Microaerophilic – Typically require

oxygen at levels of 1 – 15%oxygen at levels of 1 – 15%Above - Classification of microorganisms based on gaseous oxygen levels at which the microorganism can grow.

Limiting Microbial Growth Limiting Microbial Growth ChemicallyChemically

Adding antimicrobial agents to media Adding antimicrobial agents to media will inhibit the growth of specific will inhibit the growth of specific organisms.organisms.

Example - Media to which Colistin Example - Media to which Colistin and Nalidixic acid have been added and Nalidixic acid have been added will inhibit gram-negative bacteria will inhibit gram-negative bacteria growth but promote Gram-positive growth but promote Gram-positive cocci growth.cocci growth.

IodineIodine

Kills bacteria and endospores on human Kills bacteria and endospores on human skinskin

Presence of organic material decreases Presence of organic material decreases effectiveness of iodine to kill endosporeseffectiveness of iodine to kill endospores

Eliminate organic material to increase Eliminate organic material to increase rate at which iodine will kill endosporesrate at which iodine will kill endospores

Mode of action: Damages metabolic Mode of action: Damages metabolic compoundscompounds

Formaldehyde GasFormaldehyde Gas

Kills bacteria and endospores in Kills bacteria and endospores in enclosed areasenclosed areas

Kills vegetative cells quickerKills vegetative cells quicker To be effective temperature must be To be effective temperature must be

2222°C°C Humidity needs to be approximately Humidity needs to be approximately

60-80%60-80% Mode of action: Inactivates nucleic Mode of action: Inactivates nucleic

acids and proteins.acids and proteins.

Phenolic CompoundsPhenolic Compounds

Bacteriostatic Bacteriostatic (Inhibits growth but does not kill)(Inhibits growth but does not kill) at low at low concentrationsconcentrations

Bactericidal Bactericidal (Kills)(Kills) at higher at higher concentrationsconcentrations

Mode of action: Damages Mode of action: Damages Cytoplasmic MembraneCytoplasmic Membrane

Antibiotic Mode of ActionAntibiotic Mode of Action

Can work by affecting the Peptidoglycan in Can work by affecting the Peptidoglycan in the Cell Wallthe Cell Wall

Inhibits crosslinks from forming in Inhibits crosslinks from forming in PeptidoglycanPeptidoglycan

Peptidoglycan loses rigidityPeptidoglycan loses rigidity Causing cell to absorb waterCausing cell to absorb water Cell splits and diesCell splits and dies Penicillins and Cephalosporins - antibiotics Penicillins and Cephalosporins - antibiotics

that work by targeting the Cell Wallthat work by targeting the Cell Wall

Antibiotic mode of actionAntibiotic mode of action

Some antibiotics kill pathogens by Some antibiotics kill pathogens by affecting the Cytoplasmic Membraneaffecting the Cytoplasmic Membrane

Alters the permeability of Alters the permeability of Phospholipids in the Cytoplasmic Phospholipids in the Cytoplasmic MembraneMembrane

Causes leaking of vital substances Causes leaking of vital substances from the cell resulting in deathfrom the cell resulting in death

Polymyxins – antibiotics that work by Polymyxins – antibiotics that work by targeting the Cytoplasmic Membranetargeting the Cytoplasmic Membrane

Limiting Antibiotic Limiting Antibiotic EffectivenessEffectiveness

Mutant cells that are non-responsive to the Mutant cells that are non-responsive to the antibiotic.antibiotic.

Wrong type of antibiotic used for the Wrong type of antibiotic used for the specific pathogen.specific pathogen.

Cells passing on antibiotic resistance to Cells passing on antibiotic resistance to other cells through genes.other cells through genes.

Increased use of antibiotics increases the Increased use of antibiotics increases the risk of antibiotic resistant pathogens risk of antibiotic resistant pathogens forming.forming.