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107 Cards in this Set

  • Front
  • Back
definition of bacterial GROWTH:
orderly increase of all cellular components

during a period of baalnced growth a doubling of biomass is accompanied by a doubling of all other components such as protein, RNA and DNA
bacteria reproduce by
binary fission = division of cell (after doubling in size) into two identical cells
not involved in human disease

can utilize carbon dioxide as sole source of carbon (and synthesize from it carbon compounds required for growth)

require only: WATER, SALTS and CO2 for growth

energy is derived from: LIGHT or from oxidation of one or more inorganic materials

fix CO2 (similar to plants)
heterotrophic bacteria
require carbon supplied in the organic form

require complex organic molecules (like glucose), portion of compounds that serve as energy source is also used for the syntehsis of some or all of the organic compounds
all bacteria that cause human disease are part of what group?
(based on required source of carbon)
heterotrophic bacteria (require carbon supplied in organic form, unable to utilize CO2 as sole source of carbon)
role of CARBON in bacterial growth:
dual role
(2) the SOURCE OF CARBON for SYNTHESIS of all cellular components
simple sugars, such as glucose are commonly used for what two needs in bacterial growth?
source of energy and carbon for synthesis of cellular components
oxidation of one mole of glucose to water and CO2 provides what?
in the presence of O2, what do bacteria do with glucose
oxidize ~50% to CO2 and H2O
this, produces enough energy to...
convert the other 50% of glucose to cell material
why do bacterial cells need nitrogen for growth?
needed as building material (in protens, nucleic acids)
sources of Nitrogen for bacteria
some bacteria: simple ammonia (NH4+) salts, which can be incorporated into amino acids and protein

however, many require N preformed as amino acids or nucleic acids (e.g. Lactobacillus, Listeria) (amino acids can be supplied in digests of tissue protein, aa's considered growth factors)
peptone broth + glucose
convenient medium for growing bacteria
peptic digest of meat, containing peptides and amino acids (serves as nitrogen source) and can also be utilized as energy souce (along with glucose)
to obtain pure cultures of bacteria and to observe colonial morphology bacteria must be grown in...
solid rather than liquid media

(accomplished by adding agar to liquid media)
growth factors
organic (carbon) compounds that are not metabolized to supply energy, but are used to make metabolites that the bacterium cannot make from a simple carbon source such as glucose
categories of growth factors
1) B-complex vitaments (coenzymes or prostehetic groups of enzymes)
2) Amino acids for synthesis of protein (humans require 16 aa's)
3) Pyrimidines and purines for synthesis of DNA and RNA
inorganic ions required by all bacteria include:
phosphate, potassium, magnesium, sulfur, calcium, iron and zinc
role of iron chelation in bacterial defense and success
in human host powerful iron-binding proteins in tissue fluids function to deprive iron from microbial invaders

successful microbial invaders make their own powerful iron chelators (SIDEROPHORES) that extract iron from a variety of environments and make it available to the bacterium
Obligate anaerobes
grow only under conditions of high reducing intensity
oxygen is toxic for obligate anaerobes
Aerotolerant anaerobes
not killed by exposure to oxygen, but do not benefit from oxygen since they don't utilize it
Facultative anaerobes
are capable of growth under both aerobic and anaerobic conditions
Obligate aurobes
require oxygen for grwoth
growh best at low oxygen tensions, high tensions being inhibitory
metabolism is strictly fermentive in what type of bacteria/
obligate anaerobes
aurotolerant anaerobes
optimal temperature for pathogens
usually 37 degrees C (body temp)
environmental bactera generally grow best at
room temp (22-30 degrees C)
Mycobacterium lebrae (bacteria causing leprosy)
grows at what temperature?
growth in vivo is poor at 37 degrees (core body temp)

but lesions on skin and in innoculated footpad reflect growth at sites of reduced body temperature
storage in what will prevent growth of most pathogens?
a good refrigerator (below 4 degrees C)

