Bacteriology Exam 2 (Antibiotic Resistance and ID) Flashcards
Responsibilities of the lab director
- direct observation of test performance
- monitoring reporting of test results
- review of QC results/preventative maintenance records
- observation of instrument maintenance
- assessment of test performance through PT
- competency assessment reviews
Gram negative color in gram stain
pink/red
Gram positive color in gram stain
purple
What color will salmonella be on HE/XLD plates?
Black from production of H2S
What color will Shigella be on HE/XLD plates?
clear - color will remain original color of the plate (blue/green on HE and red/orange on XLD) because they do not ferment the carbohydrates
What color will normal flora be on HE/XLD plates?
bright yellow color
CNA agar
allows gram-positive bacteria to grow and inhibits gram-negative bacteria
What is Chocolate agar used to grow? What type of agar is this?
Neisseria gonorrhoeae and Haemophilus influenzae.
It is an enriched agar
HE agar
Selective - inhibit the growth of nonpathogenic GNR and selects for Salmonella and Shigella spp.
Differential - non-enteric pathogens that do grow will appear as orange to salmon-color colonies (e. coli)
EMB agar
Selective - inhibits the growth of gram positive and allows GN bacilli to grow
Differential - fermentation of lactose appears as dark purple to black, or with a green metallic sheen and non-lactose fermenters remain colorless and translucent
Blood agar plate
Nutritious - supports growth for all organisms except most fastidious
Differential - shows different hemolysis abilities
Beta hemolysis on blood agar plate
Complete clearing around colonies due to complete lysis of RBC
Alpha-hemolysis
partial lysis - greenish discoloration around colony
Gamma-hemolysis
no hemolysis of RBC - no halo or change produced around colonies
MAC agar
Selective - only allows for gram negatives to grow, inhibits gram positive
Differential - lactose fermenters will be pink and non-lactose fermenters will be clear/yellow (color of the plate)
PEA agar
sheep BA supplemented with PEA to inhibit the growth of GN bacteria
MTM agar
enriched and selective media to allow N. gonorrhoeae and Neisseria meningitidis to grow
Thioglycollate broth
Allows for the growth of anaerobes
XLD agar
like HE agar; inhibits non-enteric GN bacilli and gram positive organisms to allow for the detection of Shigella and Salmonella spp.
Differential by exhibiting colors for the fermentation of carbohydrates
Bile Esculin Agar (BEA) - primary purpose
differential for group D streptococci vs enterococci
differential for enterobacteriaceae
differentiation of listeria monocytogenes
Blood Agar (BA) - primary purpose
cultivation of non-fastidious microorganisms, determination of hemolytic reactions (nutritious and differential)
Bordet-Gengou agar - primary purpose
Bordetella pertussis - pearl-like colonies with narrow zone of hemolysis
Bordetella parapertussis - brown colonies with green/black color on reverse side
Bordetella bronchiseptica - brown colonies with a rough pitted surface
Brain-heart infusion agar or broth (BHI) - primary purpose
Cultivation of fastidious and nonfastidious organisms (not selective or differential)
Buffered charcoal-yeast extract agar (BCYE) - primary purpose
Enrichment for Legionella spp.
Supports the growth of Francisella and Nocardia spp.
Campy-blood agar - primary purpose
Selective for Campylobacter spp.
CDC anaerobe 5% sheep blood agar - primary purpose
improved growth of fastidious, obligate, slow-growing anaerobes
Cefsulodin-irgasan novobiocin (CIN) agar - primary purpose
Selective for Yersinia spp; may be useful for isolation of Aeromonas spp.
Chocolate agar - primary purpose
cultivation of fastidious microorganisms
ex. Haemophilus spp, Brucella sp, and pathogenic Neisseria spp.
Chromogenic media - primary purpose
Used for the identification of Acinetobacter, MRSA, beta lactamase and carbapenemase producing organisms, and a variety of other organisms
Columbia colistin-nalidixic acid agar (CNA) - primary purpose
Selective for the isolation of gram-positive cocci
Cystine-tellurite blood agar - primary purpose
Isolation of Corynebacterium diphtheriae
Eosin methylene blue agar (EMB) - primary purpose
Isolation and differentiation of lactose-fermenting and non-lactose fermenting enteric bacilli
Hektoen enteric (HE) agar - primary purpose
Differential, selective medium for the isolation and differentiation of Salmonella and Shigella spp. from other GN enteric bacilli
LIM broth - primary purpose
Enriched and selective media for the isolation of Streptococcus agalactiae
Loeffler medium - primary purpose
Isolation and growth of Corynebacterium spp.
MAC agar - primary purpose
Isolation and differentiation of lactose fermenting and non-lactose fermenting GN enteric bacteria
MacConkey sorbitol agar - primary purpose
For the selection and differentiation of E. coli O157:H7 in stool specimens
Mannitol salt agar - primary purpose
Selective differentiation of staphylococci
Phenylethyl alcohol (PEA) agar with or without blood - primary purpose
Selective isolation of aerobic gram positive cocci/bacilli and anaerobic gram positive cocci
Regan Lowe agar - primary purpose
Enrichment and selective medium for isolation of Bordetella pertussis and Bordetella parapertussis
Selenite broth - primary purpose
Enrichment and isolation of Salmonella spp.
