Classification and Morphology of Microorganisms

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Classification and Morphology of Microorganisms
Chair of Microbiology, Virology, and Immunology
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Comparison of the three domains
Characteristic Eubacteria Archaea Eucarya
Cell type Prokaryote Prokaryote Eukaryote
Cell wall Peptidoglycan Varies Varies
Membrane lipids Unbranched Branched Unbranched
Sensitive to antibiotics? Yes No No
Circular chromosome? Yes Yes No (except in mitochondria and chloroplasts)
Histones? No Yes Yes
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Prokaryotes
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Classification Systems in the Procaryotae

• Microscopic morphology
• Macroscopic morphology colony appearance
• Physiological / biochemical characteristics
• Chemical analysis
• Serological analysis
• Genetic and molecular analysis
• G C base composition
• DNA analysis using genetic probes
• Nucleic acid sequencing and rRNA analysis

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Bacterial Taxonomy Based on Bergeys Manual

• Bergeys Manual of Determinative Bacteriology
  five volume resource covering all known
  procaryotes
• classification based on genetic information
  phylogenetic
• two domains Archaea and Bacteria
• five major subgroups with 25 different phyla

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Taxonomy

• Domain
• Kingdom
• Phylum
• Class
• Order
• Family
• Genus
• species

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Major Taxonomic Groups of Bacteria

• Vol 1A Domain Archaea
• primitive, adapted to extreme habitats and modes
  of nutrition
• Vol 1B Domain Bacteria
• Vol 2-5
• Phylum Proteobacteria Gram-negative cell walls
• Phylum Firmicutes mainly Gram-positive with low
  G C content
• Phylum Actinobacteria Gram-positive with high G
  C content

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Microbial Phylogeny

• Phylogeny of domain Bacteria
• The 2nd edition of Bergeys Manual of Systematic
  Bacteriology divides domain Bacteria into 23
  phyla.

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Microbial Phylogeny

• Phylogeny of domain Bacteria (cont.)
• Phylum Proteobacteria
• The largest group of gram-negative bacteria
• Extremely complex group, with over 400 genera and
  1300 named species
• All major nutritional types are represented
  phototrophy, heterotrophy, and several types of
  chemolithotrophy
• Sometimes called the purple bacteria, although
  very few are purple the term refers to a
  hypothetical purple photosynthetic bacterium from
  which the group is believed to have evolved

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Microbial Phylogeny

• Phylogeny of domain Bacteria (cont.)
• Phylum Proteobacteria (cont.)
• Divided into 5 classes Alphaproteobacteria,
  Betaproteobacteria, Gammaproteobacteria,
  Deltaproteobacteria, Epsilonproteobacteria

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Microbial Phylogeny

• Phylogeny of domain Bacteria (cont.)
• Phylum Proteobacteria (cont.)
• Significant groups and genera include
• The family Enterobacteriaceae, the gram-negative
  enteric bacteria, which includes genera
  Escherichia, Proteus, Enterobacter, Klebsiella,
  Salmonella, Shigella, Serratia, and others
• The family Pseudomonadaceae, which includes genus
  Pseudomonas and related genera
• Other medically important Proteobacteria include
  genera Haemophilus, Vibrio, Camphylobacter,
  Helicobacter, Rickessia, Brucella

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Microbial Phylogeny

• Phylogeny of domain Bacteria (cont.)
• Phylum Firmicutes
• Low G C gram-positive bacteria
• Divided into 3 classes
• Class I Clostridia includes genera Clostridium
  and Desulfotomaculatum, and others
• Class II Mollicutes bacteria in this class
  cannot make peptidoglycan and lack cell walls
  includes genera Mycoplasma, Ureaplasma, and
  others
• Class III Bacilli includes genera Bacillus,
  Lactobacillus, Streptococcus, Lactococcus,
  Geobacillus, Enterococcus, Listeria,
  Staphylococcus, and others

