Internal Medicine_Infectious Diseases_8 Flashcards
Bacteria_Listeria, Actinomyces, Nocardia, Acinetobacter, Bartonella, Francisella, Pasteurella, Coxiella (Q fever), Rickettsia, Ehrlichiosis
What type of bacteria is Listeria monocytogenes?
Listeria monocytogenes is a gram-positive bacillus.
What type of hemolysis does Listeria monocytogenes exhibit?
Listeria monocytogenes is beta-hemolytic, often producing narrow zones of hemolysis on blood agar.
What type of motility is characteristic of Listeria monocytogenes?
Tumbling motility in broth cultures and “actin rocket tails” for intracellular movement.
When inside a cell, Listeria monocytogenes is propelled by a process called actin polymerization, which pushes the bacterium forward, allowing it to traverse the cellular environment.
What is the habitat of Listeria monocytogenes in cold environments?
Listeria monocytogenes can survive and multiply in near-freezing temperatures, allowing it to contaminate refrigerated foods.
Listeria monocytogenes is resistant to freezing.
What foods are commonly associated with Listeria outbreaks?
Unpasteurized milk, soft cheeses, packaged meat, and refrigerated foods.
Why are pregnant women at higher risk for Listeria infections?
Pregnant women are 20 times more likely to contract listeriosis due to immunologic changes during pregnancy. Infection can lead to early termination or newborn disease (Amnionitis, sepsis, abortion).
What conditions can Listeria monocytogenes cause in newborns?
Neonatal sepsis and meningitis.
Diffuse pyogenic granulomas (granulomatosis infantiseptica).
Congenital listeriosis can lead to …
Congenital listeriosis (Neonatal listeriosis) is a neonatal infection with Listeria monocytogenes.
Significant risk factors include maternal exposure to unpasteurized dairy.
Intrauterine infection causes early-onset severe systemic infection with respiratory distress syndrome and skin lesions (granulomatosis infantiseptica).
Peripartum infection causes meningitis/encephalitis at ~ 3 weeks of age.
What population, besides neonates, is most susceptible to Listeria meningitis?
Adults over 60 years and immunocompromised individuals are most susceptible to infection with Listeria monocytogenes.
In healthy patients infection is usually self-limited with minor gastroenteritis.
What enzyme does Listeria monocytogenes produce?
Listeria monocytogenes produces catalase, which converts hydrogen peroxide into water and oxygen.
What is the first-line treatment for Listeria monocytogenes infections?
Ampicillin or Penicillin G (IV).
Gentamicin for severe cases (can cause ototoxicity).
What type of bacteria is Actinomyces israelii?
Actinomyces israelii is a gram-positive bacillus with a filamentous, branching structure.
Most Actinomyces spp. are facultative anaerobes, meaning they can survive in both oxygenated and deoxygenated environments; however, some species are obligate anaerobes, requiring an oxygen-free environment for growth and survival.
Where is Actinomyces israelii typically found as part of the normal flora?
Actinomyces israelii is part of the normal flora of the oral cavity.
What condition is commonly caused by Actinomyces israelii following jaw trauma or dental procedures?
Actinomyces israelii can cause cervicofacial actinomycosis, characterized by slow progression, jaw lump, abscess formation, sinus tracts, and yellow sulfur granules. Lesions form sinus tracts, which emit a purulent discharge containing yellow sulfur granules. Lesions can become fibrotic.
What OBGYN condition is caused by Actinomyces israelii?
Pelvic actinomycosis from IUDs.
What is the treatment of choice for Actinomyces israelii infections?
The treatment of choice is penicillin G (IV), often requiring prolonged therapy.
Alternative antibiotics are ampicillin or erythromycin.
Surgical drainage may be needed in complicated cases.
What type of organism is Nocardia asteroides?
Nocardia asteroides is an obligate aerobic, gram-positive, branching rod found in soil.
What staining characteristics are seen with Nocardia asteroides?
It stains weakly acid-fast due to the presence of mycolic acids in its cell wall.
What is the relevance of carbol fuchsin in diagnosing Nocardia asteroides?
Carbol fuchsin is utilized in acid-fast staining to identify mycolic acids in its cell wall.
