Classification of Bacteria by Shayam Kumar Mishra
- 1. Classification of bacteria Shyam Kumar Mishra Assistant Professor, Department of Microbiology Institute of Medicine Tribhuvan University 1
- 2. Basisof classification • Phenotypicclassification Morphological Anatomical Staining Cultural characteristics Nutrition Environmentalfactors Biochemicalreactions Antigenicstructure • Genotypicclassification DNA-DNAhybridization G+Ccontent 2
- 3. Morphologicalclassification • Bacteria canbe classified into sixmajor groups on morphological basis. 1. TRUEBACTERIA • Cocci–Theseare spherical or oval cells. Onthe basisof arrangement of individual organisms they canbe described as – Monococci(Cocciin singles) – Monococcus spp. – Diplococci(Cocciin pairs) – Streptococcus pneumoniae – Staphylococci(Cocciin grape-like clusters) – Staphylococcusaureus – Streptococci(Cocciin chains) – Streptococcus pyogenes – Tetrad (Cocciin group of four) - Micrococcusspp. – Sarcina(Cocciin group of eight) 3
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- 6. • 6 Bacilli–Theseare rod-shaped bacteria. Onthe basisof arrangement of organisms, they canbe describedas – Diplobacilli – Streptobacilli – Palisades – Chinese-letterform – Coccobacilli – Comma-shaped
- 7. Morphologicalclassification 2. ACTINOMYCETES(actin- ray,mykes-fungus) Theseare rigid organisms like true bacteria but they resemble fungi in that they exhibitbranching and tend to formfilaments. Theyare termed suchbecauseof their resemblance to sun rays when seenin tissue sections. 7
- 8. Morphologicalclassification 3. Spirochaetes Theseare relatively longer, slender, non-branched microorganisms of spiral shapehaving severalcoils. 8
- 9. Morphologicalclassification 4. Mycoplasmas Thesebacteria lack in rigid cell wall (cell walllacking) and are highly pleomorphic and of indefiniteshape. Theyoccur in round or oval bodies and ininterlacing filaments. 5. Rickettsiaeand Chlamydiae Theseare very small, obligate parasites, and at onetime were considered closely related to the viruses. Now, these are regarded asbacteria. 9
- 10. BasedonAnatomical features • • • Capsule – Capsulate–Streptococcus pneumoniae – Non-capsulate – Viridans streptococci Flagella – Flagellate – • Monotrichous • Lophotrichous • Amphitrichous • Peritrichous – Aflagellate – Shigella spp. Spore – Spore-forming– Bacillus spp. – Non-sporing– Escherichia coli 10
- 11. BasedonStaining reaction 11 • GRAM’SSTAIN – Gram-positivecocci–Staphylococcus aureus – Gram-negativecocci– Neisseria gonorrhoeae – Gram-positiverods– Clostridium spp. – Gram-negativerods– E. coli • ACIDFASTSTAIN – Acid-fastbacilli–Mycobacterium tuberculosis – Non-acid-fastbacilli– Staphylococcus aureus
- 12. BasedonCultural characteristics 12 • Extra growth factors requirements – Fastidious– Hemophilus influenzae – Non-fastidious– Escherichia coli • Hemolysis on SheepBloodAgar – Alpha-hemolysis – Streptococcus pneumoniae – Beta-hemolysis– Streptococcus pyogenes • Utilization of carbohydrates – Oxidative - Micrococcus – Fermentative– Escherichiacoli
- 13. BasedonCultural characteristics 13 • Growth rate – Rapidgrowers–Vibrio cholerae – Slowgrowers– Mycobacterium tuberculosis • Pigment production – Pigmentproducer– Staphylococcus aureus – Pigmentnon-producer – Escherichia coli
- 14. Basedon Nutrition 14 • Autotrophs • Heterotrophs
- 15. Basedonenvironmental factors 15 • Temperature • Oxygendependence • pH • Saltconcentration • Atmosphericpressure
- 16. Temperature • Psychrophiles(15-200C) – Pseudomonas fluorescens • Mesophiles(20-400C) – Escherichia coli, Salmonella enterica, Staphylococcus aureus • Thermophiles(50-600C)- Bacillus stearothermophilus • Extremelythermophiles (ashigh as 2500C) 16
- 17. Oxygendependence • Aerobe (grow in ambient temperature,which contains 21%O2and asmall amount of CO2 , 0.03%) • Obligate aerobes– Strictly require O2for their growth (Pseudomonasaeruginosa) • Microaerophilic (grow under reduced O2,5- 10%and increased CO2 ,8-10%)- Campylobacter jejuni,Helicobacter pylori 17
- 18. Oxygendependence • 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. Otherwaysofclassification 21 • • • • • Motile/Non-motile Pathogenic/Non-pathogenic Sensitive/Resistant (to particular antibiotic/ chemicals) Lactosefermenter/Lactose non-fermenter Bergey’sManual of Determinative Bacteriology – Gram-negative eubacteria that havecell walls – Gram-positiveeubacteria that havecell walls – Cellwall-lesseubacteria: Mycoplasma – Archaeobacteria
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