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Exam 1 > Micro Lab Diagnosis > Flashcards

Micro Lab Diagnosis Flashcards

1
Q

what part of gram-negative cell walls contribute to shock

A

lipopolysaccharides, particularly lipid A, which is an endotoxin

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2
Q

stain for mycobacteria

A

acid-fast, gram staining won’t work because of waxy lipid layer

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3
Q

stain for spirochetes

A

wright-giemsa, gram staining won’t work, even though they’re gram negative, because they’re too thin to resolve

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4
Q

culture dependent diagnostic tools

A

microscopy and tissue cultures from a sample off where you think the organism resides

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5
Q

culture independent diagnostic tools

A

serology and molecular biology (nucleic acid detection, viruses)

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6
Q

what are all the places you can collect specimen from

A

sputum, urine, feces, tissue lesion (center and border), pus, blood culture, abscess fluid, CSF, vaginal discharge

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7
Q

what are the tools with which you can collect specimen

A

blood culture and swabs

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8
Q

Normal flora of the upper respiratory tract

A

staphylococcus, streptococcus pneumonia and viridans, haemophilus, and anaerobes

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9
Q

normal flora of the skin

A

staphylococcus, coryneform bacteria or diptheroids, and propionibacterium

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10
Q

normal flora of the GI tract

A

anaerobes, enterococcus, enterobacteriacaea (e coli and klebsiella), streptococcus anginosus, lactobacillus, and candida

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11
Q

normal flora of the GU tract

A

lactobacillus and streptococcus agalactiae

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12
Q

neutrophils on slides look like

A

multi-lobed nuclei

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13
Q

epithelial cells in sputum

A

rejected because heavily contaminated with saliva

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14
Q

selectivity of MacConkey

A

inhibits growth of gram positive organisms, grows gram negative

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15
Q

differentiation of MacConkey

A

distinguishes between those with the ability to ferment lactose (pink), and this without (colorless)

