Micro: TUBERCULOSIS

Morphology: Nocardia asteroides

- Gram positive, partially acid-fast, filamentous bacteria (look like hyphal elements in tissue) - Produces filaments which fragment to yield bacillary or coccoid forms. - Partial acid-fastness is attributed to the presence of mycolic acids of chain lengths shorter than those of the mycobacteria (45-50 carbon atoms versus 50-90 carbon atoms for mycobacteria).

Mycobacterium 4 most important species

- M. tuberculosis causing a chronic pulmonary disease (tuberculosis) - M. leprae causing a disease of skin and connective tissue destruction (leprosy). -A third category of opportunistic mycobacteria referred to as "atypical mycobacteria" contain species which may cause infections of the lungs or other organs. -M. avium-M. intracellulare has emerged as a causative agent of disseminated infection in AIDS patients, a form of infection which was rarely encountered before HIV.

Mycobacterium tuberculosis cell wall

- Mtb cell wall contains a thick peptidoglycan layer attached to arabinogalactans. -These are esterified to 60-90 carbon hydrophobic mycolic acids. -Additional lipids are also present. -Lipids represent 60% of the cell wall structure. -Anchored in the cell membrane are many proteins and lipoarabinomannan (LAM) which is functionally related to O-antigenic lipopolysaccharides. -Mycobacterial cell walls do not take up the dyes used in the Gram stain due to the high concentration of waxes and mycolic acids in their cell walls. -Special stains, Ziehl-Neelson or Kinyoun are used.

treat: Nocardia asteroides

- Sulfonamides are the agents of choice.

Mycobacterium tuberculosis morphology

- aerobic slender straight or curved, rod-shaped bacteria that are unusually resistant to drying, many disinfectants, acids and alkalis. - They are heat sensitive.

Nocardia asteroides transmission and disease state

- found in soil and disease is initiated by inhalation - with the production of pulmonary infection; or by direct inoculation into the skin or subcutaneous tissue. -The infection may disseminate hematogenously with subsequent involvement of any organ system, but there is a predilection for brain abscess formation.

Tuberculosis infection ( primary and 2nd)

- positive skin test, no physical findings of disease, chest X-ray normal or reveals old granulomas or calcification in lung or regional lymph nodes, may require preventative therapy. -90% of individuals with infection remain asymptomatic, ~5% develop disease within 2 years of infection (primary tuberculosis) and ~5% develop disease at some time later in life requentlywhen the individual's immune response wanes as a result of old age, immunosuppressive disease or therapy (reactivation disease).

Mycobacterium tuberculosis: pathenogenesis

- reach the lung they are ingested by alveolar macrophages where reproduce -The organisms are facultative intracellular pathogens that grow within non-activated macrophages and also outside of them. -The development of lesions and their healing or progression are determined by 1) the number of mycobacteria inhaled and their subsequent multiplication and 2) the immune response of the host -Macrophages and neucrotic lung tissue come together= granuloma

Two Step TST Testing

- should be conducted in certain populations. -The immune system's response to tuberculin may gradually wane over time. - may result in a false negative reaction in some people who were previously infected with TB if tested years after infection. -Two step testing allows "boosting" to occur in persons with TB infection in distant past. - An initially negative TST due to waning cutaneous immunity, may convert to positive due to awakening of the immune response if a second TST is placed within 2-3 weeks of the initial test. -Two step testing is recommended in healthcare workers and elderly patients, esp. people residing in nursing homes.

primary infection tb

-- positive skin test, normal chest X ray or old ganulomas -many -> assymptomatic = latent state for rest of life ( not clear if get rid of bacteria) 5%= local progression of infection so Gohn complex larger-> pna-> pulmonary disease some dissemination to other organs= miliary TB: small millets all over lungs 5%: Reactivation TB (2nd)= when hoset immunity is compromised with HIV, transplantm IV drug user ( new exposure can also do this)

Nucleic Acid Amplification Techniques: Mycobacterium tuberculosis

-- rapid tests that can identify M. tuberculosis in clinical specimens within a few hrs. -Sensitivity for smear positive specimens is very high, for smear negative - range of 45-75%. -The organisms must still be cultured for sensitivity testing. Technically complex and very expensive

comparing a large and small ag burden of tb

-A small antigenic burden may result in killing of the bacteria with minimal tissue damage, no symptoms develop and a positive skin test is the only evidence of infection. -A large infectious dose or an ineffective immune response may result in large areas of granuloma production with tissue necrosis and the development of disease associated with characteristic signs and symptoms.

Extrapulmonary TB: renal disease

-An infection of the renal parenchymal can occur. - Symptoms may include dysuria, frequency, flank pain. Fever & constitutional symptoms uncommon. -Patients have "sterile pyuria" meaning WBCs in the urine with no organisms seen on routine urine culture. - organism frequently grows in urine if repeated AFB urine cultures are performed.