Skirrow agar - primary purpose
Selective for Campylobacter spp.
Streptococcal Selective agar (SSA) - primary purpose
Selective for streptococcus pyogenes and Streptococcus agalactiae
TM and MTM agar - primary purpose
Selective for N. gonorrhoeae and N. meningitidis
Supports the growth of Francisella and Brucella spp.
Thioglycollate broth - primary purpose
Supports growth of anaerobes, aerobes, microaerophilic, and fastidious microorganisms
Thiosulfate citrate-bile salts (TCBS) agar - primary purpose
Selective and differential for Vibrio cholerae and Vibrio parahaemolyticus
Todd-Hewitt broth supplemented with antibiotics (LIM) - primary purpose
Selection and enrichment for Streptococcus agalactiae in female genital specimens
What is the incubation temperature for most medically relevant bacteria?
35-37 degrees C
What temperature does Listeria monocytogenes and Yersinia enterocolitica grow at optimally?
20-40 degrees C
What temperature can Campylobacter jejuni grow at?
42 degrees C
Positive and negative reaction for Catalase testing
Which MOs are catalase positive and which are catalase negative?
Positive reaction: production of bubbles (most staphylococci)
Negative reaction: no production of bubbles (streptococci and enterococci)
Oxidase testing - what does a positive and negative reaction look like? What is the test used for? What organisms are typically oxidase pos/neg?
Used for the differentiation of enterobacteriaciae and non-enterobacteriaciae.
Positive oxidase reaction - production of a purple color (pseudomonas and aeromonas non enterobacteriaceae)
Negative - no purple color present (enterobacteriaeceae)
Slide Coagulase testing - what does a positive reaction look like? What is the test used to distinguish?
Positive reaction - clumping shown on slide
Negative reaction - no clumping
Slide coagulase indicates bound coagulase present (found on cell wall).
Used to distinguish Staph aureus from Coagulase negative Staph
Free coagulase test - what is a positive/negative reaction? What is it used for?
Free coagulase is a test done in a tube to distinguish staph aureus from coagulase negative staph.
Positive - turbid tube
Negative - clear tube
*done after slide coagulase to confirm
Indole testing - positive result and what is the test used for
Positive indole - blue/green color
This test detects the degradation of tryptophan into indole.
Used to confirm E. coli (indole positive)
PYR testing - what is it used for and what is a positive result
Positive result is a bright pink/red color
PYR test is useful in the identification of Strep pyogenes and enterococcus spp. which test positive.
What does IMViC stand for? (what are the 4 tests involved in this tube)
Indole, Methyl Red, Voges-Proskauer, and Citrate
Describe all of the positive results found in IMViC tests. Interpret what they mean.
Indole + = red ring color (production of tryptophanase)
Methyl Red + = red color (production of acid from glucose fermentation)
Voges-Proskauer + = red color (production of acetoin from glucose metabolism)
Citrate + = blue color (utilization of citrate as carbon source pH turns alkaline)
T/F: An organism can be positive for methyl red and voges-proskauer
False. These have inverse relationships. If an organism is positive for one, it cannot be positive for the other.
What is E. coli IMViC result?
Positive Indole (red)
Positive Methyl Red (red)
Negative Voges-Proskauer (yellow)
Negative citrate (green)
What is Enterobacter spp. and Klebsiella pneumoniae IMViC result?
Negative indole
Negative Methyl Red
Positive Voges-Proskauer
Positive citrate
What is found in the slant of TSI slants? What is found in the butt?
Slant = lactose and sucrose
Butt = glucose
What are the four things to look for in TSI slant? Describe the colors which will be seen if each are found.
The slant and the butt (alkaline will be red, acid will be yellow)
H2S production - black color
Gas production - cracks in the butt
What would a K/A tube look like? Interpret what this means.
Alkaline, red slant = no sucrose or lactose fermented
Acidic, yellow butt = glucose fermented
What would a K/K tube look like? Interpret the results.
Red tube throughout, no sugars fermented
What would an A/A tube look like? Interpret the results.
Yellow tube throughout indicating acid production, all sugars fermented
Mechanisms of antibiotic resistance (5 of them)
Lack of drug affinity
Inaccessibility
Efflux pumps/ABC transporters (removal of drug)
Innate enzymes to break down the drug
Biofilms (capsule)
Fluoroquinolones: what do they target in bacteria and what drug names are included in this group of antibiotics?
Inhibit DNA synthesis -> target topoisomerases and dna gyrase
Any drug ending in “floxacin” (ciprofloxacin and naladixic acid)
Trimethoprim sulfamethoxazole: what does it target in bacteria
Targets DNA synthesis by inhibiting folic acid/B12 synthesis
Rifamycins: what do they target in bacteria and what antibiotics are included in this group?
Inhibits RNA synthesis by targeting DNA-dependent RNA polymerase
Any drugs starting in “Rif” are included in this group (Rifampin)
Beta lactams - what they do they target in bacteria and what classes of drugs are included in this group?
