Tuberculosis: Pathophysiology, Clinical Features, Diagnosis and Antitubercular Activity of an
Actinomycin Produced by a New Species of Streptomyces
Ravi G Patel, Chirag
K Patel, B Panigrahi and CN Patel
Department of Pharmaceutical
Chemistry,
ABSTRACT:
Tuberculosis is an infection caused by the
rod-shaped, non–spore-forming, aerobic bacterium Mycobacterium tuberculosis.Mycobacteria
typically measure 0.5 ěm by 3 ěm, are classified as acid-fast bacilli, and have
a unique cell wall structure crucial to their survival. The well developed cell
wall contains a considerable amount of a fatty acid, mycolic acid, covalently
attached to the underlying peptidoglycan-bound polysaccharide arabino galactan,
providing an extraordinary lipid barrier. Mycobacterium tuberculosis is spread
by small airborne droplets, called droplet nuclei, generated by the coughing,
sneezing, talking, or singing of a person with pulmonary or laryngeal
tuberculosis. These minuscule droplets can remain airborne for minutes to hours
after expectoration. During the course of a systematic search for new
antibiotics, an actinomycin complex was isolated from Streptomyces regensis sp.
This actinomycin complex differs from other actinomycins described in
literature in its amino acid composition and is very highly active against Staphylococcus
aureus and Mycobacterium tuberculosis. The strains of Staph. aureus highly
resistant to penicillin, streptomycin, chloramphenicol, tetracyclin and
erythromycin are equally susceptible to its action.
INTRODUCTION:
Tuberculosis
has recently emerged as a major health concern. Each year, approximately 2
million persons worldwide die of
tuberculosis and 9 million become infected.1 In the United States,
approximately 14000 cases of tuberculosis were reported in 2006, a 3.2% decline
from the previous year; however, 20 states and the District of Columbia had
higher rates.2 The prevalence of tuberculosis is continuing to
increase because of the increased number of patients infected with human
immunodeficiency virus, bacterial resistance to medications, increased
international travel and immigration from countries with high prevalence, and
the growing numbers of the homeless and drug abusers.3With 2 billion
persons, a third of the world population, 1 estimated to be infected with
mycobacteria, all nurses, regardless of area of care, need to understand the
pathophysiology, clinical features, and procedures for diagnosis of
tuberculosis. The vulnerability of hospitalized patients to tuberculosis is
often under recognized because the infection is habitually considered a disease
of the community.
Most
hospitalized patients are in a suboptimal immune state, particularly in
intensive care units, making exposure to tuberculosis even more serious than in
the community. By understanding the causative organism, pathophysiology,
transmission, and diagnostics of tuberculosis and the clinical manifestations
in patients, critical care nurses will be better prepared to recognize
infection, prevent transmission, and treat this increasingly common disease.
Causative
Organism:
Tuberculosis is
an infection caused by the rod-shaped, non–spore-forming, aerobic bacterium Mycobacterium
tuberculosis.4Mycobacteria typically measure 0.5 ěm by 3 ěm, are
classified as acid-fast bacilli, and have a unique cell wall structure crucial
to their survival. The well developed cell wall contains a considerable amount
of a fatty acid, mycolic acid, covalently attached to the underlying
peptidoglycan-bound polysaccharide arabino galactan, providing an extraordinary
lipid barrier. This barrier is responsible for many of the medically
challenging physiological characteristics of tuberculosis, including resistance
to antibiotics and host defense mechanisms.
The composition
and quantity of the cell wall components affect the bacteria’s virulence and
growth rate.5 The peptidoglycan polymer confers cell wall rigidity
and is just external to the bacterial cell membrane, another contributor to the
permeability barrier of mycobacteria. Another important component of the cell
wall is lipoarabinomannan, a carbohydrate structural antigen on the outside of
the organism that is immunogenic and facilitates the survival of mycobacteria
within macro - phages.5,6 The cell wall is key to the survival of
mycobacteria, and a more complete understanding of the biosynthetic pathways
and gene functions and the development of antibiotics to prevent formation of
the cell wall are areas of great interest.6
Transmission:
Mycobacterium
tuberculosis is spread by
small airborne droplets, called droplet nuclei, generated by the coughing,
sneezing, talking, or singing of a person with pulmonary or laryngeal
tuberculosis. These minuscule droplets can remain airborne for minutes to hours
after expectoration.5 The number of bacilli in the droplets, the
virulence of the bacilli, exposure of the bacilli to UV light, degree of
ventilation, and occasions for aerosolization all influence transmission.7
Introduction of M. tuberculosis into the lungs leads to infection of the
respiratory system; however, the organisms can spread to other organs, such as
the lymphatics, pleura, bones/joints, or meninges, and cause extrapulmonary
tuberculosis.
