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Step 1 Deluge > Microbiology > Flashcards

Microbiology Flashcards

1
Q

Thayer-Martin Agar culture for what organism? What additional contents

A

Neisseria meningitidis, gonorrhea
+Vancomycin, nystatin, trimethroprim, colistin.
Inhibit growth of other organism

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2
Q

Chocolate agar + factors V (NAD) and factor X (hematin). What organism?

A

Heamophillus influenza

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3
Q

Bordet-gengou agar

A

Bordetall pertussis (Whooping cough)

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4
Q

Eaton agar + cholesterol

A

Mycoplasma pneumoniae

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5
Q

MacConkey agar

A

Lactose fermenting enterics (think E. coli). Agar turns pink for positive fermentation

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6
Q

Legionella culture requirements

A

Charcoal yeast extract buffered with cysteine & iron

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7
Q

Sabourad agar

A

Used for fungi. “Sab’s a funny guy”

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8
Q

Inactivation of elongation factor-2. Which two bugs do this? Subsequent effect?

A

Corynebacterium Diphtheria & pseudomonas A.
Results in host cell protein inhibition.
Remember “macroslides” and diptheria

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9
Q

2 bugs work by removing adenine from 60s ribosome, thus disrupting protein synthesis in host.

A

Shigella and EHEC via shiga-like toxin (O157:H7)

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10
Q

Bordetella pertussis toxin mechanism (two parts)?

A

1) A&B toxin. Binding (B) toxin binds to cells allowing penetration by toxin A -> attaches to ADP-ribosyl to disrupt protein synthesis
* Don’t confuse this with diptheria that also inhibits protein synthesis*
2) Inactivates Gi thus increasing cAMP production. This inhibits phagocytosis

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11
Q

Lecithinase (type of phospholipase) in what bug? Subsequent effect?

A

Clostridium perferinges. Lecithinase degrades the membrane phosopholipid lecithin and causes gas gangrene & muscle necrosis.
Also causes hemolysis of blood agar

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12
Q

Novibiocin sensitive and resistant bacteria

A

Gram positive, catalase positive, coagulase negative cocci. Novibiocin sensitive: staph epidermis. Novibiocin resistant: Staph saprophyticus

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13
Q

Lancet shaped gram positive bacteria?

A

Gram positive, catalase negative, alpha-hemolytic, optochinin sensitive, bile soluble: Strep pneumonia

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14
Q

Oxidase positive, gram negative bacteria (comma shaped)

A

H. pylori
Vibrio cholera
Campylobacter jejuni

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15
Q

Gram negative diplococci and how to distinguish between them with lab tests?

A

Neisseria species.
Maltose fermentation: N. meningitidis
Maltose non fermenter: N. gonorrhea

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16
Q

Distinguishing gram negative rods with basic lab tests?

A

Lactose fermenters: E. coli, klebsiella, enterobacter.

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17
Q

Gram negative, rod, non-lactose fermenting, oxidase positive bacteria

A

Pseudomonas

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18
Q

Gram negative, rod, non-lactose fermenting, oxidase negative rod. Next step to distinguish?

A

TSI agar. If H2S is produced: salmonella, proteus, yersinia

If not H2S produced: shigella

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19
Q

Bug transmitted from pet feces, contaminated milk, or pork. Causes psuedo appendicitis

A

Yersinia enterocolitica. Causes inflammation of mesentery or terminal ileum in that region

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20
Q

Use of antibiotics on flagellated species that can cause bloody diarrhea and produces H2S in TSI agar? FC

A

Salmonella species. Gram negative, rod, non-lactose fermenting, oxidase negatve, produces H2S on TSI agar. Abx prolong duration of salmonella. (Note that shigella doesn’t produce H2S in the agar and has no flagella: “salmon swim.”)

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21
Q

Rose spots on abdomen, constipation, fever, diarrhea infection by a gram negative rod with flagella? FC

A

Typhoid fever from salmonella typhi. Likely a non-bloody diarrhea (contrast with other salmonella species with bloody diarrhea). Reside in peyer’s patches after ingestion by GI M cells.
FC: Gram negative, rod, non-lactose fermenting, oxidase negatve, produces H2S on TSI agar.