(exception = Listeria, causative agent of food poisoning)
optimal temperature range for a given bacterium is determined by:
heat stability of proteins
How does pH effect bacterial grwoth?
effects growth rate

for pathogens usual range is from 6.0-8.0 with optimum growth at 7.4
Osmotic conditions required for bacterial growth
most bacteria do not need to regulate their internal osmolarity with precision, because they are enclosed by a cell wall, capable of withstanding a considerable internal osmotic pressure
concentration of osmotically active solutes is generally higher inside or outside a bacterial cell?
generally higher INSIDE a bacterial cells

bacteria can grow on media w/ low concentrations of NaCl,

very high salt and sugar concentrations inhibit growth of many pathogens
Ways to measure bacterial growth
1. Measurement of cell mass:
-optical density (really cell density)
2. Measurement of cell number
-direct count
-plate count
-determination of metabolic activity
measurement of bacteria, by measuring cell mass
impractical since 5 billion bacteria weigh only about 1 milligram
measurement of bacteria, by optical density
determination of amount of light scatter by a suspension of cells

increase in turbidity is a measurement of cell density

however, low cell densities cannot be detected even with spectrophotometer
measurement of bacteria, by direct count
requires: high concentrations of bacteria

viability is not measured, count includes both viable and non-viable cells
measurement of bacteria, by plate count
made by plating dilutions of a sample on a nutrident medium and counting # of colonies that arise

can back-calculate the # of viable cells in undiluted sample
measurement of bacteria, by determination of metabolic activity
sensitive method, in current clinical use
(production of metabolic products such as CO2 or ATP)

sensitive method for detecting bacteremia
describe bacterial growth curve under favorable conditions
incrases exponentially (since bacteria are unicellular) after doubling in size, divide to yield 2 cells
"generation time"

often used to describe the rate of growth during the log phase of growth
generation time of E. coli
~20 minutes
generation time of Myobacterium tuberculosis
~20 hours
growth of bacteria is limited when...
-a certain density is reached
-supply of certain nutrients is exhausted
-accumulation of toxic products prevents further growth
Stages of growth of a bacterial culture
LOG PHASE (exponential growth)
metabolic activity, but no increase in #s

cell mass and size begin to increase and syntehsis of macromolecules needed for growth in the new medium occurs
length of the lag phase depends on:
kind of bacteria
age and size of inoculum
nature of medium from which they were taken
and nutrients present in the new medium
cell numbers increase in logarithmic manner, with a constant generation time, and with cell # and mass increasing in coordinate manner
rate of cell division in log phase is dependent on:
rate of cell divison dependent on the type of organism, the nature of the medium, the temperature, and, for aerobic organisms, the rate of aeration
Bt = Bo x 2^n
Bo= initial # of bacteria
Bt = # of bacteria at time "t"
n = # of generations that have occured
logarithmic growth evneetually slows because of:
logarithmic growth eventually slows due to:
accumulation of waste products, exhaustion of nutrients, change in pH or a decrease in oxygen tension
population enters STATIONARY PHASE when
logarithmic growth slows to a point at which # of viable cells remains about constant (steady state in which some cells die as others continue to divide)
almost all pathogenic bacteria will grow to what concentration at the stationary phase in vivo?
between 5x10^8 and 1x10^9 bacteria /ml
when rate of death exceeds rate of reproduction and the number of viable cells declines

length of phase varies

cells often assume unusual shapes, making it difficult to recognize bcteria in old cultures
bacteria both divide and generally die in what type of pattern
factors which influence the bacterial colonization of the skin are:
1) low pH
2) fatty acid in sebaceous secretions
3) presence of lysozyme
why can't sweating nor washing eliminate normal flora?
surface flora are reconstituted by organisms that reside deeper within the hair follicles
individuals may shed up to how many bacteria in 30 minutes of exercise
10^6 (from flakes of skin)
vigorous surgical scrubbing diminishes the flora of the skin by:

but within 8 hours the flora is rapidly replenished, even when skin is kept out of contact with the environment

