Download 17. BW_7.19 Bacteria..

Bacterial Cell Wall
Morphology; Mechanism of
Pathogenicity
Brandy Welch
[email protected]
Content Objectives
❖ Bacterial Cell Wall Morphology
➢ Understand the different biological factors used to classify bacteria
➢ Understand the bacterial cell wall composition and characteristics
➢ Understand the major components of peptidoglycan and the major difference between gram
positive and gram negative cell walls
➢ Know the external cell wall structure and their purpose
❖ Mechanism of Pathogenicity
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Identify the principal portals of entry
Explain how microbes adhere to host cells
Explain how capsule and cell wall components contribute to pathogenicity
Identify and understand the role of bacterial enzymes in pathogenicity
Compare the types of bacterial exotoxins, their mechanism of action, and the
bacterium/diseases associated with each
➢ Define and give an example of antigenic variation
➢ Contrast the nature and effect of exotoxins and endotoxins
Bacterial Cell Wall
Morphology
Prokaryotes
❖ Prokaryotes include bacteria and archaea
❖ Lecture will focus on bacteria
❖ Bacteria may be classified by:
➢ Morphology
■ shape
➢ Nutritional requirements
➢ Chemical composition
➢ Biochemical activities
➢ Source of energy
■ Sunlight or chemical
The Bacterial Cell
❖ Size range
➢ Diameter = 0.2 - 2.0 um
➢ Length = 2 - 8 um
❖ Shapes
➢ Coccus (cocci)
➢ Bacillus (bacilli)
➢ Spiral
■ Vibrio
❖ Arrangement
➢ Diplo
➢ Strepto
➢ staphylo
Arrangement of Cocci
❖ Cocci are usually
round but can appear
oval, elongated, or
flattened on one side
Arrangement of Bacilli
❖ Bacilli divide only across
their short axis
➢ They do not form the same
number of groupons as cocci
❖ Most bacilli appear as
single rods
Arrangement of Spiral Bacteria
❖ Spiral bacteria have one or more twists
➢ Bacteria that look like curved rods are called
vibrios
➢ Spiralla have a helical shape like a corkscrew
and fairly rigid bodies
■ Use flagella to move
➢ Spirochetes are helical and flexible
■ Move via means of axial filaments
The Bacterial Cell
The Cell Wall: Composition and Characteristics
❖ Complex, semi-rigid
❖ Responsible for cell shape
❖ Protects the interior of the cell from the external environment
❖ Maintains osmotic pressure
❖ Composed of macromolecular network called peptidoglycan
Lipopolysaccaride - LPS
Found in the outer leaflet of the outer membrane
Is also called endotoxin
Can induce shock
Composed of lipid A, core antigen, and O somatic antigen
Biological activity is due to lipid A
Lipopolysaccharide
Peptidoglycan
Provides shape and structure to the cell
Composed of B 1-4 linked N-amino sugars
N-acetyl glucosamine (NAG)
N-acetyl muramic acid (NAM)
Composed of L and D amino acids
Composed of cross linked amino acids
Peptidoglycan
❖ Consists of repeating disaccharides
(NAG/NAM) attached by
polypeptides
❖ Alternating NAG and NAM molecule
are linked within rows
❖ Polypeptides link adjacent rows
❖ Penicillin blocks peptide cross
bridges, causing lysis
Peptidoglycan
Peptidoclycan: Gram Positive Cell Wall
❖ In most gram positive bacteria, the cell wall consists of many layers of
peptidoglycan
➢ Forming a thick rigid structure
Gram Positive Cell Wall
❖ Cell wall contains teichoic acid (LTA)
➢ Provides a negative charge to regulate cation movement in/out the cell
Peptidoglycan: Gram Negative Cell Wall
❖ Consists of only one or a few layers of peptidoglycan
➢ More susceptible to breakage
❖ Has an outer membrane with LPS
➢ LPS is lipopolysaccharide
❖ Do not contain teichoic acid
Antiobiotics That Inhibit Bacterial Cell Wall Formation
Penicillin
Binds to PBP
Inhibits transpeptidase activity
Cephalosporin
Binds to PBP
Inhibits transpeptidase activity
Vancomycin
Complexes with D-Ala-D-Ala, blocking transpeptidase action
Bacitracin
Inhibits the transfer of peptidoglycan subunits from bactoprenol to preexisting peptidoglycan cell
wall
Cycloserine
Structural analog of D-Ala
External Cell Wall
❖ External structures may function to facilitate actions such as movement,
attachment, and propagation
➢ Glycocalyx (dugary coat) is the general term for the substance that surrounds the cell
