USMLE Step 1 - Micro

Staph Aureus

Gram "+" in clusters

β-Hemolytic

Catalase "+"

Coagulase "+"

Risk Factors

-IV Drug use

-Intravascular Catheters (For Nocosomial infections)

Virulence Factors

-Exfoliative Toxin A (Protease which targets Desmoglein in Bullous Impetigo)

-Preformed Enterotoxin

Azoles

MOA

-Inhibition of Cytochrome P450-dependent Demethylation reaction which synthesizes Ergosterol from Lanosterol

Used for Oral Tx of Vulva Candidiasis

Ascaris Lumbricoides

Dx

-Large white worms in stool

Transmission

-Egg-contaminated food or H2O

**Hematogenous spread to the Liver**

Haemophillus Influenzae Vaccine

Neisseriaa Meningitidis Vaccine

Streptococcus Penumoniae Vaccine

Conjugated Capsular Polysaccharide vaccine

Oral Typhoid Vaccine

Live Attenuated Bacterial vaccine

Clostridium Tetani Vaccine

Corynebacterium Diptherie Vaccine

Bortadella Pertussis Vaccine

Toxoid-based Vaccines

Haemophilus Influenzae

Dx

-Inflammation + Edema of Supraglottic tissue

Bortadella Pertusis

Dx

-Clearance/Loss of Ciliated Respiratory Epithelial Cells

Influenza Virus

Retrograde Virus

Viruses which replicate inside the Cell Nucleus

Staph Aureus

Reservoir

-Anterior Nare colonization

Sx

-Osteoarthritis

-Endocarditis (Most commonly affects the Tricuspid Valve)

-Skin + Tissue (I.e. Hepatic) Abscess

-Scalded Skin Syndrome

-Hepatic Fluid-filled Cavity/Abscesses (D/t Hematogenous spread)

-Right-sided Endocarditis

-Toxic Shock Syndrome

-Bullous Impetigo (Honey-crusted blistering skin rash)

**Immune response is mediated by Neutrophils + B-cells**

Mycoses Fungoides

Cutaneous T-Cell Lymphoma

Commonly affects the Axilla + Buttocks

Sx

-Erythematous wrinkled scaly skin patches

Complications

-Thickening of skin patches

-Progression of skin patches into tumors

Hypochlorite

Important compound which is involved in the efficient killing of bacteria as it is a component of the Respiratory Burst → Rapid Bacterial killing

Bacteroides Fragilis

Gram "-" Rod

Does NOT grow well on McConkey Agar

It causes infections when displaced from the Colon (I.e. Appendix rupture)

Higher chance than E. Coli to be infiltrated in Appendix Rupture since its a commensal of the GIT

Death Receptor Extrinsic Pathway

Risk Factors

-Viral Hepatitis

Mitochondrial Intrinsic Pathway

Risk Factors

-Radiotherapy

-Oxidative damage

-Ischemia

-Toxin exposure

Taenia Solium

Pork Tapeworm

Transmission

-Fecal Oral

Sx

-Adult-onset seizures

-Headaches

-Vomiting

MRI

-Cysts within the Brain

Tx

-Praziquantel

Neurocysticercosis

Etiology

-Taenia Solium

Dx

-Calcified Nodules + Cysts in the Brain

-Seizures

Staph Epidermidis

Dx

-Gram "+" Cocci

-Catalase "+"

-Coagulase "-"

-Novobiocin Sensitive

**Urease "+"

α-Hemolytic

Strep Pneumo

Strep Mitis

Strep Mutans

are all _____________________ bacteria

β-Hemolytic

Strep Agalactiae

Strep Pyogenes

are all _____________________ bacteria

γ-Hemolytic

Strep Bovis

Enterococcus Faecium

Enterococcus Faecalis

are all _____________________ bacteria

Staph Saphrophyticus

Dx

-Gram "+" Cocci

-Catalase "+"

-Coagulase "-"

-Noboviocin Resistant

**2nd most common cause of uncomplicated UTIs in women**

Strep Viridans (Strep Mutans + Strep Mitis)

Dx

-Gram "+" Cocci

-Catalase "-"

-Optochin Sensitive

-Bile Soluble

Strep Pneumo

Dx

-Gram "+" Cocci

-Catalase "-"

-Optochin Resistant

-Bile Insoluble

**More common than N. Meningitidis to cause Meningitis**

Strep Pyogenes

Dx

-Gram "+" Cocci

-Catalase "-"

-Bacitracin Sensitive

-PYR "+"