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22
Q

Key to pathogenicity of shigella in contrast with E coli O157:H7? FC

A

Shigella invades mucosal cells and thus doesn’t need to produce much toxin.
FC: Gram negative, rod, non-lactose fermenting, oxidase negative, produces H2S on TSI agar.

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23
Q

Osteomyelitis & cellulite associated with animal bites (cats, dogs, ets)?

A

Pasteurella multocida

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24
Q

Pathogen that grows as a mold at 20degrees and yeast at 37degrees. General category of pathogen?

A

Systemic mycoses are all dimorphic fungii (except coccidio). Histoplasmosis, blastomycosis, coccidiodies, Paracoccidiodomycosis

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25
Q

Reduviid bug infects you with what protozoa? Manifestations?

A

Trypanosoma cruzi (Chagas disease) which can infiltrate ganglion of esophagus and colon. Typically also causes dilated cardiomyopathy

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26
Q

Genus of bacteria that are obligate intracellular organisms? Why?

A

Chlamydia. They don’t produce their own ATP

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27
Q

3 most common causes of meningitis in infants <6mos

A

E coli, group B strep (Strep agalacticae), listeria

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28
Q

Most common causes of meningitis in kids (6mos-6yrs)

A

Strep pneumo, H influenza ,

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29
Q

Two pathogens causing liver cysts. One a parasitic tapeworm associated with wild animals, the other a protozoan? Rx?

A 
Echnicoccus granulosus tapeworm. Rx: Albendazole
Entemoeba histolytica (anchovy paste exudate) Rx: metronidazole
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30
Q

Staph scalded skin mechanism of pathogenicity?

A

Exotoxins that bind desmoglein in the desmosomes. Destruction of desmosomes causes separation of skin at stratum granulosum and subsequent Nikolsky’s sign

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31
Q

Species w/ no cell wall

A

Mycobacterium. Don’t stain well on GS

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32
Q

Urease positive organisms, and why you should care?

A

Urease positive organisms have increased risk for creating struvite kidney stones: Proteus, cryptococcus, H pylori, nocardia, klebsiella, staph epidermis & saprophyticus

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33
Q

Yellow sulfur granules of bacteria

A

Actinomyces israelii

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34
Q

Bacterial toxins that are a product of transduction? Define transduction?

A

Transduction: injection of DNA material through bacteriophages. Examples (ABCDE): shigA-like toxin (E coli O157:H7), Botulinum toxin, Cholera, Diphtheria, Erythogenic toxin in strep pyogenes

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35
Q

Infection associated with “rusty sputum”

A

gram-positive lancet-shaped, catalase negative, alpha-hemolytic, optochinin sensitive strep pneumo

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36
Q

Hippurate test positive bacteria?

A

Strep agalactiae (Group B strep)

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37
Q

Elek test for what toxin?

A

Corynebacterium diphtheriae toxin

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38
Q

Only bacterium with polypeptide capsule?

A

Bacillus anthracis: gram-positive, spore-forming rod with D-glutamate containing polypeptide capsule

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39
Q

Only gram positive bacteria which produces endotoxin?

A

Listeria monocytogenes

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40
Q

Otitis externa bug? FC

A

Pseudomonas aeruginosa. Gram negative rod, non-lactose fermenting, oxidase positive.
Also common bug in burn victims

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41
Q

Virulence factor that is responsible for most common bug causing a UTI

A

E. coli causes cystitis and pyelo due to fimbriae

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42
Q

Patient presents with RLQ pain very similar to appendicitis, but had an appendectomy a decade ago. Recently was playing with pet feces. Dx? FC

A

Yersinia enterocolitica causes pseudoappendicitis. Usually transmitted from pet feces, contaminated milk, or pork.
Gram negative rod, non-lactose fermenting, oxidase negative, H2S producing on TSI media

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43
Q

Globoside (type of P-antigen) is important in virulence of what pathogen?

