Microbiology Notes 21 Flashcards
Gas requirements of microorganisms
The atmospheric gases that most influence the growth of microorganisms are oxygen (O2) and carbon dioxide (CO2)
Oxygen concentration in air is about 20%
CO2 concentration is about 0.003% (3,000 ppm)
Which atmospheric gases influence the growth of microorganisms the most?
oxygen (O2) and carbon dioxide (CO2)
What is the concentration of oxygen in the air?
about 20%
What is the concentration of CO2 in the air?
about 0.003% (3,000 ppm)
How do capnophiles grow better?
grow better at 3-10% concentrations of CO2
Name 3 capnophiles
Neisseria, Brucella and Streptococcus pneumonia
What is oxygen essential for?
LIFE
What is a powerful oxidizing agent that exists in many toxic forms for life?
Oxygen
Microorganisms can be:
Oxygen users- aerobes
Oxygen detoxifiers
Non-oxygen users or detoxifiers- anaerobes
Non-oxygen users but detoxifiers
Dangerous metabolic products of O2 include:
1O2 singlet oxygen (extremely reactive molecule produced by both living and non-living processes)
-O2 superoxide ion
H2O2 peroxide molecule
OH- hydroxyl radicals
Which bacteria mostly have enzymes to neutralize O2 by-products?
Aerobic
Aerobic Bacteria
Superoxide dismutase catalyzes which reaction?
-O2 + -O2 + 2H + ==> H2O2 + O2
-O2 from phagocytes
Aerobic Bacteria
Catalase catalyzes which reaction?
H2O2 + H2O2 ==> 2H2O + O2
Most bacteria, fungi, algae and protozoa are: aerobes or anaerobes?
Aerobes
Which type of bacteria lack superoxide dismutase and catalase to process deleterious forms of oxygen?
Anaerobes
Which type of bacteria can not deal with the presence of oxygen and die due to its toxicity?
Anaerobic
Growing which type of bacteria usually requires special media, methods of incubation, and handling chambers that exclude oxygen?
Anaerobic bacteria
Which bacteria live in deep mud, bottom of oceans, deep soil, and inside animal bodies?
Anaerobic
Which bacteria’s metabolism does not require O2 for growth and is not affected by its presence?
Faculative anaerobic bacteria
Which type of bacteria can adopt an anaerobic mode of metabolism (fermentation) or opt for aerobic respiration?
Faculative anaerobic bacteria
Which bacteria have both superoxide dismutase and catalase enzymes?
Faculative anaerobic bacteria (and aerobic bacteria)
Which bacteria do not utilize oxygen but can tolerate its presence?
Aerotolerant anaerobes
Which bacteria possess alternate mechanisms for the breaking down of peroxide and superoxide?
Aerotolerant anaerobes
Certain lactobacilli and streptococci use manganese ions or peroxidases instead, to perform the task of breaking down peroxide or superoxide.
Aerotolerant anaerobes
Which bacteria require only a very small amount of oxygen for growth?
Microaerophilic
Which type of bacteria is Treponema pallidum?
Microaerophillic
What is Treponema pallidum?
The causative agent of syphilis
Where are microaerophilic bacteria found?
In soil, water and some human bacterial microflora
The majority of microorganisms live or grow in habitats with a pH of?
between 6 and 8
Why do the majority of microorganisms live or grow in habitats with a pH between 6 and 8?
because strong acids and bases can be highly damaging to enzymes and other cellular substances
In what pH do human pathogens grow in?
6.5-7.5
What pH does Euglena mutabilis (algae) tolerate?
0-1 (acidophil)
What pH does Thermoplasma (an archaea bacterum with no cell wall) tolerate?
1-2 (lyses at 7)
What can molds and yeasts (fungi) spoil?
pickled foods
What are molds and yeasts?
Acidophiles
Acidophiles
A few species of algae and bacteria can actually survive at a pH near that of concentrated hydrochloric acid.
What are alkalinophiles?
bacteria found in soils with high concentrations of ammonia (NH4)
Alkalinophiles
Metabolism of urea is one way that Proteus spp. can neutralize the acidity of the urine to colonize and infect the urinary system.
Most microbes exist under what kind of osmotic pressure?
hypotonic or isotonic conditions
Which microorganisms are resistant to high-salt environments?
Osmophilic microorganisms
Halophiles
Halobacterium, Halococcus (10-25% NaCl)
What bacteria resists or grows in high salt concentration but can also live in a non-salty environment? Staphylococcus aureus (0.1-20% NaCl)
Faculative halophiles
Which bacteria stand high hydrostatic pressures (bottom of oceans up to 1000x atm)? These bacteria are so adapted to high pressures that they will rupture or lyse when exposed to normal atmospheric pressure.
