AMBOSS: HIGH YIELD Flashcards
Escherichia coli and Neonatal Meningitis
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.
Treatment of E. coli Infection
Antibiotic treatment with ampicillin should be initiated as soon as possible for neonatal meningitis caused by E. coli.
Irritability, difficulty feeding, fever, and a bulging anterior fontanelle in a newborn should raise concern for
Neonatal meningitis
Haemophilus influenzae and Growth Requirements
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.
Haemophilus influenzae Type b (Hib) and Epiglottitis
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.
Unencapsulated Strains of H. influenzae
These strains (not covered by the Hib vaccine) are common causes of otitis media, sinusitis, conjunctivitis, and pneumonia, particularly in the pediatric population.
Atypical Pneumonia Symptoms
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.
Mycoplasma pneumoniae Characteristics and Treatment
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.
Pseudomonas aeruginosa Overview
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.
Toxins and Effects of Pseudomonas aeruginosa
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.
Diphtheria toxin (Corynebacterium diphtheriae) also inactivates EF-2. Other exotoxins inhibiting protein synthesis include
Shiga toxin (Shigella spp.) and Shiga-like toxin (enterohemorrhagic E. coli), which deadenylate the 60S subunit of eukaryotic rRNA.
Symptoms and Diagnosis of Lobar Pneumonia
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.
Common Causes of Community-Acquired Pneumonia (CAP)
The most common cause of CAP is Streptococcus pneumoniae, an alpha-hemolytic coccus
Virulence Factor of Streptococcus pneumoniae
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).
Vaccination and Immune Response
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.
Down Syndrome Overview
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.
Quad Screen Test for Down Syndrome
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).
Leukemia Risk in Down Syndrome
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.
Chronic Myeloid Leukemia (CML) Overview
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.
Neurofibromatosis Type II
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.
Von Hippel-Lindau Disease
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).
Beckwith-Wiedemann Syndrome
Caused by a mutation in the WT2 gene on chromosome 11. Associated with Wilms tumor, macrosomia, hemihyperplasia, macroglossia, and other embryonal tumors (neuroblastoma, rhabdomyosarcoma).