Strep Agalactiae

Dx

-Gram "+" Cocci

-Catalase "-"

-Bacitracin Resistant

-PYR "-"

Ehrlichia Chaffeensis

Histo

-Mullberry-shaped Intraleukocytic inclusions

Franscicella Tularensis

Gram "-" Coccobacilli

Risk Factors

-Contact w/ infected rabbits

Sx

-Tender regional lymphadenopathy

-Single ulcerative lesion w/ eschar

Tx

-Streptomycin

Naegleria Fowleri

Amoeba

Risk Factors

-Exposure to recreational H2O activities

Transmission

-Enters via Cibriform Plate

Sx

-Fever

-Menigitis Sx

-Confusion

-Rapidly Fatal Meningoencephalitis

CSF

-Motile Trophozoites

Tx

-Amphotericin B

Transduction

Process in which infection by a virus results in DNA being transferred from one bacterium to another

Parts of Bacterial chromosomal DNA may become packaged in Phage capsid. Phage infects another Bacteria transferring those genes

Ascaris Lumbricoides

Roundworm/Parasite

Transmission

-Ingestion of contaminated food or water

Sx

-Transient Pulmonary sx

-Eosinophilic Pneumonitis

-GI sx

Histo

-Oval egg w/ thick outer shell

Tx

-Albendazole

Lichen Planus

Skin disease often associated w/ Hep C

Sx

-Purple, pruritic polygonal planar papules + plaques

gp160

Only HIV protein which gets glycosylated in the rER + Golgi apparatus. It is then cleaved into gp120 (Mediates Viral attachment) + gp40 (Mediates Viral fusion)

POL gene

HIV gene which encodes for Reverse Transcriptase + Integrase + Protease

**Nearly ALL causes of Antiretroviral resistance is d/t inconsistent use of Antiretroviral therapy**

Glycosyltransferase

Enzyme which is a crucial component of Peptidoglycan synthesis, thus if a drug is given which inhibits this enzyme, it will prove non-effective against bacteria which lack a Cell Wall (I.e. Mycoplasma species)

2o Bacterial Pneumoniae

Risk Factors

-Influenza A infection

Etiology

-Staph Aureus

-Strep Pneumo

-Haemophilus Influenzae

Dx

-Pt w/ Influenza has improved symptoms, but then develops worsening fever + but develops Lower Respiratory Tract infection symptoms (I.e. Productive cough + Pleuritic chest pain + Shortness of breath)

Anaerobic Infection

Organisms

-Postostreptococcus

-Prevotella

-Bacteroides

-Fusobacterium

Risk Factors

-Alcoholism

-Drug abuse

-Seizures

-Strokes

-Esophageal strictures

Chikungunya Fever

Risk Factors

-Tropical + Subtropical areas (I.e. Puerto Rico)

Transmission

-Aedes mosquito

Sx

-High fevers

-Polyarthralgias

-Conjunctivitis

-Diffuse maculopapular rash

Labs

-Lymphopenia

-Thrombocytopenia

Dofetilide

Class 3 Antiarrhythmic

MOA

-K+ Channel Blocker

Tx

-Atrial Fib

AE

-Torsades de Pointes

-Headaches

-Chest pain

Contraindications

-Pts w/ ↑↑ QT (As this drug increases QT as it is)

Tropheryma Whippeli

Gram "+" Actinomycete

-Intracellular

Sx

-Whipple Disease (I.e. Abdominal discomfort + Greasy stool + Weight loss)

Dx

-Macrophages loaded w/ PAS "+" granules in the Lamina Propria of the Intestines

Norovirus

Most common cause of Viral Gastroenteritis in Developed countries

ssRNA virus

-Linear genome

-Non-enveloped

Risk Factors

-Crowded settings

Transmission

-Fecal Oral

Sx

-Watery Diarrhea

-Vomiting

-Fever

-Malaise

Squamous Cell Carcinoma

Risk Factors

-HPV (If the lesion appears in the Throat)

-EBV (If lesion appears in the Nose)

Bacteria which Cause COPD Excacerbation

Haemophilus Influenzae

Strep Pneumo

Moraxella Catarrhalis

Pseudomonas Aeruginosa

Rhino Virus

Encapsulated Bacteria

Streptococcus Pneumoniae

Haemophilus Influenzae

Neisseria Meningitidis

Escherichia Coli

Salmonella

Klebsiella Pneumoniae

Strep Pyogenes

Catalase "+" Bacteria

Staphylococcus Aureus

Burkholderia Cepaciaè

Serratia Macescens

Aspergillus Fumigatus

Nocardia

Rhino Virus

"+" ssRNA Virus → Picornaviridae

-Naked

-Acid sensitive

Sx

-Common Cold (I.e. Fever + Cough + Sore Throat)

