Mycobacterium assist. Prof. - PowerPoint Presentation

Slide1

Mycobacterium

assist. Prof.

Zainab

Abdul

jabar

Aldhaher

Slide2

According to the World Health Organization (WHO),

nearly 2

billion people,

one-third of the world

’

s population

,

have disease

caused by mycobacteria, particularly tuberculosis.

Mycobacteria are widespread both in the environment

and in

animals and cause two major human diseases –

tuberculosis and

leprosy. They are aerobic, acid-fast bacilli (

not stained

by the Gram stain because of the high lipid

component of

the cell wall). The major medically important

pathogens are

:

•

Mycobacterium tuberculosis

, the

agent of

tuberculosis

;

one of the top three infectious diseases

affecting humans

globally

Slide3

Pathogenicity

This organism is the agent of tuberculosis, a chronic,

granulomatous, slowly

progressive infection, usually of the

lungs; eventually

, many other organs and tissues may be affected.

A pandemic disease, tuberculosis is especially common

in the

developing world owing to HIV infection (15–20%

of individuals

with HIV disease may have tuberculosis).

Slide4

Mycobacterium

Mycobacterium

is a

genus

of

Actinobacteria

, given its own family, the

Mycobacteriaceae

.

The genus includes

pathogens

known to cause serious diseases in mammals, including:

tuberculosis

(

Mycobacterium tuberculosis

)

leprosy

(

Mycobacterium

leprae

).

Slide5

Slide6

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mycobacterium tuberculosis

(MTB) is a

pathogenic

bacterial

species in the genus

Mycobacterium

and the causative agent of most cases of

tuberculosis

(TB)First discovered in 1882 by

Robert Koch

,

Slide8

M. tuberculosis

has an unusual, waxy coating on its cell surface (primarily

mycolic

acid

), which makes the cells impervious to

Gram staining

, so

acid-fast

detection techniques are used, instead. The physiology of

M. tuberculosis

is highly

aerobic

and requires high levels of oxygen.

Slide9

Microbiologic characteristics

Mycobacteria

are

aerobic

and

nonmotile

bacteria.

Mycobacteria

do not contain

endospores

or

capsules

and are usually considered

Gram-positive

.

All

Mycobacterium

species share a characteristic

cell wall

, thicker than in many other bacteria, which is

hydrophobic

, waxy, and rich in

mycolic

acids

/

mycolates

.

Slide10

Many

Mycobacterium

species adapt readily to growth on very simple

substrates

, using

ammonia

or

amino acids

as nitrogen sources and

glycerol

as a carbon source in the presence of mineral salts. Optimum growth temperatures vary widely according to the species and range from 25 °C to over 50 °C.

Some species can be very difficult to

culture

(i.e. they are

fastidious

),

Slide11

M

. tuberculosis

requires oxygen to grow

. It does not retain any bacteriological stain due to high lipid content in its wall, and thus is neither Gram-positive nor Gram-negative; hence

Ziehl-Neelsen

staining

, or acid-fast staining,

Slide12

M. tuberculosis

divides every 15–20 hours, which is extremely slow compared to other bacteria, which tend to have division times measured in minutes (

Escherichia coli

can divide roughly every 20 minutes). It is a small

bacillus

that can withstand weak

disinfectants

and can survive in a dry state for weeks. Its unusual cell wall, rich in

lipids

(e.g.,

mycolic

acid

), is likely responsible for this resistance and is a key virulence factor.

Slide13

symptoms

Fever

Malaise – tired, achy

Lung degeneration – pneumonia

Chronic cough

Septicemia, multiple organ failure

Weight loss despite increased appetite – “consumption”

Slide14

Virulence Factors

Waxy cell wall.

Major factor is ability to invade and survive within macrophages as surface protein called “exported repetitive protein” prevents

phagosome

from joining with lysosome.

It produces no exotoxins or no LPS.

Slide15

Pathogenicity

The organism generally transmitted by droplets from person with active case of tuberculosis.

The microorganism is very stable in sputum droplets and can remain viable in very even dry sputum for up 6 days.

M. tuberculosis in droplets is then inhaled and reach the highly aerobic environment of the lung where it produce non specific

pneumonitis

.

Slide16

Inflammation occurs such that more phagocytes travel to the site this is called an “exudative lesion” end up with a mass of live and dead bacteria, live and dead phagocytes surrounded by an outer layer of macrophages called a granuloma – due to large number of granulocytes, granuloma becomes surrounded by fibrin which calcifies called a tubercle, can be seen by chest X – ray. The infection may stop at this point and the individual may have no more symptoms

Slide17

The tubercle can break though the lung into blood vessels and then be disseminated throughout the body – becomes systemic infection, 50% mortality rate.

Tubercle can be coughed up and swallowed, becoming systemic via the gastrointestinal tract

Tubercle can burst years after

primery

infection –

Reactivation TB

Slide18

diagnosis

demonstration

of acid fast bacilli in smear made from sputum sample is indicative of tuberculosis.

M.tuberculosis

can be culture from

suptum

or other contaminated fluids onto egg yolk containing agar or onto oleic acid albumin agar following 2-4 weeks of

incubation.

The 

Löwenstein

–Jensen medium

, is a growth medium specially used for culture of

Mycobacterium

species, notably 

Mycobacterium tuberculosis

.

Slide19

Löwenstein

–Jensen medium 

Löwenstein

-Jensen agar

Slide20

When grown on this medium appears as brown, granular colonies (sometimes called "buff, rough and tough"). The medium must be incubated for a significant length of time, usually four weeks, due to the slow doubling time of 

M. tuberculosis

 (15–20 hours) compared with other bacteria

.

Chest

X – ray

Tuberculin skin test (

Mantoux

Test)

Purified protein derivative (PPD), part of cell wall is injected under the skin, 24 – 48 hours measure the size of the welt that forms. Cell have been primed and recognize the

PPD

.

Slide21

Positive reaction means you have been exposed to the organism:

Could have active infection

Could have been infected but were one of the 90% who are Asymptomatic.

You have been immunized

Slide22

Antigenic structure:

The

mycobacterial

antigens have been classified as:

1- Soluble (

cytoplasmic

) and insoluble (cell wall lipid bound).

2- Carbohydrates or proteins

3- by their distribution within the genus

Slide23

T

reatment

Antibiotic sensitivity and

control

Long-term

therapy (6–9 months) with

antituberculous

drugs (isoniazid

, rifampicin,

pyrazinamide,

ethambutol

). As

drug resistance

is growing and a persistent

problem,

combination therapy

should always

be given. Tubercle bacilli resistant

to a

number of

antituberculous

drugs (

multidrug-resistant tuberculosis

(MDR-TB)) is a growing problem.

Hence, regimentation of

drug delivery is a cornerstone of managing

the disease

, which is achieved by a global

programme

termed

directly

observed therapy

(

DOT

). Prevention

is by

bacille

Calmette

–

Gu

é

rin

(

BCG

)

vaccination

containing

live attenuated organisms, in childhood.

Slide24

vaccine

BCG (Bacilli

Calmete

Guerin)

vacine

Made to stimulate the cell mediated immune response as

M. tuberculosis

is largely an intracellular pathogen

Uses live attenuated

M.

bovis

, causes TB in cows

Most effective in children, given as part of early childhood regime in endemic regions

Some cases of human contracting

M.

bovis

from vaccine, or from drinking unpasteurized milk from infected cow.

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