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Microbial Phylogeny

• Phylogeny of domain Bacteria (cont.)
• Phylum Actinobacteria
• High G C gram-positive bacteria
• Includes genera Actinomyces, Streptomyces,
  Corynebacterium, Micrococcus, Mycobacterium,
  Propionibacterium
• Phylum Chlamidiae
• Small phylum containing the genus Chlamydia

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Microbial Phylogeny

• Phylogeny of domain Bacteria (cont.)
• Phylum Spirochaetes
• The spirochaetes
• Characterized by flexible, helical cells with a
  modified outer membrane (the outer sheath) and
  modified flagella (axial filaments) located
  within the outer sheath
• Important pathogenic genera include Treponema,
  Borrelia, and Leptospira
• Phylum Bacteroidetes
• Includes genera Bacteroides, Flavobacterium,
  Flexibacter, and Cytophyga Flexibacter and
  Cytophyga are motile by means of gliding
  motility

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Procaryotae Kingdom has 4 Divisions according
to the structure of cell wall and Gram staining
Gracilicutes (gracilis - thin, cutis - skin)
Gram-negative bacteria, Firmicutes (firmus -
firm) Gram-positive bacteria, Tenericutes
(tener soft, tender) microbes without cell
wall, Mendosicutes (mendosus - mistaket)
microbes with atipical peptidoglican
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Bacterial Nomenclature

• Binomial naming system
• Two word naming system
• First word is genus name
• Always capitalized
• Escherichia
• Second word is species name
• Not capitalized
• coli
• When writing full name genus usually abbreviated
• E. coli
• Full name always italicized
• Or underlined

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Species is population of microbes, which have the
only source of origin, common genotype, and
during the present stage of evolution are
characterized by similar morphological,
biochemical, physiological and other signs
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If deviations from the typical species
properties are found on examination of the
isolated bacteria, then culture is considered a
subspecies. Infrasubspecies subdivisions serovar
(antigenic properties) morphovar (morphological
properties) chemovar (chemical properties)
biovar (biochemical or physiological properties)
pathovar (pathogenic properties) phagovar
(relation to phages)
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The term clone was applied to population of
cells derived from a single cell
Population is an elementary evolutional unit
(structure) of a definite species
The term strain designates a microbial culture
obtained from the different sources or from one
source but in different time Or A subgroup
within a species with one or more haracteristics
that distinguish it from other subgroups in the
species
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Bacteria (Gk. bakterion - small staff) are
unicellular organisms lacking chlorophyll.
Morphological Classification of Bacteria

• Morphologically, bacteria possess four main
  forms
• spherical (cocci)
• rod-shaped (bacteria, bacilli, and clostridia)
• spiral-shaped (vibrios, spirilla and
  spirochaetes)
• thread-shaped (non-pathogenic)

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Cocci groupings
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Cocci (Gk. kokkos berry). These forms of bacteria
are spherical, ellipsoidal, bean-shaped, and
lanceolate. Cocci are subdivided into six groups
according to cell arrangement, cell division and
biological properties
Micrococci (Micrococcus). The cells are arranged
singly or irregularly. They are saprophytes, and
live in water and in air ( M. roseus, M. luteus,
etc.).
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Diplococci (Gk. diplos double) divide in one
plane and remain attached in pairs. These
include Meningococcus (causative agent of
epidemic cerebrospinal meningitis, and
gonococcus, causative agent of gonorrhoea and
blennorrhoea) Pneumococcus (causative agents of
pneumonia)
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Streptococci (Gk. streptos curved, kokkos berry)
divide in one plane and are arranged in chains of
different length. Some streptococci are
pathogenic for humans and are responsible for
various diseases.
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Tetracocci (Gk. tetra four) divide in two planes
at right angles to one another and form groups of
fours. They very rarely produce diseases in
humans.
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Staphylococci (Gk. staphyle cluster of grapes)
divide in several planes resulting in irregular
bunches of cells, sometimes resembling clusters
of grapes. Some species of Staphylococci cause
diseases in man and animals
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Sarcinae (L. sarcio to tie) divide in three
planes at right angles to one another and
resemble packets of 8, 16 or more cells. They are
frequently found in the air. Virulent species
have not been encountered
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• Rods. Rod-shaped forms are subdivided into
• bacteria,
• bacilli,
• clostridia
• Bacteria include those microorganisms which, as a
  rule, do not produce spores (colibacillus, and
  organisms responsible for enteric fever,
  paratyphoids, dysentery, diphtheria,
  tuberculosis, etc.).
• Bacilli and clostridia include organisms the
  majority of which produce spores (hay bacillus,
  bacilli responsible for anthrax, tetanus,
  anaerobic infections, etc.)

