Microbiology Flashcards
(745 cards)
Cysticercosis vs. taeniasis.
Taenia solium, a tapeworm, causes disease endemically in Mexico, Central and South America, Asia, and Africa. Cysticercosis occurs during an infection by the larval stage of T solium when ova are ingested. The ova develop into larvae, penetrate the intestinal wall, disseminate throughout the body via the vascular system, and encyst in tissue as cysticerci. Cysticerci have a propensity for developing in the CNS (60% of cases). Alternatively, taeniasis occurs during an infection by the adult tapeworm of T solium when the human definitive host ingests cysticerci. The cysticerci evaginate, attach to the intestinal wall, and develop into sexual mature cestodes.
In what 3 situations can asymptomatic bacteriuria be diagnosed?
- In asymptomatic women, 2 consecutive voided urine specimens with isolation of the same bacterial strain in quantitative counts of >10^5 cfu/mL. 2. In asymptomatic men, a single voided urine specimen with isolation of a single bacterial species in a quantitative count of >10^5 cfu/mL. 3. In men and women, a single catheterized specimen with a single bacterial species in a count of >10^2 cfu/mL.
Hemorrhagic cystitis due to adenoviruses, especially type 11, is most often seen in (type of patient).
Hemorrhagic cystitis due to adenoviruses, especially type 11, is most often seen in bone marrow transplant recipients.
The most common cause of acute infectious diarrhea is ___.
Viruses, especially noroviruses (calicivirus, Norwalk virus), enteric adenoviruses, and rotavirus. These agents account for at least 50% of community-acquired acute infectious diarrhea. And if there is nothing unusual in the history, such as hospitalization, antibiotic use, or travel, these agents cause 80-90% of cases.
What bacterium is the most commonly identified cause of Guillain-Barre syndrome?
C. jejuni, most commonly type O:19, is the most commonly identified cause, implicated in ~30% of cases.
The syndrome of cholera is caused principally by what two serogroups of V. cholerae?
Serogroup O1 and serogroup O139. Noncholera (non-01 and non-139) strains may cause less severe gastroenteritis and/or wound infections.
What 2 bacterial organisms can cause an HLA-B27-linked post-infectious arthritis?
C. jejuni and Y. enterocolitica can cause the development of a reactive arthropathy (so-called enteropathic arthritis) in persons with HLA-B27.
What are the HACEK organisms?
Haemophilus (H. parainfluenzae, H. aphrophilus, H. paraphrophilus), Actinobacillus (A. actinomycetemcomitans, Aggregatibacter aphrophilus), Cardiobacterium hominis, Eikenella corrodens, Kingella kingae. These are all slow growing Gram negative bacteria that form part of the normal oropharyngeal flora. They account for 5-10% of infective endocarditis involving native valves, are the most common Gram negative cause of endocarditis among non-IVD users, and are a frequent cause of culture-negative endocarditis. In addition to valvular infections in the heart, they can also produce other infections such as bacteremia, abscess, peritonitis, otitis media, conjunctivitis, pneumonia, arthritis, osteomyelitis, and periodontal infections.
HSV 1 is a common cause of (encephalitis and/or meningitis), and HSV 2 is a common cause of (encephalitis and/or meningitis). The best way to diagnose both of these is ___.
HSV 1 is a common cause of encephalitis, and HSV 2 is a common cause of meningitis. The best way to diagnose both of these is CSF PCR.
Erysipelas is caused by (organism). Erysipeloid is caused by (organism).
Erysipelas is caused by S. pyogenes. Erysipeloid is caused by Erysipelothrix rhusiopathiae.
Adiaspiromycosis is caused by (organism).
Adiaspiromycosis is caused by Chrysosporium parvum.
Coxsackie A virus causes (conditions). Coxsackie B virus causes (conditions).
Coxsackie A virus causes hand-foot-mouth disease and herpangina. Coxsackie B virus causes myocarditis, pericarditis, and epidemic pleurodynia (the grippe).
What is the vector for B. burgdorferi?
The Ixodes tick. I. dammini (scapularis?) (AKA blacklegged ticks or deer tick) in the Eastern US, I. pacificus (AKA western blacklegged tick) in the Western US, I. ricinus (AKA sheep tick or castor bean tick) in Europe, and I. persulcatus (AKA taiga tick) in China. The natural reservoir is the white-footed mouse, but in endemic areas, deer are an important reservoir.
Polyoma viruses include the ___ virus and ___ virus. Both are typically acquired in childhood and enter latency, supposedly within the ___ and ___. If immunosuppression occurs, viral reactivation may lead to the development of progressive multifocal leukoencephalopathy due to ___ virus or ___ virus-induced hemorrhagic cystitis.
