Bacterial Infections

The Types and Examples of Bacterial Diseases Easily Explained

Common Bacterial Diseases

1. What are some human diseases caused by bacteria and what are their respective modes of transmission?

The main human bacterial infections transmitted by respiratory secretions (sneezes, coughing) and saliva are bacterial pneumonia, tuberculosis, whooping cough (pertussis), diphtheria, and bacterial meningitis. The main bacterial diseases transmitted by blood or sexual contact are: gonorrhea and syphilis. The main bacterial diseases transmitted by animal vectors are the bubonic plague, endemic typhus, and leptospirosis. Some bacterial diseases transmitted through the fecal-oral route and contaminated food are cholera and typhoid fever. Other important bacterial infections are: Hansen's disease, possibly transmitted by saliva and contact with injured skin and mucosae; trachoma, an eye disease transmitted by ocular secretions; and tetanus, which is transmitted when the etiological agent enters the body through skin wounds. 

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Bacterial Infections - Biology Questions and Answers


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2. What is tuberculosis? How is the disease transmitted? Is there treatment for tuberculosis?

Tuberculosis is a disease caused by Mycobacterium tuberculosis, a bacteria which attacks other organs of the body but mainly the lungs, leading to respiratory failure. Before 1940, tuberculosis was one of the main causes of death in the USA and Europe. The disease can remain latent, without manifestation for several years, and even throughout the life of a person.

Tuberculosis is highly contagious, transmitted via the air through sneezes and coughs from a person with the active disease. Transmission is common between members of the same family or even in work environments. Today, the disease can be effectively treated with antibiotics. Generally, the patient receives three different drugs for several months until recovery is complete. However, there exist some strains of multiresistant TB bacteria that emerged by mutation and natural selection due to the intense use of antibiotic drugs in hospitals and treatment facilities; in these cases, treatment is more difficult. 

3. Is there a vaccine against tuberculosis?

The vaccine against tuberculosis is called BCG (bacillus Calmette-Guérin). BCG is not used in some countries where tuberculosis is rare because it can distort subsequent diagnostic studies of the disease. In other countries, it is obligatory for children. The vaccine is made of attenuated TB bacteria.

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The Definition of Pneumonia

4. Is pneumonia always caused by bacteria?

Pneumonia is the generic name for the inflammation of the lungs. Besides bacterial pneumonia, pneumonia can be caused by viruses, fungi, toxins, etc. 

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Hansen's Disease

5. What is Hansen’s disease (its etiological agent, mode of transmission, clinical manifestations and prevention)?

The etiological agent of Hansen’s disease is the bacteria Mycobacterium leprae. The mode of transmission is not yet  known definitively but it is believed that respiratory secretions and saliva can spread the disease. Hansen’s disease is a chronic disease (slow progression) that generally attacks the skin and the peripheral nerves, although other areas of the body can be affected. In skin, nodules, reddish spots, the thickening of the dermis and a lack of sensitivity appear; the mucosae, and especially the nasal mucosa, may be injured and the viscera may be affected. The main form of prevention is information, since there is available treatment. Infected people should look for health services for the evaluation and treatment of the disease as soon as possible.

In the past, Hansen’s disease was called leprosy. 


6. What is the etiological agent and the main manifestations of cholera?

Cholera is a bacterial disease caused by Vibrio cholerae. The disease is transmitted via the fecal-oral route and the main mode of transmission is the ingestion of contaminated water or food. It is most prevalent in places that lack adequate sanitary conditions.

Inside the human gut, the cholera vibrion releases toxins called enterotoxins. The infection can cause intense diarrhea, vomiting, dehydration and even death in more severe cases.  

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7. What is meningitis?

Meningitis is the generic name given to the inflammation of the meninges, the membranes that cover the central nervous system. Meningitis can have several causes (infectious, toxic, traumatic, neoplastic infestation, autoimmune). Bacterial infections caused by meningococcus, haemophilus, pneumococcus or by tuberculosis bacteria are severe and contagious.

The main symptoms of bacterial meningitis are a high fever, rigidity of the neck, intense headaches, vomiting and sometimes convulsions. The disease should be treated with antibiotics.

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8. What is syphilis?

Syphilis is a disease caused by the bacteria Treponema pallidum. Before the discovery of penicillin, syphilis was a fatal disease. Today, the use of antibiotics can cure the disease completely. Patients with primary syphilis present a single and painless wound in the skin, sometimes called a chancre, in the region where the treponema penetrated; the chancre is highly infective. Syphilis is one of the main STIs or sexually transmitted infections. Generally, the chancre develops on the penis, vagina, anus, hands or mouth, and the bacteria is often transmitted by sexual contact. Syphilis later develops into the systemic diseases secondary and tertiary syphilis.

Syphilis can also be transmitted by blood transfusions, accidents with contaminated objects and vertically from the mother to the child (congenital syphilis). It is very important for patients with the disease to seek treatment as soon as possible and to undergo tests to check for other STIs, such as HPV and HIV infection.

Antibiogram and Antimicrobial Resistance

9. What is an antibiogram?

An antibiogram is a laboratory test intended to guide the choice of the adequate antibiotic to treat a given bacterial infection. In an antibiogram, cultures of bacteria obtained from tissues contaminated by the infection under study are submitted to the effect of different antibiotics. After some time, the antibiotics successful in interrupting bacterial growth or in killing the bacterial population are verified.

The antibiogram is a very important tool to avoid the excessive and inefficient use of antibiotics and the emergence of multiresistant bacteria.  

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