A

Parvovirus B19 uses globoside as a receptor. Found mainly on erythrocyte precursers (in the bone marrow). Think of aplastic anemia

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44
Q

Most common pathogens in aspiration pneumonia

A

Pathogens from the oropharynx (not from the GI tract!) Fusobacterium, peptostreptococcus, bacteroides

45
Q

Things spread by the Ixodes tick

A

Babesia (babesiosis, protozoa)
Burrellia (Lyme)
Anaplasma (zoonotic bacteria)

46
Q

Vector for rocky mountain spotted fever

A

Rickettsia rickettsii transmitted by Dermacentor (dog tick)

47
Q

Most common cause of culture negative endocarditis

A

Coxiella burnetti (Q fever). No rash, no vector.

48
Q

Rash that starts centrally and spreads to periphery but completely spares the palms and soles

A

Typhus: Rickettsia typhi (endemic) or R. prowazekii (epidemic, from louse)

49
Q

Patient with cough that started 2 weeks ago and has slowly gotten worse presents. High titer of antibodies that cause agglutination of RBCs in cold. Dx?

A

Mycoplasma pneumonia (atypical, walking pneumonia) causes high titers of cold agglutinins (IgM)

50
Q

Patient presents with scattered areas of hypopigmentation during summer months. Microscopy shows yeast-like fungus with “spaghetti & meatballs appearance.” Dx? Mechanism of pathology? Rx?

A

Tinea versicolor (Malassezia species). Degradation of lipids causes acid accumulation and destruction of melanocytes. Rx: selenium sulfide, antifungals

51
Q

Immunocompromised patient with meningitis. India ink stain reveals yeast with halos. Dx? Most specific lab test?

A

Cryptococcus neoformans. Dx with latex agglutination test which detects polysaccharide capsular antigen

52
Q

Rose gardener pricks himself. Later develops ascending lymphangitis up his arm with ulcers, etc. Dx? Rx?

A

Sporothrix schenckii causing sporotrichosis. Rx: Potassium iodide

53
Q

Transmission of malaria

A

Anopheles mosquito transmitting plasmodium vivax/ovale, malariae, or falciparum

54
Q

Patient from Africa presents with malaise, headache, anemia, and splenomegaly. Smear shows rings inside RBCs. He has had a fever every 48hrs. Dx? Transmission? Rx?

A

Plasmodium Vivax/ovale (48hrs fever)
Transmitted by anophele mosquito
Rx: Chloroquine + primaquine (liver hypnozoites) for vivax/ovale
IV quinidine or artesunate if life threatening
Primaquine not necessary if not vivax/ovale

55
Q

Rx of trypanosoma species

A
  • Trypanosoma brucei (Africa sleeping sickness, Tsetse fly) Rx: Suramin if bloodborne, Melarsoprol if CNS penetration
  • Trypansoma cruzi (Chagas disease, Reduviid bug) Rx: Benznidazole or nifurtimox
56
Q

Forms of saline responsive metabolic alkalosis? How to diagnose?

A

Urine chloride is low in saline responsive alkalosis. Causes: vomiting/NG aspiration, or prior diuretic use. Saline-unresponsive is excess mineralcorticoid activity, barter/gitelman’s syndromes, etc (with high urine Cl)

57
Q

How to accentuate an S3 sound on auscultation?

A

Lie patient in lateral decubitus position and listen during full exhalation

58
Q

Pathognomonic histology of rabies infection

A

Eosinophilic round inclusion intracellularly in hippocampal neurons (Negri bodies). Yep, the collect in the hippocampus, aint that some shit.

59
Q

Only DNA virus to carry its own DNA-dependent RNA polymerase

A

Poxvirus (smallpox & mollscum contagiosum)

60
Q

Herpes viruses HHV-3,4,5?

A

3: VZV, 4: EBV, 5: CMV (5 kinda looks like a G from gancyclovir)

61
Q

Where does VZV hide out latent?

A

Dorsal root ganglion of the dermatome it will later reinfect

62
Q

Picornaviruses

A

Single stranded RNA viruses, positive sense, linear

PERCH: Polio, echovirus, rhinovirus, coxsackie, Hep A

63
Q

Hepatitis viruses A, B, C family names

A

HepA: Picornavirus (PERCH)
HepB: Hepadnavirus (DNA virus)
HepC: Flavivirus (RNA virus: yellow fever, dengue, STL encephalitis, west nile virus)

64
Q

Most common togavirus

A

Rubella (RNA virus). See also eastern & western equine encephalitis

65
Q

Paramyxoviruses

A

Negative sense, helical RNA viruses

Parainfluenza (croup), RSV (bronchiolitis), measles, mumps

66
Q

Negative sense RNA viruses worth caring about (4)? Significance?