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According to their arrangement, cylindrical forms
can be subdivided into three groups
monobacteria
monobacilli
C. tetani
E. coli
Y. pestis
C. botulinum
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diplobacteria
diplobacilli
K. pneumoniae
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streptobacteria
streptobacilli
Haemophilus ducreyi (chancroid)
Bacillus anthracis (anthrax)
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Spiral-shaped bacteria
Vibriones (L. vibrio to vibrate) are cells which
resemble a comma in appearance. Typical
representatives of this group are Vibrio
cholerae, the causative agent of cholera, and
aquatic vibriones which are widely distributed in
fresh water reservoirs.
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Spirilla (L. spira coil) are coiled forms of
bacteria exhibiting twists with one or more
turns. Only one pathogenic species is known
Spirillum minus which is responsible for a
disease in humans transmitted through the bite of
rats and other rodents (rat-bite fever, sodoku)
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Spirochaetes (L. spira curve, Gk. chaite cock,
mane) differ from bacteria in structure with a
corkscrew spiral shape
Borrelia. Their cells have large, obtuse-angled,
irregular spirals, the number of which varies
from 3 to 10. Pathogenic for man are the
causative agents of relapsing fever transmitted
by lice (Borrelia hispanica), and by ticks
(Borrelia persica, etc.). These stain blue-violet
with the Romanowsky-Giemsa stain
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Leptospira (Gk. leplos thin, speira coil) are
characterized by very thin cell structure. The
leptospirae form 12 to 18 coils wound close to
each other, shaping small primary spirals. The
organisms have two paired axial filaments
attached at opposite ends (basal bodies) of the
cell and directed toward each other.
Leptospira interrogans which is pathogenic for
animals and man cause leptospirosis
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Treponema (Gk. trepein turn, nema thread)
exhibits thin, flexible cells with 6-14 twists.
The micro-organisms do not appear to have a
visible axial filament or an axial crest when
viewed under the microscope
A typical representative is the causative agent
of syphilis Treponema pallidum
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Properties of prokaryotes and eukaryotes
Prokaryotes Eukaryotes
The nucleoid has no membrane separating it from the cytoplasm Karyoplasm is separated from the cytoplasm by membrane
Chromosome is a one ball of double twisted DNA threads. Mitosis is absent Chromosome is more than one, There is a mitosis
DNA of cytoplasm are represented in plasmids DNA of cytoplasm are represented in organelles
There arent cytoplasmic organelle which is surrounded by membrane There are cytoplasmic organelle which is surrounded by membrane
The respiratory system is localized in cytoplasmic membrane The respiratory system is localized mitochondrion
There are ribosome 70S in cytoplasm There are ribosome 80S in cytoplasm
Peptidoglycan are included in cells wall (Murein) Peptidoglycan arent included in cells wall
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The structure of procaryotes
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Nucleus. The prokaryotic nucleus can be seen with
the light microscope in stained material. It is
Feulgen-positive, indicating the presence of DNA.
Histonelike proteins have recently been
discovered in bacteria and presumably play a role
similar to that of histones in eukaryotic
chromatin
The DNA is seen to be a single, continuous,
"giant" circular molecule with a molecular weight
of approximately 3 X 109. The unfolded nuclear
DNA would be about 1-3 mm long (compared with an
average length of 1 to 2 µm for bacterial cells)
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• Plasmids
• small circular, double-stranded DNA
• free or integrated into the chromosome
• duplicated and passed on to offspring
• not essential to bacterial growth metabolism
• may encode antibiotic resistance, tolerance to
  toxic metals, enzymes toxins
• used in genetic engineering- readily manipulated
  transferred from cell to cell
• There may be several different plasmids in one
  cell and the numbers of each may vary from only
  one to 100s in a cell

