TRANSCRIBED BY: CNDV
Page 1 of 4
Mary Ann Bunyi, M.D.
Walang iyo, Nicole. Akin ang asawa ko!!! Monica, The Legal Wife Paulo Coelho
Bacterial Morphology
1.1 11 June 2014
Note: When writing scientific names:
Saccharomyces cerevisiae
GENUS NAME + SPECIFIC EPITHET 1. Without specific epithet, you can write sp.
(Lactobacillus sp.) but if asked what microbe specifically, include the specific epithet na talaga! 2. Type-written scientific names must be ITALICIZED. 3. Hand-written scientific names must be UNDERLINED. (With break between the genus name and specific epithet)
*kahit sa peso bills mali yung scientific names kaya huhuhu push natin yung maayos (challenge to the youth, charaught)!!!
BACTERIAL MORPHOLOGY
Refers to size, shape and arrangement of bacteria Clearly visible under the microscope Size ranges from 0.1 20 m
Bacterial Forms
1.Coccus/ cocci May occur singly, in pairs, in chains
(Streptococcus) or in clusters (Staphylococcus
aureus) May be small, large or oval-shaped Most cocci when stained appear as gram
positive (violet)
2.Bacillus/ bacilli
May be long with square cut ends or short with rounded ends
Coccobacilli very short bacilli appearing like cocci
No cluster arrangement (Hemophilus influenzae) Stain as gram negative (red)
3. Vibrio/ curved Bacteria with a single turn, comma shaped Stains gram negative (red)
TOPIC OUTLINE
I. Bacterial Morphology
A. Bacterial Forms II. Bacterial Cell Components A. Cell Surface Layer
B. Appendages C. Other Structures
TRANSCRIBED BY: CNDV
Page 2 of 4
Bacterial
Morphology
4. Spiral/ spirillum May be regular or irregular, with hook on one end
or both ends. Some bacteria have to be visualized under special
microscope using a special stain. Leptospira sp.
Other Bacterial forms
Spirochete Star Square
BACTERIAL CELL COMPONENTS
The general structure is divided into three (3) main components:
1. Cell Surface Layer Cytoplasm
Cell Membrane/ Plasma Membrane Cell Wall Capsule
2. Appendages Flagella Pili
3. Other Structures
teichoic acid inclusion bodies spores lipopolysaccharide
Cell Surface Layer
A. CYTOPLASM
o Total of everything inside the cytoplasmic space
o Main components Proteins (mostly enzymes) Ribosomes (composed of RNA and protein)-
sedimentation 70s (80s monomers) composed of 30S and 50S subunit
o Other components include: Cytoplasmic granules/ storage granules
Represent stored food reserves consisting of starch, fat, sulfur or phosphate (for later use)
Examples:
Poly--hydroxybutyric acid (PHB): produced when source of nitrogen, sulfur or phosphorous is limited and there is excess carbon in the medium
Glycogen: produced when carbon is in excess, and (together with PHB) used as carbon source when protein and nucleic
acid synthesis are resumed Volutin/metachromatic/Babes-Ernst
granules: granules of polyphosphate, produced when there are large reserves
of inorganic phosphate, termed metachromatic because they stain red
with a blue dye (characteristic of Corynebacteria diphtheriae)
Much granules: produced by Mycobacterium tuberculosis
Plasmids Small circular extra-chromosomal DNA
molecules carrying extra genes used for
special situations (i.e. antibiotic resistance and penetrating other bacteria)
Circular genome Composed of DNA; chromosome
B. CYTOPLASMIC MEMBRANE
o Thin ductile, elastic, trilaminar structure that
encloses the cytoplasm o Acts as a selective barrier which confers selective
permeability o Has a phospholipid bilayer which has an inner
hydrophobic and outer hydrophilic layer o Contains enzymes for electron transport chain =
generation of ATP o Mesosomes
saclike invaginations of the cytoplasmic membrane containing circular or tubular structures attached to DNA chromatin; believed to be associated with cell division
C. CELL WALL o Constituent of all bacteria
o In close approximation to the cytoplasmic membrane
o Confers rigidity and shape to the bacterial cell o Acts as a barrier to low molecular weight
substances
o Rigidity and shape attributable to a 3D latticework layer which lies closest to the cytoplasmic membrane called peptidoglycan layer
o Peptidoglycan Layer A bipolymer consisting of alternating units of
sugar N-acetyl-D-muramic acid and N-acetyl-
D-glucosamine with a short peptide linked to the lactyl moiety of the M residues
Sugars are bound by -glycosidic linkages
TRANSCRIBED BY: CNDV
Page 3 of 4
Bacterial
Morphology
GRAM POSITIVE GRAM NEGATIVE
- thick walls (multilayer, compact)
