Anaerobic Bacteria Overview
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Questions and Answers

Which bacterium is the most common anaerobe associated with actinomycosis?

  • Nocardia
  • Propionibacterium
  • A. israelii (correct)
  • Bifidobacterium

    • What is a characteristic feature of the Actinomyces Gram stain?

  • Spore-forming structure
  • Beaded appearance with branching filaments (correct)
  • Uniformly round shape
  • Coccoid appearance

    • What are sulfur granules associated with in actinomycosis?

  • Biofilm development
  • Fistula drainage (correct)
  • Toxin production
  • Chronic abscess formation

    • Which of the following statements about Bacteroides fragilis is true?

    <p>It is bile resistant and can hydrolyze esculin.</p> Signup and view all the answers

    What is the characteristic growth pattern of A. israelii in culture?

    <p>Presence of molar-tooth colonies after 7-9 days</p> Signup and view all the answers

    Which of the following statements is true regarding Propionibacterium?

    <p>It is often found as a contaminant in blood cultures.</p> Signup and view all the answers

    Peptostreptococcus species are primarily characterized by which of the following?

    <p>GPR in chains</p> Signup and view all the answers

    Which of the following bacteria is known for its association with 'lumpy jaw'?

    <p>A. israelii</p> Signup and view all the answers

    What type of bacteria does Kanamycin-vancomycin laked blood (KVLB) agar primarily select for?

    <p>Bacteroides and Prevotella</p> Signup and view all the answers

    Which gas mixture is predominantly used in anaerobic incubation?

    <p>Nitrogen, hydrogen, and carbon dioxide</p> Signup and view all the answers

    What is the key indicator used in anaerobic jars to determine the oxidative state?

    <p>Methylene blue or resazurin</p> Signup and view all the answers

    Which agar is selective for identifying Clostridium difficile?

    <p>Cycloserine-cefoxitin-fructose agar</p> Signup and view all the answers

    What temperature range is optimal for anaerobic incubation?

    <p>35 to 37°C</p> Signup and view all the answers

    Which of the following statements about anaerobic chambers is accurate?

    <p>They provide a controlled environment for inoculating and examining media.</p> Signup and view all the answers

    Which type of bacteria is indicated by a Gram stain displaying Gram negative rods?

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

    What characteristic is utilized by C. difficile to increase the pH of its environment?

    <p>Metabolism of proteins</p> Signup and view all the answers

    What does a growth pattern of only on anaBAP indicate regarding the isolate's aerotolerance?

    <p>It is a strict anaerobe.</p> Signup and view all the answers

    Which of the following statements is true regarding the antibiotic sensitivity of Gram-positive and Gram-negative bacteria?

    <p>Most GP are sensitive to vancomycin and resistant to kanamycin.</p> Signup and view all the answers

    What is the purpose of the Nagler test?

    <p>To detect the alpha toxin of C. perfringens.</p> Signup and view all the answers

    How can one determine if an isolate is an aerotolerant anaerobe?

    <p>Equal growth on both anaBAP and CHOC.</p> Signup and view all the answers

    What does a positive lecithinase reaction on Egg Yolk Agar (EYA) indicate?

    <p>An opaque zone surrounds the growth.</p> Signup and view all the answers

    What distinguishes a strict anaerobe from a facultative anaerobe during growth observation?

    <p>Growth pattern on anaerobic media only.</p> Signup and view all the answers

    Which of the following organisms is likely to be sensitive to sodium polyanethol sulfonate (SPS) disks?

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

    Which bacterial characteristic is determined using the motility test?

    <p>Movement through a liquid medium.</p> Signup and view all the answers

    At what temperature does L.monocytogenes exhibit tumbling motility?

    <p>25°C</p> Signup and view all the answers

    What is the umbrella-like growth pattern characteristic of?

    <p>L.monocytogenes</p> Signup and view all the answers

    Which test is positive for L.monocytogenes that distinguishes it from other Listeria species?

