AMBOSS: HIGH YIELD

Question 1

Escherichia coli and Neonatal Meningitis

Answer 1

Gram-negative rod; common cause of neonatal meningitis. Infection is primarily caused by strains expressing the K1 capsular polysaccharide, which provides resistance to phagocytosis and antibacterial factors in serum, facilitating bacterial invasion.

Question 2

Treatment of E. coli Infection

Answer 2

Antibiotic treatment with ampicillin should be initiated as soon as possible for neonatal meningitis caused by E. coli.

Question 3

Irritability, difficulty feeding, fever, and a bulging anterior fontanelle in a newborn should raise concern for

Answer 3

Neonatal meningitis

Question 4

Haemophilus influenzae and Growth Requirements

Answer 4

Pathogen requiring factors X (hematin) and V (NAD) for growth, which are absent in regular sheep blood agar. Staphylococcus aureus produces NAD and lyses erythrocytes, releasing hematin, allowing H. influenzae to grow in the hemolytic zone—a phenomenon known as satellitism.

Question 5

Haemophilus influenzae Type b (Hib) and Epiglottitis

Answer 5

In unvaccinated children, Hib is the most common cause of epiglottitis. Before routine Hib vaccination, it was also a leading cause of pediatric bacterial meningitis, pneumonia, empyema, pericarditis, bacteremia, and septic arthritis. Vaccination has significantly reduced epiglottitis incidence.

Question 6

Unencapsulated Strains of H. influenzae

Answer 6

These strains (not covered by the Hib vaccine) are common causes of otitis media, sinusitis, conjunctivitis, and pneumonia, particularly in the pediatric population.

Question 7

Atypical Pneumonia Symptoms

Answer 7

Symptoms include long-standing cough, low-grade fever, and malaise, with chest x-ray findings that are markedly out of proportion to the patient’s symptoms. Suggestive of Mycoplasma pneumoniae infection.

Question 8

Mycoplasma pneumoniae Characteristics and Treatment

Answer 8

Organisms are absent on Gram staining; growth on Eaton agar shows “fried-egg colonies.” M. pneumoniae is penicillin-resistant due to lack of a cell wall. Treatment options include macrolides, tetracyclines (e.g., doxycycline), or fluoroquinolones (e.g., levofloxacin). Eaton agar contains yeast extract, horse serum, cholesterol, and penicillin G.

Question 9

Pseudomonas aeruginosa Overview

Answer 9

Gram-negative, oxidase-positive, non-lactose fermenting rod; significant cause of burn wound infections. Secretes exotoxin A, which inactivates elongation factor-2 (EF-2) via ADP-ribosylation, inhibiting protein synthesis.

Question 10

Toxins and Effects of Pseudomonas aeruginosa

Answer 10

P. aeruginosa also produces phospholipase C, degrading cell membranes, contributing to infection and local necrosis. Septic shock features (hypotension, tachycardia, confusion, leukocytosis) are likely due to endotoxins, released by bacterial lysis.

Question 11

Diphtheria toxin (Corynebacterium diphtheriae) also inactivates EF-2. Other exotoxins inhibiting protein synthesis include

Answer 11

Shiga toxin (Shigella spp.) and Shiga-like toxin (enterohemorrhagic E. coli), which deadenylate the 60S subunit of eukaryotic rRNA.

Question 12

Symptoms and Diagnosis of Lobar Pneumonia

Answer 12

Acute onset of fever, chills, dyspnea, and productive cough; crackles on auscultation; x-ray findings confirm lobar pneumonia. Normal CD4+ T-lymphocyte count makes opportunistic infection unlikely.

Question 13

Common Causes of Community-Acquired Pneumonia (CAP)

Answer 13

The most common cause of CAP is Streptococcus pneumoniae, an alpha-hemolytic coccus

Question 15

Virulence Factor of Streptococcus pneumoniae

Answer 15

The most important virulence factor is its polysaccharide capsule, which masks subcapsular antigens, prevents opsonization, and protects against phagocytosis (e.g., by macrophages in the spleen).

Question 16

Vaccination and Immune Response

Answer 16

Conjugate vaccines against S. pneumoniae target capsular polysaccharide and proteins, crucial for patients with anatomic or functional asplenia. Antibodies produced by plasma cells against the polysaccharide capsule enhance the host’s ability to fight the infection.

Question 17

Down Syndrome Overview

Answer 17

Down syndrome (trisomy 21) is the most common liveborn chromosomal anomaly and cause of intellectual disability in the U.S. It is screened for during both the first and second trimesters.

Question 18

Quad Screen Test for Down Syndrome

Answer 18

The quad screen (15-22 weeks gestation) is a blood test screening for genetic disorders and birth defects. It examines four factors: α-fetoprotein (AFP), estriol, f-βhCG, and inhibin A. Findings indicating increased risk of Down syndrome include decreased AFP and estriol, and increased f-βhCG and inhibin A. Abnormal results are not diagnostic and require further investigation (e.g., ultrasound, amniocentesis).

Question 19

Leukemia Risk in Down Syndrome

Answer 19

Children with Down syndrome have a 10-20x higher risk of developing acute lymphoblastic leukemia (ALL) and an increased risk of acute myeloid leukemia (AML), specifically megakaryoblastic leukemia (M7 subtype). Symptoms include bone marrow suppression (anemia, thrombocytopenia, neutropenia), lymphadenopathy, and hepatosplenomegaly, usually presenting within the first four years of life.

Question 20

Chronic Myeloid Leukemia (CML) Overview

Answer 20

CML is commonly caused by the t(9;22) translocation, leading to an abnormal tyrosine kinase protein. Clinical features include constitutional symptoms (fatigue, weight loss, myalgias) and splenomegaly. CML can transform into acute leukemia (AML, ALL) during a blast crisis.

Question 21

Neurofibromatosis Type II

Answer 21

Results from a mutation in the NF2 tumor suppressor gene on chromosome 22, coding for the protein merlin. Patients are at risk for bilateral acoustic neuromas and meningiomas.

Question 22

Von Hippel-Lindau Disease

Answer 22

An autosomal dominant condition due to a mutation in the VHL tumor suppressor gene on chromosome 3, affecting hypoxia-inducible factor ubiquitination. Patients are at risk for cerebellar and retinal hemangioblastomas, pheochromocytoma, and renal cell carcinoma (clear cell subtype).

Question 23

Beckwith-Wiedemann Syndrome

Answer 23

Caused by a mutation in the WT2 gene on chromosome 11. Associated with Wilms tumor, macrosomia, hemihyperplasia, macroglossia, and other embryonal tumors (neuroblastoma, rhabdomyosarcoma).