First Aid: Microbiology Flashcards Preview

USMLE Step 1 Prep > First Aid: Microbiology > Flashcards

Flashcards in First Aid: Microbiology Deck (38):

What sort of response does Lipoteichoic Acid (gram+ cell wall) and Lipid A (g- outer membrane) induce?

TNF and IL1


What is the periplasm of a bacterium and what is unique about this structure?

Space between cytoplasmic membrane and outer membrane in g- bacteria

Contains many hydrolytic enzymes, ilncuding beta-lactamases


What is unique about the structure of mycoplasma and mycobacteria?

Mycoplasma - membrane contains sterols and no cell wall
Mycobacteria - contain mycolic acid and HIGH lipid content - acid fast staining


What are the major gram + bacteria?

Circular - Staphylococcus, Streptococcus

Rods - Clostridium, Corynebacterium, Bacillus, Listeria, Mycobacterium (acid fast), Gardnerella (gram variable)

Branching Filamentous - Actinomyces, Nocardia (weakly acid fast)


Which microbes do not gram stain well and why?

These Microbes May Lack Real Color

Treponema (too thin for visualization)
Mycobacteria (hihg lipid content, use acid fast-carbol fuchsin stain)
Mycoplasma (no cell wall)
Legionella pneumophila (primarily intracellular)
Rickettsia (intracellular parasite)
Chlamydia (intracellular parasite; lacks muramic acid in cell wall)


When is a Giemsa stain useful?

Certain Bugs Really Try my Patience

Chlamydia, Borrelia, Rickettsiae, Trypanosomes, Plasmodium


When would a PAS (periodic acid-Schiff) stain be helpful?

Whipple Disease (Tropheryma whipplei)- because PAS stains glycogen, mucopolysaccharides



What is silver stain useful for identifying?

Fungi (pneumocystis), Legionella, H. Pylori


Match the bacteria with the media culture used

Page 122 First Aid


What aerobic bacteria can often be found in burn wounds, complications of diabetes, nosocomial pneumonia, and pneumonias in cystic fibrosis patients?

Pseudomonas aeruginosa


What are two situations that could lead to reactivation of TB, and what lung areas would be affected?

Immune compromisation or TNF-alpha inhibitor use

Predilection for apices of lung (highest PO2)


What are the main obligate aerobes?

Nagging Pests Must Breathe

Nocardia, Pseudomonas aeruginosa, MycoBacterium tuberculosis


You discover foul smelling bacteria that are difficult to culture and produce gas (CO2 and H2) in tissues. What are some main possibilities as to the identity of this bug and what makes them unique?

Obligate Anaerobes - Cant Breathe Air
-Clostridium, Bacteroides, Actinomyces

Lack catalase and/or superoxide dismutase --> susceptible to oxidative damage


What are the obligate intracellular bugs and facultative intracellular bugs?

Stay inside cells when it's Really Cold --> Rickettsia, Chlamydia (can't make own ATP)

Some Nasty Bugs May Live FacultativeLY
Salmonella, Neisseria, Brucella, Mycobacterium, Listeria, Francisella, Legionella, Yersinia pestis


Which bacteria have capsules that serve as an antiphagocytic virulence factor?


Streptococcus pneumoniae, Haemophilus influenzae type B, Neisseria meningitidis, Escherichia coli, Salmonella, Klebsiella pneumoniae, and group b Strep


How does the body get rid of encapsulated organisms and what considerations do you have to take in compromised patients?

Opsonized and cleared by spleen

Asplenics are at risk of infection so give prophylactic vaccines for Strep pneumo (PCV, PPSV, Pneumovax), H Flu (type B conjugate vaccine), and N. meningitidis (Meningococcal conjugate vaccine)


Which organisms are catalase positive and what patients are at risk for recurrent infections with catalase + organisms?

youu need PLACESS for your cats

Pseudomonas, Listeria, Aspergillus, Candida, E. coli, S. aureus, Serratia

People with chronic granulomatous disease (NADPH oxidase deficiency)


What are the urease positive bugs?

CHuck norris hates PUNKSS

Cryptococcus, H plyori, Proteus, Ureaplasma, Nocardia, Klebsiella, S epidermidis, S saprophyticus


A bacteria is found to produce yellow sulfur granules composed of filaments of bacteria, what could be the origin?
Yellow Pigment? Blue-Green pigment? Red pigment?

Actionmyces israelii (israel has yellow sand)

S. Aureus (aureus = gold, yellow)
Pseudomonas aeruginosa (Aerugula is green)
Serratia marcescens (red maraschino cherries)


What enzyme is secreted by S. pneumo, H flu and Neisseria that allows them to colonize respiratory mucosa?

IgA protease


What do virulence factors "Protein A" and "M protein" cause in the host? Which bacteria release each?

