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CAPÍTULO 4 LAS CLASES DE ACREEDORES EN LOS
3. LOS ACREEDORES EN LOS SCHEMES INGLESES
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BACTERIAL MORPHOLOGY
• Only two types of cells are produced by all living organisms on earth.
1. Prokaryotes (pro. or primitive nucleus) do not have a membrane bound nucleus
i. Eubacteria (true bacteria) ii. Archaebacteria (ancient bacteria)
2. Eukaryotes (eu, or true nucleus) have a
Cytoplasm no cytoskeleton or cytoplasmic
Mitochondria Absent present
Lysosomes Absent present
Ribosomes 70s free in the
Cell wall chemically
complex; Locomotion flagella that
rotate; gliding
BACTERIAL CELL 1. Most bacteria produce a layered cell
includes the plasma membrane, cell wall and associated proteins and polysaccharides.
2. Some bacteria produce capsules or slimes.
3. External filamentous Appendages ( may also occur.
4. The cell wall is a rigid structure that enclose protects the protoplast from physical conditions of low external osmotic pressure.
5. The cell wall also generally all
tolerate a wide range of environmental conditions.
6. The protoplast comprises the naked cytoplasmic membrane and its contents.
7. Internally, bacteria are relatively simple cells.
8. Major cytoplasmic structures
fibrillar chromatin network surround amorphous cytoplasm that contains ribosomes.
9. Cytoplasmic inclusion bodies or e
granules vary in chemical nature accordin species and in amounts depending on growth phase and environment.
10. Some cytoplasmic structures, such as endospores, are limited to only a few bacteria.
11. Typical gram positive and gram negative bacterial cells differ primarily in cell envelope organization.
Size of bacteria
• Units of microbial measurement 1. micrometers (µm) approximately 0.4 to 2 µm in size
BACTERIAL CELL
Most bacteria produce a layered cell envelope that includes the plasma membrane, cell wall and associated proteins and polysaccharides.
Some bacteria produce capsules or slimes.
Appendages (flagella and pili)
The cell wall is a rigid structure that encloses and protects the protoplast from physical damage and
external osmotic pressure.
The cell wall also generally allows bacteria to wide range of environmental conditions.
The protoplast comprises the naked cytoplasmic
Internally, bacteria are relatively simple cells.
include a central chromatin network surrounded by an
that contains ribosomes.
Cytoplasmic inclusion bodies or energy storage in chemical nature according to depending on growth phase
s, such as endospores, to only a few bacteria.
Typical gram positive and gram negative bacterial differ primarily in cell envelope organization.
of microbial measurement b. Protein particles c. Enzymes
d. Surface structures iv. Polysaccharides v. Lipids - 6%
vi. Phospholipids
Components of the Bacterial Cell A. Structures external to the cell wall
1. Glycocalyx i. Capsules ii. Slime layer
Chemical Composition of Bacteria
30% composed of:
5% MW 2,000,000,000 12%
70% found in Ribosomes(10,000) – rna Protein particles - mw 3,000,000 Enzymes
Surface structures Polysaccharides - 5%
6%
Phospholipids - 4%
Components of the Bacterial Cell Structures external to the cell wall
layer
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Bacterial Morphology3
© BRIHASPATHI ACADEMY ׀ SUBSCRIBER’S COPY ׀ NOT FOR SALE 2. Flagella
3. Axial filaments 4. Pili or fimbriae B. Cell Wall
C. Structures internal to the cell wall
1. Plasma membrane or cytoplasmic membrane 2. Cytoplasm
b. Polysaccharide granules c. Lipid inclusions d. Sulphur granules e. Carboxysomes external to the cell wall
• Composed of polysaccharide and polypeptide or both
• Produced inside the cell and excreted on the cell surface
