a 32-year-old woman presented with a cough for several weeks and a 15-lb weight loss. she also had...

A 32-year-old woman presented with a cough for several weeks and a 15-lb weight loss. She also had night sweats and fevers and felt fatigued.

Despite erythromycin treatment for suspected pneumonia given by her family physician, her fever and cough got progressively worse. She complained about coughing blood-tinged sputum.

She had emigrated from Venezuela to the United States 3 years before her illness, but she frequently returned to Venezuela to visit relatives.

Physical examinationTemperature: 38.6˚CPulse: 96/minRespiration: 18/minBlood pressure: 112/60 mm HgExamination was remarkable for bilateral rales and

lymphadenopathyChest X-ray revealed right upper lobe infiltrates

Likely causes of illness

Actinomyces spp.Anaerobes (aspiration pneumonia)Endemic fungi (Histoplasma capsulatum)Legionella pneumophilaMycobacterium tuberculosisMycoplasma pneumoniaeNocardia spp.

MYCOBACTERIA

The captain of all the men of death that came against him to take him away, was the Consumption, for it was that that brought him down to his grave

John Bunyan (1628-1688)English author

MYCOBACTERIA

Died of tuberculosis:

ChopinPaganiniThoreauKeatsElizabeth Barrett BrowningEmily and Charlotte Bronte

MYCOBACTERIA

In the 19th Century, one quarter of the population of Europe is thought to have died of tuberculosis

MYCOBACTERIA

1.9 billion people infected with Mycobacterium tuberculosis

Tuberculosis kills about 2 million people and infects about 8 million others every year

Risk factors: poverty, malnutrition and poor housing

MYCOBACTERIA

May proceed toa generalizedinfection(“miliary”Tuberculosis)

Transmission electronmicrograph of

M. tuberculosis

Primarily a disease of the lungs

Mycobacteria stained with theZiehl-Neelsen stain

Acid-fast staining “Acid-fast bacteria”

M. tuberculosis colonies onLowenstein-Jensen agar

MYCOBACTERIA

Physiology and structure

Complex cell wall

Peptidoglycan layer linked with arabinose-galactose-mycolic acid (arabinogalactan mycolate)

Mycolic acidsMajor lipidsLong chain (C78-C90)

Mycobacterialcell wallstructure

MYCOBACTERIA

Physiology and structure

Free lipidsWaxes: wax D (Freund's adjuvant)

Helps withstand drying and thus increases survival

Mycosides: complex saturated glycolipids Cord factor: 6,6'-dimycolate of trehalose

Inhibits neutrophil migrationThought to mediate granuloma

Trehalose 6,6’-dimycolateRCO: mycolyl

MYCOBACTERIA

Physiology and structure

PolypeptidesAct as antigensUsed in skin testing (PPD)

MYCOBACTERIA

Physiology and structure

Runyon classification according to rate of growth and pigmentation

Photochromogens: Organisms that produce pigments after exposure to light

Scotochromogens: Produce pigments both in the light and dark

Photochromogenic M. kansasi colonieson Middlebrook agar

Pathogenesis

Infection via inhalation of infectious aerosols

Replicates in alveolar macrophages and destroys the cells

Infected macrophages migrate to the local (tracheobronchial) lymph nodes, the bloodstream and other tissues

Mycobacterium tuberculosis

Tubercle bacilli enter through the respiratory tract

Stealth invader:MTB in macrophages

Tubercle bacilli multiply in phagocytes and spread to lymph nodes and the circulation

Pathogenesis

No exotoxin or endotoxin

”Exported repetitive protein" prevents the phagosome from fusing with the lysosome

Mycobacterium tuberculosis

Pathogenesis

Two types of lesions

Exudative: Acute inflammatory response at the initial site of infection (usually lungs)

Granulomatous: A central area of infected giant cells (Langhans’cells) surrounded by epithelioid cells (tubercles)

Mycobacterium tuberculosis

Pathogenesis

TuberclesMay heal spontaneouslyMay become fibrotic or calcified

Caseous (cheesy) necrosis and cavitation in the center of the granuloma, due to:

Cellular immune responseEnzymes and reactive oxygen intermediates from

dying macrophages

Mycobacterium tuberculosis

Pathogenesis

The exudative lesion and the draining lymph nodes fibrose, and sometimes calcify, to produce theGhon complex seen in X-rays

Latent bacilli can be re-activated when the patient's immune system is weakened (malnutrition, alcoholism, diabetes, old age, emotional stress)

Mycobacterium tuberculosis

Pulmonary tuberculosis

MTB can cause devastating damage to the lungs

Pathogenesis and immunity

Intracellular replication stimulates helper and cytotoxic lymphocytes

T-cells release interferon- and other cytokines-> Macrophage activation -> MTB killing

Tuberculin skin test: purified protein derivative (PPD)Positive 4-6 weeks after infection

Mycobacterium tuberculosis

Pathogenesis and immunity

Localized activated macrophages can penetrate into small granulomas (< 3 mm) and kill all bacilli

Larger necrotic or caseous granulomas become encapsulated with fibrin that protects the bacilli

Mycobacterium tuberculosis

Pathogenesis and immunity

The pathogen population does not increase, but the immune system cannot get rid of the bacteria

It is not known how MTB can sit around in tissues for years or decades

MTB eats carbon from lipids via the glyoxylate pathwayIsocitrate lyase critical for this pathway

Mycobacterium tuberculosis

Epidemiology

Transmitted by aerosols

More common amongThe urban poorPatients with suppressed immune systems Immigrants from high-incidence areas

Health care workers are at risk for infection!