Pathophysiology:
Once inhaled, the
infectious droplets settle throughout the airways. The majority of the bacilli
are trapped in the upper parts of the airways where the mucus-secreting goblet
cells exist. produced catches foreign substances, and the cilia on the surface
of the cells constantly beat the mucus and its entrapped particles upward for
removal.8 This system provides the
body with an initial physical defense that prevents infection in most
persons
exposed to
tuberculosis.9Bacteria in droplets that bypass the mucociliary
system and reach the alveoli are quickly surrounded and engulfed by alveolar
macrophages,7,8 the most abundant immune effecter cells present in
alveolar spaces.10 These macrophages, the next line of host defense, are part of the innate immune
system and provide an opportunity for the body to destroy the invading
mycobacteria and prevent infection.11 Macrophages are readily
available phagocytic cells that combat many pathogens without requiring
previous exposure to the pathogens. Several mechanisms and macrophage receptors
are involved in uptake of the mycobacteria.11 The mycobacterial
lipoarabinomannan is a key ligand for a macrophage receptor.12 The
complement system also plays a role in the phagocytosis of the bacteria.13
The complement protein C3 binds to the cell wall and enhances recognition of
the mycobacteria by macrophages. Opsonization by C3 is rapid, even in the air
spaces of a host with no previous exposure to M tuberculosis.14
The subsequent phagocytosis by macrophages initiates a cascade of events that
results in either successful control of the infection, followed by latent
tuberculosis, or progression to active disease, called primary progressive
tuberculosis.8 The outcome is essentially determined by the quality
of the host defenses and the balance that occurs between host defenses and the
invading mycobacteria.11,15 After being ingested by macrophages, the
mycobacteria continue to multiply slowly,8 with bacterial cell
division occurring every 25 to 32 hours.4,7 Regardless of whether
the infection becomes controlled or progresses, initial development involves
production of proteolytic enzymes and cytokines by macrophages in an attempt to
degrade the bacteria.11,12 Released cytokines attract T lymphocytes
to the site, the cells that constitute cell-mediated immunity. Macrophages then
present myco - bacterial antigens on their surface to the T cells.11
This initial immune process continues for 2 to 12 weeks; the microorganisms
continue to grow until they reach sufficient numbers to fully elicit the
cell-mediated immune response, which can be detected by a skin test.4,8,11
For persons with intact cell mediated immunity, the next defensive step is
formation of granulomas around the M tuberculosis organisms16
(Figure 1).
Clinical
Manifestations:
As the cellular
processes occur, tuberculosis may develop differently in each patient,
according to the status of the patient’s immune system. Stages include latency,
primary disease, primary progressive disease, and extrapulmonary disease. Each
stage has different clinical manifestations (Table 1).
TB can be
diagnosed in several different ways, including chest x-rays, analysis of
sputum, and skin tests. Sometimes, the chest x-rays can reveal evidence of
active tuberculosis pneumonia. Other times, the x-rays may show scarring
(fibrosis) or hardening (calcification) in the lungs, suggesting that the TB is
contained and inactive. Examination of the sputum on a slide (smear) under the
microscope can show the presence of the tuberculosis-like bacteria. Bacteria of
the mycobacterium family, including atypical mycobacteria, stain positive with
special dyes and are referred to as acid-fast bacteria (AFB). A sample of the
sputum also is usually taken and grown (cultured) in special incubators so that
the tuberculosis bacteria can subsequently be identified as tuberculosis or
atypical tuberculosis. Several types of skin tests are used to screen for TB
infection.
Figure 1. Pathophysiology of tuberculosis:
Inhalation of bacilli (A), Containment in a granuloma (B), and breakdown of the
granuloma in less inmmunocompetent individuals (c).
Images courtesy of Centers for Disease
Control and Prevention.
