Multi-Systems Post-Midterm QStream Flashcards
A 22-year-old man is admitted to the hospital with Neisseria meningitides meningitis. His family reports that he had meningococcemia four years ago. Which of the following conditions is associated with recurrent N. meningitides infections?
- Complement deficiency
- Solid organ transplantation
- Neutrophil dysfunction
- HIV
- Poorly controlled diabetes
Answer: Complement deficiency
Explanation: Recurrent meningogoccal infections are associated with deficiencies in terminal complement proteins C5-9.
Which of the following is an example of a pathogen-associated molecular pattern?
- E. coli
- Gram negative septic shock
- Toll-like receptor 4
- Lipopolysaccharide
- Flagellar locomotion
Answer: Lipopolysaccharide
Explanation: Pathogen-associated molecular patterns (aka PAMPS) are distinct molecules that are present in a set of pathogens and that are recognized by cells of the innate immune system. The classic example of a PAMP is lipopolysaccharide (LPS), which is present on the membrane of gram negative bacteria. There are many other PAMPS, including flagellin, lipoteichoic acid, peptidoglycan and double-stranded RNA. PAMPS are recognized by molecules on innate host cells called pattern recognition receptors (PRRs). The PRR for LPS is toll-like receptor 4 (TLR4).
A 65-year-old homeless man is found deceased in Rock Creek Park by the side of the road. His body and clothing are blood soaked and the clothing torn in multiple places, and the police suspect he was a victim of assault. On autopsy external examination, he has multiple abrasions and lacerations of the head and torso. On internal examination, his has multiple areas of subgaleal hemorrhage, right occipital subdural hemorrhage, and lacerations of the liver and spleen with a 1000 ml hemoperitoneum. There are no other significant findings, and his toxicology is negative for ethanol and drugs of abuse. What is best determination of the cause of death?
- Multiple sharp force wounds of the head and torso
- Blunt force injuries
- Assault
- Homocide
- Traumatic brain injury (TBI)
Answer: Blunt force injuries
Explanation: The cause of death is blunt force injuries of the head and torso, with laceration, contusions, and subsequent internal hemorrhage. Homicide is a manner of death, not a cause of death. Assault is a circumstance, neither a cause or manner of death. No sharp force injuries were identified. Traumatic brain injury is present, but other lethal wounds including abdominal hemorrhage are also found.
Which of the following statements is most accurate when describing the “Virulence” of anaerobic organisms, in general?
- Anaerobes possess a wide array of tissue lytic enzymes which can breach healthy epithelia or integument barriers.
- Anaerobes are essentially “invisible” to host phagocytes, and thus can replicate to high numbers prior to detection.
- Anaerobes often take advantage of a pre-existing tissue injury, where compromised tissue perfusion presents an opportunity for infection.
- Since these are “anaerobic” organisms, they can grow anywhere, and can invade any tissue type.
Answer: Anaerobes often take advantage of a pre-existing tissue injury, where compromised tissue perfusion presents an opportunity for infection.
Explanation: Most anaerobic infections arise from normal flora at or near the site of injury, where they then find the environment more hospitable due to compromised blood flow and reduced oxygenation. In general the commensal anaerobes are NOT highly invasive, but become pathogens when the opportunity comes along to support their proliferation. When they do invade tissues they are subject to the usual host immune responses. They are NOT able to grow in a wide variety of niches, only those of reduced oxygen tension.
This 67 y/o male with known lung cancer presents with hypotension. His heart (subxiphoid and parasternal long views), lung, and inferior vena cava images are shown. For the lung images, the same findings are present on both left and right sides throughout the entire lung fields. What is the most likely cause of his hypotension?
- septic shock
- tension pneumothorax
- cardiac tamponade
- massive pulmonary embolism
Note: The images are likely hard to see, but there’s an awful lot of black around the heart and the lungs on ultrasound.
Answer: cardiac tamponade
Explanation: The ultrasound images show a pericardial effusion and a dilated inferior vena cava; this combined with the patient history are most consistent with cardiac tamponade. There is normal pleural sliding (sand on the seashore sign, eg – no pneumothorax), so this is not tension pneumothorax. With septic shock or hypovolemic shock, the IVC will be small.