Protein A - Binds Fc region of IgG, prevents opsonization and phagocytosis (S. Aureus)

M protein - helps prevent phagocytosis (group A strep)


A patient presents with fever, hypotension and DIC. A toxin is isolated that is found to be stable at 100 degrees C and induces TNF, IL1 and IL6. What is the origin of this toxin?

Endotoxin - outer cell membrane of most gram - bacteria

Lipopolysaccharide (structural bacteria part, released when lysed)


What are the 9 key features of ENDOTOXIN?

Nitric Oxide release from active macrophages
DIC/Death from a


What do novobiocin, optochin, and bacitracin help differentiate among the gram + cocci?

"On the office's STAPH retreat, there was NO StRESs"
-STAPHylococci --> Novobiocin --> Saprophyticus is Resistant; Epidermidis is Sensitive

OVRPS (overpass) --> Optochin - Viridans is Resistant; Pneumoniae is Sensitive

B-BRAS --> Bacitracin - group B strep are Resistant; group A strep are sensitive


You plate some bacteria that form a green ring around colonies on blood agar. Which organisms could be there?

alpha-hemolytic bacteria - Strep pneumonia or Viridans strep


You plate some bacteria that form a clear area around colonies on blood agar, what could they be?

beta-hemolytic bacteria - Staph aureus, Strep pyogenes, strep agalactiae, listeria monocytogenes


A 54 year old man with a history of sickle cell disease presents with congestion, cough and "rusty" sputum production. Chest X-Ray reveals a patchy infiltrate in the lower right lung lobe. Sputum culture reveals lancet shaped, gram + diplococci that are sensitive to (blank)? What could have prevented this disease and how can you treat the patient now?

Streptococcus Pneumoniae - sensitive to Optochin

23 valent adult vaccine could have prevented

Tx: Macrolides or Cephtriaxone


Match these HIV Associations:
1. Low fevers, cough, HSmeg, tongue ulcer, oval yeast cells w/in Mphage,

1. Histoplasma Capsulatum
2. C. Albicans (


What is the number one cause for meningitis in all adults of any age?

Strep Pneumo


Major HIV associations:
1. Ring enhancing lesions on brian, CD4 Demyelination, narrow based budding yeast w/ large capsule

1. Toxoplasma gondii
2. HIV dirrect association
3. JC virus reactivation (cause of PML)
4. Cryptococcus neoformans
5. CMV


Major HIV associations:
1. Non hodgkin (large cell) lymphoma on oropharynx
2. Primary CNS lymphoma, focal/multiple, no sign of yeast organisms
3. Squamous cell CA in anus or cervix
4. Superficial neoplastic proliferation of vasculature, lymphocytic inflammation on biopsy

1. EBV possibly
2. EBV often
3. HPV
4. HHV8 (kaposi sarcoma) - not lymphocyte inflammation NOT neutorphils - this differentiates from Bartonella henselae)


Major HIV associations:
1. Interstitial pneumonia, w/ Owl eye inclusion bodies
2. Pleuritic pain, hemoptysis, and infiltrates on imaging
3. Pneumonia w/ CDV 200
5. TB like disease w/

1. CMV
2. INVASIVE aspergillosis (Aspergillus fumigatus)
3. Pneumocystis jirovecii pneumonia
4. Strep pneumo
5. Mycobacterium Avium-intracellulare (MAC)


How are Ampicillin and Amoxicillin different from penicillin? What are they used for?

Wider spectrum (but sitll penicillinase sensitive)

AMinoPenicillins are AMP-ed up pinicillin. amOxicillin has greater Oral bioavailability.

Both HELPSS kill enterococci (H. flu, E coli, Listeria monocytogenes, Proteus mirabilis, Salmonella, Shigella)


When can you use nafcillin? (other ABs in this class?)

Use for Staph Aureus, except MRSA


How can you make penicillin ABs more effective (specific drugs)?

Use Beta-lactamase inhibitors - CAST

Calvulanic Acid, Sulbactam, Tazobactam


How can you quickly identify protease inhibitors used in HIV treatment?

NAVIR tease a protease -- -navir ending

Ritonavir, Atazanavir, Lopinavir,, indinavir etc. etc.


Which drugs are not structurally related to nucleosides but have anti-reverse transcriptase effects and do not require phosphorylation to be active?

the END

Efavirenz, Nevirapine, Delavirdine


What drugs can be used for severe gram negative rod infections and are synergistic with beta-lactam antibiotics and their side effects? (hint: they are ineffective vs. anaerobes)

Aminoglycosides - Mean GNATS caNNOT kill anaerobes.
Gentamicin, Neomycin, Amikacin, Tobramycin, Streptomycin

Nephrotox (esp with cephalosporins), Neuromuscular block, Ototoxicity (especially with loop diuretics), Teratogen

MOA: disrupt 30S ribosomal subunit