[Microbiology] Use of Colonial Morphology for the Presumptive Identification of Microorganisms

Use of Colonial Morphology for the Presumptive Identification of Microorganisms, Haemophilus, atlas in medical, atlas in microbiology, tuyenlab.net,

Fig 1.  Clockwise from the top: chocolate agar (CHOC),
blood agar (BAP), MacConkey agar (MAC). The large colonies
growing on all three plates are gram-negative rods
(enterics). These gram-negative rods grow larger, gray, and
mucoid on BAP and CHOC. Notice the smaller grayish-brown
fastidious colonies of Haemophilus organisms growing on
CHOC (arrow), which are not growing on BAP or MAC.

Fig 2.  A, Example of lactose-fermenting gram-negative rods producing pink
colonies on MacConkey agar (MAC). B, Example of nonlactose-fermenting gram-negative
rods producing colorless colonies on MAC.

Fig 3.  A, Lactose-fermenting Escherichia/Citrobacter-like organisms growing on
MacConkey agar (MAC). Notice the dry appearance of the colony and the pink
precipitate of bile salts extending beyond the periphery of the colonies. B, Close-up of
dry, flat Escherichia/Citrobacter-like lactose fermenters growing on MAC. Compare with
Figure 4, B.

Fig 4.  A, Klebsiella/Enterobacter-like lactose fermenters growing on MacConkey
agar (MAC). Notice the pink, heaped, mucoid appearance. B, Close-up of Klebsiella/
Enterobacter-like colonies on MAC. Notice the mucoid, heaped appearance and the
slightly cream-colored center after 48 hours’ growth.

 Fig 5. The use of transillumination to determine
whether the colonies are hemolytic. The technique can be
used for MacConkey agar also to see slight color differences
in nonlactose fermenters.

Fig 6.  Chocolate agar (CHOC) does not display true
hemolysis because the red cells in the medium have already
been lysed. Bacteria that are hemolytic on blood agar plate
usually are green around the colony on CHOC.

Fig 7.  Left, Blood agar plate (BAP): small white
colonies are gram-positive cocci; right, BAP: large, gray,
mucoid colonies are enteric gram-negative rods.

Fig 8.  Illustration of form or margin to describe
colonial morphology.

Fig 9.  Swarming colonies of Proteus spp. The organism
was inoculated in the middle of the blood agar plate
(arrow).

Fig 10. “Diphtheroid” colonies with rough edges, dry
appearance, and umbonate center growing on blood agar.

Fig 11.  Illustration of elevations to describe colonial
morphology.

Fig 12. Density.

Fig 13.  Example of white colonies of coagulasenegative staphylococci on blood agar.

Fig 14.  Example of the yellow colonies characteristic
of certain nonpathogenic species of Neisseria organisms on
blood agar.

Fig 15.  A, Pseudomonas aeruginosa illustrating the
metallic sheen and green pigmentation of colonies on blood
agar plate (BAP). B, Not all strains of the same organism
have the same colonial appearance. This is a mucoid strain
of P. aeruginosa on BAP.

Fig 16.  Brick-red pigment of Serratia marcescens,
which is evident on the MacConkey agar (right). This
brick-red pigment should not be confused with lactose
fermentation. The pigment is slightly visible on chocolate
agar (left). Additional incubation at room temperature
enhances the brick-red pigmentation.

Fig 17.  Large, rough, greenish-appearing, hemolytic
colonies of Bacillus cereus on blood agar plate.

Fig 18.  Small, “fuzzy-edged,” umbonate centerappearing colony of Eikenella corrodens on chocolate agar. This organism has the tendency to “pit” the agar.

Fig 19.  A, “Vine” or “streamer” effect exhibited by
certain species of streptococci when growing in
thioglycollate. Notice that the effect is more prevalent
toward the bottom of the tube. B, Example of the “puffed
balls” effect exhibited by certain streptococcal species when
growing in thioglycollate.

Fig 20.  Turbidity produced by enterics when growing
in thioglycollate. Notice the gas bubbles at the surface of
and in the middle of the medium (arrow).

Fig 21.  Production of “scum” by yeast at the surface
of the thioglycollate.

Fig 22.  Illustration of Pseudomonas organisms
producing surface “scum” at the sides of the thioglycollate.
Occasionally Pseudomonas aeruginosa produces a diffusible
green pigment and a metallic sheen at the surface.

Fig 23.  Yeast growing in the microaerophilic area of
thioglycollate.

Fig 24. A, Differentiation of Streptococcus pneumoniae and α-hemolytic viridans
streptococci by colonial morphology. B, S. pneumoniae growing on blood agar plate
(BAP). Notice the strong zone of α-hemolysis, umbilicate center, and wet (mucoid)
appearance of the colonies. C, Enterococcus growing on BAP. It does not have an
umbilicate or umbonate center, but it is more heaped and gray-appearing than S.
pneumoniae. Enterococci have larger colonies, and a smooth, darker margin, unlike
many strains of α-hemolytic streptococci. The green color on the plate is not hemolysis
but is a characteristic of growth.

Fig 25.  A, Differentiation of Streptococcus pyogenes and Streptococcus agalactiae
by colonial morphology. B, Pinpoint colony of S. pyogenes exhibiting large, deep zone of
β-hemolysis on blood agar plate (BAP). C, Colonies of S. agalactiae growing on BAP. This
organism produces a larger colony and a smaller, more diffuse zone of hemolysis than
S. pyogenes. Notice that the hemolysis is not evident in this photograph. Compare with
B. D, Colonies of S. agalactiae growing on BAP. Through the use of transillumination,
the hemolytic pattern is now evident; hemolysis is diffuse, and it remains close to
the periphery of the colony. The same colonial morphology is produced by Listeria
monocytogenes, a gram-positive rod. Compare with B. Arrow: S. pyogenes produces two
hemolysins; one is oxygen stabile (S), and the other is oxygen labile (O). Stabbing the
medium with an inoculating loop carries the organism into areas where anaerobic
conditions are more prevalent, allowing the enhanced hemolysin (O) to be seen.

Fig 26.  A, Differentiation between staphylococci and Candida albicans (a yeast)
by colonial morphology. B, Large, white, convex, shiny, moist, β-hemolytic colonies of
Staphylococcus aureus growing on blood agar plate (BAP). C, “Heaped” or convex,
white, dull appearance and butyrous texture of Candida albicans on BAP. Notice the tiny
projections or “feet” at the edge of the colonies.

This is a part of the book : Textbook of Diagnostic Microbiology 4th edition 2011 of authors: Connie R. Mahon, Donald C. Lehman and George Manuselis. If you want to view the full content of the book and support author. Please buy it here: http://amzn.to/2ctxo02