Treatment of Active Tuberculosis:

-Before antibiotic sensitivity studies are reported the patient is treated in accordance with risk for multi-drug-resistant infection. - Initially all patients are treated with 4 drugs,then, those without multi-drug resistant disease are given 3 drugs. -with multi-drug resistant disease treated with 5 drugs based on the resistance patterns. -Appropriately treated individuals should have negative sputum cultures (i.e. no TB seen in sputum) in 85% of cases after 2 months of treatment and in 90-95% of cases at 3 months of treatment. - If the sputum culture remains positive at 3 months of treatment, consider nonadherence (patient not taking medication as prescribed. -You would also need to reevaluate for resistance to the current regimen.

Dx tb when there is a hx but findings are variable

-History of compatible symptoms in a patient with potential exposures/risk factors should raise your suspicious for TB. -The physical exam is often not specific and therefore not helpful. -Routine labs are also not specific. - Patients often have a normocytic anemia and may have an elevated ESR. -The WBC count varies widely and may be normal.

Culture: Mycobacterium tuberculosis

-Isolation and growth of the suspected mycobacterial species constitutes a confirmed diagnosis. -Specimens are inoculated onto complex media containing organic substances e.g., egg yolk, animal serum, tissue extracts. -These media often contain antibiotics or malachite green to inhibit the growth of other bacteria. - Biochemical tests may be used for identification but the use of species specific molecular probes is becoming widely available.

Media: Mycobacterium tuberculosis

-Lowenstein-Jensen (solid medium)- slow growth 3 to 8 weeks, Middlebrook 7H10 (liquid broth), liquid broth based media - combined with radiometric methods can yield results in 1-3 weeks, however not all strains grow in liquid broth so both types of culture must be done.

Lab dx: Nocardia asteroides

-Microscopic examination of sputum, skin lesions and surgical materials. Look for the presence of Gram-positive, branched filaments. May be mis-diagnosed as tuberculosis. -Grows on normal laboratory media over a wide range of temperatures. Incubate at 40°-50°C to inhibit the growth of most other bacteria. Culture under aerobic conditions.

Reactivation TB (Secondary pulmonary TB)

-Most cases of reinfection= reactivation of an old primary infection usually in apical portions of lung which then leads to chronic pulmonary disease characterized by one or more productive lesions. - associated underlying conditions which affect the immune system including alcoholism, diabetes, old age, immunosuppressive therapy and now AIDS. -Clinical manifestations : cough (most common symptom) and systemic symptoms such as fatigue and fever. -Chest radiographs usually show upper lobe involvement, usually with a cavitary lesion. - The sputum smear is usually positive and tuberculin skin testing is positive. -These patients can have TB pleurisy with rupture of the cavity or granuloma into pleural space and resultant empyema

Extrapulmonary TB: Mengitisis

-Patients can have meningitis which manifests as an indolent onset headache with systemic symptoms. CSF shows a lymphocyte predominance (polys early), low glucose, high protein. Imaging shows enhancement of the basilar meninges

infection control for pt with tb

-Patients with suspicion for TB should be placed on respiratory isolation to prevent transmission. -Respiratory isolation includes placement in a negative pressure room with doors closed. -All personnel caring for the patient should wear N95 masks will in the patient's room. -For patients with known pulmonary TB, respiratory isolation should be maintained during first 2 weeks of effective chemotherapy. -Contact tracing and screening programs are both important parts of TB infection control

CXR findings in primary vs secondary tb

-Primary disease is more likely to show a lower lobe infiltrate and possibly a Ghon complex. - reactivation pulmonary disease, CXR is more likely to show upper lobes involvement with a possible cavity.

Preventive Therapy:

-The main purpose of preventive therapy is to prevent latent (asymptomatic) infection from progressing to clinical disease. -Such therapy also is used to prevent initial infection and to prevent recurrence of past disease. -The usual preventive therapy regimen is isoniazid for 6 months in non-HIV infected individuals. -If the risk factor for multidrug-resistant infection is high, the preventive therapy regimen may be composed of as many as three drugs.

TB and HIV Infection:

-There is an increased prevalence of TB in HIV infection. -All patients with TB need HIV testing and vice versa. -In early HIV infection, the clinical presentation is similar to that of the immunocompetent host with the indolent onset of cough, fever, sweats. -The PPD is usually positive and the CXR reveals upper lobe infiltrates +/- cavitation. -Extrapulmonary manifestations occur in only 10-15% of those with early HIV (i.e. relatively preserved immune function. -Patients with advanced HIV infection may present atypically. -The PPD is usually negative due to anergy (lack of immune response). -The CXR shows lower lobe or diffuse infiltrates and cavitation is rare. - extrapulmonary disease occurs frequently in this group (>50%), and often occurs in the absence of pulmonary disease.