Mycobacterium tuberculosis

Annualincidenceof MTB inthe US1981-1995

In 2005:14,093 cases4.8 per 100,000

California:2,900 cases8 per 100,000

Epidemiology

An estimated 10-15 million people in the US are infected with M. tuberculosis without displaying symptoms

1 in 10 of these individuals will develop active TB at some time in their lives

Mycobacterium tuberculosis

Epidemiology

What caused TB to return?HIV/AIDS epidemicImmigration from countries with many TB casesIncreased poverty, injection drug use, homelessnessFailure to take antibiotics as prescribedIncreased number of people in long-term care

Mycobacterium tuberculosis

Clinical syndromes

Primary tuberculosismild and asymptomatic in 90% of cases does not proceed further

In the remaining 10%malaise, weight loss, productive cough, night

sweatsBloody and purulent sputum

Mycobacterium tuberculosis

Clinical syndromes

Reactivation of latent bacilli years later when the patient's immunologic responsiveness wanes:

Old ageImmunosuppressive disease or therapyMalnutritionAlcoholismDiabetesStress

Mycobacterium tuberculosis

Clinical syndromes

Necrosis may erode blood vessels -> hemorrhage

Most infections in the lungs

Can disseminate to the lymph nodes, pleura, the liver, genitourinary tract, bone marrow, spleen, kidneys,central nervous system

M. tuberculosis can also cause meningitis

Mycobacterium tuberculosis

Acutemiliarytuberculosisleading tomeningitis

Latin:milium, milletseed

Each tubercleresemblesa millet seed

Laboratory diagnosis

Skin test: "purified protein derivative" injected into the intradermal layer of the skin. Induration of 10 mm or more 48 hours later indicates exposure to MTB

Microscopy: Clinical specimen stained with carbolfuchsin (Ziehl-Neelsen and Kinyoun stains) or fluorochrome dyes (Truant auramine-rhodamine), de-colorized with acid-alcohol solution, and counterstained

Mycobacterium tuberculosis

Acid-fast stain(carbolfuchsin)of Mycobacteriumtuberculosis

M. tuberculosis stainedwith the fluorescentdyes auramine andrhodamine

Laboratory diagnosis

Culture: After treatment of specimen with 2% NaOH(to kill rapidly growing bacteria) MTB is grown on Lowenstein-Jensen (egg-based) medium, or Middlebrook (agar-based) medium

BACTEC measures the metabolism of 14C-palmitic acid to 14CO2

Mycobacterium tuberculosis

Laboratory diagnosis

Biochemical tests: The production of niacin, and nitrate reductase. Analysis of cell wall lipids Nucleic acid probes and nucleic acid sequencing

PCR

Mycobacterium tuberculosis

Treatment and control

Isoniazid: inhibits mycolic acid biosynthesis (used for prophylaxis)

Rifampin Pyrazinamide (active at low pH; mechanism unknown)Ethambutol (inhibits arabinogalactan synthesis)

American Thoracic Society recommendations:Initial treatment with these 4 drugs for 2 months, followed by INH/RIF for 4-6 months

Mycobacterium tuberculosis

Treatment and control

Multiple-drug-resistant (MDR) strains

Mutations in genes formycolic acid synthesiscatalase-peroxidase

required to activate isoniazid

Need in vitro susceptibility testing

Mycobacterium tuberculosis

Treatment and control

Noncompliance -> emergence of MDR strains

Directly observed therapy (DOT)

BCG: Bacille Calmette-Guérin (attenuated M. bovis)Used in most developing countries to reduce the severe consequences in infants and children Variable efficacy in adults

Mycobacterium tuberculosis

Treatment and control

PA-824 New drug in clinical trials(“nitroimidazopyran”)

Active against both actively dividing and slow growing MTB

Mycobacterium tuberculosis

Pathogenesis

Asymptomatic colonization: immunocompetent patients

Localized pulmonary disease: patients with chronic bronchitis

Disseminated disease: immunocompromised individuals

Organ dysfunction due to abundance of bacteria and host response to infection

Mycobacterium avium-intracellulare

M. avium-intracellulareinfected tissue froman AIDS patient

M. avium-intracellulare in fixed-tissue macrophages in a bone marrow biopsy from a patient with AIDS

(anti-mycobacterial Ab immunoperoxidase stain)

