Categories
Microbiology

Chaga’s Disease

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Triatomine bugs bite the victim near the face at night. They suck their blood.
After the bite, these bugs defecate on the victim.
The bug’s feces contains Trypanosoma cruzi (T. cruzi)
T. cruzi enters the victim’s blood via the mucous membrane, skin break, or when the victim scratches the bite area and unknowingly pushes the feces in the wound.

 

Acute Phase

During the acute phase (days to months) the victim has no symptoms or mild flu-like symptoms (fever, aches, rash, loss of appetite, diarrhea, vomiting, etc.)
Liver, spleen, and lymph nodes might be mildly enlarged. A chagoma (swelling) at the site of the bite may develop.

Less than 5% of the young patients may die due to severe inflammation, infections of the heart muscle (myocarditis) or brain (meningoencephalitis.)

 

Chronic Phase

This phase can last for decades. About 20%-30% of patients develop cardiac or gastrointestinal complications. Enlarged heart, arrhythmias, heart failure, can occur. Megaesophagus and megacolon may develop making it difficult to eat or poop.

 

Diagnosis

  • Parasite in patient’s blood smear.
  • IgM in the acute phase.
  • PCR

Reference: https://www.cdc.gov/parasites/chagas/diagnosis.html?fbclid=IwAR3y6jLjiwtC-pNqfFwl02xfbWKIoMA0aK_7nZX4n90aarT2old0YrXXIGo

Treatment

Benznidazole is FDA approved for children 2-12 years of age.
Nifurtimox, not FDA approved, but available under the investigational protocol.
Symptomatic treatment may be needed as well.

 

Reference: https://www.cdc.gov/parasites/chagas/gen_info/detailed.html

 

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Categories
Microbiology Pharmacology Surgery

Treatment of Methicillin Resistant S. Aureus Bacteremia

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Disclaimer: this is not a prescription. Using medicines without the guidance of a licensed provider  can be lethal.

This is not a prescription for any specific patient. For methicillin RESISTANT (MRSA) staphylococci following antimicrobial therapy can be used:

Vancomycin 15-20mg/kg IV every 8 to 12 hours. Not to exceed 2 g per dose. Or Daptomycin 6-10 mg/kg IV once daily.

Alternative agents can be:

Ceftaroline 600 mg IV every 12 hours

Telavancin 10 mg/kg IV once daily

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Categories
Microbiology Pharmacology Surgery

Treatment of Methicillin Sensitive S.Aureus Bacteremia

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Disclaimer:

This is not a prescription. Using medicines without the guidance of a licensed provider  can be lethal

This is not a prescription for any specific patient.

For methicillin sensitive staphylococci following antimicrobial therapy can be used:

  1.  Nafcillin 2g IV every 4h. Or
  2.  Oxacillin 2g IV every 4h. Or
  3.  Flucloxacillin 2g IV every 6h.

If the pathogens are penicillin sensitive then penicillin 4 million units IV every 4h is the drug of choice. Keep in mind that mostly the isolates are not penicillin sensitive.

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Categories
Microbiology Pharmacology

Empiric Treatment of Staphylococcus Bacteremia

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Disclaimer:

This is not a prescription. Using medicines without the guidance of a licensed provider  can be lethal

This is not a prescription for any specific patient.

Staphylococcus Aureus is the leading cause of community and hospital-acquired bacteremia. Treatment failure is common in S. Aureus patients, especially in MRSA infected patient. Treatment failure means:

  •  Death within 30 days following treatment. Or,
  •  Persistent bacteremia after 10 days of suitable therapy. Or,
  •  Recurrence of bacteremia after 60 days of discontinuing the therapy.

The treatment approach is to remove the source (catheter etc.) and antimicrobial therapy. Therapy needs culture and susceptibility tests. While waiting for these the empiric therapy can be:

Vancomycin (15-20 mg/kg every 8-12 h, not to exceed 2g/dose)

Daptomycin (6 mg/kg once daily) is a reasonable alternative.

