Monday, September 23 Group A
Wednesday, September 25 Group B
Introduction to Pure Culture Techniques, C. Comparative morphology of the microbial cell.
In this exercise prepared slides were provided to reintroduce the use of the oil immersion
lens microscope and to help you gain some familiarity with the
staining properties, physical arrangement and morphology of clinical
microorganisms. One advantage of presenting eight separate
organisms on one slide is that you get to see their properties
under the same optical conditions and with the same magnification.
Of course the microscopes differ, the quality of those smears can vary from
slide to slide, and the stains tend to fade over time. We invite you to
examine the images. Please let me know if you find
them useful: John.Loper@UC.Edu
Gram-positive cocci that can
divide in any plane and tend to be arranged in grape-like clusters,
(so there will be some cells out of focus in any plane) (staph=
bunch of grapes, cell morphology, aureus= gold, colony pigmentation).
Compare to Streptococcus pyogenes (group A
hemolytic strep). For both of these organisms, older cells
lose the cell integrity necessary to retain the crystal violet,
so some cells may appear Gram-negative in even newly prepared
slides. Note also that single cells and pairs of cells may be
seen for both organisms, and that staphyococci can form short
chains - the microbiologist must look at several fields and may
need additional information to avoid making a misidentification.
(Group A Hemolytic Strep)
Gram-positive cocci, small and ovoid in shape usually arranged in chains with the oval cells
touching. May vary from a continuous chain to a single pair.(strepto = twisted string, pyo = pus).
(Compare to Staphylococcus aureus).
Gram-positive, large rod with squarish ends.
This organism grows as a typical budding yeast with round or oval cells.
Under certain growing conditions they form pseudohyphae or hyphae.
Yeast stain gram-positive, although the stain has faded in some of the
laboratory slides.
Organisms of the Enterobacteriaceae and the Pseudomonas
of even a single species can vary enough from culture to culture,
in size, specific shape and chain formation, that it is generally
impossible to propose an identification by microscopic examination.
Short Gram-negative rods with rounded ends that make many of them appear
as round or coccobacillilary foms. With standard microscopy they appear as the picture on the left.
In fresh clinical specimens
H. influenza often forms
long chains, as is shown in the enlarged picture on a yellow
background.
Return to Medical Microbiology Homepage