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USMLE - Micro Systems

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The skin’s normal dominant flora is Staphylococcus epidermidis, a non-pathogenic bacterium that helps protect against harmful microbes by competing for space and nutrients.

Normal Dominant Flora of Skin

Staphylococcus epidermidis

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Key Terms

Term
Definition

Normal Dominant Flora of Skin

Staphylococcus epidermidis

Normal Dominant Flora of Nose

Staph epidermidis. Colonies by Staph aureus

Normal Dominant Flora of Oropharynx

Viridans Group Strep

Normal Dominant Flora of Dental plaques

Streptococcus mutans

Normal Dominant Flora of Colon

Bacteroides fragilis (more)

E. coli (less)

Normal Dominant Flora of Vagina

Lactobacillus

Colonies by E coli and GBS

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TermDefinition

Normal Dominant Flora of Skin

Staphylococcus epidermidis

Normal Dominant Flora of Nose

Staph epidermidis. Colonies by Staph aureus

Normal Dominant Flora of Oropharynx

Viridans Group Strep

Normal Dominant Flora of Dental plaques

Streptococcus mutans

Normal Dominant Flora of Colon

Bacteroides fragilis (more)

E. coli (less)

Normal Dominant Flora of Vagina

Lactobacillus

Colonies by E coli and GBS

Neonates delivered by Cesarean section re flora?

They have no flora but are rapidly colonized after birth

Staph aureus and B cereus food poisoning course

Starts quickly and ends quickly

Contaminated seafood

Vibrio parahaemolyticus and V vulnificus (can cause wound infection from contact with contaminated water or shellfish)

Reheated rice

“be serious”

B cereus

Meats, Mayonnaise, Custard

S aureus

Reheated meat dishes leading to watery diarrhea

Clostridium perfringens

Improperly canned foods (bulging cans)

Clostridium botulinum

Undercooked meat

E coli O157:H7

Poultry, meat, eggs

Salmonella

Bugs that can mimic appendicitis

Yersinia enterocolitica causes mesenteric adenitis

Nontyphoidal Salmonella

Campylobacter jejuni

Causes of Bloody Diarrhea with signs

Campylobacter: Comma or S shaped, grows at 42

Salmonella: Lac-, Flagella

Shigella: Lac-, low ID50

EHEC, EIEC

Yersinia enterocolitica: Daycare outbreaks, pseudoappendicitis

Entamoeba histolytica

Causes of Watery Diarrhea

Enterotoxigenic E coli: Traveler’s, ST and LT toxin

V Cholerae: comma-shaped, rice-water

C difficile: bloody w/ pseudomembranous colitis

C perfringens: also gas gangrene

Protazoa: Giardia, Cryptosporidium (in immunocompromised)

Rotavirus, Norovirus

Pneumonia in neonate (less than 4 weeks)

GBS, E coli

Pneumonia in children (4 weeks to 18 years)

“Runts May Cough Chunky Sputum”

RSV, Mycoplasma, C. pneumoniae (school age), Chlamydia trachomatis (infant to 3 years), Streptococcus pneumoniae

Pneumonia in adults (18 years to 40 years)

Mycoplasma, C pneumoniae, S pneumoniae

Pneumonia in adults (40 years to 65 years)

S pneumoniae, H influenzae, Anaerobes, Viruses, Mycoplasma

Pneumonia in elderly

S pneumoniae, Influenza, Anaerobes, H influenzae, H influenzae, Gram- rods

Special Nosocomial Infections

Staph, Enteric Gram negative Rods

Special Immunocompromised infections

Staphylococcus, Enteric Gram- rods, Fungi, Viruses, Pneumocystis jirovecii - w/ HIV

Special infections with aspiration

Anaerobes

Special infections w/ EtOH and IV drug users

S pneumoniae, Klebsiella, Staph

Special infections in CF

Pseudomonas, S aureus, S pneumoniae

Special infections in Post-Viral pt

Staph, H influenzae, S pneumoniae

Bugs that cause atypical pneumonia

Mycoplasma, Legionella, Chlamydia

Meningitis in a newborn (0 to 6 months)

GBS, E coli, Listeria

Meningitis in a child (6 months to 6 years)

PathoPhys

Presentation

Streptococcus pneumoniae

Neisseria meningitidis

Enteroviruses

Haemophilus influenzae type B

Polio

Last 2 in non immunized children

Microbe colonizes nasopharynx leading to myalgias and paralysis

Meningitis in a adults (6 years to 60 years)

S pneumoniae

N meningitidis (#1 in teens)

Enteroviruses

HSV

Meningitis in elderly (60+)

S pneumoniae

Gram- rods

Listeria

Meningitis Treatment

Ceftiazone and Vancomycin empirically

| Add ampicillin if Listeria is suspected

Viral causes of meningitis

Enterovirus (esp coxsackievirus), HSV2 (HSV1 = encephalitis), HIV, West Nile Virus, VZV

Meningitis in HIV pt

Cryptococcus, CMV, toxoplasmosis (brain abscess), JC virus (PML)

Recent changes in H influenzae meningitis

Decreased with introduction of conjugate H influenzae vaccine in last 10-15 years.