(scrubbing does remove any non-resident pathogens which are present on the skin, thus hand washing is critical for minimizing infections transmitted from patient to patient)
2 important points that distinguish microbial energy metabolism from eukaryotic energy metabolism
bacteria are more metabolically diverse
(some can utilize almost any organic compound for energy, pathogens usualyl more constrained)

FERMENTATION is relatively important way for many bacterial pathogens to gain energy (oxygen independent)
with the exception of photosynthetic organisms, all cells obtain energy by:
some kind of biological oxidation
in simplest sense the 2 main consequences of biological oxidation are:
-production of ATP (via direct or indirect processes)
-generation of high-energy electrons (MUST ultimately be transferred to an electron acceptor or carrier, not freely available in solution)
Fate of electrons generated by biological oxidation of growth substrates
1) respiration
2) fermentation
both routes allow for generation of ATP
NADH donates electrons to respiratory chain (series of cytochromes in IM) that converts energy of electrons into proton gradient

proton gradient (=PMF), used to indirectly generate ATP by way of IM-bound ATPase
production of ATP via resipiration is known as
terminal electron acceptors in
AEROBIC respiration
ANAEROBIC respiration
in AEROBIC respiration: OXYGEN is the final electron acceptor (O2 becomes H2O)

in ANAEROBIC respiration: a terminal electron acceptor OTHER THAN oxygen is used (e.g. NO3- is converted to N2)
electron acceptor in fermentation
either the starting substrate, or one of its catabolic products (such as pyruvate)
ATP is made in fermentation
directly, via transfer of high-energy phosphate bond to ADP

direct synthesis of ATP during fermentation is called
C(6)H(12)O(6) ---> 2 C(3)H(6)O(3) (lactic acid)

process is known as:
energy produced:
electron-acceptor is:
NAD+ is regenerated by:
energy produced = 58,000 cals
electron acceptor = pyruvate (intermediate)

NAD+ is regenerated via reduction of pyruvate to lactic acid
characteristics of bacteria that rely on fermentation
because fermentations are inefficient, generally have RAPID METABOLISM and/or GROW MORE SLOWLY
both fermentation and respiration
can begin with the same initial steps:

oxidation of glucose to form pyruvate (generating NADH and small amount of ATP)
fermentation and respiration differ in which steps?
NAD+ is regenerated by different mechanisms

ATP is formed by different processes
NAD+ regeneration in respiration
NADH donates its electrons to ETC to generate additional ATP and regenerate NAD+

*most energy generated at elvel of cytochrome system via ox/phos
cytochromes are found in:
-mitochondria of mammalian cells and yeast
-and some anaerobic bacteria
NAD+ regeneration in fermentation
NADH donates electrons to pyruvate to generate lactate (w/ NO additional ATP generation)
in fermentation most of the utilized carbohydrate appears as:
other reduced organic compounds

(accumulations are characteristic for different species of bacteria, used to id pathogenic bacteria)
in aerobic respiration, large portion of utilized carbohydrate appears as:
is assimilated into cellular materials
Pseudomonas aeruginosa (obligate aerobe that can respire in absence of oxygen)
can grow via nitrate (NO3-) respiration, form of respiration that occurs w/o oxygen, but NOT a type of fermentation
nitrate respiration
cytochrome system (similar to aerobic respiration) transports electrons to generate a proton gradient and to syntehsize ATP
Obligate anaerobes
can gain energy ONLY from fermentation
NO cytochromes
(examples: Bacteroides fragilis and Clostridium tetani)
Potential theories explaining existence of obligate anaerobes:
a) LACK CATALASE (toxic H2O2 accumulates)
b) LACK SUPEROXIDE DISMUTASE (superoxide accumulates)
c) Essential enzymes are inhibited or inactived by oxygen and reactive oxygen species (superoxide and peroxide)
Essential enzymes can be inhibited or inactived by oxygen and ROS via:
oxidation of SH groups
DNA damage and generation of mutations
Damage to proteins and lipids
anaerobic bacteria found in mouth and urinary tract indicate
that anaerobic conditions must exist there
what allows anaerobes to grow in surface tissues?
-presence of other bacteria or host tissues that use up oxygen and allow anaerobes to grow
what allows anaerobes to grow in vitro?
-presence of reducing agents in medium (cysteine, thioglycollic acid) that remove oxygen
Facultative anaerobes or aerobes
contain functional respiratory system and also have fermentive capacity

