Classification of bacteria
Mrs. Dalia Kamal Eldien
MSC in Microbiology
Lecture NO: 3
Questions for revision the previous lecture
What are the function of bacterial cell wall?
The movement organ in bacterial cell is ……
Define the germination process in bacteria?
Objectives
• At the end of this lecture, the student should know:The types of bacteria classified depending on different
methods
Emphasis on morphological& staining classification
Introduction
 Based on the difference in cellular organization and
biochemistry, the kingdom protista has been divided into
two groups namely prokaryotes and eukaryotes.
 Bacteria and blue-green algae are prokaryotes, while
fungi, other algae, fungi and parasite are eukaryotes.
 Bacteria are prokaryotic microorganisms that do not
contain chlorophyll.
 They are unicellular and do not show true branching,
except in higher bacteria like actinomycetales.
Classification
 The bacteria are classified depending on different
methods, include: Morphology
 Staining reactions
 Growth Requirements(Cultural characteristics)
 Biochemical reactions
 Antigenic structure
 Increasingly by their genetic composition using
specialized molecular biology techniques.
Mrs.:Dalia Kamal Eldien
MSC in microbiology
Morphological Classification of bacteria
Bacteria are classified according to morphology in to: Cocci: are spherical or oval cells
 Bacilli: rod shaped cells
 Cocobacilli
 Vibrios: comma shaped curved rods
 Spiral: rigid spiral forms
 Spirochetes: flexuous spiral forms
Mrs.:Dalia Kamal Eldien
MSC in microbiology
Basic shapes of bacteria
 Cocci (Singular: coccus) are spherical or oval cells
 Bacteria sometime show
arrangement or grouping
characteristic
Mrs.:Dalia Kamal Eldien
MSC in microbiology
cellular
 According to the plane of cellular division, cocci may be
arranged in
 Pairs (diplococci)
 Chains (streptococci)
 Grape like clusters (staphylococci).
 Groups of four (tetrads) or eight (sarcina)
Mrs.:Dalia Kamal Eldien
MSC in microbiology
Cocci in pairs
Cocci in cluster
Cocci in chain
Cocci in tetra
Cocci in sarcina
Basic shapes of bacteria
 Bacillus (Singular: bacillus) stick-like bacteria, also name
rod shaped
 Bacilli are arrange in fewer groups, or singly, or in short
chain
Mrs.:Dalia Kamal Eldien
MSC in microbiology
Bacilli arrangement
Bacilli in chain
Bacilli in chain
Bacilli in single
Vibrios
Vibrios (Singular: vibrio) are small slightly curved rods,
comma shape
Mrs.:Dalia Kamal Eldien
MSC in microbiology
Vibrio (Helicobacter pylori)
Spiral
Spiral (Singular: spirillum) are small, regularly coiled,
rigid organisms
Mrs.:Dalia Kamal Eldien
MSC in microbiology
Spiral bacteria
Spirochetes
Spirochetes (Singular: spirochaete) have a helical
shape and flexible bodies
Mrs.:Dalia Kamal Eldien
MSC in microbiology
Spirochetes
Identify the following bacteria structure?
Bacterial Classification
Staining reaction
Classification according to staining reactions depend
in different type of stains
The main stain is Gram stain
The Gram staining method is named after the Danish
bacteriologist Hans Christian Gram (1853 – 1938)
who originally devised it in 1882 (but published in
1884), to discriminate between pneumococci and
Klebsiella pneumoniae bacteria in lung tissue
Mrs.:Dalia Kamal Eldien
MSC in microbiology
Principle of Gram stain
 The procedure is based on the ability of microorganisms
to retain color of the stains used during the gram stain
reaction.
 Gram-negative bacteria are decolorized by the
alcohol, losing the color of the primary stain, purple.
 Gram-positive bacteria are not decolorized by alcohol
and will remain as purple.
 After decolorization step, a counter stain is used to
impart a pink color to the decolorized gram-negative
organisms.
Gram stain
 Gram staining consists of four components:
 Primary stain (Crystal violet, methyl violet or Gentian
violet)
 Mordant (Gram's Iodine)
 Decolourizer (ethyl alcohol, acetone or 1:1 ethanol-acetone)
 Counter stain (safranin or neutral red, dilute carbol fuchsin)
Technique of Gram stain
 Flood the slide with crystal violet solution for one minute.
Wash off briefly with tap water
 Flood slide with Gram's Iodine solution, and allow to act
(as a mordant) for about one minute. Wash off with tap
water.
 Flood slide with 95% alcohol for 10 seconds and wash off
with tap water. It is most important step
 Flood slide with safranin solution and allow to
counterstain for 30 seconds. Wash off with tap water
 All slides of bacteria must be examined under the oil
immersion lens of light microscope
Set of Gram stain
Results of Gram stain
 The results of Gram stain will depend on the cell wall
 Gram-positive bacteria have a thick mesh-like cell wall
which is made up of peptidoglycan (50-90% of cell wall),
so it stains as violet.
 Gram-negative bacteria have a thinner layer of
peptidoglycan (10% of the cell wall) and lose the crystal
violet-iodine complex during decolorization with the
alcohol rinse, but retain the counter stain Safranin, so it
stains as red
Cell wall of Gram positive& negative
bacteria
Classification of bacteria according to
Gram stain
 According to Gram stain, bacteria classify into large
groups: Gram-positive bacteria (violet color)
 Gram-negative bacteria (red color)
Gram-positive bacteria
Gram-negative bacteria
Identify ???