**Uses I-CAM as a target receptor to enter cells**

Cellulitis

Risk Factors

-DM

Sx

-Skin warmth + erythema (Strep Pyogenes)

-Painful erythema (Staph Aureus)

Mycoplasma

Bacteria which lack a Cell Wall, thus antimicrobials which target the Cell Wall (I.e. Penicillins + Cephalosporins + Carbapenems + Vancomycin) would be ineffective against these bacteria

Cell-mediated Immunity

Intracellular pathogens which are reliant on _____________________ for their clearance

Dengue Virus

Risk Factors

-Brazil

-Caribbean

-South Asia

Transmission

-Aedes Mosquito

Sx

-Acute-onset fever

-Headaches

-Retroorbital pain

-Joint + muscle pain

-Diffuse maculopapular rash

-Scattered petechiae

Labs

-Thrombocytopenia

HHV-8

Histo

-Spindle + Endothelial cell proliferation

-RBC extravasation + inflammation

Lactose Fermenters

Bacteria which grow pink + mucoid colonies in MacConkey agar

I.e.

-E. Coli

-Enterobacter

-Klebsiella

Non-Lactose Fermenters

Bacteria whose colonies remain yellow in MacConkey agar

Klebsiella Pneumoniae

Gram "-" Rod

Urease "+"

Risk Factors

-Alcohol use

-DM

Sx

-Currant Jelly sputum

-UTIs

-Pneumonia

Q Fever

Etiology

-Coxiella Burnetti

Risk Factors

-Animal wastes

Sx

-Headaches

-Cough

-FLu-like symptoms

Cx

-Culture "-" Endocarditis

Q fever

Sx

-Shortness of breath

-Fatigue

-Myalgias

-Pneumonia

-Retroorbital headaches

CXR

-Lung consolidation

Labs

-Thrombocytopenia

Pox Virus

dsDNA virus

-Linear genome

-Enveloped

Sx

-Molluscum Contagiosum (Firm + Dom-shaped papules w/ central indentation)

Pox Virus

Transmission

-Direct contact

Histo

-Intracytoplasmic Eosinophilic inclusion bodies

**Only dsDNA virus which replicates outside of the Nucleus**

Roseola Infantum

Etiology

-HHV6

Dx

-High fevers for 3 days followed by a Rash which starts at the Trunk then spreads to the Extremities but spares the Face (Only when pt is afebrile)

**Self-limiting**

Rhizopus/Mucor Species

Saprophytic Fungi

Risk Factors

-Neutropenic pts

-Diabetic Ketoacidosis

Transmission

-Spore inhalation

Location

-Infects Paranasal sinuses

Rhizopus/Mucor Species

Histo

-Broad non-septate hyphae that branch at 90 degree angles/Right Anglebranching

Sx

-Black Necrotic eschar in Nasal cavity + Face

-Periorbital tenderness

-Purulent Nasal discharge

Tx

-Amphotericin B

Strongyloides Stercoralis

Threadworm

Transmission

-Larvae in Soil penetrate skin

Sx

-Duodenitis

-Dry cough

-Hemoptysis

-Skin pruritus

Dx

-Rhabditiform larvae on stool

Tx

-Albendazole

-Ivermectin

Pasteurella Multiloida

Gram "-" Coccobacilli

Risk Factors

-Cat or Dog bites

Sx

-Acute skin infection following a bite

-Mouse-like odor of infection

Bacillus Anthracis

Gram "+" Rod

-Spore-forming

-Large + nonmotile

CXR

-Widened Mediastinum

-Lung infiltrate

**Grows colonies resembling a Medusa Head**

Bacillus Anthracis

Risk Factors

-Sheep handlers

Virulence Factors

-Poly D Glutamate Capsule → Antiphagocytic

-Edema Factor → Increases cAMP

-Lethal Factor → Inhibits protein kinase signaling

Sx

-Black Eschar → Painles papule surrounded by vesicles

Bacillus Cereus

Gram "+" Rod

Virulence Factors

-Spores → Survive cooking rice

Sx

-Nausea

-Vomiting

-Watery Diarrhea

Pseudomonas Aeruginosa

Gram "-" Rod

Oxidase "+"

Non-Lactose Fermenter

Produces pigment on Culture medium

Tx

-Ticarcillin

-Piperacillin

-Ceftazidime

-Cefepime

-Aminoglycosides

-Fluoroquinolones

-Monobactams (I.e. Aztreonam)

