Classification of bacteria

Mrs. Dalia Kamal EldienMSC 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

methodsEmphasis on morphological& staining classification

IntroductionBased 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:- MorphologyStaining reactionsGrowth Requirements(Cultural characteristics)Biochemical reactionsAntigenic 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 cellsBacilli: rod shaped cellsCocobacilliVibrios: comma shaped curved rodsSpiral: rigid spiral formsSpirochetes: 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 characteristic cellular arrangement or grouping

Mrs.:Dalia Kamal Eldien MSC in microbiology

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

VibriosVibrios (Singular: vibrio) are small slightly curved rods,

comma shape

Mrs.:Dalia Kamal Eldien MSC in microbiology

Vibrio (Helicobacter pylori)

SpiralSpiral (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 wallGram-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 ???