Micro Exam 2

Examples of mycobacterium diseases

TB & leprosy

Gram stain & morphology for M. tuberculosis?

Doesn’t stain. Bacilli. Need acid fast stain, doesn't become decolorized. Similar to Gram + w thicker peptidoglycan layer, also w waxy coat & liparabinomannam. Cultures very slowly.

Gram stain & morphology for M. leprae?

Neither + or -. Bacilli. Doesn’t culture at all.

Reservoir M. tuberculosis

Human

Transmission M. tuberculosis? At risk?

Aerosol, low infectious dose. Immuocompromised at risk (old, young, AIDS, Humira)

Reservoir M. leprae

Human

Transmission M. leprae?

Skin breaks & respiratory. Not very infectious, low incidence. From armadillos

Virulence factors of M. tuberculosis

1. Inhibits production of ROS

2. Siderophores compete for Fe resources

3. Protection by waxy coat

4. Evades killing/lysis after phagocytosis by macrophages (phagolysosome fusion). Body forms granulomas to contain infected cells.

Virulence factors of M. leprae

1. Avoids killing like M. tuberculosis to survive in the body long term

2. Infects only Schwann cells (needed for myelination of periphery) → nerve damage

Clinical symptoms of M. tuberculosis? Phases/types?

1. Pulmonary

   • Primary, latent, secondary phases

   • Chronic cough, hemoptysis, fever, malaise, difficulty breathing, cachexia

2. Extrapulmonary spread

   1. Spinal TB: degradation of cartilage between vertebrae, collapse of spinal column

   2. Military TB: Spreads through blood, white nodules in lungs

Clinical symptoms of M. leprae? Phases/types?

Leprosy/Hansen’s Disease

1. Tuberculoid leprosy: ring-shaped, pale, flat, scaly, numb, red-ringed lesions. Disease is contained within granulomas.

2. Lepromatous leprosy: permanent damage to skin, nerves, limbs, eyes causes crippled hands

Compare & contrast M. tuberculosis & M. leprae.

• Neither fit Gram characteristics / traditional morphology & culture categories

• Reservoir is in humans

• Both transmit via respiratory aerosol

• TB is more infectious than leprosy

• M. leprae also spread via skin contact

• Both have systemic symptoms & symptoms that worsen over time

• TB is primarily pulmonary, leprosy is primarily skin-based

• long-term treatment with Abx

What is the Mantoux test? How does it work?

Diagnosis for TB. Inject small amount of tuberculin (protein extract) into skin. If previously exposed (infected) will form a wheal ~48-72h later due to delayed type hypersensitivity (type 4 overreaction of immune system). Caused by memory T cells activating macrophages.

Ways to confirm TB diagnosis?

Clinical symptoms, chest radiograph, sputum culture & stain

How is leprosy diagnosed?

• Observation of skin lesions: usually numb and patchy

• Biopsy of skin → acid fast rods, dermal nerve inflammation, neuromuscular granulomas present

• Doesn’t culture at all, requirements unknown

• Obtain travel history

What is Hansen’s disease?

leprosy

How is TB treated?

Long term treatment with a multi-drug cocktail for 6-9 months to prevent Abx resistance. Waxy coat protects bacteria.

What is the BCG vaccine?

Named after founder, ses attenuated strain of Mycobacterium bovis from a cow to protect against TB. Used in regions w high TB rates, not in U.S. to better monitor rare infections that do occur.

What are IGRAs?

Interferon gamma release assays: Mix blood sample with TB antigens, leukocytes release IFNy which is measured. Can be used in addition to BCG vaccine.

How is leprosy treated? Prevented?

Treatment w multi-drug cocktail until lesions disappear. No form of prevention.

What is NTM?

Non-tuberculous mycobacteria are organisms in the environment, opportunistic. Outbreaks in tattoo parlors.

What kind of virus is Dengue virus?

Flaviviridae genus & RNA virus

Where is the reservoir for DENV? Transmission method?

