growth of bacteria

Question 1

how can you measure bacterial growth

Answer 1

• direct counting by microscope (cant distinguish viable from non-viable cells)
• colony counting
• absorbance in liquid culture

Question 2

describe the growth phases of bacteria

Answer 2

• lag phase: bacteria adjust to new medium and strat to metabolize and grow
• exponential phase: bacteria grow at their best, this is the phase where growth rate is determined
• stationary phase: bacteria reach their limit on resources in the media and can not exceed a maximum population (growth rate = death rate)
• decline/death phase: medium is exhaused of a component needed for growth => new bacteria can not grow and bacteria are still dying

Question 3

describe the different respiration types of bacteria

Answer 3

aerobe: require oxygen to grow
microaerophile: can cope with low amounts of oxygen
facultative anaerobe: can grow with and without oxygn
anaerobe: cannot grow in presence of oxygen

CR: deep woulds colonized by different bacteria based on oxygen gradient

Question 4

what is the pH range for most bacteria

Answer 4

5.5-8.5 (known as neutrophiles)

Question 5

what temp do bacteria that infect most animals require

Answer 5

mesophilic temps (15-45 degrees)

Question 6

what is the impact of osmolarity on bacterial growth

Answer 6

• the membrane f bacteria is semi-permeable
• bacteria need to balance their water potential to excessive movement of water in or out of the cell
• bacteria accumulate or lose solutes to balance the water potential across the membrane
• bacteria prefer to maintain a slight positive pressure and inflow of water which is resisted by the cell wall
• hypertonic (high salt) environments draw water out of bacteria leading to changes in the concentrations of solutes in the cytoplasm and disrupts cell physiology

Question 7

describe the nutritional requirements of bacteria

Answer 7

• bacteria acquire nutrition from the immediate environment => patients wound, intestines, blood etc.
• bacteria can be: fastidious (require specific supplements) or non-fastidious (grow from basic chemicals)
• most veterinat relevant organisms pathogens are chemoheterotrphs (they use organic chemicals as sources of energy and carbon)
• part of the host defence is to limit access to certain nutrients to reduce bacterial growth
• bacteria can compete for compounds so one organism can potentially block colonisation.infection by another

Question 8

list methods of getting rid of unwanted bacteria (not in bodies)

Answer 8

• sterilisation (heat, chemicals, irradiation)
• washing
• disinfection (not all disinfectants kill all pathogens, prions very tolerant