1. Slime layer - if the substance is unorganized and only loosely attached to the cell wall 2. Capsule
If the substance is organized and is firmly attached to the cell wall
Found in both gram positive and gram negative cells
Presence denotes virulence
Encapsulated cells form smooth or
Methods to distinguish the capsule 1. India Ink Technique
o Most satisfactory method of demonstrating the capsule o Bacteria are suspended in
diluted India ink
o Bacterial cells appear to lie in lacunae
2. Quellung Reaction
o Homologous antibody is added to a preparation of capsule
o Micro precipitation at the periphery of the capsule altering its refractive index rendering the capsule to be visible
Functions of the Capsule 1. Protection
2. Identification 3. Vaccine preparation 4. Tissue attachment 5. Antibiotic barrier
Medical Importance
o Rapid serological identification of:
1. Several groups of streptococci 2. Meningococcus
3. Hemophilus influenzae 4. Klebsiella pneumoniae 5. Some of the coli forms 6. Yersinia and Bacillus specie
FLAGELLA
• Organ of locomotion
• Long filamentous appendage originating in a spherical body or basal granules
• Occur most commonly although not exclusively among the rod-shaped bacteria
Morphological Regions 1. Helical filament
Long outermost region; composes up to 90% of its length
Contains the globular (roughly spherical) protein flagellin, arranged in several chains that intertwine and form a helix around a hollow core
2. Hooked or curved area
Filament is attached; consists of a different protein
3. Basal body
Terminal portion of the flagellum
Anchors the flagellum to the cell wall and plasma membrane
Composed of a central rod inserted into a series of rings
o Gram negative - 2 pairs of rings i. Outer pair - anchored to the outer
membrane (L ring) and peptidoglycan layer (P ring) ii. Inner pair - anchored to the
plasma membrane (SM ring) o Gram positive - only inner pair is
present
Types of arrangement of flagella 1. Atrichous - no flagella
2. Monotrichous - one polar flagellum
3. Lophotrichous - tuft of several polar flagella 4. Amphitrichous - flagella at both poles
5. Peritrichous - flagella over the entire cell surface
Motility
• Presumptive evidence that bacteria possesses flagella although it gives no indication of the number or rearrangement of the flagella
Types of bacterial motility
• Stately motility: Bacillus sps
• Active motility: Pseudomonas sps
• Darting motility: Vibrio cholerae
• Tumbling motility: Listeria monocytogens
• Corkscrew, extension-flexion motility:
Spirochetes
• Examples of non-motile bacteria: Most cocci, Shigella, Klebsiella
Demonstration of motility 1. Direct or Microscopic
Hanging drop preparation or wet mount preparation
Distinguishes,
i. Brownian movement - when the bacteria show molecular movement with no apparent effort to change their position and direction to the field
ii. True motility - if a bacterium describes a rotatory, undulatory or sinuous movement
2. Indirect or Macroscopic
Stab inoculation of the semisolid media i. Non motile - growth is limited at the
point of inoculation
ii. Motile - growth is diffuse or moves away from the line of inoculation;
turbidity of the medium
Antigenicity
Flagellar or H antigen - useful in the serological identification of serotypes of Salmonella organisms
AXIAL FILAMENTS
• Bundles of fibrils that arise at the ends of the cell beneath the outer sheath and spiral around the cell
• Rotation moves an opposing movement of the outer sheath that propels the spirochetes by causing them to move like corkscrews
• Found in Spirochetes and are similar to flagella, but are located between the cell wall and an outer sheath, and are attached to one end of the organism.
