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Biological Characteristics of BacteriaBiological Characteristics of Bacteria
•The Growth, Survival & Death of
Microorganism
•Cultivation of Microorganism
•Microbial Metabolism
The growth of microorganisms
Growth is the orderly increase in all the components of an organism such as size and/or population number.
The rule for bacteria growth can be described as
single cell dynamics and population dynamics
Bacteria multiply by binary fission, the process in which a parent cell splits into two daughter cells with approximately equal size.
Growth:Growth: single cell dynamics
a. Bacterial cell first can been seen to enlarge or elongate.
a
b. Then followed by the formation of transverse membrane and new cell wall.
b
c. The new membrane and cell wall grow inward from the outer layers.
c
d. The cell divided into two daughter cells.d
•Under optimal conditions, the average time required for a
population of bacteria to double in number (for complete cell
division) is called as generation time or doubling time.
•The generation time for many common bacteria is 20-30 min, for a
few of slow-growing bacteria such as Tuberculosis bacteria might be
up to 18-20 h.
Growth:Growth: single cell dynamics
•When microorganisms are grown, due to some factors such as
nutrient limitation and waste accumulation, growth rate cannot
maintain for a long time.
Growth:Growth: population cell dynamics
•If a liquid medium is incubated with microbial cells, and the
number of viable bacterial cells per milliliter is measured and
plotted, we can obtain a curve that called as growth curve.
•Normally characterized by the phases lag, log (or exponential)
growth, stationary growth, and death.
How to Graph Bacterial Growth (i)How to Graph Bacterial Growth (i)
(I) Measuring the numbers of bacteria.
Common methods include:
a) Turbidity: to measure the total bacteria (live and dead) in liquid
cultures. This is usually quantitated with a spectrophotometer,
the absorption wavelength at 600 nm will be measured.
b) Colony counting method: that means counting the colony
numbers on a medium plate after inoculated with a known
volume of bacterial liquid culture.
Measuring total bacteria (live + dead) in liquid culture——Turbidity (Cloudiness)
The cloudiness of a liquid media caused by
bacteria growth that are generally invisible to
the naked eye, similar to smoke in air.
Measuring viable bacteria
colony
A visible cluster of bacteria
growing on the surface of or
within a solid medium,
presumably cultured from a
single cell
How to Graph Bacterial Growth (ii)How to Graph Bacterial Growth (ii)
(II) Plotting the log of turbidity or number of living cells
versus time is referred to as the growth curve (four or six
phases):
GrowthGrowth Curve (four Curve (four
phases)phases)
Y-axis presents the log number of living cellsX-axis presents the period of time (usually in hours)The curve can be divided into six phages represented by the letters A-F
GrowthGrowth curve (six phases)
A: lag phase,B: acceleration phase,C: log (exponential) phase,D: deceleration phase,E: stationary phase,F: death phase
What are the characteristics of bacteria in each phase?
Growth curve (four phases)
•The Lag Phase (A and B):
Bacteria are becoming "acclimated" to the new environmental conditions (pH, temperature, nutrients, etc.) (A).
Enzymes and intermediates are formed and accumulate until they are present in concentrations that are permit growth (B).
An increase in bacterial mass per unit of
volume, but no increase in cell count.
The metabolism of the bacteria adapts to the
conditions of the nutrient medium.
Growth curve (four phases)
•The Exponential/log Phase (C):
Conditions are optimal for growth.
The living bacteria population increases rapidly with
time at an exponential growth in numbers, and the
growth rate increasing with time.
The bacteria are suitable for biochemical and morphological identification,
The bacteria are suitable to use for drug sensitivity test
Growth curve (four phases)
•The Maximum Stationary Phase (D and E):
With the exhaustion of nutrients and accumulation of
metabolic wastes, the growth rate has slowed to the
point where the growth rate equals the death rate (D).
Effectively, there is no net growth in the living bacteria
population (E).
The bacteria produce spores, toxins (e.g.
exotoxin) and antibiotics.
Growth curve (four phases)
•The Decline Phase (F):
The living bacteria population decreases with time, due to a
lack of nutrients and toxic metabolic by-products.
In many cases (but not always) the bacteria autolyse (during
the death phase) and the turbidity decreases.