Table 1 Differences
in the stages of tuberculosis
|
Early
infection |
Early
primary progressive (active) |
Late
Primary Progressive (active) |
Latent |
|
Immune
system fights infection |
Immune
system does not control initial infection |
Cough
becomes productive |
Mycobacteria
persist in the body |
|
Infection
generally proceeds without signs or symptoms |
Inflammation
of tissues ensures |
More signs
and symptoms as disease progresses |
No signs or
symptoms occur |
|
Patients
may have fever, Paratracheal
lymphadenopathy, or dyspnea |
Patients
often have nonspecific signs or symptoms (eg. Fatigue, weight loss, fever) |
Patients
experience progressive weight loss, rales, anemia |
Patients do
not feel sick Patients
are susceptible to reactivation of disease |
|
Infection
may be only subclinical and may not advance to active disease |
Nonproductive
cough develops |
Findings on
chest radiograph are normal |
Granulomatous
lesions calcify and become fibrotic become apparent on the chest radiographs |
|
|
Diagnosis
can be difficult : findings on chest radiographs may be normal and sputum
smears may be negative for mycobacteria |
Diagnosis
is via cultures of sputum |
Infection
can reappear when immunosuppression occurs |
TABLE 2: Antitubercular
activity of an actinomycin complex
|
Culture |
Drug |
Minimum
inhibitory concentration in µg/ml |
|
|
Complete Inhibition |
Partial inhibition |
||
|
M. tuberculosis H3, RV |
Actionomcin
complex |
1 |
0.25-0.5 |
|
M. tuberculosis Ravenel |
“ |
1 |
0.25-0.5 |
|
M. tuberculosis ATCC 607 |
“ |
10 |
5 |
|
M. avium B 19.2 |
“ |
2 |
0.5 – 1 |
|
M. tuberculosis H37RV |
Streptomycin |
0.5 |
0.25 |
|
M. tuberculosis Ravenel |
… |
1 |
0.5 |
|
M. avium B 19.2 |
… |
1 |
… |
These so-called tuberculin skin tests
include the Tine test and the Mantoux test, also known as the PPD (purified
protein derivative) test. In each of these tests, a small amount of purified
extract from dead tuberculosis bacteria is injected under the skin. If a person
is not infected with TB, then no reaction will occur at the site of the
injection (a negative skin test). If a person is infected with tuberculosis,
however, a raised and reddened area will occur around the site of the test
injection. This reaction, a positive skin test, occurs about 48 to 72 hours
after the injection. If the infection with tuberculosis has occurred recently,
however, the skin test can be falsely negative. The reason for a false negative
test with a recent infection is that it usually takes two to 10 weeks after the
time of infection with tuberculosis before the skin test becomes positive. The skin test can also be falsely
negative if a person's immune system is weakened or deficient due to another
illness such as AIDS or cancer, or while taking medications that can suppress
the immune response, such as cortisone or anticancer drugs. Remember, however,
that the TB skin test cannot determine whether the disease is active or not.
This determination requires the chest x-rays and/or sputum analysis (smear and
culture) in the laboratory. The organism can take up to six weeks to grow in culture in the microbiology lab.
A special test to diagnose TB called the PCR (polymerase chain reaction)
detects the genetic material of the bacteria. This test is extremely sensitive
(it detects minute amounts of the bacteria) and specific (it detects only the
TB bacteria). One can usually get results from the PCR test within a few days.
ANTITUBERCULAR ACTIVITY OF AN ACTINOMYCIN PRODUCED BY A NEW SPECIES OF
STREPTOMYCES:17
During the course of a systematic search for
new antibiotics, an actinomycin complex was isolated from Streptomyces
regensis sp. nov. (Gupta et al., 1963). This actinomycin complex
differs from other actinomycins described in literature in its amino acid
composition and is very highly active agairtst Staphylococcus aureus and
Mycobacterium tuberculosis. The strains of Staph. aureus highly
resistant to penicillin, streptomycin, chloramphenicol, tetracyclin and
erythromycin are equally susceptible to its action. This report deals with the
antitubercular activity of this actinomycin complex. Antitubercular activity
was tested by serial dilution method in Youman’s medium containing Tween 80 and
bovine albumin Fraction V. The tubes containing the desired concentration of
the drug in the medium were inoculated with 0.03 ml. of 14 days old culture of
Mycobacterium tuberculosis H37 RV, M. tuberculosis Ravenel
and M. avium B 19.2, The results were read after 14 days of incubation
at 37°C. In the case of M. tuberculosis ATCC 607, the reading were taken
after 48 hours. The results of antitubercular activity of the actinomycin
complex are shown in Table 1. It is obvious from the perusal of the table that
the actinomycin complex shows a very high antitubercular activity. The growth
of M. tuberculosis H37RV and M. tuberculosis Ravenel is inhibited
in a concentration of 1 /µg/ml. There is a partial inhibition of growth in a
concentration of 0.25 to 0.5 /ug/ml. The growth of M. avium B
19.2 and M. tuberculosis 607 is inhibited in concentration of 2 and 10
/µg/ml. respectively.
