Lecture 31 - Bacterial Growth and Physiology Flashcards
Steps of Prokaryotic Cell Division
- replication of the bacterial chromosome is initiated at the cytoplasmic membrane
- the process triggers cell division
- each daughter chromosome is anchored to a different portion of the membrane
- binary fission
- as the membrane grows, the daughter chromosomes are pulled apart
- a septum (S) grows from opposite sides toward the center of the cell and divides that daughter bacteria into two cells
Cell Division (Complete) Requires …..
- transpeptidases (like PBP -Penicillin Binding Proteins
- along with other enzymes
- incomplete cleavage yields linked chains (Streptococcus) or clusters (Staphylococcus)
Energy Sources
Phototroph - energy from light (the sun)
Chemotroph - energy from oxidation of organic/inorganic compounds
Electron Sources
Lithotrophs - reduced inorganic molecules
Organotrophs - organic molecules
Carbon Sources
Autotrophs - CO2 is principal bio-synthetic carbon source
Heterotrophs - reduced, preformed, organic molecules from other organisms
Obligate Aerobes
- require oxygen (terminal electron acceptor)
- die without oxygen
Obligate Anaerobes
- oxygen kills these
- they obtain energy (ATP) from fermentation
Facultative Anaerobes
- capable of fermentation in presence of lack of oxygen
- but still prefer oxygen
- KEY = can switch btwn respiration and fermentation
Microaerophiles
- can withstand very low levels of oxygen
- pneumococcus & strep pnuemonae
Why is oxygen toxic to anaerobes?
- lack of SOD - super oxide dismutase
- lack of catalase or peroxidase to decompose H2O2
**both super-oxide and H2O2 are toxic to bacteria
Thermophillic
- optimum temp (55-75 C)
- minimum temp (35-40 C)
- thermaphillus aquaticus (Yellowstone)
Mespophilic
- optimum temp (30-45 C)
- minimum temp (10-15 C)
- these inhabit humans often (pathogenic bugs)
Psychrophilic
- Facultative (similar to mesophiles, but can grow slowly near 0 C)
- obligate (optimum temp 15-18 C), killed above 20 C
- in lakes in Antarctica
Typical Bacterial Growth Curve
- lag phase
- exponential phase
- stationary phase
- decline
Lag Phase
- grow is slow at first
- happens while bacteria get acclimated to food/nutrients of new habitat
- biochem activity is high
- bacteria store nutrients, synthesize enzymes & prepare for binary fission
Log Phase
- once you have the metabolic machinery running
- bacteria start multiplying exponentially
- do this until nutrients run out
Stationary Phase
- more bacteria competing for dwindling nutrients
- replicative growth stops and the number of bacteria stabilizes
Decline Phase
-toxic waste products build up and the bugs may begin to die
Generation Time (Doubling Time)
- the generation time is the time interval required for the cells (or population of cells) to double in number
- g = t/h
t- time interval (min, hr), n - number of generations (# times cell population doubles during time interval)
How to quantify Doubling Time?
- the pour plate
- serial dilution method
- plate after dilution
- look at CFU’s (colony forming units)
- can finally see population and count them, then backtrack to determine original population
Aspesis
-the state of being free of microorganisms
Sterilization
-inactivation or elimination of ALL viable organism and their spores
Disinfection
-process of removing or killing MOST of the microorganisms on or in a material
Sanitization
-a cleaning process which REDUCES pathogen levels to produce a healthy clean environment
Germicide
- substance that kills vegetative bacteria (bacteria that can divide) and SOME spores
- attain disinfection but not sterilization
Disinfectant
- substance used on non-living objects to render them non-infectious
- kills vegetative bacteria, fungi, viruses, but NO SPORES
Antiseptic
- substance used to prevent multiplication of microorganism when applied to living systems
- antiseptic is BACTERIOSTATIC in action but not necessarily bactericidal
Physical Sterilization/Disinfection
- Autoclave
- Hot Air Sterilization
- Radiation (Gamma, Beta, X-ray sterilization)
- Filtration Disinfection
- Radiation (UV light)
Autoclave
- 15 lbs/sq inch pressure at 120C for 15-20 mins
- sterilizes with moisture, microorganisms destroyed at lower temp than dry heat
- method of choice if material is compatible
- fast, least toxic, cheap, large spectrum
Hot Air Sterilization
- 160C for 1-4 hours
- sterilizes and used on materials that would be damaged by moist heat (gauze, dressings, powders)
Filtration Disinfection
-via
Radiation
-used on materials that would be destroyed by heat (petri dishes, gloves, syringes)
- UV = Thymine Dimers (disinfects, but poor penetration)
- Ionizing (gamma, beta, X-rays) = breaks DNA backbone and sterilizes
Chemical Sterilization/Disinfection
- Ethylene Oxide (C2H4O)
- Alcohols
- Halogens
Ethylene Oxide (C2H4O)
- sterilizes powerful alkylating agent
- carcinogenic & explosive
- used as low-temp sterilization for heat-labile materials & delicate instruments
Alcohols
- 60-90% ethyl and isopropyl
- disrupts cellular membranes, solubilization of lipids, denatures prot. by acting as S-H functional group
- problem = evaporate rapidly (need extended contact times)
- ineffective against spores
Halogens
- Chlorine = 1:10 - good as disinfectant, but must be made fresh daily
- Iodine = good as disinfectant and antiseptic
- method of action - oxidizes microbial proteins
Disinfecting the Skin
- alcohol scrub better than soap and water
- NEED SOAP for C.difficile
- use of chlorohexidine alcohol for skin antisepsis, not povidone-iodine for surgical = significant reductions in hospital acquired infections
Biofilm
-microbes that are:
- attached to hydrated surface
- embedded in polysaccharide slime
- behave as community
- demonstrate antibiotic resistance and resistance clearance by the host immune system
- removed from the biofilm, the bacteria is sensitive to the antibiotic
-think splinters, teeth, knee replacement, etc.
Biofilm Diseases
- CF
- endocarditis
- osteomyelitis
- chronic UTI
- prostatitis
- otitis media
- dental infections
- endophthalmitis
- serious skin infections
- indwelling medical device
Significance of Biofilms
- 65-80% of all infections are biofilm related
- biofilm infection resolution = cut it out
- antimicrobial agents dont work (100-1000x more resistant)
- host immune response dont work
-$90 billion, 17 million infections/yr, 550,000 deaths/yr in United States alone
Why are biofilms resistant to bacteria?
- biofilms reduce antibiotic penetration
- cells within a biofilm are very slow growing (DNA and protein synthesis inhibitors not effective)
- cells within a biofilm express many stress response genes that resist antibiotic action
Implications of Biofilms to Infectious Disease
- inaccurate MIC/MBC (min inhibitory/bactericidal conc) prediction of bacterial populations
- inaccurate CFU determination from clinical samples (ex. UTI)
- viable but not cultureable
- missing the nidus of infection
