Microbiology Quiz: Antibiotic Resistance and Chlamydia
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Questions and Answers

What gene is primarily associated with methicillin-resistant Staphylococcus aureus (MRSA)?

  • mecC gene
  • mecB gene
  • mecD gene
  • mecA gene (correct)

    • Which mechanism describes anaerobes being intrinsically resistant to aminoglycosides?

  • Transformation mechanism
  • Bypass mechanism (correct)
  • Constitutive resistance
  • Inducible resistance

    • What type of DNA are plasmids classified as?

  • Extrachromosomal circular DNA (correct)
  • Chromosomal DNA
  • Double-stranded RNA
  • Linear DNA

    • What type of resistance expression is characterized by organisms constantly expressing a resistance mechanism?

    <p>Constitutive resistance</p> Signup and view all the answers

    Which of the following statements is true regarding Chlamydia species?

    <p>They are dependent on hosts for ATP.</p> Signup and view all the answers

    What form of Chlamydia is considered infectious?

    <p>Elementary body</p> Signup and view all the answers

    The major outer membrane protein (MOMP) in Chlamydia is used for:

    <p>Species and subspecies identification</p> Signup and view all the answers

    Chlamydia trachomatis has how many recognized biovars?

    <p>Three biovars</p> Signup and view all the answers

    What does β-lactamase testing detect?

    <p>Resistance to penicillinase-susceptible penicillins</p> Signup and view all the answers

    Which of the following methods is NOT used for β-lactamase testing?

    <p>MIC</p> Signup and view all the answers

    Which organisms typically produce ESBLs?

    <p>Klebsiella spp.</p> Signup and view all the answers

    What is the outcome when ESBL-producers are tested against cephalosporins?

    <p>They are reported as resistant</p> Signup and view all the answers

    What color indicates a positive result in the Nitrocefin test for β-lactamase?

    <p>Red</p> Signup and view all the answers

    Which of the following statements about inducible β-lactamase expression is true?

    <p>It requires exposure to an inducing agent.</p> Signup and view all the answers

    Which β-lactamase inhibitor is commonly used to confirm ESBL production?

    <p>Clavulanic acid</p> Signup and view all the answers

    Which organisms are known for constitutive expression of β-lactamases?

    <p>Haemophilus and Neisseria spp.</p> Signup and view all the answers

    What type of disease is caused by Bartonella henselae?

    <p>Bacillary angiomatosis</p> Signup and view all the answers

    Which method is used for the detection of 'Donovan bodies' in Klebsiella granulomatis?

    <p>Giemsa-stained tissue smears</p> Signup and view all the answers

    What is the transmission method for Spirillum minus?

    <p>Rat bites and scratches</p> Signup and view all the answers

    Which of the following is a characteristic of Barttonella henselae?

    <p>Slow growth on CHOC and BAP</p> Signup and view all the answers

    Which staining method is associated with detecting organisms in tissue from Bartonella infections?

    <p>Warthin-Starry stain</p> Signup and view all the answers

    What is a common characteristic of Ureaplasma urealyticum?

    <p>It causes non-chlamydial urethritis.</p> Signup and view all the answers

    What is required for specimen collection of Mycoplasma and Ureaplasma?

    <p>Immediate plating or storage at -70°C.</p> Signup and view all the answers

    What is typically observed in cultures of Mycoplasma?

    <p>Fried-egg colony morphology.</p> Signup and view all the answers

    How long are cultures typically incubated for M.pneumoniae?

    <p>3-4 weeks.</p> Signup and view all the answers

    What is the recovery rate sensitivity for Mycoplasma from cultures?

    <p>40%</p> Signup and view all the answers

    What type of organisms do the Rickettiaceae family primarily consist of?

    <p>Obligate intracellular parasites.</p> Signup and view all the answers

    Which of the following methods is used for the diagnosis of M.pneumoniae?

    <p>Radiography.</p> Signup and view all the answers

    What is not a characteristic feature of a culture for Ureaplasma?

    <p>Fried-egg colony morphology.</p> Signup and view all the answers

    Which type of immune response is primarily associated with Ehrlichia chaffeensis?

    <p>Cell-mediated immunity</p> Signup and view all the answers

    Which of the following is a characteristic of Anaplasma phagocytophilum?

    <p>Infects neutrophils</p> Signup and view all the answers

    What is one of the primary symptoms associated with Coxiella burnetii infection?

    <p>Flulike symptoms</p> Signup and view all the answers

    What kind of organism is Coxiella burnetii classified as?

