S1B5 - Acid-Fast Bacteria Flashcards
What is sterile pyuria in the context of Mycobacterium tuberculosis infection?
Kidney infection will cause red and white blood cells to be present in urine, but no bacteria are seen by gram stain or culture. The presence of white blood cells in the absence of bacteria is called sterile pyuria.
What is the clinical presentation of Mycobacterium tuberculosis infection?
Patients with Mycobacterium tuberculosis infection typically present with symptoms associated with macrophage activation releasing cytokines such as TNFα:
- Cough for longer than 3 weeks duration
- Night sweats/chills
- Fever
- Weight loss
- Hemoptysis
What is the treatment regimen for tuberculoid leprosy compared to the lepromatous form?
Treatment for leprosy consists of dapsone and rifampin for 6 months in the tuberculoid form. The lepromatous form is treated for 24 months, with the addition of clofazimine.
What is the purpose of Directly Observed Therapy in treatment of Mycobacterium tuberculosis infection?
Response to the 4-drug therapy should be closely monitored throughout the course of the treatment. This is termed Directly Observed Therapy. Weekly or biweekly sputum samples are tested for disappearance of acid-fast bacilli during the treatment period. Any sign of continued infection should be evaluated for resistance, so that the drug regimen can be changed appropriately.
What is physically measured in a PPD skin test?
After a healed tuberculosis, the patient gains hypersensitivity to purified protein derivative (PPD+) skin test and immunity. The reaction is read by measuring the diameter of induration (palpable raised hardened area). Erythema (redness) should not be measured.
How is Actinomyces israelli transmitted?
A. israelli is transmitted during the event of personal injury or trauma.
Nocardia species are catalase positive or negative?
Nocardia species are catalase positive.
(Remember, Cats Need PLACESS to hide)
How are Nocardia species transmitted?
Nocardia species are transmitted through inhalation of airborne organisms or less commonly through direct inoculation into a wound.
What risk factor in women makes them more susceptible to Actinomyces israelli infections?
In women, intrauterine devices are a risk factor for A. israelli infection.
What is Hansen’s disease? What are the 2 forms of Hansen’s disease?
M. leprae causes leprosy, also known as Hansen’s disease. Leprosy reflects a spectrum of clinical and pathological features that can range from tuberculoid to lepromatous, characterized by a strong or poor immune response, respectively.
What would skin biopsy show on tuberculoid leprosy compared to lepromatous leprosy?
Diagnosis for leprosy is made via PCR or skin/nerve biopsy showing either granulomas in the tuberculoid form or acid-fast bacteria in the lepromatous form.
What is the most common outcome of infection with Mycobacterium tuberculosis in a healthy person?
Most people who are exposed develop a latent infection as immune cells (macrophages and T Helper lymphocytes) wall off the infection into a granuloma.
How does Mycobacterium tuberculosis appear on appropriate staining?
Mycobacterium tuberculosis (TB, tubercles bacillus) is an acid-fast (shows up red), obligate aerobic rod.
Why is a multi-drug regimen used for a Mycobacterium tuberculosis infection?
A multi-drug regimen is used to achieve the goals of tuberculosis treatment: to quickly remove active bacteria, to kill as many latent bacteria as possible, and to avoid emergence of drug resistant strains
How should actinomycosis be managed?
Treatment for A. israelli infection is penicillin/amoxicillin; excise sinus tracts if needed.
Remember treatment of Actinomyces vs Nocardia with mnemonic: Treatment is a SNAP
- *S**ulfonamides → Nocardia
- *A**ctinomyces → Penicillin
A 28-year-old woman receives a kidney transplant and is started on long-term immunosuppression. She develops fever, cough, and sputum production. CXR shows a cavitary lesion. A gram stain reveals gram positive rods that form hyphae. What are features of the most likely organism causing this infection?
A) Conversion from mycelial form to yeast form at 37C
B) Acid fast bacilli
C) Catalase positive, weakly acid fast
D) Catalase negative, acid fast bacilli
Catalase positive, weakly acid fast
Answer Explanation
In a patient with a gram positive staining organism that forms hyphae, think Nocardia asteroides and Actinomyces israelii. N. asteroides is the more likely of the two to cause a pulmonary lesion in someone immunosuppressed. Given the cavitating pulmonary lesion in an immunosuppressed patient, this is most consistent with nocardiosis. Nocardia are partly/weakly acid fast and catalase positive. Strongly acid fast bacilli in the setting of a cavitating pulmonary lesion are most consistent with tuberculosis, although tuberculosis does not form hyphae. Conversion from mycelial form to yeast form at body temperatures is a feature of several fungi, including Histoplasma capsulatum. While histoplasmosis presents initially with nonspecific pulmonary symptoms, CXR findings are often normal and mortality occurs after systemic spread.
