First Aid Microbiology 2

Question 1

”. . . organism is isolated and cultured, forming pink colonies on McConkey augar. . .”

Answer 1

• This indicates that the organisms are lactose fermenters
• Narrows it down to:
  
  • E. coli
  • Klebsiella pneumoniae
  • Serratia marcescens
  • Enterobacter species
• These organisms are all common causes of pneumonia and UTI, especially nosocomial pneumonia and UTI
• Note on Serratia: It ferments lactose slowly, so it may appear negative on culture at first. However, it also produces a slight pink pigment – in fact you have probably seen this pigment if you ever had a moldy bathtub, because Serratia likes to grow on wet tile surfaces.

Question 2

The three A’s of Klebsiella

Answer 2

• Alcoholics
• Abscesses
• Aspiration

Question 3

“Currant jelly sputum”

Answer 3

Klebsiella pneumoniae buzz word

Question 4

What is going on in this image?

Answer 4

Oral hairy leukoplakia

Often mistaken for thrush, but it only occurs on the lateral undersides of the tongue and cannot be scraped off.

This is almost exclusively seen in individuals co-infected with HIV and EBV

Question 5

Why must patients with EBV avoid contact sports?

Answer 5

Due to risk of traumatic splenic rupture

Question 6

What is going on in this infant?

Answer 6

Blueberry muffin rash

Characteristic of congenital CMV or rubella infection (two ToRCHES-group infections)

Question 7

CMV Torch infection

Answer 7

• >80% asymptomatic, but when it is not:
  
  • Blueberry muffin rash
  • Sensorineural deafness
  • Hepatosplenomegaly
  • Jaundice
  • Ventricular enlargement
  • Periventricular calcifications
  • Developmental delay and/or seizures
• In asymptomatic individuals, CMV activation may later cause unilateral or bilateral sensorineural hearing loss. It is the #1 cause for childhood sensorineural hearing loss.

Question 8

When are HIV patients at risk for CMV?

Answer 8

When CD4 count is below 50

Most common presentation is necrosing retinitis, with “pizza pie” retina.

Esophagitis in a single, deep, linear ulceration is also common. Colitis with ulceration may also occur.

Question 9

Treatments of choice for CMV

Answer 9

1st line: Gancyclovir

2nd line: Foscarnet (use when UL97 resistance mutation to gancyclovir is present)

Question 10

“Mononucleosis” may be caused by. . .

Answer 10

EBV, CMV, or initial HIV

Tell them apart w/ monospot, which will be negative for CMV and HIV. If it returns negative, further CMV and HIV workup is required. Since monospot is sometimes falsely negative, a different EBV test may also be warranted.

Question 11

Drawing the line between HIV and AIDS

Answer 11

CD4 < 200

OR

Low CD4 in the context of an AIDS-defining opportunistic infection

OR

Low CD4 in the context of an HIV-driven diffuse large B cell lymphoma

Question 12

Testing for HIV in a neonate

Answer 12

HIV is a TORCHES-group infection. So, it can be passed from mother to child.

This presents a diagnostic problem. The way we usually diagnose HIV is with a screening ELISA, followed by a confirmatory Western blot.

But, of course, if mom is infected, the baby will for sure have HIV anti-IgG that it acquired from mom even if the baby is not infected!

So, in neonates, we instead look for HIV genetic material directly.

Question 13

Antiretrovirals for pregnant women infected with HIV

Answer 13

Ziduvodine is the drug of choice

Question 14

Antiretroviral summary

Answer 14

Question 15

Donovanosis

Answer 15

Aka granuloma inguinale

Sexually transmissible genital ulcer disease caused by Klebsiella granulomatis.

Characterized as painless ulcers with raised borders and “kissing” apperance. May be complicated by subsequent coinfection.

Diagnosed by presence of “Donovan bodies” (bacteria within macrophage cytoplasm) on biopsy

Treat w/ azithromycin

Question 16

The four “C”s of Measles

Answer 16

Remember that measles = rubeolla!

Koplik spots are pathognomonic for measles. Here they are shown on the tongue, but they can also appear on the cheeks. They are often white, but may be bluish, and are surrounded by red erythematous mucosa.

Four C’s are followed by a maculopapular rash that starts from the head and moves down.

Question 17

Complications of measles

Answer 17

• Bacterial superinfection (usually pneumonia)
• Sclerosing pan-encephalitis
  
  • May present DECADES after the infection, or without known history of infection at all, but CSF will contain anti-rubeolla antibodies. There is no treatment.

Question 18

What is going on in this pathology section?

Answer 18

This is a Warthin-Finkeldey cell, pathognomonic for measles/rubeolla.

It is a syncytial cell created by multiple cells expressing rubeolla’s fusion proteins.

Question 19

Nutritional treatment for rubeolla

Answer 19

Measles is less severe if the patient is replete with vitamin A!

So, any rubeolla patient should receive vitamin A, just in case.

Question 20

Respiratory syncytial virus

Answer 20

• Infects primarily those < 6 months of age
• Most common cause of pneumonia and bronchiolitis in infants
• Treated in infants w/ palivizumab (mAb against RSV) and in non-pregnant adults with Ribavirin (not safe in kiddos)

Question 21

Parainfluenza virus

Answer 21

• Common infection in those <2 years of age
• Causes croup / laryngotracheobronchitis
• Characterized by “barking” cough with inspiratory stridor and Steeple sign on CXR
• Treat mild cases w/ oral corticosteroid. Moderate w/ oral corticosteroid + racemic epinephrine
• Severe cases require admission and supplemental oxygen

Question 22

IgG anti-FHA

Answer 22

FHA stands for filamentous hemagglutinin adhesin

Major host protective factor against Bordetella pertussis infection, as FHA is required for B. pertussis to adhere to host epithelium. In hosts with anti-FHA, it slides right off.

