Download M. tuberculosis

Chapter 13
Respiratory Bacilli
•M. tuberculosis (结核分枝杆菌）
•C. diphtheria (白喉棒状杆菌)
•L. pneumophila(嗜肺军团菌)
•B .pretussis (百日咳鲍特菌)
•H. influenzae(流感嗜血杆菌)
•K. pneumoniae(肺炎克雷伯菌)
Section 1
M. tuberculosis
结核分支杆菌
Ziehl-Neelsen stain
pink in a contrasting background
Mycobacterium (fungus-bacterium) :
form mould-like pellicles when grow in the liquid
media
acid-fastness :
impermeability by certain dyes and stains
once stained, acid-fast bacteria will retain dyes
when heated and treated with acidified organic
compounds.
???
thick, complex, lipid-rich, waxy cell walls !
Mycobacterium
tuberculosis
Tubercle Bacilli
Characteristics
large nonmotile
rod-shaped
bacterium
facultative
intracellular
parasite
obligate aerobe
slow generation
time, 15-20 hours
Chains of cells in
smears made
from in vitrogrown colonies
often form
distinctive
serpentine cords.
(cord factor)
Characteristics
Middlebrook's medium
Lowenstein-Jensen medium
•small and
buff colored
colonies
•4-6 weeks
inhibitors to keep contaminants
from out-growing M.TB.
Characteristics
M.TB acid-fast bacteria(AFB)
Ziehl-Neelsen stain
the M.TB. smear is fixed, stained
with carbolfuchsin (a pink dye)
decolorized with acid-alcohol.
The smear is counterstained with
methylene-blue or certain other
dyes.
Characteristics
very sensitive to ultraviolet light
heat-sensitive
destroyed in the process of
pasteurization
susceptible to alcohol,
formaldehyde and glutaralddehyde
resistant acid, alkalis and
quaternary ammonium compounds.
Constituents
A. Cell Wall Structure
peptidoglycan
Lipid:
Mycolic acids
unique alpha-branched lipids ,
strong hydrophobic molecules
Cord Factor
Wax-D : Freund's complete adjuvant (CFA)
Constituents
properties of lipids
Impermeability to stains and dyes
Resistance to many antibiotics
Resistance to killing by acidic and
alkaline compounds
Resistance to osmotic lysis via
complement deposition
Resistance to lethal oxidations and
survival inside of macrophages
Constituents
B. Proteins:
elicit the tuberculin reaction
C. Polysaccharides:
uncertain
D. capsule
Virulence Factors
M.TB. has special mechanisms for cell entry
M.TB. can grow intracellularly.
M.TB. interferes with the toxic effects of
reactive oxygen intermediates produced in
the process of phagocytosis
Slow generation time.
High lipid concentration in cell wall,
Cord factor.
Tuberculosis
TB infection
TB infection means that M.TB. is in the body
but the immune system is keeping the
bacteria under control.
Macrophages surround the tubercle bacilli
dfas form a hard shell.
( infiltration of macrophages and lymphocytes with
development of granulomas)
TB infection: not TB disease, NOT infectious
a positive reaction to the tuberculin skin
test
normal chest x-ray.
Tuberculosis: Infection vs Disease
TB Infection
TB disease in lungs
M.TB. present
M.TB. present
Tuberculin skin test positive
Tuberculin skin test positive
Chest X-ray normal
Chest X-ray usually reveals lesion
Sputum smears and cultures
negative
Sputum smears and cultures
positive
No symptoms
Symptoms such as cough, fever,
weight loss
Not infectious
Often infectious before treatment
Not defined as a case of TB
Defined as a case of TB
Pathogenesis
•
10% of infected persons with normal immune
systems develop TB at some point in life
•
HIV strongest risk factor for development of TB if
infected
- Risk of developing TB disease 7% to 10% each
year
•
Certain medical conditions increase risk that TB
infection will progress to TB disease
Conditions That Increase the Risk of
Progression to TB Disease
• HIV infection
• Substance abuse
• Recent infection
• Chest radiograph findings suggestive of previous TB
• Diabetes mellitus
• Silicosis
• Prolonged corticosteriod therapy
• Other immunosuppressive therapy
Conditions That Increase the Risk of
Progression to TB Disease (cont.)