AABB
CC
DD
EE
FF
/exponential growth/exponential growth
accelerationacceleration
retardationretardation
/decline
maximummaximum
AABB
CC
DD
EE
FF
/exponential growth/exponential growth
accelerationacceleration
retardationretardation
/decline
maximummaximumSection Phase Growth rate
A Lag Zero
B Acceleration Increasing
C Exponential
/Log
Constant
D Retardation Decreasing
E Maximum stationary
Zero
F Decline/death Negative
GrowthGrowth curve
Biological Characteristics of BacteriaBiological Characteristics of Bacteria
• The Growth, Survival & Death of
Microorganism
• Cultivation of Microorganism
• Microbial Metabolism
What are the requirements for
bacterial growth?
Bacterial chemical components
• Water: free water and compound water.
• Inorganic salt: phosphus, potassium, magnesium, calcium, nitrium, etc.
• Protein: 50-80% of dry weight according bacterial kinds and age.
• Sugar: mainly distributing in cell wall and capsule.
• Lipids: composed of lipid, fatty acid, wax, etc.
• Nucleic acid: RNA and DNA.
Sources of metabolic energy
• fermentation An enzyme-induced chemical change in organic compounds
that takes place in the absence of oxygen. The change usually
results in the production of organic acids and energy
• respiration The process cells use to convert the energy in the chemical
bonds of nutrients to ATP energy.
Aerobic respiration
Anaerobic respiration
Sources of metabolic energy
•photosynthesis Reduction of an oxidant via a specific series of electron carriers
establishes the proton motive force.
Respiration: the energetically favorable oxidation of organic matter
by an electron acceptor such as oxygen
Photosynthesis: the reductant and oxidant are created
photochemically by light energy absorbed by pigments in the membrane
Bacterial Nutrition and Growth
•Nutrient Requirements:
Water
Carbon source (C)
Nitrogen source (N)
Inorganic salts
Growth factors
Sulfur source (S)
Phosphorus source (P)
•Environmental factors for bacteria growth:
Temperature
Gas (oxygen)
pH
Osmotic pressure
1) Carbon source
Based on their source of carbon including nitrogen, bacteria are
divided into two groups : Autotrophs and Heterotrophs.
Autotrophs: This group of bacteria has a more complete enzyme
system so they can obtain energy and various nutrients from simple
compounds such as carbon from CO2.
Nutrient Requirements
None of these organisms are pathogenic !
Heterotrophs: This group of bacteria has a simpler set of
enzymes so they must use organic carbon for growth.
It can be further divided into:
Parasitic bacteria: grow in and feed on a different organism.
Saprophytic bacteria: obtain their nutrients from dead or decaying organic
matter.
Most of pathogenic bacteria are parasitic bacteria.
Some saprophytic bacteria cause disease by acting on food to
produce toxins.
2) Nitrogen source
A major component of proteins, nucleic acids, and other
compounds.
Nitrogen fixation: The ability to assimilate N2 reductively via
NH3. This process requires a large amount of metabolic energy and is
readily inactivated by oxygen. It is a property unique to prokaryotes,
especially in divergent bacteria, that have evolved quite different
biochemical strategies to protect their nitrogen-fixing enzymes from
oxygen.
Nutrient Requirements
3) Mineral source
Required for appropriate osmotic pressure.
Additionally, also needed to stabilize or activate certain
enzymes.
Nutrient Requirements
In formulating a medium for the cultivation of most microorganisms,
it is necessary to provide sources of potassium, magnesium, calcium,
and iron, usually as their ions (K+, Mg2+, Ca2+, and Fe2+).
4) Growth factors
A growth factor is an organic compound which a cell
must contain in order to grow but unable to synthesize.
A number of different growth factors are required for
bacterial growth such as amino acids, purines, pyrimidines,
and some certain vitamins.
Nutrient Requirements
5) pH
Most bacteria have a narrow optimal pH range.
Neutralophiles: grow best at neutral pH (pH 6.0-8.0, 7.5)
Some can survive/grow
- Acidophiles (pH 1.0-6.5 )
- Alkaliphiles (pH 9.0-11 )
Environmental factors for bacteria growth
Internal pH is regulated by a set of proton transport systems in the
cytoplasmic membrane, including a primary, ATP-driven proton pump.
6) Temperature
Different microbial species are vary widely in their optimal
temperature ranges for growth:
Mesophilic forms 30-37 ℃
All human microbial pathogens belong to this forms
Psychrophilic forms 15-20 ℃
Thermophilic forms 50-60 ℃
Environmental factors for bacteria growth
High Temperature
static action cidal action
6) Temperature
Heat-shock response:a transient synthesis of a set of "heat-shock proteins," when
exposed to a sudden rise in temperature above the growth
optimum. These proteins appear to be unusually heat-
resistant and to stabilize the heat-sensitive proteins of the
cell.