Plasmids R, Col, Hly, Ent, Sal
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Prokaryotic Ribosome

• A ribosome (70 S) is a combination of RNA and
  protein, and is the site for protein synthesis
• Composed of large (50S) and small (30S) subunits
• S Svedverg unit, measures molecular size

The 80S ribosomes of eukaryotes are made up of
40S and 60S subunits.
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Inclusions, granules

• Storage granules
• Metachromatic granules
• Polysaccharide granules
• Lipid inclusions
• Sulfur granules
• Carboxyzomes
• Magnetosomes
• Gas vesicles

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Volutin granules Corynebacterium diphtheriae
Loeffler's technique
Neisser's staining
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Cell Envelope
Composted of A. The cytoplasmic
membrane To act as a physical barrier btw
cytoplasm and environments and selectively
controls the movement of substaces into and out
of the cell Semipermeable B. Cell
wall The rigid layer that protect the fragile
cytoplasmic membrane from rupturing To maintains
cells shape C. Capsule or slime layer
(glycocalyx)
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Cell membrane
Bacterial plasma membrane are composed of 40
percent phospholipid and 60 percent protein. The
phospholipids are amphoteric molecules with a
polar hydrophilic glycerol "head" attached via an
ester bond to two nonpolar hydrophobic fatty acid
tails, which naturally form a bilayer in aqueous
environments. Dispersed within the bilayer are
various structural and enzymatic proteins which
carry out most membrane functions.
Peripheral Membrane Protein
Phospholipid
Integral Membrane Protein
Peripheral Membrane Protein
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Mesosome
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The predominant functions of bacterial membranes
are 1. Osmotic or permeability barrier 2.
Location of transport systems for specific
solutes (nutrients and ions) 3. Energy
generating functions, involving respiratory and
photosynthetic electron transport systems,
establishment of proton motive force, and
transmembranous, ATP-synthesizing ATPase 4.
Synthesis of membrane lipids (including
lipopolysaccharide in Gram-negative cells) 5.
Synthesis of murein (cell wall peptidoglycan)
6. Assembly and secretion of extracytoplasmic
proteins 7. Coordination of DNA replication and
segregation with septum formation and cell
division 8. Chemotaxis (both motility per se
and sensing functions) 9. Location of
specialized enzyme system.
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Cell wall

• Unique chemical structure
• Distinguishes Gram positive from Gram-negative
• bacteria and archaea bacterial species
• Rigidity of cell wall is due to peptidoglycan
  (PTG)
• Compound found only in bacteria
• Archaea psudomurein or other sugars, proteins,
  glycoproteins
• Many antimicrobial interfere with synthesis of
  PTG
• Penicillin Lysozyme

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Structure of peptidoglycan

• Basic structure of peptidoglycan
• Alternating series of two subunits
• N-acetylglucosamin (NAG)
• N-acetylmuramic acid (NAM)
• Joined subunits form glycan chain
• Glycan chains held together by string of four
  amino acids
• Tetrapeptide chain
• L-ala-D-glu-DAP-D-ala
• L-ala-D-glu-Lys-D-ala
• Interpeptide bridge

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Differences of cell wall structure in
Gram-positive and Gram negative cells
Structures associated with gram-positive and
gram-negative cell walls.
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L Forms
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Glycocalyx

• Capsule
• Protects bacteria from phagocytic cells
• Slime layer
• Enable attachment and aggregation of bacterial
  cells

