Exam 2 Flashcards
In broth media how is bacterial growth indicated
turbidity
What does enrichment media do
has specific nutrients that are needed for fastidious pathogens.
What is XLD agar for
selective inhibits non enteric GN bacilli and inhibits GP
and differential for Shigella and Salmonella
phenol red indicator detects acidity from carb fermentations
What can be interpreted if there is growth on an XLD agar that is colorless?
and black? yellow?
colorless- no carb fermentation
black-H2S production
yellow-lactose fermenting
What does nutritive media do
has nutrients that support non fastidious organism growth
What does selective media do
has inhibitory agents that prevent the growth of an organism and allow another to grow
What does differential media do
has chemicals or substrates that allow bacteria to be IDed based on their metabolic capabilities
Differential for group D streptococci vs enterococci, and Enterobacteriaceaevs other enteric bacteria and can also be used for differentiation ofListeria monocytogenes
Bile esculin agar (BEA)
Cultivation of non-fastidious microorganisms, determination of hemolytic reactions
Blood agar (BA)
Bordetella pertussis(small, smooth, pearl-like colonies with a narrow zone of hemolysis); Bordetella parapertussis (brown colonies with a green-black coloration on the reverse side); Bordetella bronchiseptica(brown, medium sized colonies with a rough, pitted surface)
Bordet-Gengou agar
Cultivation of fastidious and nonfastidious organisms
Brain-heart infusion agar or broth
Contains azide to inhibit gram-negative bacteria, vancomycin to select for resistant gram-positive bacteria, and bile esculin to differentiate enterococci from other vancomycin-resistant bacteria that may grow
Bile esculin azide agar with vancomycin
Nutrient agar base with ferric citrate. Hydrolysis of esculin imparts a brown color to medium; sodium deoxycholate inhibits many bacteria.
Bile esculin agar (BEA
Enrichment forLegionellaspp.
Supports the growth ofFrancisellaandNocardiaspp.
Buffered charcoal–yeast extract agar (BCYE)
Selective forCampylobacterspp.
Campy-blood agar
Improved growth of fastidious, obligate, slow-growing anaerobes
CDCanaerobe 5% sheep blood agar
Selective medium for isolation ofCampylobacterspp.
Cefoperazone, vancomycin, amphotericin (CVA) medium
Selective forYersiniaspp.; may be useful for isolation ofAeromonasspp.
Cefsulodin-irgasan-novobiocin (CIN) agar
Cultivation of fastidious microorganisms such asHaemophilusspp.,Brucellaspp., and pathogenicNeisseriaspp.
Chocolate agar
Used in the identification ofAcinetobacter,extended-spectrum β-lactamase and carbapenemase producing organisms,E. coli, Listeria monocytogenes, Enterococcusspp.,Pseudomonas aeruginosa, Salmonellaspp., shiga toxin-producingE. coli, E. coliO157-H7, group B streptococcus,Vibriospp.,Yersinia enterocolitica,yeasts, MRSA, and a variety of other organisms
Chromogenic media
Selective isolation of gram-positive cocci
Columbia colistin-nalidixic acid (CNA) agar
Isolation ofCorynebacterium diphtheriae
Cystine-tellurite blood agar
Isolation and differentiation of lactose-fermenting and non–lactose-fermenting e.coli
Eosin methylene blue (EMB) agar (Levine)
Differential, selective medium for the isolation and differentiation ofSalmonellaandShigellaspp. from other GN enteric bacilli
Hektoen enteric (HE) agar XLD agar
Enriched, selective media for the isolation of cultivation ofStreptococcus agalactiae.
LIM broth
Isolation and growth ofCorynebacteriumspp.
Loeffler medium
Isolation and differentiation of lactose fermenting and non–lactose-fermenting enteric bacilli
MacConkey agar
For the selection and differentiation ofE. coliO157:H7 in stool specimens
MacConkey sorbitol agar
Selective differentiation of staphylococci
Mannitol salt agar
Selective isolation of aerobic gram-positive cocci and bacilli and anaerobic gram-positive cocci. This agar should not be used for observation of hemolytic reactions.