Cold shock response: the killing of cells by rapid as opposed to slow cooling.
7) Gas Requirements According to the requirement of O2 during bacteria growth,
bacteria can be divided into four groups:
Aerobic Anaerobic
1. Obligate aerobe: Growth No growth
2. Microaerophile: Growth at low O2 No growth
3. Obligate Anaerobe: No growth Growth
4. Facultative aerobe: Growth Growth
Environmental factors for bacteria growth
Obligate aerobes
• grow in presence of oxygen
• no fermentation
• oxidative phosphorylation
(Electron transfer through the cytochrome system liberating free
energy which is transformed into high-energy phosphate bonds)
Microaerophile (Microaerophilic bacteria)
grow – low oxygen (2-5%)
killed – high oxygen
• no oxidative phosphorylation• fermentation• killed by oxygen• lack certain enzymes：
Obligate anaerobes
peroxidase
O2-
+2H+
H2O2
superoxide dismutase
catalase
H2O + O2
H2O /NAD NADH
Facultative anaerobes
• fermentation and oxidative phosphorylation • aerobic respiration• survive in oxygen
Cultivation methods
Concerning two parts:
I. Choice of suitable medium
II. Isolation of bacteria for pure culture
I. Choice of suitable I. Choice of suitable
mediummedium
Medium (I)
(1) raise a crop of cells of a particular species that is on ha
nd;
(2) determine the numbers and types of organisms present
in a given material;
(3) isolate a particular type of microorganism from a natur
al source.
Medium (I)
• A classification of media based on their respective usages:
Basic medium
Enrichment medium
Selective medium
Differential medium
Basic medium:
supplies only the minimal nutritional requirements of a
particular microorganism. e.g. broth
Enrichment medium:
Nutrient broth, nutrient agar, peptone water are commonly used
in enrichment media. e.g. blood agar plate
Selective medium:
Supports the growth of desired bacteria while inhibiting the
growth of many or most of the unwanted ones, either by
adding one or more selective agents which is a "poison" to the
unwanted bacteria but not harmful to desired bacteria, or by
including certain nutrients for the desired ones and deleting
certain nutrients for the unwanted ones.
e.g. L-G medium for M. tuberculosis
Differential medium
This medium allows two or more different bacteria to grow,
but it contains dyes and/or other components upon which
different bacteria act in various ways to produce a variety of
end products or effects (usually by showing different colors).
e.g. SS agar
Medium (II)
• Classification according to physical condition
(according to the content of solidifying agent):
liquid medium
Solid medium
Semi-solid medium
• Agar
•The major solidifying agent used in bacteriological media.
• An polysaccharide gum that extracted from certain red algae.
• Agar can be dissolved at 100 C, and solidified at about 43 C.
•Added 1.5-2.0% of Agar for solid plates or slanted media, 0.1-
0.5% for semisolid media.
Usage of different media
• liquid medium
Used to obtain a large number of bacteria, and to perform
drug sensitivity test and bacterial growth assay.
The bacteria grown in liquid medium will display some
certain characteristics of bacteria (alignment and clustering)
that can't be seen easily in solid media.
• Phenomena of bacterial growth in liquid medium
(i) forming cloudiness in broth
(growth with uniform turbid pattern),
(i) forming a ring at the top of broth
(growth with suspension pattern)
(ii) forming sediment at the bottom of
broth
(growth with sedimentary pattern)
ii ii ii iii iii
Solid medium
Used to obtain a large number of bacteria, isolate identical clones
of bacteria (colony), and to perform drug sensitivity test.
A colony is a bacterial cluster which propagated (multiplied)
from a single initial bacterial cell (So a colony is a pure bacterial
culture).
Colony can be used to determine the original bacterial numbers
by counting colonies and to evaluate viability of bacteria (colony
forming units, CFU).
Semisolid medium
Test the motility of bacteria (a bacterium has a flagellum or
flagella whether or not )
Positive: bacteria grow into the medium
give cloudiness to the medium.
Negative: bacteria grow in situ.
Cultivation methods
II. Isolation of bacteria in pure II. Isolation of bacteria in pure
culture culture
•In order to study the properties of a given bacterium, it is
necessary to handle it in pure culture (free of all other
types of bacteria).
