Fluorescent viability stain for showing live
(green) and dead (red) bacteria
• Pigment production:
o Endopigment (restricted to the colonies):
• Golden yellow with
• White with Staph. epidermidis.
o Exopigment (the color diffuses in the
• Green exopigment with
Hemolysis on blood agar:
o Complete (beta) hemolysis:
• Staphylococcus aureus and
o Partial (alpha) hemolysis:
• Streptococcus viridans and
o No (gamma) hemolysis:
Effect on lactose of MacConkey’s agar:
o Lactose fermenters:
• Appear as rose pink colonies.
• Example: E. coli & klebsiella.
o Non Lactose fermenters:
• Appear as pale colonies.
• Example: salmonella & shigella.
1) Sugar fermentation
2) Indol test
3) Urease test
4) Oxidase test
5) Catalase test
6) Coagulase test
7) DNAse test
8) Gelatinase test
- Catalase test:
• Is used to differentiate between staphylococci(catalase +ve)
and streptococci(catalase –ve).
2 H2O2 2 H2O + O2
– Smear a colony of the organism to a slide
– Drop H2O2 onto smear
is used to differentiate Staphylococcus aureus from
• All Enterobacteriaceae are oxidase-negative.
• This test is used to differentiate enterobacteriaceae
from Pseudomonas which is oxidase positive.
• to determine whether a bacterium is motile.
• Non-motile organisms which lack flagella, are usually going to
form a single line of growth that does not spread into the
surrounding area. While a motile bacterium will grow and
make a hazy zone around the stab line.
Automated bacterial identification systems:
- Examples: Vitek system
- These systems identify the organism and its antibiotic
sensitivity by detecting color changes or turbidity in special
plastic cards inoculated with the organism.
- Such cards are composed of tiny wells that contain substrates
for detection of biochemical reactions and antibiotic sensitivity.
- Once the card has been inoculated and placed in the
instrument, it will automatically perform all readings.
- Results are available within 4-6 hours.
• Antigen detection
– e.g. latex agglutination
• Antibody detection
– e. g. agglutination tests, complement fixation tests, indirect
• The use of laboratory animals (mice, guinea pigs, rabbits) is now
limited due to the advancement in medical microbiological
Guinea pig Mouse
But they could be used :
1. For growing the organisms that do not grow
on culture such as lepra bacilli.
2. To determine the virulence factor of an
organism. For example if injection of diphtheria
in a guinea pig caused its death, this means
that the organism is toxigenic.
• Bacteriophages are viruses which infect the bacterial
cells and cause their lysis.
• Different types of a certain bacteria are lysed by
different phage groups.
• If a phage is added to a plate inoculated with
susceptible bacteria, a zone of lysis will appear around
the phage drop.
Nucleic acid probes:
The probe consists of sequence of single stranded DNA or RNA
that forms a covalently bonded hybrid with the specific
complementary strand of the nucleic acid of the organism.
The probe is labeled either to radioactive substance as iodine 131