MIcrobiology Exam 3

Mycobacterial morphology

• thin straight rods

• aerobic

• nonmotile

• nonspore forming

• facultatively intracellular

where do mycobacterium replicate

inside cell macrophages

Hallmark features of mycobacterium

• grow slowly

• antibiotic resistance

• strongly acid fast due to complex cell wall

Mycobacterium cell wall

• has a 60% lipid composiiton

• contain acyl lipids, LAM, and mycolic acid

mycolic acid

• a unique alpha branched lipid with 70-90 carbons

• makes up 50% of mycobacterial cell wall weight

• hydrophobic

• antibiotic resistance and acid fast

• protect from cationic proteins, lysozyme, and free radicals

• prevent lysis by serum complement

Th1 response to mycobacteria

• utilizes CD8, NK, and macrophage cells

• produces granulomas

• host protective

Th2 response to mycobacteria

• involves antibodies

• bacteria will disseminate

• ineffective

Tuberculosis epidemic

• 2 billion people are infected

• thats about 1/3 of the population

• 9 million new cases per year

• leading cause of death in HIV infected individuals

mycobacterium tuberculosis

• 5-200 organisms required for infection

• transmitted when a person with active TB sneezes, coughs, or talks

• aerosolized droplets can remain airborne for hours

pathogenic cycle of tuberculosis

• 90-95% are contained in granulomas for latent infection

• 5-10% are actively infectious and can trasmit disease

• there is a 10% risk of reactivation during lifetime

granuloma

focal collection of inflammatory cells at sites of tissue infection and includes activated macrophages, Langhan’s giant cells, and lymphocytes

tubercle

a granulomatous lesion due to infection by mycobacterium tuberculosis

caseous necrosis

• bacteria replicate extracellularly in pocket

• can disseminate if host immunity is compromised

mantoux TB skin test

• intradermal administration of 0.1 mL PPD from MTB

• read after 48-72 hours

• positive test = induration of greater than 5-15 mm

• does not distinguish between infection and disease

TB infection

• MTB present but inactive

• noninfectious and nonsymptomatic

• positive PPD test

• normal chest xray and negative sputum smear

• no isolation required

• not defined as a TB case

TB disease

• MTB present and actively multiplying

• infectious and symptomatic

• positive PPD

• abnormal chest xray and positive sputum smear

• respiratory isolation required

• defined as a TB case

diagnosis of TB disease

• 3 positive sputum smears by acid fast stain

• chest xray

• M tuberculosis colonies in culture of lowenstein jensen agar (may take 8 weeks to appear)

TB symptoms

• coughing

• blood stained sputum

• weight loss and poor appetite

• night sweats

• tuberculosis of the tongue

CDC guidelines for preventing transmission of B in dental settings

• asses patient history of TB

• is suspected, refer patient for assessent

• use precuations for urgent treatment

CDC recommendations for monitoring TB exposure in dental practices

• Tb skin test at beginning of employment in low risk settings

• every 12 months in medium risk settings

• every 8-10 weeks in event of potential ongiong transmission

mycobacterium leprae

• strongly acid fast bacilus

• similar to MTB

• sowest growing bacterium, with 14 day division time

• incubation can be a few weeks or up to 20 years

mycobacterium leprae cultivation

• cannot be cultivated in cell free cultures

• propogated in mouse footpads or in armadillos

• humans are only other natural reservoir

transmission of mycobacterium leprae

• human to human via aerosols or direct contact

• environmental acquisition (amoebas)

• zoonotic

leprosy global prevalance

• primarily in tropical regions

• 6 million people affected

• 2-3 million has disabilities related to M leprae

M. leprae pathogenesis

• intracellular

• infects skin, schwann cells, and mucous membranes

• cooler areas of the body

• lesions, hypopigmentation, and loss of sensation

• wide range of severity

M leprae presentation: mild to severe

• tuberculoid

• borderline tuberculoid

• borderline lepromatous

• lepromatous

Tuberculoid/Paucibacillary leprosy

• low organism count with low infectivity

• normal IG levels

• strong Th1 response with positive lepromin test

• few anesthetic skin lesions that are hypopigmented with raised, well demarcated borders

• severe asymmetric peripheral nerve danage leading to sensory loss and motor paralysis

multibacillary or lepromatous leprosy

• high number of organisms with high infectivity

• hypergammaglubulinemia via Th2 is not protective

• low Th1 response

• no reaction to lepromin

• multiple erythematous skin lesions, nodules, and papules

• diffuse peripheral nerve damange may cause deformities of extremities due to unintentional self mutilation

• destruction of facial cartilage and bone

multibacillary HD facial disfiguration

• loss of eyebrows, hair, and eyelashes

• altered pigmentation

• leonine facies

• blindness

• destruction of nasal cartilage

• facial nodules

M leprae diagnosis

• difficult, nonculturable agent

• acid fast bacilli in lesions

• skin test reactivity to lepromin is greater than 5 mm

• “fernandez reaction”

M. leprae treatment

• may be lifelong due to latency

• tuberculoid treated with dapsone and rifampin for 6 months

• multibacillary treated with dapsone, rifampin, and clofazimine over 12 months

nontuberculosis mycobacteria

• all other disease causing mycobacteria (30 species)

• atypical or environmental bacteria

• humans are not reservoirs

• opportunistic pathogens

• cuase morbidity but little mortality

Mycobacterium avium complex (MAC)

• mycobacterium avium and intracellulare

• acquired y ingestion or inhaaltion

• from environmental reserovirs like water soil, and animals

MAC pathogenesis

• immunocompromised patients, specifically HIV

• typically desseminated

• replicate and localize in lymph nodes

• overhwleming systemic infection effecting every organ

• MOST COMMON MYCOBACTERIAL INFECTION IN AIDS PATIENTS

MAC diagnosis

microscopy and culture

MAC treatment

• prolonged antiobiotic combination therapy

• ethambutol and rifabutn PLUS clarithromycin or azithromycin

• antibiotic prophylaxis recommended for HIV patients with low CD4

NTM rapid growers

• M fortuitum, chelonae, and abscessus

• colonies grow in less than 7 days

• more susceptible to traditional antibiotics

• introdcued to skin and subcutaenous tissue via trauma and iatrogenic infections

• rarely dessminated

mycobacterium abscessus

• more common in denstiry, especially after pulpotomy

• due to high levels of bacteria in dental water system

legionella pneumophilia

• ubiquitous and aquatic

• environmental acquisition

• gram negative coccbacillus

• facultative intracellular

• motile

legionella risk factors

• over 50

• current or former smokers

• chronic lung disease

• weak immune systm

acquisition of legionella

• spreads thru water droplets

• showers, coolers, hot tubs

clinical manifestations of legionella pneumphilia

• 2-10 day incubation period

• legionnaries disease ( severe pneumonia with high mortality)

• pontiac fever

• walking pneumonia