Microbial growth controlling.docx

Microbial growth controlling

All microbes require nutrients (chemicals) to grow and develop (build molecules and cellular structures)
The essential nutrients are carbon, oxygen, nitrogen, hydrogen
When microbes interfere with the host’s nutrition or metabolism to gain nutrients, they can cause disease

Autotrophs and heterotrophs

Organisms feed themselves in two ways:

Using Carbon dioxide (CO2) as a source of carbon
Making CO2 into organic compounds obtaining carbon from nutrients, nutrients which include proteins, carbohydrates, amino acids, and fatty acids

Autotrophs: organisms that use CO2 as a source of carbon
Heterotrophs: organisms that feed on organic compounds

Carbon: is essential for microbial growth as all living things are made up of carbon

Oxygen

Some microbes require oxygen to produce energy and survive, some can use it, but they don’t need it, and for some it’s harmful
Oxygen ca act as the final electron acceptor in the electron transport chain, producing ATP
Obligate aerobes: organisms that require oxygen
Facultative anaerobes: organisms that can use oxygen, but don’t need it
Obligate anaerobes: organisms to which oxygen is poisonous

Culture media

Culture media is used by scientist to study the grow of microbes
It is a sterile material that provides the microbes with the nutrients they need
Sterile: no living organisms in the culture until the researcher introduces the microbes
To let the microbes grow it’s essential to provide the right nutrients, pH, moisture level, and level of oxygen

Common culture media

Agar: a solidifying agent, it’s an excellent culture medium, as most microorganisms cannot degrade it
To grow microbes, agar media are kept in test tubes or Petri dishes and the lid of the tube/Petri dish must remain closed to prevent contamination

Phases of growth

The life cycle of a bacterial culture has four phases:

Lag phase: an intense metabolic activity occurs inside the microbes
Log phase: the cells divide, and the organism grows. Currently, the organisms are susceptible to serve environmental conditions
Stationary phase: the rate of growth slows down, some microorganisms die, and the number of living and dead are roughly equal. The nutrients may be used up, and the living organisms have produced waste. To keep a population growing in a culture medium, the researcher might use a chemostat to remove expired medium and add fresh medium
Death phase: the dead cells exceed the new living cells and eventually, the population diminishes

Measurements of microbial growth

Plate count: a method of measuring bacterial growth which involves counting the microbe’s viable cells. There are two usual methods:

Pour plate: it involves adding 1 or 0.1 ml of bacterial solution to a Petri dish with melted agar, when the agar solidifies, the plate is incubated to measure the growth of the bacteria
Special/spread plate: 0.1 ml of the bacteria is added to pre-poured agar, and spread evenly over the solution

Filtration methods: are another way of measuring bacteria. Also, filtration measures pollution in drinking water. Water is poured through a membrane with small pores that doesn’t allow bacteria through. The bacteria caught is added to a Petri dish
Direct microscopic count: in this method bacteria are suspended in a liquid in a select area of a microscopic slide. Then, the area is viewed through an objective lens to take an average of the number of bacteria in several different fields. The observer can calculate the number of bacteria by multiplying it by the area of the spread, so, if the number in an area of 0.01 ml is counted, it must be multiplied by a hundred to find the number of bacteria in a millilitre of the sample

Establishing bacterial numbers by indirect methods

There are three ways of working out the number of bacteria without counting them:

Turbidity: means the cloudiness of a liquid due to the presence of insoluble matter. A spectrometer is an instrument that transmits light through bacteria suspended in a liquid medium, hitting a photoelectric cell. The light detected is inversely proportional to the number of bacteria. Measuring the light detected over time shows how much the bacteria have increased
Metabolic activity: bacteria metabolise and produce waste; these waste products are measured in a colony (such as CO2) and they can indicate how many bacteria there are
Dry weight: in the case of moulds, it’s possible to remove them from their growth media, filter them, and remove their water with a desiccator, and then, weighing the mould gives its dry weight

Controlling microbial growth

Controlling microbial growth is vital to prevent certain types of microbial growth that may lead to dangerous infectious pathogens, especially in hospitals and food preparation areas
Types of control of microbial growth:

Sterilisation: destroying all microbes, viruses, and endospores and carries them out using steam under pressure, incineration, or a sterilising gas, to prepare cultured media and tinned foods
Antisepsis: reducing pathogens and viruses on living tissue using antimicrobials such as iodine or alcohol, which disinfects the living tissue without killing them
Disinfection: using chemical or physical agents to destroy microbes and viruses on non-living tissue
Degerming: using mechanical means to remove microbes (cleaning the area of injection using an alcohol wipe)
Pasteurisation: using heat to kill pathogens and microbes that cause food spoilage
Sanitation: removing microbes from eating and drinking utensils, which involves washing the objects at high temperatures, or putting them in disinfectant baths

Aseptic: something free from pathogen contaminants
Microbial death: a microbe becomes permanently unable to reproduce under normal conditions
Microbial death rate tells how effective an antimicrobial agent is
Once microbes are exposed to heat or chemicals, they should die at a constant rate
Chemical antimicrobials may take longer to have an effect on especially resistant microbes or endospores

Action of antimicrobial agents

Antimicrobial agents either affect a microbe’s cytoplasmic membranes or cell walls, or its ability to metabolise and reproduce
If the semipermeable membranes are damaged, the cells’ contents may leak out, killing the cell
Heat, certain chemicals and strong acids or alkalis can denature proteins that enable cellular activity, and if protein cannot function, the cell can die. These proteins may form structural components in the cell’s membranes and cytoplasm
Heat, radiation, and some chemicals can damage nucleic acids (DNA, RNA), and considering that they contain the cell’s genetic information, the cell cannot replicate, or synthesise enzymes without them
Chemical agent: a chemical that enhances or inhibits a microbe’s growth, some examples: phenols and phenolics, glutaraldehyde and formaldehyde

Phenols and phenolics

Phenols and phenolics (alcohols and halogens) denature proteins in cells and disrupt plasma membranes
Features of alcohols as chemical agents:

Effective against bacteria, fungi, and viruses
Not effective against fungal spores or bacterial endospores
Can denature proteins and disrupt cytoplasmic membranes when mixed with water
Evaporate quickly, which minimises contact time with bacteria and may make them less effective

Halogens: are effective against vegetative bacterial cells, fungal cells, fungal spores, protozoan cysts, and some viruses. Halogens include iodine, which inhibits protein function in microbes. Halogens include:

Chlorine: used to treat drinking water, swimming pools, and wastewater
Chloramines: used as skin antiseptics and in water supplies
Oxidising agents: oxidise the enzymes in microbes and prevent them from metabolising

Heavy metals: including zinc, silver, nickel, and copper all denature enzymes and inhibit proteins in microbes. Therefore, they’re bacteriostatic and fungistatic agents (they inhibit bacteria and fungi)
Glutaraldehyde: is used to disinfect medical and dental equipment of bacteria, fungi, and viruses. It’s dissolved in water before application
Formaldehyde: is dissolved in water to make formalin, which is used to disinfect surgical equipment and other equipment, including dialysis machines