Microbiology Exam 2

What is the reagent in the optochin test?

What is the reagent in the optochin test?

Ethylhydrocupreine hydrochloride

What is the optochin test?

• Differentiates between streptococcus veridans and streptococcus pneumonia

• Uses an optochin disc

What is the quelling test?

• It can demonstrate capsules in an organism

Which tests are used to identify Streptococcus pneumoniae?

Quelling test, optochin test, bile solubility, latex agglutination/counterimmunoelectrophoresis

What species can sometimes give a false positive for coagulase?

Enterococcus

What is the most common cause of SBE?

Streptococcus viridans

Quantitative vs qualitative

• Quantitative: Numerical measurement

• Qualitative: Quality, not numerical value

Is Kirby-Bauer qualitative or quantitative?

Qualitative

What is the kirby-bauer test?

• Qualitative test

• Agar disc diffusion

• Uses mueller hinton agar with a 3-5 mm depth in 100 or 150 mm plates

• Stored at 4 C, pH 7.2-7.4

• Divalent Ca2+ and cationic Mg2+ present affect the results of aminoglycosides, polymixinns, tetracyclines against Pseudomonas

• 4% NaCl enhances the ability to detect MRSA

Is MIC quantitative or qualitative?

Quantitative

What are dilution tests?

• Quantitative

• Give a more accurate measure of the probable in vivo effect of a drug

• Results are expressed as the minimal concentration to inhibit (MIC) or to kill (MBC) the test strain

Why would a dilution test be done?

• Blood cultures: Endocarditis and septicemia

• Patients who fail to respond to adequate therapy

• Patients who relapse while undergoing therapy

• Pediatric cases of meningitis and septicemia

What is the antimicrobial gradient strip method, E-Test (Epsilometer)?

• Quantitative MIC on agar containing a gradient of antimicrobial agent applied

• 0.5 McFarland and streak to agar twice within 15 minutes of adjusting turbidity

• Do NOT incubate with CO2

What is the main test for beta-lactamase?

Chromogenic cephalosporin

What is the D-Test?

• Inducible clindamycin resistance

• Macrolide resistance in Staph and Strep are conferred by the erm gene which results in resistance to erythromycin and either inducible or constitutive resistance to clindamycin

What is the turbidity standard?

0.5 McFarland

Extended Specrum B-lactamase (ESBL)

Spontaneous mutations which result in novel B-lactamases can inactivate extended-spectrum cephalosporins, penicillins, and aztreonam

AmpC B-lactamase

Members of Enterobacteriaceae produce plasmid-mediated or chromosomal AmpC B-lactamase which confers resistance to cephamycins

Carbapenemase B-lactamase (CRE)

• Members of Enterobacteriaceae that produce carbapenemase are often resistant to one or more of the carbapenems

• Acinobacter is a major CRE organism

• Resistance is to carbapenems, penicillins, cephalosporins, and aztreonam

Metallo-B-lactamase

• New Delhi strain

• Pseudamonas was the original organism, but now there are enterobacterialis

Bacteriacidal activity of serum

• Testing the antibiotic that’s in the patient’s serum to see if it’s at the level they need to treat that organism

• Known as the Schlichter test

• Do NOT use plasma

What is synergism?

Effect of a combination is GREATER than the sum of the effect of each agent tested independently

What is additive or indifferent?

Effect of a combination is EQUAL to the sum of the effects of each agent or is no greater than that of the more active drug

What is antagonism?

Effect of a combination is less than the effect of the more active agent

What are the clinical uses of combination therapy?

• Endocarditis caused by Enterococcus

• Tuberculosis

Checkerboard/chessboard titration

Two drugs are diluted as for MIC determinations and then combined in sets consisting of each concentration of one drug against serial dilutions of the other

What is therapeutic drug monitoring?

• Serum levels of antimicrobial agents

• Don’t want the antimicrobial levels in the patient to get too high or low

• Serum samples are drawn at certain times to monitor antibiotic levels

What is pharmacodynamics?

The absorption/presence of antibiotic in different tissues and sites

What is pharmacokinetics?

Concentration of drug in certain areas

What are the inhibitors of cell wall synthesis?

• B-lactams: Penicillin, cephalosporins

• Carbapenems: Imipenem

• Glycopeptides: Vancomycin

• Monobactams: Aztreonam

What are the inhibitors of cell membrane functions?

• Most are against gram positive

• Gram positives: Lipopeptides: Daptomycin

• Gram negatives: Polymixins

• Fungi: Amphotericin B

What are the inhibitors of protein synthesis?

• Gram-positive and negative

• Aminoglycosides

• SPS counteracts aminoglycosides in some blood cultures

• Tetracycline

• Macrolides

What are the inhibitors of nucleic acid? (DNA and RNA)

• Gram positive and negative

• Quinolones

• Fluoroquinolones

• Most inhibit DNA

• Rifampin: RNA

• Nitrofurantoin: Urinary tract only

• Nitromidazoles

What are the inhibitors of folic acid synthesis?

