Propagation of bacteria in vitro

The growth and reproduction of bacteria is a series of biochemical and physical processes.

The growth cycle consists of the following parts:
 * cell growth - coordinated formation of macromolecule and cellular components;
 * septum formation;
 * cell division.

Generation time is the time between two divisions.

Doubling time is the time it takes for the number of bacteria to double.

Under ideal conditions, the division of bacteria follows a geometric series, but in reality this is not the case for the following reasons:
 * nutrient depletion (or nutrients not reaching everyone);
 * inhibition by the products of its metabolism.



Growth curve
The growth curve shows the dependence of the number of living cells (on a logarithmic scale) on the age of the culture. We describe the following parts of the growth curve:
 * lag-phase - delay in division at the beginning, enzyme synthesis, volume increase, length of the phase depends on the state of the inoculum (short if cells from the growth phase are used), the beginning of division has an unstable rate;
 * logarithmic (exponential) phase - constant rate of division, depends on microbe species, temperature, environmental composition
 * specific growth rate is the growth rate per unit biomass;
 * stationary phase' - cells hardly divide anymore, the amount of waste products increases, cells neither increase nor decrease, the length of the phase depends on the type of bacteria and the nature of the environment
 * x = Y × s
 * x is the concentration of biomass produced, s is the concentration of nutrient consumed, Y is the growth yield (informs about the physiology of the growing bacterium);
 * death phase (autolysis) (neisserie or pneumococcus), induction of enzymes destroying the cell wall, disruption of the balance between lytic action and wall synthesis;
 * sometimes the velocity is constant (the only adverse factor), but usually several factors are at work, so the kinetics vary;
 * The specific death rate is the rate of cell death per cell.

In continuous cultivation there is a maintenance in logarithmic phase, nutrient supply and waste removal are needed. Continuous cultivation is carried out in apparatus called fermenters', it is used, for example, to produce ATB, and occurs naturally in the GIT. Under natural conditions, bacteria usually multiply more slowly due to limited supply, suboptimal temperature and the action of other microbes. In practice, bacterial growth is monitored by measuring the increase in cell mass in the following ways:
 * spectrophotometrically;
 * cell counting (microscopically in a counting chamber);
 * by culture on a constricted culture medium in a petri dish.

Factors affecting bacterial proliferation

 * oxygen
 * aerobic - Pseudomonas, oxygen electron acceptor
 * facultatively anaerobic - Enterobacteriaceae
 * anaerobic - clostridia
 * microaerophilic - Neisseria
 * capnophilic - meningococci, gonococci
 * water
 * most hygrophilic (x lyophilization - drying of frozen bacteria in vacuum), more resistant to drying G+ and acid resistant (staphylococcus and corynebacteria on skin)
 * xerophilic - water on particle surface (soil), Nocardia, actinomycetes, fungi
 * temperature - minimum, optimum and maximum growth temperature - temperature range
 * psychrophiles - 0-20°C
 * psychrotolerant - yersenia, listeria, salmonella, S. aureus
 * mesophiles - 20-40 °C
 * thermophiles - above 40 °C
 * hyperthermophiles - above 80 °C
 * hydrostatic pressure - deep-sea
 * osmotic pressure - mostly hypotonic environment, protection by wall
 * hypertonic - plasmolysis (food preservation)
 * halophiles - halotolerant and obligate (enterococci, staphylococcus genus, Vibrio genus) or extreme halophiles
 * pH
 * neutrophils - most
 * alkaliphiles - Vibrio cholerae, alkali-tolerant - Proteus, enterococci
 * acidophiles - lactobacilli
 * Oxido-reduction potential
 * aerobes - oxidized environment
 * anaerobes - low potential required
 * Radiation - ultraviolet and ionizing radiation damage

Related articles

 * Cultivation of cells and tissues in vitro, importance in medicine
 * Cell culture