Diagnostic Bacteriology MMSC438 Exam 1 Practice Questions

What is the role of the clinical microbiologist in patient care?

Ensure specimens are properly collected, labeled, transported, and processed; identify pathogens; interpret results; and communicate important findings to clinicians.

What are the 3 phases of laboratory testing?

Pre-analytical → Analytical → Post-analytical

What happens during the pre-analytical phase?

Patient preparation, specimen collection, labeling, handling, and transportation.

What phase has the MOST laboratory errors?

Pre-analytical phase

What happens during the analytical phase?

The actual testing of the specimen, including instruments, reagents, QC, and validation.

What happens during the post-analytical phase?

Results are interpreted, reported, communicated, stored, and followed up.

Why should microbiologists communicate with infectious disease clinicians?

To discuss unusual or significant pathogens and help guide appropriate treatment.

Why should microbiologists communicate with pharmacists?

To help optimize antimicrobial selection and dosing.

Why should microbiologists communicate with infection-control personnel?

To identify potential outbreaks and help prevent the spread of infectious organisms.

What are Standard Precautions?

Minimum infection-control practices used when handling human specimens

All human body fluids are treated as what?

potentially infectious

What is another term historically associated with Standard Precautions?

Universal precautions

What does PPE stand for?

Personal Protective Equipment.

What are examples of PPE?

Gloves, gowns/protective clothing, eye protection, masks/face shields, respirators, and specialized footwear.

What information must be on a properly labeled specimen?

• Patient ID/name

• Room/location

• Physician

• Culture/specimen site

• Date of collection

• Time of collection

What happens if a specimen is improperly or incompletely labeled?

It may need to be rejected and recollected.

What information belongs on a specimen requisition?

• Patient name

• age/DOB

• sex

• location

• physician information

• anatomic site

• date/time collected

• diagnosis/relevant history

• and antimicrobial therapy when appropriate.

What makes a specimen acceptable for culture?

• Correct anatomic site

• proper collection technique

• minimal contamination

• adequate volume

• correct labeling

• rapid transport

• proper storage

Why is the exact anatomic site important?

It helps determine which organisms are clinically significant versus normal flora.

Why should specimens be collected before antibiotics when possible?

Antibiotics can decrease the number of viable organisms and cause false-negative cultures.

During what phase is the best time to collect a specimen during infection?

acute phase, when organism numbers are usually highest.

Ideally, how quickly should specimens reach the microbiology laboratory?

Within 30 minutes when possible.

What can happen if specimens are transported too slowly?

Changes in oxygen, pH, and temperature can kill some organisms and allow others to overgrow.

What is generally a reason for specimen rejection?

Improper collection, labeling, transport, container, storage, contamination, leakage, or insufficient specimen.

How should CSF be stored?

it should be processed immediately and not stored

How should urine be preserved if processing is delayed?

refrigeration at 2-8C or boric acid preservative added

What medium can be used for stool if transport is delayed?

Cary-Blair transport medium

What anticoagulant is used in blood culture bottles?

SPS (sodium polyanethol sulfonate).

What should happen when a specimen is rejected?

Contact the person responsible for collection, request a new specimen when appropriate, and document the reason for rejection.

What if a physician insists on testing a compromised specimen?

Document that the results may be compromised.

What is a Level 1 specimen?

Critical/invasive specimens — highest priority.

Examples of level 1 specimens?

Blood, CSF, brain, amniotic fluid, heart valves, pericardial fluid.

What is a Level 2 specimen?

Unpreserved specimens such as bone, wound drainage, feces, sputum, and tissue.

What is a Level 3 specimen?

Specimens requiring quantitation, such as urine and catheter tips.

What is a Level 4 specimen?

Preserved specimens — lowest priority.

What questions should you ask when working up an isolate?

1. What is the specimen source?

2. Does the site have normal flora?

3. What organisms are normally present?

4. What pathogens are likely?

5. What is the colony morphology?

6. What media shows growth?

7. What is the purpose of the media?

8. Does the organism require full identification?

What are important considerations when deciding how much workup to perform?

Patient care, quality, cost, available resources, and clinical significance.

How should microbiology results be reported?

Clearly, accurately, and promptly.

What should be avoided in reports?

Unnecessary technical jargon and confusing abbreviations.

What should happen with critical values?

Report immediately to the appropriate healthcare professional.

What is the main goal of antimicrobial treatment?

Kill or suppress microorganisms while minimizing harm to the patient.

What are the two major natural sources of antimicrobial drugs?

Bacteria and fungi.

What is an antibiotic?

A substance naturally produced by a microorganism that inhibits or destroys other microorganisms.

What is an antimicrobial agent?

A chemical substance used to kill or inhibit microorganisms.

What is antimicrobial chemotherapy?

Use of drugs to control an infection.

What is prophylaxis?

Using an antimicrobial drug to prevent infection in a person at risk.

What is a synthetic drug?

A drug produced entirely through chemical reactions

What is a semisynthetic drug?