What are the key enzymes produced by Nocardia asteroides?
It produces catalase and urease.
Which populations are most at risk for Nocardia infections?
Immunocompromised patients, especially those with impaired cell-mediated immunity (e.g., HIV, transplant patients, glucocorticoid users).
What are the primary clinical manifestations of Nocardia asteroides infection?
Pulmonary nocardiosis – manifests as pneumonia with lung abscess formation.
CNS nocardiosis – causes brain abscesses and multiple ring-enhancing lesions.
Cutaneous nocardiosis – results in indurated lesions.
How does pulmonary nocardiosis resemble tuberculosis?
It manifests with multiple solid nodules and cavities, similar to TB.
What is a rare manifestation of cutaneous nocardiosis?
It can present with indurated lesions or pyogenic responses due to skin exposure to dirt.
What is the gender predilection for Nocardia infections?
It is more common in men than in women (approximately 2:1-3:1).
What is the treatment of choice for Nocardia asteroides infections?
Sulfonamides, specifically trimethoprim-sulfamethoxazole (TMP-SMX).
Acinetobacter baumannii most commonly affects … ?
hospitalized patients
patients usually develop pneumonia or bacteremia
Why is Acinetobacter baumannii hard to treat?
often this bacteria multidrug resistant
How is Acinetobacter baumannii treated?
carbapenem
polymyxin
cefepime
What type of bacteria is Bartonella henselae, and how is it visualized?
Bartonella henselae is a gram-negative bacillus and is visualized using the Warthin-Starry silver stain.
How is cat-scratch disease primarily transmitted?
Cat-scratch disease is transmitted through cat scratches, bites, or bites from infected fleas.
What is a common clinical presentation of cat-scratch disease?
A common presentation includes erythematous painful axillary lymphadenopathy following a cat scratch or bite, this is after a papule or nodule is at the inoculation site.
Fever could be present or not.
Who is most commonly affected by cat-scratch disease?
Cat-scratch disease predominantly affects immunocompetent individuals but can occur in immunocompromised patients with more severe symptoms.
What condition does Bartonella henselae cause in immunocompromised individuals?
In immunocompromised individuals, Bartonella henselae causes bacillary angiomatosis.
The skin lesions often start as small reddish papules and can progress to larger, highly vascular nodules.
What are the primary treatments for Bartonella henselae infections?
Bartonella henselae infections are treated with doxycycline or a macrolide antibiotic (azithromyocin or erythromycin).
How is cat-scratch disease diagnosed?
Clinically and confirmed with serology.
What is the causative agent of brucellosis?
Brucella spp., a gram-negative coccobacillus.
Facultative intracellular bacteria capable of surviving within host macrophages.
How is brucellosis primarily transmitted to humans?
Through direct contact with infected farm animals (cows, pigs, sheep, goats) or consumption of improperly handles unpasteurized dairy products of infected animals.
What are the characteristic symptoms of brucellosis?
Brucellosis is characteristically associated with undulant fever, marked by fever intensification and remission.
Other symptoms include night sweats and anorexia.
Which organ systems are commonly affected by Brucella spp.?
The reticuloendothelial system, including the liver, spleen, and lymph nodes, often causing hepatosplenomegaly.
What are potential complications of chronic brucellosis?
Osteomyelitis and other musculoskeletal complications such as sacrolitis or spondylitis.
Endocarditis
Meningitis
Encephalitis
What is the structure and staining characteristic of Rickettsia spp.?
Obligate intracellular coccobacilli.
Stain weakly gram-negative.
Can be visualized using Giemsa or Gimenez stain.
How is Rickettsia rickettsii transmitted, and where is it common?
Transmitted by the Dermacentor tick.
Occurs primarily in the eastern United States.
ehrlichiosis is considered _________ while anaplasmosis is considered _________
ehrlichiosis is considered monocytic (infects monocytes for Ehrlichia)
anaplasmosis is considered granulocytic (infects granulocytes for Anaplasma)
What is the likely diagnosis in a patient that presents with flu-like symptoms without a rash after being bitten by a tick two weeks ago? Laboratory exam reveals leukopenia, thrombocytopenia, and elevated LFTs.
Ehrlichiosis