SUMMARY:
The actinomycin
complex isolated from S. regensis sp. nov. shows very high
antitubercular activity which is comparable
to that of streptomycin (Table 2).
REFERENCES:
1.
Centers
for Disease Control and Prevention. World TB day—
2.
Centers
for Disease Control and Prevention. Trends in tuberculosis incidence,
3.
Goldrick
BA. Once dismissed, still rampant: tuberculosis, the second deadliest
infectious disease worldwide. Am J Nurs. 2004; 104(9):68-70.
4.
Porth
CM. Alterations in respiratory function: respiratory tract infections,
neoplasms, and childhood disorders. In: Porth CM, Kunert MP. Pathophysiology:
Concepts of Altered Health States.
5.
Lee RB,
Li W, Chatterjee D, Lee RE. Rapid structural characterization of the
arabinogalactan and lipoarabinomannan in live mycobacterial cells using 2D and
3D HR-MAS NMR: structural changes in the arabinan due to ethambutol treatment
and gene mutation are observed. Glycobiology. 2005;15(2):139-151.
6.
Joe M,
Bai Y, Nacario RC, Lowary TL. Synthesis of the docosanasaccharide arabinan
domain of mycobacterial arabinogalactan and a proposed octadecasaccharide
biosynthetic precursor. J Am Chem Soc.
2007;129 (32):9885-9901.
7.
American
Thoracic Society and Centers for Disease Control and Prevention. Diagnostic
standards and classification of tuberculosis in adults and children. Am J
Respir Crit Care Med. 2000;161(4 pt 1):1376-1395.
8.
Frieden
TR, Sterling TR, Munsiff SS, Watt CJ, Dye C. Tuberculosis. Lancet. 2003;362: 887-899.
9.
Jensen
PA, Lambert LA, Iademarco MF, Ridzon R; Centers for Disease Control and
Prevention. Guidelines for preventing the transmission of Mycobacterium
tuberculosis in health-care settings, 2005. MMWR Recomm Rep. 2005;54(RR-17):1-141.
10.
Korf
JE, Pynaert G, Tournoy K, et al.Macrophage reprogramming by mycolic acid
promotes a tolerogenic response in experimental asthma. Am J Respir Crit
Care Med. 2006;174(2):152-160.
11.
van
Crevel R, Ottenhoff THM, van der Meer JWM. Innate immunity to Mycobacterium
tuberculosis. Clin Microbiol Rev. 2002;15: 294-309.
12.
Nicod
LP. Immunology of tuberculosis. Swiss Med Wkly. 2007;137(25-26):357-362.
13.
Li Y, Petrofsky M, Bermudez LE. Mycobacterium tuberculosis uptake by recipient host macrophages is
influenced by environmental conditions in the granuloma of the infectious
individual and is associated with impaired production of interleukin-12 and
tumor necrosis factor alpha. Infect Immun. 2002;70:6223-6230.
14.
Ferguson JS, Weis JJ, Martin JL, Schlesinger LS. Complement protein C3 binding to Mycobacterium
tuberculosis is initiated by the classical pathway in human bronchoalveolar
lavage fluid. Infect Immun. 2004;72: 2564-2573.
15.
Goyot-Revol
V, Innes JA, Hackforth S, Hinks T, Lalvani A. Regulatory T cells are expanded
in blood and disease sites in patients with tuberculosis. Am J Resp Crit
Care Med. 2006;173:803-810.
16.
Rosenkrands
I, Slayden RA, Crawford J, et al. Hypoxic response of Mycobacteria tuberculosis
studied by metabolic labeling and proteome analysis of cellular and
extracellular proteins. J Bacteriol. 2002;184:3485-3491.
17.
Gupta,
K. C., Sobti, R. R., and Chopra,
Received on 30.12.2009
Accepted on 10.02.2010
© A&V Publication all right reserved
Research J. Pharmacology and
Pharmacodynamics 2(1): Jan. –Feb. 2010: 23-26