•
Cancer of the head and neck
•
Hematologic and reticuloendothelial diseases
•
End-stage renal disease
•
Intestinal bypass or gastrectomy
•
Chronic malabsorption syndromes
•
Low body weight (10% or more below the ideal)
Transmission of M. tuberculosis
• Spread by droplet nuclei
• Expelled when person with infectious TB coughs,
sneezes, speaks, or sings
• Close contacts at highest risk of becoming infected
• Transmission occurs from person with infectious
TB disease (not latent TB infection)
Common Sites of TB Disease
•
Lungs
•
Pleura
•
Central nervous system
•
Lymphatic system
•
Genitourinary systems
•
Bones and joints
•
Disseminated (miliary TB)
Stages of the Disease
Droplet
nuclei are
inhaled.
Stage 1
Stages of the Disease
Stage 2
7-21 days after
M.TB. multiplies
macrophages are unactivated
Stages of the Disease
Stage 3
lymphocytes infiltrate:
MHC molecules T-cell activation
liberate cytokines (IFN)
activation of macrophages
tuberculin-positive : the result of
the host developing a vigorous cell
mediated immune (CMI) response
Stages of the Disease
Stage 3
tubercle formation begins
The center of the tubercle is characterized
by "caseation necrosis" meaning semisolid or "cheesy" consistency.
M.TB. cannot multiply within these
tubercles because of the low pH and
anoxic environment.
M.TB. can persist within these tubercles
for extended periods
Stages of the Disease
Stage 4
M.TB replicate in unactivated macrophages
the growing tubercle invade bronchus or blood supply line.
hematogenous spread result in extrapulmonary
tuberculosis otherwise known as miliary tuberculosis.
at almost any anatomical location
Stage 4
two types
Stages of the Disease
1.Exudative lesions
result
from
the
accumulation
of
PMN's around M.TB.
bacteria
replicate
with virtually no
resistance.
This situation gives
rise to the formation
of a "soft tubercle".
2.Productive
or
granulomatous
lesions
hypersensitive to
tuberculoproteins.
This
situation
gives rise to the
formation of a
"hard tubercle".
Stages of the Disease
Stage 5
the caseous centers of the tubercles
liquify.
M.TB begins to rapidly multiply
extracellularly
large antigen load causes the walls of
nearby bronchi to become necrotic and
rupture.
cavity formation.
M.TB. to spill into other airways and
rapidly spread to other parts of the
lung.
Classification System for TB
Description
Class
Type
0
No TB exposure
Not infected
No history of exposure
Negative reaction to tuberculin skin test
1
TB exposure
No evidence of
infection
TB infection
No disease
History of exposure
Negative reaction to tuberculin skin test
3
TB, clinically active
M. tuberculosis cultured (if done)
Clinical, bacteriological, or radiographic
evidence of current disease
4
TB
Not clinically active
History of episode(s) of TB
or
Abnormal but stable radiographic findings
Positive reaction to the tuberculin skin test
Negative bacteriologic studies (if done)
and
No clinical or radiographic evidence of
current disease
5
TB suspected
Diagnosis pending
2
Positive reaction to tuberculin skin test
Negative bacteriologic studies (if done)
No clinical, bacteriological, or radiographic
evidence of active TB
Drug-Resistant TB
• Drug-resistant TB transmitted same way as
drug-susceptible TB
• Drug resistance is divided into two types:
- Primary resistance develops in persons initially
infected with resistant organisms
- Secondary resistance (acquired resistance)
develops during TB therapy
Testing for
TB Disease and Infection
Purpose of Targeted Testing
•
Find persons with LTBI who would benefit
from treatment
•
Find persons with TB disease who would
benefit from treatment
•
Groups that are not high risk for TB should
not be tested routinely
All testing
activities should
be accompanied
by a plan for
follow-up care.
Administering
the Tuberculin Skin Test or Mantoux test
• Inject intradermally 0.1 ml of 5TU(0.000lmg) PPD
tuberculin
• PPD(purified protein derivative)
• Produce wheal 6 mm to 10 mm in diameter
• Do not recap, bend, or break needles, or remove
needles from syringes
• Follow universal precautions for infection control
Reading the Tuberculin Skin Test
• Read reaction 48-72 hours after injection
• Measure only induration
• Record reaction in millimeters
Tuberulin Test
positive if the diameter of the
resulting lesion is 5 mm or greater.