Reservoir: Humans

Transmission: Aedes aegypti mosquito species vector, lives in warmer climates like Africa → global warming increasing prevalence.

How does a hematocrit test work?

1. Centrifuge blood

2. It separates into plasma on top and RBCs on the bottom.

3. Determine the % volume of RBCs to plasma. Should be ~50%.

Is DENV an obligate or facultative pathogen?

Obligate: needs host cell to survive & replicate

Initial pathogenesis of dengue?

1. Virus infects immune & endothelial cells

2. Infected cells release cytokines

3. Plasma leakage, causes inc. hematocrit (diff ratio)

4. Platelets decline (thrombocytopenia)

5. Less bone marrow produced

6. Fragile vascular system from decreased platelet function

Clinical features of dengue? Phases/types?

Febrile phase: virus replication → fever, headache, vomiting

Critical phase: inc. hematocrit, dec. platelets, risk for:

• Dengue hemorrhagic fever: bleeding in urine, stool, vomit, skin, nose, gums

• Dengue shock syndrome: plasma leakage causes hypovolemic shock bc heart can’t pump blood

Recovery phase: Fluids reabsorbed (no leakage), regeneration of platelets, Ab titer inc.

Primary dengue: Infection w 1st serotype

Secondary dengue: Infection with a different serotype (there are 4). Abs from the primary infection can’t neutralize 2nd serotype. They bind to the 2nd strain partially, allow it to bind to receptors and into the cell. The virus doesnt neutralize in the endoscope and replicates.

How does neutralization work? (Its blocked in dengue)

1. Multiple Abs bind to virus.

2. Virus cant bind to receptors and enter the cell.

3. Virus can’t escape the vacuole once endocytosed.

What is ADE?

Antibody dependent enhancement: Abs from primary infection enhance entry of secondary serotype. Causes worse infection.

Treatment for DENV?

Supportive care such as IV fluids & blood transfusion

How should dengue be diagnosed?

• Look for IgM (first Abs produced) and IgG (produced within days of infection) via serology

• PCR

• NS1 presence: an antigen, part of viral protein

Use these to distinguish between primary and secondary. Be able to use examples of primary and secondary infection serology and patient samples at diff timepoints to diagnose with primary or secondary.

Describe analytical sensitivity/specificity & clinical sensitivity/specificity.

Analytical sensitivity: Smallest amount of Ag that can be detected.

• You won’t test positive for COVID until a few days after infection.

Analytical specificity: If the test can distinguish between strains

• The COVID test can differentiate between SARS-CoV2 and common cold viruses.

Clinical sensitivity: % of people who have infection that actually test positive

• Can you use the test to determine if a patient has disease?

• Does high analytical sensitivity = high clinical sensitivity? B. pertussis

Clinical specificity: % of people who don’t have disease that actually test negative

• A COVID test that has false positive from a cold virus

Neisseria gonorrheae Gram stain? Morphology?

Gram - diplococci, within neutrophils

Neisseria gonorrheae reservoir and transmission?

Reservoir: asymptomatic infections

Transmission: contact of mucosal surfaces (oral, anal, vaginal)

Virulence factors of Neisseria gonhorreae

Siacilic acid coat mimics host molecules, allows for evasion.

Uses antigenic variation

Describe antigenic variation

Group of pathogens. One has a variation, eg in spike protein. Abs attack everything but the variant. The variant can now proliferate, expand, and spread. (Think COVID)

How do clinical features of Neisseria gonorrheae differ in males and females? General clinical features? Spread?

Presents as urethritis in males. Also urethritis in females, may progress to pelvic inflammatory disease when it spreads to uterus, ovaries, fallopian tubes. Can be spread to child during birth. Clinical features reported by case study patient: chills, malaise, painful urination, discharge, tenderness

Disseminated gonococcal infection: infection spreads to blood, may cause joint pain (septic arthritis)

How is gonorrhea diagnosed

1. Gram stain & culture of urethral discharge and/or synovial fluid (if septic arthritis), should see bacteria within neutrophils

2. NAAT

How should gonorrhea be treated and prevented?