Todays cases are in un-immunized children

CSF findings in Bacterial meningitis

Opening pressure

Cell type

Protein

Sugar

Opening pressure ↑

PMNs

Protein ↑

Sugar ↓

CSF findings in Viral meningitis

Opening pressure

Cell type

Protein

Sugar

Opening pressure Normal or ↑

Lymphocytes

Protein is Normal or ↑

Sugar is Normal

CSF findings in Fungal/TB meningitis

Opening pressure

Cell type

Protein

Sugar

Opening pressure ↑

Lymphocytes

Protein is Normal or ↑

Sugar ↓

Osteomyelitis w/ nothing else

S aureus

Osteomyelitis in sexually active individual

Neisseria gonorrhoeae (rare), septic arthritis more common

Osteomyelitis in diabetic or IV drug user

Pseudomonas aeruginosa, Serratia

Osteomyelitis in Sickle cell disease

Salmonella

Osteomyelitis in Prosthetic replacement

S aureus and S epidermidis

Osteomyelitis in Vertebral disease

Mycobacterium Tuberculosis (Pott's disease)

Osteomyelitis in cat and dog bite/scratches

Pasteurella multocida

Osteomyelitis

Mostly in…

Signs

Children

| Elevated CRP and ESR

UTIs

Presentation

Labs

PathoPhys

Causes in males

Causes in elderly

Can progress to...

Dysuria, Frequency, Urgency, Suprapubic pain

WBCs (but not casts) in urine

Males: infants w/ congenital defects, vesicoureteral reflux

Elderly: Enlarged prostate

Pyelonephritis

Pyelonephritis presentation

Fever, Chills, Flank pain, CVA tenderness, Hematuria, WBC casts

UTIs in women

Frequency

Predisposing factors

10x more likely in women because of shorter urethra colonized by fecal flora

Obstruction, Kidney surgery, Catheterization, GU malformation, Diabetes, Pregnancy

UTI Dx markers

+Leukocyte esterase test = bacterial UTI

+Nitrite test = Gram- bacterial UTI

+Urease test = Proteus, Klebsiella

-Urease test = E coli or Enterococcus

UTI bugs

E coli: #1. Green metallic sheen on EMB

Staph saprophyticus: #2

Klebsiella: #3. Large mucoid capsule + viscous colonies

Serratia: Red pigment. Nosocomial and drug resistant

Enterobacter cloacae: Nosocomial and drug resistant

Proteus mirabilis: Swarming on agar, Urease+, Struvite stones

Pseudomonas aeruginosa: Blue-green pigment, fruity odor. Nosocomial and drug resistant

ToRCHeS Infection

What are they?

Presentation

Mother --> fetus. Transplacental in most cases or via delivery (HSV2)

HSM, Jaundice, Thrombocytopenia, Growth retardation

Names of ToRCHeS Infection

Toxoplasma gondii

Rubella

CMV

HIV

HSV2

Syphilis

Toxoplasma gondii

Mode of transmission

Maternal manifestation

Neonatal manifestation

Cat feces or ingestion of undercooked meat

Usually asymptomatic; Lymphadenopathy (rarely)

Classic Triad: Chorioretinitis, Hdyrocephalus, and Intracranial calcification

Rubella

Mode of transmission

Maternal manifestation

Neonatal manifestation

Respiratory droplets

Rash, Lymphadenopathy, Arthritis

Classic triad: PDA (or pulmonary artery hypoplasia), Cataracts, and Deafness

Blueberry muffin rash

CMV

Mode of transmission

Maternal manifestation

Neonatal manifestation

Sexual contact, organ transplant

Usually asymptomatic. Mononucleosis-like illness

Hearing loss, Seizures, Petechial rash, Blueberry muffin rash

HIV

Mode of transmission

Maternal manifestation

Neonatal manifestation

Sexual contact, Needlestick

Variable presentation depending on CD4 count

Recurrent infections, Chronic diarrhea

HSV2

Mode of transmission

Maternal manifestation

Neonatal manifestation

Skin or mucous membrane contact

Usually asymptomatic. Herpetic (vesicular lesions)

Encephalitis, Herpetic (vesicular) lesions

Syphilis

Mode of transmission

Maternal manifestation

Neonatal manifestation

Sexual contact

Chancre (primary) and disseminated rash (secondary) are the 2 stages likely to result in fetal infection

Stillbirth, Hydrops Fetalis

If child survives presents with facial abnormalities [notched teeth (Hutchinson's teeth), saddle nose, short maxilla, Dry wrinkled skin, yellow-brown hue, hemorrhagic rhinitis], saber sings, CN VIII deafness