    <p>Obligate intracellular gram-negative coccobacilli</p> Signup and view all the answers

    Which diagnostic method is noted for having 90% sensitivity and 100% specificity for Ehrlichia and Anaplasma identification?

    <p>Nucleic acid amplification testing (PCR)</p> Signup and view all the answers

    Which zoonotic disease is associated with Coxiella burnetii?

    <p>Q fever</p> Signup and view all the answers

    What type of cells do both Ehrlichia chaffeensis and Anaplasma phagocytophilum replicate within?

    <p>Phagocytes</p> Signup and view all the answers

    What symptom is commonly associated with Bartonella quintana infection?

    <p>Trench fever</p> Signup and view all the answers

    What type of infection is associated with psittaci?

    <p>Acute lower respiratory infection</p> Signup and view all the answers

    Which term describes the lowest concentration of antibiotic that kills more than 99.9% of an organism?

    <p>Minimum bactericidal concentration (MBC)</p> Signup and view all the answers

    What does 'susceptible' indicate in antimicrobial susceptibility testing?

    <p>The organism is inhibited by the standard drug level</p> Signup and view all the answers

    What is the purpose of the Clinical and Laboratory Standards Institute (CLSI)?

    <p>Create interpretative standards for susceptibility testing methods</p> Signup and view all the answers

    What is an important factor in selecting an ideal antibiotic?

    <p>It has selective toxicity without harming the patient</p> Signup and view all the answers

    In susceptibility testing, which group reports the primary antimicrobial agents used first?

    <p>Group A</p> Signup and view all the answers

    What does it mean if an organism is categorized as 'intermediate'?

    <p>Higher doses may be needed for inhibition</p> Signup and view all the answers

    What is the primary requirement for preparing an inoculum for antimicrobial susceptibility testing?

    <p>Ensuring the culture is pure</p> 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 - covers only certain groups
      • Broad spectrum - covers gram-positive and gram-negative
    • Mechanism of action - the way an agent harms an organism
      • 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 the sum of the activity of individual antimicrobial agents (1+2=3)
    • Synergism - effect is amplified (1+2=4)
    • Antagonism - one agent interferes with the activity of another (1+2=1)

    Cell Wall Characteristics

    • Not found in mammalian cells
    • Cell wall characteristics affect the spectrum of antibiotic activity
    • Gram-positive - thick peptidoglycan cell wall
    • Gram-negative - thin peptidoglycan surrounded by an outer membrane
    • Peptidoglycan is also known as the murein layer

    Gram-Positive and Gram-Negative Cell Walls

    • Gram-positive cell wall structure: Shows a thick layer of peptidoglycan, teichoic acid, and an inner cytoplasmic membrane
    • Gram-negative cell wall structure: Shows a thin peptidoglycan layer and an outer membrane with lipopolysaccharides (LPS), proteins, lipoproteins etc, and an inner cytoplasmic membrane

    Gram-Positive and Gram-Negative Cell Walls - Inner (Cytoplasmic) Membrane

    • 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 (cephalexin, cefotaxime, ceftriaxone)
      • Monobactams (aztreonam)
      • Carbapenems (imipenem, doripenem, ertapenem)
    • Glycopeptides
      • Vancomycin
      • Dalbavancin

    Other

    • Polymyxins
      • Plasma membrane disruption
      • Active against gram-negative bacteria
    • Nitrofurantoin
      • Treat 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)
    • For UTIs, enteric infections

    DNA and RNA

    • DNA replication
    • DNA gyrase
    • DNA transcription/RNA polymerase

    DNA Replication Inhibition

    • Enzymes required for DNA replication
      • Topoisomerases
      • DNA gyrases
    • Quinolones/fluoroquinolones
      • Ciprofloxacin, levofloxacin, gemifloxacin
    • Inhibit topoisomerase IV and/or DNA gyrase
    • 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 anaerobes
    • 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
    • Oxazolidinone (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 are 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 alterations in cellular physiology or structure due to genetic change.
      • 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 features)

    • 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 GP and GN organisms
      • Most common = penicillinase
      • Virtually all GN bacteria are intrinsically resistant via beta-lactamase production, Staph are common GP producers.
      • Cephalosporins were created to be forever resistant to all beta-lactamase enzymes
      • Extended-spectrum beta-lactamases (ESBLS) - inactivate all penicillins and cephalosporins
    • Target site modification
      • Drug binds poorly (or not at all) to target site, altering of PBP decreases affinity
      • Mutations to topoisomerase IV and DNA gyrase increases resistance
      • Addition of methylase to ribosome decreases binding

