Bacterial infections Flashcards
The commensal microbiota within the oral cavity is influenced to a major extent by:
- an eruption of the first dentition.
- tetracycline.
- amoxicillin.
The use of antibiotics, particularly those with a broad spectrum of activity, have a profound effect on the human commensal microbiota. Microbes have evolved to adhere to particular types of surface, and so when teeth first appear, this presents a new type of surface to which microbes become attached. This, in turn, leads to the mouth becoming colonized with a new array of microbes. It is the enamel on teeth that is important for this adhesion, and not whether the tooth is a first set or second set. False teeth provide yet another surface, providing for a different array of colonizers. Diet has little effect on the resident microbiota of the mouth, but it may influence the transient microbiota.
Septicaemia due to Escherichia coli is commonly associated with:
- endotoxic shock.
- acute pyelonephritis.
Escherichia coli is an important component of the aerobic bowel flora. It is commonly associated with ascending urinary tract infections, resulting in pyelonephritis with positive blood cultures. It can also escape directly from the bowel into the bloodstream in patients rendered neutropenic as a result of disease or chemotherapy. It is a well-recognized cause of meningitis, but in neonates and not in adults. The endotoxin associated with the outer leaflet of the outer membrane may lead to septic shock.
Concerning the laboratory diagnosis of syphilis:
- screening of donated blood is routine in the United Kingdom to prevent the horizontal spread of the disease.
- once positive, the TPPA test remains so for life.
- once positive, the FTA(abs) test remains so for life.
Treponema pallidum will not grow on conventional laboratory media. While animals may be used for the propagation of Treponema pallidum in the laboratory, the usual model is the eyes or testes of rabbits; the nine-banded armadillo is used for the propagation of Mycobacterium leprae. Screening of blood for syphilis is used for all donations in the UK. The diagnosis of syphilis typically relies on serological testing. The tests may be specific for treponemal antigens or non-specific, seeking antibodies to antigens other than those expressed by Treponema pallidum. Once positive, the specific antigen tests such as FTA(abs), the fluorescent treponemal antibody absorption test, and the TPPA - Treponema pallidum particle agglutination test - remain positive for life. Non-specific tests such as the rapid plasma reagin (RPR) test become negative following successful treatment of the infection. Such non-specific tests are useful in the monitoring of therapy.
Causes of meningitis include:
- Mycobacterium tuberculosis.
- Cryptococcus neoformans.
- Naegleria fowleri.
- Coagulase-negative staphylococci.
All can cause meningitis. The coagulase-negative staphylococci cause meningitis often associated with implanted medical devices such as ‘shunts’. Cryptococcus neoformans is a yeast that causes meningitis in the immunocompromised, particularly people with AIDS. Naegleria fowleri is an amoeba that causes chronic meningitis after inhalation of cysts that release amoebae that burrow into the base of the brain. One of the extra-pulmonary sites of infection with Mycobacterium tuberculosis is the meninges, leading to meningitis.
The following statements are true concerning infective endocarditis:
- the valves on the right side of the heart are most commonly affected in intravenous drug users.
- infection may occur on prosthetic valves.
- splinter hemorrhages are occasionally seen in people with endocarditis.
- Staphylococcus aureus is a common cause of infection with natural valves.
The left-sided heart valves are most commonly involved in this condition although tricuspid and, less often, the pulmonary valve is associated in endocarditis seen in intravenous drug users. These are the valves on the right side of the heart and receive venous blood from the main circulation. Staphylococcus aureus is a cause of endocarditis on natural heart valves, particularly in injecting drug users. Prosthetic heart valves may be involved in endocarditis, often caused by coagulase-negative staphylococci such as Staphylococcus epidermidis. Splinter hemorrhages are rarely seen now but are formed by septic emboli from vegetations lodging there. Negative blood cultures certainly do not exclude this type of infection.
Haemolytic uraemic syndrome is caused by:
- E. coli O157
E. coli O157 causes hemolytic uremic syndrome. “Chinese restaurant syndrome” is an intoxication caused by Bacillus cereus. Enteric fever is caused by Salmonella Typhi. Another name for dysentery, caused by Shigella dysenteriae is the “bloody flux”. “Rice-water” stools are characteristic of cholera, caused by Vibrio cholerae.
Legionnaire’s disease is diagnosed by:
- a rising antibody titer over 14-21 days
The diagnosis of Legionnaire’s disease relies upon a demonstration of a rising antibody titer over a 14-21 day period. A seven-day interval between tests is too short to demonstrate a clear difference in antibody titers between the acute and the convalescent samples. Although the causative agent, Legionella pneumophila, can be grown in artificial culture, it is fastidious and can be difficult to isolate. Urine is an inappropriate sample for culture examination in this disease.
In non-specific urethritis:
- the most common causative bacterium is an obligate intracellular parasite.
- the condition may be associated with an eye infection.
- the condition may be associated with reactive arthritis.
- the most common causative bacterium may cause co-infection with Neisseria gonorrhoeae.
The most common cause of non-specific urethritis, also known as non-gonococcal urethritis is Chlamydia trachomatis. Despite the alternative name for the infection caused by this bacterium, it commonly causes co-infection with Neisseria gonorrhoeae. Chlamydia trachomatis is an obligate intracellular parasite that cannot be grown on conventional laboratory media. It grows in McCoy cells and may be detected by DNA amplification. A common complication of non-specific urethritis is an eye infection, caused by autoinoculation with Chlamydia trachomatis. Much more rarely, the chlamydial infection may lead to Reiter’s syndrome, reactive arthritis associated with people with the HLA-B27 tissue type.
Pneumocystis jiroveci:
- is classified as a fungus.
- colonizes many healthy adults asymptomatically.
Studies of the ribosomal RNA structure of this organism has placed its classification with the fungi, even though its microscopic appearance and general behavior would tend to place it together with the Protista. It can be found colonizing many healthy individuals, and antibodies are frequently found in normal persons. Pneumocystis jiroveci pneumonia is an AIDS-defining infection, but the disease caused by this organism was first described in severely malnourished children.
Immunization is useful for the prevention of:
- whooping cough.
- pneumococcal pneumonia in particularly susceptible patients.
- tuberculosis.
The BCG vaccine protects against tuberculosis, and the DPT vaccine provides cover against the causative agents of diphtheria, whooping cough and tetanus. Haemophilus influenzae vaccines are available but do not provide protection against all the strains that can cause bronchopneumonia. Pneumococcal vaccines are now available.