■ Capsule
■ Slime layer
➢ Flagella
➢ Axial filament
➢ Fimbriae
➢ Pili
❖ Movement of bacteria toward or away from stimuli is call taxis
Bacterial Endospores
Spore formation is characteristic of two genera
Bacillus and Clostridium
Sporulation occurs when the bacterium is under environmental stress
Lack of nutrients
Extreme temperature
The structure of the spore allows it resist detrimental physical and chemical
conditions
Ca2+ and dipicolinic acid of the spore coat contribute to its heat resistance
Bacterial spores are destroyed via autoclaving at 121oC for 20 minutes
Flagella
❖ Flagella are long filamentous
appendages that propel
bacteria
➢ Four arrangement of flagella
❖ Certain bacteria can be
identified by the protein of
the flagella
❖ Bacteria cells can alter the
speed and direction of
rotation of flagella for motility
➢ Escherichia coli O157:H7
Axial Filaments
❖ Spirochetes move by means of
axial filaments
❖ Axial filaments are anchored at one
end
❖ Rotation of filaments propels the
organism in a spiral motion
❖ Examples
➢ Treponema pallidium
■ Agent of syphilis
➢ Borellia burgdorferi
■ Agent of lyme disease
Fimbriae and Pili
❖ Fimbriae (fimbria)
➢ Occur at the pole or are evenly
distributed
➢ Enable cell adherence
➢ Absences of fimbriae often means no
disease
➢ Example
■ Neisseria gonorrhoea
● Agent of gonorrhoeae
❖ Pili (pilus)
➢ Usually longer than fimbriae
➢ Join bacterial cell for the transfer of
DNA
■ Sex pili
Staining Properties
❖ Bacteria can be classified majorly by their staining properties
➢ The most common is the gram stain
❖ Other stains are used on more complex organisms
❖ Additional biochemical tests can be performed to identify microorganism in
the laboratory
Gram Stain Procedure
Atypical Cell Walls
❖ Certain cells have no walls or very
little wall material
❖ Plasma membranes contain lipids
that offer similar protective effect
❖ Example
➢ Mycoplasma spp.
Mycoplasma
Pleomorphic cells that lack a cell wall
Biochemical Classification
Cell Protein Profile
Cell Lipid Profile
Mycolic acid +/-
Enzymatic Properties
Catalase +/-
Oxidase +/-
Nucleid Acid Analysis
Molar G/C Ratio
Nucleic Acid Ratio
DNA Restriction Fragment Analysis
Plasmid Analysis
DNA Hybridization
Ribosomal RNA
PCR (polymerase chain reaction)
Mechanism of
Pathogenicity
Introduction to Epidemiology
❖Epidemiology
➢The study of the distribution and determinants of health-related states or events in specified
population, and the application of this study to the control of health problems
■Involves the study of incidence, distribution, and control of diseases
■Addresses other health factors
❖Pathology
➢The scientific study of disease
❖Etiology
➢The cause of disease
❖Pathogenesis
➢The manner in which a disease develops
❖Infection
➢The invasions or colonization of the body by microorganisms
❖Disease
➢Occurs when an infection result in any change from a state of health
Koch’s Postulate
❖ Was the framework for the study of etiology
➢ Four principles of Koch’s Postulate
■ The same pathogen must be present in every case of the disease
■ The pathogen must be isolated from the disease host and grown in pure culture
■ The pathogen from the pure culture must cause the disease when it is inoculated into a
healthy, susceptible laboratory animal
■ The pathogen must be isolated from the inoculated animal and must be shown to be the
original organism
Types of Transmission
❖ Contact
➢ Direct
■ Person to person
➢ Indirect
■ Contact with non-living object
➢ Droplet
■ coughing , sneezing, laughing, talking
❖ Vehicle
➢ Transmission through a medium
■ Food, water, air
■ Bodily fluids
■ vectors
Pathogenicity
❖ Pathogenicity is the ability of a pathogen to produce a disease by overcoming
the defenses of the host
➢ This is also known as the mechanism of action
❖ Virulence is the degree of pathogenicity
❖ Pathogenesis is how the disease develops
Pathogenicity
Many properties that determine a microbe’s pathogenicity or virulence are
unclear or unknown
When a microbe overpowers the host's defenses, disease results
Pathogenecity
❖ Host organisms cause disease via attachment to tissue and penetration of
evasion of host defenses.
