classification of bacteria.pptx
- 2. BACTERIAL TAXONOMY All organisms have a name consisting of two parts: the genus followed by the species (i.e., Homo sapiens). This is no different from bacteria Genus species Bacillus subtilis Clostridium tetani Staphylococcus aureus 2
- 3. Basis of classification • Phenotypic classification ❖ Staining ❖ Morphological ❖ Anatomical ❖ Cultural characteristics ❖ Nutrition ❖ Environmental factors ❖ Biochemical reactions ❖ Antigenic structure • Genotypic classification ❖ DNA-DNA hybridization ❖ G+C content 2 3
- 4. Based on Staining reaction Because bacteria are colourless and usually invisible to light microscopy, colourful stains have been developed to visualize them. The most useful is the Gram stain, which separates organisms into 2 groups: gram-positive bugs gram-negative bugs Note: The different stains are the result of differences in the cell walls of gram-positive and gram-negative bacteria. 4
- 5. Based on Staining reaction 5 • GRAM’S STAIN – Gram-positive cocci – Staphylococcus aureus – Gram-negative cocci – Neisseria gonorrhoeae – Gram-positive rods – Clostridium spp. – Gram-negative rods – E. coli • ACID FAST STAIN – Acid-fast bacilli –Mycobacterium tuberculosis – Non-acid-fast bacilli – Staphylococcus aureus
- 6. Morphological classification • Bacteria can be classified into FOUR major groups on morphological basis. Cocci: These are spherical or oval cells. Bacilli: rods. Short bacilli are called coccobacilli. Spiral forms: comma-shaped, S-shaped, or spiral- shaped. Pleomorphic: lacking a distinct shape (like jello) The different shaped creatures organize together into more complex patterns, such as pairs (diplococci), clusters, strips, and single bacteria with flagella. 3 6
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- 9. Gram-Positive Bacteria There are 6 classic gram positive bugs that cause disease in humans, and basically every other organism is gram-negative. Of the gram-positives, 2 are cocci, and the other 4 are rod- shaped (bacilli). The 2 gram-positive cocci both have the word coccus in their names: 1) Streptococcus forms strips of cocci. 2) Staphylococcus forms clusters of cocci. Two of the 4 gram-positive rods produce spores. These are: 3) Bacillus 4) Clostridium The last 2 gram-positive rods do not form spores: 5) Corynebacterium 6) Listeria 9
- 10. Gram-Negative Bacteria Of the gram-negative organisms, there is only one group of gram- negative cocci. It is actually a diplococcus. Example: Neisseria spp. There is also just 1 group of spiral-shaped organisms: the Spirochetes. This group includes the bacterium Treponema spp., Borrelia spp. and Leptospira spp. The rest are gram-negative rods or pleomorphic. EXCEPTIONS 1) Mycobacteria are weakly gram-positive but stain better with a special stain called the acid-fast stain 2) Spirochetes have a gram-negative cell wall but are too small to be seen with the light microscope and so must be visualized with a special darkfield microscope. 3) Mycoplasma do not have a cell wall. They only have a simple cell membrane, so they are neither gram-positive nor gram-negative 1 0
- 11. Based on Anatomical features • Capsule – Capsulate– Streptococcus pneumoniae – Non-capsulate – Viridans streptococci Flagella – Flagellate – vibro cholerae – Aflagellate – Shigella spp. Spore – Spore-forming – Bacillus spp. – Non-sporing – Escherichia coli • 10 1 1
- 12. Based on Cultural characteristics 12 • Extra growth factors requirements – Fastidious – Hemophilus influenzae – Non-fastidious – Escherichia coli • Hemolysis on Sheep Blood Agar – Alpha-hemolysis – Streptococcus pneumoniae – Beta-hemolysis – Streptococcus pyogenes • Utilization of carbohydrates – Oxidative - Micrococcus – Fermentative – Escherichia coli
- 13. Based on Cultural characteristics 13 • Growth rate – Rapid growers– Vibrio cholerae – Slow growers – Mycobacterium tuberculosis • Pigment production – Pigment producer – Staphylococcus aureus – Pigment non-producer – Escherichia coli
- 14. Based on Nutrition 14 • Autotrophs: use inorganic sources, such as ammonium and sulphide as energy sources. Heterotrophs: use organic carbon sources as energy sources
- 15. Based on environmental factors 15 • Temperature • Oxygen dependence • pH • Salt concentration • Atmospheric pressure
- 16. Temperature • Psychrophiles (15-200 C) – Pseudomonas fluorescens • Mesophiles (20-400 C) – Escherichia coli, Salmonella enterica, Staphylococcus aureus • Thermophiles (50-600 C)- Bacillus stearothermophilus • Extremely thermophiles (as high as 2500 C) 16
- 17. Oxygen dependence • Aerobe (grow in ambient temperature, which contains 21% O2 and a small amount of CO2 , 0.03%) • Obligate aerobes – Strictly require O2for their growth (Pseudomonas aeruginosa) • Microaerophilic (grow under reduced O2 , 5- 10% and increased CO2 , 8-10%)- Campylobacter jejuni, Helicobacter pylori 17
- 18. Oxygen dependence • Facultative anaerobe (capable of growing either in presence or absence of O2 )- E. coli • Obligate anaerobe – Clostridium spp. • Capnophilic (require increased concentration of CO2 , i.e., 5-10%) – H. influenzae, N. gonorrhoeae • Aerotolerant 18
- 19. pH • Acidophiles (Lactobacillus acidophilus) • Alkaliphiles (Vibrio) • Neutralophiles (pH 6-8) Majority of the medically important bacteria grow best at neutral or slightly alkaline reaction (pH 7.2-7.6) 19
- 20. Salt concentration • Halophiles • Non-halophiles 20
- 21. Other ways of classification 21 • • • • Motile/Non-motile Pathogenic/Non-pathogenic Sensitive/Resistant (to particular antibiotic/ chemicals) Lactose fermenter/Lactose non-fermenter
- 22. 5 Time (Minutes) Bacterial Growth Curve 1 10 Lag phase Stationary phase Death phase Log phase 22