- thinner (1-2 layers) - less compact - composed of periplasmic
space
- almost exclusively peptidoglycan
- outer membrane 1. Lipoproteins
most abundant protein
lipid end inserted into the outer membrane
protein end covalently linked to peptidoglycan
2. Phospholipids
form the outer membrane matrix and contributes to outer membrane stabilization
3. Porins
protein trimers that form channels that permit small molecules to diffuse across the membrane
4. Lipopolysaccharide (LPS)
Lipid A endotoxin
toxic for humans and may cause hypotension, shock, DIC, tissue necrosis
- Techoic acid (polymer of ribitol or glycerol phosphate) responsible for virulence and negative charge of cell surface
- more complex cell envelope
- with transmembrane proteins: integral and porins
- Gram stain: Crystal Violet takes the primary dye due to its thick peptidoglycan layer
- Gram stain: Red/Pink takes the color of counterstain (safranin red) due to its thin peptidoglycan layer
D. CAPSULE
o Closely surrounds the cell wall of some bacteria o Well-defined mucoid polysaccharide structure o Anti-phagocytic properties
prevent ingestion by WBCs
virulence factor for some bacteria o Presence of antigenic diversity influence:
pathogenesis
effective vaccine preparation
ability to make a rapid and accurate diagnosis o Roles:
protection from desiccation
extra source of nutrition
adherence of bacteria to surfaces in the environment
may be toxic to a hosts defense system
APPENDAGES
A. FLAGELLA o Long slender protein structures which originates
from the cytoplasmic membrane o Most flagellated pathogens are surrounded by
numerous flagella called peritrichous o Flagellin is the single protein unit of the structure o Responsible for bacterial motility and may enhance
bacterial invasion o Arrangement is the basis for classification
MONOTRICHOUS single flagellum
LOPOTRICHOUS tuft of flagella at one end
AMPITRICHOUS flagella at both ends
PERITRICHOUS flagella all around bacteria
B. PILI
o Hairlike, rigid structures originating from the
cytoplasmic membrane
o Found predominantly in gram negative organisms
o Composed of structural protein subunits called
PILINS
o Two classes:
1. Sex pili
TRANSCRIBED BY: CNDV
Page 4 of 4
Bacterial
Morphology
Hollow, found at random bacterial sites
Participate in the transfer of genetic
material from one cell to another
(conjugation)
2. Common/fimbriae
More numerous
Evenly distributed over the surface of the
organism
May act as virulence factor by mediating
adherence to host cell surfaces
Other Structures
ENDOSPORE
o 2 most common are gram-positive rods: Bacillus (obligately aerobic) and Clostridium (obligately anaerobic)
o Also occurs in Thermoactinomyces, Sporolactobacillus, Sporosarcina, Sporotomaculum, Sporomusa, and Sporohalobacter
o Sporulation - cycle of differentiation triggered by near depletion of any of several nutrients (carbon, nitrogen, or phosphorous)
o Spore Resting cell Highly resistant to desiccation, heat, and chemical
agents Germinates to vegetative cell when returned to
favorable nutritional conditions o Properties Core-spore protoplast; contains chromosome Spore wall Cortex- thickest layer; with unusual type of
peptidoglycan which is extremely sensitive to lysozyme
Coat -composed of keratin-like protein Exosporium - lipoprotein membrane
SUMMARY
Bacteria consist of a unique cell wall, a cytoplasmic
membrane enclosing the cytoplasm, a nuclear apparatus,
ribosomes and various cytoplasmic granules. Some have
capsules, flagella, or pili.
1. Differences in the cell wall of gram positive and gram negative exist and these account for the functional properties as well as their susceptibility to antimicrobial agents.
2. Capsules, usually polysaccharides, closely surrounding the cell wall or some bacteria. These capsules may be antiphagocytic, vaccinogenic, and/for
identifiable in rapid diagnostic test utilizing specific antiserum.
3. Flagella are composed of a single protein subunit called flagellin and responsible for motility. Flagella may function as virulence factors by enhancing invasion and may be useful in classification of some organisms.
4. Common and sex pili are hair-like surface protein appendages. Sex pili mediate conjungation while common pili (fimbriae) may be associated with virulence by mediating adherence of bacteria to host cell surfaces.
5. Ribosomes, located in the cytoplasm, are are sites of protein synthesis.
Top Related