Phenylethyl alcohol (PEA) agar with or without blood
Enrichment and selective medium for isolation ofBordetella pertussisandBordetella parapertussis.
Regan Lowe
Enrichment and isolation ofSalmonellaspp.
Selenite broth
Selective forCampylobacterspp.
Skirrow agar
Selective forStreptococcus pyogenesandStreptococcus agalactiae
Streptococcal selective agar (SSA)
Selective forN. gonorrhoeaeandN. meningitidis.
Supports the growth ofFrancisellaandBrucellaspp.
Thayer-Martin agar (TM) (modified Thayer Martin [MTM])
Supports growth of anaerobes, aerobes, microaerophilic, and fastidious microorganisms
Thioglycollate broth
Selective and differential forVibrio choleraeandVibrio parahaemolyticus
Thiosulfate citrate–bile salts (TCBS) agar
Selection and enrichment forStreptococcus agalactiaein female genital specimens
Todd-Hewitt broth supplemented with antibiotics (LIM)
What interpretation of a TA broth:
generally diffuse evenly growth throughout the broth
Facultative anaerobe
What interpretation of a TA broth:
tend to grow toward the surface of the broth
strict aerobic bacter
Interpretation of TA broth:
grow at the bottom of the broth
strict anaerobic
What type of plate is MAC
selective- inhibits GPO and fungi with crystal violet dye
differential- pH indicator that shows lactose fermentation
Explain why salmonella turns black on its agar
they do not ferment any carbs but they do produce H2S causing the black color
What type of media is HE agar
Selective-inhibits growth of nonpathogenic GNR
selects for salmonella and shigella
Differential-non enteric pathogens show as orange, fermentation causes blue, H2S causes black
What kind of agar is EMB
selective- inhibits GP and allows GN
differential-green metallic color for E.coli
dark purple or black for lactose fermentation
Colistin disrupts the cell membranes of GN organisms, and nalidixic aid blocks DNA replication in susceptible organisms
Columbia colistin-nalidixic acid (CNA)
What kind of media is blood agar
nutritional- blood for hemolytic
differential- beta-hemolysis, partial lysis alpha, nonhemolytic- gamma
What is a catalase test
Testing for catalase production, release of water and oxygen causes bubbles +
no bubbles -
What is an oxidase test
a drop of tetramethyl-p-phenylenediamine dihydrochloride to a colony
positive- purple
negative- no color change
tests for the presence of oxidase
What is a coagulase test
Used to distinguish staph aureus from coagulase negative staph
rabbit plasma, positive if clumping or a clot occurs
What is an indole test
looking for bacteria that have enzyme tryptophanase which can degrade tryptophan into indole
positive- pink to red
What is PYR testing
looking for enzyme enzyme PYR
ID for gram positive cocci
positive if pink red color
What is a urease test
testing if urease is produced
hydrolyzes urea into ammonia, causes pH increase
positive- dark pink color
What is a glucose oxidative fermentation test
2 tubes are used- yellow if fermentation occurs
if acid in both, it is glucose fermenter and oxidizer
if acid only in open/ aerobic tube, it is a oxidizer
if acid only in mineral oil tube, it is a fermenter
if neither it is a nonutilizer
What is an IMViC test
Indole- red if positive- looks for indole production from tryptophanase enzyme
Methyl red - red if positive- looks for glucose fermentation
Voges Proskauer- red if positive- looks for acetoin from glucose metabolism
Citrate- blue if positive-looking for use of citrate in metabolism, alkaline pH causes color change
What organisms are ++– for IMViC reaction
E. Coli
What organisms are –++ for IMViC
Klebsiella pneumoniae
Enterobacter spp.
