mycobacteria Flashcards
acid fastness property of mycobacterium is mainly due to
organism’s high content of mycolic acids, long
chained cross-linked fatty acids and other cell
wall lipids
treatment regimen for M. tb for initial therapy
Rifampicin
Isoniazid
Pyrazinamide
ethambutol
Routine culture uses
nonselective egg medium
Lowenstein-Jensen or Middlebrook 7H10
Typical TB lesion
epithelioid granuloma w/ central caseation
necrosis
Bacilli proliferate locally & spread through the
lymphatics to a hilar node, forming
Ghon complex
4 cellular zones
1.central caseation necrosis
2. inner cellular zone of epithelioid macrophages&
Langhans giant cells admixed with lymphocytes
3. outer cellular zone of lymphocytes, plasma cells, &
immature macrophages
4.rim of fibrosis in healing lesions
3 zones of productive lesions
Central area of large, multinucleated giant cells
containing tubercle bacilli
─ A mid zone of pale epithelioid cells, often
arranged radially
─ Peripheral zone of fibroblasts, lymphocytes and
monocytes
consists of an acute inflammatory reaction with edema fluid, PMN leukocytes, and later monocytes around the tuberfcle bacilli
exudative lesion
mycobacteria reide principally intracellularly where
monocytes
Reticuloendothelial cells and giant cells
If a person has ever been exposed to the TB bacteria
(Mycobacterium tuberculosis), the skin will react to the
antigens by developing
firm red bump at the site
w/in 2 days – induration, edema, erythema
Done by putting a small amount of TB protein (antigens)
under the top layer of skin on the inner forearm.
(intradermal)
tuberculin skin test
disadvantage of tuberculin skin test
can’t tell how long px is infected & if infection’s latet or active
most often site of infection of tb in the lungs
at the bae
reactivation TB is char by
chronic tissue lesions, formation of tubercles, caseation and fibrosis
reactivation type almost begins at the apex of the lung, why
oxygen tension is highest
LV
Lupus vulgaris
SD
Scrofuloderma
MTA
Metastatic tuberculosis abscess
(AMT)
Acute miliary tuberculosis
OT
Orificial tuberculosis (
PIT
Primary inoculation Tuberculosis
TVC):
Tuberculosis verrucosa cutis
lymphadenitis or tuberculosis of bones & joints,
results in
SD
lymphatic spread to skin, results
LV
hematogenous dissemination, results in
AMT, LV, or
MTA
initial lesion due to direct infection of the skin or
mucous membranes from an outside source of
mycobacteria lesion
Primary-inoculation TB or Tuberculous chancre
asymptomatic, firm shallow, crust-covered ulcers w/ a
granular base
Primary-inoculation TB or Tuberculous chancre
Occurs after direct inoculation of TB into the skin
in someone who has been previously infected w/
mycobacteria
Tuberculosis Verrucosa Cutis
Presents as a purplish or brownish-red warty growth
Lesions most often occur on the knees, elbows,
hands, feet & buttocks
Tuberculosis Verrucosa Cutis
Initial flat papule is ill-defined and soft and evolves
into well-defined, irregular plaque.
Lupus Vulgaris
Small sharply defined reddish-brown lesions w/ a gelatinous consistency (called apple-jelly nodules)
• Lupus Vulgaris
Skin lesions result from direct extension of underlying
TB infection of lymph nodes, bone or joints.
• Often associated w/ TB of the lungs
SCROFULDERMA
SD most often results from
continuous spread from
affected lymph nodes or tuberculous bones (phalanges,
sternum, ribs) or joints
Chronic TB infection that has spread from the primary
infection (usually in the lungs) to other organs & tissues
via the bloodstream
MILIARY TUBERCULOSIS
rare manifestation of fulminant miliary TB resulting
from hematogenous spread of mycobacteria to
multiple organs, including skin
Miliary TB of the skin
histological char of miliary TB of the skin
lesions show microabscesses w/tissue
necrosis & nonspecific inflammatory infiltrates
Generalized exanthem in patients w/ moderate or high
degree of immunity to TB because of previous infection;
usually in good health with no identifiable focus of active
TB in skin or elsewhere
TUBERCULID
presents as recurring nodules or lumps on the back of the legs (mostly women) that may ulcerate and scar. It is a type of nodular vasculitis
Erythema induratum (Bazin disease)
results in crops of recurrent crusted skin papules on
knees, elbows, buttocks or lower trunk that heal with
scarring after about 6 weeks
Papulonecrotic tuberculid
extending eruption of small follicular papules in young
persons w/ underlying TB
Lichen scrofulosorum
Also called tuberculous gumma
METASTATIC TUBERCULOUS ABSCES
Hematogenous infection of the skin from an internal
lesion may result in a large dermal or subcutaneous
nodule that is necrotic & ultimately ulcerates the
epidermis
METASTATIC TUBERCULOUS ABSCES
Small yellowish nodule on mucosa breaks down to
form painful circular or irregular ulcer w/ undermined
borders & pseudomembranous material
• Orificial Tuberculosis
Subcutaneous abscess, nontender, “cold,” fluctuant
METASTATIC TUBERCULOUS ABSCES
the standard diagnostic skin test for tuberculosis
MANTOUX TEST
The PPD contains a very small amount of tuberculosis
proteins, called
antigens.
TVC: is characterized by
massive
pseudoepitheliomatous hyperplasia of epidermis and
abscesses.
the infection commences as a cutaneous nodule that
ulcerates down to fat & bone w/ extensive undermining
of the epidermis
MYCOBACTERIUM ULCERANS
antecedent factor in M ulcerans
penetrating trauma
an infectious disease that is characterized by disfiguring
skin sores & nerve damage
LEPROSY
enzyme characteristic
of leprosy bacilli
O-diphenoloxidase
Positive lepromin skin test
TUBERCULOID
in tuberculoid TB Skin is infiltrated with
helper T cells
more severe leprosy, contagious & may be transmitted from
person to person
LEPROMATOUS
Negative lepromin skin test
LEPROMATOUS
in lepromatous
leproy Cell –mediated immunity is markedly deficient the skin
is infiltrated with
suppressor T Cells
can be used to distinguish between tuberculoid &
lepromatous leprosy
Lepromin skin test
standard combination for the treatment of leprosy
dapsone, rifampin &
clofazimine.
Other antibiotics used to treat leprosy
ethionamide, minocycline
clarithromycin, ofloxacin
hallmark of infections with M tuberculosis
granulomas
You observe a 40-year-old man begging on a street in a town
in India. He has clawing of the fourth and fifth digits with loss
of distal parts of the digits of both hands, strongly suggesting
leprosy. The causative agent of this disease
(A) Is susceptible to isoniazid and rifampin
(B) Grows in parts of the body that are cooler than 37°C
(C) Can be cultured in the laboratory using Middlebrook 7H11
medium
(D) Is seen in high numbers in biopsies of tuberculoid leprosy
lesions
(E) Commonly infects people in Texas because armadillos are
hosts of Mycobacterium leprae
B
produce
pigment in light but not in darkness
Photochromogens
develop pigment when growing in the dark
scotochromogens
nonpigmented or have
light tan or buff-colored colonies
nonchromogens
