List of thirteen important diseases caused by bacteria in humans:- 1. Diphtheria 2. Whooping Cough 3. Tetanus 4. Tuberculosis 5. Plague 6. Cholera 7. Typhoid Fever 8. Gonorrhoea 9. Syphilis 10. Botulism 11. Staphylococcal Poisoning 12. Dental Plaque 13. Dental Caries.
Disease # 1. Diphtheria:
Diphtheria (Gk. diphthera = membrane; ia = condition) is an acute contagious respiratory disease caused by Corynebacterium diphtheriae which is a gram-positive, non-motile, aerobic bacterium forming irregular rod- shaped or club-shaped cell during growth. The pathogen enters the body via the respiratory passage with cells lodging in the throat and tonsils (Fig. 47.3).
The inflammatory response of throat tissues to the pathogen leads to the formation of a characteristic lesion referred to as pseudo-membrane. The latter consists of damaged host cells and the cells of bacteria.
Certain strains of C. diphtheriae are lysogenized by bacteriophage β and these strains secrete powerful exotoxin called diphtheria toxin that inhibits eukaryotic protein synthesis and thus kills the host cells. The diphtheria toxin, if absorbed in the circulatory system and distributed throughout the body, damage the peripheral nerves, heart and kidneys.
Penicillin, erythromycin or gentamycin antibiotics are generally effective against the. disease. Prevention is by active immunization with the DPT (diphtheria-pertussis-tetanus) vaccine.
Disease # 2. Whooping Cough (Pertussis):
Whooping cough or pertussis (L. per = intensive; tussis = cough) is a highly contagious, primarily childhood respiratory disease caused by Bordetella pertussis which is small gram-negative, aerobic coccobacillus.
The disease is characterized by a recurrent, violent cough which usually last upto some weeks. The spasmodic coughing gives the disease its name because a whooping sound results from the patient inhaling in deep breaths to obtain sufficient air.
The pathogen is air-droplet transmitted and incubates 7-14 day in the body of the victim. Once inside the upper respiratory tract, the pathogens adhere to the ciliated epithelial cells and secrete several toxins, the most important being the pertussis-toxin.
The disease can be prevented by vaccinating children by DPT-vaccine when they are 2-3 months old. Antibiotics erythromycin, tetracycline, ampicillin or chloramphenicol are used to cure the disease.
Disease # 3. Tetanus:
Tetanus (Gk. tetanos = to stretch) is a serious, often life-threatening disease caused by Clostridium tetani, a motile anaerobic gram-negative spore-forming and soil-inhabiting bacterium. The pathogen enters in human body through a soil-contaminated wound, typically a deep puncture.
These are the anaerobic conditions in the wound that allow the germination of endospores and emergence of the new cells which divide and increase in number. The pathogens secrete a potent exotoxin, tetanus-toxin (tetanospasmin) that causes uncontrolled stimulation of skeletal muscles.
In the beginning, the tetanospasmin causes cramping and twisting in skeletal muscles surrounding the wound and tightness of the jaw muscles. Later on, there is trismus, i.e., “Lockjaw” resulting in inability to open the mouth.
Tetanus treatment is not very effective because the toxin already bound to tissues cannot be neutralized.
Therefore, the best treatment is the prevention by:
(i) Active immunization with toxoid,
(ii) Proper care of soil- contaminated deep wounds, and
(iii) Administration of antibiotics, usually penicillin.
Disease # 4. Tuberculosis:
Tuberculosis (TB), a disease still accounting for almost 1.5 million deaths per year throughout the world, is caused by Mycobacterium tuberculosis. At one time, TB was rampant infectious disease causing 1/7 of all deaths worldwide. Studies indicate that there exists a close association between TB and AIDS. Therefore, spread of AIDS among the people is resulting in dramatic increases in TB.
Human tuberculosis infections can be distinguished as primary and post primary (or reinfection). Primary infection is the first infection which an individual acquires by inhalation of air-droplets and the bacteria are phagocytosed by macrophages inside the lung forming small, hard nodules called tubercles (the characteristics of tuberculosis).
In individuals with low resistance post primary infection is quite apparent as the remaining bacteria which are not effectively controlled start further growth.
As a result, acute pulmonary infection takes place leading to the extensive destruction of lung tissue, spread of the pathogen to other parts of the body, and ultimately death. Prevention and control of tuberculosis needs rapid specific therapy. In many countries, individuals particularly children are vaccinated with BCG (Bacilla Calmette-Guerin) vaccine.
Disease # 5. Plague:
Plague (L. plaga = pest) causes more human deaths than any other infectious diseases except malaria and tuberculosis. It is caused by Yersinia pestis, an aerobic gram-negative rod-shaped bacterium. Plague is a natural disease of domestic and wild rodents; rats being the primary disease reservoir, Fleas are the intermediate hosts responsible to spread the disease from rats to mammals (Fig. 47.4).