    Mechanisms of Resistance (Continued)

    • Vancomycin resistance
      • vanA, vanB, vanC genes
      • vanA on plasmid = transmissible
      • Van-R enterococci transfer resistance to staph
      • Vancomycin intermediate S. aureus (VISA) and vancomycin resistant S. aureus (VRSA)
    • Acquisition of new target site
      • mecA gene in MRSA encodes for a low affinity PBP, resistant to all penicillins, found in mobile SCCmec cassette
    • Bypass mechanisms
      • Organisms circumvent consequences of antimicrobial action
      • Anaerobes are intrinsically resistant to aminoglycosides (lack oxidative electron transport system)

    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 expresses resistance
    • Heterogeneous - some bacteria in population express resistance (MRSA)

    Chlamydia

    • Three species cause human diseases: C. trachomatis, C. pneumoniae, C. psittaci
    • Differ from other bacteria:
      • Do not grow on nonliving media
      • Sensitive to interferon
      • Obligate intracellular parasites
    • Characteristics
      • Obligate intracellular parasite
      • Dependent on host for adenosine 5'-triphosphate (ATP)
      • Lack energy metabolism
      • Grow and multiply only inside animal or host epithelial cells
    • Replication cycle
      • Elementary body (EB) - infectious
      • Reticulate body (RB) - non-infectious
      • EB infects host cell, organizes into RB, then multiply
      • Host cell ruptures and releases EB
    • Antigens
      • Outer membrane similar to Gram-negative but no peptidoglycan
      • Components = Lipopolysaccharide (LPS), Major outer membrane protein (MOMP)
      • Species subdivided into serotypes (serovars) based on MOMP

    C. trachomatis biovars

    • Trachoma (serovars A-K) - chronic eye infection
    • Inclusion Conjuctivitis (serovars D-K) - milder eye infections, colonizes nasopharynx
    • Lymphogranuloma venereum (LGV, serovars L1, L2, L2a, L2b, L3) - invasive urogenital disease
    • Newborn Chlamydia trachomatis - passed through birth canal, conjunctivitis, pneumonia, or nasopharyngeal infection

    C. Pneumoniae

    • Mild or asymptomatic infection in young adults
    • Prolonged pharyngitis, bronchitis, or pneumonia
    • Potential risk factor for Guillain-Barré Syndrome, asthma, and cardiovascular disease

    C. psittaci

    • ornithosis (psittacosis, parrot fever)
    • zoonotic infection
    • occupational hazard for pet bird handlers and poultry workers
    • acute lower respiratory infection, cultures are not sensitive; diagnosed serologically

    Antimicrobial Susceptibility Testing and Therapy

    Ideal Antibiotic

    • Selective toxicity - exerts effects on the agent of disease without harming the patient
    • Treats diseases caused by both Gram-positive and Gram-negative organisms
    • Host does not develop hypersensitivity or allergic reaction
    • Agent penetrates into tissues and crosses the blood-brain barrier
    • Cost is minimal

    Susceptibility Terms

    • Minimum inhibitory concentration (MIC): lowest antibiotic concentration that inhibits microbial growth
    • Minimum bactericidal concentration (MBC): lowest antibiotic concentration that kills >99.9% of microorganisms
    • Susceptible/sensitive: interpretive category; indicates organism is inhibited by a particular dose of antibiotic.
    • Intermediate: interpretive category; indicates organism may require higher dose of antibiotic for longer period to be inhibited
    • Resistant: interpretive category; indicates organism is not inhibited by recommended antibiotic dose or achievable level

    Susceptibility Standards (e.g., CLSI or NCCLS)

    • Develops standards for susceptibility methods
    • Testing categories: susceptible (S), intermediate (I), resistant (R)

    Test Batteries

    • Panel of 10-15 antimicrobial agents for routine testing
    • Panels selected based on organism group (GN, GP, urine)
    • Group categorization for primary agents and any supplemental groups

    Preparation of Inoculum

    • Requires pure culture
    • Most important step of all susceptibility testing
    • Determine # of bacteria per mL
    • Compare to McFarland standards (e.g., McFarland 0.5)

    Standardized Testing Methods

    • Broth dilution method: antibiotic suspended in a solution
    • Agar dilution method: antibiotic incorporated into the agar medium
    • Diffusion method: uses antibiotic-impregnated disks or strips
    • Special methods: additional techniques for specific organisms/ situations

    Broth Dilution Tests

    • Provides MIC
    • Uses Mueller-Hinton broth for serial dilutions, adding 2-5% horse blood (when needed).
    • Final bacterial concentration = 5 x 105 CFU/mL.
    • Methods: macrodilution (tubes with 1-2 mL broth), microdilution (microtiter trays with 0.05-0.1 mL)
    • Internal controls (growth control, sterility check)
    • MBC involves culturing on BAP to get bacterial colonies vs. initial colony count.

