Microbiology Flashcards
what is microbiology used for?
useful but expensive and time-consuming diagnostic tool
identifying organisms can determine treatment
what do facilities usually do with samples for microbiology diagostics?
some send out all samples and others will plate the organisms and only send out if there is growth
are most microbes pathogenic or non-pathogenic?
non-pathogenic and make up normal flora
can normal flora be opportunistic?
yes
microbes from smallest to largest
prions, viruses, bacteria
prions
proteinaceous infectious agents
abnormally folded proteins
causes transmissible spongiform encephalopathies
doesn’t trigger immune response
viruses
obligate intracellular organisms = have to go into a cell to live
DNA or RNA surrounded by a protein coat
requires a host to replicate
types of viruses
bacteriophage, adenovirus, human immunodeficiency virus
bacteriology
study of bacteria
bacteria
prokaryotes= DNA is free in the cytoplasm
reproduce by binary fission= cell division
life cycle of bacteria
lag phase: adjustment
log phase: exponential growth (division)
stationary phase: cells stop dividing, growth is limited
death phase: cell loss
mycology
study of fungi
fungi
eukaryotes: DNA in the nucleus, organelles in the cytoplasm and membrane
reproduce by binary fission: budding (fruiting body is the spore)
protozoa
unicellular eukaryotes
binary fission to reproduce
how are protozoa classified?
by locomotion
amoeboids: pseudopodia
ciliates: cilia
sporozoa: non-motile
flagellates: flagella
bacteria growth requirements
pH: 7
oxygen or no oxygen (depends on type)
growth requirement factors affect which media we choose
oxygen tension
concentration of oxygen at a specific pressure
mesophilic bacteria temperature requirements
moderate temperature
20-40 C
psychrophile bacteria temperature requirements
low temperature
thermophile bacteria temperature requirements
high temperature
fastidious bacteria growth requirements
complex nutritional needs
oxygen requirements
aerobes: require O2
anaerobes: require absence of O2 (will die or have inhibited growth in O2 presence)
facultative
describes a bacteria that can grow under a variety of conditions
can survive without O2 but may have inhibited growth or grow with O2
microaerophilic
describes bacteria that prefer reduced O2 tension
O2 tension means it needs O2 at a lower concentration than is present in the atmosphere with enhanced CO2
capnophilic
describes bacteria that requires high levels of CO2
culture media
can be solid or liquid form
supports the growth of microorganisms
come as plates, tubes, or slants
can be general purpose, enriched, selective, or differential
Mueller-Hinton (MH) media
general purpose
used for antibiotic sensitivity testing
Kirby-Bauer antibiotic susceptibility testing
culture and sensitivity test
agar diffusion test used to determine which antimicrobial to use
done by performing a pure culture on MH media
antibiotic impregnated discs placed on top of streaks
Kirby-Bauer antibiotic susceptibility testing: plating process
- pure culture of bacteria in agar
- bacteria grown overnight (18-24 hours) with a thin wafer that contains a known amount of a relevant antibiotic
reading a Kirby-Bauer test
if the bacteria are susceptible to the particular antibiotic from the disc, there will be an area of clear media where the bacteria are not able to grow around the disc: known as zone of inhibition
what does a larger zone of inhibition indicate?
the bacteria are more sensitive to the antibiotic in that specific disc
considered to be sensitive to antibiotic
what does a smaller zone of inhibition indicate?
the bacteria is considered to be resistant to that antibiotic
what is the relationship between zone of inhibition and minimum inhibitory concentration (MIC)?
they are inversely related
minimum inhibitory concentration (MIC)
the amount of an antibiotic required to prevent bacterial growth in an overnight culture
the MIC graph is used in conjunction with the zone of inhibition to determine the best antibiotic to use
TSA agar plate
general purpose media
enriched media version: TSA with blood (blood agar plates: BAP)
enriched blood agar plates (BAP)
promotes growth of even fastidious bacteria
grows a wide range of pathogens especially those that are difficult to grow
differential blood agar plates (BAP)
detects and differentiates hemolytic bacteria particularly streptococcus spp.
hemolysis results on BAP
beta= complete hemolysis (creates a clear zone around the bacteria)
alpha= partial hemolysis or “greening” of agar (greenish or slimy discoloration around colony)
gamma= no hemolysis
thioglycolate broth
differential media in liquid form
grows most bacteria
used for anaerobes
macconkey media
contains crystal violet
selective: selects for gram negative bacteria by suppressing growth of gram positive bacteria
differential: differentiates into groups by their use of lactose, differentiates gram negative since they release acid that turn the agar red
Simmons citrate media
differential
uses citrate which makes it blue
bile escalin agar
differential media
enterococci: brown/black
brain-heart infusion broth
enriched media used for blood cultures and fastidious bacteria
differential: turns transparent if positive for strep
inoculation
goal is to isolate bacteria of interest with aseptic method
inoculation process
- streak the plate
- incubate (37 C for most pathogenic bacteria)
- evaluate
what characteristics do we look at while evaluating an agar plate?
colony form, elevation, margin, texture, and pigmentation
how often should agar plates be checked on throughout incubation?
check on the plates and report if growth is observed or not every 12-24 hours
sub-culturing
determine the number of different colony morphologies present and sub-culture each one to a separate plate so there are pure cultures available for analysis
streaking the agar plate
use 4 streaks in the 4 quadrants of the plate in order to get distinct isolated colonies of bacteria
hyphae
fungal filaments that are branching
they grow towards food sources and release digestive enzymes that break food up into small molecules
how do fungi reproduce?
via sexual and asexual spores
different fungi groups produce different spores
fungi can be differentiated on the basis of hyphae structure and spore presence
types of asexual spores
sporangiospores and conidia
conidia are exposed to the external environment at maturity but sporangiospores are enclosed from the external environment at maturity
example of a spore
molds which are dispersed in the wind
there is 1 type of sexual spore produced by molds
yeasts
candida (vaginal) and Malassezia (ears)
reproduce by budding
dermatophytes
cutaneous mycotic organisms
which dermatophytes cause ringworm?
Microsporum spp. and Trichophyton spp.
dermatophyte spores
conidia
types: macroconidia- large, multicellular conidium
microconidia- single cell, small conidium
why do we usually ID dermatophytes?
for fungal skin infections
which media is used for IDing dermatophytes?
Sabouraud media which has antifungal and antibacterial agents to retard contaminant growth
how can we tell if a DTM or Fungassay plate test is positive?
dermatophytes release alkaline metabolites which change pH indicator red so the media turns red if it is positive
how can dermatophytes be viewed under the microscope?
in KOH on a slide with a cover slip
use clear tape and Lactophenol blue stain
evaluate on 10x-40x
what are we looking for when viewing dermatophytes under the microscope?
look for hyphae and then macroconidia
may take up to 10 minutes to appear
when performing a DTM test what type of fur do we try to pluck?
fur that appears to be damaged or crusting
use Mackenzie toothbrush method: using a toothbrush to brush along the damaged fur to collect a sample
is using a Woods lamp reliable for ringworm?
no, it gives ambiguous results depending on the growth stage
histoplasma
found worldwide
transmission: humid nitrogenous soil (especially increased bird/bat droppings), inhaled spores
histoplasma CS
non-specific signs
usually see mild fever, depression, anorexia, weight loss
dogs can have respiratory/GI signs
blastomycosis
“Chicago dz”
soil fungus
seen in warm moist environments
dogs are most susceptible
causes pulmonary disease, skin lesions, eye infections that could to blindness
blastomycosis treatment
long term antifungal treatment
usually lasts up to 6 months