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Categories
Microbiology

Staphylococcus Tests

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Disclaimer:

This is not a prescription. Using medicines without the guidance of a licensed provider  can be lethal.

 

Remember to read their difference from the Streptococci as well,

Staphylococci are abundantly present in the hospitals and also in the nasopharynx  and skin of 50% of the population.

1. Gram Staining:
Staphylococci are seen in grape-like clusters when gram stained.


2. Catalase Test:
Staphylococci are catalase positive.


3. Culture:
These are beta-hemolytic, that is, they completely hemolyze the blood cells on an agar medium.
Staphylococcus Aureus exhibit a golden color on the sheep blood agar. Aureus means gold.

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Categories
Microbiology

Difference between Streptococcus Pneumoniae and Streptococcus Viridans

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Disclaimer:

The treatment offered here is for medical professional’s note and not a prescription for a specific patient. Don’t take medicines without a doctor’s prescription. Incorrect medication can cause severe health issues and even death.

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Remember that S. Pneumonia is a single species while S. Viridans is a large group of species.

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Category

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Morphology

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S. Pneumoniae

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Lancet shaped

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S. Viridans

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Elongated, oval, or rounded

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Capsule

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Present

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Absent

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Quellung Test

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Positive

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Negative

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Gram Stain

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Gram positive

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Gram positive

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Bile Solubility

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Soluble

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Insoluble

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Optochin Sensitivity

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Sensitive

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Resistant

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Hemolysis

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Beta hemolytic

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Alpha Hemolytic or non hemolytic

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Lancefiled Class

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None

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None

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Important Diseases

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C-MOPS.

Conjunctivitis

Meningitis

Otitis Media

Pneumonia

Sinusitis

Penicillin (resistance is common 40%
or more patient are resistant)

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Subacute infective endocarditis (SBE)

Dental Carries

Liver and Brain Abscesses

SBE (S. Viridans)

IV Benzyl Penicillin 1.2 g 6 times daily

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Treatment

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Ceftriaxone (not in children < 2 years)

Cefotoxime in children < 2y
Vancomycin

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4 weeksIV Gentamicin 1 mg/Kg 3 times daily

2 to 4 weeks Mind the penicillin allergies.

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Here is a visual mnemonic for you. Can you find the two pathogens?

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Categories
Bacteriology Microbiology

Corynebacterium Diphtheriae

Any medical concept and for that matter any item to be memorized has following needs, acquire the concept, commit it to short and then long term memory, attach a handle to it for later recall, and rapid recall.

While flying for AANP conference I sat back in my seat and thought about how to present this pathogen in a way that it becomes sticky in student’s mind. It might be interesting for some of you to see how the lecture and images evolved as I strived to accomplish other goals. This pathogen is still in progress though!

Corynebacterium Properties

Gram +ive, non spore forming rods. Usually arranged in V or L shaped. These rods are club shaped with beady appearance. Beads are filled with highly polymerized polyphosphate. This is how high energy phosphate bonds are stored. These beads appear metachromatic. Metachromatic means that these beads appear red when stained with a dye that stains the rest of the cell blue. See the images below where I try to capture these ideas.

Corynebacterium Diptheriae (01)

Figure 1.1: Gram +ive (purple color). Club shaped rods. Polychromatic beads with high energy phosphate bonds (reddish). Arranged in V or L.

Target Population

Corynebacterium primarily targets children.

Corynebacterium diptheriae 02

Figure 1.2: Corynebacterium Diphtheria standing amongst children ready to infect them.

Mode of Transmission

Both the toxic and non-toxic species of Corynebacterium reside in the upper respiratory tract. Humans are the only reservoir for this pathogen. Transmission occurs via air-borne droplets. It can also infect an existing skin wound in people with poor skin hygiene.

Corynebacterium diptheriae 03

Figure 1.3: Corynebacterium flying on a droplet from one person to another person.

