Lecture 10 Mycobacteriology And Other Odd Bacteria (Chapters 48, 49, 50, 51)

I. Mycobacteria

    A. Description of Genus - Thin, rod shaped, non-motile, acid fast bacteria (AFB), unique waxy-lipid cell wall - mycolic acid, resistant to drying, slow growing

(related bacteria include Nocardia, Actinomycetes, and Corynebacterium)

     B. Mycobacterial species

        1. (71 species) Most well known are M. tuberculosis, M. bovis, M. avium, M. leprae  -typically divided into two main groups dependent upon whether they can produce tuberculosis or not. Tuberculosis complex slow growing, non-pigmented (M. tubersulosis, M. bovis, M. bovis BCG, M. africaanum) and NTM (non-tuberculosis mycobacteria - Runyon) - pigmented and some relatively fast growers e.g. M. avium (np). M. gordonae (s), M. kansasii (p).

        2. Significant as normal flora as well as pathogens, ubiquitous

        3. BCG - (PPD) is the vaccine form of M. bovis - used outside of the US with controversial efficacy

        4. Tb skin test is used for epidemiology reporting and control in the US

    C. Significant Laboratory characteristics for identification

        1. Culture - due to slow growth, potential contamination, desire to get typical colony morphology -  specialized media such as Lowenstein Jensen L-J (an egg based medium) and Middlebrook 7H10 are used.

These images come from the archives of Dr. W. Keith Hadley, M.D., Ph.D

        2.  Specimens - typically sputum - (usually mulitple X3), Gastric lavage, urine, blood, bone, feces (HIV patients - controversial utility), wounds

        3. Decontamination procedures for specimens - digestion - NaOH

see chart page 549

These images come from the archives of Dr. W. Keith Hadley, M.D., Ph.D

            4. NTM classified as photochromogens (pigmented only when grown in the light) and scotochromogens (pimented in light or dark)

        5. Stain and cultural morphology are essential

        6. Staining - Zeihl-Neelsen, Kinyoun, fluorochrome

        7. Rapid growth for Mycobacteria is less than 7 days, tuberculosis complex specimens are not conseidered negative under regular culturing techniques for 6 weeks; MIGIT and RIA methods are faster, Probes are very useful

        8. Biochemical tests - see page 556, key tests include Niacin and nitrate reduction

    D. Pathology

        1. Ancient disease known as consumption, 1.7 million = 1/3 of world, 10 million in US

        2. Transmission through air, contact, consumed milk

        3. Can cause local and disseminated disease

        4. Major protection against Tb is the T-cell system, immunocompromised conditions predispose people to infection

    E. Issues related to Microbiology of Mycobacteria

        1. Non-compliance with treatment - due to length of regimen, must refrain from alcohol, length until diagnosis, chronic nature of disease, social factors (homeless, drug addicts, alcoholics), MDRTB

II. Obligate Intracellular Bacterial Pathogens - all require special transport, special culturing, serology (ELISA and fluorescent methods), Genomic identification

    A. Chlamydia trachomatis - STD, PID,

    B. Chlamydia psittaci - psittacosis

    C. Ricketssia - typhus

    D. Ehrlichia-

    E. Coxiella burnetti - Q fever

III. Cell Wall deficient - therefore not robust growers, direct detection best

    A. Mycoplasma pneumoniae-

    B. Ureaplasma

IV. Spirochetes - long, slender, helical, curved GNR that do not culture, serodiagnosis e.g. rpr, VDRL, fluorescent abs

    A. Treponema pallidum - syphilis

    B. Leptospira interrogans - leptospirosis

    C. Borrelia burgdorferi - lyme disease

Mycobacteria

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