Barophiles
Microbial interactions
Microorganisms coexist in varied relationships in nature.
Reciprocal, obligatory and beneficial relationship between two organisms.
Symbiotic interactions
Mutualism
An organism receiving benefits from another without harming the other organism in the relationship.
“Making a living” as intestinal normal flora
Could become a parasite or cause disease
Lactobacillus protects vagina against infections due to
low pH
Staphylococcus epidermis lives on human skin
Many thrive in mouth and large intestine
Symbiotic interactions
Commensalism
Lactobacillus is involved in which type of symbiotic interaction?
Commensalism
What does Lactobacillus help with?
Protects the vagina against infections due to low pH
Where does staphylococcus epidermis live?
On human skin
Staphylococcus epidermis is involved in which type of symbiotic interaction?
Commensalism
Name the 3 Symbiotic interactions
- Mutualism
- Commensalism
- Parasitism
Occurs between a host and an infectious agent; the host is harmed in the interaction
Symbiotic interaction
Parasitism
A mutually beneficial but not obligatory coexistence in which organisms cooperate to produce a reaction
Non-symbiotic interaction
Synergism
Entails competition, inhibition, and injury directed against the opposing organism
Non-symbiotic interaction
Antagonism
Antibiotic production is a special case of which non-symbiotic interaction?
Antagonism
An interactioin among members of a biofilm that results in a coordinated reaction, such as secretion of inducer molecules
By behaving as a unit, the biofilm remains stable and organized
It can occupy and exploit a wide variety of habitats
Quorum sensing
Microbial growth
Steps of the binary or transversal fission in bacteria
Cell enlarges
Duplication of chromosomes
Formation of central transverse septum
Septum breaks into two daughter cells
Time needed for a bacterial population to double in number
Generation time (GT)
The length of the __ is a measure of the growth rate of an organism
Generation time (GT)
Compared to other living organisms, bacteria are notoriously rapid
Generation time (GT)
Population doubles by a factor of
two (binary) 2,4,8,16,32,64 and so on
Generation time
2^n; what is n?
n is the number of generations
Bacterial population growth is…
geometric or exponential
Bacterial populations can grow at a constant rate if all conditions are…
favorable
Microbial populations grow slor or fast according to…
species
The average generation time (GT) is…
30-60 min under optimum conditions, and longer GT require even days
Mycobacterium leprae generation time (GT)
10-30 days/gen
Salmonella enteritidis generation time (GT)
20-30 min/gen
Staphylococcus aureus generation time (GT)
20-30 min/gen
Growth curve of a bacterial culture
Lag phase Log phase Stationary phase Death phase (relative rates of these events change as the curve proceeds)
Lag phase
few or no cells
Log phase
exponential; most cells are alive
Stationary phase
decrease growth
Death phase
curve dips downwards
If the GT of a bacterial species is 20 min then each cell in the total population will reproduce every 20 min in its ___ phase.
log
In a few hours, a population of bacteria can easily grow from a small number of cells to several _________
million
Large bacteria growth numbers
a population may rise from 1,000 in 30 min to 1,000,000,000 in 16 hours
Logarithmic (log) numbers
are used to express bacterial populations in a shorter form
9,658,780 is transformed to a logarithmic form as: log10 9,658,780=6.73
10^6.73 is equal to 9,658,780
Enumeration of microorganisms
Cell numbers can be counted directly by
Microscopic counting chamber
Coulter chamber
Flow cytometer
Other new methods
Cell growth can be determined by
turbidometry and a total cell count
Practical importance of the growth curve
Populations grow slow or fast
Microbes in log phase are more sensitive to changes in the environment
Microbes in log phase are more numerous and virulent than those released later
An infected person sheds more bacteria in early and middle stages of infection
Faster multiplication rate may overwhelm the slower growth rate of the host’s cellular defenses
Do not culture cells beyond stationary phase
Stain young cultures not old ones
Heat and disinfectants increase death rates
Calculations
Size of population over time: Nf=Ni(2^n)
Ni = initial number of bacteria
Nf = final number of bacteria
n = number of generations
2^n = number of bacteria in the generation
Solve for n: Log Nf = log Ni + nlog2 Where n= Log Nf-logNi/log2
refer to pg 7 notes 21 for example
One million bacteria are enough to…
spoil food (approximately equivalent to a population derived from 20 generations) look at example on pg 8 notes 21
When bacterium grows in a culture medium its log phase is
relatively short
A bacteriums log phase is limited by
nutrient depletion, oxygen depravation, accumulation of inhibitory products, etc.