    <p>CAMP test</p> Signup and view all the answers

    What type of hemolysis is typically associated with Erysipelothrix rhusiopathiae?

    <p>Gamma hemolysis</p> Signup and view all the answers

    Which organism is implicated in causing bacterial vaginosis?

    <p>Gardnerella vaginalis</p> Signup and view all the answers

    Which characteristic best describes Lactobacillus?

    <p>Non-spore forming</p> Signup and view all the answers

    What is a key distinguishing feature of Arcanobacterium haemolyticum?

    <p>Beta hemolysis</p> Signup and view all the answers

    Which statement about Erysipelothrix rhusiopathiae is correct?

    <p>It causes erysiploid lesions in animals and humans.</p> Signup and view all the answers

    What is the minimum volume of sputum required for collection?

    <p>5-10 ml</p> Signup and view all the answers

    What is the role of the BACTEC 9000MB system in specimen collection?

    <p>To check oxygen concentration</p> Signup and view all the answers

    Which characteristic describes slow growers among mycobacteria?

    <p>Visible colonies only after more than 7 days</p> Signup and view all the answers

    Which test is likely performed first to confirm the presence of mycobacteria?

    <p>Acid fast stain</p> Signup and view all the answers

    How is the catalase test conducted for mycobacterium identification?

    <p>By adding hydrogen peroxide to heated and room temperature samples</p> Signup and view all the answers

    What does positive growth on TB liquid or solid media indicate?

    <p>Potential presence of mycobacteria</p> Signup and view all the answers

    What is evaluated when determining the photoreactivity of mycobacteria?

    <p>Their ability to produce pigments in response to light</p> Signup and view all the answers

    Which of the following tests can be used to evaluate the biochemical properties of mycobacteria?

    <p>Tween 80 hydrolysis test</p> Signup and view all the answers

    What is the primary symptom associated with Stage 1 of Lyme disease?

    <p>Erythema chronicum migrans</p> Signup and view all the answers

    Which organism is responsible for causing relapsing fever?

    <p>Borrelia recurrentis</p> Signup and view all the answers

    Which laboratory method is most commonly used for the microscopic examination of blood during febrile periods in relapsing fever?

    <p>Giemsa or Wright’s stain</p> Signup and view all the answers

    What stage of Lyme disease is characterized by systemic symptoms such as fever, bone pain, and malaise?

    <p>Stage 2</p> Signup and view all the answers

    What factor complicates the serologic testing for relapsing fever?

    <p>Antigenic variation</p> Signup and view all the answers

    Which type of tick is responsible for spreading Borrelia burgdorferi?

    <p>Ixodes tick</p> Signup and view all the answers

    What characterizes the cyclic relapses experienced by patients with relapsing fever?

    <p>Antigenic variation</p> Signup and view all the answers

    Which of the following symptoms is NOT typical of Lyme disease in its late stage?

    <p>Erythema migrans</p> Signup and view all the answers

    Study Notes

    Anaerobic Bacteria

    • Anaerobic bacteria do not need oxygen to grow
    • They vary in their tolerance to oxygen
    • Obligate anaerobes require anaerobic conditions for growth; oxygen is toxic to them and kills them
    • Aerotolerant anaerobes can grow in the presence of oxygen but grow best in anaerobic environments
    • Facultative anaerobes do not require oxygen but will use it if it is available

    Oxygen Reduction

    • Superoxide anion and hydrogen peroxide are toxic
    • Strict aerobes and facultative anaerobes have superoxide dismutase and/or catalase to neutralize these toxic substances

    Oxidation-Reduction (Redox) Potential

    • Anaerobic bacteria require low redox potential
    • High redox environments contain oxygen
    • Normal human tissue and aerobic culture media have high redox potential
    • Reducing agents like thioglycollate, cysteine, and dithiothreitol are included in anaerobic media

