Step 1 Basics (USMLE)

3.18 Bartonella Henselae Microbiology review for the USMLE Step 1 exam Bartonella henselae is an intracellular gram negative rod that causes several different diseases Bartonella targets and lives inside specialized immune cells called CD34+ cells Bartonella creates a protective vacuole that protects it and helps it evade immune detection Bartonella henselae is a facultative intracellular bacteria...

3.17 Brucella Species Microbiology review for the USMLE Step 1 exam Brucella species are gram-negative intracellular coccobacilli that are spread from animals to humans, causing a zoonotic infection called Brucellosis. B. melitensis is the most common species that causes infection in humans and is also the most virulent. Brucella only requires a very small dose (10-100 bacteria) to cause full-blow...

3.16 Pasteurella Multocida Microbiology review for the USMLE Step 1 exam Pasteurella multocida is a gram-negative coccobacillus that commonly causes infection following animal bites or scratches Classic presentation is a young male with swollen, red, and tender skin at the site of the bite or scratch Symptoms develop rapidly, usually within 3-48 hours after injury In rare cases, infection can prog...

3.15 Bordetella Pertussis Microbiology review for the USMLE Step 1 exam Bordetella pertussis is a gram-negative bacterium that causes whooping cough Spread through respiratory droplets, most people are vaccinated against it Adheres to ciliated respiratory epithelial cells and produces toxins that cause inflammation and systemic effects Pertussis toxin and tracheal cytotoxin are important toxins se...

3.14 Haemophilus Influenzae Microbiology review for the USMLE Step 1 exam Haemophilus influenzae is a gram negative coccobacilli that is often encapsulated, encapsulated strains are broken up into subgroups a through f, non-encapsulated strains are referred to as non-typable The most common pathogenic strain is type b, which causes disease in children and immunocompromised individuals, it is the s...

3.13 Moraxella Catarrhalis Microbiology review for the USMLE Step 1 exam Moraxella Catarrhalis is a gram negative diplococcus that is part of normal upper respiratory tract flora Mainly causes three different types of infections: otitis media in children, lower respiratory tract infections in COPD patients, and pneumonia in elderly patients Otitis media is the most common bacterial infectious dise...

3.12 Neisseria Species Microbiology review for the USMLE Step 1 exam Neisseria species are gram negative diplococci that infect and live inside neutrophils Two main species that cause infections in humans: Neisseria gonorrhoeae and Neisseria meningitidis Neisseria gonorrhoeae causes the sexually transmitted infection gonorrhea, which is the second most common STI Risk factor for gonorrhea is unpro...

3.11 Nocardia and Actinomyces (Branching Filamentous Species) Microbiology review for the USMLE Step 1 exam Nocardia and Actinomyces are two gram positive bacteria that grow in filaments, resembling fungal hyphae. Both are associated with chronic pulmonary lesions, subcutaneous abscesses, and multiple draining sinuses. Both are capable of producing sulfur granules. Actinomyces is anaerobic and col...

3.10 Clostridium Species Microbiology review for the USMLE Step 1 exam Clostridium species are spore-forming anaerobic gram-positive rods that secrete toxins Four main species: Clostridium difficile, Clostridium perfringens, Clostridium botulinum, Clostridium tetani Clostridium difficile: common cause of antibiotic-associated diarrhea, caused by overgrowth of C. diff in gut after taking antibiotic...

3.09 Corynebacterium Diptheriae Microbiology review for the USMLE Step 1 Exam Corynebacterium diphtheriae is an aerobic gram positive rod that causes diphtheria, commonly spreads through respiratory droplets C. diphtheriae produces an exotoxin called diphtheria toxin which can cause systemic effects by inactivating elongation factor (EF-2) via ADP-ribosylation and shutting down protein synthesis D...

3.08 Bacillus Species Microbiology review for the USMLE Step 1 exam Bacillus species are aerobic, sporulating, gram + rod-shaped bacteria found in nature such as soil, water, and air Two main species to discuss: Bacillus cereus and Bacillus anthracis Bacillus cereus is associated with foodborne infections and specifically with reheated rice, as spores can survive cooking and continue to grow in re...

3.07 Listeria Monocytogenes Microbiology review for the USMLE Step 1 exam Listeria monocytogenes is an intracellular, aerobic, gram-positive rod that can cause foodborne illness It can live inside various types of cells, including epithelial cells, macrophages, and monocytes, and spreads from cell to cell through actin polymerization It is most commonly found in refrigerated deli meats and unpaste...

3.06 Staphylococcus Species Microbiology review for the USMLE Step 1 Exam Staphylococcus bacteria are gram-positive cocci that form clusters in the shape of grapes on a vine Three pathogenic species of staph: staph aureus, staph epidermidis, and staph saprophyticus Differentiation between species can be done using coagulase and novobiocin sensitivity tests Staph aureus is a major pathogen that cau...

3.05 Streptococcus Species   Microbiology review for the USMLE Step 1 Exam.   Streptococcus bacteria are gram positive cocci that form linear chains Hemolysis refers to the ability of bacteria to break down red blood cells and is classified as alpha (partial), beta (complete), or gamma (none) Alpha hemolytic streptococci include viridans streptococci and Streptococcus pneumoniae Viridans streptoco...

3.04 Gram Negative Bacteria   Microbiology review for the USMLE Step 1 Exam.   Gram negative bacteria are characterized by a thin cell wall surrounded by a lipid outer membrane They do not retain the violet gram stain and appear pink after staining Gram negative bacteria can be classified by shape: cocci, coccobacilli, bacilli, and spirals Gram negative cocci include Neisseria species, which can b...

3.03 Gram Positive Bacteria   Microbiology review for the USMLE Step 1 Exam.   Gram positive bacteria are characterized by their ability to retain the violet stain during the gram stain procedure, due to their thick peptidoglycan cell walls Gram positive bacteria can be cocci (spherical) or bacilli (rod-shaped) Cocci can be grouped in clusters, pairs, or chains Gram positive cocci in pairs or chai...

3.02 Bacterial Toxins   Microbiology review for the USMLE Step 1 Exam.   Bacterial toxins are harmful compounds produced by bacteria that cause damage to the host Exotoxins are toxins that are actively secreted by some species of gram positive and gram negative bacteria Examples of exotoxins include botulinum toxin, Corynebacterium diphtheriae toxin, and cholera toxin Endotoxins are toxins that ar...

3.01 Bacteria Basics   Microbio review for the USMLE Step 1 Exam: Bacteria are single-celled organisms that can cause infection Structural components of bacteria include: capsule, cell wall, flagella, fimbriae, plasma membrane, ribosomes, endospores, and DNA Capsules help bacteria evade the immune system by inhibiting phagocytes Flagella are tail-like appendages that allow bacteria to move, fimbri...

2.12 Idiopathic Pulmonary Fibrosis   Pulmonary system review for the USMLE Step 1 exam.

2.11 Bronchiectasis   Pulmonary system review for the USMLE Step 1 exam.

2.10 Asthma   Pulmonary system review for the USMLE Step 1 exam.

2.09 COPD   Pulmonary system review for the USMLE Step 1 exam.

2.08 Obstructive vs Restrictive Lung Diseases   Pulmonary system review for the USMLE Step 1 exam.

2.07 Pulmonary Embolism   Pulmonary system review for the USMLE Step 1 exam.

2.06 Physical Findings for Lung Diseases   Pulmonary system review for the USMLE Step 1 exam.