1/6/20, 9:12:02 PM
Compare Results
New File:
Old File:
First Aid for the USMLE Step 1 2020, Thirtieth
FA 2019.pdf
versus edition-1.pdf
82 pages (293.11 MB)
82 pages (109.99 MB)
1/5/20, 12:57:57 PM
1/5/20, 12:52:18 PM
BY u/verified-idiot
To the only girl i've ever loved, to soufia.
BLUE new in FA 2020
YELLOW text of FA 2019 was edited; the note box next to the yellow highlight will show the difference between
them the old text and the new text of FA 2020
Some pages might look scary! because of note boxes and highlighting , but it is not, my recommendation for
you is to study your book and after than look for the new stuff and edits.. I DONT recommend comparing while
you are studying since it will consume your time.
Go to First Change (page 1)
file://NoURLProvided[1/6/20, 9:12:02 PM]
,HIGH-YIELD PRINCIPLES IN
Microbiology
“Support bacteria. They’re the only culture some people have.” ` Basic Bacteriology 124
—Steven Wright
` Clinical Bacteriology 134
“What lies behind us and what lies ahead of us are tiny matters
compared to what lies within us.” ` Mycology 151
—Henry S. Haskins
` Parasitology 155
“Infectious disease is merely a disagreeable instance of a widely prevalent
tendency of all living creatures to save themselves the bother of building, ` Virology 162
by their own efforts, the things they require.”
—Hans Zinsser ` Systems 178
` Antimicrobials 187
Microbiology questions on the Step 1 exam often require two (or
more) steps: Given a certain clinical presentation, you will first need
to identify the most likely causative organism, and you will then need to
provide an answer regarding some features of that organism or relevant
antimicrobial agents. For example, a description of a child with fever
and a petechial rash will be followed by a question that reads, “From
what site does the responsible organism usually enter the blood?”
This section therefore presents organisms in two major ways: in
individual microbial “profiles” and in the context of the systems
they infect and the clinical presentations they produce. You should
become familiar with both formats. When reviewing the systems
approach, remind yourself of the features of each microbe by returning
to the individual profiles. Also be sure to memorize the laboratory
characteristics that allow you to identify microbes.
123
,124 SEC TION II MICROBIOLOGY `M̀ICROBIOLOGY—BASIC BACTERIOLOGY
``
MICROBIOLOGY—BASIC BACTERIOLOGY
Bacterial structures
STRUCTURE CHEMICAL COMPOSITION FUNCTION
Appendages
Flagellum Proteins Motility
Pilus/fimbria Glycoprotein Mediate adherence of bacteria to cell surface;
sex pilus forms during conjugation
Specialized structures
Spore Keratin-like coat; dipicolinic acid; Gram ⊕ only
peptidoglycan, DNA Survival: resist dehydration, heat, chemicals
Cell envelope
Capsule Discrete layer usually made of polysaccharides Protects against phagocytosis
(and rarely proteins)
Slime (S) layer Loose network of polysaccharides Mediates adherence to surfaces, especially
foreign surfaces (eg, indwelling catheters)
Outer membrane Outer leaflet: contains endotoxin (LPS/LOS) Gram ⊝ only
Embedded proteins: porins and other outer Endotoxin: lipid A induces TNF and IL-1;
membrane proteins (OMPs) antigenic O polysaccharide component
Inner leaflet: phospholipids Most OMPs are antigenic
Porins: transport across outer membrane
Periplasm Space between cytoplasmic membrane Accumulates components exiting gram
and outer membrane in gram ⊝ bacterial ⊝ cells, including hydrolytic enzymes
(peptidoglycan in middle) (eg, β-lactamases)
Cell wall Peptidoglycan is a sugar backbone with peptide Net-like structure gives rigid support, protects
side chains cross-linked by transpeptidase against osmotic pressure damage
Cytoplasmic Phospholipid bilayer sac with embedded Site of oxidative and transport enzymes; PBPs
membrane proteins (eg, penicillin-binding proteins involved in cell wall synthesis
[PBPs]) and other enzymes Lipoteichoic acids induce TNF-α and IL-1
Lipoteichoic acids (gram positive) only extend
from membrane to exterior
Cell envelope
Unique to Common to both Unique to
gram ⊕ gram ⊝
Flagellum
Lipoteichoic acid Pilus
Capsule
Endotoxin/LPS Outer
Porin membrane
Cell wall
Peptidoglycan Periplasmic space
(β-lactamase location)
Cytoplasmic
membrane
Gram ⊕ Gram ⊝
, MICROBIOLOGY `M̀ICROBIOLOGY—BASIC BACTERIOLOGY SEC TION II 125
Stains
Gram stain First-line lab test in bacterial identification. Bacteria with thick peptidoglycan layer retain crystal
violet dye (gram ⊕); bacteria with thin peptidoglycan layer turn red or pink (gram ⊝) with
counterstain.