•Several methods are used to get pure-culture purpose:
a) Platingpour-plate methodStreaking
b) Dilution
Pour-plate methodPour-plate method
Pour Plate
A suspension of bacteria is mixed
with melted agar at 50 C and poured
into a dish. When the agar solidifies,
the bacterial cells are immobilized in
the agar and grow into colonies after
incubation.
If the suspension was sufficiently
dilute, the colonies will be well
separated.
StreakingStreaking
Procedure:
1. Flame the loop and streak a loopful of broth culture as at A in the diagram. 2. Reflame the loop and cool it. 3. Streak as at B to spread the original inoculum over more of the agar. 4. Reflame the loop and cool it. 5. Streak as at C. 6. Reflame the loop and cool it. 7. Streak as at D. 8. Incubate the plate inverted.
StreakingStreaking
By spreading a large amount of bacteria over the surface of a plate,
the amount of bacteria is diluted and individual cells are spread.
From these individual cells a single colony arises.
Wire loop
Dish
Colony (pure culture)
• DilutionDilution
•A much less reliable method for pure culture.
a) The suspension is serially diluted and samples of each
dilution are plated.
b) If only a few samples of a particular dilution exhibit
growth, it is presumed that some of these cultures started
from single cells.
Steps in isolation and identification
•Sample collection
•Isolation (pure culture)
•Identification (microscopy and biochemical)
•Classification (species, type)
•Susceptibility to antibiotics
• Sample collection:
Depending on the disease suspected, different types of
specimens can be taken for culture,
e.g. stool for diarrhoea, and urine for urinary tract
infection.
• Susceptibility to antibiotics
A pure culture of bacteria can be tested for antibiotic resistance
by evenly swabbing it over an agar plate and pressing discs of
antibiotic into the agar. After a period of incubation, sensitivity
or resistance to the antibiotic can be determined by measuring
the zone that forms around the disc.
Large zones mean the bacteria
are sensitive to the drug
Small or nonexistent zones are
signs of resistance.
Biological Characteristics of BacteriaBiological Characteristics of Bacteria
• The Growth, Survival & Death of
Microorganism
• Cultivation of Microorganism
• Microbial Metabolism
Microbial Metabolism
Metabolism refers to all the biochemical reactions that occur in a
cell or organism.
1) pathways for the interconversion of focal metabolites
2) assimilatory pathways for the formation of focal metabolites
3) biosynthetic sequences for the conversion of focal metabolites to
end products
4) pathways that yield metabolic energy for growth and
maintenance.
Microbial Metabolism
The key concepts of glycolysis, Krebs Cycle, oxidative
phosphorylation have been or will be discussed in biochemistry.
Concentrates here are put on the products of bacterial metabolism
with medical importance (e.g. for laboratory diagnosis or for
bacterial pathogenesis).
• Medical Important Metabolic Products
1. anabolic processes (synthesis or build up)
2. catabolic processes (decomposition or break down)
Catabolic Products and Biochemical Testing
a. Carbohydrate Fermentation Tests
Medium: Carbohydrate fermentation broth with a
Durham tube (a small inverted vial filled with the
carbohydrate fermentation broth).
If gas is produced during fermentation of the sugar, it is
trapped at the top of the Durham tube and appears as a
bubble.
pH indicator: phenol red
a. Carbohydrate Fermentation Tests
Principle: Because the type of enzyme(s) produced by
bacteria is genetically controlled, the fermented pattern of
sugars may be unique to a species, but may be different
between different species.
Fermentation products are usually acid (lactic acid, acetic
acid etc.), neutral (ethanol etc.) or gases (carbon dioxide,
hyrogen, etc).
a. Carbohydrate Fermentation Tests
Result:
positive
yellow color
yellow color with gas bubble
negative
red color, no gas bubble
b. Methyl Red (MR) Test
Medium: contains glucose and peptone
Indicator: methyl Red
All enterics oxidize glucose for energy; however the end
products vary depending on bacterial enzymes.
b. Methyl Red (MR) Test
For bacteria (e.g. E. coli ) that produces acids, causing the pH to
drop below 4.4. When the pH indicator methyl red is added to this
acidic broth it will be cherry red (a positive MR test).
