Morphology And Physiology Of Bacteria Flashcards
The bacteria which are not really strained and require special strain for demonstration
- Spirochaetes (Treponema and Leptospira) thin spirally coiled bacilli
- Mycoplasma
- Rickettsiae and Chlamydiae (obligate intercellular bacteria)
Gram positive cocci:
Paired lanceolate shaped
Paired or in short chain, spectacle shaped
Tetrad
…
Pneumococcus-lanceolate shaped
Enterococcus-spectacle shaped
Micrococcus- tetrad
…
Gram negative cocci
Paired lens shaped: meningococcus
Paired kidney shaped: gonococcus
Bacteria which contain two chromosomes
Vibrio
Leptospira interrogans
Brucella
Bacteria which do not contain muramic acid in their cell wall
Chlamydia
Biofilm
If there is a colony of bacteria sometimes their slime-glycocalyx (polysaccharide) combined to form biofilm Roles for bacteria: 1. Anti-phagocytic 2. Adhesion 3. Mechanical barrier for antibiotics
Bacteria which produce slime
Streptococcus mutans Staphylococcus epidermidis (of nostril) Pseudomonas aeruginosa
Smooth to rough variation
When repeated subcultures off bacteria are done , it will lose its capsule (loss of its most important virulence factor)
Quellung reaction
When specific antibodies react with the bacterial capsule, the capsule swells
Demonstration of capsule
By negative staining using India ink or nigrosine
Capsulated bacteria mnemonic
Yes some very smart bacteria have killer and mean capsules
Capsulated bacteria (based on mnemonic)
Yersinea pestis Streptococcus pneumoniae Vibrio parahemolytic Vibrio cholera Some groups of beta haemolytic streptococcus Bacteroides fragilis Bordetella pertussis Haemophilus influenzas Klebsiella pneumoniae Bacillus anthracis Meningococcus Clostridium perfringes
Specialty of the capsules of Bacteroides fragilis
Zwitter ionic capsule
The most common bacteria of the GIT of human
Specialty of the capsule of Bordetella pertussis
Non antigenic capsule
Specialty of the capsule of Bacillus anthracis
Polypeptide capsule
Peptidoglycan layer of cell wall
Each layer is a murein chain, composed of alternating units of N-Acetyl muramic acid and N-Acetyl glucosamine (cross linked to each other)
Tetrapeptide:L-alanine~D-glutamine ~L-lysine ~D-alanine
L-lysine of one tetrapeptide chain is covalent you linked to the terminal D-alanine of adjacent chain via apentaglycine bridge
Gram positive bacilli arranged in Chain Cuneiform Palisade Branched and filamentous
Chain :Bacillus anthracis
Cuneiform: Corynebacterium diphtheriae
Palisade: Diphtheroids
Branched and filamentous: Actinomycetes and Nocardia
Gram negative bacteria Pleomorphic Thumb print Curved Chain Spirally coiled, flexible Rigid spiral
Pleomorphic: Haemophilus, Proteus Thumb print: Bordetella pertussis Curved: Campylobacter and Helicobactor Chain: Streptobacillus Spirally coiled, flexible: Spirochaetes Rigid spiral: Spirillum
Difference between peptidoglycan part of gram positive and gram negative bacteria
- 80 nm thick in gram positive while 10-25 nm thick in gram negative
- Gram positive contains 50-100 layers of cross-linked murein monomers but gram negative contains only 2 non cross linked layers
Differences between gram positive and gram negative cell wall (except that of peptidoglycan part)
- Only gram negative contains aromatic and sulphur containing amino acids
- Only gram positive contains teichoic acids
- Only gram negative contains: outer membrane, periplasmic space, endotoxin/ lipopolysaccharide
Cross linking of the tetrapeptides of the NAM molecules is mediated by
Carboxypeptidases and transpeptidases (penicillin binding proteins PBP)
All beta lactam antibiotics bind to these transpeptidases and inactivate them
Teichoic acid of gram positive bacteria
Polymers of glycerol or ribitol joined by phosphate group
Two types:
1. Cell wall teichoic acid
2. Lipoteichoic acid/ cell membrane teichoic acid
Have role in adhesion and integrity of cell wall
Cell wall teichoic acids
Polymers of ribitol phosphate
covalently linked to NAM molecules of peptidoglycan
Cell membrane teichoic acid
Polymers of glycerol phosphate
Also called lipoteichoic acid
attached to lipid groups of the membrane
Layers of cell wall in a gram negative bacteria
Cell membrane
2 layers of main or peptidoglycan in the periplasmic space
Outer phospholipid bilayer with lipopolysaccharide
The outer phospholipid layer contains:
- Two types of proteins, porins (or channels) and integral or structural proteins (located only on the outer surface)
- Lipopolysaccharide forming the outer surface
Parts of endotoxin or lipopolysaccharide
1. Lipid A: Embedded in outer membrane Actual endotoxins activity 2. Core polysaccharide: Short chain of 6-10 carbohydrates Unique carbohydrates-KDO (ketodeoxyoctanoic acid) and heptose 3. O / somatic antigen: Polysaccharide Outermost Most variable
Effects of endotoxin or lipopolysaccharide
- Activates alternate complement
- Activated tissue factor
- Induces cytokines release from immune cells
Toll like receptor-4 (TLR-4)
On the surfaces of macrophages and dendritic cells
Binds to the lipid-A part of the released LPS of lysed gram negative bacteria