    Normal Habitat

    • Soil, water, and animals
    • Human normal flora (NF) includes oral cavity, upper respiratory tract (URT), intestinal tract, genitourinary tract, and skin.
    • Facultative organisms use oxygen in protected areas, to reduce redox potential and inactivate harmful oxygen molecules

    Diseases

    • Exogenous infections are caused by organisms, spores, or toxins entering the body through ingestion or trauma (e.g., tetanus, botulism)
    • Endogenous infections occur near mucosal surfaces (e.g., bacteremia, abscesses, gas gangrene, pneumonia)

    Clues to Anaerobic Diseases

    • Deep or puncture wounds; animal or human bites
    • Foul-smelling, gaseous discharge
    • Necrotic tissue, vascular stasis
    • Presence of sulfur granules (actinomycosis)
    • Black or fluorescent red color
    • Previous therapy with aminoglycosides (aminoglycosides are ineffective against anaerobes)
    • Failure to grow organism on a Gram stain

    Specimen Collection

    • Appropriate specimens include blood, sterile body fluids (CSF), bone marrow, cavity fluid, urine (when collected as a suprapubic aspirate), abscesses, ulcers, and draining wounds.
    • Biopsy material.
    • Inappropriate specimens include superficial skin sites; voided or catheterized urine; expectorated sputum, throat, or nasopharyngeal swabs, bronchial washings; vaginal, cervical, and urethral swabs; and stool or rectal swabs.

    Transport and Processing

    • Inoculate media and place immediately in an anaerobic environment
    • Limit exposure to room air; do not allow to dry out
    • Do not refrigerate specimens
    • Minimize time at room temperature.
    • PRAS media, anaerobically sterilized transport medium is needed; modified Cary-Blair or Amies agar is used
    • Rezasurin indicator, used to show the amount of oxygen. Reducing substances help protect against oxygen and inhibit NF.
    • A sterile container is required

    Culture

    • Specimens for anaerobic culture are cultured aerobically on BAP, CHOC, MAC, and on anaerobic media to correlate aerotolerance
    • Anaerobes require vitamin K, hemin, and yeast extract.

    Nonselective Media

    • CDC (or anaerobic blood agar plates) support the growth of obligate and facultative anaerobes
    • Anaerobic broth, supplemented with thioglycollate or chopped (cooked) meat, supports the growth of all obligate and facultative anaerobes, with anaerobes growing towards the bottom and facultative organisms growing throughout.

    Aerotolerance

    • Testing determines whether an isolate is strict or facultative by incubating the isolate in both aerobic and anaerobic environments.
      • Growth only on anaBAP suggests a strict anaerobe
      • Growth on both anaBAP and CHOC suggests a facultative anaerobe
      • Growth only on CHOC suggests an aerotolerant anaerobe

    Fluorescence

    • Fluorescence occurs under ultraviolet light (366 nm) with colors of red, orange, pink, and chartreuse

    Rapid Identification Tests

    • Catalase test
    • Motility test
    • Urease test
    • Indole
    • Esculin hydrolysis
    • Aerotolerance
    • Fluorescence
    • Disk tests
    • Lecithinase
    • Naglar test
    • Lipase
    • Reverse CAMP

    Specimen Collection (Mycobacteria)

    • Sputum, bronchial washings, gastric contents, urine, stool, and tissue
    • First morning sputum, on 3 consecutive mornings, 5-10 ml volume, refrigerate overnight.
    • If sputum isn't produced, bronchoscopic washings (BAL) or biopsy.
    • Gastric aspirate or washing
      • Young children < 3 years cannot produce their own sputum, often swallow sputum. The mycobacteria can be destroyed by stomach acid. If this is the specimen, neutralize the aspirates or urine with sodium bicarbonate.
    • Urine
      • Neutralize with sodium bicarbonate if refrigerated overnight.
    • Stool
    • AIDS patients need M. avium screening.
    • Inappropriate specimens, such as swabs, may not contain enough material or the mycobacteria may not dislodge. 24-hour pooled sputum or urine specimens may hinder the analysis due to contamination or organism inhibition from the interference.

