Here is a list of some bacteria and its etiological agents which causes diseases in humans. Also learn about its prevention and control.
Shigella:
The shigellae are rods, non-motile and Gram-negative. Possess distinctive antigenic structures. Pathogenic, causing dysenteries, or non-pathogenic species, all living in bodies of warm-blooded animals. Found in polluted water supplies and flies.
Shigella Dysenteriae:
Rods, 0.4 to 0.6 by 1 to 3 μ, occurring singly. Non-motile. Gram-negative.
Disease Produced – The cause of bacillary dysentery in man and monkeys. Disease characterized by acute onset accompanied by diarrhea, sometimes fever in severe cases, tenesmus, and frequent stools containing blood and mucus. Severe infections most frequent in infants and in elderly debilitated persons. Synonym – shigellosis.
S. dysenteriae produces an active exotoxin which can be changed to toxoid by formalin and heat. It is believed the lesions produced in the gastrointestinal tract of persons suffering from the disease are caused by the toxin rather than the direct action of the organisms.
Carriers – Dysentery may be transferred from person to person by carriers. A carrier is one who has recovered from the disease but still continues to discharge the bacilli in the intestinal contents. These organisms are no longer pathogenic to the carrier but are capable of producing dysentery when they reach the intestinal tracts of other persons.
Source of Infection – Bowel discharges of infected persons and carriers. Healthy carriers are common.
Mode of Transmission – By direct contact; by eating contaminated foods; by articles soiled with discharges from infected persons or carriers; by drinking contaminated water; and by flies. Disease most prevalent in the summer months.
Incubation Period – From 1 to 7 days, usually less than 4 days.
Susceptibility and Immunity – Susceptibility to disease is general. Disease is more common and symptoms are more severe in children than in adults. Slight acquired immunity of relatively short duration after recovery from the disease.
Prevalence – May be endemic, epidemic, or sporadic. Reduction occurs wherever water supplies are rendered safe, milk is pasteurized, and sewage is disposed of in a hygienic manner. More common in summer months.
Prevention and Control – Purification of public water supplies; pasteurization of public milk supplies; sanitary disposal of sewage; hygienic preparation and handling of public food supplies; periodic examination of individuals who handle foods for public consumption; extermination of flies.
Isolation of infected persons during period of communicability.
Aureomycin, Terramycin, streptomycin, and chloramphenicol given parenterally very effective in relieving symptoms and greatly reducing numbers of organisms in from 24 to 48 hr. Sulfadiazine may be used alone where antibiotics are not available.
Shigella Flexneri:
Rods, 0.5 by 1 to 1.5 μ, occurring singly, often filamentous and irregularly shaped in old cultures, Non-motile. Gram-negative.
Disease Produced – The most common cause of dysentery epidemics and sometimes of infantile gastroenteritis. Found in feces of sick and convalescents and of carriers of dysentery bacilli. Disease characterized by acute onset accompanied by diarrhea, sometimes fever, tenesmus, and frequent stools containing blood and mucus. Symptoms generally milder than in S. dysenteriae infections.
Carriers – Disease may be transferred from person to person by carriers. A carrier is one who has recovered from the disease but still continues to discharge the bacilli in the intestinal contents. Organisms are no longer pathogenic to the carrier but may produce dysentery when they reach the intestinal tracts of other persons.
Source of Infection – Bowel discharges of infected persons and carriers. Healthy carriers are common.
Mode of Transmission – By direct contact; by eating contaminated foods; by articles soiled with discharges from infected persons or carriers; by drinking contaminated water; and by flies.
Incubation Period – From 1 to 7 days, usually less than 4 days.
Susceptibility and Immunity – Susceptibility to disease is general. Disease is more common and symptoms are more severe in children than in adults. Slight acquired immunity of relatively short duration after recovery from the disease.
Prevalence – May be endemic, epidemic, or sporadic. Reduction occurs wherever water supplies are rendered safe, milk is pasteurized, and sewage is disposed of in a hygienic manner. More common in summer months.
Prevention and Control – Purification of public water supplies; pasteurization of public milk supplies; sanitary disposal of sewage; hygienic preparation and handling of public food supplies; periodic examination of individuals who handle foods for public consumption; extermination of flies.