These bugs do not Gram stain well (These Little Microbes May Unfortunately Lack Real Color
But Are Everywhere):
Treponema, Leptospira Too thin to be visualized
Mycobacteria Cell wall has high lipid content
Mycoplasma, Ureaplasma No cell wall
Legionella, Rickettsia, Chlamydia, Bartonella, Primarily intracellular; also, Chlamydia lack
Anaplasma, Ehrlichia classic peptidoglycan because of muramic
acid
Giemsa stain Rickettsia, Chlamydia, Trypanosomes A , Ricky got Chlamydia as he Tried to Please the
Plasmodium, Borrelia, Helicobacter pylori Bored Hot “Geisha”
Periodic acid–Schiff Stains glycogen, mucopolysaccharides; used PaSs the sugar
stain to diagnose Whipple disease (Tropheryma
whipplei B )
Ziehl-Neelsen stain Acid-fast bacteria (eg, Mycobacteria C , Auramine-rhodamine stain is more often used
(carbol fuchsin) Nocardia; stains mycolic acid in cell wall); for screening (inexpensive, more sensitive)
protozoa (eg, Cryptosporidium oocysts)
India ink stain Cryptococcus neoformans D ; mucicarmine
can also be used to stain thick polysaccharide
capsule red
Silver stain Fungi (eg, Coccidioides E , Pneumocystis
jirovecii), Legionella, Helicobacter pylori
Fluorescent antibody Used to identify many bacteria, viruses, Example is FTA-ABS for syphilis
stain Pneumocystis jirovecii, Giardia, and
Cryptosporidium
A B C D E
Compare Results
New File:
Old File:
First Aid for the USMLE Step 1 2020, Thirtieth
FA 2019.pdf
versus edition-1.pdf
82 pages (293.11 MB)
82 pages (109.99 MB)
1/5/20, 12:57:57 PM
1/5/20, 12:52:18 PM
BY u/verified-idiot
To the only girl i've ever loved, to soufia.
BLUE new in FA 2020
YELLOW text of FA 2019 was edited; the note box next to the yellow highlight will show the difference between
them the old text and the new text of FA 2020
Some pages might look scary! because of note boxes and highlighting , but it is not, my recommendation for
you is to study your book and after than look for the new stuff and edits.. I DONT recommend comparing while
you are studying since it will consume your time.
Go to First Change (page 1)
file://NoURLProvided[1/6/20, 9:12:02 PM]
,HIGH-YIELD PRINCIPLES IN
Microbiology
“Support bacteria. They’re the only culture some people have.” ` Basic Bacteriology 124
—Steven Wright
` Clinical Bacteriology 134
“What lies behind us and what lies ahead of us are tiny matters
compared to what lies within us.” ` Mycology 151
—Henry S. Haskins
` Parasitology 155
“Infectious disease is merely a disagreeable instance of a widely prevalent
tendency of all living creatures to save themselves the bother of building, ` Virology 162
by their own efforts, the things they require.”
—Hans Zinsser ` Systems 178
` Antimicrobials 187
Microbiology questions on the Step 1 exam often require two (or
more) steps: Given a certain clinical presentation, you will first need
to identify the most likely causative organism, and you will then need to
provide an answer regarding some features of that organism or relevant
antimicrobial agents. For example, a description of a child with fever
and a petechial rash will be followed by a question that reads, “From
what site does the responsible organism usually enter the blood?”
This section therefore presents organisms in two major ways: in
individual microbial “profiles” and in the context of the systems
they infect and the clinical presentations they produce. You should
become familiar with both formats. When reviewing the systems
approach, remind yourself of the features of each microbe by returning
to the individual profiles. Also be sure to memorize the laboratory
characteristics that allow you to identify microbes.