    Serum Bactericidal Test

    • Tests patient's serum (with antibiotics) against infecting organism
    • Incubation overnight and examining for growth
    • Measures peak and trough serum samples

    Microdilution

    • Similar to macrodilution, but uses plastic panels with wells for precise concentrations.

    Agar Dilution Tests

    • Semi-quantitative, incorporated antimicrobial agents into agar medium, uses agar plates with varying concentrations, standardized suspension is inoculated and incubated and examined for growth.

    Disk Diffusion Tests (Kirby-Bauer)

    • Paper disks impregnated with antibiotic placed on inoculated plates.
    • Incubated at 35˚C → measure zone of inhibition.
    • Larger zones = more antimicrobial activity/greater diffusion.
    • No zone = complete resistance.
    • Mueller-Hinton Agar criteria = standard media, QC strains are tested with E. coli, S. aureus & P. aeruginosa
    • Agar depth: 4 mm, too thin = increases zones, too thick = decreases zones, False susceptibility + resistance
    • pH 7.2-7.4 (important for results) , Decreased pH = decreased activity of aminoglycosides, erythromycin, and clindamycin & increased activity of tetracyclines, Increased pH has opposite effect.
    • Fixed cation concentration (Ca++ & Mg++) = increased concentrations = decreased aminoglycosides activity against P. aeruginosa and decreased activity of tetracyclines

    Diffusion E-Test

    • Agar plates inoculated → plastic strip containing gradient of antimicrobial agent on agar surface → incubated & examined for an elliptical zone of inhibition.

    Test Performance

    • Inoculum from overnight growth
    • MHA plus sheep blood for strep
    • Incubated in 5-7% CO2
    • Use Chocolate MHA as needed
    • Store disks properly
    • Check for potency
    • Allow disks to warm to room temperature before use

    Reading and Interpretation

    • Lawn of growth must be confluent
    • Ignore small colonies, Proteus Spp., swarming
    • Contamination & mixed cultures cannot be ignored
    • Resistant subpopulation

    Special Tests

    • Beta-lactamases, ESBLs, carbapenemases, altered PBPs
    • Inducible macrolide resistance
    • Oxacillin resistance
    • High-level aminoglycoside resistance
    • Anaerobes

    Beta-Lactamase Tests

    • Detects beta-lactamase-mediated resistance (penicillin, ampicillin)
    • Rapid tests are useful for H. influenzae, N. gonorrhoeae, Morexella catarrhalis → Staphylococcus spp.,Bacteroides spp.
    • Methods
      • Nitrocefin
      • Acidimetric
      • lodometric

    ESBLs (Extended-Spectrum Beta-Lactamase) Tests

    • Typically seen in Klebsiella, Proteus, & E. coli
    • Test against cephalosporins & monobactams (cefpodoxime, ceftazidime, cefotaxime, ceftriaxone, aztreonam)
    • Confirm with Clavulanic acid

    Carbapenemases

    • Initially identified in K. pneumoniae (KPC)
    • Now in many Enterobacteriaceae
    • Resistance to carbapenems (imipenem, meropenem, ertapenem)

    Altered PBPs

    • Detect penicillin resistance in pneumococci w/ Oxacillin disk → more accurate than penicillin disk

    Macrolide Resistance

    • Isolate appears erythromycin resistant but clindamycin is susceptible
    • Inducible clindamycin resistance may be present
    • D test must be performed

    Oxacillin-Resistant Staphylococci (MRSA)

    • Oxacillin is more reliable than methicillin
    • Belong to same class of agents as penicillinase-resistance penicillins
    • Isolate resistant to one = resistant to all
    • Mec-A-mediated resistance makes staph heteroresistant/difficult to detect
    • Modifications
      • Supplement MH with 2% NaCl
      • Incubate at <35°C for 24 hrs

    Vancomycin Resistance

    • MRSA isolates with resistance to vancomycin (VISA, VRSA)
    • Recommended method of detection in staph/enterococci — Broth dilution
    • Vancomycin agar screen (at 6 µg/mL) for heteroresistant strains (hVISA)