❖ Damage of host tissues produce the symptoms that are associated with the
disease process
❖ Number of microbes and their ability to adhere to host tissue greatly impacts
an organism's likelihood to establish infection
★ Most pathogens leave the body the same way in which they entered
Principle Portals of Entry
❖ Portal of entry is a specific route by which as particular pathogen gains
access to the body
➢ Mucous membrane
■ Respiratory tracts
■ Gastrointestinal tracts
■ Genitourinary tracts
■ Conjunctiva
➢ Skin
➢ Parenteral route
Mucous Membrane
❖ Respiratory tract
➢ Through droplets of moisture, dust particles, and inhalation
➢ Most common portal of entry
■ Easiest and most frequent
❖ Gastrointestinal tract
➢ Food, water, and contaminated fingers
➢ Most microbes that enter the G.I. tract are destroyed by HCl, enzymes of stomach or bite, and
enzymes of small intestine
❖ Genitourinary tract
➢ Microorganisms enter the body through mucous membranes
❖ Conjunctiva
Common Disease Contracted via the Respiratory Tract
Common cold
Flu
Tuberculosis
Whooping cough
Pneumonia
Measles
Strep Throat
Diphtheria
Common Diseases Contracte via the G.I. Tract
Salmonellosis
Salmonella sp.
Shigellosis
Shigella sp.
Cholera
Vibrio cholerea
Ulcers
Helicobacter pylori
Botulism
Clostridium botulinum
Fecal - Oral Diseases
These pathogens enter the G.I. tract at one end and exit at the other end
Spread by contaminated hands and finger or contaminated food and water
Poor personal hygiene
Mucus Membranes of the Genitourinary Systems - STDs
Gonorrhea
Neisseria gonorrhoeae
Syphilis
Treponema pallidum
Chlamydia
Chlamydia trachomatis
HIV
Herpes Simplex II
Diseases of the Conjuctiva
Conjunctiva is the mucus
membrane that covers
the eyeballs and lines
the eyelid
Trachoma
Chlamydia trachomatis
Skin
❖ Microorganisms cannot penetrate intact skin
➢ When unbroken is an effective barrier for most microorganisms
➢ Enter via hair follicles and sweat ducts
■ Openings of the skin
Parenteral Route
Gain of access to tissues by inoculation through the skin and mucous
membranes
Injections, bites, and other wounds
Splitting of skin due to swelling or dryness
Preferred Portal of Entry
A pathogen entering your body does not guarantee that a disease will occur
Pathogens
Streptococcus pneumoniae
If inhaled can cause pneumonia
If enters the G.I. tract, causes no disease
Salmonella typhi
If enters the G.I. tract, can cause typhoid fever
If on skin, causes no disease
Number of Invading Microbes
❖ Virulence can be expressed as LD50 and ID50
➢ LD50
■ Lethal dose for 50% of the inoculated hosts
➢ ID50
■ infectious dose for 50% of the inoculated hosts
How Do Bacterial Pathogens Penetrate Host Defenses?
Adherence
Almost all pathogens have a way to attach to host tissue
Binding sites
Adhesins
ligands
Binding Sites: Adhesins and Ligands
Adhesins and ligands are usually on fimbriae
Neisseria gonorrhoeae
ETEC (Enterotoxigenic E. coli)
Bordetella pertussis
Adherence
❖ Invasion can occur by adherence
➢ Adhesins
■ Surface projection on a pathogen
■ Adhere to complementary receptors on the host cells
■ Can be glycoproteins or lipoproteins
■ Frequently associated with fimbriae
➢ Mannose
■ The most common receptor on pathogens
■ MBL (Mannose binding lectin) pathway recognizes pathogens by the binding of lectin on
the surface of phagocytes to mannose to initiate the complement cascade
➢ Biofilms
■ Provide attachment and resistance to antimicrobial agents
■ Diphtheria forms biofilms in the throat
● Can cause death if it isn’t detected early
Capsule and Cell Wall Components
❖ Both the capsule and cell wall components contribute to pathogenicity
➢ Some pathogens are enclosed by capsule which prevent them from being phagocytized
■ Streptococcus pneumoniae
■ Klebsiella pneumoniae
■ Haemophilus influenzae
■ Bacillus anthracis
■ Streptococcus mutans
■ Yersinia pestis
➢ The cell wall contains proteins that facilitate adherence or prevent a pathogen from being
phagocytized
➢ Some microbes can reproduce inside phagocytes
Enzymes
❖ Leukocidins
➢ Destroy some immune cells (WBCs)
➢ Release and rupture lysosomes
