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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

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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

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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

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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.