The term “Proximity” refers to what findings regarding the evolution of an anaerobic infection?
- Anaerobes must be in the proximity of a ready source of pre-digested nutrients to flourish.
- Anaerobes are stimulated to replicate by the local cytokines released in response to infection of a specific tissue or an organ.
- Anaerobes are often part of the normal microbial flora adjacent to an area of injury, which they then can infect.
- The spectrum of types of anaerobes found in an individual often reflects the regional environment close to where that person lives and works.
- Anaerobes migrate rapidly through the body to sites of opportunity.
Answer: Anaerobes are often part of the normal microbial flora adjacent to an area of injury, which they then can infect.
Explantion: Anaerobes inhabit several niches in the human body including the oral, gastrointestinal and genitourinary tract. The infections they cause generally arise due to injury at the sites where populations of anaerobes are already present.
Which of the following statements is most accurate regarding the general therapy of serious anaerobic infections?
- Anaerobes respond best to combinations of two to three antibiotics which must work in synergy.
- Anaerobic infections often require debridement or removal of devitalized tissue.
- Most anaerobic infections above the waist possess a wide variety of beta-lactamases and require sophisticated antibiotics, often with beta-lactam inhibitors.
- Since anaerobic infection are often focal, locally applied antibiotics work well in treatment of infections caused by these organisms.
- Newer vaccines have greatly reduced the need to treat anaerobic infections.
Answer: Anaerobic infections often require debridement or removal of devitalized tissue.
Explanation: Anaerobic infections often originate adjacent to sites where anaerobes are found as normal flora. Although these infections may be mixed, they generally are not highly drug resistant and respond well to antimicrobial therapy. The difficulty is often that anaerobic infections establish themselves where there is low oxygenation and tissue damage. Therefore, debridement and reestablshment of good circulation may be the first step in achieving access to the site of antibiotics and a cure.
A 72-year old women develops an infection near the site of her bowel surgery. The wound has been left open. Her temperature is 103.5º F and her leukocyte count is 19,800/mm3. The attending physician notices that her room has a foul odor when he enters it. A Gram stain of the pus from her wound is prepared and shows Gram negative rods and Gram positive cocci. Which one of the following pairs of organism is MOST likely to be present in this specimen?
- Bacillus cereus plus Clostridium tetani
- Streptococcus pneumonie plus Chlamydia pneumoniae
- Streptococcus pyogenes plus Staphylococcus aureus
- Mycobacterium tuberculosis plus Mycobacterium avium
- Bacteroides species plus Peptostreptococcus
Answer: Bacteroides species plus Peptostreptococcus
Explanation: Bacteroides and Peptostretococci are correct. A Foul-smelling room suggests that the women’s infection may involve anaerobes. Most anaerobic infections are polymicrobial (mixed). Only two answers include anaerobes. Bacillus cereus and C. tetani are wrong because both are Gram positive rods. Both Bacteroides and Peptostreptococci are anaerobes and these organisms are very commonly found in mixed infections near the abdomen. Bacteroides are Gram negative rods and Peptostrep are Gram positive cocci.
A 22 year-old woman experiences a crushing leg injury in an automobile accident Within 72 hours of the accident, she develops a bluish red margin near the site of injury that moves toward her trunk. Her attending physician makes a presumptive diagnosis of myconecrosis and performs a biopsy of muscle in the area of the injury. The results of that biopsy reveal muscles cells and Gram positive organisms but no neutrophils. The MOST LIKELY organism seen in the biopsy specimen is
- Staphylococcus aureus
- Actinomyces israelii
- Propionibacterium acnes
- Streptococcus agalactiae
- Clostridium perfringens
Answer: Clostridium perfringens
Explanation: The link between myonecrosis and the absence of PMNs is a hallmark of Clostridial infection (particularly C. perfringens). Also, C.perfringens is the leading cause of gas gangrene.
Which of the following tissue samples is most likely to abundantly grow anaerobic bacteria in the laboratory?
