1.4. prokaryotic cell: bacterial growth, physiology & metabolism Flashcards
autotrophs
synthesize organic compounds using CO2 (source of carbon) and N2 (no medical importance)
heterotrophs
unable to synthesize own metabolites
- depend on preformed organic compounds as source of carbon (all pathogens)
Eh
redox potential
describe the concept of bacterial physiology
- nutrition
- environmental factors affecting survival of bacteria
- growth & multiplication
- metabolism
based on nutrition, what can microbes be classified as?
- Autotroph
2. heterotroph
Autotrophs:
Synthesize organic compounds using CO2 (source of carbon)and N2
(no medical importance)
Heterotrophs:
Unable to synthesize own metabolites and depend on preformed organic compounds as source of carbon
(All pathogens)
what are the Minimum requirements for growth and multiplication of a normal bacterial cell?
- Water (80%), carbon, nitrogen and inorganic salts
what are the requirements for growth of a pathogenic (disease-causing) species?
- Organic compounds and growth factors (bacterial vitamins)
- Essential: growth does not occur in their absence
- Accessory: enhances growth without being really necessary for some bacteria - Growth factors: produced by body fluids and tissues ‘in vivo’ and from yeast extract, blood and blood products ‘in vitro’ include: B complex vitamins
- Thiamine(B1)
- Riboflavin(B2)
- Nicotinic acid(B3)
- Folic acid (B9, Folate)
- B 12
discuss and describe bacterial growth
- Increase in the number of microbes, rather than an increase in size of a microbe
•Involves increase in cell mass and number of ribosomes, duplication of bacterial chromosome, synthesis of new cell and plasma membrane, partitioning of the two chromosomes, septum formation and cell division
•When growth reaches critical mass, cell divides
•Bacteria grow and divide by binary fission (asexual reproduction) and nuclear division precedes cell division
•“In vivo” growth of bacteria depends on our nutritional status, immunity, humoral factors, pH, redox potential..
what is generation time?
- Interval of time between two cell divisions OR
- Time required for a bacterium to give rise to two daughter cells under optimum conditions
- Knowledge of microbial growth is useful for understanding population dynamics and control in infectious diseases and food preservation
•Treating life-threatening infectious diseases
•Disinfection of living (animate) or non-living (inanimate) surfaces
•Informing processes related to cell division in higher organisms
what are factors affecting bacterial growth?
- Temperature
- Atmospheric O2 and CO2
- H –ion concentration
- Moisture and drying
- Osmotic Pressure
- Mechanical and sonic stress
- Radiation
Classification by temperature
- Mesophilic: 250C-400C (pathogens)
- Psychrotrophilic: can grow at 0-70C , optimum 20-300C (cold loving) –Listeria monocytogenes
- Thermophilic: 55-880C (Bacillus sterothermophilus)
By oxygen requirement
- Strict obligate aerobe: love O2 (P. aeruginosa, Staphylococcusspp)
- Strict obligate anaerobe: don’t love O2, may die (Bacteroides fragilis, Clostridium spp)
- Microaerophilic: best in low O2 (Helicobacter, Campylobacter spp)
By CO2 requirement
- Facultative aerobe: can grow in O2 also (most aerobes)
- Aerotolerant anaerobe: may tolerate O2exposure (Streptococcus pyogenes, Clostridium perfringens)
- Capnophilic: needs CO2 (5-10%) (Neisseria spp, Streptococcus pneumoniae, Brucella abortus)
H –ion (pH) requirement
•Human body –neutral (pH 7.3-7.5)
•Human pathogens-Neutrophiles (pH 5.4-8.5)
•Lactobacillusspp–acidophile(pH 0.1-5.4)
-Acidic products of bacterial metabolism interfere with growth. Buffers are used to stabilize pH
•Vibrio cholerae–alkalophile( pH 8-12)
Moisture and drying
•Water(constitutes 80% of total bacterial cell weight) is essential for bacterial protoplasm; drying is lethal to bacterial cells
Effect of drying varies (give examples of bacteria where it varies)
- Treponema pallidum (cause of syphilis) and Neisseria gonorrhoae (cause of gonorrhoea) –highly sensitive to drying and die
- Staphylococcus spp–withstands drying for months
- Bacterial spores –resistant to drying, survive very high and low temperatures and high UV radiation for decades; difficult to kill during sterilization e.g. Bacillus anthracis–cause of anthrax
Osmotic Effect
Osmotic pressure(OP): Cells are 80-90% water:
•Isotonic solution:not net movement of H20
•Hypertonic solution: ↑OP removes H20 moves from cell membrane causing shrinkage (plasmolysis)
-Used in control spoilage and microbial growth: salt in meat
•Hypotonic solution: ↓OP H20 moves into cell
-If cell wall is strong, it contains swelling
-If cell wall is weak/damaged, cell bursts –osmotic lysis, plasmoptysis
Mechanical and Sonic Stress Radiation
- Cell wall may be ruptured by grinding and vigorous shaking
- May be disintegrated by exposure to ultrasonic vibration
- X-rays and gamma rays exposure -lethal
Culture medium
- must be sterile
- contain appropriate nutrients
- must be incubated at appropriate temperature
draw the bacterial growth curve
(refer to pg 28 in written notes)
Lag phase
- Little or no cell division, population size does not increase
- Period of adjustment to new environment
- Phase of intense metabolic activity as individual organisms grow in size
- Cell synthesizes its own cellular components
- Enzymes and metabolites build up, varies within species, medium and temperature
- Lasts from one to several days
* *Clinical significance –incubation period of diseases
log phase (exponential/ logarithmic)
- Population number of cells undergo binary fission doubles at a constant interval called generation time
- Period of most rapid growth and constant
- New cells> dying cells
- Cells are at highest metabolic activity
- Grows as long as cells have adequate nutrients and good environment (Metabolically active state)
- Cells most susceptible to adverse environmental factors:
•Radiation
•Antibiotics: Inhibiting protein synthesis active as cells rapidly divide in culture where proteins are rapidly synthesized, B-lactams effective when cells are making peptidoglycan
** Clinical significance –symptoms and signs appears. ***Host defences limit this phase
Stationary Phase
•Cell division stops as nutrients depletes, toxic waste builds up,
•Death and growth of cells are equal
•Viable count is stationary
•Cells gram-variable and stain irregular due to storage granules
•Sporulation (spore formation) takes 6-8hrs due to insufficient nutrients.