FIMBRIAE AND PILI
• Hair like appendages that are shorter, straighter and thinner than flagella
• Used for attachment rather than for motility
• Consist of a protein called pilin arranged helically around a central core
Fimbriae
Can occur at the poles of the bacterial cell or they can be evenly distributed over the entire surface of the cell
Allow a cell to adhere to surfaces
Pili
Usually longer than fimbriae and number only one or two per cell
Genetically determined by a fertility factor called F factor which is carried on an Episome (sex or F pilus)
Types
1. Sex or conjugation pili for the transfer of extra chromosomal DNA between donor and recipient
2. Attachment pili or fimbriae: There are many and are used for attachment to surfaces
Functions of Pili
1. Sites of adsorption for RNA and DNA viruses 2. Act as a means of genetic transfer between
MICROBIOLOGY
Bacterial Morphology5
© BRIHASPATHI ACADEMY ׀ SUBSCRIBER’S COPY ׀ NOT FOR SALE similar or related Gram negative enteric species
3. Provide the channel through which DNA from the donor (male) cell is transferred to the recipient (female cell)
CELL WALL
• The layers of cell envelope lying between the cytoplasmic membrane and the capsule are referred to collectively as cell wall
• In gram positive bacteria, the cell wall mainly consists of peptidoglycan and teichoic acid while the cell wall in gram negative bacteria includes peptidoglycan, lipoprotein, outer membrane and lipopolysaccharide layers
• Cell wall does not take up any stain and hence are not seen by light microscope
• Most bacteria have a complex cell wall consisting of peptidoglycan (also called murein, mucopeptide)
• This complex polymer consists of three parts,
A backbone consisting of alternating units of NAG (N-acetyl glucosamine) and NAM (N-acetyl muramic acid)
Tetrapeptide side chain attached to NAM
Peptide cross-bridges, which are short Aromatic & sulphur
Containing
Amino acid Absent Present Lipids Absent Present Teichoic acid Present Absent Peptidoglycan More Less
Significance of cell wall
• Maintains cell shape, any cell that loses its cell wall, loses its shape as well.
• Protects bacteria from osmotic lysis
• Acts as a barrier, protects cell contents from external environment
• Determines reactivity to Gram stain, cells become gram negative if they lose cell wall
• Attachment site for flagella
• Site of action of certain antimicrobial agents (E.g. Penicillins, Cephalosporins)
• Bacteria may attach to surface, produce slime, divide and produce microcolonies within the slime layer and construct a biofilm. E.g.
formation of dental plaque mediated by the bacterium Streptococcus mutans.
• Confer specific antigenicity to a strain/species that can be exploited to detect and identify an isolate.
Substances acting against cell wall
• Lysozyme, an enzyme found in tears and saliva breaks down a component of cell walls
• Antibiotics that inhibits cell wall synthesis such as Penicillins and cephalosporins
• Autolytic enzymes produced by some bacteria such as Streptococcus pneumoniae
Demonstration of cell wall
• Since cell wall does not take up stain, they can’t be demonstrated by light microscopy
• Their presence can be demonstrated by placing a cell in hypertonic solution, where they undergo plasmolysis. The cytoplasm shrinks as the water is lost by osmosis but the cell wall retains its original shape (due to its rigidity).
This is described as "bacterial ghost"
• The cell wall may also be demonstrated by micro-dissection, electron microscopy and immunological reactivity
Atypical cell walls
• Naturally occurring wall less microorganisms 1. Genus Mycoplasma and related organism
Smallest known bacteria that can grow and reproduce outside living host cells
Pass through most bacterial filters and were first mistaken for viruses
Require cholesterol or sterols for growth
Cultivated in the laboratory only in hypertonic media
2. Archaebacteria
Lack walls or may have unusual walls composed of polysaccharides and proteins but not peptidoglycan
Walls contain n-acetylalosaminuronic acid but lacks the d amino acids found in the bacterial cell walls
PLASMA MEMBRANE (CYTOPLASMIC MEMBRANE/INNER MEMBRANE)
• A thin structure lying inside the cell wall and enclosing the cytoplasm of the cell
• Consists primarily of phospholipids which are