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Capsules Most prokaryotes contain some sort of a
polysaccharide layer outside of the cell wall
polymer
Only capsule of B. anthracis consist of
polypeptide (polyglutamic acid)
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Capsule

• The capsule is covalently bound to the cell wall.
• Associated with virulence in bacteria.
• Example
• Streptococcus pneumoniae

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Slime Layer

• The slime layer is loosely bound to the cell.
• Carbohydrate rich material enhances adherence of
  cells on surfaces
• Example
• Streptococcus mutans and plaque formation

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Biofilms

• The slime layer is associated with cell
  aggregation and the formation of biofilms
• Example
• Staphylococcus epidermidis biofilms on catheter
  tips

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General capsule function

• Adhesion
• Avoidance of immune response
• Protection from dehydration
• Protection of bacterial cells from engulfment by
  protozoa or white blood cells (phagocytes), or
  from attack by antimicrobial agents of plant or
  animal origin.
• They provide virulent properties of bacteria
  (S. pneumoniae, B. anthracis)

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Flagella

• 3 parts
• filament long, thin, helical structure composed
  of proteins
• hook- curved sheath
• basal body stack of rings firmly anchored in
  cell wall
• rotates 360o
• 1-2 or many distributed over entire cell
• functions in motility

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Flagellar arrangements

• 1. Monotrichous single flagellum at one end
  (cholera vibrio, blue pus bacillus),
• 2. Lophotrichous small bunches arising from one
  end of cell (blue-green milk bacillus,Alcaligenes
  faecalis)
• 3. Amphitrichous flagella at both ends of cell
  (Spirillum volutans),
• 4. Peritrichous flagella dispersed over surface
  of cell, slowest E. coli, salmonellae of enteric
  fever and paratyphoids A and B

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Bacterial Motility

• Flagella are important for
• Motility (dispersal)
• Antigenic determinant
• Number and location species specific

The rotation of the flagella enables bacteria to
be motile.
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Pili and Fimbriae

• Short, hair-like structures on the surfaces of
  procaryotic cells
• Proteinaceuse filaments (20 nm in diameter)
• Very common in Gram-negative bacteria
• Functions
• Adherence to surface/ substrates teeth, tissues
• Involved in transfer of genetic information btw
  cells
• Have nothing to do with bacterial movement
  (Except the twitching movement of Pseudomonas)

Fimbriae are smaller than flagella and are
important for attachment
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Bacterial endospores

• Bacterial spores are often called endospore
  (since they are formed within the vegetative
  cell)
• Produced in response to nutrient limitation or
  extreme environments
• Highly resistant
• Highly dehydrated (15 water)
• Metabolically inactive
• Stable for years
• Not reproductive
• Functions to survive under an extreme growth
  conditions such as high temperature, drought,
  etc.
• Bacillus, Clostridium, Sporolactobacillus,
  Thermoactinomyces, Sporosarcina, Desulfotomaculum
  species sporulate

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Spore
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Spores

• Key compositions
• Dipicolinic acid (DPA)
• Calcium (Ca2)
• Structure
• Core / Cytoplasm
• Plasma membrane
• Core wall/ spore wall
• Cortex
• Spore coat
• Exosporium

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Endospores
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The sporulation process begins when nutritional
conditions become unfavorable, depletion of the
nitrogen or carbon source (or both) being the
most significant factor. Sporulation involves the
production of many new structures, enzymes, and
metabolites along with the disappearance of many
vegetative cell components.
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• Spores are located
• Centrally (B. anthracis)
• 2) Terminally (?. tetani)
• 3) Subterminally (C. botulinum, C. perfringens)

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The spores of certain bacilli are capable of
withstanding boiling and high concentrations of
disinfectants. They are killed in an autoclave
exposed to saturated steam, at a temperature of
115-125 ?C, and also at a temperature of 150-170
?C in a Pasteur hot-air oven.
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