For bacteria (e.g. Klebsiella and Enterobacter) that produce more
neutral products from glucose (e.g. ethyl alcohol, acetyl methyl
carbinol). In this neutral pH the growth of the bacteria is not
inhibited. The bacteria thus begin to attack the peptone in the broth,
causing the pH to rise above 6.2. At this pH, methyl red indicator is
a yellow color (a negative MR test).
Result:Result:
c. Voges-Proskauer (VP) Test
Medium: contains glucose and peptone Indicator: Barritt's A (alpha-napthol) and Barritt's B (potassium hydroxide)
When these reagents are added to a broth in which acetyl methyl carbinol is present, they turn a pink-burgundy color (a positive VP test).
This color may take 20 to 30 minutes to develop.
E. coli does not produce acetyl methyl carbinol, but Enterobacter and Klebsiella do.
c. Voges-Proskauer (VP) Test
d. Citrate Utilization Test
The citrate test utilizes Simmon's citrate
media to determine if a bacterium can grow
utilizing citrate as its sole carbon and
energy source.
Growth of bacteria in the media leads to
development of a Prussian blue color
(positive citrate).
e. Indole TestThe test organism is inoculated into tryptone broth, a rich
source of the amino acid tryptophan.
Indole positive bacteria such as E. coli produce tryptophanase,
an enzyme that cleaves tryptophan, producing indole and other
products.
When Kovac's reagent is added to a
broth with indole in it, a dark pink
color develops.
I M Vi C test
VP testCitrate utilization test
Indol testMethyl test
I M Vi CE. coli + + — —
C. perfringens — — + +
• f. Hydrogen Sulfide (H2S ) formation
To determine the ability of a bacterium to produce hydrogen
sulfide (H2S) by enzymatic reaction on amino acids such as
cysteine, cystine and methionine.
The hydrogen sulfide combines with ferrous
sulfide (Fe2S) in the triple sugar iron (TSI)
agar to form a black to dark insoluble
precipitate.
• g. Urease Test
Medium: urea agar slant
Indicator: phenol red
Principle: The hydrolysis of urea by urease produces ammonia and carbon dioxide. The formation of ammonia alkalinizes the medium, and the pH is detected by the color change from light orange to pink-red.
Positive result: pink-red color
Negative result: light orange
What are the medically important
anabolic products of bacteria?
Synthetic Products
• Pyrogens • Toxins and Invasive Enzymes• Antibiotics• Vitamins• Bacteriocins• Pigments
• Pyrogens Pyrogens
• the products of many bacteria, especially gram-negative
bacteria, which resulting in fever when injected into animals or
humans.
• They are polysaccharides in cell wall (G+ bacteria) or LPS
(G- bacteria).
• They are highly resistant to high heat (not being destroyed
heating at 121C for 15-20 min), but can be destroyed by
heating to 250 C for 30 min.
• They can be removed from most fluid materials by adsorption
using special materials.
• Toxins Toxins andand Invasive Enzymes Invasive Enzymes
• According to difference on the chemical composition,
toxicity, bioactivity, antigenicity and so on, bacterial
toxins can be divided into exotoxin (polypeptide or
protein) and endotoxin (LPS).
• Invasive enzymes secreted by bacteria can help bacteria
to invade host. So they contributed to the pathogenesis of
bacteria.
• AntibioticsAntibiotics
• The substance produced by many fungi and a
small number of bacteria that selectively kill or
inhibit other organisms.
• VitaminsVitamins
• A few bacteria produce various vitamins, e.g.
some certain bacteria growing in the intestine
produce vitamin K. This action is thought to be
beneficial to the host.
• BacteriocinsBacteriocins
• Substances produced by specific strains of bacteria
that are lethal against other strains of the same or
related species.
• They are protein or lipopolysaccharide-protein
complexes.
• pigmentspigments
• Produced by a small number of bacteria with
characteristic colors.
I) water soluble Pseudomonas aeruginosa can produce a green water soluble
pigment, so that the color is distributed throughout the culture.
II) liposolubleStaphylococcus aureus can produce a golden yellow liposoluble
pigment and this color only show in their colonies.
• Help to identify some of bacteria.
Pseudomonas aeruginosa produces a blue-green pigment, which diffuses into the medium giving the plate a characteristic color.
Staphylococcus aureus produces a golden yellow pigment and give the colonies this color.
