The study of biology has assumed vital significance today. This topic deals with bacteria and the
diseases they cause. There is no doubt that there are many books which are very rich so far as the subject
matter is concerned, but most of them present lengthy accounts. The subject matter has been presented
in a very simple language and comprehensive tables. This would help students to understand and
memorize the whole thing easily without any confusion.
If any error might have crept in this book, suggestions for improvement will be gratefully acknowledged.
OCTOBER 2019 DIMPLE TALUKDAR
3. A disease is a condition that impairs the proper functioning of the body or of one of its part.
Hundreds of different diseases exist. Every disease has a cause, although the causes of some
remain to be discovered. Diseases may be epidemic (strikes many persons in a community),
endemic (strikes a particular region every year), acute (quick onset) or chronic (slow onset).
Diseases are of two types- communicable and non-communicable.
Communicable diseases are infectious and can be passed among persons.
Non-communicable diseases are non infectious and are caused by malfunctions of the
body.Communicable Diseases can be contagious or non contagious. Contagious diseases are
transmitted from infected persons to healthy persons through contact whereas non
contagious diseases are passed without two people coming in contact. The passage of
pathogens is through water, food or vector. Communicable diseases are categorized according
to the type of pathogens like viral, bacterial, fungal etc.
Some common bacterial diseases are-
NAME OF DISEASE PATHOGEN
CHOLERA Vibrio cholerae
PNEUMONIA Streptococcus pneumoniae
TYPHOID Salmonella typhi
TETANUS Clostridium tetani
TUBERCULOSIS Mycobacterium tuberculosis
ANTHRAX Bacillus anthracis
PLAGUE Yersinia pestis
LEPROSY Mycobacterium leprae
DIPHTHERIA Corynebacterium diphtheria
WHOOPING COUGH Bordetella pertussis
Vibrio cholera 0:1 & 0:139 produce the exotoxin, cholera toxin which causes the host cells
to secrete water & electrolytes (potassium) resulting in watery stools containing masses of
intestinal mucus called “rice water stools” from their appearance. The sudden loss of fluids
and electrolytes causes violent vomiting, shock, collapse & often death. The microbes are
not invasive and a fever is usually not present.
Preventive measures include proper community sanitation, purification of water, personal
cleanliness, isolation of patient.
Treatment : Rehydration, doxycycline.
Pneumonia caused by Streptococcus pneumonia is the most common. Pneumonia caused
by other micro-organisms are called atypical pneumonias. Fluids get collected in the
alveoli due to which lungs do not get sufficient oxygen. It is characterized by chest pain,
cough, rapid shallow breathing and high temperature.
Some common bacterial pneumonia are-
DISEASE NAME PATHOGEN SYMPTOMS
Pneumococcal pneumonia Streptococcus pneumoniae Infected alveoli of lung fills with fluids,
difficulty in oxygen uptake
Haemophilus influenza pneumonia Haemophilus influenzae Symptoms are same as Pneumococcal
Mycoplasmal pneumonia Mycoplasma pneumoniac Low fever, cough, headache
Important drugs for pneumonia are- erythromycin, tetracycline and sulphonamide.
It is caused by Salmonella typhi. It is characterized by high fever and continual headache.
Diarrhea appears only during the 2nd
week and the fever then tends to decline. The
bacteria enters the phagocytic cells and multiply within them and gets disseminated into
multiple organs. Eventually, the phagocytic cell lyse and release the bacteria into the
bloodstream. In severe cases, ulceration and perforation of the intestinal wall can occur.
Typhoid is diagnosed by Widal test.
Antibiotics are – Ampicillin and Chloramphenicol.
Causative agent of tetanus is Clostridium tetani. Tetanus is caused by the neurotoxin,
tetanospasmin, that is released upon death & lysis of the growing bacteria. It enters the
central nervous system via peripheral nerves or blood. Tetanus results in painful spasm
of involuntary muscles and paralysis that begins with jaw and neck muscles. When the
muscles of the jaw are affected, it prevents the mouth from opening, the condition known
as lock jaw. In extreme cases, spasm of back muscles cause the head and heels to bow
backward, a condition called opisthotonos. Gradually, other skeletal muscles are affected
and death results from spasms of the respiratory muscles. Effective vaccines for tetanus
have been available since 1940.
Prevention and Treatment – Toxoid vaccine (DTaP, Td), debridement (removal of tissue)
and antibiotics may be used to control the infection.
6. TUBERCULOSIS (TB)
TB is an infectious disease caused by the bacterium Mycobacterium tuberculosis.
TB is most commonly acquired by inhaling the bacteria. The bacterium may be ingested
by alveolar macrophages, but some often survive and multiply (reproduce) in the
macrophages. Lesions forms by the bacterium are called tubercles. Tubercle bacilli
multiplying in macrophages causes a chemotactic response that brings additional
macrophages to the area. Most of the surrounding macrophages that are not successful
in destroying the bacteria release enzymes and cytokines which cause a lung damaging
inflammation. If body’s defenses fail, the tubercle breaks down and the bacteria are then
released into cardiovascular and lymphatic systems.
TB is characterized by coughing, fever, weight loss, blood in sputum. Mantoux test,
X-Ray are carried out to diagnose TB. BCG vaccine gives considerable protection
Anti-tuberculosis drugs include streptomycin, rifampicin, ethambutol etc.
