Microbiology Quiz: Antimicrobial Resistance and Chlamydia

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is the mecA gene responsible for in MRSA?

Facilitating aerobic respiration

Producing a unique lipopolysaccharide

Encoding for high affinity PBP

Encoding for a low affinity PBP (correct)

Which bacterial population expresses resistance in a heterogeneous manner?

Resistance is absent in heterogeneous populations

Some bacteria in the population express resistance (correct)

Only resistant bacteria express the trait

All bacteria in a population express resistance

What is a key characteristic of Chlamydia species?

They are facultative intracellular parasites

They rely on the host for ATP (correct)

They can grow on nonliving media

They have a peptidoglycan layer

Which part of the Chlamydia replication cycle is non-infectious?

Reticulate body Signup and view all the answers

Which mechanism is NOT a way antimicrobial resistance is disseminated?

Adenosine salvage Signup and view all the answers

What type of resistance expression occurs only when the organism is exposed to an agent?

Inducible resistance Signup and view all the answers

Which component is present in all Chlamydia species?

Lipopolysaccharide (LPS) Signup and view all the answers

Which biovar of Chlamydia trachomatis is associated with genital infections?

Lymphogranuloma venereum (LGV) Signup and view all the answers

What is the minimum inhibitory concentration (MIC)?

The lowest concentration of antibiotic that visibly inhibits growth Signup and view all the answers

Which interpretive category indicates that an organism may require a higher dose of antibiotic?

Intermediate Signup and view all the answers

What does selective toxicity in an ideal antibiotic refer to?

Exerting effects on the agent of disease without harming the patient Signup and view all the answers

Which organization develops interpretative standards for susceptibility testing?

Clinical and Laboratory Standards Institute (CLSI) Signup and view all the answers

What is considered the most important step of all susceptibility testing?

Preparation of inoculum Signup and view all the answers

Which term refers to antibiotics that are specifically used for urine infections?

Group U agents Signup and view all the answers

What characterizes a resistant organism in antimicrobial susceptibility testing?

Not inhibited by recommended dose Signup and view all the answers

What defines an ideal antibiotic regarding cost?

Has a minimal cost Signup and view all the answers

What is the primary reason for high-level aminoglycoside resistance in enterococci?

Enzymatic inactivation Signup and view all the answers

What is the main purpose of combining ampicillin or penicillin with aminoglycosides in treating enterococci?

To achieve a bactericidal effect Signup and view all the answers

What is the recommended screening concentration of aminoglycosides for testing enterococci?

500 to 1000 µg/mL Signup and view all the answers

What is the primary mechanism of resistance in KPC-producing Enterobacteriaceae?

β-lactamase production Signup and view all the answers

Which method is recommended for detecting vancomycin resistance in staphylococci?

Broth dilution method Signup and view all the answers

Which method is considered the reference method for testing anaerobes?

Agar dilution Signup and view all the answers

What indicates positive inducible clindamycin resistance when using the D test?

No inhibition zone around erythromycin Signup and view all the answers

What is the primary function of an antimicrobial agent?

Kills or inhibits the growth of organisms Signup and view all the answers

What is the purpose of using QC strains in susceptibility testing?

To ensure consistent testing results Signup and view all the answers

Which of the following is a key characteristic of MRSA isolates?

Mec-A mediated resistance Signup and view all the answers

Which type of agent specifically affects bacteria?

Antibacterial agent Signup and view all the answers

What is the incubation time required for broth microdilution testing of anaerobes?

48 hours Signup and view all the answers

What should be reported for enterococci that are resistant to ampicillin?

R to all penicillin derivatives Signup and view all the answers

How should the testing conditions be modified for detecting MRSA?

Supplement MH with 2% NaCl Signup and view all the answers

What does a bactericidal agent do?

Kills bacteria Signup and view all the answers

Which automated system is mentioned as a method for detecting susceptibility endpoints?

All of the above Signup and view all the answers

Which term describes an effect where the combined activity of two antimicrobial agents is less than the sum of their individual effects?

Antagonism Signup and view all the answers

What does the vancomycin agar screen test for MRSA entail?

Inoculating with a 0.5 McFarland suspension Signup and view all the answers

Which group of bacteria is known to have intrinsic resistance to vancomycin?

Leuconostoc spp. Signup and view all the answers

What characteristic distinguishes gram-positive bacteria from gram-negative bacteria?

Thick peptidoglycan cell wall Signup and view all the answers

What is the significance of a hazy zone around an oxacillin disk during MRSA testing?