Cytokine release by lipopolysaccharide LPS of gram negative bacteria
When it binds to TLR-4, it activated Nuclear transcription factor-kappa B (NK-kB)
Release of cytokine like interleukins 1, 6 and TNF-alpha
Pharmacological effects of endotoxins
- Fever
- Hypotension
- Increased vascular permeability
- Intravascular coagulation ➡️ DIC ➡️ shock
Gram positive bacteria with LPS in cell wall
Listeria
Exotoxins which is released only in lysis (like endotoxins)
Botulinum toxin
Limulus amebocyte lysate (LAL) assay
Detects endotoxins of gram negative bacteria via coagulation
Very sensitive
Special functions of cell membrane of bacteria
- Contains permeases for transport
2. Cytochromes, respiratory chain enzymes and synthetic enzymes of cell wall
Parts of a flagellum
- Filament
- Hook
- Basal body rings:
Rotated by proton dependent pump
In gram -ve; 4 MSPL rings
In gram +ve; 2 MS rings
Examples of monotrichous flagella
Vibrio
Pseudomonas aeruginosa
Lophotrichous flagella examples
Helicobactor pylori
Campylobacter
Amphitrichous flagella are present in
Campylobacter
Spirillum
Peritrichous flagella
Bacillus and Clostridium (spore forming genera)
Enterobacteriaceae
Vibrio parahemolyticus: on solid medium
Listeria: only at room temperature (not body temperature)
Endoflagella
Flagella present in periplasmic space
Present in spirochaetes
Flagella demonstration
- Direct method (EM, impregnation strain)
- Indirect
A) Hanging drop preparation
B) Soft agar medium (0.2-0.5 %): motility test agar, Craigie’s tube, U-tube
Corkscrew motility
Treponema pallidum
Darting or shooting star motility is exhibited by
Vibrio and campylobacter
Stately motility is exhibited by
Clostridium and Salmonella
End to end or tumbling motility is exhibited by
Listeria
Special motility exhibited by non flagellate bacteria
Gliding- Mycoplasma
Twitching- Eikinella corrodens
Differential motility
Non motile at 37•C but motile at 25-28•C
Listeria
Yersinia enterocolitica
Yersinia pseudotuberculosis
Common pili/ fimbriae
Mediate adhesion
Only in the surface in gram negative bacteria
Sex pili
For conjugation
Takes part in horizontal transfer of plasmids (having tra genes/ sex pilus genes)
Gram positive and gram negative containing F plasmid
Examples of spore producing bacteria
Only 2 genera (among the pathogenic ones) form spores 1. Bacillus: non bulging only in soil and culture 2. Clostridium: bulging soil, culture and human body (except C. perfringes which does not sporulate in the human body)
Layers of bacterial spore
- Core
- Spore wall
- Spore cortex
- Spore coat
- Exosporium-lipoprotein in nature
Core of a bacterial spore
Contains the genome
Glycolytic enzymes
Stored energy (3-phospho glycerate)
Calcium dipicolinate (heat resistance)
Spore wall of bacteria
Contains typical peptidoglycan
Future wall of the vegetative bacterium
Spore cortex of bacteria
Atypical peptidoglycan
Thickest layer
Spore coat of bacteria
Keratin like protein
Resistance to chemical disinfection
Conjugative plasmids
Plasmids which can take part in vertical or horizontal transfer Examples: F/sex plasmid R plasmid Col plasmid
Bacteriocin
Encoded by Col plasmids Antibiotic like proteins which only kill related bacteria Survival advantage Examples: 1. E. coli , Shigella-colicins 2. P. aeruginosa - pyocin 3. Klebsiella - klebocins 4. C. diphtheriae - diphthericins
Metabolic plasmids
Encode enzymes for metabolising special substrates. Example urea
Virulence plasmids
They encode special virulence factors Example: Capsule of B. anthracis (polypeptide) Labile toxin of ETEC (enterotoxigenic E. coli) Anthrax toxin
How does phenol kill bacteria
Phenols work by disrupting cell membrane which causes lysis and release of cell contents
What is phenol coefficient
Efficacy of disinfectant as compared to phenol
The efficacy is measured via the dilution
Other methods of testing disinfectants:
1. Chick Martin test
2. Kelsey Sykes (capacity) test
3. Kelsey and Maurer (in use) test
Normal human microbiota classification
1. Resident flora: Harmless Life long 2. Transient flora: Do not produce disease as long as resident is intact Temporary
Total 10^14 (around 10 times more than human cells)
Human viral microbiota
Collection of viruses in and on human body
Example: skin virome
In bottle feed infants the human microbiota is
Bifidobacterium- major
Comes from core milk or solid food
Enterics, bacteroids
Human microbiota of jejunum , ileum, colon
Enterococci
Lactobacillus
Human microbiota of nostril
Staphylococcus epidermidis
Staphylococcus aureus
Human microbiota of nasopharynx
Streptococcus
Human microbiota of oral cavity
Virodans streptococci
Those involved in dental plaque (opportunistic tooth infections)
Streptococcus sanguis
Streptococcus mutans
The sterile sites of the human body with respect to human microbiota are
Bladder, cervical, uterus, middle ear, sinuses, brain
Most common flora of the GIT is
Bacteroides fragilis
Among aerobes it is E. coli
Advantages of human microbiota
- Prevents colonisation of pathogen
- Vitamin synthesis
- Waste produced may antagonise other bacteria
- Immune stimulation
- Prevents allergic diseases (hygiene hypothesis)
- Complement activation
