Micro Flashcards
Diabetes + rhinocerebral infections?
Zygomycosis:
Affects ketoacidotic diabetics and cancer patients
Prefrontal headache, fever, sinusitis
Hyphae branch at 90-degree angles and have irregular width
Spreads to the central nervous system from the sinuses
Treat with debridement and amphotericin B
Frequently fatal
This patient has zygomycosis, caused by fungi of the genera Rhizopus, Absidia, or Mucor. Ketoacidotic diabetics are at risk for developing rhinocerebral infections following inhalation of the sporangiospores of these normally harmless bread molds. The fungi are identified by the nonseptate (ribbon-like) hyphae that branch at 90-degree angles.
Chagas disease: Caused by: Spread by: Associated with: Geographic risk:
Trypanosoma cruzi is the cause of Chagas disease, spread by triatomids called reduviid bugs (“kissing bugs”).
Chagas disease can be associated with myocarditis or esophageal involvement, producing achalasia.
Geographic risk: South America (e.g., Brazil)
This rapidly progressing dementia is usually accompanied by motor dysfunction (e.g., startle myoclonus) and abnormal EEG activity.
Creutzfeldt-Jakob disease (CJD):
A spongiform encephalopathy caused by a prion
Rapidly progressive dementia (over months), characterized by memory loss and startle myoclonus
EEG shows recurrent bursts of high-voltage slow waves
What happens when a patient demonstrates a positive BCG skin text for tuberculosis?
The tuberculin response is the classic example of type IV hypersensitivity, which is mediated by TH1 cells and macrophages. The initial recognition signal involves interaction between MHC class II and the T-cell receptor. The B7 molecule on the cell surface of the antigen-presenting cell reacts with the CD28 molecule on the T-cell surface for maximal co-stimulatory signals.
“Who” causes reactive arthritis?
Reiter syndrome (reactive arthritis): triad of arthritis, urethritis, and conjunctivitis.
It is an autoimmune reaction to a previous infection with one of the following organisms: Shigella, Salmonella, Yersinia, Campylobacter, Chlamydia
Pneumonia in cystic fibrosis:
Pseudomonas aeruginosa
Gram-negative bacillus, aerobic, oxidase-positive, blue-green pigments, fruity odor
Most important pathogenic feature is a capsule that protects against phagocytosis
Herpes encephalitis is scary.
Herpes simplex virus type 1 (HSV-1) encephalitis is the most common cause of sporadic viral encephalitis in the United States.
The diagnosis of viral encephalitis is aided by demonstrating elevated lymphocytes in the cerebrospinal fluid.
HSV-1 encephalitis is specific to the temporal lobes of the brain.
Cowdry type A inclusions can be seen in neurons and glia in HSV-1 encephalitis.
Interstitial pneumonia that responds to macrolides?
Interstitial pneumonia that responds to macrolides (erythromycin): Mycoplasma pneumoniae or Legionella pneumophila.
Legionella is most common in elderly smokers who are alcoholics and immunosuppressed.
M. pneumoniae is a cell wall-less prokaryote that requires cholesterol, purines, and pyrimidines in medium.
65% of patients with this infection produce cold agglutinins.
Bronchiolitis infection: first step?
Bronchiolitis in an infant: respiratory syncytial virus (RSV)
RSV is a paramyxovirus with negative single-stranded RNA, helical shape, and an envelope.
The first thing that RSV does when it enters the cell is to use its RNA-dependent RNA polymerase to create an mRNA (positive-sense RNA) in order to start the translation process.
What is the special virulence factor of streptococcus pneumoniae that allows it to attach to respiratory epithelium?
Streptococcus pneumoniae meningitis.
This organism is able to attach to the respiratory mucosa because it has teichoic acids in its envelope, and because it produces an IgA protease. The IgA protease physically cleaves the immunoglobulin molecules, leaving the Fc parts to coat the bacterium. This allows the organisms to bind to the Fc receptors on various mucosal cells.
Streptococcus pneumoniae attaches to the respiratory mucosa because of the teichoic acids in its envelope and its IgA protease production.
The IgA protease physically cleaves the immunoglobulin molecules, leaving the Fc component to coat the bacterium.
This allows the organisms to bind to the Fc receptors on various mucosal cells.
What does primary tuberculosis look like?
Primary infection with Mycobacterium tuberculosis is most frequently located in the lung parenchyma and hilar lymph nodes, often generating a granulomatous reaction called the Ghon complex.
Which virus families have segmented genomes?
There are four families of viruses with segmented genomes: Reovirus, Orthomyxovirus, Bunyavirus, and Arenavirus.
What is the most common cause of neonatal meningitis?
Streptococcus agalactiae (group B Streptococcus) is the most common causative agent of neonatal meningitis. Strep. agalactiae is a gram-positive microorganism characterized by the following features: catalase-negative, beta-hemolytic, bacitracin-resistant, and CAMP test-positive.
Transduction is the transfer of bacterial DNA via a phage vector. There are two types of transduction:
Generalized transduction: error of lytic virus life cycle, any chromosomal DNA can be transferred.
Specialized transduction: error of temperate virus life cycle, genes near the virus insertion site may be transferred.
Which test will identify the genus cause of golden crusted impetigo on a child’s skin?
This is likely a case of Streptococcus pyogenes impetigo, based on the description of golden-crusted lesions. The other major cause of impetigo is Staphylococcus aureus, and these two genera are distinguished on the basis of the catalase test: Staphylococcus is catalase-positive and Streptococcus is catalase-negative.