Epidemiology

Ingestion of contaminated food or water

Found in soil and water, and infected poultry and swine

Inhalation of infectious aerosols: minor role

Immunocompromised patients (esp. AIDS) and those with long-standing pulmonary disease at greatest risk

Mycobacterium avium-intracellulare

Clinical syndromes

The most common mycobacterial isolate in AIDS patients

Disseminated disease: Tissues filled with MAC

Bacteremia: 100-1000/ml in blood

Mycobacterium avium-intracellulare

Treatment and control

Resistant to most antimycobacterial drugs

Combination therapyClarithromycin (or azithromycin) + Ethambutol +

Rifabutin

For prophylaxis in AIDS patients with low CD4 counts: Clarithromycin or Azithromycin

Mycobacterium avium-intracellulare

Pathogenesis

Causes leprosy or Hansen's disease

Tuberculoid leprosyStrong cellular immune reactionLymphocytes and granulomas, but relatively few

bacteriaProduction of interferon- and IL-2 -> macrophage

activation, phagocytosis and bacterial clearance

Mycobacterium leprae

A. TuberculoidleprosyMacules withhypo-pigmentation

B. Lepromatousleprosy withextensiveinfiltration,edema andcorrugation ofthe face

Pathogenesis

Lepromatous leprosy Specific defect in the cellular immune response to

M. leprae antigensBacilli populate dermal macrophages and

Schwann cells of peripheral nervesThe most infectious form of leprosy

Mycobacterium leprae

Tuberculoid leprosy

Lepromatous leprosy

Ziehl-Neelsen staining of Mycobacterium leprae

Clinical syndromes

Tuberculoid

Lepromatous leprosyMost infectious, with large numbers of bacilli in

infected tissuesCauses disfigurations in the skin

Mycobacterium leprae

Epidemiology

> 12 million cases of leprosy worldwide

250 cases annually in the U.S. ( California, Texas, Louisiana and Hawaii), mostly in immigrants

Spread by person-to-person contactInhalation of infectious aerosols, skin contact with respiratory secretions or wound exudates.

Arthropod vectors? Armadillos?

Mycobacterium leprae

ArmadillosandM. leprae?

Treatment and control

Tuberculoid leprosyDapsone (antifolate) + Rifampin (min 6 months)

Lepromatous leprosyClofazimine in addition to Dapsone and Rifampin (therapy extended to 12 months)

Controlled by prompt recognition and treatment of infected people

Mycobacterium leprae

Mycobacterium kansasii

Causes chronic pulmonary disease

Disseminated disease in immunocompromised patients

Mycobacterium marinum

Causes "swimming pool granulomas”nodular lesions along the lymphatics

-> ulceration

Fish tank granulomacaused byMycobacteriummarinum infectionof a lesion acquired while cleaning outa fish tank

NOCARDIA

Strict aerobic, Gram-positive bacilli

Form branched hyphae

The cell wall contains mycolic acids

"acid-fast” (in contrast to Actinomyces)

Nocardia

Nocardia asteroides causes bronchopulmonary disease that can spread to the skin and CNS

Nocardia brasiliensis causes cutaneous disease

Nocardia

Acid-fast stain of Nocardia asteroidesin expectorated sputum

Gram stain of Nocardia asteroidesin expectorated sputum

Pathogenesis

Found worldwide in organic-rich soil

Colonizes the oropharynx

Aspiration of oral secretions causes infection of the lower airways

Nocardia

Pathogenesis

Causes necrosis and abscess formation

Can survive in phagocytes

Traumatic introduction into subcutaneous tissue > Cutaneous nocardiosis

Nocardia

Epidemiology

Infections are exogenous (not caused by normal human flora)

Nocardia asteroides infections occur in patients with impaired cell-mediated immunity

Nocardia

Epidemiology

Immunocompetent patients with chronic pulmonary disease (bronchitis, emphysema)

Nocardia brasiliensis infections of the skin can occur in immunocompetent persons

Nocardia

Mycetoma caused by Nocardia brasiliensis

The foot is grosslyenlarged and coveredwith multiple drainingsinus tracts

Clinical syndromes

Bronchopulmonary infections: Cough, dyspnea (difficulty in breathing), fever

Cutaneous infections: Cellulitis (inflammation of the soft or connective tissue), pustula, pyoderma (purulent skin disease), chronic ulcerative lesions, subcutaneous abscesses

Nocardia

Clinical syndromes

Lymphocutaneous infections: Regional lymph nodes

Mycetoma: Chronic granulomatous disease; may involve bone, connective tissue and muscle

CNS: Single or multiple brain abscesses

Nocardia

Treatment

Proper wound care and trimethoprim-sulfamethoxazole for 6 weeks or more

Prognosis is poor for immunocompromised patients with disseminated disease

Nocardia