Tuberculin skin test what it means

-This test is useful in the dx and control of tb - based on if infected with tubercle bacilli have T cells that will mediate a Type IV hypersensitivity response (DTH) to the proteins of the organism. -A positive test ids a recent or past tuberculosis infection. -a positive test provides NO info about activity of disease. -Once a TST is positive in a particular patient it NEVER needs to be repeated.

Morphology and cultivation: Mycobacterium tuberculosis

-Typical morphology is a slender, straight or slightly curved rod, 1-4 µm in length. - colonies appear as rough, granular and buff-colored. - "atypical mycobacteria" are rapid growers; most other mycobacteria including M. tuberculosis grow very slowly with generation times of up to 18 hours on laboratory media

Mycobacterium tuberculosis epidemlogy

-US, there has been a steady decline in incidence 1970's to early 1980's due to improvement in standard of living and treatment. -There was an increased incidence in early 1980's primarily due to HIV. -Since 1993, the incidence has been decreasing again due to strengthening of TB control programs - In the1990's, multi-drug resistant TB (MDR-TB) became an increasing problem. -Risks for increased transmission occur in overcrowded areas, prisons, foreign born and HIV-infected individuals

symptoms of tb

-chronic pneumonia. -The onset is insidious. -Primary TB is usually mild. -Clinical disease is marked by fatigue, weight loss, night sweats, weakness and fever. -TB is an indolent, wasting, febrile illness. -With pulmonary TB there is a characteristic chronic cough productive of sputum which may be blood tinged.

Mycobacterium tuberculosis transmission

-cquired by inhalation of mycobacteria in droplet nuclei. - A single cough may generate 3000 droplet nuclei and less than 10 bacilli may initiate infection. -Droplet nuclei dry and may become airborne and remain infectious long after the person who coughed or sneezed left the room.

Ghon complex

-lymph node and granuloma - see on CXR an area of lung inflammation (granuloma) associated with a granuloma in a draining hilar lymph node.

Progressive primary TB

-may directly result from a number of early lesions eroding into bronchioles with subsequent cavitation and dissemination to other sites in the lung. -Access to the lymphatics and blood stream may lead to miliary tuberculosis. -Young children <5yr are at high risk for developing progressive primary disease.

IGRA - Interferon gamma release assay: Mycobacterium tuberculosis

-measure in vitro IFN-g response to specific Mtb antigens. -These antigens are not present in non- tuberculous mycobacteria or BCG strains so they are useful in screening individuals who have been vaccinated with BCG. -Since IGRA is a blood test, the patient only needs to come for a single visit. -Technical complexity of the test limits its use

Mantoux test.

-most accurate and reliable method of skin testing -intracutaneous injection of 0.1 ml of purified protein derivative (PPD) equivalent to 5 tuberculin units. -A positive reaction is indicated by an erythematous, indurated area at the site of application. -The indurated reaction must measure at least 5-10 mm in diameter to be considered positive. -Individuals with AIDS or other T cell immunodeficiencies can be infected with Mycobacterium tuberculosis yet have a negative skin test. -They may be ANERGIC. ->5 for immunosuppresed -TST testing requires the patient return for a reading of the result 48-72 hours after the test is performed

prevalence of multi drug resistant TB

-mutation frequency to drug resistance among mycobacteria is relatively high -o prescribe multiple drugs simultaneously to limit the multiplication of drug resistant mutants.

the problem of TB in under developed countries

-underdeveloped countries, death due to tuberculosis (approximately 3,000,000 per year) ranks among the top three infectious diseases. -In this country TB has regained national attention as a serious health problem. -Since 1985, the number of reported cases has increased significantly; this may be due to the AIDS epidemic. -the emergence of M. tuberculosis strains resistant to multiple drugs has complicated the treatment and prevention of tuberculosis

, Ziehl-Neelson or Kinyoun stain procedure is as follows:

1. Apply primary stain, carbol fuchsin 2. Decolorize with acid alcohol. 3. Counterstain with methylene blue. Bacteria (mycobacteria) that retain the primary stain after decolorization are called acid-fast. - AFB acid fast bacilli. - visualized by fluorescent staining (auramine-rhodamine)

Pathology: : Nocardia asteroides

1. Morbidity attack rate is approximately 500 to 1,000 cases per year; non-communicable. 2. Pulmonary disease begins as lobar pneumonia following inhalation of the organisms. 3. Metastatic foci may involve the brain, kidney or skin -multiple abscesses with infiltration of PMN's and central necrosis resembling pyogenic infections. Burrowing sinuses and granulomas are not characteristic. - inhibits lysosome-phagosome fusion.

virulence factors that allow mycobacteria to survive within macrophages are:

1. Sulfatides or sulfalipids: inhibit fusion of phagosome with lysosome. - 2 Lipoarabinomannan (LAM) - inhibits macrophage activation, scavenges oxidative radicals also plays a role in inhibition phagolysosome fusion.