-Carbapenems (I.e. Imipenem)

**Grape-like odor**

Pseudomonas Aeruginosa

Dx

-Gram "-" Rod

-Oxidase "+" that produces pigment on Culture medium

Lactose-fermenting Gram "-" Rods

Enterobacter

Klebsiella

E. Coli

Hot Tub Folliculitis

Superficial infection of the Hair follicle

Etiology

-P. Aeruginosa

Risk Factors

-Pool H2O

Sx

-Pruitic Papulopustular rash

Hepatitis A

"+" ssRNA Virus → Picornaviridae

Transmission

-Selfish

Risk Factors

-Mexico

Sx

-Malaise

-Fatigue

-Anorexia

-Hepatosplenomegaly

**Usually self-limiting in adults, thus supportive treatment is only necessary**

Biopsy

-Hepatocyte swelling

-Councilman bodies

-Momocyte infiltration

Hepatitis C

"+" ssRNA Virus → Flaviviridae

Transmission

-IV

-Post-transfusion

-Hemodyalisis

Sx

-Jaundice

-Abdominal pain

-Can remain asymptomatic

**Can develop Chronic HCV if not treated**

Labs

-↑↑ Hepatic aminotransferases

-↑↑ Cryoglobulins

Cx

-Hepatocellular Carcinoma

-Decomensated Liver cirrhosis

**Very rare**

Cryoglobulin

Immune complexes that create a fluffy white precipitate after freezing donor serum

Can manifest as a reddish-purple rash + possible end-organ dysfunction

Hepatitis B

Partially dsDNA Virus → Hepadnaviridae

-Enveloped

-RNA-DNA Pol

Transmission

-IV

-Sex

-Birthing

Sx

-Jaundice

-Abdominal pain

-Arthralgias

-Skin rash

-Fatigue

-Can remain asymptomatic

**Full resolution most of the time**

Labs

-↑↑ Hepatic aminotransferases

Cx

-Hepatocellular Carcinoma

-Decomensated Liver cirrhosis

**Very rare**

Pathogen

-Cytotoxic T cells mediate damage

Hepatitis E

ssRNA Virus → Hepeviridae

-Naked

-Icosahedral capsule

Transmission

-Fecal Oral

Sx

-Fulminant Hepatitis in Pregnant women

Biopsy

-Patchy Necrosis

**NO Carrier state**

Ground Glass Hepatocytes

Histo

-Hepatocytes filled w/ Finely Granular Homogenous Pale Pink Cytoplasm

**Seen in Hep B infections**

Echinococcus Granulosus

Tapeworm → Most common cause of Hydatid Cysts

Risk Factors

-Dogs

-Sheep

Sx

-Generally asymptomatic

-Enlarged Liver

-Upper Abdominal pain

Biopsy

-Enlarged Liver w/ Cystic lesions

-Encapsulated + Calcified cysts

Complications

-Anaphylactic Shock if cysts are not manipulated wit caution during removal surgery since the Cysts can rupture and spill all their contents into the patient

Tx

-Albendazole

Schistosoma Mansoni

Histo

-Eosinophilic granulomatous inflammation + Fibrosis

-Round Oval eggs w/ lateral Spines

Schistosoma Mansoni

Sx

-Diarrhea

-Abdominal pain

PE

-Hepatomegaly

Biopsy

-Intestinal ulceration

-Periportal Fibrosis

Cx

-Iron-deficinecy Anemia

Schistosoma Mansoni

Trematode/Blood Fluke

Transmission

-Contaminated H2O w/ cercariae from infected snails

Epidemiology

-Africa

-Middle East

-South America

-Caribbean

Tx

-Praziquantel

Salmonella Typhi

Gram "-" Bacilli

-H2S "+"

-Oxidase "-"

-Non-Lactose Fermenter

-Acid Labile

Pathogen

-Enterocyte invasion → Blunted Neutrophil response → Intracellular replication in Macrophages → Spread through Lymphatics

Prophylaxis

-Live-attenuated vaccine

-Capsular Polysaccharide vaccine

Salmonella Enteritica

Gram "-" Bacilli

-H2S "+"

-Oxidase "-"

-Non-Lactose Fermenter

-Acid Labile

Pathogen

-Enterocyte invasion → Massive Neutrophil inflammatory response → Control of infection

Risk Factors

-Poultry/Eggs

-Handling Reptiles

-PPIs (Since these organisms are usually acid sensitive)