Serratia marcescens
What organisms are +-++ for the IMViC reactions
Klebsiella oxytoca
What is TSI test
Triple Sugar Iron Agar
phenol red as indicator
ferrous sulfate and sodium thiosulfate as H2S indicator
Slant-has lactose/sucrose- aerobic
Butt-Glucose-anaerobic
must read the slant, butt, black precipitate for H2S positive, cracks in medium mean gas
What does K/K for a TSI slant mean
no sugars used
alkaline slant, no change in butt
What does K/A in TSI agar mean
glucose fermented only
alkaline slant and acid butt
What does A/A mean in TSI agar
acid slant, acid butt
all sugars fermented
What does black precipitate in the butt of TSI agar mean? What do bubbles and cracks mean
H2S produced
gas produced
What does an antimicrobial agent need to successfully inhibit or kill an organism
the agent must be in an active form
must have sufficient levels or concentrations at the site of infection
What does bactericidal vs bacteriostatic mean
static- inhibits growth
icidal- kills the organism
What are the common targets of antibiotics
bacterial cell wall synthesis folate synthesis DNA replication RNA transcription mRNA translation
What are the natural mechanisms of resistance that bacteria can have
- lack of affinity for a drug
- lack of bacterial target
- inaccessibility
- efflux pumps that remove drugs
- ABC transporters
- enzymes that break down drugs
- biofilms
How do fluroroquinolone antibiotics work?
target topoisomerase II and IV, inhibits DNA synthesis
What are fluoroquinolones effective against
most gram positive and gram negative aerobic and facultative anaerobes
some anaerobic GPRs
What type of drugs are these? Nalidixic acid Ciprofloxacin Levofloxacin Gemifloxacin
floxacin
fluoroquinolone
How do trimethoprim sulfamethoxazole antibiotics work?
inhibits DNA synthesis by inhibiting folic acid and B12 production
impacts nucleotide synthesis
What organisms are thrimethoprim sulfamethoxazole effective against
aerobic and facultative anaerobic gram positive and gram negative
What is the drug composition of Trimethoprim sulfamethoxazole?
1:5 trimethoprim and sulfamethoxazole
How do Rifamycin antibiotics work?
inhibits RNA synthesis
targets ddRNA polymerase
impacts RNA transcription, DNA replication and SOS response
What organisms are Rifamycins effective against
Gram positive, negative and mycobacterium tuberculosis
What type of drugs are these
Rifampin
Rifapentine
Rif
Rifamycin
How do Beta lactam antibiotics work?
inhibit cell wall synthesis by targeting and using penicillin binding proteins
- alters peptidoglycans
- affects wall synthesis and ROS formation
What organisms are B lactams effective against
aerobic and anaerobic gram positive and negative organisms
What type of drugs are these
-penicillin, ampicillin, oxoacillin
Beta lactams
cillin
cef
penem
What type of drugs are these
- cefazolin, cefoxitin, ceftriaxone, cefepime
- imipenem
Beta lactams
cef
penem
How do glycopeptide and glycolipopeptide drugs work?
inhibit cell wall by targeting peptidoglycan
-decrease cell wall stability
What drugs inhibit transglycosylation and transpeptidation?
glycopeptides and glycopopeptides
What organisms are glycopeptides and glycopopeptides effective against
gram positive organisms
What types of drugs are these
vancomycin
teiplanin
glycopeptides and glycolipopeptides
How do lipopeptides work? What organisms are they effective against
inhibit cell wall synthesis by targeting membrane
gram positive and gram negative
What types of drugs are these?
daptomycin
polymyxin B
What are each of them effective against
lipopeptides
dapto- gram positive
poly-gram negative
How do aminoglycoside antibiotics work?
inhibit protein synthesis by targeting 30S ribosome- tiny subunit
What organisms are aminoglycosides effective against?
aerobic and facultative gram positive and negative
M. tuberculosis
What type of drugs are these Gentamicin Tobramycin Streptomycin Kanamycin
mycin
aminoglycosides
How do tetracyclines antibiotics work?
inhibit protein synthesis
inhibit 30S ribosomes
inhibits tRNA binding ribosomes
What organisms are tetracyclines effective against
aerobic and facultative gram positive and gram negative, maybe tuberculosis
What kind of drugs are these
Tetracycline
Doxycycline
cycline
tetracyclines
How do macrolides work
inhibit protein synthesis
target 50S- large subunit
inhibits elongation and translation steps
What organisms are macrolides effective against?