1. Phospholipid molecule
Polar head - composed of a phosphate group and glycerol that is hydrophilic(water loving) and soluble in water
Non polar tail - composed of fatty acids that are hydrophobic (water fearing) and are insoluble in water; lies in the interior of the bilayer
2. Protein molecule
Peripheral proteins
o Easily removed from the membrane by mild treatment o Lie at the inner or outer surface of
the membrane o Functions
i. Act as enzymes that catalyze chemical reactions
ii. Act as a scaffold for support iii. Act as mediators of changes
in membrane shape during movement
Integral proteins
o Can be removed from the membrane only after disrupting the bilayer
o Penetrate the membrane completely
o Contain channels through which substances enter and exit the cell
Functions
1. Holds the intracellular contents within the cytoplasm and prevents their leakage
2. Concentrates nutrients by effecting their transport from the external environment of the cell to the cytoplasm of the cell
3. Provides the enzymes necessary for capsules,
cell wall and cell membrane synthesis
4. Serves as the site for enzymes involved in electron transport and energy metabolism
Associated structures
1. Chromatophores or thylakoids
Infolding of the plasma membrane that extend into the cytoplasm
Contains the pigments and enzymes involved in photosynthesis
2. Mesosomes
One or more large, irregular folds in the plasma membrane; believed to be artefacts
Functions of Mesosomes
i. Site for energy metabolism and respiration
ii. Site for attachment of DNA to membrane and are the site of growing septum formation
iii. Contain enzymes instrumental in the synthesis of the cell wall, cell membrane and other components external to the cytoplasmic membrane iv. Site of exoenyzme synthesis and
secretion for penicillinase
CYTOPLASM
• The internal matrix of the cell contained inside the plasma membrane
• Thick, aqueous, semitransparent and elastic
Composition 1. Water - 80%
2. Proteins (enzymes) 3. Carbohydrates 4. Lipids 5. Inorganic ions
6. Low molecular weight compounds
Major Structures 1. DNA 2. Ribosomes 3. Inclusions
Nuclear area or Nucleoid A. Bacterial chromosomes
Single long, circular molecules of double stranded DNA
Carries all the information required for the cell structures and functions
Bacterial chromosomes do not include histones
MICROBIOLOGY
Bacterial Morphology7
© BRIHASPATHI ACADEMY ׀ SUBSCRIBER’S COPY ׀ NOT FOR SALE and are not surrounded by a nuclear envelope
(membrane)
Attached to plasma membrane, the proteins of which are responsible for the replication of DNA and segregation of the new chromosomes to daughter cells in cell division
B. Plasmids
Small, circular, double stranded DNA molecules
Extra chromosomal genetic elements
Replicate independently of chromosomal DNA
Associated with plasma membranes
Usually contain from five to 100 genes
Maybe gained or lost without harming the cell
May carry genes for such activities as o antibiotic resistance
o tolerance to toxic metals o production of toxins o synthesis of enzymes
Can be transferred from one bacterium to another
Ribosomes
• Sites for protein synthesis
• Composed of two subunits, each subunit being composed of protein and a type of RNA called ribosomal RNA (r RNA)
• Prokaryotic ribosomes are called 70s ribosomes
• MA: inhibition of protein synthesis on the ribosomes Ex. Streptomycin, Tetracyclines
Inclusions
• Reserve deposits
1. Metachromatic granules or volutin or Babes polymetaphosphate or polymerized phosphoric acid or polymerized polymetaphosphate or volutin
Characteristic of Corynebacterium diphtheria
2. Polysaccharide granules
Not usually enclosed by a membrane
Consist of glycogen and starch
Glycogen granules - reddish brown with iodine
Starch granules - blue with iodine
3. Lipid inclusions
Appear in various species of Mycobacterium, Bacillus, Azobacter, Spirillum
Polymer polybetahydroxybutyric acid - storage material
4. Sulphur granules
Sulphur bacteria – (Genus Thiobacillus) deposit sulphur granules in the cell, where they serve as an energy reserve
5. Carboxysomes
Polyhedral and hexagonal inclusions
Contain the enzyme ribulose 1,5 diphosphate carboxylase
Required by bacteria for carbon dioxide fixation during photosynthesis
Ex. Nitrifying bacteria, cyanobacteria, thiobacilli
6. Gas vacuoles