Childhood rash that begins at head and moves down --> fine truncal rash

Rubella virus

| Usually associated with lymphadenopathy

Childhood rash beginning at head and moving down preceded by cough, coryza, conjunctivitis, and blue-white spots on buccal mucus

Measles

Childhood vesicular rash beginning on trunk and spreading to face and extremities with lesions of different ages

Chickenpox (VZV)

Childhood (infant) macular rash over body appears after several days of high fever, febrile seizures

Roseola (HHV6)

Childhood "slapped cheek" rash on face

Erythema infectionsum (parvovirus B19)

Can cause hydrops fetalis in pregnant women)

Childhood erythematous sandpaper rash with fever and sore throat

Scarlet fever from Strep pyogenes

Childhood vesicular rash on palms and soles with ulcers in oral mucosa

Hand-Foot-Mouth Disease (Coxsackievirus A)

Urethritis, Cervicitis, PID, Prostatitis, Epididymitis, arthritis, Creamy purulent discharge

Neisseria gonorrhoeae

Painless Chancre

Primary syphilis (Treponema pallidum)

Fever, lymphadenopathy, Skin rashes, Condylomata lata

Secondary syphilis (Treponema pallidum)

Gummas, Tabes Dorsalis, General Paresis, Aortitis, Argyll Robertson pupil

Tertiary syphilis (Treponema pallidum)

Painful genital ulcer with inguinal adenopathy

Chancroid caused by Haemophilus ducreyi

| "It's so painful, you DO CRY"

Painful penile, vulvar, or cervical vesicles and ulcers

| Fever, Headache, Myalgia

Genital herpes

| HSV2. Less commonly HSV1

Urethritis, Cervicitis, Conjunctivitis, Reiter's Syndrome, PID

Chlamydia from Chlamydia trachomatis (D-K)

Infection of lymphatics, Genital ulcers, Lymphadenopathy, Rectal strictures

Lymphogranuloma venereum from Chlamydia trachomatis (L1-L3)

Vaginitis, Strawberry colored mucosa, motile in wet prep

Trichomonas vaginalis

Opportunistic infections Kaposi sarcoma, Lymphoma

AIDS from HIV

Genital warts, Koilocytes

HPV 6 and 11

Jaundice

HBV

Non-Inflammatory, Malodorous Discharge (fishy smell), Positive whiff test, Clue cells

Gardnerella vaginalis

PID

Causes

Presentation

May include…

Chlamydia trachomatis (subacute, often undiagnosed), Neisseria gonorrhoeae (acute)

Cervical motion tenderness (chandelier sign), Purulent cervical discharge

Salpingitis, Endometriosis, Hydrosalpinx, Tubo-Ovarian Abscess

PID can lead to…

Hugh-Curtis Syndrome

| Infection of the liver capsule and violin string adhesion of parietal peritoneium to liver

Salpingitis is a risk factor for…

Ectopic pregnancy, Infertility, Chronic pelvic pain, Adhesions

Nosocomial infections in a newborn nursery

CMV, RSV

Nosocomial infections in urinary catheterizations

E coli, Proteus, Mirabilis

Nosocomial infections in Respiratory Therapy Equipment

Pseudomonas aeruginosa

| "Presume Pseudomas when Air or Water are involved"

Nosocomial infections for work in renal dialysis unit

HBV

Nosocomial infections in hyperalimentation

Candida albicans

Nosocomial infections in water aerosols

Legionella

Painful throat. Grayish oropharyngeal exudate in painful throat in an un-immunized child

Corynebacterium diphtheriae elaborating toxin that causes necrosis pharynx, cardiac and CNS tissue

Fever, dyspnea, Drooling, difficulty breathing due to cherry red edematous epiglottis in un-immunized child

H influenzae type B

| Can cause epiglottitis in fully immunized children too

Pus, Empyema, Abscess

S aureus

Pediatric infection

Haemophilus influenzae (including epiglottitis)

Pneumonia in CF or burn pt

Pseudomonas aeruginosa

Branching rods in oral infection w/ sulfur granules

Actinomyces israelii

Traumatic open wound

Clostridium perfringens

Surgical wound

S aures

Dog or cat bite

Paseurella multocida

Currant jelly sputum

Klebsiella

+PAS stain

Tropheryma whippelei

Sepsis/Meningitis in a newborn

GBS

Healthcare provider

HBV from needlestick

Fungal infection in diabetic or immunocompromised pt

Mucor or Rhizopus

Asplenic pt

Encapsulated microbes

"SHiN"

S pneumoniae, H influenzae type B, N Meningitidis

Chronic Granulomatous disease

Catalase+ microbes esp S aureus

Neutropenic pt

Candida albicans (systemic), Aspergillus

Facial nerve palsy

Borrelia burgdorferi (Lyme disease)

Infectious cause of pericarditis

Coxsackie B

Best Way to Prevent Tetanus?

Vaccinate Mother

Most common causes of UTIs?

E coli

| Staph saprophyticus

Sepsis with black rash

Pseudomonas