aerobic and anaerobic gram positive and gram negative
What kinds of drugs are these
Azythromcyin
Erythromycin
macrolides
ythromycin
How do streptogramin antibiotics work
inhibit protein synthesis
target 50S-large subunit
stop translation by inhibiting initiation and elongation
What organisms are streptogramins effective against
aerobic and anaerobic gram positive and gram negative
What types of drugs are these
Pristinamycin
Dalfopristin
Quinupristin
pristine
streptogramins
How do Phenicol antibiotics work?
inhibit protein synthesis
-target 50S large
What organisms are Phenicols effective against
some GPO some GNO
B. fragilis, N. meningitdis, H. influenzae, S. pneumonaie
What kind of drug is this
chloramphenicol
phenicol
What is an additive effect
when 2 drugs cause twice the effect
What is an indifferent effec
when a combination of drugs has no effect
What is an antagonistic effect? Name an example
when one drug counteracts the other
penicillin and erythromycin
What does empiric therapy mean?
antibiotics that are administered before blood culture and susceptibility results
What is the difference between biological and environmental resistance
biologic- observably reduced susceptibility
environmental- resistance due to physical or chemical stimuli in environment
What factors could cause environmental resistance
pH changes, cation concentration, thymidine content
What is intrinsic microorganism mediated resistance
resistance from genetics
What is acquired resistance
resistance that is due to altered cellular physiology and changes in genetic makeup
gene mutation
gene transfer
Transduction, transformation and conjugation are all examples of things that can cause what type of resistance?
acquired resistance
What natural resistance does Klebsiella have to ampicillin
have beta lactamase enzymes that destroy ampicillin before it reaches PBP target
inactivation
What natural resistance do entercocci have to all cephalosporin antibiotics
no penicillin binding protein that can bind to beta lactam agents
What do beta lactamase look like in chemical composition
like a square with O and N in bottom corners
How does beta lactamase cause resistance in gram positive and negative organisms
positive- beta lactam cant bind to mutated penicillin binding protein. have beta lactamase enzyme that hydrolyzes beta lactam antibiotic
negative-decreased uptake through porin through porin channels, harder to get in, all other reasons above also
In a Kirby Bauer Disk, the ___concentration is closest to the disk
highest
What affects the zone of inhibition and susceptability breakpoints?
thickness of agar
too thick-falsely large zone of inhibition (false resistance)
too thin-falsely low zone of inhibition (false susceptibility)
Why are Kirby Bauer disks stored upside down
to avoid condensation from interfering with the interpretation of test results. could alter diffusion or give area for bacteria to spread
What is the maximum of antibiotic disks that can be placed on a single Mueller Hinton agar plate
12 disks in 150mm plate
What temperature and for how long can Kirby Bauer disks be stored
2-8C for 1 week
bring to room temp before using
What type of test is the E test
the one with the strip that measures MIC
What does the MecA gene cause resistance to?
resistance to penicillin, methicillin, nafcillin, cloxacillin and dicloxacillin
encodes for penicillinases- penicillin binding protein
modifies binding site
What do MRSA organisms have resistance to
oxacillin resistant stap aureus
What treatment is used to gauge staph species with MecA gene
oxacillin
What does the erm gene create resistance for
resistance to erythromycin/ macrolide and induces clindamycin
encodes for methylation 23S rRNA
What does the msrA gene create resistance for
resistance to erythromycin
susceptible to clindamycin
encodes for efflux mechanism that spits antibiotic out
What does it mean if the D test has a flattened edge on erythromycin?
erm gene
resistant to clyndamycin
What does it mean if a D test has resistance to erythromycin only and no flattened edge
msrA gene only
not resistant to clindamycin
What is the MHT modified Hodge test for?
testing for carbapenamase enzyme
gives resistance to all carbapenems
What is MBC minimum ___ concentration
bactericidal
If an antibiotics MBC value is 32+ times higher than the MIC value, this means
the organisms could be tolerant to the drug,
drug cannot be used because the high dosage required could be toxic to patient
What are macro vs micro broth dilution tests
tests in serial dilutions
macro- larger broth volume- impractical
micro-smaller broth volumes
