Microbiology Flashcards
What enzyme in TB helps to activate isoniazid?
Mycobacterial catalase peroxidase.
Why do antibodies against the hepatitis C envelope proteins not confer effective resistance?
Antigenic variation.
How does hepatitis B help with hepatitis D co-infection?
The hep B surface antigen must coat the hep D antigen before the hep D virus can infect hepatocytes.
How does the release of INF-alpha and beta help fight viral infections?
They suppress viral replication by halting protein synthesis and promoting apoptosis of infected cells.
How can disseminated Mycobacterium avium complex (MAC) infections be distinguished from extrapulmonary M. tuberculosis?
Both have nonspecific symptoms of fever, weight loss, and diarrhea. However, MAC infections also can show marked anemia, hepatosplenomegaly, and elevated alkaline phosphatase and lactate dehydrogenase levels. Also, MAC prefers higher temperatures and grows well at 41 C. Prophylactic treatment with azithromycin should be given in HIV+ patients with a CD4+ count <50 cells/µL.
What is lymphogranuloma venereum (LGV)?
LGV is caused by Chlamydia trachomatis serotypes L1 through L3. It is characterized initially by a painless, small, shallow genital ulcer containing infected cells. This ulcer is followed weeks later by swollen, painful, coaslescing inguinal nodes (“buboes”) that can develop stellate abscesses and rupture. Histologically, LGV lesions contain areas of mixed granulomatous and neutrophilic inflammation with intracytoplasmic chlamydial inclusion bodies in epithelial and inflammatory cells.
Where do herpes viruses (e.g. cytomegalovirus) get their envelope?
From the host cell nuclear membrane. Most other enveloped nucleocapsid viruses acquire lipid bilayer envelopes by budding through the plasma membrane of the host cell.
What are some major features of enterococcus?
Gram-positive cocci in chains. Gamma-hemolytic. Grows in bile and 6.5% NaCl, pyrrodolidonyl arylamidase (PRY) positive (as opposed to the other gram-positive gamma-hemolytic cocci Strep bovis which does not grow in 6.5% NaCl and is PRY negative).
What is the most common route of meningeal contamination by Neisseria meningitidis?
Pharynx → blood → choroid plexus→ meninges
What is the best treatment for herpes-zoster (shingles) in a patient who is HIV-positive?
Cidofovir (antiviral nucleotide analogue) or foscarnet (viral DNA polymerase inhibitor). These agents do not require viral thymidine kinase to be activated. Thymidine kinase-deficient (and therefore acyclovir-resistant) varicella zoster virus isolates tend to be obtained almost exclusively from AIDS patients.
How are urease breath tests conducted to test for H. pylori infections?
A patient ingests 13C-labeled carbon. When present, urease (produced by H. pylori) degrades the urea into carbon dioxide and ammonia. The isotopically-labeled carbon dioxide is absorbed into the bloodstream and exhaled in the patient’s breath. Sensitive and specific test.
What is the most common route of infection for Enterococcal endocarditis?
The genitourinary tract (e.g. cystoscopy) is the most common portal of entry. It can also enter via the GI tract (e.g. colonoscopy) or obstetric procedures.
What is the most common cause of death in the acute setting of rheumatic fever?
Pancarditis (inflammation of the endocardium, myocardium, and epicardium). This can cause cardiac dilation, heart failure, and death
How do H. pylori infections of the gastric antrum vs body and fundus present?
Antral infection: increased gastrin production and gastric acid secretion leading to development of duodenal ulcers.
Body and fundus: atrophic gastritis leading to loss of G cells and decreased gastric acid production. Less likely to develop ulcers but have an increased risk for gastric adenocarcinoma.
What neoplasm is subacute bacterial endocarditis caused by Streptococcus gallolyticus (S. bovis) associated with?
Colonic cancer in ~25% of cases