Isolation of infected persons during period of communicability.
Aureomycin, Terramycin, streptomycin, and chloramphenicol given parenterally very effective in relieving symptoms and greatly reducing numbers of organisms in from 24 to 48 hr. Sulfadiazine may be used alone where antibiotics are not available.
Shigella Sonnei:
Rods. Non-motile. Gram-negative.
Disease Produced – A cause of mild dysentery in man and of infantile gastroenteritis. Found in feces of sick and convalescents and of carriers of dysentery bacilli. Disease characterized by acute onset accompanied by diarrhea, sometimes fever tenesmus; and frequent stools containing blood and mucus. Symptoms generally milder than in S. dysenteriae infections.
Carriers – Disease may be transferred from person to person by carriers.
Source of Infection – Bowel discharges of infected persons and carriers. Healthy carriers are common.
Mode of Transmission – By direct contact; by eating contaminated foods; by articles soiled with discharges from infected persons or carriers; by drinking contaminated water; and by flies.
Incubation Period – From 1 to 7 days, usually less than 4 days.
Susceptibility and Immunity – Susceptibility to disease is general. Disease is more common and symptoms are more severe in children than in adults. Slight acquired immunity of relatively short duration after recovery from the disease.
Prevalence – May be endemic, epidemic, or sporadic. Reduction occurs wherever water supplies are rendered safe, milk is pasteurized, and sewage is disposed of in a hygienic manner. More common in summer months.
Prevention and Control – Purification of public water supplies; pasteurization of public milk supplies; sanitary disposal of sewage; hygienic preparation and handling of public food supplies;, periodic examination of individuals who handle foods for public consumption; extermination of flies.
Isolation of infected persons during period of communicability.
Aureomycin, Terramycin, streptomycin, and chloramphenicol given parenterally very effective in relieving symptoms and greatly reducing numbers of organisms in from 24 to 48 hr. Sulfadiazine may be used alone where antibiotics are not available.
Staphylococcus:
Spherical cells occurring singly, in pairs, in tetrads, and in irregular clusters. Non-motile. Gram- positive. Many strains produce an orange or yellow pigment, particularly on media containing high levels of sodium chloride. Most commonly found in boils, furuncles, abscesses, and other suppurative processes.
Normally present on skin, and their entrance into a cut or scratch may lead to infection. Under some conditions, especially during periods of weakened tissue resistance, organisms may invade unbroken skin. Coagulase-positive strains produce a variety of toxins and are thus potentially pathogenic and may cause food poisoning. Facultative parasites and saprophytes.
Staphylococcus Aureus:
Spheres, 0.8 to 1μ in diameter, occurring singly, in pairs, in short chains, and in irregular clumps. Non-motile. Gram-positive.
Some strains develop a golden-yellow, water-insoluble pigment; others show a lemon-coloured, water-insoluble pigment; still others are non-pigmented.
Disease Produced – Found on skin and mucous membranes. The causative organism of boils, furuncles, abscesses, and suppuration in wounds. Pus consists of an accumulation of bacteria and polymorphonuclear leucocytes in the infected area. The organism rarely produces septicemia but may be a secondary invader in peritonitis, pyemia, cystitis, and meningitis.
Certain strains under favourable conditions produce not only exotoxins (hemotoxin, dermatoxin, lethal toxin, etc.) but also a potent enterotoxin which is a significant cause of food poisoning. Normally also capable of coagulating citrated human or rabbit plasma. Many strains produce an enzyme capable of dissolving such clots 8 to 12 hr. after incubation.
Source of Infection – Pus, skin, air, contaminated clothing, food, water, etc.
Mode of Transmission – Transmitted by entrance of organisms into a cut or break in the skin or even the unbroken skin.
Susceptibility and Immunity – Susceptibility to infections is general. Stock polyvalent bacterins, autogenous bacterins, and other heat-killed preparations have been used with some success. However, very little immunity is produced.
Prevention and Control – Aseptic surgery; destruction of soiled dressings by burning; oral and skin cleanliness. The introduction of penicillin and other antibiotics has revolutionized the treatment of staphylococcal infections. Sometimes a combination of penicillin and one of the sulfa drugs may be more effective against some resistant strains.