Of note, B. pertussis does not invade tissue, so if it can’t adhere it is shit out of luck.

The acellular vaccine (DTaP, for diphtheria, tetanus, and acellular pertussis) induces production of this antibody.

Question 23

Treatment of choice for pertussis

Answer 23

Macrolides

Question 24

Phases of pertussis

Answer 24

Question 25

Patient presents with focal deficits, high fever, and neck stiffness following a weekend trip to Yellow Stone, where they went to swim in the park's fresh water rivers. Lumbar puncture reveals trophozoites in the CSF. What was the original source of the causative organism?

Answer 25

Animal pee This is ***Naegleria fowleri***, the cause of **acute amoebic meningoencephalitis**. It recently caused an epidemic in Texas where the local water supply was contaminated. Trophozoites enter through the nasal pathway and cribriform plate. Treat w/ **amphotericin** -- remember, amoebae are protists and closely related to fungi!

Question 26

Infectious organisms found in fresh water that got there via animal urine

Answer 26

* Leptospira * N. fowleri

Question 27

Patient presents with flu-like symptoms following return from a vacation to Hawaii. They are perscribed oseltamavir for symptoms. Two days later, they return with continued occular symptoms, the following occular finding, and in severe distress. They are found to have significantly elevated creatinine and bilirubin. What is the likely diagnosis?

Answer 27

Leptospirosis precipitating Weil's disease (hematogenous leptospirosis affecting multiple organ systems) It was most likely acquired from fresh water swimming in Hawaii in a waterbed that had been contaminated by animal urine

Question 28

A premature infant in the NICU develops high fever and respiratory distress. The infant had been receiving total parenteral nutrition containing a high fat content. Blood test reveals beta-D-glucan present in the infant's blood. KOH preparation reveals a "spaghetti and meatballs" appearance. The organism that likely caused fungal sepsis in this infant is a common cause of what other disease in adults?

Answer 28

Pityriasis versicolor, a mimic of vitiligo This is Malassezia furfur, or a closely related Malassezia species. **Topical selenium sulfide** is used in the treatment of **pityriasis versicolor,** but for **Malassezia sepsis** the treatment is **IV** **amphotericin B.**

Question 29

How does selenium sulfide fight against some fungal species like the Malassezia genus?

Answer 29

It promotes shedding of the stratum corneum, which is where the fungi reside.

Question 30

Rose Gardener's Disease

Answer 30

Sporothix schenckii: When a rose shanks you A local pustule or ulcer forms at the site of trauma. Nodules then develop along the path of draining lymphatics, which if biopsied will show granulomas (similar to *M. marinum*). They will *also* contain budding yeast (unlike *M. marinum*). The treatment of choice is **oral itraconazole.** An old-timey treatment was **potassium iodide**, which contributed to the naming of the disease since it was also a pesticide used in rose gardens (but not used for either any more).

Question 31

Neonatal gonorrheal conjunctavitis vs neonatal chlamydial conjunctavitis

Answer 31

The big difference is in **time of onset**. When comparing gonorrhea and chlamydia, they are always similar, but **gonorrhea is always faster and worse.** It grows faster, it spreads faster, it causes a live arthritis as opposed to a reactive arthritis, its discharge is thicker, etc. Note: This table has a mistake. Whenever you see gonorrhea or chlamydia, be it in the genitals or in the eyes, you always assume that the other is present as a coinfection. So, you treat both forms of conjunctavitis the same way: **erythromycin AND ceftriaxone.**

Question 32

"Comma-shaped"

Answer 32

Buzz word *specifically* for the **Vibrio** genus

Question 33

What do you need to know about non-cholera Vibria species?

Answer 33

They contaminate seafood, especially oysters. That's really it.

Question 34

How can you tell that Cholera likes alkaline media?

Answer 34

It causes secretion of tons of bicarbonate in the gut! Also, as it happens, cholera is acid labile, so a large dose is needed for gut inoculation.

Question 35

Based on the following x-ray, what is the likely causative organism? How should the patient be treated?

Answer 35

***Proteus mirabilis*** This is a **staghorn calculus** in the renal pelvix, most commonly caused by Proteus infection. These calculi are made of ammona, magnesium, and phosphate. The optimal treatment is with **sulfonamides.**

Question 36

While stomach ulcers can be caused by several pathologies, almost all *duodenal* ulcers are caused by \_\_\_.

Answer 36

While stomach ulcers can be caused by several pathologies, almost all *duodenal*​ ulcers are caused by ***Helicobacter pylori***

Question 37

Treatment for H. pylori

Answer 37

Combination of: PPI, amoxicillin, clarithromycin

Question 38

"Cherry red epiglottis"

Answer 38

Buzz word for **epiglotitis**, which is itself a buzz word for ***Haemophilus influenzae***

Question 39

Treating and preventing haemophilus influenzae

Answer 39

* Treatment: **Ceftriaxone** (especially for meningitis) * Prevention: * For contacts: **Rifampin** * For the encapsulated strain that causes meningitis: **Polysaccharide conjugate vaccine w/ diphtheria toxoid, given between 2-18 months**