The medical significance of these products
Products Medical significance
pyrogen
Pathogenicity of bacteriatoxin
Invasive enzyme
Antibiotic Treatment of infectious diseasesVitamin
Bacteriocin Identification of bacteria
pigment
Antibiotics and
Antibiotic Resistance
Antibiotics
Antibiotics are powerful medicines that fight bacterial infection
Literal translation• anti – against• biotic – living things
How antibiotics workAntibiotics can be either• Broad Spectrum
– Kill a wide range of bacteria e.g. Penicillin
• Narrow Spectrum
– Kill a specific type or group of bacteria e.g. Isoniazid, Rifampicintablets
Antibiotics work in one of two ways• Bactericidal
– Kills the bacteria
• Bacteriostatic– Prevents the bacteria from dividing
Miracle Cure?
– Before the 1930s there were no treatments for bacterial infections
– Following the discovery of penicillin industry started searching for more antibiotics in nature
– Streptomycin was the first drug to have an effect on tuberculosis – a condition previously untreatable
– Surgeons could attempt more dangerous operations
Miracle Cure?
– Many antibiotics prescribed by the doctor are broad spectrum
– These kill the body’s good bacteria as well as the bad
– With the good bacteria gone there is more room for bad microbes to invade!
Overuse of antibiotics can damage our normal/good bacteria.
Miracle Cure?
Antibiotics resistance Many bacteria have developed the ability to become
resistant to antibiotics.
These bacteria are now a major threat in our hospitals.
Antibiotic resistant bacteria include Methicillin Resistant Staphylococcus aureus (MRSA)
Antibiotic Resistance
The Causes
– Overuse
• Antibiotics used to treat infections when they are not needed or not effective i.e. for the flu
– Misuse
• Not completing a prescribed course
• Using antibiotics not prescribed for you
Bacterialcidal Mechanism
Cell Wall Cell Membrane
Mitochondria DNA RibosomalComplex
Bacterialcidal Mechanism
• Damaging or inhibiting synthesis of the bacterial cell
wall (penicillins, cephalosporins, monobactams,
carbapenems, bacitracin, vancomycin, cycloserine,
fosfomycin)
• Damaging or inhibiting synthesis of the cell
membrane (polymyxins)
Bacterialcidal Mechanism
• Metabolizing or inhibiting DNA synthesis of nucleic acids
(rifampin, nitrofurantoins, nitromidazoles)
• Modifying ribosomal energy metabolism (sulfonamides,
trimethroprim, dapsone, isoniazid)
• Inhibiting ribosomal protein biosynthesis (aminoglycosides,
tetracyclines, chloramphenicol, erythromycin, clindamycin, spectinomycin,
mupirocin, fusidic acid)
Acquired Bacterial Resistance
VirusPlasmid
Acquired Bacterial Resistance
• Receiving a plasmid bearing a resistance gene from
another bacterium directly
• Receiving a resistance gene from other bacterium by
viral transfection
• Chromosomal mutation
• DNA scavenged from dead bacteria
Mechanisms of resistance
Penicillins,Cephalosporins
Tetracycline
Streptococcus pneumoniae resistance to penicillins
MRSA penicillin
binding protein PBP2A
Imipenem resistant Pseudomonas aeruginosae
Mechanisms of resistance
• Antibiotic modification: some bacteria have enzymes that cleave or modify antibiotics: e.g. β-lactamase inactivates penicillin
• Denied access: membrane becomes impermeable for antibiotic: e.g. imipenem
• Pumping out the antibiotic faster than it gets in: e.g. tetracyclines
• Altered target site: antibiotic cannot bind to its intended target because the target itself has been modified
• Production of alternative target (typically enzyme): e.g. Alternative penicillin binding protein (PBP2a) in MRSA
Loss of Antibiotic Resistance
• Antibiotic resistant bacteria are at a selective
disadvantage - they must expend energy and
resources to manufacture proteins that confer
resistance
• The prevalence of resistant bacteria declines after
antibiotics are withdrawn
How antibiotic resistance can be prevented
– Antibiotics should be the last line of defence NOT the first
• Most common infections will get better by themselves through time, bed rest, liquid intake and healthy living.
– Only take antibiotics prescribed by a doctor
– If prescribed antibiotics, finish the course.
– Do not use other peoples or leftover antibiotics • they be specific for some other infection
Summary
1) Definitions: pyrogen, antibiotic and acteriocin
2) Bacteria growth curve, especially the characteristics and application of log
phase and maximum stationary phase.
3) The medically important antibiotic products of bacteria
4) The requirements of bacterial growth
5) The mode of bacterial reproduction
