Chapter 1 (Bacterial Cell Ultrastructures) Flashcards
Part 3
The structure and organization of the cell envelope differs in Gram (+) and Gram (-) bacteria.
It contains components that frequently induce a specific antibody response.
Cell envelope
- Cytoplasmic membrane
- Thick peptidoglycan
- Variable capsule
Gram (+)
- Cytoplasmic membrane = inner membrane
- Single planar sheet of peptidoglycan
- Complex layer known = outer membrane
- Variable capsule
Gram (-)
Parts of the cell envelope
Surface adherent structures
Outer membrane
Cell wall
Periplasmic space
Cell membrane
Appendages of a bacterium
Flagellum
Axial filaments
Microfibrils
Cytoplasmic structures of a bacterium
Mesosomes
Nucleiod
Ribosomes
Cytoplasmic granules
Endospore
Extrachromosomal factors
Parts of a bacteria
Cell envelope
Appendages
Cytoplasmic structures
Slime layer
Capsule
Glycocalyx
Surface adherent structures
If only a small amount is produced
It is seen as surface layers that are loosely attached to the cell wall and tend to diffuse into the surrounding of the bacterial cell
More easily washed off
Slime Layer
Example with slime layer
S. lutea
If polymer forms an additional definite surface layer and is firmly attached to the cell wall
Clearly differentiated from the cell and surrounding
Easily visualized by neg stain (halo)
Fresh isolates of capsulated organisms produce colonies with moist and slimy appearance
Capsule
Example with capsule
S. pneumoniae
Klebsiella pneumoniae
H. influenzae
B. anthracis
Clostridium perfringens
If the polymer is seen as a network of fibrils extending from the cell surface,
Seen only be E/M
Glycocalyx
Example with glycocalyx
Streptococcus mutans
Among pathogenic bacteria, the presence of capsule is associated with their virulence because it interferes with phagocytosis
Antigenic (Vi antigen) and used in the ID of capsulated organisms
Glycocalyx plays a major role in the adherence of bacteria to cell surfaces
Surface adherent structures
Found only in Gram (-)
Phospholipid bilayer in which the phospholipids of the outer portion are replaced by lipopolysaccharides (LPS)
Outer Membrane
Consists of a lipid A and a polysaccharide composed of a core and terminal repeating units
Attached to the OM by noncovalent hydrophobic bonds
lipopolysaccharides (LPS)
A LPS; component of the outer membrane of Gram neg
Its toxicity is associated with lipid A causing fever and shock
Endotoxin
Scattered throughout the LPS that form transmembrane diffusion channels that control passage of nutrients and other solutes and provide attachment sites (receptors) for viruses and harmful substances
Porins
Beneath the OM where, one end is directly attached to the PEPTIDOGLYCAN and the other end to the OM.
Helps anchoring the OM to the underlying peptidoglycan.
Lipoprotein layer
Outer Membrane parts
Lipopolysaccharides
- endotoxin
- porins
- lipoprotein layer
Carrier of surface antigens and phage receptors
Act as selective permeability barrier which allows diffusion of molecules with a molecular weight up to about 800
Significance of an Outer Membrane
Cell wall is also referred to as
Peptidoglycan
Murein
Mucopeptide
Glycopeptide
Give shape, protection from osmotic lysis and mechanical disruption, and provides necessary support for the propulsion by the flagella
Cell wall
Cell wall parts
Composed of:
- Disaccharide pentapeptide subunits
- Teichoic acids
- Other auxiliary molecules
- Protoplast
- Spheroplast
Peptidogylcan sheets made up of alternating sugar compounds [N-acetylglucosamine (NAG) & N-acetylmuramic acid (NAM)] that surrounds the entire cell
Murein sacculus or sack
In gram (+) bacteria that is glycerol or ribitol phosphate polymers in combination w/ various sugars, amino acids and amino sugars
Teichoic acids
They impart properties to the outer surface of gram (+) cells that influence their ability to cause disease
Other auxiliary molecules
The major surface antigens of gram (+) CW
Teichoic acid and CW associated proteins
The disintegration of a cell by rupture of the cell wall or membrane
Lyse/ lysis
It is liberated if stabilized in hypertonic solution of sucrose or salts, a wall-less osmotically sensitive spherical body
Protoplast
The osmotically sensitive body if the cell envelope components are retained
Spheroplast
Found only in Gram (-)
Bounded by the internal surface of the OM and the external surface of the CM
Consists of a gel-like substance that helps secure nutrients from the environment
Contains several enzymes that degrade macromolecules and detoxify environmental solutes that enter through the OM
Contains membrane- derived oligosaccharides, various hydrolytic enzymes and proteins that specifically bind sugars, transport materials, amino acids and inorganic ions
Periplasmic space
Found in both Gram (+) and (-)
Lipid bilayer heavily laced with various proteins, including a number of enzymes vital to cell metabolism
Besides being an additional osmotic barrier, it functions similarity to several of the eukaryotic cell’s organelles
Cell membrane
Function of Cell Membrane
- Transport solutes (in out permeability)
- House enzymes (synthesis, assembly, secretion)
- Generation of chemical energy (ATP)
- Mediation of chromosomal segregation during replication
- House molecular sensors
Appendages of a bacterium
Flagellum
Axial filaments
Microfibrils
Filament of uniform length and diameter composed of a protein
Flagellin
External to the cell and connects to the hook at the cell surface
Filament
Attached to the basal body
Hook
Anchored to the plasma membrane and is composed of a rod and 2 or more sets of encircling rings which appear contiguous with the plasma membrane, peptidoglycan and the OM of the cell envelope
Basal body
When flagellated Proteus spp. sometimes swarm in a phenomenon as a thin film of growth in agar media surfaces gave rise to term that indicates a spreading film of growth like breath condensing on a cold glass surface