Salmonella Enteritica

Pathogen

-Enterocyte invasion → Massive Neutrophil inflammatory response in Peyer's Patches → Control of infection

Sx

-Self-limited Diarrhea

Cx

-Osteomyelitis

-Endocarditis

-Aneurysms

Shigella

Gram "-" Bacilli

-Oxidase "-"

-Non-Motile

-Acid Stable

Pathogen

-Invasion of M-cells → Mucosal invasion

Sx

-Bloody + Mucoid stools

-Crampy abdominal pain

**NO Intestinal invasion, only Mucosal**

Shigella

Virulence Factors

-Shiga Toxin → Enterotoxin which binds to 60S Ribosomal subunit to inhibit translation

-Type 3 Secretion System → Aids w/ infectivity

Risk Factors

-Fingers

-Flies

-Food

-Feces

Typhoid Fever

Etiology

-Salmonella Typhi

Risk Factors

-Contaminated H2O + Food

Sx

-Rose spots on abdomen

-Constipation

-Abdominal pain

-Fever

-Non-bloody diarrhea

Tx

-Ceftriaxone

-Fluoroquinolone

Enterobius Vermicularis

Pinworm/Helminth

Sx

-Itching in Perianal region

Life Cycle

-Female worms travel to the Perianal region at night to lay eggs

Dx

-Cellulose Tape test (Reveals oval eggs which are flattened on one side)

Tx

-Albendazole

Scalded Skin Syndrome

Etiology

-Staph Aureus

Pathophys

-Exfoliative Toxin cleaves Desmoglein into Desmosomes → Separation of Keratinocytes

Sx

-Irritability

-Poor feeding

-Desquamating rash (Prominent in skin folds)

-Epidermis easily comes off with gentle pressure

**Mucous membranes are NOT involved in this disease**

Plasmodium

Protozoa

Transmission

-Anoepheles mosquito

Histo

-Intraerythrocytic Ring inclusions in Giemsa stain

Sx

-Malaria (Myalgia + Fatigue + Headaches + Anemia + Hepatosplenomegaly + Indirect Bilirubinemia)

Tx

-Chloroquine (Targets Erythrocytic phase)

-Primaquine (Targets Hepatic Dormant phase)

**Dormancy occurs in the Liver**

Viridans Strep

Gram "+" Cocci

-Can synthesize Dextrans from Sucrose to facilitate adherence to Fibrin + Platelets

Risk Factors

-Dental procedures

-Pre-existing Valvular conditions

Sx

-Infective Endocarditis

Recurrent Respiratory Papillomatosis

Etiology

-HPV 6 + 11

Transmission

-Vertical direct spread in Infants

-Sexual contact in adults

Histo

-Fibrovascular Core w/ Benign Squamous Cells

Sx

-Hoarseness

-Respiratory distress

Imaging

-Verrucous polypoid growths in clusters

**Must test pt for HIV**

Condyloma Acuminatum

Etiology

-HPV 6 + 11

Transmission

-Sexual contact in adults → Affects True Vocal Cords

Histo

-Hyperplastic papillary Squamous epithelium with Parakeratosis

-Nuclear irregularity and Perinuclear Halos

Sx

-Thickening of Stratum Corneum

**Must test pt for HIV!**

HPV 6

HPV 11

HPV strains which result in Warts

HPV

Dx

-Post-Coital bleeding

Histo

-Koilocytes (Immature Squamous cell w/ dense irregular staining cytoplasm + perinuclear halo)

HIV-associated Dementia

Risk Factors

-Untreated HIV

Pathogen

-Release of neurotoxic compounds hy activated macrophages

Histo

-Microglial nodules w/ Multinucleated Giant cells

Sx

-Progressive cognitive decline

-Memory deficits

-Executive dysfunction

-Slow information processing

Candidiasis

Karposi Sarcoma (HHV-8)

Opportunistic HIV infections when CD4+ T-cell count is between 500-200 cells/mm3

PCP

Histoplasmosis

Coccidiomycosis

JC Virus

Opportunistic HIV infections when CD4+ T-cell count is <200 cells/mm3

Toxoplasmosis

Cryptococcosis

Opportunistic HIV infections when CD4+ T-cell count is <100 cells/mm3

Mycobacterium Avium Complex

CMV

Opportunistic HIV infections when CD4+ T-cell count is <50 cells/mm3

CMV Pneumonitis

Risk Factors

-Immunosupressive Durgs following Organ Transplant

Histo

-Infected cells w/ prominent Basophilic nuclear inclusions