Bacteria Growth Curve and Nutrition Lecture 7 PDF

LECTURE 7 Bacteria Growth Curve and Nutrition Ms. Peters  Bacteria Growth Curve In bacteria growth refers as increase in number. The growth process only occurs when environmental conditions are appropriate and proper chemicals and nutrition are also present Onc...

LECTURE 7 Bacteria Growth Curve and Nutrition Ms. Peters  Bacteria Growth Curve In bacteria growth refers as increase in number. The growth process only occurs when environmental conditions are appropriate and proper chemicals and nutrition are also present Once these factors are present, a given number of bacteria incubated for a given period of time, gives a characteristic growth pattern of bacteria Generation time -The time interval for the formation of two daughter cell from one (doubling time)  Bacteria Growth Curve The growth takes place exponentially i.e., one cell divides into 2, then 4, then 8, 16, 32 etc. Generation time vary widely among organisms Example: E.coli – 20min S. aureus – 30 mins M. tuberculosis – 12- 18hrs Incubation period –the time that elapses between entry of the microorganism and beginning of signs and symptoms In the lab it is the time between inoculation of a medium and visible colonies or nutrients are used up  Bacteria Growth Curve In a closed system, bacterial population can be measured periodically and log of number of viable bacteria is plotted in a graph against time, it gives a characteristic growth curve The growth curve has four phases: – Lag phase – Log phase or exponential phase – Stationary phase – Death phase or decline phase Bacteria Growth Curve  Bacteria Growth Curve Lag Phase: The time period in which bacteria is metabolically active but do not divide. ( no net growth) When bacteria is inoculated into new culture media, it takes some time to adjust to the new environment and does not divide immediately It is the phase of adjustment necessary for the synthesis of enzymes and co-enzymes for physiological activities.  Bacteria Growth Curve Lag Phase: Size of bacteria increase continuously Duration of lag phase varies according to conditions and species of bacteria. At the end of lag phase, bacteria become fully prepared for cell division  Bacteria Growth Curve Log Phase (exponential phase) During this phase bacteria divides at constant rate and the number of bacteria increase exponentially. Bacteria are in their rapid stage of cell division and show balanced growth. (cell division > cell death) Due to rapid cell division, bacteria have smallest size in this phase.  Bacteria Growth Curve Log Phase (exponential phase) Generation time is shortest during log phase and is strongly dependent upon growth factors present in the medium. Observation of colonies on solid media or turbidity in liquid medium This phase lasts for several hour depending on the type of organism, conditions of growth and density of organism.  Bacteria Growth Curve Stationary Phase The bacteria growth reaches a state during which there is no net increase in bacterial population (plateau). A constant bacterial population is maintained by balance between cell division and cell death. (cell division = cell death) In some bacteria, complete cessation of cell division occurs hence there is no net increase or decrease in number of bacteria. Stationary phase results from the increased bacterial cell density, depletion of nutrition in media and accumulation of toxic secondary metabolic wastes.  Bacteria Growth Curve Death Phase (Decline Phase) Number of bacteria decrease continuously; total remain constant but the viable count decreases. It is inverse of log phase. (cell division < cell death) Results from depletion of nutrition, accumulation of toxic wastes, change in pH etc. Not all bacteria die at the same rate, some die faster, and some are more resistant, remaining viable for longer time. Example; spore forming bacteria remain viable for longer periods  Bacteria Growth Curve Question: If the generation time of Bacillus cereus is given as 20 mins. At 8:00 am the bacteria was introduced into your body when you ate fried rice for breakfast which you bought from a restaurant the night before. How many cells will be in your body at 12:00pm? Bacteria Growth Requirements  Bacteria Growth Nutrition Nutrition: Nutrition is the process by which nutrients are acquired from the environment and used for metabolism and growth All organisms require a source of carbon, nitrogen , oxygen, hydrogen, phosphorous, sodium