Classification and Chracterisation of Bacteria

Characterization and classification

These are the group of microscopic single celled organism that live enormous number in almost every environment on the surface of earth, from deep vents to the digestive tracts of humans.

It can be classified and characterized on the bases of morphology, biochemical characterization, physiological characterization……………..

SHAPE………….

Coccus

Chain = StreptoccusCluster = Staphylococcus

Bacillus

Chain = Streptobacillus

Coccobacillus

Vibrio = curved

Spirillum

Spirochete

Square

Star

Shapes……………

Flagella, Fimbriae, pili……..

Short protein appendagessmaller than flagella

Adhere bacteria to surfacesE. coli has numerous types

K88, K99, F41, etc.Antibodies to will block adherance

F-pilus; used in conjugationExchange of genetic information

Flotation; increase boyancyPellicle (scum on water)More oxygen on surface

Gram-positive cell walls Gram-negative cell walls

Thick peptidoglycan90% peptidoglycanTeichoic acids1 layerNot many polysaccharides In acid-fast cells, contains mycolic acid

Thin peptidoglycan5-10%

peptidoglycanNo teichoic acids3 layersOuter membrane

has lipids, polysaccharides

No acid- fast cells (mycolic acid)

Neisseria

Streptococcus

Pseudomonas

Attach to outer surface of cell wall“Glycocalyx” (gly-koh-kay’licks) is the general

term of the polysaccharide capsule/ slime layer

Produced when proper growth conditionsExcess of nutrients

Made from a variety of polysaccharidesPoly D-glutamate in Bacillus sp.

Capsule: the polysaccharide that has a uniform thickness & can be thicker than cell

Streptococcus pneumoniae infectious to human, capsule help protect the cell against phagocytosis

Can be observed by performing Negative staining with India Ink

Slime layer: the polysaccharide adhered to the cell wall in a diffuse arrangement

Bacteria that cause dental carries help bacteria to colonise surface

Flagella PiliCapsulePlasma MembraneCytoplasmCell WallLipopolysaccharidesTeichoic AcidsInclusionsSpores

Colonial Morphology………….Colonial Morphology………….

• Shape• Edge• Elevation • Size• Chromogenesis• Opacity• Surface• Consistency• Emulsifiability• Odor

Carbon SourcesAutotrophs CO2 sole or principal

biosynthetic carbon source.Heterotrophs Reduced, preformed, organic molecules from other

organisms Energy Sources Phototrophs Light Chemotrophs Oxidation of organic or

inorganic compounds (chapter 9) Electron SourcesLithotrophs Reduced inorganic moleculesOrganotrophs Organic molecules

. Psychrophiles-- cold loving microbes

2. Mesophiles--moderate-temperature loving

organism-- most pathogens and indigenous

flora3. Thermophiles

-- heat loving microbes-- ex. Thermophilic cyanobacteria

found in hot springs-- Thermodurics: organisms that

can survive or endure boiling -- ex. Endospores and viruses

1. Minimum Growth temperature- lowest temperature at which the species

will grow2. Optimum Growth temperature

- temperature at which the species grows

best3. Maximum Growth temperature

- highest temperature at which growth is possible

Classification Temperature Range (°C) Optimum Growth Temperature (°C)

Psychrophile -10 to 20 10

Psychrotroph 5 to 30 25

Mesophile 10 to 45 37

Thermophile 40 to 75 55

Hyperthermophile 65 to 120 90-100

Acidity or alkalinity of a solution1. Neutrophiles

-- neutral growth medium (pH 7)-- most microorganisms

2. Acidophiles--prefer a pH of 2-5--microbes that can live in the

stomach3. Alkaliphiles (Basophiles)

--prefer pH greater 8.5-- found in intestine

-Based on relationship to O2

1. Aerobes---use molecular O2 for life and reproduction

a. Obligate aerobes - require an atmosphere that contains

O2 similar to room air (20-21% O2), Ex. Mycobacteria

b. Microaerophiles - require O2 lower than room air (=5%

O2) - ex. Neisseria, Campylobacter

2. Anaerobes- do not require O2 for life and

reproduction- vary based on sensitivity to O2a. Obligate anaerobe - unable to grow in O2, ex.

Clostridium

Source of Energy--Phototrophs---light--Chemotrophs– inorganic or organic compounds

Source of Carbon-- Autotrophs---CO2-- Litotrophs—inorganic compound except CO2-- Heterotrophs (Organotrophs) ---Organic compounds

Energy Source and Carbon Source--Photoautotrophs---Light + CO2

---ex. Plants, algae, cyanobacteria, purple and green

sulfur bacteria--Photoheterotrophs (Photoorganotrophs) --- Light + organic compounds

—ex. Green and purple non-sulfur bacteria

--Chemoautotrophs– Chemical + CO2 ex. Nitrifying, hydrogen, iron and sulfur bacteria

--Chemolitotrophs--- Chemical + inorganic compound except CO2

-- Chemoheterotrophs– Chemical + organic compound ex. All animals, protozoa, fungi, most bacteria

-- Photolithotrophs – Light + inorganic compound except CO2 ex. Plants and algae: producers of food and O2 for chemoheterotrophs

Bacteria are susceptible to certain antibiotics which can be tested by sensitivity test. Kurby baur method is used to test the susceptibility, by diffusion method.