Name 3 environments that are conducive to the transmission of Mycobacterium tuberculosis infection.
High-risk settings for acquiring Mycobacterium tuberculosis infection include:
- Prisons
- Hospitals
- Homeless shelters
How is secondary Mycobacterium tuberculosis infection diagnosed on a chest X-ray (CXR)
Diagnosis of secondary tuberculosis is by chest x-ray (CXR) demonstrating cavitary lesions in the upper lobes.
How is Mycobacterium leprae transmitted?
Transmission of M. leprae occurs from contact of nasal discharge from an affected individual.
What areas of the body does Mycobacterium leprae preferentially affect?
M. leprae has a predilection for lower temperatures, favoring cooler areas of the body that include:
- Skin
- Nerve segments close to the skin
- Mucous membranes of the upper respiratory tract
What is the usual radiographic finding of thoracic actinomycosis?
Usual radiographic finding is of a mass lesion.
What is the most common outcome of Mycobacterium tuberculosis infection?
Tuberculosis can be asymptomatic. Latent infection is most common.
Is actinomyces israelli acid fast or not acid fast?
Actinomyces is not acid fast
Where are most cases of leprosy reported?
The majority of cases of leprosy are in developing countries, with most cases reported from India, Brazil, Indonesia, Bangladesh, and Nigeria.
What disease(s) does Mycobacterium tuberculosis cause?
M. tuberculosis causes primary tuberculosis, which occurs in previously unexposed hosts, and secondary tuberculosis, which occurs by reactivated infection due to immunosuppression (AIDS, drugs, malnutrition).
What is the treatment for a Nocardia species infection?
Treatment of choice for Nocardia species infections is TMP-SMX (Bactrim).
Remember treatment of Actinomyces vs Nocardia with mnemonic: SNAP
- *S**ulfonamides → Nocardia
- *A**ctinomyces → Penicillin
What growth media can be used to isolate Mycobacterium tuberculosis?
Lowenstein-Jensen agar can be used to isolate M. tuberculosis.
What can cause a false positive purified protein derivative (PPD) skin test for Mycobacterium tuberculosis infection?
A purified protein derivative (PPD) test can be falsely positive if the patient had a Bacillus Calmette–Guérin (BCG) vaccination, which is a routine live-attenuated vaccine adminstered in many countries where tuberculosis is endemic, as well as the United Kingdom.
Because Actinomyces israelli is part of the normal flora of the oral cavity, infection from A. israelli often follows what event?
In the setting of trauma/surgery, disruption of the mucosal barrier causes local infection and inflammation. Slow expansion can spread to other tissues, forming sinus tracts and possible hematogenous spread to other sites.
In what cases does Mycobacterium tuberculosis infection usually cause clinical disease?
Clinical disease occurs due to immunosuppression (HIV, cancer, steroids), as the bacteria spread hematogenously before encapsulation in a granuloma, or the immune system loses the ability to suppress an old infection.
A 36-year-old man presents with a 5-year history of facial abscesses with chronically draining sinus tracts. On examination, the affected areas are indurated and have a “wooden” appearance. Pus collected from a sinus tract contains yellow granules. Which would you expect to find on Gram stain?
A) Gram positive rods in pairs
B) Gram positive rods in a filamentous pattern
C) Gram positive cocci in clusters
D) Gram negative rods
E) Gram positive cocci in pairs and chains
Gram positive rods in a filamentous pattern
Answer Explanation
Chronic sinus tracts involving yellow granules suggest Actinomyces israelii. The granules are sulfur granules and can be seen with the naked eye. Actinomyces are gram-positive rods that form long, branching hyphae – i.e., a filamentous pattern. While abscesses can also form from staphylococci (gram-positive cocci in clusters), or streptococci (gram-positive cocci in pairs/chains), these do not persist for years and they do not involve granules.
What staining technique is used to identify Mycobacterium tuberculosis?
Diagnosis is made with Ziehl-Neelson (carbol fuchsin). The culture is stained with carbolfuchsin (red) and acid alcohol is applied to dissolve most bacterial cultures. M. tuberculosis doesn’t dissolve in acid and remains red. This indicates active tuberculosis infection.
What stain can be used help visualize Mycobacterium leprae?
Is M. leprae found intracellularly or extracellularly?
Describe the basic morphology of M. leprae.
Mycobacterium leprae is an acid-fast, facultative intracellular bacteria that forms thin rods.
In the context of Mycobacterium tuberculosis, what is a Ghon focus?
A Ghon focus is a granuloma located near the pleura in either the upper part of the lower lobe or the lower part of the upper lobe; the center of the Ghon focus often undergoes caseous necrosis.