Streptococcus:
The streptococci are spherical or ovoid cells, rarely elongated into rods, occurring in pairs or short or long chains. Non-motile. Gram-positive. Capsules not regularly formed but may become conspicuous with some species under certain conditions. Growth on artificial media slight. Agar colonies very small. Bile-insoluble.
Latter property used to differentiate streptococci from pneumococci, which are bile-soluble. Found wherever organic matter containing sugars accumulates. Regularly found in mouth and intestine of man and other animals, dairy products, fermenting plant juices.
Found associated with a variety of pathological conditions including erysipelas, septicemia, puerperal fever, focal infections, sore throat, rheumatic fever, scarlet fever, tonsillitis, arthritis, and vegetative endocarditis.
Classification of Streptococci:
The streptococci are among the most difficult groups of bacteria to classify.
One of the earliest classifications is that proposed by Brown (1919), who divided the organisms into three groups according to their effect on blood agar:
i. Alpha streptococci, producing a greenish colouration (methemo-globin formation) of the medium and partial hemolysis in the immediate vicinity of the colonies.
ii. Beta streptococci, producing completely hemolyzed clear, colourless zones around the colonies.
iii. Gamma streptococci, having no effect on blood agar.
The most important contribution to methods for the classification of the streptococci is the serological technique (precipitin test) proposed by Lancefield (1933).
On the basis of this method, the streptococci may be placed into the following groups:
Group A. S. Pyogenes:
Under this species are placed those organisms causing scarlet fever, erysipelas, tonsillitis, puerperal fever, septicemia, and sore throat. They are hemolytic, liquefy fibrin, do not curdle milk or hydrolyze sodium hippurate.
Group B. S. Agalactiae:
This species has been isolated from mastitis in cows and occasionally from human sources. It curdles milk, hydrolyzes sodium hippurate, and does not liquefy fibrin. Most strains are hemolytic.
Group C:
This group includes three rather clearly defined biochemical groups:
(i) S. equi, the cause of “strangles” in horses,
(ii) The “animal pyogenes” Streptococcus, and
(iii) The “human C” Streptococcus.
Some of these have been isolated from animals; others are of human origin.
Group D:
This group includes both hemolytic and non-hemolytic types. The most important member is S. faecalis var. zymogenes. Other members are S. faecalis and S. faecalis var. liquefaciens.
Group E:
This group includes nonpathogenic streptococci isolated from milk. They are hemolytic, do not liquefy fibrin or hydrolyze sodium hippurate.
Group F:
This organism is generally present in normal throats and is sometimes referred to as the “minute hemolytic streptococcus.” On blood agar plates, the organism produces extremely small pin-point colonies, frequently barely visible, but surrounded by a zone of true hemolysis.
Group G:
This is a heterogeneous group of hemolytic streptococci which have been isolated from the normal human throat and nose, vagina, skin, and feces. They are not believed to be of any importance in producing disease in humans.
Streptococcus Pyogenes:
Spherical or ovoid cells, 0.6 to 1 μ in diameter in cultures, usually spherical in blood and inflammatory exudates, occurring in chains or pairs; in broth culture, usually long chains. Gram-positive.
S. pyogenes placed in Lancefield’s group A. This group may be subdivided into serological types by precipitin technique on basis of capsular protein M antigen. Antigen associated with virulence, and antibodies to which it gives rise are primarily concerned with the specific protective action of immune sera. At least 40 types have been identified.
Culture filtrates of typical strains capable of hemolyzing red blood cells. Soluble toxin called a hemolysin. Two types of hemolysin elaborated: one being oxygensensitive (streptolysin O) and the other oxygen-stable (streptolysin S). On blood agar, organism produces a type of hemolysis referred to as β-hemolysis that possesses considerable diagnostic importance.
Disease Produced – Found in human mouth, throat, respiratory tract, inflammatory exudates. Produces septic sore throat, septicemia, erysipelas, scarlet fever, puerperal fever, cellulitis, mastoiditis, osteomyelitis, otitis media, peritonitis, and various skin and wound infections.