Possible heteroresistance Signup and view all the answers

What is the function of penicillin-binding proteins (PBPs)?

Facilitate peptidoglycan biosynthesis Signup and view all the answers

Which of the following is NOT a mechanism of action for antibiotics?

Promotion of DNA repair Signup and view all the answers

What type of antibiotics are ampicillin and methicillin classified as?

Beta-lactams Signup and view all the answers

Which of the following best describes broad-spectrum antibiotics?

Effective against a wide range of bacteria, including both gram-positive and gram-negative Signup and view all the answers

What is the role of clavulanic acid when combined with amoxicillin?

Inhibits beta-lactamases to prevent inactivation of amoxicillin Signup and view all the answers

What type of organism causes Human Monocytic Ehrlichiosis (HME)?

Ehrlichia chaffeensis Signup and view all the answers

Which testing method has the highest sensitivity and specificity for identifying Ehrlichia and Anaplasma infections?

Nucleic acid amplification testing (PCR) Signup and view all the answers

What is a common symptom associated with Coxiella burnetii infections?

Pneumonia-like symptoms Signup and view all the answers

What characterizes the morphology of Ehrlichia and Anaplasma bacteria?

Pleomorphic gram-negative coccobacilli Signup and view all the answers

What complication can arise from a Coxiella burnetii infection?

Endocarditis Signup and view all the answers

How is Bartonella quintana commonly transmitted?

Insect vectors Signup and view all the answers

What signature feature is seen in cells infected by Ehrlichia and Anaplasma species?

Presence of morulae Signup and view all the answers

Which of the following organisms is primarily associated with causing Trench fever?

Bartonella quintana Signup and view all the answers

Study Notes

Antimicrobial Agents

Antimicrobial agent - kills or inhibits organisms
Natural: antibiotic
Semisynthetic: chemically modified antibiotics
Synthetic: man-made
Antibiotics - substances produced by bacteria and fungi that inhibit the growth of other organisms
Antibacterial agent - antimicrobial agents that affect bacteria
Chemotherapeutic agent - substance used to treat disease; includes antimicrobial and anticancer drugs
Bactericidal - "cide" means kill; agent kills bacteria
Bacteriostatic - "static" means no change; agent inhibits bacteria

Spectrum of Activity

Narrow spectrum - only certain groups covered
Broad spectrum - gram positive and gram negative coverage

Mechanism of Action

Inhibition of bacterial cell wall synthesis
Interference of plasma membrane
Inhibition of folate synthesis
Interference of DNA replication
Interference of DNA transcription
Interference of mRNA translation

Drug Combinations

Additive - effect is sum of activity of individual antimicrobial agents (1+2=3)
Synergism - effect is amplified (1+2=4)
Antagonism - one agent interferes with activity of other (1+2=1)

Cell Wall Characteristics

Not found in mammalian cells
Cell wall characteristics affect antibiotic spectrum of activity
Gram-positive - thick peptidoglycan cell wall
Gram-negative - thin peptidoglycan surrounded by outer membrane; peptidoglycan is AKA murein layer

Gram-Positive and Gram-Negative Cell Walls

Diagrams depicting the structures of gram-positive and gram-negative cell walls are provided; showing the differences in cell wall structure and membrane composition.
Inner (cytoplasmic) membrane - osmotic barrier
Outer membrane (gram-negatives only)
Lipopolysaccharides
Phospholipids
Porins

Peptidoglycan Biosynthesis

Synthesis of precursors in cytoplasm
Transport of precursors across cytoplasmic membrane
Insertion of precursors into cell wall
Transpeptidation and transglycolation

Cell Wall Inhibitors

Beta-lactam antibiotics
Penicillins (Ampicillin, Oxacillin, Methicillin)
Cephalosporins (Cephems) - 1st through 4th generation (Cephalexin, cefotaxime, ceftriaxone)
Monobactams (Aztreonam)
Carbapenems (Imipenem, doripenem, ertapenem)
Broad and narrow spectrum
Bind to penicillin binding proteins (PBPs)
PBPs are transpeptidase/transglycosylase enzymes
Beta-lactam and beta-lactamase Inhibitor combinations (Amoxicillin and Clavulanic Acid/Augmentin)
Glycopeptides (Vancomycin, Dalbavancin)
Inhibit peptidoglycan synthesis
Bind to terminal D-ala-D-ala
Active vs. GP only
Active vs. MRSA, C. difficile
Large molecules can't enter GN

Other

Polymyxins - plasma membrane disruption, active against gram-negative bacteria
Nitrofurantoin - treats UTIs

