The bacterial growth is influenced by several factors, both biotic and abiotic factors.
biotic factor
In nature microbes can not be grown in pure culture forms but grow together with other microbes and establish a relationship of mutual influence among microbes with each other. The relationships formed can be mutualism, commensalism, parasitism, antagonism, synergism, and competition.
abiotic factors
a). The concentration of nutrients
The concentration of nutrients will determine the speed of transport of nutrients into cells. At low concentrations of transport is more difficult to do so affects the availability of nutrients in the cells.
b). temperatures
Temperature affects microbial growth because the enzymes that carry out metabolism is very sensitive to temperature. Based on the minimum temperature, optimum and maximum microbes can be classified into three groups:
- Microbial thermophilic (polytermik): the bacterium that can grow with minimum and maximum limits of temperature between 400C to 800C while the optimum temperature of 550C to 650C
- Microbial mesophilic (mesotermik): the bacterium that can grow with a temperature range between -50C to 600C while the optimum temperature between 250C to 400C.
- Microbial psikrofil (oligotermik): the bacterium that can grow at temperatures between 00C to 300C, while the optimum temperature between 100C to 200C.
c). pH
Electron transport enzymes and nutrient transport systems in the cell membranes of microbes are very sensitive to pH. Based on the pH minimum, optimum and maximum growth, microbes are classified into:
- Acidophilic microbes: pH between 2.0 to 5.0
- Microbes mesophilic: pH between 5.5 to 8.0
- Microbes alkalifilik: pH between 9.5 8,4-
d). osmotic pressure
Solute concentration determines the osmotic pressure of a solution. The higher the solute concentration, the higher the osmotic pressure of the solution, and vice versa. Osmotic pressure affects microbial cells as it relates to the availability of water for microbial cells. Microbes resistant to high osmotic pressure called microbes osmofilik, while the microbes that are resistant to high salt levels is called halophilic.
e). Oxygen (O2)
Many microbes can not grow if it is not available O2 but some microbes can grow if there is a free O2. Based on O2 purposes, then there are microbes are aerobic, anaerobic, facultative anaerobic and aerofil.
f). toxic compounds
Ions of heavy metals such as Hg, Cu, Zn, Li, Pb although at a very low state would be toxic to the microbes as ions of heavy metal cluster compounds will react with the cells.
g). Radiation
Light has the power to damage the microbial cells that do not have photosynthetic pigments. If the radiation energy is absorbed by microbes would cause ionization of cell components.
h). antimicrobial materials
The antimicrobial is one example bacteriosida (bacteria-killing ingredient). No antimicrobial material that has a broad spectrum, but others have a narrow spectrum. Effectiveness of the work of an antimicrobial agent is influenced by several factors, among others: the size and volume of microbial populations, moisture, heat, antimicrobial concentration, pH and organic matter content.
The presence of antimicrobial agents will be able to initiate the changes that lead to cell death include:
(1). Damage to the cell wall
The structure of the cell wall can be undermined by inhibiting the formation or change after the finished building.
(2). Changes in cell permeability
Cytoplasmic membrane regulate entry and exit of the dangers of certain substances into cells and to maintain the integrity of the cellular components. Damage to this membrane will result in inhibition of cell growth or cause cell death.
(3). Changes in proteins and nucleic acids
Cell survival is highly dependent on the molecules of proteins and nucleic acids. A condition / substances that change the status quo as denaturation of proteins and nucleic acids can damage cells irreparably. The high temperatures and dense concentrations of some chemicals may result in coagulation (denaturation) irreversible (irreversible) cellular components that are important.
(4). Inhibition of the enzyme
A number of enzymes in the cell is the target for the operation of a deterrent. Many chemicals that may interfere with biochemical reactions. This inhibition may lead to disruption of the metabolism so that the cell will die.
(5). Inhibition of the synthesis of DNA, RNA, and protein
DNA, RNA, and protein plays a very important in the process of living cells. With the presence of the antimicrobial agent, there will be disturbances in the formation and function of DNA, RNA, and protein so that it can result in damage to the cell.