Source of Infection – Contaminated milk, pus, sputum, nasal discharges, droplets from mouth and nose, etc.
Mode of Transmission – By direct contact; by inhaling droplets expelled during coughing, sneezing, or talking; by consumption of contaminated milk, etc.
Incubation Period – Usually 2 to 5 days.
Susceptibility and Immunity – Immunity against types of one group does not protect against infection with types from other groups. Immunity slight and of temporary duration. The exception is immunity to scarlet fever. This organism secretes an extracellular toxin against which an antitoxin is produced.
Prevalence – Most prevalent in temperate zones, less common in semitropical and tropical climates. Highest incidence of scarlet fever and streptococcal sore throat occurs during late winter and spring.
Prevention and Control – Pasteurization of milk supplies. Exclusion of infected individuals or carriers from handling foods. Care in treating cuts and abrasions.
Isolation of Infected Individuals – Disinfection of dressings, discharges, clothing from infected persons. Disinfection of floors, table tops, and contaminated objects. Various forms of penicillin all effective when administered parenterally. Therapy should be started early and continued for about 10 days. The tetracyclines may be employed for those sensitive to penicillin.
Scarlet Fever:
Scarlet fever is an acute febrile disease of the throat accompanied by a scarlet rash. Invasion of other parts of the body may occur, resulting in infections of the middle ear, kidneys, etc.
The scarlet rash is due to the elaboration by the organisms of an extracellular erythrogenic toxin. Immunity to the disease is an immunity to the toxin rather than to the organisms.
Scarlet fever is diagnosed by its clinical symptoms and by the isolation of the specific organisms from the throat. For susceptibility to the disease, the Dick test may be used. This test consists of the intradermal injection of 0.1 ml. of a known strength of toxin; the reaction is read after 24 hr. A positive test manifests itself as a bright red area 1.5 to 3 cm. or more in diameter, with swelling and tenderness of the skin.
An antitoxin may be prepared by immunizing animals against culture filtrates of the scarlet fever strain of S. pyogenes. Administration of the antitoxin in cases of scarlet fever produces a favourable result on the outcome of the infection. The antitoxin neutralizes the damaging effect of the toxin and, in so doing, decreases the duration of the rash, changes the character and extent of desquamation, and reduces the number of complications.
Various forms of penicillin all effective when given parenterally. Therapy should be started early and continued for about 10 days. The tetracyclines may be employed for those sensitive to penicillin.
Treponema:
Organisms in this genus measure 3 to 18 μ in length, with acute, regular or irregular spirals; longer forms are due to incomplete division. Terminal filament may be present. Weakly refractive by dark-field illumination in living preparations. Cultivated under strictly anaerobic conditions. Some are pathogenic and parasitic for man and other animals. Generally produce local lesions in tissues.
Treponema Pallidum:
Cells occur as very fine protoplasmic spirals, 0.25 to 0.3 by 6 to 14 μ. Spiral amplitude 1 μ, regular, fixed; spiral depth, 0.5 to 1 μ. Terminal spiral filament present. Weakly refractive in living state by dark field. Motile by means of a sluggish, drifting motion; stiffly flexible, rarely rotating. Appear black with silver impregnation methods. Cultivated with difficulty under strict anaerobiosis in ascitic fluid with addition of fresh rabbit kidney.
Disease Produced – The cause of syphilis in man. Syphilis is acquired almost entirely by sexual contact. In an acquired infection, disease first manifests itself as a primary lesion. This starts as a papule at the site of infection, increases in size, and finally ulcerates. The ulcer is generally referred to as a chancre. This is followed by constitutional symptoms and lesions of the skin and mucous membranes. Secondary lesions eventually heal and may reappear during the first 5 years after infection.
Later manifestations may include disturbances of the cardiovascular and central nervous systems. In congenital syphilis, only secondary and late manifestations are observed.
Diagnosis – Disease in primary stage may be diagnosed by examining the serous exudate from a chancre under dark-ground illumination. Presence of spirochetes indicates a syphilitic infection. Disease in later stages may be diagnosed by serological reactions.
Source of Infection – Discharges from lesions of the skin and mucous membranes; from blood of infected individuals; only rarely from articles freshly soiled with discharges.