Polyoma viruses include the JC virus and BK virus. Both are typically acquired in childhood and enter latency, supposedly within the brain and urothelium. If immunosuppression occurs, viral reactivation may lead to the development of progressive multifocal leukoencephalopathy due to JC virus or BK virus-induced hemorrhagic cystitis. BK virus causes the appearance of decoy cells within urine cytology, with the characteristic smudgy nuclear inclusions and lack of the usual chromatin detail as seen in CIS. Similar inclusions are seen within oligodendroglial cells in the demyelinative lesions of PML.
What HPV types (in order of frequency) are seen mostly commonly in the following lesions? Plantar wart, common wart, flat (juvenile) wart, oral squamous papilloma, oral focal epithelial hyperplasia (Heck disease), epidermodysplasia verruciformis, laryngeal papillomas, condyloma acuminatum, cervical LSIL, cervical HSIL, cervical AIS and invasive cervical adenocarcinoma.
Plantar wart: 1, 2. Common wart: 2, 1, 4, (HPV 7 in fish and meat handlers). Flat (juvenile) wart: 3, 10. Oral squamous papilloma: 6, 11. Oral focal epithelial hyperplasia (Heck disease): 13, 32. Epidermodysplasia verruciformis: 2, 3, 10, 5, 8. Laryngeal papillomas: 6, 11. Condyloma acuminatum: 6, 11. Cervical LSIL: 6, 11. Cervical HSIL: 16, 18, 31, 33, 35. Cervical AIS: 18. Invasive cervical adenocarcinoma: HPV 16 and 18 are detected with equal prevalence in most subtypes of cervical adenocarcinoma.
What are some organisms that stain AFB+?
Mycobacteria, Nocardia, Corynebacteria, Cryptosporidium, Microsporidium, Isospora, Cyclospora, Sarcocystis, Legionella micdadei, Rhodococcus equi, Saccharomyces.
What are the differences between the Ziehl-Neelsen, Kinyoun, and Fite acid-fast stains?
The acid-fast stains are based on the ability of certain organisms to retain the red dye carbol fuchsin despite acidic decolorization. The carbol fuchsin stain is a mixture of fuchsin with phenol (carbolic acid). In the Ziehl-Neelsen technique, heat is used to aid penetration of the carbol fuchsin, and a strong acid (3% HCl) is used for decolorization. The Kinyoun technique is a “cold” technique; heat is not applied; instead, a detergent is used to aid penetration of the dye. The Fite technique is a modified acid-fast stain, where a weaker acid such as 1% H2SO4 is applied instead of HCl for decolorization. Bacteria that are not acid-fast by the Ziehl-Neelsen technique, such as Nocardia and M. leprae, may be acid-fast with the Fite technique (cells with a thin capsule, as may be the situation with many rapidly growing strains, are more susceptible to decolorization, so weaker acid will not decolorize as much). Also, the Ziehl-Neelsen technique may be more sensitive than the Kinyoun technique in detecting lightly staining organisms, since the Kinyoun technique may cause easier decolorization.
How are the tube coagulase test, slide coagulase test, and commercial latex agglutination test different in ability to identify S. aureus?
The tube coagulase test tests for free/secreted coagulase; it is a definitive ID for S. aureus and the gold standard. But you need to incubate the plasma + colony for 24 hours to call it negative. The slide and latex agglutination tests test for bound coagulase/cell-bound coagulase/clumping factor; they are quicker tests but may not always differentiate S. aureus from coag-negative Staph.
MRSA strains produce an altered penicillin-binding protein, ___, which is encoded by the gene ___.
MRSA strains produce an altered penicillin-binding protein, PBP 2a, which is encoded by the gene mecA.
Macrolide-resistant isolates of S. aureus come in what 2 classes?
Macrolides include erythromycin. Lincosamides include clindamycin. 1. Those that demonstrate constitutive or inducible clindamycin resistance. Is referred to as MLS B resistance (affects macrolides, lincosamides, and type B streptogramins). The mechanism is target modification - methylation of 23S rRNA. 2. Those that are resistant only to macrolides. The mechanism is efflux.
What enzyme does C. perfringens produce that differentiates it from the other Clostridium species?
Lecithinase. Evident on egg yolk agar and lecithin lactose agar.
A double zone of hemolysis is characteristic of what organism?
C. perfringens.
Which Plasmodium spp are associated with fever spikes every 48 hours, and which are associateed with fever spikes every 72 hours?
Fever spikes every 48 hours (tertian fever) characterize P. ovale, P. vivax, and P. falciparum. Due to its lethality, P. falciparum is also called “malignant tertian malaria”. P. ovale and P. vivax are also known as “benign tertian malaria”. Fever spikes every 72 hours (quartan fever) characterizes P. malariae.
Which Plasmodium spp are associated with: Nephrotic syndrome? CNS involvement? True disease relapse? Recrudescence?
Nephrotic syndrome is associated with P. malariae. CNS involvement is associated with P. falciparum. True disease relapse is seen only with P. vivax and P. ovale. Recrudescence is possible with any of the species.