Treatment: Abx, test for other STIs

Prevention: Use condoms. Vaccine can’t be made due to antigenic variation

Gram stain & morphology of Neisseria meningitidis

Gram - diplococci (see coccus in name)

Describe the reservoir and transmission of neisseria meningitidis

Reservoir is nasopharyngeal carriage. Transmitted via respiratory → close quarters, mass gatherings have higher risk from prolonged exposure. More common in young people

Virulence factors of neisseria meningitidis

• Antiphagocytic capsule

• Antigenic variation

• Lots of endotoxin produced → risk of capillaries leaking leading to sepsis and other systemic problems

Describe the clinical symptoms of Neisseria meningitidis

Spreads quickly, systemic effects in young people:

1. Sepsis from endotoxin

2. Headache & nuchal rigidity from meningitis

3. Bleeding in the dermis (skin petechiae)

4. Disseminated intravascular coagulation: If clots obstruct flow, tissues have lack of oxygen & nutrients (ischemia), hemorrhage

What is disseminated intravascular coagulation & what is it caused by?

If clots obstruct flow, tissues have lack of oxygen & nutrients (ischemia), hemorrhage. Can be a severe consequence of Neisseria meningitidis

How is Neisseria meningitidis diagnosed & treated?

Diagnosis: Meningitis & petechiae (see image). Gram stain of CSF will confirm.

Treatment: Abx. Prophylactic treatment for close contacts

What is the meningococcal vaccine, who is it given to?

Abs for Neisseria meningitidis. Given to age 25 and below & at risk groups.

Gonococcus refers to

Neisseria gonorrheae

Meningococcus refers to

Neisseria meningitis

Major difference between gonococcus and meningococcus

Gonococcus: Stays relatively local (urethra)

Meningococcus: Spreads quickly, evades, sepsis, meningitis

Gram stain, culture, & morphology of Treponema pallidum?

Does not Gram stain, need silver stain. Spirochete. Does not culture (fastidious)

What disease does Treponema pallidum cause

Syphilis

What is the reservoir and transmission method for Treponema pallidum

Reservoir: Humans

Transmitted via mucous membrane contact & lesions. Mostly MSM demographic. Increasing in the US.

Describe the phases of syphilis and clinical features:

1. Primary syphilis

   • Chancre at infection site

   • Weeks later

   • Disappears untreated

2. Secondary syphilis

   • Months later

   • From untreated chancre

   • Spread = systemic features: fever, malaise, lymphadenopathy

   • Rash on palms & soles (maculopapular)

   • Wart-like genital lesions (condyloma lata)

   • Resolves untreated

3. Latent syphilis

   • Secondary syphilis has resolved, asymptomatic

   • Seroreactive: Abs present

   • Can spread to child

   • 30% of cases progress from here

4. Tertiary syphilis

   • Decades later

   • Granuloma formation = tissue damage: skin, liver, bone, testes, aortic aneurysm

   • Dementia, ataxia, vision loss, seizure

Virulence factors of Treponema pallidum (syphilis)

“Stealth pathogen”: balance between the immune system & pathogen allows it to stay present for decades

How is syphilis diagnosed

• Clinical skin signs

• Skin scraping under silver stain shows spirochetes

• Treponemal test: Abs present for life

• Nontreponemal test: Looks for related markers of cell damage

Treponemal test vs Nontreponemal test

Treponemal: Abs against pathogen present for life

Nontreponomal test: Looks for biomarkers from cell damage

How can syphilis be treated & prevented

Treatment: Penicillin will cure primary or secondary. Tertiary can be treated but any damage done is permanent.

Prevention: Condom use. No vaccine bc stealth pathogen.