It is caused by spore forming bacterium Bacillus anthracis. It most commonly occurs in
wild and domestic herbivores animals. Humans contract anthrax by handling infected
animals. The spores (endospores) enter through cuts in the skin, respiratory tract or
mouth. Anthrax infection can occur in three forms- cutaneous, inhalation and
gastro-intestinal. Cutaneous anthrax results from contact with material containing
anthrax endospores. It is characterized by itchy bump which develops into an ulcerated
area that is covered by a blood eschar. Inhalation (pulmonary) anthrax is the most
dangerous form of anthrax in human, as the endospores inhaled into the lungs have a
high probability of entering the bloodstream. It is usually fatal and is characterized by
common cold, severe breathing problems and shock.
7. Gastrointestinal anthrax is caused by ingestion of food containing endospores. Symptoms
are nausea, abdominal pain and bloody diarrhea.
Antibiotics include ciprofloxacin and doxycycline.
Plague is caused by a gram negative, rod shaped bacterium Yersinia pestis. Plague is
also called black death. It is primarily a disease of rat. Plague is transmitted from one rat
to another by the rat flea Xenopsylla cheopis. Infection can be caused from skinning of
infected animals, scratches, bites and licks by domestic cats. The infection can also be
transmitted from man by head louse (Pediculus) and bed bug (Cimex).
Plague is of three types- (i) bubonic (ii) pneumonic (iii) septicemic.
Bubonic plague is caused by multiplication of the bacteria in bloodstream and lymph
nodes, especially those of armpits, neck and groin. The lymph nodes in the groin and
armpit become enlarged and fever develops as the body’s defenses react to the infection.
Pneumonic plague is caused when the bacteria are carried by the blood to the lungs.
It spreads from human to human through droplets.
Septicemic plague arises when the bacteria proliferate causing septic shock. It is
characterized by fever, chill etc leading to death.
Streptomycin and tetracycline are effective against the bacteria.
Leprosy is caused by Mycobacterium leprae. The bacterium can grow in the peripheral
nervous system as well as in skin cells. It is also known as Hansen’s disease. It occurs
in two forms- tuberculoid (neural) and lepromatous (progressive) forms.
In tuberculoid form, the disease is characterized by loss of sensation in the skin
surrounded by nodules.
8. In the lepromatous form, tissue necrosis occur.
Leprosy is not highly contagious. It is spread by prolonged contact with someone with
Dapsone, rifampin and clofazimine are the principal drugs used for treatment.
It is a respiratory disease caused by Corynebacterium diphtheria. It is most common in
children. It infects the upper respiratory system. The disease is characterized by
formation of a tough grayish membrane in the throat. Penicillin, erythromycin in
conjunction with antitoxin is used against this disease. Another form of diphtheria,
cutaneous diphtheria infects the skin, usually at a wound. Cutaneous diphtheria is most
common in tropical countries.
It is caused by the bacterium Bordetella pertussis. The first or initial stage is called
catarrhal stage and it resembles a cold. The second stage is called the paroxysmal stage
is characterized by deep cough due to accumulation of mucus in the trachea and bronchi.
The third stage, convalescence stage can last for months. It is characterized by a chronic
cough that becomes less paroxysmal in nature.
DTaP vaccination is used as prevention against this disease.
Some other common diseases are summarized in the table below-
9. Name of the disease Pathogen Symptoms Method of
Acne Propionibacterium acnes Inflamatory lesions with
accumulations of sebum
that rupture a hair
Haemophilus influenza Fever, Headache Infections aerasals
Listeriosis Listeria monocytogenes Fever, Nausea, Muscle
Food borne infection
Botulism Clostridium botulinum Difficulty swallowing,
Food borne infection
Conjunctivitis Haemophilus influenzae Redeness of eye Direct Contact
Otitis externa Pseudomonas aeruginosa Infection of external ear Swimming water
Pericarditis Streptococcus pyogenes Fever, Weakness Focal infection
Rheumatic Fever Group A B-hemolytic
Arthritis, Fever, Heart
Lyme Disease Borrelia burgdor feri Rashes that appear near
Rickettsia rickettsii Rash, Headache Dermacentar ticks
Epiglottitis Haemophilus influenzae Inflammation of the
Pharyngitis Streptococcus pyogenes Inflamed mucous
membranes of the
throat, Scratchy throat
Staphylococcus aurous Nausea, Vomiting &
Ingestion of food
infected with the
Shigellosis Gram negative rods of
Dysentry Ingestion of food
infected with the
Salmonellosis Salmonella enterica Fever, Nausea &
Ingestion of food
infected with the
10. Traveller’s diarrhea Escherichia coli Watery diarrhea Ingestion of food
infected with the
Helicobacter pylori Peptic ulcers Infections
Yersinia gastro enteritis Yersinia enterocolitica Abdominal pain,
Painful urination Reaction to certain
drugs, Sexual activity
(Infection of kidney)
E.coli Fever, Back pain,
Bacteria enter the body
Leptospira interrogans Fever, Muscle pain,
Direct contact with
urine from infected
animals or via water ,
soil contaminated with
Gonorrha Neisseria gonarrhoeae
Painful urination &
discharge of pus in
males. In females few
symptoms but possible
complications such as
Spreads by sexual
Neisseria gonarrhoeae Chronic abdominal
pain, painful urination,
Syphilis Treponema pallidum Sore at the site of
infection, mild fever,
damage to nervous &
in final stages
Sexual contact, By
mother to babies in
Bacterial vaginosis Gardnerella vaginalis Fishy order, Frothy