Inhibits cell wall synthesis by targeting penicillin binding proteins (alter peptidoglycan structure)
Drugs included are:
Pencillins (anything ending in cillin)
Cephalosporins (anything starting with cef)
Carbapenems (anything ending in penem)
Glycopeptides and glycolipopeptides: what do they target in bacteria and what antibiotics are included in this group?
Target cell wall synthesis by inhibiting transglycosylation and transpeptidation
Examples: Vancomycin
Aminoglycosides: What do they target in bacteria and what drugs are included in this group?
Inhibit protein synthesis by targeting the 30S ribosome function
Drugs included are anything ending in “mycin/micin”
Tetracyclines: what do they target in bacteria and what drugs are included in this group?
Inhibit protein synthesis by targeting the 30S ribosome.
Examples are anything ending in cycline.
Macrolides: what do they target in bacteria and what drugs are included in this group?
Inhibit protein synthesis by targeting the 50S ribosome.
Examples are anything ending in “ythromycin” (erythromycin)
Phenicols: what do they target in bacteria and what drugs are included in this group?
Inhibits protein synthesis by targeting the 50S ribosome
Examples: Chloramphenicol
Additive effect
2 drugs cause twice the effect
Indifferent drug combination therapy
combination of drug causes no effect
Synergistic drug combination therapy
2 drugs effect is greater together than it is individually
Antagonistic drug combination therapy
one drug counteracts the other (better apart)
example: birth control and antibiotics
Beta-lactamase
What organisms typically possess these?
enzyme produced by bacteria that breaks down beta lactams
Ex. H. influenzae, M. catarrhalis, N. gonorrhoeae, and staph species
Clavulanic acid + amoxicillin
Good for use on organisms that are resistant to beta lactams.
Includes a beta lactamase inhibitor + beta lactam
2nd generation cephalosporins
very effective against gram negatives
3rd generation cephalosporins
first generation that can cross the blood brain barrier
Antibiotics used for the treatment of infections suspected to be caused by MDR bacteria
Carbapenems
Vancomycin - group it belongs to, what is it effective against, and role of inhibition
Great for gram positive, cannot cross the cell wall of gram negative bacteria (great for Clostridium difficile)
Inhibits cell wall synthesis
A part of Glycopeptides
Inhibitors of cell wall synthesis
beta lactams (carbapenems, penicillins, cephalosporins)
glycopeptides (vancomycin)
inhibitors of protein synthesis
aminoglycosides, tetracyclines, macrolides, chloramphenicol
Chloramphenicol
protein synthesis inhibitor that is not used often because it is very toxic and can cause aplastic anemia by suppressing bone marrow
inhibitors of DNA and RNA synthesis
quinolones (DNA), fluoroquinolones(DNA), metronidazole(DNA), rifampin (RNA)
Rifampin
great for M. tuberculosis
Sulfonamides/Trimethoprim
Combined to make SXT (aka Bactrim) - inhibitor of folic acid pathway
Nitrofurantoin
synthetic antibiotic used to treat recurrent cystitis; inhibitor of DNA/RNA/protein synthesis
empiric vs definitive therapy
empiric therapy is drugs given before test results are given (“educated guess”)
definitive therapy is drugs given after test results received
Intrinsic resistance
resistance resulting from the normal genetic, structural, or physiologic state of a MO
Acquired resistance
resistance to antibiotics gained by transfer of genetic material through horizontal transmission
MIC
minimum amount of drug to stop bacterial growth
Larger zone of inhibition = more _______ to drug
susceptible
Smaller zone of inhibition = more _______ to drug
resistant
MacFarland standard and what is the density of bacterial suspension
0.5, 1.5 x 10^8 CFU/mL
Broth dilution method for measuring MIC of antibiotics
The MIC is the lowest concentration of antibiotics that prevents visible growth
Microdilution vs macrodilution total broth volumes
Microdilution = 0.05-1 mL
Macrodilution = 1 mL or greater
Relationship between MIC and zone of inhibition
As MIC increases, zone of inhibition decreases (inverse relationship)
How to interpret the E-test
MIC determined where the growth ellipse intersects the E test strip at the highest and clearest point (always round up!)
MecA gene
Gene found in MRSA; causes resistance to penicillinases
If organism has this gene, penicillin or oxacillin will not work
erm gene
Found in inducible clindamycin resistant staphylococci - having this gene means that the organism has resistance to erythromycin and induces clindamycin resistance so you cannot use clindamycin to treat
msrA gene
having this gene means bacteria has resistance to erythromycin but it does not have genes to induce resistance to clindamycin –> can still use clindamycin to treat
D zone test
Used to determine if clindamycin is truly susceptible or resistant
Flattened clindamycin indicates that erythromycin induced resistance -> erm gene
No flattening indicates that there is erythromycin resistance only -> msrA gene
Modified Hodge Test (MHT) purpose and interpretations
Detects carbapenemase enzyme production
Positive control, negative control, and sample
Positive results show a clover leaf-like indentation meaning bacteria are resistant to all carbapenems