Pathogenesis

Corynebacterium Diphtheria causes nervous and cardiac tissue damage by releasing an exotoxin in the blood. This is why the gray membrane in child’s throat should not be scrapped as it will cause bleeding and send a pile of exotoxin in the blood.

Corynebacterium needs a temperate lysogenic bacteriophage to be able to cause pathology.

Corynebacterium diptheriae 05

Figure 1.4: a bacteriophage must become part of the Corynebacterium Diphtheria to enable it to make diphtheria exotoxin. Notice the spider like bacteriophage with models to make exotoxin unit B (hand) and the unit A (action guy).

Diphtheria Exotoxin and its Mechanism of Action

Exotoxin has two subunits:

  • Subunit A for action.
  • Subunit B for binding.

Corynebacterium diptheriae 04

Figure 1.5: Club shaped beady rod with an exotoxin hanging from it, ready to go to work. The B subunit is the hand that will grab a receptor on the cell, and the A subunit is the action guy who will disable elongation factor 2 (EF2) leading to halting of the protein synthesis. Causing cell to die. (Note ideally there should be a bacteriophage sitting in this CD cell.)

Mechanism of Pathogenies

  • Subunit B that helps bind with the receptor on a cell. Binding in turn leads to internalization of both the subunits as a vesicle. In our diagrams I made this subunit as a hand to grab the cell.
  • Subunit A helps with action. This subunit is cleaved in the vesicle and then released in the cytoplasm. There it causes ADP-ribosylation of the elongation factor 2. Elongation factor 2 is responsible to grab transfer RNAs with amino-acids and bring them to ribosome where proteins are manufactured. The amino-acid attached to the tRNA is used to elongate the protein chain. Elongation factor 2 when ADP-ribosylated fails to bind with the tRNA. Result is halting of the protein synthesis which leads to the cell death.

Corynebacterium diptheriae 06

Figure 1.6: A rough sketch showing diphtheria exotoxin subunit B binding to the cell receptor (hand grabbing the cell receptor). Note the subunit A sitting ready to go in and stop the EF2 (lower right.) Middle right shows that the EF2 (fish) is bringing a tRNA to a ribosome to help elongate the protein being synthesized in the ribosome.

Clinical Findings

  • Rare in the US.
  • Thick gray sticky pseudomembrane composed of necrotic epithelial cells, inflammatory cells, dead bacteria, exotoxin, etc. This membrane is observed over the tonsil and throat. It is usually darker, thicker, and larger in quantity than strep throat.
  • Fever
  • Sore throat
  • Cervical adenopathy

Complication

  • Airway obstruction due to the membrane extending into the larynx and trachea.
  • Myocarditis with arrhythmia and circulatory collapse.
  • Weakness or paralysis due to damage to the nerves. Cranial nerves are more frequently involved. Regurge of fluids through nose due to weakness or paralysis of the soft palate and pharynx.

Cutaneous Diphtheria

  • Gray membrane on ulcerated skin.
  • Indolent and noninvasive to the surrounding tissue.

Treatment

As soon as you suspect that the patient has diphtheria you should immediately start them on the diphtheria antitoxin. This antiserum is made in horse so hypersensitivity must be checked. The antitoxin will bind the free exotoxin and neutralize it. This is the treatment of choice.

Penicillin G or Erythromycin will then kill the pathogen reducing the exotoxin production.

Culture

Corynebacterium Diphtheriae grows on potassium tellurite and loffler’s medium.

Corynebacterium diptheriae 07

Figure 1.7: two loafs of bread (loaffler’s) had a bet that the pathogen is corynebacterium or not. One of them was correct. So the other one is saying that I TELL you U were RITE (K+ Tellurite).

Note

Hope you enjoyed studying with such sketches. Feedback is appreciated. And, if you can contribute even better art then we all will be grateful to you.

Mobeen Syed