- A biopsy of inflamed gingival (gum) tissue from a 47 year old heavy smoker
- A biopsy of a stomach ulcer obtained during an upper GI tract endoscopy performed on a 28 year old woman.
- A biopsy of an unusual skin lesion next to the anus in a 70 year old man.
- A trans-urethral biopsy of an enlarged prostoate gland in a 63 year old man.
Answer: A biopsy of inflamed gingival (gum) tissue from a 47 year old heavy smoker
Explanation:
- A biopsy of an unusual skin lesion next to the anus in a 70 year old man while the anus is the terminus of the distal GI tract where anaerobes flourish, the external skin would be much less likely to harbor anaerobic bacteria.
- A biopsy of inflamed gingival (gum) tissue from a 47 year old heavy smoker, as a biopsy of inflamed gingival (gum) tissue from a 47 year old heavy smoker would likely contain many species of anaerobic bacteria. Oral gingival tissues and their associated spaces have been found to contain several hundred different species of anaerobes, which often play a significant role in dental and other oral infections. (correct answer)
- A biopsy of a stomach ulcer obtained during an upper GI tract endoscopy performed on a 28 year old woman. as the stomach generally has among the lowest numbers and diversity of anaerobes within the long course of the GI tract. Once might however find Helicobacter species (aerobic gram negative bacteria), which have a proven association with gastric and duodenal ulcers.
- A trans-urethral biopsy of an enlarged prostoate gland in a 63 year old man as the male genito-urinary tract is much less likely than the female GU tract to have an anaerobic flora.
A 59-year-old homeless man is found deceased in Rock Creek Park by the side of the road. His body and clothing are blood-soaked and the clothing is torn in multiple places. The police suspect he was a victim of assault. On autopsy external examination, no wounds are identified. On internal examination, the liver is markedly cirrhotic and there is blood in the esophagus and stomach. There are no other significant findings, and his toxicology is negative for ethanol and drugs of abuse. What is best classification of the manner of death?
- Accident
- Homicide
- Suicide
- Manslaughter
- Natural
Answer: Natural
Explanation: Natural death resulted from ruptured esophageal varices from cirrhosis is a natural disease, no evidence of any unnatural process, ie external or internal trauma or substance ingestion. Note that Manslaughter is not an accepted manner of death.
You are an intern reporting for duty in the ICU. Your resident tells you that an 85-year-old patient in shock just arrived from the Emergency Department. The patient received no fluid resuscitation, but has an elevated central venous pressure (CVP) reading of 19 cm H2O. Which of the following causes of her shock state is most likely.
- Pneumonia
- Myocardial infarction
- Pelvic Fracture
- GI Bleed
- Splenic laceration
Answer: Myocardial infarction
Explanation: A patient in cardiogenic shock from an acute myocardial infarction would likely have a normal or elevated CVP. The patient is not volume depleted (as in hypovolemic shock), but has an impaired cardiac output. The fluid “backs up” through the circuit and the CVP would be abnormally high. If the patient were experiencing hemorrhagic shock (a type of hypovolemic shock), you would expect a low CVP. The total body fluid would be low and this would manifest as low central venous pressure which would be the case in a GI bleed, a pelvic fracture or a splenic laceration. A patient with pneumonia would have septic shock and would likely have a low CVP (vasodilation from the inflammatory cascade decreases CVP).
Malaria parasites first enter which cells after they infect a human being?
- Lymphocytes
- Sensory nerve cells
- Intestinal epithelial cells
- Red blood cells
- Hepatocytes
Answer: Hepatocytes
Explanation: Hepatocytes is the correct answer. Malaria sporozoites injected into the bloodstream from mosquitoes first invade hepatocytes. There, over 1-2 weeks they produce thousands of haploid forms called merozoites. These rupture out of liver cells and invade circulating red blood cells, where they then enter a cycle of repeat red bood cell infections through asexual replication and rupture out of red blood cells. A fraction of merozoites leave the red cell cycle by developing into sexual forms (male and female gametocytes) which remain in circulation and are infectious for mosquitoes. In mosquitoes, the human RBCs break up and release the gametocytes, which develop further and then fuse to become diploid zygotes in the mosquito. These zygotes develop into oocysts which produce haploid sporozoites, which are infectious for humans (completing the cycle). Of note, in P. vivax and P. ovale, a some parasites in hepatocytes can enter a dormant or latent phase called a hypnozoite, allowing for release of merozoites and development of clinical disease at repeated distant time intervals from initial infection.