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16
Q

the keys to a good blood culture

A

draw before antibiotics, volume, two bottles of 2 draws for 4 bottles total

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17
Q

alpha hemolytic will appear ___ on blood agar

A

green

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18
Q

beta hemolytic will appear ___ on blood agar

A

cleared

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19
Q

gamma hemolytic will appear ___ on blood agar

A

white/colorless, no clearing

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20
Q

if you see yellow colonies on blood agar, think

A

staphylococcus aureus

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21
Q

if you see red/pink colonies on blood agar, think

A

serratia marcescens

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22
Q

if you see blue/green metallic colonies on blood agar, think

A

pseudomonas aeruginosa

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23
Q

if you see “feet” or projections on a colony, think

A

yeast infection, or candida albicans

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24
Q

if you see mucus on a colony, think

A

klebsiella pneumoniae

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25
if you see swarming off the streak link on blood agar, think
proteus vulgaris
26
know a species is gram positive, what's the next think you want to know
cocci or bacilli?
27
know your species is a gram positive cocci, what's the next question?
clusters or diplococci/chains?
28
clusters of gram - cocci indicate
staphylococcus
29
diplococci or chains of gram - cocci indicate
streptococci
30
know you have a streptococci, what's the next step?
aerobic or anaerobic
31
anaerobic streptococci need to know
peptostreptococcus
32
know you have an aerobic streptococci, what's the next question?
what type of hemolysis does it undergo
33
alpha hemolytic streptococci
S. pneumonia, mutans, and viridans
34
beta hemolytic streptococci
S. pyogenes (group A strep, GAS), and agalactiae (group B strep, GBS)
35
gamma hemolytic streptococci
enterococcus
36
know you have a gram negative isolate, whats the next question?
bacillus/coccobacillus or cocci?
37
gram negative cocci to know
neisseria and moraxella
38
know you have gram negative bacili/coccobacilli, what's the next question?
does it grow on macconkey agar
39
gram negative isolate grows on macconkey agar, what's the next question?
does it ferment lactose (pink) or not (colorless)
40
lactose-fermenting macconkey positive gram negative organisms
Escherichia, klebsiella, or enterobacter
41
non lactose-fermenting maconkey positive gram negative organism
does it ferment glucose
42
gram negatives that ferment glucose
are also lactose non-fermenters, and grow on maconkey agar, and include salmonella, shigella, proteus, serratia
43
gram negatives that don't ferment glucose
also don't ferment lactose, grow on maconkey agar, and include pseudomonas burkholderia and acinetobacter
44
if your gram negative isolate doesn't grow on maconkey
test its oxygen tolerance
45
oxygen tolerant gram negative isolates
campylobacter, helicobacter, vibrio
46
oxygen intolerant gram negative isolates
bacteroides, fusobacterium, prevotella, porphyromonas
47
PCR-based susceptibility testing
detects genes associated with drug resistence
48
mecA gene
associated with methicillin resistance in staph aureus
49
vanA/B genes
associated with vancomycin resistance in enterococcus faecium
50
bla KPC gene
associated with carbapenem resistance (beta lactamase, bla) in Klebsiella pneumonia carbapenemase (KPC)
51
pros and cons of PCR susceptibility testing
fast, sensitive, specific, but expensive and only single target, when resistance may be caused by a combination of many mutations
52
MIC
minimal inhibitory concentration, minimum concentration of a drug that will inhibit the growth of an organism
53
culture-dependent phenotypic susceptibility testing
agar dilution, broth microdilution, disk diffusion, strip test
54
microbroth dilution
broth and increasing concentration of antibiotic in well plate, lowest concentration without bacterial growth is the MIC
55
strip testing (Etest)
paper/plastic strip with increasing concentration of a drug, placed in center of a lawn of isolate on a plate, MIC is point of growth inhibition
56
disk diffusion test
paper disk with single concentration of antibiotic placed on bacterial lawn on agar, measure zone of inhibition, does not give a MIC
57
PCR test
extract nucleic acid from sample, denature, anneal primers, elongate, repeat, fluorescently detect DNA
58
NAAT test
single target, multiplex, or broad range amplification and sequencing/detecting
59
single target NAAT
uses amplification and detection to identify single organism or resistance marker; most sensitive
60
multiplex NAAT
uses amplification and detection to identify a pathogen from a panel of common syndromic options i.e. patient has respiratory symptoms, PCR compared to respiratory pathogen pane, less sensitive than single
61
broad range PCR
targets 16S rRNA on any bacterial pathogen, can only prove that you have an infection, last resort, done when all other tests are negative, least sensitive
62
MALDI-TOF MS
isolate spotted onto metal plate, coated with protective matrix, laser vaporizes bacteria, travel up to analyzer, mass spec profile compared to database
63
current use of MALDI TOF MS
identification of cultured bacteria
64
future use of MADLI TOF MS
susceptibility testing, strain typing, direct from sample detection
65
Serology: antigen detection
administer a lab generated antibody to detect antigen in specimen, which can be urine, serum, sputum, stool, CSF
66
Serology: antibody detection
administer lab generated antigen to detect IgG or IgM, or total antigen-specific patient antibodies, only works for blood serum
67
IgM
present in acute infection, detectable within 7 days of infection, wanes after 2-3 months
68
IgG
present in chronic disease and immunity, detectable within 14 days, detectable for entire life, indicative of either current, chronic, or past infection
69
agglutination
antibody or antigen fixed to latex beads, specimen added, visible clumping is a positive result for the antibody/antigen in question
70
lateral flow immunoassay
e.g. pregnancy test, antibodies on conjugate pad, antigen in sample wicked along pad, accumulation of antigen antibody complex detectable s visible line
71
ELISA sensitive or specific?
high sensitivity, low specificity, high negative predictive value, so all positive results must be confirmed with a secondary assay, which, if negative, indicates negative result
72
ELISA method
antibody or antigen immobilized in well, patient sample added, reporter antibodies/antigen added, substrate for colometric change added, read
73
immunoblot aka western blot
antigens printed/transferred onto membrane, incubated with patient serum, bound antibodies detected with secondary antibody and color detection substrate
74
immunodiffusion
antigen put in center well of gel matrix patient samples put on periphery, samples diffuse outward during incubation, precipitation complex visible in gel
75
when to use as serology test
determining vaccine status, infection with culture-independent organisms, infection with organism cleared too quickly, screening for HIV/HCV/HBV
76
why would you get a false positive with a serology test
heterophile antibodies, rheumatoid factor, closely related antigens cross react (especially with IgM), and maternal transfer aka passive immunity (especially of IgGs)
77
why would you get a false negative with a serology test
patient is immunocompromised or the test is administered either too soon or too late
78
factors to consider when ordering a lab
cost-benefit ratio, time to result, do I know how to interpret, will the result change anything
79
role of bacterial cell wall
structural rigidity, shape, osmoregulation, defense
80
drugs that target bacterial cell walls
penicillins, monobactams, carbapenems, cephalosporins, vancomydin
81
how do bacteria develop resistance to cell wall attacking drugs
enzymatic inactivation, modification of target, porin mutations to reduce permeability, and efflux pumps
82
components of peptidoglycan layer
NAG and NAM, NAM tetrapeptide side chain, peptide inter bridge cross-linker
83
steps of building the peptidoglycan layer
peptidoglycan polymers exported from cell, transglycosylase attaches them, penicillin binding protein creates transpeptidase crosslinks
84
how do beta lactam drugs work?
structurally mimic NAM, bind the enzymatic domain of PBP, preventing peptide crosslinking, leading to weak peptidoglycan wall
85
beta lactamase
which cleaves and degrades the beta lactic ring at the N-C=O bond e.g. penicillinase, secreted extracellularly in gram positives and into periplasmic space in gram negatives
86
mechanisms of resistance to beta lactams
beta lactamase synthesis, modification of target, porin mutations, efflux pumps
87
modification of target in staph aureus
via mecA gene that encodes the PBP2a protein, low affinity for penicillin after it's been modified, develops resistance
88
ways to check for resistant mega gene
targeted molecular testing for mecA, antigen testing for PBP2a, and phenotypic testing for oxacillin resistance
89
what are them most likely causes of culture negative endocarditis
recent antimicrobial therapy, fastidious organism
90
opportunities to narrow down your broad spectrum antibiotics
3 hours after presentation, direct gram stain reported, take rapid AST, de-escalate 1-2 days after presentation, organism growth and ID reported, take another rapid AST, de-escalate antibiotics if differential further narrowed finally, when AST report comes back after 2-3 days, narrow antibiotics based on organism resistance

Exam 1 (7 decks)

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