A

Neg sense RNA viruses must bring along an RNA dependent RNA polymerase to synthesize the positive sense RNA for translation. Also have helical capsids
Orthomyxovirus (influenza), paramyxoviruses (parainflu, RSV, measles, mumps), rabies, hepatitis Delta

67
Q

2 most important viruses with segmented genomes

A

Orthomyxovirus (influenza) and rotavirus (dsRNA infantile diarrhea virus)

68
Q

Virulence factor of paramyxoviruses. Therapeutic agent targeting this virulence factor?

A

Surface F (fusion) protein which causes fusion of epithelial cells to form multinucleated cells. Targeted by monoclonal antibody Palivizumab

69
Q

Pyrrolidonyl arylamidase positive bacterium (gram positive)

A

Strep pyogenes. Gram positive cocci, catalase negative, beta-hemolytic, bacitracin sensitive

70
Q

Parts of duodenum not retroperitoneal

A

Only one part: 1st part (just distal to stomach pylorus)

71
Q

80 year old patient with systolic BP 180 with a super wide pulse pressure. What’s going on?

A

Normal aging. Aortic compliances decreases with age and preferentially raises the systolic BP

72
Q

Patient presents with swollen parotid glands and tender swollen testes. No vaccinations. Dx? What is the 3rd possible manifestation?

A

Mumps (Paramyxovirus). Also causes meningitis

73
Q

Hepatitis B window period antibodies?

A

Anti HBe IgM may be the only thing present during window period

74
Q

Significance of anti HBe IgG development

A

This means low infectivity. When just HBe antigen, patient is highly infectious

75
Q

Anti HBsAg IgG significance

A

Only appears after hepatitis has cleared! Chronic infections only exhibit HBsAg without anti HBsAg

76
Q

HIV patient with ring enhancing lesion on brain MRI. Could be two things?

A

Toxoplasmosis (multiple ring-enhancing lesions)

EBV non-Hodgkin lymphoma (often solitary lesion, patient much more severely immunocompromised)

77
Q

Prion pathophysiology at the molecular level

A

Conversion of normal alpha-helical protein (PrP^c) to beta-pleated form (PrP^sc) which creates a positive feedback cycle and accumulation in neural tissue

78
Q

Bug associated with mayonnaise or custard ingestion

A

Staph aureus (usually preformed toxin causing quick onset vomiting)

79
Q

Heparin vs. enoxaparin MOA

A

Both bind antithrombin but only unfractionated heparin has long enough of a chain to bind thrombin (factor II) into the antithrombin complex. Thus enoxaparin (LMWH) only inactivates factor X primarily. Heparin does X and II

80
Q

Worms treated with diethylcarbamazine

A

Wuchereriria bancrofti (elephantitis) and Loa Lao

81
Q

Infections treated with praziquantel

A

Schistosoma

82
Q

Chlorpheniramine MOA

A

1st generation anti-histamine drug. Same class as diphenhydramine

83
Q

Serum levels of tryptase useful in detecting what

A

Mast cell degranulation (think anaphylaxis)

84
Q

DNA virus with RNA-dependent DNA polymerase?

A

Hepatitis B. This is a reverse transcriptase that converts mRNA to DNA in the progeny viruses

85
Q

Location of receptors for glucocorticoids, steroid hormones, and thyroid hormone?

A

Glucocorticoids and steroid hormone receptors are in the cytoplasm. Thyroid hormone receptors are in the nucleus itself (as are PPAR and retinoid receptors)

86
Q

Chorda tympani…expound

A

Branch of facial nerve (CN VII) that carries taste information from the anterior 2/3 of tongue (sensation: CN V3 lingual branch). Posterior 1/3 taste and sensation CN IX

87
Q

Biotin cofactor for what kind of enzymes

A

Carboxylase enzymes: pyruvate carboxylase, acetyl CoA carboxylase, propionyl CoA carboxylase, etc

88
Q

Vancomycin resistant enterococcus mechanism of resistance

A

Change of Van binding site from D-alanyl-D-alanine to D-alanine-D-lactate

89
Q

Hernia above the inguinal ligament, medial to inferior epigastric vessels and lateral to rectus abdominis. Pathophys?