Folate Synthesis

Folic acid pathway provides precursors for DNA synthesis
Two key enzymes in pathway
Dihydropteroate synthase
Dihydrofolate reductase
Folate Synthesis Inhibition
Sulfamethoxazole and trimethoprim - broad spectrum

Sulfonamides

Sulfamethoxazole
Mechanism of action: inhibits folic acid synthesis (DNA synthesis)
Humans do not synthesize folic acid
Competitively binds PABA an essential component of metabolism
Used for UTIs, enteric infections

DNA & RNA

DNA Replication Inhibition
Enzymes required for DNA replication (Topoisomerases, DNA gyrases)
Quinolones/Fluoroquinolones (Ciprofloxacin, levofloxacin, gemifloxacin)
Broad spectrum, including P. aeruginosa.
DNA Transcription Inhibition
Transcription mediated by RNA polymerase
Rifampin binds to RNA polymerase
Blocks RNA chain elongation
Used to treat mycobacteria, staph, strep, enterococci

mRNA Translation

30S and 50S ribosomal subunits bind to mRNA

Protein Synthesis Inhibition

Aminoglycosides (Gentamicin, tobramycin, amikacin) - Inhibit 30S ribosomal subunit, Active against GP and GN but not anerobes, Ototoxicity and nephrotoxicity.
Tetracyclines (Doxycycline, minocycline, tetracycline)- Inhibit 30S ribosomal subunit- Broad spectrum, including mycoplasma and chlamydia
Macrolides (Erythromycin, clarithromycin, azithromycin)- Inhibit 50S ribosomal subunit - Broad spectrum
Lincosamides (clindamycin) and Streptogramins (dalfopristin/quinupristin) - Inhibit 50S ribosomal subunit- Broad spectrum, MLS group
Oxazolidinones (linezolid), Glycylcycline (tigecycline), Chloramphenicol - Toxicity - aplastic anemia

Mycobacterial Chemotherapy

Isoniazid (INH) - inhibits synthesis of mycolic acid (cell wall)
Rifampin - blocks RNA polymerase
Ethambutol - ?inhibits cell wall synthesis
Streptomycin - inhibits protein synthesis

Mycobacterial Chemotherapy - Therapeutic Considerations

Mutations are common (drug resistance is high)
Multiple drugs used to kill and prevent MDR-TB

Mechanisms of Resistance

Intrinsic - resistance resulting from normal genetic, structural, or physiologic state of the microorganism; naturally occurring
Acquired - Resistance resulting from altered cellular physiology and structure due to genetic changes, transfer or mutation to genetic code.
Decreased uptake or accumulation (Impermeability, Efflux, Biofilms)
Enzymatic inactivation or modification (Target site modification, Acquisition of new target, Pathway bypass)

Mechanisms of Resistance - Specific Examples

Impermeability of cell wall (LPS and porins restrict entry of antimicrobials, all GN resistant to vancomycin, cannot cross outer membrane)
Biofilms (Bacteria in polysaccharide matrix, highly drug resistant, persister cells)
Enzymatic inactivation or degradation (Modification of aminoglycosides, inactivation by beta-lactamases)

Beta-Lactamases

Hydrolyze the beta-lactam ring
Produced by both GP and GN organisms
Beta-lactamases vary in spectrum
Most common beta-lactamase enzyme is penicillinase
Virtually all GN bacteria are intrinsically resistant via beta-lactamase production
Staph are most common GP producers

Beta-Lactamases - Other Details

Cephalosporins were created to be forever resistant to all beta-lactamase enzymes thus extending their spectrum of use
Bacteria fought back and created extended spectrum beta-lactamases (ESBLs) - beta-lactamase enzymes that can inactivate all penicillins and cephalosporins

Mechanisms of Resistance - Further Details

Target site modification - drug binds poorly (or not at all) to target site, altering of PBP decreases affinity for beta-lactam drugs, mutations to topoisomerase IV and DNA gyrase increases resistance to quinolones, addition of methylase to ribosome decreases binding of MLS antimicrobials, vancomycin-resistant enterococci altered cell wall.
Acquisition of new target site (mecA gene, encodes for a low affinity PBP, resistant to all penicillins, found in mobile SCCmec cassette).
Bypass mechanism (Organism circumvents consequences of antimicrobial action, anaerobes are intrinsically resistant to aminoglycosides, lack of oxidative electron transport system, required for uptake of aminoglycosides).