H antigen (flagellar antigen)
- from the German word = Hauch
Employs a chemical (mordant) that precipitates onto the appendage and increases its apparent diameter to resolvable dimensions
Flagellar stain
Messea’s classification of bacteria w/ flagella based on location on the bacterial cell:
a. Monotrichous
b. Amphitrichous
c. Lophotrichous
d. Peritrichous
e. Atrichous
Flagella:
V. cholerae
C. jejuni
Pseudomonas aeruginosa
Monitrichous
Flagella:
Pseudomonas spp
Amphitrichous & Lophotrichous
Flagella:
Salmonella typhi
Proteus vulgaris
Peritrichous
Flagella:
Shigella dysenterjae
K. pneumoniae
Atrichous
Significance of flagella
- responsible for rapid motility
- antigenically distinct, specific antibody
- useful in ID
Motility can be detected by the ff:
- hanging drop prep examined under LM
- unstained prep (DWM) examined under DF/ PC
- spread of bacterial growth as a film over the agar plate - swarming
- as turbidity spreading through semisolid agar
Some bacteria are able to switch from the production of one antigenic type of flagella to another
Phase variation of flagella
- Found only in spirochetes
- Consists of protein fibrils wound spirally around the organism and attached to the 2 poles of the cell
- Located just beneath the OM where they function as a flagella-like structure to impart rapid motility to the spirochete (travelling helical wave)
- Only seen by EM
Axial filaments
Hairlike structures extending from the cell membrane into the external environment
- straighter + thinner + shorter than flagella
- observable only by EM
Microfibrils (pili or fimbriae)
Microfibrils is made of protein known as
Pilin
Type of microfibril that is more numerous and found all over the cell surface
Common + Somatic pili
Type of microfibril that is fewer in the number
Sex / conjugal pili
T/F: Both microfibril types may occur either independently or simultaneously on the same cell
True
Common pili are adhesins that help bacteria attach to animal host surfaces and are called _____ when they bind to specific sugars on cell surfaces
Lectins
Serve as conduit for the passage of DNA from donor cell to recipient cell during conjugation
Sex pili
Microfibrils have been implicated in the ______ motion of nonflagellated bacteria on surfaces (surface translocated)
Slow twitching or gliding motion
Usually seen as membrane-associated cytoplasmic sac in Gram (+) cells
Contains lamellar tubular or vesicular structures and is often associated with the division septa
Cytoplasmic structures
Parts of the cytoplasmic structures
- Mesosomes
- Nucleoid
- Ribosomes
- Cytoplasmic granules
- Endospore
- Extrachromosomal factors
Septal mesosomes function in DNA replication and cell division
Lateral mesosomes function in secretion
Mesosomes
Attached to the CM but more often to the special mesosome rather than directly that houses information for bacterial functions and directs the synthesis of cellular products
Nucleoid
Small roughly spherical cytoplasmic particles
Composed of 30% protein + 70% RNA
Site of action of many antibiotics that inhibit protein synthesis
- Engaged in protein synthesis
Ribosomes
Indicate accumulation of food reserves (storage granules)
- used in taxonomy
Cytoplasmic granules
Common types of cytoplasmic granules
Glycogen
Polyphosphate granules
Storage form of glucose; major material of enteric bacteria
Glycogen
Storage form of inorganic phosphates that are visible in certain bacteria stained with specific dyes (metachromatic granules, volutin granules)
- abundant in M. tuberculosis, C. diptheriae, Yersinia pestis
Polyphosphate granules
Some bacteria are able to form this under adverse physical and chemical conditions, or when nutrients are scarce
Spore (sporulate)
Its formation is a distinguishing feature of the aerobic Genus Bacillus and anaerobic Genus Clostridium
- contains large amounts of calcium dipicolinate which confer extreme resistance to adverse environmental conditions
Endospore
The process that restore the actively growing vegetative state
Germination
A highly refractile body within the vegetative bacterial cell
True endospore
They are responsible for heat resistance by making proteins and nucleic acids more resistant to denaturation
Calcium dipicolinate -> dehydration
The core of the spore contains DNA and small cytoplasm w/ stable components of protein synthesis surrounded by several layers that are:
- pore wall
- cortex
- coat
- exosporium
Classification of spores based on location within the cell
- Central
- Subterminal
- Terminal
Size and location is constant within a species, therefore, it is useful in ID
Taxonomic
Highly resistant to the different methods of sterilization
Clinical
- small, circular, double-stranded pieces of DNA (determine bacterial traits crucial to adaptation, may be antibiotic resistance, tolerance to toxic metals, production of toxins and synthesis of enzymes)
- commonly found in the cytoplasm
- transferred by conjugation
Extrachromosomal factors
All extrachromosomal pieces of DNA are called
Plasmids
Most plasmids that are transferred by conjugation contains 2 genetic regions
1 - sex pilus
2 - other characteristics of the donor bacteria
Spore is at the long end
Terminal
Spore is at the center
Central
Spore is near end in short
Subterminal
Types of Extrachromosomal factors
a. F
b. R
c. Colicinogenic
d. Virulence plasmids
Provided for the discovery of bacterial sexuality
(F)ertility factor
w/ F factor
Male, donors
F+
w/o F factor
Female, recipe
F-
Plasmids that contain genes which convert drug-sensitive bacteria to antibiotic resistant cells
Drug resistance
(R)esistance factor
Tolerance of microorganisms to antibiotics; may also be brought about by mutation
Drug resistance
Responsible for synthesis of bactericidal proteins (colicins) which are active only against other strains of the same species
(col)icinogenic plasmids
Code for toxin production, like in diphteria toxin production
Virulence plasmids