How is active primary Mycobacterium tuberculosis infection diagnosed on a chest X-ray (CXR)
Diagnosis of active primary tuberculosis is made by chest X-ray (CXR) demonstrating a Ranke complex. Cavitary lesions are rare. In addition, CXR may reveal pleural effusion.
Where do abscesses from actinomycoses form in the body? What is the colloquial term for the hard lump formed from abscesses in one of these places?
A. israelli infections cause abscess in the mouth, lungs, GI tract, and GU tract. Abscesses in the mouth can produce cervicofacial mycetoma, which manifests as a hard lump, often in the jaw, commonly known as “lumpy jaw.”
What is a positive purified protein derivative (PPD+) skin test used for?
Diagnosis of latent tuberculosis is made via skin conversion, positive purified protein derivative (PPD+) skin test. Once exposed to M. tuberculosis, PPD will be positive for life.
What is Pott Disease?
Skeletal infection with M. tuberculosis can cause Pott’s disease which most commonly involves the spine, leading to destruction of intervertebral discs and vertebral bodies.
How is Mycobacterium tuberculosis transmitted?
M. tuberculosis is transmitted via inhalation of droplet nuclei (airborne particles).
What situations can cause a false negative purified protein derivative (PPD) skin test for Mycobacterium tuberculosis infection?
A purified protein derivative (PPD) test can be falsely negative in cases of
- Steroid use
- Malnutrition
- Immunocompromised states
How can Nocardia species be differentiated from TB?
Presentation and acid-fast staining may resemble TB, such as caseous necrosis, but can be distinguished by beaded, filamentous growth.
What stain can be used to identify Nocardia species?
Nocardia species can be stained with Ziehl-Neelsen (carbol fuchsin) because they are weakly acid-fast.
In lepromatous leprosy, is there a strong or weak immune response? Is the disease characterized by a high or low cell-mediated immunity? What T-cell response is most prominent?
In lepromatous leprosy, the weak immune response means host defenses are unable to contain microorganism allowing diffuse inflammatory damage. This form of leprosy is characterized by a low cell-mediated immunity and mainly a Th2-type immune response.
What component of the cell membrane is responsible for the unique staining of Mycobacterium tuberculosis?
The cell membrane of M. tuberculosis contains mycolic acid, a strongly hydrophobic lipid that increases the bacterium’s virulence.
Which federal institution receives reports of confirmed Mycobacterium tuberculosis infections?
It is mandatory to notify the county and state health departments of verified TB diagnoses. These departments ultimately report this information to the Centers for Disease Control.
What methods are used to prevent the spread of Mycobacterium tuberculosis infection in healthcare settings?
Respirators and negative-pressure isolation rooms are used to prevent the spread of Mycobacterium tuberculosis infection in healthcare settings.
What are some common physical exam findings and symptoms seen in lepromatous leprosy?
The diffuse inflammatory damage often presents as:
- Loss of eyebrows
- Saddle-nose deformity (thick nose)
- Leonine facies (thick cheeks)
- Neuropathy of peripheral nerves that may present as glove and stocking paresthesias
- Infertility from testicle involvement
A 68-year-old man is found to have a cavitary lesion in the upper lobe on chest x-ray. Cultures demonstrate acid-fast bacilli. Which form of this disease does he most likely have?
A) Primary infection
B) Anergy
C) CD4 count
D) Meningitis
E) Secondary reactivation
Secondary reactivation
Answer Explanation
Cavitating lesions with acid-fast bacilli indicate reactivation TB. Cavitation is uncommon in primary TB, seen only in 10-30% of cases. In most cases, the infection becomes localized and a caseating granuloma forms (tuberculoma) which usually eventually calcifies and is then known as a Ghon lesion
Anergy refers to lack of immune response to presentation of an antigen, as in the PPD skin test. Meningitis can occur with TB, but this patient has pulmonary disease. CD4 count
Dullness on chest exam of Mycobacterium tuberculosis infection might indicate what manifestation of the infection?
Tuberculosis can infect the pleural and pericardial spaces, causing pleural and pericardial effusion, recognizable as dullness to percussion.
What is the morphology, gram staining, oxygen requirement, urease positive/negative of Nocardia organisms?
Nocardia species (Nocardia asteroides, Nocardia brasiliensis) are aerobic, urease-positive, gram-positive rods that form long, branching “beaded” hyphae (similar to Actinomyces).
Tuberculosis infection that affects the joint can lead to what pathology?
Joint infection in tuberculosis can cause chronic arthritis.
How do each of the 3 disease forms of Nocardia species infection commonly present?
Patients who are infected are often immunocompromised and typically present with pneumonia (pulmonary), cellulitis/abscess secondary to trauma (cutaneous), or abscesses in the kidney or brain (disseminated).
The interferon-gamma release assay is used to diagnose what infection?
