Bacteria growth Flashcards
Definition of bacterial growth
-change in the total population rather than an increase in mass or size of the individual organism
Method for bacterial reproduction
Bacteria divide by binary fission:
- increase of cell mass
- duplication of genome
- cell membrane and cell wall separation
Stages in Binary fission
1) cell elongates and DNA is replicated
2) cell wall and plasma membrane begin to divide
3) cross wall forms a completely around divided DNA
4) cells separate
What shapes can binary fission form?
- A chain of cocci is formed when the cell devides in one plane (coccus –> diplococcus–>chain of cocci (tetrad)
- A packet of cocci whent he cell divides in two or more planes perpendicular to one another
- A cluster of cocci when cell divides in several planes at random
what are the growth phases?
- lag phase
- log/exponential growth phase
- stationary phase
- death or logarithmic decline phase
Describe Lag Phase
- population remains unchanged TEMPORARILY
- bacterial cells may be growing in volume or mass, synthesize enzymes, proteins, RNA and increasing in metabolic activity
Describe exponential growth phase
- expressed as generation time or doubling time of the bacterial population
- generation time= time(t) per generation (n=number of generations)
Stationary phase - describe
- exhaustion of available nutrients
- accumulation of inhibitory metabolites or end products
- exhaustion of space
Exponential growth phases
- one cell divides producing 2 daughter cells
- increase in population is by GEOMETRIC PROGRESSION
- total population b at the end of a given period (starting with one cell) = 1 x 2^n where n is the number of generation assuming no cell death
GENERATION TIME - DEFINITION
The time interval required for the cells(or population) to divide
G=t/n, where G=generation time; t = time in minutes or hours; n=number of generations
b=B x 2^n (expression of growth by binary fission)
G= t/(3.3 log b/B)
Chemostat
-chemostat =bioreactor to which fresh medium is continuously added, while culture liquid is continuously removed to keep the culture volume constant
This: controls growth rate and optimizes production
-continuous fermentation and batch fermentation
What are the chemical requirements for growth
- Energy source: CHEMOTROPHS (chemical compounds); PHOTOTROPHS (radiant energy- light)
- Source of electrons: LITOTROPHS (reduced inorganic compounds) and ORGANOTROPHS (use of organic compounds)
- Carbon source: AUTOTROPHS (CO2 as their major source of carbon); HETEROTROPHS (organic compounds as their main carbon source)
- Nitrogen source: ATMOSPHERIC NITROGEN;INORGANIC NITROGEN (nitrate,nitrite or ammonium salts); organic compounds (amino acids)
- Ions
- Oxygen, sulphur and phosphorus
Describe OXYGEN, SULPHUR AND PHOSPHORUS AS CHEMICAL REQUIREMENTS
- -Oxygen: water,nutrients, molecular oxygen
- Sulphur: needed for the synthesis of certain amino acids:cysteine, cystine and methionine): use of organic sulphur or elemental sulphur
- phosphorus: usually supplied in the form of phsphate nucleotides, nucleic acids, phospholipids, teichoic acids
ions as a chemical requirement for growth
- metal ions such as K+, Ca2+, Mg2+, Fe2+ for normal growth
- trace elements (low concentrations in support of growth): Zn2+, Mn2+, Cu2+, Mo6+, Ni2+, B3+, Co2+
- enzyme cofactors: Zn2+, Mn2+, Cu2+, Mo6+, Mg2+, Fe2+
Aerobic bacteria requirements for growth
- aerobic bacteria need oxygen for growth
Anaerobic bacteria requirements for growth
- do not use oxygen to obtain energy
- strict (obligate anaerobe) = oxygen is toxic
- tolerant anaerobe= tolerate low levels of oxygen
- facultative anaerobe: do not require oxygen for growth; they use oxygen if present
- microaeophilic bacteria tolerate low levels of oxygen for growth
Describe oxygen toxicity
- inactivation of enzymes: oxidation of thiol groups or enzymes
- damage due to toxic derivatives of oxygen:
formation of super oxide radical: O2 + e –> O2-
formation of hydrogen peroxide: 2 O2- + 2H+ –> O2 +H2O2
formation of hydroxyl radicals: O2- + H2O2 –>O2 + OH radical + OH-
Protective mechanisms against the toxic forms of oxygen that aerobic and facultative organisms use
- superoxide dismutase: elimination of superoxide radicals
- catalase and peroxidase: elimination of hydrogen peroxide
Physical requirements for growth of bacteria
- temperature
- pH
Describe temperature as a requirement for the growth of bacteria
Give the optimum termperatures for the growth of bacteria in man, mesophiles, thermophiles, psychrophiles
- optimum growth temperature allows maximum growthduring a short period of time
- Bacteria that cause disease in man grow best at 37-39 degrees celsius
- Psycrophiles: 0-20 (optimum temp= 15 degrees celsius)
- Mesophiles: 25-40 degrees celsius
- Thermophiles: >45 degrees celsius
Temperature requirements for pharmaceutical products
- TPN, raw materials: deep freeze (-20 degrees celsius)
- reconstituted syrups and multi-dose eye drops (expiry date) at 8-12 degrees celsius
- WFI at 80 degrees celsius (regrowth of gram-negative bacteria and release of toxins)
pH requirements for optimul bacterial growth
- 6.5-7.5
- limits: 5-9
- exception: Thiobacillus thiooxidans (0.5-6; optimum: 2-3.5) and alkaline spring isolate (8-11; optimum:2-3.5)
How is pH used to prevent growth in pharmaceutical preparations?
- extreme pH prevent microbial growth
- neutral pH: bacterial spoilage e.g: in antacid mixtures, flavored mouthwashes, distilled and deionised water
- pH>8: spoilage is rare (soap-based emulsion)
- low pH: spoilage my moulds and yeast: fruit juices and flavored syrups
Water activity
- estimates the proportion of uncomplexed water avaiable in a formulation
- the greater the solute concentration, the lower water activity
- most microorganisms grow best in dilute solutions, except halophiles (high Aw)
- limiting Aw values: Gram negative rods:0.95; staphylococci, streptococci:0.9
- most yeast: down to 0.73
How to use water activity to prevent growth of microorganisms in pharmaceutical products
-water activity of aqueous formulations can be lowered to decrease microbial growth:
Syrup BP: Aw= 0.86
Tablets
Sterile products requirement
- preparations required to be sterile on the dosage form and other preparations labelled sterile
- need to comply with test for sterility