Chlamydia trachomatis Gram stain & morphology

Similar to Gram -, minimal peptidoglycan. Round.

Reservoir & transmission of Chlamydia trachomatis?

Reservoir is humans, obligate intracellular (can’t live outside). Transmitted via mucous membranes (genital, anal, oral). Can pass from mother to child during birth (perinatal) as conjunctivitis. More common in women.

How are clinical features of chlamydia trachomatis different between males & females?

Males: Infection of urethra & epididymis → painful urination, cloudy discharge, testicle tenderness

Females: Infection of cervix epithelium & urethra → painful urination, vaginal discharge, bleeding. Also can ascend to become PID

Pelvic inflammatory disease

See gonorrhea also! Infection ascends to uterus, ovary, fallopian tube; can be transmitted during childbirth. Can also cause infertility & ectopic pregnancy (implants outside uterus)

What is trachoma, what is it caused by?

Eye infection

Chlamydia trachomatis

More common in crowded places, poverty, poor hygiene (not U.S.)

Virulence factors of chlamydia trachomatis? How do they contribute to disease development?

Adheres to urinary epithelium (elementary bodies). Gets endocytosed. Prevents phagolysosome fusion. Becomes reticulate bodies to replicate, then exocytosis

What are elementary bodies? What is their complement?

Elementary: Present outside the vacuole, used to infect.

Reticulate bodies: within the vacuoles, grow and replicate after endocytosis of elementary bodies

How is chlamydia trachomatis diagnosed

NOT gram stain: too small, lack peptidoglycan

NAATs

Case study used endocervical swab to collect sample. Also ultrasound.

How is chlamydia trachomatis treated

Abx besides beta lactase since there is no peptidoglycan to act against.

How can chlamydia be prevented

Use of condoms. To prevent trachoma, practice hygiene.

Gram & morphology of all pathotypes of E. coli?

Gram - rods

Reservoir & transmission of ETEC

Reservoir: infected humans

Transmission: fecal oral w high infectious dose

Commonly causes traveler’s diarrhea, high risk of infection in Asia, Africa, Middle East, Mexico, South America

Virulence factors / pathogenesis of traveler’s diarrhea?

Adhesion to micropili. Enterotoxin disrupts ion transport in GI epithelium, causing net secretion of fluid & watery diarrhea

What clinical features does ETEC cause

Gastroenteritis: refers to diarrhea & vomiting.

Infectious traveler’s diarrhea (secretory/watery).

Also nausea, vomiting, fever, delayed 1-2 days from exposure

What is traveler’s diarrhea usually caused by? What kind of diarrhea is it?

ETEC. Secretory/watery

How is ETEC infection diagnosed, treated, and prevented

Diagnosed by presence of watery diarrhea (no clinical test).

Self limiting, basic oral rehydration can be used.

Prevent by eating only well cooked food & drinking bottled water in high risk areas

Differences between ETEC and STEC

• STEC has lower infectious dose

• STEC more severe clinical features, larger outbreaks

STEC stand for

Shiga toxin producing E.coli

Reservoir & transmission of STEC

Reservoir: animals

Transmission: fecal oral via food, low infectious dose

Major serotype causing STEC?

O157:H7

Virulence factors & pathogenesis of STEC

1. Adhesion to GI epithelium.

2. Type 3 secretion system to inject into cells

3. Shiga toxin - AB5, acquired by horizontal gene transfer from Shigella dysenteriae. Endocytosed, escapes to cytoplasm, binds rRNA & blocks protein synthesis, cell dies

What clinical conditions can STEC cause?

1. Inflammatory/Bloody Diarrhea: Shiga toxin damage to intestine epithelium, causes loss of fluid, epithelial cell death → Capillaries exposed → bleeding

2. Hemolytic Uremic Syndrome (HUS): Shiga toxin damages EC’s. Causes clots in small capillaries. Damages kidneys. Thrombocytopenia. RBS fragment in capillaries (hemolytic anemia). Also damages filter in kidneys, clogs them. Causes electrolyte imbalance → uremia, hematuria. Can lead to acute renal failure.