IndoleMethyl RedCitrateH2S production Urea hydrolysisMotilityLactose fermentationSucrose fermentationGlucose fermentation & gas

production

How to Perform Test: Inoculate Tryptone broth with inoculating loop.

Property it tests for: This test is performed to help differentiate species of the family Enterobacteriaceae. It tests for the bacteria species’ ability to produce indole. Bacteria use an enzyme, tryptophanase to break down the amino acid, tryptophan, which makes by-products, of which, indole is one.

Media and Reagents Used: Tryptone broth contains tryptophan. Kovac’s reagent—contains hydrochloric acid, dimethylaminobenzaldehyde, and amyl alcohol—yellow in color.

Reading Results: Kovac’s reagent reacts with indole and creates a red color at the top part of the test tube.

How to Perform Tests: Inoculate glucose broths with inoculating loop. After 48 hours of incubation, add a few drops of MR to tube.

Properties they test for: tests is used to help differentiate species of the family Enterobacteriaceae. MR—tests for acid end products from glucose

fermentation.

Media and Reagents Used: Glucose Broth Methyl Red indicator for acid

Reading Results: MR— a + result is red (indicating pH below 6) and a – result is yellow (indicating no acid production)

How to Perform Test: Inoculate slant with inoculating loop.

Property it tests for: This test is used to help differentiate species of the family Enterobacteriaceae. It is selective for bacteria that has the ability to consume citrate as its sole source of carbon and ammonium as sole nitrogen source.

Media and Reagents Used: Simmon’s Citrate Agar contains sodium citrate (carbon source), ammonium ion (nitrogen source), & pH indicator—bromthymol blue.

Reading Results: A + result is blue (meaning the bacteria metabolised citrate and

produced an acid end product) and a – result remains green

Left positive and right negative

How to Perform Test: Stab media with inoculating needle.

Property it tests for: This test is used to help differentiate species of the family Enterobacteriaceae. This test is used to determine the ability to reduce sulfur into H2S.

Media and Reagents Used: media contains the sulfur containing amino acid, cysteine, sodium thiosulfate, & peptonized iron or ferrous sulfate.

Reading Results: H2S will react with the iron or ferrous sulfate and produce a black precipitate. A positive result has a black precipitate present and a negative result has no black precipitate.

How to Perform Test: Inoculate Urea broth with inoculating loop.Property it tests for: This test is done to determine a bacteria’s ability to hydrolyze urea to make ammonia using the enzyme urease.Media and Reagents Used: Urea broth Contains a yeast extract, monopotassium phosphate, disodium phosphate, urea, and phenol red indicator.Reading Results: Urea broth is a yellow-orange color.

The enzyme urease will be used to hydrolyze urea to make ammonia. If ammonia is made, the broth turns a bright pink color, and is positive. If test is negative, broth has no color change and no ammonia is made.

How to Perform Test: Stab motility media with inoculating needle.

Property it tests for: This test is done to help differentiate species of bacteria that are motile.

Media and Reagents Used: Motility media contains tryptose, sodium chloride, agar, and a color indicator.

Reading Results: If bacteria is motile, there will be growth going out away from the stab line, and test is positive. If bacteria is not motile, there will only be growth along the stab line. A colored indicator can be used to make the results easier to see

From left to right:

+ –+

How to Perform Test: Inoculate lactose broth with inoculating loop.

Property it tests for: This tests for the bacteria’s ability to ferment lactose.

Media and Reagents Used: Lactose broth contains beef extract, gelatin peptone, and lactose. A phenol red indicator is added to indicate acid production from fermentation.

Results A positive result is yellow after indicator is added

(indicating lactose fermentation) A negative result will have no color change or will be

redish

How to Perform Test: Inoculate sucrose broth with inoculating loop.

Property it tests for: This test is done to help differentiate species of the family Enterobacteriaceae. This tests for the bacteria’s ability to ferment sucrose and production of acid end-product

Media and Reagents Used: Sucrose broth contains beef extract, gelatin peptone, and sucrose. Phenol red indicator is added to indicate an acid end-product.

Results A positive result is yellow after indicator is added

(indicating sucrose fermentation) A negative result has no color change or is reddish.

How to Perform Test: Inoculate broth with inoculating loop.

Property it tests for: This test is done to help differnetiate species of the family Enterobacteriaceae. This tests for the bacteria’s ability to ferment glucose and produce gas and/or an acid end-product..

Media and Reagents Used: Glucose broth contains beef extract, gelatine peptone, and glucose. A phenol red indicator is added to indicate an acid enproduct. A Durham tube is added to indicate gas production.

Results A positive result for acid is yellow after indicator is

added (indicating glucose fermentation) A positive result for gas is a bubble in the Durham tube. A completely negative result has no color change or

reddish color and no bubble.

Thank you………………….