    Digestion and Decontamination

    • Specimens from sterile sites can be concentrated and directly inoculated. Specimens with normal flora and mucus need digestion (like N-acetyl-L-cysteine, or NALC) then decontamination with NaOH.
    • Concentration increases the number of organisms per mL of sample.
    • Centrifuge, then make AFB smear and inoculate media with the sediment. Use both liquid and solid media in the testing.

    Specimen Processing

    • Digestion frees bacteria from protein clumps using NALC (mucolytic agent)
    • Decontamination removes normal flora (NF)
    • Mycobacteria resist many bactericidal effects due to their high lipid concentration
    • Decontaminate to kill contaminants without harming mycobacteria.

    Staining for AFB Smear

    • Ziehl Neelsen (hot stain) and Kinyoun stain (cold stain) use heat or the reagent, respectively, to force the stain into the cell, due to a high lipid cell wall content

    Mycobacteria Identification

    • Slow-growing mycobacteria are distinguished from rapid-growing mycobacteria by their growth rate, which takes longer to complete.
    • Different colony morphologies will vary (e.g., ruffled, buff colored, cording, or cauliflower shape)
    • The presence or absence of pigmentation differs between species.
    • Photoreactivity tests evaluate the production of carotenoid pigments in different species.
    • Several biochemical tests will differentiate species (like catalase, niacin, nitrate reduction, Tween 80 hydrolysis, and tellurite reduction

    Culture Examination

    • Examine twice weekly for the first month, once per week thereafter.
    • Examine agar-based cultures (microcolonies) with a microscope at 4x-10x.
    • Examine egg-based cultures (hand-lens)

    Other Pathogenic Species

    • These include M. genavense, M. simiae, M. xenopi, M. szulgai.

    Newer Identification Tests

    • These tests use different methods to identify mycobacteria (e.g., chromatography and molecular identification)

    Antimicrobial Susceptibility Tests

    • Susceptibility tests of M. tuberculosis include isoniazid. rifampin, ethambutol, and streptomycin
    • Susceptibility methods include absolute concentration methods, resistance ratio, and proportional testing procedures

    Classification of Mycobacteria

    • M. tuberculosis Complex (including M. tuberculosis)
    • Nontuberculous mycobacteria (NTM) (also known as mycobacteria other than tuberculosis or MOTT) such as those in the M. avium complex
    • Uncultivable mycobacteria (which are difficult to grow in the laboratory)

    Anaerobic GNR

    • Normal flora of mucous membrane. This group includes Bacteroides, Prevotella, Prophyromonas, Fusobacterium, and Veillonella
    • The Bacteroides fragilis are a subgroup

    Anaerobic GPC

    • includes Peptostreptococcus, which are chains, and Peptococcus, which are clusters. Specific tests like the sodium polyanethel sulfonate test differentiate these genera.

    Anaerobic GPR

    • includes Actinomyces spp, Bifidobacterium spp, Propionibacterium spp, Eggerthella spp. and Eubacterium, and all can present in actinomycosis

    Other Non-spore-forming GPR

    • includes Corynebacterium, Listeria, Erysipelothrix, Acranobacterium, Lactobacillus, and Gardnerella

    Spirochetes

    • Examples include Borrelia, Leptospira, and Treponema. There are many subgroups, which can have diverse characteristics.

    Borrelia

    • The Borrelia genus is responsible for Lyme disease, which is transmitted by arthropods. Some Borrelia cause relapsing fever.

    Treponema

    • T. pallidum, including the subtypes pallidum, pertenue, endemicum, and carateum, are responsible for syphilis infections. There are various stages of disease.

    Leptospira

    • This genus is responsible for Leptospirosis, often a zoonotic spread from animals, like dogs, rats, or cattle, through contact with contaminated water from urine.

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