123
,124 SEC TION II MICROBIOLOGY `M̀ICROBIOLOGY—BASIC BACTERIOLOGY
``
MICROBIOLOGY—BASIC BACTERIOLOGY
Bacterial structures
STRUCTURE CHEMICAL COMPOSITION FUNCTION
Appendages
Flagellum Proteins Motility
Pilus/fimbria Glycoprotein Mediate adherence of bacteria to cell surface;
sex pilus forms during conjugation
Specialized structures
Spore Keratin-like coat; dipicolinic acid; Gram ⊕ only
peptidoglycan, DNA Survival: resist dehydration, heat, chemicals
Cell envelope
Capsule Discrete layer usually made of polysaccharides Protects against phagocytosis
(and rarely proteins)
Slime (S) layer Loose network of polysaccharides Mediates adherence to surfaces, especially
foreign surfaces (eg, indwelling catheters)
Outer membrane Outer leaflet: contains endotoxin (LPS/LOS) Gram ⊝ only
Embedded proteins: porins and other outer Endotoxin: lipid A induces TNF and IL-1;
membrane proteins (OMPs) antigenic O polysaccharide component
Inner leaflet: phospholipids Most OMPs are antigenic
Porins: transport across outer membrane
Periplasm Space between cytoplasmic membrane Accumulates components exiting gram
and outer membrane in gram ⊝ bacterial ⊝ cells, including hydrolytic enzymes
(peptidoglycan in middle) (eg, β-lactamases)
Cell wall Peptidoglycan is a sugar backbone with peptide Net-like structure gives rigid support, protects
side chains cross-linked by transpeptidase against osmotic pressure damage
Cytoplasmic Phospholipid bilayer sac with embedded Site of oxidative and transport enzymes; PBPs
membrane proteins (eg, penicillin-binding proteins involved in cell wall synthesis
[PBPs]) and other enzymes Lipoteichoic acids induce TNF-α and IL-1
Lipoteichoic acids (gram positive) only extend
from membrane to exterior
Cell envelope
Unique to Common to both Unique to
gram ⊕ gram ⊝
Flagellum
Lipoteichoic acid Pilus
Capsule
Endotoxin/LPS Outer
Porin membrane
Cell wall
Peptidoglycan Periplasmic space
(β-lactamase location)
Cytoplasmic
membrane
Gram ⊕ Gram ⊝
, MICROBIOLOGY `M̀ICROBIOLOGY—BASIC BACTERIOLOGY SEC TION II 125
Stains
Gram stain First-line lab test in bacterial identification. Bacteria with thick peptidoglycan layer retain crystal
violet dye (gram ⊕); bacteria with thin peptidoglycan layer turn red or pink (gram ⊝) with
counterstain.
These bugs do not Gram stain well (These Little Microbes May Unfortunately Lack Real Color
But Are Everywhere):
Treponema, Leptospira Too thin to be visualized
Mycobacteria Cell wall has high lipid content
Mycoplasma, Ureaplasma No cell wall
Legionella, Rickettsia, Chlamydia, Bartonella, Primarily intracellular; also, Chlamydia lack
Anaplasma, Ehrlichia classic peptidoglycan because of muramic
acid
Giemsa stain Rickettsia, Chlamydia, Trypanosomes A , Ricky got Chlamydia as he Tried to Please the
Plasmodium, Borrelia, Helicobacter pylori Bored Hot “Geisha”
Periodic acid–Schiff Stains glycogen, mucopolysaccharides; used PaSs the sugar
stain to diagnose Whipple disease (Tropheryma
whipplei B )
Ziehl-Neelsen stain Acid-fast bacteria (eg, Mycobacteria C , Auramine-rhodamine stain is more often used
(carbol fuchsin) Nocardia; stains mycolic acid in cell wall); for screening (inexpensive, more sensitive)
protozoa (eg, Cryptosporidium oocysts)
India ink stain Cryptococcus neoformans D ; mucicarmine
can also be used to stain thick polysaccharide
capsule red
Silver stain Fungi (eg, Coccidioides E , Pneumocystis
jirovecii), Legionella, Helicobacter pylori
Fluorescent antibody Used to identify many bacteria, viruses, Example is FTA-ABS for syphilis
stain Pneumocystis jirovecii, Giardia, and
Cryptosporidium
A B C D E