3. Other general symptoms: Fatigue, fever, headache, low abdominal pain, pale, blood in stool, albumnuria

How is STEC infection diagnosed

• Stool culture & look for blood

• Detection of Stx

• Urinalysis

• CBC: should be more leukocytes

• NAAT

How is STEC treated & prevented

Treated w oral rehydration. Rarely w Abx, might stress bacteria to produce more toxin.

Prevention: Handwashing, cooking food hot enough

What do commensal strains of E. coli cause? Why?

Opportunistic infections occur from bacteria in the gut. Usually cause UTIs: rectal bacteria adheres to perineum. Mechanical disruption, bacteria enters urethra. Also transmitted via birth.

Motility: they have flagella

Exotoxin released with growth, damages epithelium, inflammation & hemorrhage

Define UTIs and the diff types

Infection causes frequent, burning, cloudy urination.

Lower UTI: Urethra & bladder, vaginitis, proastatis

Upper UTI: Kidney

What are “fecal coliforms”?

Bacteria from mammal intestines, commonly contaminate water. Screening for E. coli.

Difference between bacterial vaginosis & urinary tract infection

Vaginosis is imbalance of normal microbiome

UTI is ascending infection, usually E. coli, males & females

How are UTIs treated & prevented

Given UTIs empirically, unless “complicated” (underlying problem, men & at risk women) then urine culture for specifics.

Drink lots of water to flush bacteria.

What are the 3 types of clinical features E. coli can cause?

UTIs, neonatal meningitis, diarrhea (see diff types & examples)

Why would E. coli cause neonatal meningitis

Exposure to pathogenic strain during delivery

Gram & morphology of Enterobacterales?

Gram - rods

Reservoir & transmission of Shigella species?

Infected humans

Fecal oral, very low infectious dose (10-100)

Virulence factors of Shigella species?

1. Resistant to stomach acid

2. Facultative intracellular pathogen. Uses M cells in colon to inject VFs by T3SS. Allows bacterial uptake.

3. Intracellular motility via actin polymerization

4. Shiga toxin: destroys epithelium, exposes lamina propia

2 Shigella species we are learning about? Differences?

dysenteriae & sonnei, sonnei is more common in US. Dysenteriae more likely to cause bloody diarrhea.

How are M cells involved in shigellosis

They are epithelial cells that regularly sample the GI for Ags, give to lymphoid follicle/mucosa associated lymphoid tissue. Shigella species use them to enter epithelium.

Shigellosis clinical features

Dysentery (bloody diarrhea) days after exposure w fever, cramps. Diarrhea has mucus from shedding of GI mucus lining. Also risk for hemolytic uremic syndrome from Shiga toxins.

How is shigellosis diagnosed, treated, prevented?

Diagnosis: Stool culture. Special differential & selective media (Hektoen enteric agar). Case study: Shiga toxin test, CBC (hemolysis & thrombocytopenia), Urinalysis for albuminuria

Treatment: Oral rehydration, avoid Abx → more Shiga toxin production. If sick enough (fever >103, hypovolemia, too much diarrhea, hospitalization, etc)

Prevention: Sanitation to prevent fecal water/food contamination

What media is used for Shigella species culture

Hektoen enteric agar

Salmonella typhimurium virulence factors

1. Sensitive to acid, need to ingest more for effects

2. Uses M cell transcytosis (but NO actin polymerization)

3. Inhibits phagolysosome fusion by blocking hydrolytic enzymes, macrophage cant kill

How is Salmonella diagnosed, treated, prevented? Differences between typhirium & typhi?

Diagnosis: stool & blood culture

Differences between Shigella & Salmonella?

Clinical features of S. typhimurium

Gastroenteritis, can be mild or severe.

• Diarrhea

• Fever

• Cramping

• Usually not bloody