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PHAR 541
microbial identification
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Created by
Moira Lucero
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Cards (16)
normal flora
beneficial effects
competition for resources w/ invading pathogens
aid in digestion
production of antimicrobial substances
harmful effects
can overgrow and become pathogenic
immunocompromised pts, eradication of harmless competitors (like yeast)
can cause infection when displaced from their normal site in the body to another
called
opportunistic
infections
normally sterile body sites
blood
CSF
(cerebral spinal fluid)
pericardial
fluid
synovial
fluid/bone
pleural
fluid
peritoneal
fluid
microorgansims identified from normally sterile sites are usually treated
lack of growth of an organism does not always indicate
absence
of an infection
growth of an organisms does not always indicate
presence
of an infection
as a result,
cultures
ALWAYS need to be clinically correlated to pt
presentation
, and when available,
imaging
studies
when growth does NOT representation true infection
contamination
of a sample w/ bacteria
contamination of
blood
draws w/
low
virulence skin
bacteria
(CoNS, Corynebacterium spp.)
colonization
w/ a microorganisms
MRSA
and/or
VRE
+ pts
typically put into
isolation
when lack of growth does not rule out infection
antibiotics
given prior to culture being drawn
OR
clinical signs/symptoms and/or imaging indicate
infection
microbial identification
direct
visualization
of the microogranism
gram stain
acid fast stain, etc.
culture
growing bacteria in enriched media in vitro
media can be non-selective or selective
examples of common single enzymes and metabolic tests
coagulase
test
distinguishes btwn coagulase
negative
staphylococci
(ie. S. epidermidis) and coagulase
positive
staphylococci
(S. aureus)
lactose
fermentation
lactose fermenters (E. coli, Enterobacter, etc) vs. non-fermenters (Pseudomonas, etc)
automated systems
computer sensors utilize
fluorescent
technology to monitor for presence of growth -->
microbial
detection
automated antimicrobial
susceptibility
tests
commercial examples: Vitek, Microscan, Phoenix
matrix-assisted laser desorption/ionization (MALDI) time of flight (TOF) mass spectrometry
accurate
and
fast
bacterial identification --> compares "
protein
fingerprint
" of the bacteria to a database
no
susceptibility
information
polymerase chain reaction (PCR)
fast
turnaround time (faster than cultures)
qualitative
detection (pos or neg) --> no susceptibilities
high
sensitivity
/
specificity
examples:
most gram+ and gram- bacteria
antimicrobial resistance genes
mycobacteria
STDs
viruses
serology
detection and quantification of
antibodies
or
antigens
directed against a specific pathogen or its components --> no actual detection of microorganism
advantages
microorganisms that are hard to
grow
in lab (eg, Legionella, Treponema) or difficult to
obtain
specimen fr. site of infection (eg, H. pylori)
used to confirm
immunity
to many
vaccines
(eg, Hep B)
drawbacks:
may not differentiate btwn
active
vs.
past
infection (eg, Treponema)
antibodies usually take a few
months
to develop and will not be present during
acute
infection (ie, HIV)
no susceptibilities
culture
can it identify a microbe?
yes
turnaround time to ID -
a little fast
(
+
)
susceptibilities?
yes
automated systems
can it identify a microbe?
yes
turnaround time to ID -
fast
(
++
)
susceptibilities?
yes
MALDI-TOF
can it identify a microbe?
yes
turnaround time to ID -
very fast
(
+++
)
susceptibilities?
no
PCR
can it identify a microbe?
yes
turnaround time to ID -
very, very fast
(
++++
)
susceptibilities?
no
serology
can it identify a microbe?
yes
turnaround time to ID -
fast
(
+
+
)
susceptibilities?
no