• Sulfa drugs

• Gram positive and many gram negative

• Sulfonamides

What are the non-genetic causes of antibiotic resistance?

1. Enzymatic destruction

2. Enzymatic modification

3. Altered target (receptors)

4. Decreased uptake

5. Target overproduction

6. Efflux

7. Loss of target structure

What are the genetic causes of antibiotic resistance?

1. Intrinsic

2. Acquired resistance (Transfer)

What are beta-lactams?

Beta lactamase is produced by the organism. It hydrolyzes the beta lactam ring

What is penicillin?

• Beta lactam

• Not effective against gram negative rods

• Soft tissue and body fluid have the highest concentrations

What is cephalosporin?

• Beta lactam

• Similar tro penicillin, better withstands the action of B-lactamase

• Concentrated in soft tissue, poor concentration of CNS

• Not absorbed well from GI tract

• Treatment for urinary and respiratory infection, but not major systemic infections

• Some nephrotoxicity

What are the other beta-lactams?

Carbapens: Broadest spectrum of all antimicrobial agents. Referred to as penems

Monobactams: Aztreonam is the only one. Broad spectrum. For gram negatives

What antibiotic cannot be used during pregnancy or used on infants?

Tetracyclines. It destroys the enamel of teeth and causes bone damage. Can cause green teeth

What are the urinary tract drugs?

• Nitrofurantoin, nalidixic acid, phosphomycin is urinary tract ONLY

• Fosfomycin is for E. coli and enterococcus

What antibiotic causes ota and renal toxicity?

Aminoglycosides

What is Kawasaki disease?

• Mucocutaneous lymph node syndrome

• Toxin is from Staph aureus

• Found in children 5 and under

What is toxic shock syndrom?

• Patient is acutely ill, febrile, toxemia

• Hypotension, DIC (Disseminated intravascular coagulation)

• Toxin causes the infection

Morphology of micrococcaceae

• Spherical, gram positive cocci arranged singly, in pairs, clusters of 4 or 8 organisms

• Catalase positive

• Possess cytochrome enzymes which give a positive catalase

• Non-motile, some pigmented

At what temperature is motility and pigment produced best at?

25 C

Staphylococcus aureus

• Most important organism in this group

• Can be found in any specimen

• Responsible for a lot of skin infecetions and abscesses

• Furuncles produce sinus tractsm colony grows to other sites and are harder to treat

• Antibiotic resistant Staphylococcus are responsible for hospital acquired infection

• Staph toxin can cause food poisoning

• Metastatic lesions in lung, bone, kidney of 2/3 patients with bacteremia may develop endocarditis

How can an infection caused by Staph aureus be differentiated from Clostridium perfringes and salmonella?

Lack of fever and short duration

Scalded skin syndrome

• Also known as Ritter’s disease

• Generally in newborns, picked up from mom

• Toxin causes skin to be very red

Staphylococcus lugdunensis

• Can cause similar clinical issues as Staph aureus

• Can be typical flora, but also can be a pathogen

• Always significant in endocarditis following cardiac or open chest surgery

• Significant with stitch abscesses

• Colonies exhibit a white pigment

Staphylococcus saprophyticus

• Opportunistic. Second most common cause of UTI

• 10^4 is the significant colony count

• Seen sometimes in innear ear infections

What is the significant colony count of a UTI caused by Staphylococcus saprophyticus?

10^4

T/F: All Staphylococcus are salt tolerant

True

Staphylococcus hemolyticus

• Causes hemolysis on blood

• Very resistant to antibiotics

Primary culture of staphylococcus

• Blood agar and thioglycollate are intially inoculated

• Inoculate at 35 C

• White, golden, yellow or cream colored colonies

• Colonies appear after 24 hours on blood agar

What gene dermines if Staph aureus is going to me MRSA or not?

Mech A gene

What test separates Staphylococcus and Streptococcus?

Catalase test

Non-hemolytic (Gamma)

• Applies to enterococcus more than anything else

• No lysis of red blood cells around the colony

Alpha hemolysis

• Green color surrounding the organism due to biliverdin (methemoglobin) released as RBC hemolysis is accomplished

• Most grow better under CO2

Alpha prime hemolysis

• Colonnies producing a zone of alpha hemolysis

• Narrow zone encircles the colony with a zone of complete or beta hemolysis

Beta hemolysis

• Total lysis of RBC’s around colony

• Clear zone surrounnds the colony

Streptolysin O (SLO) is oxygen ____

labile

Streptolysin S (SLS) is oxygen ____

stable

Group A post-streptococcal diseases

• Acute glomerulonephritis

• Rheumatic fever

• Scarlet fever

• Impetigo

• Toxic shock syndrome

• Necrotizing fascitis

What antibiotic is highly concentrated in the biliary tree (liver)?

Penicillin

What antibiotic can cause aplastic anemia?

Chloramphenicol