The Quantiferon Gold assay, also known as the interferon-gamma release assay (IGRA), measures IFN-gamma levels in serum released from T-lymphocytes exposed to tuberculosis. This assay does not cross-react with the BCG vaccine and is more specific test than the PPD test, but much more expensive.
What animal is known for harboring Mycobacterium leprae?
M. leprae grows extensively in armadillos, which has a cooler core body temperature of 34°C.
What is the function of cord factor in Mycobacterium tuberculosis?
Cord factor in virulent strains inhibits macrophage maturation and induces release of TNF-α.
Where on the body can Actinomyces israelli be found?
A. israelli is part of the normal flora of the oral cavity, GI tract, and the female GU tract.
Draining sinus tracts from actinomycosis have what classical presentation?
Sinus tracts classically have yellow sulfur granules surrounded by purulence and neutrophils, but there is no sulfur actually present.
In the context of Mycobacterium tuberculosis, what is a Ghon complex?
A Ghon complex is a Ghon focus and regional (usually perihilar) lymphadenopathy.
What is miliary tuberculosis?
Miliary tuberculosis, also known as disseminated tuberculosis, is a form of tuberculosis that is characterized by a wide dissemination into the human body and by the tiny size of the lesions. Prognosis is poor with 100% fatality if not treated. Miliary tuberculosis is more common in HIV patients, but others with miliary tuberculosis have no recognizable high-risk factors.
Culture on BCYE agar reveals an aerial hypae. What is the likely microorganism?
What are the drugs administered in the 2 stages of the 6-month treatment plan for Mycobacterium tuberculosis infection?
RIPE therapy is administered for the first 8 weeks. Afterwards, continuation therapy consists of 16 weeks of isoniazid and rifampin, totaling to 6 months of therapy for uncomplicated tuberculosis.
What can most commonly be found on physical exam in tuberculoid leprosy?
Damage is localized to superficial nerves and skin, resulting in a few hypoesthetic, hairless skin plaques.
What is the morphology and gram staining of Actinomyces israelli?
Actinomyces israelli is an obligate anaerobic gram-positive bacillus that forms long, branching filaments (similar to Nocardia).
What is the Bacillus Calmette–Guérin (BCG) vaccination used for? What type of vaccine is it (killed or live-attenuated)?
The Bacillus Calmette–Guérin (BCG) vaccination is a live attenuated vaccine inducing cell-mediated immune response against Mycobacterium tuberculosis. It is not used in the United States.
Mycobacterium leprae infections tend to spare the groin and axillae. Which is the greatest contributor to this phenomenon?
A) M. leprae is an obligate intracellular organism
B) Intertrigonous regions have higher levels of antibody secretion
C) M. leprae invades peripheral nerves
D) Intertriginous regions have higher concentrations of lymph nodes
E) Intertriginous regions tend to be warmer
Intertriginous regions tend to be warmer
Answer Explanation
M. leprae grows best at about 30° C. Areas of the body that tend to be warmer, such as intertriginous regions and the scalp, tend to be less affected by infection. It is true that M. leprae is an obligate intracellular organism and that it invades peripheral nerves, but these do not intrinsically affect the distribution of the disease. Intertriginous regions, where skin faces skin, are not typically regions of antibody secretion (mucous membranes are). While the axilla and groin have regional lymph node basins, this again is not known to play a role in the sparing of these areas.
What are common reservoirs for Nocardia species?
Nocardia is found in soil and water (versus Actinomyces, which is part of the normal human flora).
What is the classic manifestation of Mycobacterium tuberculosis infection of the kidneys?
Tuberculosis can infect the kidneys, resulting in malaise, dysuria, gross hematuria, and sterile pyuria.
How is Mycobacterium tuberculosis infection treated?
The most common outcome of Mycobacterium tuberculosis infection is latent infection. Treatment is with “RIPE” therapy:
- Rifampin
- Isoniazid
- Pyrazinamide
- Ethambutol (or streptomycin)
In tuberculoid leprosy, is there a strong or weak immune response? Is the disease characterized by a high or low cell-mediated immunity? What T-cell response is most prominent?
In tuberculoid leprosy, the strong immune response allows granuloma formation, limiting the spread of the organism. This form of leprosy is characterized by a high cell-mediated immunity and mainly a Th1-type immune response.
CNS infiltration of Mycobacterium tuberculosis has a predilection for what part of the brain?
CNS infiltration of M. tuberculosis can cause meningitis and formation of granulomas in the brain, in particular the base of the brain.
Which 2 drugs are given as TB prophylaxis for patients that do not have active disease?
TB prophylaxis for patients that do not have active disease is Isoniazid + Pyridoxine (B6).
Treatment is with “RIPE” therapy:
- Rifampin
- Isoniazid
- Pyrazinamide
- Ethambutol (or streptomycin)