The lesion is characterized by
erythema (redness) and swelling
and induration (raised and hard).
Classifying the Tuberculin Reaction
>=5 mm is classified as positive in
•
HIV-positive persons
•
Recent contacts of TB case
•
Persons with fibrotic changes on chest
radiograph consistent with old healed TB
•
Patients with organ transplants and other
immunosuppressed patients
Classifying the Tuberculin Reaction (cont.)
>=10 mm is classified as positive in
•
Recent arrivals from high-prevalence countries
•
Injection drug users
•
Residents and employees of high-risk congregate
settings
•
Mycobacteriology laboratory personnel
•
Persons with clinical conditions that place them at
high risk
•
Children <4 years of age, or children and
adolescents exposed to adults in high-risk
categories
Classifying the Tuberculin
Reaction (cont.)
>=15 mm is classified as positive in
• Persons with no known risk factors for TB
• Targeted skin testing programs should only be
conducted among high-risk groups
Factors that May Affect the
Skin Test Reaction
Type of Reaction
False-positive
False-negative
Possible Cause
Nontuberculous mycobacteria
BCG vaccination
Anergy
Recent TB infection
Very young age (< 6 months)
Live-virus vaccination
Overwhelming TB disease
Anergy
•
Do not rule out diagnosis based on negative skin
test result
•
Consider anergy in persons with no reaction if
- HIV infected
- Overwhelming TB disease
- Severe or febrile illness
- Viral infections
- Live-virus vaccinations
- Immunosuppressive therapy.
•
Anergy skin testing no longer routinely
recommended
Boosting
•
Some people with LTBI may have negative skin
test reaction when tested years after infection
•
Initial skin test may stimulate (boost) ability to
react to tuberculin
•
Positive reactions to subsequent tests may be
misinterpreted as a new infection
Two-Step Testing
Use two-step testing for initial skin testing of adults
who will be retested periodically
• If first test positive, consider the person infected
• If first test negative, give second test 1-3 weeks
later
• If second test positive, consider person infected
• If second test negative, consider person
uninfected
Diagnosis of TB
Evaluation for TB
•
Medical history
•
Physical examination
•
Mantoux tuberculin skin test
•
Chest radiograph
•
Bacteriologic or histologic exam
Symptoms of Pulmonary TB
•
Productive, prolonged cough
(duration of >=3 weeks)
•
Chest pain
•
Hemoptysis
Systemic Symptoms of TB
•
Fever
•
Chills
•
Night sweats
•
Appetite loss
•
Weight loss
•
Easy fatigability
Medical History
•
Symptoms of disease
•
History of TB exposure, infection, or disease
•
Past TB treatment
•
Demographic risk factors for TB
•
Medical conditions that increase risk for TB
disease
Mantoux Tuberculin Skin Test
•
Preferred method of testing for TB infection
in adults and children
Chest Radiograph
•
Abnormalities often seen in apical
or posterior segments of upper
lobe or superior segments of
lower lobe
•
May have unusual appearance in
HIV-positive persons
Arrow points to cavity in
patient's right upper lobe.
•
Cannot confirm diagnosis of TB
Specimen Collection
•
Obtain 3 sputum specimens for smear
examination and culture
•
Persons unable to cough up sputum, induce
sputum, bronchoscopy or gastric aspiration
•
Follow infection control precautions during
specimen collection
Smear Examination
•
Strongly consider TB in patients with smears
containing acid-fast bacilli (AFB)
•
Results should be available within 24 hours of
specimen collection
•
Presumptive diagnosis of TB
Smear Examination
sputum sample is treated with
NaOH to kill other contaminating
bacteria
detection of acid-fast bacilli in
sputum via the Ziehl-Neelsen
method
culture
• Use to confirm diagnosis of TB
• Culture all specimens, even if smear
negative
LowensteinJensen
medium
4-6 weeks
NEW: BACTEC System 9-16days
Drug Susceptibility Testing
•
Drug susceptibility testing on initial M.