exhibit better growth aerobically than anaerobically
E. coli and Staphylococcus grow under what kind of oxygenation conditions?
aerobic or anaerobic (FACULTATIVE)
why do facultative anaerobes grow better aerobically?
respiratory enzymes allow more ATP to be generated than can be generated only by fermentation
Aerotolerant anaerobes
no functional respiratory system capable of ox/phos

indifferent to oxygen (not harmful)
example of an aerotolerant anaerobe
Stretococcus (contains no heme enzymes)
requires or will tolerate oxygen only at lower concentration than is found in air (<20% oxygen)
example of a microaerophile
Camplyobacter jejuni
3 important fermentations:
1. The lactic fermentation
2. The alcoholic fermentation
3. The mixed acid fermentation
Lactic fermentation
simplest fermentation, direct reduction of pyruvate by NADH and lactic dehydrogenase to lactic acid and NAD regenerated
(lactic acid accumulates, low pH discourages competing microbial growth)
bacteria that use lactic fermentation pathway
Lactic Acid bacteria:
-Lactobacilli (in vag and intestine)
(aerotolerant anaerobes, don't have respiratory enzymes)
other species involved in fermenting foods
pyruvate ---> acetaldehde and CO2 (appears as bubbles at slightly acidic pH)
acetaldehyde (reduced by NADH and alcohol dehydrogenase) --> ethanol + NAD (regenerated)
alcoholic fermentation is carried out by
yeast, such as those used to make booze
CO2 produced in alcoholic fermentation at acidic and alkaline pH?
at acidic pH ~ gas
alkalin pH ~ non-gaseous carbonate
The mixed acid fermentation is carried out by:
medically important group of GRAM NEGATIVE RODS (including: E. Coli and Salmonella)
The mixed acid fermentation
pyruvate is converted to: a 2-CARBON compound and to FORMIC ACID (HCOOH)

Formic acid can be converted to CO2 and Hydrogen gas if approprate enzyme is present (present in Salmonella, but not Shigella)

2 Carbons converted to other products, eg: ethanol, acetic acid, succinic acid
how are salmonella and shigella differentiated?
salmonella contains enzyme that can convert formic acid to Co2 and hydrogen gas

Shigella lacks this enzyme (accumulates formic acid instead of gas)
what is the unique bacterial product of mixed acid fermentation?
hydrogen gas (insoluble, readily detected in tissues durign infections by these bacteria) eg Salmonella
propionic acid
product of an unusual fermentation
w/ CO2 gives swiss cheese its flavor
organic acids have disinfectant properties
eg butyric acid
produced by anaerobe in normal human intestine

suppresses growth of intestinal pathogens, elimination of this anaerobe from intestine by antibiotics will enhance susceptibility to infection by intestinal pathogens
specialized fermentation by some Clostridia (obligate anaerobes often associated with wount infections)
energy is generated by fermentation of pairs of amino acids (one aa serves as electron donor, the other as electron acceptor)

occurs in petrefactive wounds (producing decarboxylated derivatives of amino acids ~often volatile and stinky!)
how do bacteria deal with high molecular weight compounds (such as proteins, starches, glycogen, nucleic acids)?
since cell is generally impermeable
many bacteria secretee EC enzymes (proteases, nuclease, phospholipases, cellulase, amylase) *may be periplasmic in gram-neg bacteria
some pathogens, such as gonococcus require an increased concentration of what in order to grow?

these organisms fix CO2, in mechanism quite different from that which occurs in plant photosynthesis