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Types of Bacteria based on nutrition

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- Phototrophs: derive energy from sunlight
Chemotrophs: derive energy from chemical oxidation
Autotrophs: can synthesize all organic compounds: Utilize atmospheric Co2 and N2
Heterotrophs: depends on preformed organic compounds: cannot utilize Co2 as sole source of carbon
Organotrophs: requires organic sources of hydrogen donor
Lithotrophs: use inorganic sources of hydrogen (ammonia, hydrogen sulphide)
Vast majority of medically important organisms: chemo-organotrophs

Physical conditions required for growth

  1. Obligate aerobes: require oxygen (~20%) Pseudomonas spp., Nocardia, Brucella, Bordetella, M.tb
  2. Obligate anaerobes: require complete absence of O2 ; B. fragilis, Clostridium sp., Pepto streptococci
  3. Facultative anaerobe: grow better in oxygen but still able to grow in its absence; E.coli, S.aureus
  4. Aerotolerant anaerobe: anaerobic, but tolerates exposure to oxygen; C.perfringens
  5. Microaerophilic organism: requires or prefers reduce oxygen levels (~5%); Campylobacter spp., Helicobacter spp., Leptospira, Borrelia
  6. Capnophilic : requires or prefers increased carbon dioxide levels ;  Brucella, Pneumococcus, Neisseria spp.
  7. Psychrophile : grows best at low temperature (<10oC); Flavobacterium spp.
  8. Thermophile : grows best at high temperature (>60oC);
  9. Bacillus stearothermophilus, Thermus acquaticus.
  10. Mesophile : grows best b/w 20 - 40oC; most bacterial pathogens

Which of the following is a Microaerophilic bacteria:- (AIIMS May 09)
A) Campylobacter     
B) Vibrio Cholera            
C) Pseudomonas      
D) Bacteroides


Ans. A.

 A. Typing of bacteria
  1. A population of bacteria presumed to descend from a single bacterium as found in a natural habitat, in primary cultures from the habitat and in subcultures from the primary cultures, is called strain
  2. Each primary culture from a natural source is called an isolate
  3. Culture of typhoid bacilli isolated from 10 different patients should be regarded as 10 different isolates unless epidemiological evidence indicates that the patient have been infected from a common source with the same strain
  4. Strains with demonstrable ancestral lineage have been termed as clones (this term should be used with caution)

1.     Phenotypic methods of typing


Differences in biochemical reaction which are not universally + or – with in a species                       eg. classical, & eltor Vibrio cholera, H. influenzae, C. diphtheriae


surface structures of bacteria (LPS, omp, flagella, capsule etc. ) are antigenic and antibodies raised against them can be used to group isolates eg S. pneumoniae, Shigella spp.

Phage typing

difference in susceptibility to bacteriophage: S. aureus, S. typhi, V. cholerae.

Bacteriocin Typing

Difference in production/susceptibility to bacteriocins eg Proteus spp., S. sonnei

Protein Typing

Differences in protein composition following disruption of cells & electrophoresis in gel

Anti biogram

Differences in susceptibility to a set of antibiotics


2.  Genotypic methods of typing-


a.  Restriction endonuclease typing :

  1. Chromosomal
  2. Plasmid
  3. Frequent cutter endonuclease
  4. Rare cutter endonuclease (PFGE)  

b.  Gene probe typing :

  1. Cloned specific
  2. Random/universal sequences
  3. Detect restriction site heterogeneity in the target DNA
  4. Detect variation in rDNA gene loci : ribotyping
  5. Some genera like Mycoplasma cannot be typed as they have single copy of rRNA operon

c.  PCR typing

  1. Specific DNA sequences amplified
  2. Specific primers
  3. Random primers
  4. Random amplified polymorphic DNA typing
  5. Arbitrarily primed PCR

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