•Spore producing bacteria have a two phase cell cycles
a) Vegetative (metabolically active)
b) Endospore –Dormant, non-reproductive, capable of turning to vegetative cell. Hostile conditions cause vegetative cell to change to spore forming cell, a sporangium(enclosure in which spores are formed)
* Spores can produce eXotoxins
**Clinical significance -Toxemia
Phase of Decline/Death
•Nutritional exhaustion and toxin accumulation increases
•Number of cells decreases due to death of cells caused by autolytic enzymes
•Death rate> growth rate
•Involution forms (with ageing)
•Irreversible loss of the ability to reproduce
•Often, death rate slows due to accumulation of resistant cells (resistant bacteria show extended survival)
**Clinical significance –phase of convalescence
Anabolism:
Basic building process of blocks utilized in synthesis of various cellular structures (monomers and polymers)
Catabolism:
Breakdown of macromolecules into simpler micromolecules, absorption into cell, conversion into basic blocks including interconversion of ADP to ATP
what are the three major pathways of bacterial metabolism?
•Glycolysis (Embden-Meyerhof Parnas(EMP), most common
- One glucose (O2+Ano2) →2 ATP, 2NADH, 2 Pyruvate
•TCA cycle
•Pentose Phosphate
Oxidation
•Aerobes obtain energy using 02as hydrogen acceptor
Fermentation
Anaerobes use electron donor & acceptor as nitrates and sulphites
what are the products of fermentation?
- Acids(lactic, formic, pyruvic)
- Alcohols
- Gases –H2, co2
- Phosphates(rich), bonds are transferred to ADP to form ATP
- Facultative bacteria can use both pathways
Oxidation-Reduction Potential (redox potential -Eh)
- Oxidizing or reducing system accepts or loses electrons respectively
- Strict Anaerobes require low Eh
Koch’s Postulate
- to determine the cause of infectious disease as evidence required to establish etiologic relationship between microorganism and disease.
1. Microorganism must be isolated from every diseased patient(Association)
2. It must be isolated in vitro in pure culture(Isolation)
3. When inoculated, the pure organism must cause disease in a healthy susceptible animal(Causation)
4. The organism must be recovered from the infected animal(Re-Isolation)
5. Modifications the postulates were made by Fredericks and Relmanto address non-culturable microorganisms
Role of Microbiology Laboratory in Diagnosis of Infectious Diseases Offers tests that:
Identify microorganisms from clinical specimens either, directly (visually, using a microscope, growth in culture)or direct detection from specimens using genetic probes or serological indirect detection of antibodies/antigens to the microbe)
General phenotypic, non-nucleic acid-based types of tests include
- Microscopy -Stained smears (e.g. Gram, Ziehl-Neelsen, Auramine); Wet preparations (for presence of cells, bacteria, yeasts, parasites or parasitic eggs)
- Culture and Susceptibility testing
•Characteristic of organism’s growth on culture media(colony size, colour and shape
•Manual or automated systems or chromatographic method(HPLC)
•Mass spectrometry –detects inorganic or organic compounds e.g., proteins according to mass. Specific pathogens have unique proteins and relative mass(identifies within 24 hours vs 24-72 hours in conventional way)
•MALDI-TOF –matrix-assisted laser desorption ionization time to flight (bacteria, mycobacteria, yeast, molds..)
General genotypic types of tests include: Nucleic acid-based:
Detect organism directly from specimen using probe specific DNA or RNA sequences PCR, RT-PCR, LCR
Serological test
•Immunologic tests such as: Latex agglutination, Enzyme immunoassay (ELISA), Immunofluorescent antibody (IFA)