Mode of Transmission – By direct personal contact with syphilitic individual, chiefly by sexual intercourse; occasionally by kissing; by dental instruments; only rarely through articles freshly soiled with discharges. Transmitted by syphilitic mother to offspring through placenta (congenital syphilis).
Incubation Period – From 10 to 90 days, average about 21 days.
Susceptibility and Immunity – Susceptibility to disease is universal. Recovery is said to confer some immunity, although reinfections do occur.
Prevalence – Disease world-wide in distribution, varying with age, sex, and race. Occurs most frequently between ages of eighteen and thirty.
Prevention and Control – Adequate treatment facilities, including free distribution of antibiotic agents to physicians for treatment of all cases. Legislation making examinations before marriage compulsory. Control or elimination of houses of prostitution.
Education of public to nature, characteristics, prevalence, mode of transmission, how to avoid infection, and how to secure prompt treatment in case of infection. Personal hygiene before or immediately after sexual intercourse with those who may be exposed to infection.
Isolation of infected individuals in the communicable stage. Disinfection of discharges from open lesions and of articles soiled with such discharges. Treatment consists in the use of large doses of penicillin over a period of time.
Vibrio:
Members of genus characterized as short, curved rods, single or united into spirals. Motile by means of a single polar flagellum usually relatively short; rarely two or three flagella in one tuft. Grow well and rapidly on the surface of standard media. Some aerobic; others anaerobic. Mostly water forms; also occur as parasites and pathogens.
Vibrio Comma:
Slightly curved rods, 0.3 to 0.6 by 1 to 5 μ, occurring singly and in spiral chains. Cells may be long, thin, and delicate, or short and thick. May lose their curved form on artificial cultivation. Motile, possessing a single polar flagellum. Gram-negative.
Organism tolerates high alkalinity. Optimum pH 7.6 to 8.0; for primary isolation, pH 9.0 to 9.6. Vibrios have been classified into 6 groups on the basis of their protein and polysaccharide structures.
Disease Produced – The cause of Asiatic cholera in man. In mild cases, the disease may produce only a diarrhea. In more severe or typical cases, the symptoms may include, in addition to diarrhea, vomiting, “rice-water” stools, and general symptoms of dehydration accompanied by thirst, abdominal pain, and coma.
The organisms penetrate the mucosa of the intestines and accumulate in layers next to the submucosa. The organisms may be present in large numbers in the stools. The disease runs a short course, terminating in death sometimes within 12 hr. after the appearance of symptoms.
Diagnosis – V. comma may be isolated from feces of both infected individuals and carriers. The intraperitoneal inoculation of guinea pigs with pure cultures results in the death of the animals within 24 hr.
Carriers – Patients convalescing from the disease usually continue to eliminate the organisms in the feces for about 7 to 14 days after recovery. Healthy carriers may also be found who excrete the cholera vibrio without exhibiting any signs of the disease. Both convalescent and healthy carriers play an important role in the dissemination of the disease.
Source of Infection – Intestinal contents and vomitus of infected persons and feces of convalescent or healthy carriers. Also from food and water.
Mode of Transmission – By water and foods; by contact with infected persons or carriers, or articles soiled with discharges from such persons; by flies.
Incubation Period – From a few hours to 5 days, usually 3 days.
Susceptibility and Immunity – Susceptibility to disease is general. Natural resistance to infection varies. Clinical attack confers a temporary immunity which may last for several years. Active artificial immunity for about 6 to 12 months may be produced by the use of vaccines.
Prevalence – Disease endemic in India and adjacent areas in southeastern Asia. Does not occur in Western Hemisphere.
Prevention and Control – Sanitary disposal of human excreta. Protection of water by boiling. Pasteurization of milk and dairy products. Sanitary preparation and handling of foods in public places. Control or destruction of house flies. Education of public in personal cleanliness.
Isolation of persons suffering from the disease. Disinfection of stools and vomitus and articles soiled by such discharges. Food left by patient should be destroyed by burning. Room occupied by patient should be thoroughly cleaned and disinfected. Carriers should be isolated. Use of cholera vaccine in exposed population groups.