Hollow cavities found in many aquatic prokaryotes
Consist of rows of several individual gas vesicles which are hollow cylinders covered by protein
Function: maintain buoyancy so that the cells can remain at the depth in the water appropriate for them to receive sufficient amounts of oxygen, light and nutrients
ENDOSPORES
• A refractile oval body formed within the bacterial cell found intracellularly and extracellularly in the usual stained smear
• Found in all species of Family Bacillaceae
Genus Bacillus - aerobic spore forming
Structure
1. Core or spore protoplast
Contains
o Complete nucleus
o All of the components of the protein synthesizing apparatus
o Energy generating system on glycolysis - energy for germination - stored as 3 phosphoglycerate
2. Spore wall
o Innermost layer surrounding the inner spore membrane
o Contains the normal peptidoglycan o Becomes the cell wall of the germinating
vegetative cell 3. Cortex
o Thickest layer of the spore envelope with many fewer cross links than are found in cell wall peptidoglycan
o Cortex peptidoglycan is extremely sensitive to lysozyme
o Contains dipicolinic acid, mucopeptide and calcium, all of which are significant in spore resistance
4. Coat - composed of keratin like portion containing many intra molecular disulfide bonds
5. Exosporium - lipoprotein membrane containing some carbohydrate
CLASSIFICATION OF MEDICALLY IMPORTANT BACTERIA
I. Rigid, thick walled cells A. Free living (extracellular)
1. Gram positive
Cocci Streptococcus
Staphylococcus Spore forming rods
Aerobic Bacillus
Anaerobic Clostridium Non spore forming
rods
Non filamentous Corynebacterium Listeria
Filamentous Actinomyces Nocardia
2. Gram negative
Cocci Neisseria Rods
Facultative Straight
Respiratory organisms
Haemophilus Bordetella Leigionella
Zoonoitic organisms
Brucella Francisella Pasteurella
Enteric &
related organisms
Escherichia Serratia Klebsiella Salmonella Shigella Proteus
Curved Camphylobacter Vibrio
Aerobic Pseudomonas Anaerobic Bacteroides
3. Acid fast - Mycobacteria
B. Non-free living (Obligate intracellular parasites)
1. Rickettsia 2. Chlamydia
II. Flexible, thin walled cells (Spirochetes) 1. Treponema
2. Borellia 3. Leptospira
III. Wall-less cells 1. Mycoplasma
© BRIHASPATHI ACADEMY BACTERIAL GROWTH CURVE
• When bacteria is seeded into suitable liquid medium and incubated, its growth follows a definite course.
• If it is plotted on a graph it shows 4 stages as follows
1. Lag phase
• In this period there is n
multiplication of cells but increase in the size of the cell
• This is an adaptation time for new environment during which the necessary enzymes and metabolic intermediates for multiplication to proceed.
2. Log phase
• In this stage cell starts to divide and then number increases exponentially
• Curve shows a liner relationship bet number of cells and time
• This growth rate depends on generation time and environmental factors.
Bacterial Morphology
© BRIHASPATHI ACADEMY ׀ SUBSCRIBER’S COPY ׀ NOT FOR SALE When bacteria is seeded into suitable liquid
medium and incubated, its growth follows a
If it is plotted on a graph it shows 4 stages as
In this period there is no appreciable cells but increase in the
This is an adaptation time for new environment during which the necessary enzymes and metabolic intermediates for multiplication to proceed.
In this stage cell starts to divide and then number increases exponentially
Curve shows a liner relationship between number of cells and time
This growth rate depends on generation time and environmental factors.
3. Stationary phase
• Rate of multipl
• This is due to depletion of nutrients accumulation of toxic products equilibrium exists between the dyi and newly formed cells
4. Phase of decline
• In this phase the liable count decreases due to nutritional exhaustion and
of cells by toxic substances produced during multiplication
• But no change in total count
MICROBIOLOGY
Bacterial Morphology9
NOT FOR SALE Stationary phase
e of multiplication decreases
This is due to depletion of nutrients and accumulation of toxic products equilibrium exists between the dying cells and newly formed cells
Phase of decline
In this phase the liable count decreases due to nutritional exhaustion and autolysis of cells by toxic substances produced during multiplication
But no change in total count