Dissemination of Antimicrobial Resistance

Transformation, transduction, conjugation
Plasmids (extrachromosomal, circular, replicating DNA)
Transposons and Integrons (mobile DNA elements)

Resistance Expression

Constitutive - organism constantly expressing resistance mechanism
Inducible - resistance only when exposed to agent
Constitutive-inducible - constant expression at low levels
Homogenous - entire bacterial population expressing resistance
Heterogeneous - some bacteria in population express resistance (MRSA)

Chlamydiae

Introduction - three species cause human diseases (C. trachomatis, C. pneumoniae, C. psittaci). They differ from other bacteria since they do not grow on nonliving media, are sensitive to interferon, and are obligate intracellular parasites.
Characteristics - obligate intracellular parasite, dependent on host for adenosine 5'-triphosphate (ATP); lack energy metabolism, and grow and multiply only inside animal or host epithelial cells.
Replication Cycle - elementary body (infectious), reticulate body (non-infectious)
Antigens - outer membrane similar to gram-negative bacteria, but no peptidoglycan; components include lipopolysaccharide (LPS), present in all Chlamydia species; major outer membrane protein (MOMP), specific for each species and subspecies, species subdivided into serotypes (serovars) based on MOMP
C. trachomatis (Three biovars: Trachoma, Lymphogranuloma venereum, mouse pneumonitis) - Each biovar contains serovars A-K, D-K, urogenital infections, non-chlamydial, non-gonococcal urethritis, pelvic inflammatory disease
Newborn Chlamydia - passed to newborn via birth canal, conjunctivitis, nasopharyngeal or pneumonia. Infants given prophylactic eye drops for GC/Chlamydia; assumed to be cause of all pneumonia in infants ≤6 months unless otherwise proven.
Specimens - must contain host epithelial cells (intracellular parasite). avoid wooden sticks (toxic), endocervical, urethral, conjunctival swabs, aspirates of lymph nodes (LGV), lower RT secretions
Direct Microscopic Exam - direct specimen smears, QC for presence of epithelial cells, rapid diagnosis of neonatal inclusion conjunctivitis and trachoma; sensitivity 95%; not sensitive for urogenital specimens.
Stain cells/specimen with Giemsa stain (purple inclusion bodies), iodine (stains glycogen around EB, detects only C. trachomatis)
Direct fluorescent antibody (DFA) - fluorescein-labeled anti-Chlamydia antibodies, genus specific LPS and species specific MOMP, most sensitive method
Cell Cultures - approximately 80% sensitive, viral culture techniques required (living cells/tissue cultures), avoid viral transport media, and contain antimicrobial agents, technically demanding
Non Culture Detection Methods - Enzyme immunoassay (detects LPS or MOMP antigen, false positive can occur, not as sensitive as culture), serology (limited and problematic, infections localized, antibodies can be from previous infections), nucleic acid assays (detects Chlamydia and GC, DNA probe, amplification methods, PCR, very sensitive and specific, problems with culture).
Use of Culture vs Non Culture Methods - comparing the resources, and cons/pros, of each method.
Other considerations with Chlamydia
Chlamydia pneumoniae (Mild or asymptomatic affects young adults, prolonged pharyngitis followed by bronchitis or pneumonia, potential risk factor for Guillain-Barré syndrome, asthma, cardiovascular disease, detected by serological methods, same culture techniques)
Chlamydia psittaci (Causes ornithosis, psittacosis or parrot fever, zoonotic infection, occupational hazard for pet bird handlers and poultry workers, rare in US, acute lower respiratory infection, cultures not sensitive, BSL3, diagnosis serologically)

