Download Microbiology - Laboratory Procedures

Microbiology
Laboratory Procedures
 Microbiology
= the study of microbes (bacteria,
fungi, and viruses)
Bacteriology = study of bacteria
Virology = study of viruses
Mycology = study of fungi
*Most microbes found on or in the body are nonpathogenic, however these organisms can
produce significant disease if located elsewhere.
Bacteria are:
a. Prokaryotic – unicellular organism lacking
a true nucleus & nuclear membrane, having
genetic material composed of a single
molecule of DNA.
b. microscopic organisms
c. reproduce using binary fission
d. very complex despite their small size.
http://learn.genetics.utah.edu/content/begin/cells/scale/
Most bacteria come in one of
three basic shapes: coccus,
rod or bacillus, and spiral
I. The coccus
The cocci are spherical or oval
bacteria having one of several distinct
arrangements based on their planes of
division.
diplococcus: cocci arranged in
pairs
streptococcus: cocci
arranged in chains
a tetrad: cocci arranged in
squares of 4
sarcina: cocci in arranged cubes of 8
staphylococcus: cocci arranged in
irregular, often grape-like clusters
II. The rod or bacillus
Bacilli are rod-shaped bacteria. Bacilli
all divide in one plane producing a
bacillus, streptobacillus, or
coccobacillus arrangement.
bacillus: single bacilli
streptobacillus: bacilli arranged in
chains
III. The spiral
Spirals come in one of three forms,
a vibrio, a spirillum, or a spirochete.
vibrio: a curved or comma-shaped rod
spirillum: a thick, rigid spiral
spirochete: a thin, flexible spiral
Borrelia
Leptospira interrogans
IV: Spores
A few bacteria form intracellular refractile
bodies called endospores or spores.
Clostridium are spore formers and are
resistant to heat, desiccation, chemicals,
and radiation.
Clostridium
 The
primary purpose of
microbiology examinations is to
identify bacterial pathogens.
How do we do this ???
-Size
-Shape
-Arrangement
-Cemical Activity
Bacterial Cultures
 The
primary purpose of microbiology is to
identify bacterial pathogens.
 Culture
Media = any material, solid, or
liquid, that can support the growth of
microorganisms.
Types of Culture Media
 Typically
prepared agar plates
 Agar
= dried sea algae
 Agar
plates = sea algae & gelatin
Types of Culture Media
Enriched Media
-Most used in veterinary practice
-Created to meet the requirements of many
bacteria
-Basic nutrient media w/ extra nutrients
added (egg, blood, serum)
Ex. blood agar, chocolate agar
Types of Culture Media
Selective Media
-Contain antibacterial substances which
inhibit certain bacterial growth.
-Allows the microbiologist to facilitate
isolation of a particular genus of bacteria.
Ex. MacConkey agar (contains crystal violet
which supresses gram-positive bacteria)
Bacterial Growth
Specimen Collection
 Aspiration,
scraping
 Collection
swabbing (culturette) &
techniques depend on type of
lesion, location on the body& specific test
desired
Specimen Collection
A
complete patient history is vital!!
 Specimen
collected aseptically & ASAP
after the onset of symptoms.
 Label
 Take
specimen container
your time!!
Grow Your Colonies 
 Gram
Stain For ID
Stain –used to categorize bacteria
as either gram + or gram – on the basis of
cell wall structure.
 Kits
contain crystal violet, Gram’s iodine, a
decolorizer, and safranin.
 Purple
bacteria = gram +
 Red bacteria = gram -
Mycology
 Fungal
study
 Most
common fungus studied in
veterinary medicine = dermatophytes /
ringworm
 Ringworm
invades, skin, nails & hair
 Most
common types of ringworm seen in
veterinary medicine :
-Microsporum canis: causes symptoms in
dogs, cats, humans & sometimes other
species.
-Microsporum gypseum : causes symptoms
in dogs, horses, and sometimes other
species.
Dermatophyte Testing

DTM (standard dermatophyte test medium)

Turns red in the presence of dermatophytes

The presence of the red color is not enough
for diagnosis b/c bacterial contaminants and
nonpathogenic fungi can cause a positive
color rxn.
Woods Lamp Testing
 Microsporum
may fluoresce under a black
light ( Woods Lamp)
 Approx
 No
60% of Canis will fluoresce.
fluorescence on Woods lamp DOES
NOT RULE OUT ringworm infection.
Positive Woods Lamp Exam
Malassezia (Yeast)
 Commonly
found on the skin / ears of
dogs and cats.