■ Lysosomes contain powerful
hydrolytic enzymes
■ The rupture of these cause more
tissue damage
❖ Hemolysins
➢ Cause the lysis of RBCs
❖ Coagulase
➢ Protection in a fibrin clot
❖ IgA protease
➢ Destroys IgA antibodies
❖ Spread of infection
➢ Kinases
■ Destroy blood clots
➢ Hyaluronidase
■ Destroy mucopolysaccharides
● Mucopolysaccharides hold
cells together
➢ Collagenase
■ Hydrolyzes collagen
● Collagen is present in
connective tissue
Hemolysins
Alpha Hemolytic Streptococci
Secrete hemolysins that cause the incomplete lysis of RBCs
Beta Hemolytic Streptococci
Secrete hemolysins that cause complete lysis of RBCs
Gamma Hemolytic Streptococci
Do not secrete any hemolysins
Enzymes
❖ Leukocidins
➢ Destroy some immune cells (WBCs)
➢ Release and rupture lysosomes
■ Lysosomes contain powerful
hydrolytic enzymes
■ The rupture of these cause more
tissue damage
❖ Hemolysins
➢ Cause the lysis of RBCs
❖ Coagulase
➢ Protection in a fibrin clot
❖ IgA protease
➢ Destroys IgA antibodies
❖ Spread of infection
➢ Kinases
■ Destroy blood clots
■ Streptokinase is used to dissolve
blood clots in the heart
➢ Hyaluronidase
■ Destroy mucopolysaccharides
● Mucopolysaccharides hold
cells together
■ Spreading factor
➢ Collagenase
■ Hydrolyzes collagen
● Collagen is present in
connective tissue
■ Clostridium perfringens - Gas
Gangrene
Antigenic Variation and Penetration of Host Cell Cytoskeleton
❖ Antigenic variation
➢ Some microbes can vary in the expression of antigens, escaping host immunity (antibody
response)
❖ Strains of Salmonella and E. coli make contact with the host cell via the
plasma membrane.
➢ These organisms secrete invasins that rearrange nearby actin filaments of the cytoskeleton
■ Creates a cytoplasm pedestal which facilitates entry into the cell
■ The actin structure supports the bacterial cells
● Then forms as actin basket
◆ The actin basket cuddles the Salmonella and moves it into the cell
How Bacterial Pathogens Damage Host Cells
❖ Using the host’s nutrients
➢ Bacteria can take iron from the host using siderophores
■ Siderophores are iron chelators
❖ Direct damage
➢ Destruction of host cells when pathogens metabolize and multiple inside the host cell
❖ Production of toxins
❖ Plasmids, lysogeny, and pathogenicity
➢ Plasmids carry genes for antibiotic resistance toxins, capsules, and fimbriae
➢ Lysogeny can infer pathogenicity such as in the case of diphtheria toxin
Toxins
Toxins are poisonous substances produced by microorganisms
Primary factor of pathogenicity
220 known bacterial toxin
40% cause disease by damaging the eukaryotic cell membrane
Toxemia
Toxins in the bloodstream
Two types of toxins
Exotoxins
Secreted outside the bacterial cell
Endotoxins
Part of the outer cell wall of gram negative bacteria
Endotoxins and Exotoxins
Exotoxins
Three types of exotoxins
Cytotoxins
Kill cells
Neurotoxins
Interfere with normal nerve impulses
Enterotoxins
Effect cells lining the G.I. tract
Response to Toxins
Antitoxins are antibodies against the toxin
These are produced if the body is exposed to exotoxins
Toxoids are altered exotoxins
These are inactivated by heat, formalin, or phenol and no longer cause disease
They stimulate the production of antitoxins
Injected to stimulate the production of antitoxins and provide immunity
DPT Vaccine
D = Diphtheria
Corynebacterium diphtheriae
Diphtheria toxoid
P = Pertussis
Bordetello pertussis
Pertussis antigen
T = Tetanus
Clostridium tetani
Tetanus toxoid
Nature and Effects of Exotoxins and Endotoxins
❖Exotoxins
➢Proteins produced inside gram
positive bacteria
➢Secreted or released into the
surrounding medium following lysis
➢Specific for a particular cell structure
or function
■Affects cell functions, nerves,
and GI tract
➢High toxicity
➢Unstable except Staphylococcal
enterotoxin
➢Gas gangrene, tetanus, botulism,
diphtheria, scarlet fever
❖ Endotoxins
➢ Lipids of gram negative bacteria
■ Lipid portion of LPSs
(lipopolysaccharides)
➢ Liberated when the bacteria die and
the cell wall breaks apart
➢ General effects
■ Fever, weakness, aches, and
shock
➢ Fever producing
➢ Typhoid fever, UTIs, meningococcal
meningitis