Other Miscellaneous Bacteria

Mycoplasma & Ureaplasma - belong to class Mollicutes (size of a large virus, smallest self-replicating microorganisms colonizing mucus membrane of respiratory tract and urogenital tract infections). Transmission (sexual/mother to child, respiratory secretions). No cell wall, do not gram stain, pleomorphic, resistant to cell wall antibiotics (penicillin, cephalosporins), slow growing, fastidious, cell culture.
Mycoplasma pneumoniae (primary atypical pneumonia, walking pneumonia, teenagers and young adults).
Mycoplasma hominis (colonize urogenital tract, opportunistic pathogen; PID, salpingitis, pyelonephritis;
Other Mycoplasma Species (M. genitalium, NGU, PID, cervicitis, endometriosis, sterility; M. fermentans, opportunistic respiratory pathogen; M. penetrans, urine of men with HIV; M. salivarium, synovial fluid of RA patients)
Ureaplasma urealyticum (colonize urogenital tract, non-chlamydial, non-gonococcal urethritis in men, upper genital tract infections in women). Hydrolyzes urea, Can be transmitted to newborns at delivery Set up culture for these organisms if meningitis suspected but Negative gram stain and culture
Specimen Collection and Transport - Body fluids, wound aspirates, tissue samples; NP, cervical, vaginal swabs; Incuate at bedside; Extremely sensitive to drying and heat; Transport media (Tryptic soy agar with penicillin; SP4 (sucrose phosphate buffer, serum)); Plate immediately or store at -70°C
Cultures - Special media (A7, E agar, U broth, enriched with sterols and penicillin) - 1 week for most, 3-4 weeks for M. pneumoniae - Mycoplasma: fried-egg colony morphology - Ureaplasma: small colonies
Mycoplasma, Ureaplasma ID - Recovery from culture difficult (~40% sensitivity), Detect serum IgG and IgM antibodies, Demonstrate a fourfold rise in cold agglutinin titer, Complement fixation, Enzyme immunoassay, Microimmunofluorescence, Radiography for Dx of M. pneumoniae.
Rickettsiae - Arthropod-borne, Obligate intracellular parasites, GN coccobacilli, predilection for endothelium of blood vessels, Never grown in cell-free media, Pleomorphic, Nonmotile, Spotted fever group, Typhus group, Rocky Mountain Spotted Fever (RMSF), R. rickettsiae, Vector is ticks, Flulike symptoms, Characteristic rash on palms of hands and soles of feet, May disseminate to blood vessels of lungs, brain, heart, Untreated mortality rate ~20%, R. akari (Rickettsialpox), Vector is mouse mites, Seen in Eastern US, Similar to RMSF but milder except Rash of face, body, extremities, Not on palm and soles, Endemic typhus or murine typhus, Vector is rat fleas, Flulike symptoms and +/- rash, R. prowazekii (Epidemic louse-borne typhus, War and natural disasters, Vector is human body and squirrel louse, Flulike symptoms, Rash on palms, soles, face, Untreated mortality rate ~ 40%, Brill-Zinsser disease, Reactivation of infection)
Orientia tsutsugamushi - Formerly Rickettsia, Causes scrub typhus, Vector is rat chigger, Flulike symptoms and rash, Highly infectious, Handle rickettsia in BSL3 lab, BSL2 OK for separating serum from clotted blood.
Rickettsial Diagnosis - Immunohistochemical staining for Dx and Serology; IFA - immunofluorescence assay (nonspecific), Weil-Felix agglutination reaction (nonspecific).
Ehrlichia and Anaplasma - Pleomorphic GN coccobacilli, Obligate intracellular parasite, Developmental cycle similar to Chlamydia; EB infectious form, Replicates in phagocytes, Form inclusions called morulae.
Ehrlichia chaffeensis - Causes human monocytic ehrlichiosis (HME), Associated with tick bites (Southern US), Fever, headache, muscle pain, malaise, May have leukopenia, neutropenia, thrombocytopenia and elevated liver enzymes, Can be severe
Anaplasma phagocytophilum - Formerly Ehrlichia, Human granulocytic ehrlichiosis (HGE), Infects neutrophils, Tick bites (Northern US), Similar symptoms to Ehrlichia, Peripheral blood smear (Wright, Giemsa stain or histologic stains), Nucleic acid amplification testing, PCR, Serology (retrospective)
Coxiella burnetii - Obligate intracellular GN coccobacilli, Causes Q fever, Zoonosis (cattle, sheep, goats), Found in urine, feces, milk, birth products, Remain in soil for years (spore-like lifecycle). Transmitted by inhaling infectious aerosols, Infects lungs → systemic infection, Flulike symptoms, thrombocytopenia, Highly contagious → BSL 3, Complication: endocarditis, death (fatal disease), Dx by direct immunofluorescence, serology, PCR.
Miscellaneous GNR - Bartonella spp., Spirillum minus, Klebsiella granulomatis, Chryseobacterium, Chromobacterium violaceum
Bartonella quintana (Trench fever, Bartonella spp. multiply in RBC and endothelial cells, Bacillary angiomatosis (BA), proliferation of blood vessels forming a mass, immunocompromised individuals (HIV), Bacteremia, endocarditis; transmitted by body lice.
Bartonella henselae (Cat scratch disease, lesion and fever, recovery in 2-4 months, transmitted by cat fleas, Bacillary angiomatosis, bacteremia, endocarditis, detected by silver stain).

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

Test your knowledge on key concepts related to antimicrobial resistance, particularly in MRSA and Chlamydia species. This quiz covers mechanisms of resistance, characteristics of pathogens, and important testing standards. Challenge your understanding of microbiological principles!