A natural antimicrobial that has been chemically modified in the laboratory

What is selective toxicity?

The drug is toxic to the microorganism but has little or no harmful effect on the host.

Why are drugs targeting bacterial cell walls highly selective?

Human cells do not have peptidoglycan cell walls

What happens when the microbe and human cell have very similar targets?

Selective toxicity becomes more difficult to achieve.

What does microbicidal mean?

Kills microorganisms.

What does microbiostatic mean?

Stops/inhibits microbial growth.

What is a broad-spectrum antimicrobial?

Effective against a wide variety of microorganisms.

What is a narrow-spectrum antimicrobial?

Effective against a limited range of microorganisms.

Why is narrow-spectrum therapy often preferred when possible?

It targets the pathogen while causing less disruption to normal microbiota.

What are the 5 major targets of antimicrobial agents?

1. Cell wall

2. Cell membrane

3. DNA/RNA

4. Protein synthesis

5. Metabolic pathways — especially folate

What is the major target of β-lactam antibiotics?

Bacterial cell wall synthesis.

What is the purpose of bacterial cell wall synthesis?

to build a mesh-like polymer called peptidoglycan that protects the cell from bursting under internal pressure

How do β-lactams work?

Bind penicillin-binding proteins (PBPs) and inhibit peptidoglycan cross-linking.

What happens to the bacterial cell after β-lactam treatment?

The cell wall weakens → cell lysis/death.

What are the major β-lactam families?

Penicillins, cephalosporins, carbapenems, and monobactams.

Examples of natural penicillins?

Penicillin G and Penicillin V.

What organisms are Penicillin G/V mainly active against?

Mainly Gram-positive organisms, plus some Gram-negative organis

What are examples of aminopenicillins?

Ampicillin and amoxicillin.

What organisms do aminopenicillins have expanded activity against?

Some Gram-negative enteric rods like E. coli, Klebsiella, Enterbacter, serratia marcescens, proteus mirabilis, salmonella and shigella

What is carbenicillin?

An older penicillin with activity against certain Gram-negative organisms.

What are antistaphylococcal penicillins?

Methicillin, nafcillin, cloxacillin, and dicloxacillin.

What are antistaphylococcal penicillins designed to resist?

Penicillinase

What is β-lactamase?

An enzyme that breaks the β-lactam ring and inactivates β-lactam antibiotics.

What is penicillinase?

A β-lactamase that specifically hydrolyzes penicillins.

What happens when the β-lactam ring is destroyed?

The drug can no longer effectively bind PBPs.

What are the three major β-lactamase inhibitors?

Clavulanic acid, sulbactam, and tazobactam.

What is the purpose of a β-lactamase inhibitor?

Prevent β-lactamase from destroying the β-lactam antibiotic.

What is the general trend from 1st → 5th generation cephalosporins?

1st: ↑ Gram-positive
2nd: ↑ Gram-negative
3rd: Strong Gram-negative
4th: Strong Gram-positive + Gram-negative
5th: Excellent Gram-positive, including MRSA

Which cephalosporin generation is strongest for Gram-positive organisms?

1st generation.

Which generations of cephalosporins have increased Gram-negative coverage?

2nd, 3rd, and 4th.

Which generation of cephalosporin has excellent Gram-negative activity and can penetrate CSF?

3rd generation.

Which generation of cephalosporin has broad Gram-positive and Gram-negative coverage?

4th generation

Which cephalosporins can treat MRSA?

5th-generation cephalosporins such as ceftaroline/ceftobiprole.

How do glycopeptides work?

Block peptidoglycan cross-linking/cell wall synthesis.

Main example of a glycopeptide?

Vancomycin

What type of organisms does vancomycin primarily target?

Gram-positive bacteria.

What is aztreonam?

A monobactam active primarily against aerobic Gram-negative bacteria.

How do fluoroquinolones work?

Inhibit DNA gyrase and topoisomerase IV, interfering with DNA replication.

Examples of fluoroquinolones?

Ciprofloxacin, levofloxacin, and ofloxacin

What is nalidixic acid?

An older quinolone.

How does rifampin work?

Inhibits RNA polymerase, blocking transcription/mRNA production.

What is rifampin commonly used to treat?

Tuberculosis and some other infections.

What antimicrobial class binds the 30S ribosomal subunit irreversibly?

Aminoglycosides

What do aminoglycosides do?

Cause misreading of the genetic code and interfere with tRNA binding.

Give an example of an aminoglycoside.

Gentamicin or streptomycin.

What class binds the 30S subunit reversibly?

Tetracyclines

Examples of tetracyclines?

Tetracycline, doxycycline, minocycline.

What do tetracyclines prevent?

Attachment of aminoacyl-tRNA to the A site.

What class binds the 50S subunit and inhibits protein synthesis?

Macrolides

Examples of macrolides?

Erythromycin, clarithromycin, azithromycin

What do macrolides interfere with?

Protein elongation

What are ketolides?

Protein synthesis inhibitors that bind the 50S ribosomal subunit

Example of a ketolide?

Telithromycin