Rat flea (Xenopsylla cheopis) ingests the pathogen by sucking blood from an infected rat. Bacteria multiply in flea’s intestine and can be transmitted toa healthy animal (including man) in the next bite. Once in man’s body, the pathogens reach the lymph nodes where they result in swollen areas called buboes hence the disease called bubonic plague.
If not treated in the early stage, the disease usually causes death within 3-5 days. When Y. pestis cells are either inhaled directly or reach the lungs during bubonic plague, they cause pneumonic plague. Symptoms are usually absent until the last day or two when large amounts of bloody sputum are produced.
Untreated victims rarely survive more than two days. Septisemic plague is caused due to the rapid spread of Y. pestis throughout the human body via the bloodstream without the development of bulboes and usually results in death before the diagnosis could be made.
Prevention and control involves the control of fleas and rodents, isolation of human victims, treatment with tetracyclin for prophylaxis, and vaccination (USP Plague Vaccine) of persons at high risk.
Disease # 6. Cholera:
Cholera (Gk. chole = bile) is a severe water-borne diarrheal disease frequently occurring in developing countries. It is caused by Vibrio cholerae, a gram-negative curved bacillus bacterium, transmitted almost exclusively via contaminated water, food, etc. Two biotypes of V. cholerae have been recognized: classic and E1 Tor.
Classic biotype has been virulent before 1961. In 1961, the E1 Tor biotype emerged as an important cause of cholera pandemics. However, in 1992 a newly identified strain V. cholerae O139 emerged in Asia. In Calcutta (India), strain O139 of V. cholerae displaced E1 Tor V. cholerae strain O1 (the causative agent of seventh pandemic, an event that has never happened in the recorded history of cholera).
V. cholerae multiply in the small intestine and produce the enterotoxin called choleragen which binds irreversibly to epithelial cells of small intestine and stimulates cyclic AMP within the mucosa cells. The activation of cyclic AMP initiates excessive secretion of water and electrolytes (chlorine ions) into the intestine and inhibits absorption of sodium ions.
The symptoms of disease include nausea, vomiting, abdominal pain, diarrhea with ‘rice water stools’ and severe dehydration. The rapid loss of fluid or dehydration produces shock and if infection is untreated can cause death of the patient.
The sewage must be treated before disposal and proper disinfection of water supplies must be observed to prevent the outbreak of cholera. The immediate treatment of the disease is the oral rehydration therapy with NaCI plus glucose to estimate water uptake by the intestine. The antibiotics of choice are tetracyclin, trimethoprim-sulfamethoxazole or ciprofloxacin. The killed vaccine of cholera can be taken as prophylactic.
Disease # 7. Typhoid Fever:
Typhoid (Gk. typhodes = smoke) fever is contaminated food or water (contaminated by feces of infected humans or animals) borne disease caused by Salmonella typhi.
The organisms gain entry into the body through contaminated water supplies and the food material contaminated by the bacilli. A very low dose of S. typhi establishes the infection. The bacteria enter the lymphatic system in the Peyer’s patch of the intestine forming ulcer, and disseminated through the circulatory system.
It invades the mononuclear phagocyte system and continues to multiply within the phagocytic blood cells. The organism grows and causes damage to the liver and gallbladder and sometimes to kidneys, spleen and lungs. The symptoms of typhoid include high fever (104°C), headache, weakness, abdominal pain and rash. The symptoms develop in stepwise fashion in three weeks span and begin to decline after third week.
Chlorination of water supply is able to kill the bacteria. Consumption of refrigerated food should be avoided. As a treatment, chloramphenicol is the antibiotic of choice. Besides, several other quinoline derivative and synthetic chemicals are effective.
Disease # 8. Gonorrhoea:
Gonorrhoea (Gk. gono = seed; rhein = to flow) is an acute, infectious, sexually transmitted disease of the mucous membranes of the genitourinary tract, eye, rectum and throat. It is caused by the gram-negative, oxidase-positive, encapsulated diplococcus, Neisseria gonorrhoeae (often called gonococci).
Once inside the body, the pathogens attach to the microvilli of mucosal cells by means of pili and protein II which acts as adhesive. This attachment does not allow bacteria to be washed away by normal vaginal discharges or by the forceful urination.
In women, the infection spreads to uterus causing salpingitis, the condition with abdominal pain. Gonorrhoea also leads to pelvic inflammatory disease which involves all organs of reproductive system and lead to infertility condition. Symptoms of gonorrhoea in female manifest as abdominal pain, swelling, abnormal vaginal discharge and abnormal menstrual bleeding.
The disease infected pregnant woman transmits the disease to the eyes of infant during passage through the vaginal tract and damages them. In male, symptoms of gonorrhoea include characteristic painful, purulent urethra discharge.