A

Direct inguinal hernia through Hesselbach’s triangle. Caused by weakness of transversalis fascia. Covered by external spermatic fascia only

90
Q

Blueberry muffin rash in neonate associated with what?

A

Rubella (Togavirus). Though can be present in congenital toxoplasmosis

91
Q

Triad of chorioretinitis, hydrocephalus, and intracranial calcifications in a newborn?

A

Congenital toxoplasmosis. Remember CMV manifests with periventricular calcifications specifically

92
Q

Triad of cataracts, PDA (or pulmonary hypoplasia), and deafness in a newborn?

A

Congenital rubella. May also have a blueberry muffin rash as well

93
Q

Antimicrobials that inhibit synthesis of peptidoglycan cell wall

A

Bacitracin and vancomycin. The rest of the penicillins/cephalosporins/carbapenems inhibit peptidoglycan cross-linking

94
Q

MRSA resistance mechanism

A

Change in penicillin binding protein target (i.e. transpeptidases responsible for crosslinking of peptidoglycans)

95
Q

Carbapenems administered with cilastatin. Why, but what mechanism?

A

Cilastatin inhibits renal dehydropeptidase I enzyme decreasing renal inactivation of drug

96
Q

Difference between transpeptidase and peptidyl-transferase enzymes

A

Transpeptidase cross-links peptidoglycans in cell wall (target of penicillins). Peptidyl-transferase moves the peptide chain in the ribosome during translation. Target of chloramphenicol (50s unit)

97
Q

Antimicrobial agent that inhibits that initiator complex of ribosomal assembly

A

Aminoglycosides, specifically targeting the 30s subunit

98
Q

MOA of tetracyclines

A

Binds 30s subunit and blocks the A site specifically. Prevents incoming tRNA from binding ribosome

99
Q

How are trimethroprim and methotrexate related

A

Trimethroprim inhibits bacterial dihydrofolate reductase (Abx), while methotrexate inhibits human dihydrofolate reductase

100
Q

Vitamin supplementation during isoniazid therapy

A

Vitamin B6: Pyridoxine to prevent associated neuropathy

101
Q

Rx for vancomycin resistant enterococcus

A

Linezolid or streptogramins (quinupristin, dalfospristin). Both of which target the 50s subunit

102
Q

Flucytosine (anti-fungal drug) MOA

A

DNA & RNA biosynthesis in fungi. Converted to to 5-fluorouracil by cytosine deaminase

103
Q

Patient with diarrhea and stool studies show leukocytes with neutrophil predominance

A

Invasive bacteria e.g. shigella, campylobacter, EIEC

104
Q

Bacterial species with IgA protease

A

Strep pneumo, Neisseria, H. influenza

105
Q

Acyclovir famciclovir and valcyclovir mechanism of action

A

Guanosine analogs used in treatment of VZV and HSV (weak activity against EBV). Dependent on thymidine kinase enzyme in viral cells for monophosphorylation, then triphosphorylation. Ultimately causes DNA chain termination

106
Q

Periodic acid-schiff reaction and bacterial infection MOA

A

Tropheryma whippelii infection. Stains the glycoproteins abundantly found in cell wall (turns magenta). Remember foamy macrophages as well

107
Q

Rasburicase MOA and indication

A

Recombinant urate oxidase enzyme used to increase excretion of uric acid that can accumulate in tumor lysis syndrome from increased purine catabolism (think of leukemias)

108
Q

Non-nucleotide reverse transcriptase inhibitors (HIV)

A

Delavirdine, efavirenz, nevirapine. All have “vir” in the middle of their name (except Miraviroc and Enfuvirtide). The rest are nucleotide RTIs requiring phosphorylation by thymidine kinase

109
Q

Drug that inhibits beta-D glucan synthesis?

A

Caspofungin, anidulafungin, micafungin (Echinocandin class) anti-fungal agents which prevent cell wall formation

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