tuberculosis isolate
•
Repeat for patients who
- Do not respond to therapy
- Have positive cultures despite 2 months of
therapy
•
Promptly forward results to the health department
Treatment
multiple drugs
usually lasts from 6-9 months.
rifampin (RIF)
isoniazid (INH),
pyrazinamide (PZA )
ethambutol (EMB)
streptomycin (SM)
Basic Principles of Treatment
•
Provide safest, most effective therapy in shortest
time
•
Multiple drugs to which the organisms are
susceptible
•
Never add single drug to failing regimen
•
Ensure adherence to therapy
Adherence
•
Nonadherence is a major problem in TB control
•
Use case management and directly observed
therapy (DOT) to ensure patients complete
treatment
Infection Control in Health Care Settings
Infectiousness
Patients should be considered infectious if they
•
Are coughing
•
Are undergoing cough-inducing or aerosolgenerating procedures, or
•
Have sputum smears positive for acid-fast bacilli
and they
•
Are not receiving therapy
•
Have just started therapy, or
•
Have poor clinical response to therapy
Infectiousness (cont.)
Patients no longer considered infectious if they
meet all of these criteria:
•
Are on adequate therapy
•
Have had a significant clinical response to
therapy, and
• Have had 3 consecutive negative sputum smear
results
Prevention
vaccine against M.TB. :
BCG (Bacillus of Calmette and
Guerin)
BCG consists of a live attenuated
strain derived from Mycobacterium
bovis. This strain of Mycobacterium
has remained avirulent for over 60
years.
BCG Vaccination
Recommendations for BCG Vaccination
•
recommended in immunization programs or TB
control programs in China
BCG Contraindications
Contraindicated in persons with impaired immune
response from
•
HIV infection
•
Congenital immunodeficiency
•
Leukemia
•
Lymphoma
•
Generalized malignancy
•
Receiving high-dose steroid therapy
•
Receiving alkylating agents
•
Receiving antimetabolites
•
Receiving radiation therapy
BCG Vaccination and
Tuberculin Skin Testing
•
Tuberculin skin testing not contraindicated for BCGvaccinated persons
•
LTBI diagnosis and treatment for LTBI considered for
any BCG-vaccinated person whose skin test reaction is
>=10 mm, if any of these circumstances are present:
- Was contact of another person with infectious TB
- Was born or has resided in a high TB prevalence
country
- Is continually exposed to populations where TB
prevalence is high
Mycobacterium leprae
leprosy (Hansen's Disease)
leprosy (Hansen's Disease)
• Infect skin,
nerves
• chronic disease
• disfigurement
"tuberculoid" leprosy & "lepromatous" leprosy
diagnosis
The organism does not grow in culture media
it grow at low temperature
it grows well in the armadillo
acid-fast stains of skin biopsies and clinical
picture
Lepromin is used in skin testing. (but no
value for diagnosis)
Treatment
Treatment with antibiotics (initially dapsone
and now multi-drug) is effective and the
overall disease incidence worldwide is down.
Corynebacteria
Gram-positive,
aerobic,
nonmotile,
Rod-shaped
"Chinese-letter" arrangement of
cells : club-shaped or V-shaped
"barred" appearance :
polyphosphate inclusions called
metachromatic granules(Babes-Ernst
bodies )
Corynebacterium Diphtheriae
diphtheria
a thick gray coating over back of
throat.
pseudomembrane
This coating can eventually
expand down through airway and,
if not treated, the child could die
from suffocation
Pathogenicity
Invasion
Toxigenesis:
The diphtheria toxin causes the death
eukaryotic cells and tissues by inhibition
protein synthesis in the cells
Diphtheria Toxin Production
Following lysogenic
conversion with
corynebacteriophage
ß, or closely related
corynebacteriophages,
nontoxigenic strains
of C diphtheriae
become toxigenic
Diagnosis
staining for metachromatic bodies : intracellular
polyphosphate granules (pink) compared to the
rest of the cell (blue)
Characteristic black colonies are seen on
tellurite agar
Production of exotoxin can be determined by in
vivo or in vitro tests.
Treatment & Prevention
toxinneutralizing
antibody
(antitoxin)
antibiotics
toxoid
a trivalent vaccine
containing diphtheria
toxoid, pertussis
vaccine, and tetanus
toxoid (DPT or DTP
vaccine).