The organisms are transmitted through sexual intercourse, thus, the most effective method for control is public education, diagnosing and treating the asymptomatic patient, condome use, and treating infected persons quickly to prevent any further spread of the disease. Gonorrhoea is successfully treated with almost all classes of antibiotics.
Disease # 9. Syphilis:
Syphilis (Gk. syn = together; philein = to love) is a contagious sexually transmitted disease caused by a spirochete, namely, Treponema pallidum which is about 10-15 pm in length and about 0.15 μm in diameter.
The pathogen enters the body through mucous membranes or minor breaks or abrasions of the skin. Once in the body, it migrates to the regional lymph nodes and rapidly spreads throughout the body. Syphilis occurs in three distinct stages. In primary stage, the pathogen multiplies developing a characteristic lesion called chancre formed within 3-6 weeks.
The secondary stage begins 6 to 8 weeks after appearance of the lesion. During this stage there is appearance of cutaneous lesions involving mucus membrane such as on lips, tongue, throat, penis, vagina and other body surfaces.
In addition, patient suffers from headache, low-grade fever, and enlargement of lymph nodes. The tertiary stage occurs several years after the primary stage.
Although, this stage is asymptomatic but can cause damage of any organ of the body especially damage to aorta resulting into death of patient or paralysis or may cause change in personality. The syphilis infected pregnant woman gives birth to still baby who is mentally retarded and neurologically impaired.
Penicillin is highly effective in syphilis treatment and the primary and secondary stages can be controlled by a single injection of benzathine penicillin G. In tertiary stage of syphilis, penicillin treatment must extend for longer period of time. Besides, public education and sexual hygiene are quite necessary.
Disease # 10. Botulism:
Botulism is caused by the ingestion of food containing the neurotoxin (toxin that affects the nervous system) produced by Clostridium botulinum, an anaerobic spore forming bacterium (Section 188.8.131.52).
Disease # 11. Staphylococcal Poisoning:
This is the most common type of food-poisoning caused due to the food contaminated with a potent toxin, namely, enterotoxin. This toxin is produced by certain strains of Staphylococcus aureus. A sudden onset of illness starts usually within 3 to 6 hours after ingestion of the contaminated food (Section 184.108.40.206).
Disease # 12. Dental Plaque:
The bacterial colonization of tooth surfaces begins with the initial colonization of the pellicle or organic covering (the natural defence mechanism of teeth) by a few species of Streptococcus (e.g., S. sangius, S. sobrinus, S. oralis, S. gordonii, S, inutans and S. mitis).
These bacteria selectively adhere to the pellicle and once the tooth surface is colonized, subsequent attachment of other bacteria takes place by coaggregation.
The latter is the result of cell-to-cell recognition between genetically distinct bacteria through the interaction between lectin on one bacterium and a complementary carbohydrate receptor on the other. The most important bacteria at this stage are Actinomyces viscosus and A. naeslundii.
The bacteria (especially the streptococci) secrete glucosyItransferases, the extracellular enzymes, that polymerise the glucose monomers of sucrose into glucan polymers and other polysaccharides acting like a cement to bind bacterial cells together. This thick cement like layer rich of bacteria is called dental plaque.
Once plaque becomes established, a low oxidation-reduction potential develops on tooth-surface leading to the growth of many obligate anaerobes (e.g., Bacteriodes melaninogenicus, B. oralis, Veillonella sp.) especially between teeth and the dental-gingival crevices. Anaerobic nature of oral flora seems surprising when there is availability of oxygen in the mouth.
In fact, the plaque build-up produces a dense matrix which decreases oxygen diffusion on to the surface of the tooth thus creating an anoxic microenvironment. The microbes of the dental plaque, therefore, survive in a self-created microenvironment and maintain themselves in the face of wide variations in the macro-environment of the oral cavity.
Once the dental plaque ecosystem is formed, the bacteria produce acids like lactic, acetic and formic from sucrose and other sugars. Since the plaque is impermeable to saliva, the acids are not diluted or neutralized. These acids demineralize the enamel creating a lesion on the tooth and it is this chemical lesion which initiates decay of the tooth.
Disease # 13. Dental Caries (Decay of Teeth):
The acids produced in dental plaques begin the decay of tooth. Once these acids start the demineralization of the tooth enamel, proteolysis of the matrix of the tooth enamel takes place through the action of proteolytic enzymes released by bacteria.
Microorganisms penetrate further into the decomposing matrix leading to dental decay or dental caries. Once the hard enamel barrier has been broken, the bacteria invade the dentin and pulp of the tooth resulting in its death.
Minimal ingestion of sucrose, daily brushing, flossing and mouthwashes are the only ways to protect teeth from decay because there arc no drugs available against dental caries. Dental plaques should be removed by professional cleaning at-least twice a year.