    High-Level Aminoglycoside Resistance in Enterococci

    • Enterococci may be treated with ampicillin/penicillin
    • Bacteriostatic only
    • Combined with aminoglycoside to achieve bactericidal effect
    • Enterococci are intrinsically resistant
    • Synergistic with cell wall active agent High-level aminoglycoside resistance due to enzymatic inactivation. Detect using broth, agar, or disk. Screening concentrations (broth = 500 to 1000 µg/mL)

    Anaerobes

    • Agar dilution (use supplemented Brucella laked sheep blood agar)
    • Broth microdilution (Brucella broth with lysed horse blood)
    • Inoculum is higher (1 x 106 CFU/mL)
    • Incubation is longer (48 hrs)

    Automated Systems

    • Optical methods to detect susceptibility endpoints
    • Turbidometric
    • Hydrolysis of fluorometric growth substrate (analyses in shorter period: 5-15 hours)
    • Use microprocessors

    QC (Quality Control)

    • Interpretations determined by CLSI
    • Reference strains (ATCC)
    • Defined susceptibility/resistance patterns
    • Range of endpoints (S, I, R)
    • Endpoint is on-scale
    • Acceptable results defined → Weekly testing
    • Supplemental QC: periodic testing (MRSA, ampicillin-resistant E. cloacae)
    • Predictor Drugs
      • Staphylococci resistant to oxacillin
      • Enterococci with high-level aminoglycoside resistance
      • Enterococci resistant to ampicillin

    Susceptibility Testing (required for specific organisms)

    • Full susceptibility testing is required for staphylococci, S. pneumoniae, viridans strep (if from a sterile site), enterococci, Enterobacteriaceae, P. aeruginosa, & Acinetobacter spp
    • Testing occasionally required (beta-lactamase testing) for H. influenzae, N. gonorrhoeae, Morexella catarrhalis, anaerobes, Beta-hemolytic streptococci, Neisseria meningitidis, Listeria monocytogenes

    Miscellaneous Bacteria

    • Mycoplasma, Ureaplasma, Rickettsia, Ehrlichia, Coxiella burnetii, miscellaneous GNR.

    Mycoplasma & Ureaplasma

    • Belong to class Mollicutes
    • Size of a large virus; smallest self-replicating microorganisms
    • Colonize mucous membranes of RT & UGT
    • Humans and animals
    • Sexual contact
    • Mother-to-child and respiratory secretions
    • No cell wall, do not gram stain, pleomorphic
    • Utilize sterols to create membrane support; resistant to penicillin & cephalosporins
    • Slow-growing, fastidious; cell culture.
    • Mycoplasma pneumoniae (primary atypical pneumonia; walking pneumonia)
    • Mycoplasma hominis (colonizes UGT, opportunistic pathogen — PID, salpingitis, pyelonephritis)
    • Other mycoplasma species (M. genitalium, M. fermentans, and M. penetrans)

    Ureaplasma urealyticum

    • Colonizes urogenital tract, nonchlamydial & nongonococcal urethritis in men, associated with upper genital tract infections in women
    • Hydrolyzes urea.
    • Can be transmitted to newborns at delivery; set up culture if meningitis is suspected; negative gram stain & culture.

    Rickettsiae & Similar Organisms

    • Arthropod-borne
    • Obligate intracellular parasite
    • Gram-negative coccobacilli
    • Rickettsia spp.
    • Ehrlichia spp.
    • Coxiella burnetii
    • Predilection for endothelium of blood vessels; never grown in cell-free media
    • Nonmotile
    • Two groups (spotted fever group, typhus group)

    Rickettsial Spotted Fever Group

    • R. rickettsiae: Rocky Mountain Spotted Fever, vector is ticks, flu-like symptoms, characteristic rash on hands & feet, disseminated infection (lungs, brain, heart), 20% mortality rate if untreated
    • R. akari: Rickettsialpox, vector is mouse mites, similar to RMSF but milder, rash on face, body, and extremities (not on palms & soles), Eastern US

    Rickettsial Typhus Group

    • R. typhi: Endemic typhus or murine typhus, vector is rat fleas, flu-like symptoms & +/- rash
    • R. prowazekii: Epidemic louse-borne typhus, war & natural disasters, vector is human body & squirrel louse, flu-like symptoms, rash on palms, soles, face; 40% mortality if untreated, Brill-Zinsser disease = reactivation of infection.

    Orientia tsutsugamushi

    • Formerly Rickettsia, causes scrub typhus, vector is rat chigger, flu-like symptoms & rash.

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