Urine cultures tb testing

30 to 40% of urine cultures may be positive in the case of extrapulmonary infections.

Extrapulmonary TB : other areas

Gastrointestinal Tract; Pericarditis, or Peritonitis.

Immunity to tb

Mycobacteria grow uninhibited within non-activated macrophages early during infection. - their ingestion into macrophages activates innate immune mechanisms and induces the release of IL12, TNF-α, IL-6 and IL-1. -These mediators call PMNs, macrophages and T cells to the focus of infection and lymphocytes are activated in the nearby lymph nodes. - s T cell-mediated responses which are responsible for containment and/or resolution. -takes ~6 weeks. -T cell-derived cytokines e.g., IFN-γ activate macrophages which can then partially inhibit mycobacterial growth. -Activated macrophages can differentiate into epithelioid cells and the process of granuloma formation (Type IV hypersensitivity) is initiated and results in the walling off of infected cells frequently resulting in fibrosis and calcification (tubercle formation). -the immune response limits infection but also causes damage to the lung.

Biochem test: Mycobacterium tuberculosis

Production of niacin distinguishes M. tuberculosis from the atypical mycobacteria

Extrapulmonary TB: bone disease

TB can affect the spine (Potts disease) in about 50% of cases of bone involvement. - The hips and knees are less likely to be affected. -Patients with bone involvement most commonly complain of pain. - Presence of fever is variable

vaccine for tb

Vaccination with Bacillus Calmette-Guerin (BCG), an attenuated strain of M. bovis is used in several European and South American countries. - The success rate in preventing tb is highly variable and ranges from 10-70%. - effective in reducing the risk of miliary and meningeal forms of tb which are prevalent in children. -Vaccination with BCG converts an individual to skin test (PPD) positive. - skin test is not a good screening tool in those countries where BCG is used. -This is one reason why BCG is not used in the USA. -The other reason is its variable efficacy which ranges from 0 to 90%. -A more effective vaccine is needed. -The interpretation of PPD results in a BCG vaccinated patient is essentially same as in unvaccinated persons. -Interferon Gamma Release Assay may be preferred screening tool for persons who have received BCG vaccine.

Staining: Mycobacterium tuberculosis

acid-fast positive smears are only presumptive evidence for M. tuberculosis as false positives can occur from environmentally present mycobacteria. -Also only 60% of culture positive specimens yield positive smears. -Therefore a definitive diagnosis is made only by culture isolation.

Mycobacterium avium complex (MAC) Complex

common opportunist in immunocompromised patients, especially AIDS and transplant recipients. Ubiquitous organism present in soil. 1. Not transmitted person to person 2. Frequently disseminates and causes non-pulmonary disease 2. Difficult to treat because the organisms are more resistant or antimicrobial therapy and because of the immune status of the host

Tb Exposure

individual has had contact with a person with contagious pulmonary TB, individual is -Skin test negative and has normal chest X-ray. -Some exposed persons develop infection with subsequent skin test conversion, others do not.

Tuberculosis disease

infected individual with signs, symptoms and/or radiographic findings consistent with disease, disease may be pulmonary and/or extrapulmonary

Miliary tuberculosis

is the dissemination and seeding of TB bacilli to various distant organs with development of foci of infection in the meninges, urogenital tract, peritoneum, skin, bones (skeletal) etc. - occurs in immunocompromised individuals. - This most commonly occurs with primary infection, but can also occur during reactivation. -Patients often have fever, night sweats, weight loss. -Focal symptoms may be absent and therefore difficult to diagnose. -Tuberculin skin testing is often negative. -If the lungs are involved, the CXR will show a "military" pattern that looks like scattered millet seeds. -The communicability of military TB is relatively low

what happens in primary infection of tb

may be completely asymptomatic or may progress to primary progressive disease usually within 2 years of initial infection. - Within the lungs a productive lesion develops. -This lesion is a granuloma and is often called a tubercle -In the center are multinucleated giant cells which contain the organisms. -These are surrounded by epitheloid cells and then a zone of fibroblasts, lymphocytes and monocytes. - The central area may undergo caseous necrosis. -It may heal by fibrosis and calcification causing lung scarring. -Some patients develop a Ghon complex -Granulomas may contain viable organisms within them for many years. - Initial infection is also associated with lymphohematogenous spread throughout the body and seeding of the lung apices. -During the early part of the infection prior to the development of an immune response, the organisms grow uninhibited at the pulmonary site and additional sites.

Extrapulmonary TB: local lymph

most commonly occurs in children less than 15 years. -The cervical nodes are most commonly involved (Scrofula). -This can be caused by M. tuberculosis or M. scrofulaceum. -Excisional biopsy or fine-needle biopsy is required for diagnosis