etc. The quantities in which they are needed varies Any substance that must be provided for the organism is called an essential element. Essential elements are of two categories: Macronutrients Micronutrients  Bacteria Growth Nutrition Nutrition Cont. Macronutrients – those required in large amounts and plays an important role in cell structure and metabolism. E.g., proteins, carbohydrates, lipids (CHONPS) Micronutrients (trace elements) – required in smaller amounts and are important enzyme function and maintenance of protein structure. E.g., manganese, zinc, nickel  Bacteria Growth Nutrition Nutrition Cont. The main determinants of a microbe’s nutritional type are its sources of carbon and energy. Source of carbon: – Autotrophs – make their own foods – Heterotrophs – depends on other organisms for food. Source of Energy: – Phototrophs – uses light – Chemotrophs – uses oxidation – reduction reactions on inorganic and organic compounds  Bacteria Growth Nutrition Carbon Categories Source Energy Source Examples Autotroph Photosynthetic organisms Photoautotroph CO2 Sunlight such as algae, plants certain bacteria such as Chemoautotroph CO2 inorganic chemical reactions methanogens Heterotroph Photoheterotroph Organic Sunlight nonsulphur bacteria metabolic conversion of nutrients from other Chemoheterotroph Organic organisms Protozoa, fungi organic matter from dead Saprobe Organic organisms Fungi, bacteria tissues and fluids from a various parasites such as Parasite Organic living host Ascaris spp.  Bacteria Growth Temperature Temperature Microorganisms are unable to control their temperature thus assuming their temperature of their environment Range of temperatures for microbial growth can be expressed as three cardinal temperatures: – Minimum temperature – lowest temperature that permits a microbe's growth and metabolism – Maximum temperature – highest temperature at which growth and metabolism can occur – Optimum temperature – small range between maximum and minimum temperature that promotes the fastest growth rate and metabolism  Bacteria Growth Temperature Temperature Cont. Another expression of temperature is description of the organism optimal growth in cold, moderate, or hot range: Psychrophile – microorganism with an optimal temperature below 150C with growth even at 0⁰C. Cannot grow above 20⁰C E.g., Flavibacterium spp. Mesophiles – grow at intermediate temperatures (20 – 40⁰C). Most human pathogens and medically significant microorganisms. Organisms in this group inhabit animals and plants in temperate, subtropical and tropical regions. E.g., P. aeruginosa  Bacteria Growth Temperature Temperature Cont. Thermophiles – grows optimally at temperatures greater than 45⁰C.Usually found in soil and water associated with volcanic activity E.g., T. aquaticus Extreme Thermophiles – few organisms that can grow between 80⁰C – 110⁰C. usually found in hot springs E.g., Thermococcus spp. Bacteria Gas Requirements Bacteria Gas Requirements  Bacteria Growth Nutrition Gas Requirements Cont. Regarding oxygen, several categories are outlined: Obligate aerobe – organism that is completely dependent on O2 for growth. E.g., Bacillus sp. Most fungi and protozoa Facultative anaerobe – grows in the presence or absence of O2. But grows best in aerobic conditions. E.g., E. coli Microaerophile – requires small mount of O2 for growth. E.g., Campylobacter sp.  Bacteria Growth Nutrition Gas Requirements Cont. Obligate anaerobes- cannot grow in the presence of O2 as they do not posses the enzymes needed to use O2 for respiration e.g., Clostridium spp. Aerotolerant – does not use O2 but can survive in its presence E.g., Some Lactobacilli sp. Capnophiles – Grows best in the presence of CO2. E.g., Neisseria spp.  Bacteria Growth Nutrition pH Requirements Cont. Majority of organisms live between a pH of 6 to 8 since strong acids and bases damages enzymes. Organisms can be classified as: Acidophiles – grows best at pH below 5. The cytoplasm of these bacteria are acidic in nature. E.g., Thiobacillus thioxidans Neutrophiles - bacteria that grow best at neutral pH (6.5-7.5) Most human pathogenic bacteria E.g., E. coli Alkaliphiles - Those bacteria that grow best at alkaline pH E.g., V. cholerae  Bacteria Growth Nutrition Salt Requirements Cont. Halophiles -Those bacteria that require high concentration of salt for growth. E.g., Halococcus spp. Halotolerant - Bacteria that do not require salt but can tolerate low concentrations E.g., Lactobacillus sp.