The following is seen on a peripheral blood smear. Which of the following is the most likely diagnosis?
- Plasmodium ovale
- Plasmodium falciparum
- Plasmodium knowlesi
- Plasmodium malariae
- Plasmodium vivax
Answer: Plasmodium falciparum
Explanation: The slide shows banana-shaped gametocytes. These are diagnostic for Plasmodium falciparum.
A 22 year-old male presents to the emergency department with an erythematous and swollen right hand following a cat bite that occurred less than 24 hours ago. He is otherwise healthy without other medical problems. Ultrasound of the dorsum of the hand revealed a fluid collection, and frank purulence was extracted on incision and drainage. Cultures revealed growth of Pasteurella multocida.
All of the following antibiotics would provide appropriate coverage for this organism EXCEPT:
- Amoxicillin-clavulanate
- Clindamycin
- Doxycycline
- Piperacillin-tazobactam
Answer: Clindamycin
Explanation:
Clindamycin is the correct answer, as P. multocida is inherently resistant to clindamycin. This is important to note, as clindamycin is often provided as an oral option for coverage of infections when MRSA or other staphylococci or streptococci species are possible culprits. However, it has poor gram negative coverage and should not be used for cat or dog bites were Pasteurella multocida (a Gram negative) is a frequent problem .
- Doxycycline is incorrect, as doxycycline has excellent activity against P. multocida.
- Amoxicillin –clavulanate is the drug of choice for outpatient management of animal bite infections, as it has excellent coverage for P. multocida as well asCapnocytophaga canimorsus.
- Piperacillin-tazobactam is an IV β-lactam antibiotic with similar coverage as amoxicillin-clavulanate and therefore covers P. multocida
A 19-year-old arrives at his physician’s office with a history of fever and a skin lesion shown below. On history you learn that he has just returned from serving as a counselor at summer camp on the Maryland eastern shore. The vector that transmits the organism responsible for the lesion below is a
- rodent flea ( genus Xenopsylla)
- deer tick( genus Ixodes)
- dog tick (genus Dermacator)
- mosquito (genus Aedes)
- body louse (genus Pediculus)
Answer: deer tick (genus Ixodes)
Explanation: The skin lesion in the picture is classic erythema migrans. That clinical presentation with fever plus a history of camping on the Eastern Shore of Maryland strongly indicate Lyme disease. The vector for Lyme disease is Ixodes scapularis or the deer tick).
Large Gram- positive rods are observed on a blood smear from a 60-year –old patient with a severe flu-like illness accompanied by the chest X-ray as below. The virulence of this organism is associated with its capacity to survive in the blood stream and to the production of two toxins, one of which is a/an
- cytotoxin that inhibits protein synthesis.
- hemolysin.
- super antigen.
- hyaluronidse.
- adenylate cyclase
Answer: adenylate cyclase
Explanation: This is a likely case of pulmonary anthrax. The main clues here are the widening of the mediastinum on Xray (think inhalational anthrax) supported by the fact that the disease is severe and the organism can survive in the blood stream. The causative agent of anthrax, Bacillus anthracis makes two toxins: lethal toxin and edema toxin (an adenylate cyclase).
The arrow in the figure below points to an inclusion in a human polymorphonuclear leukocyte in a bone marrow aspirate from a 9 year old Maryland boy with fever, headache, and a faint rash and history of a deer tick bite. The organism is MOST LIKELY
- Anaplasma phagocytophilum.
- Bartonella henselae.
- Borrelia burgdorferi.
- Rickettsia rickettsii.
- Erlichia chaffeensis
Answer: Anaplasma phagocytophilum.
Explanation: Anaplasma phagocytophilum is correct because of the intracytoplasmic inclusion (also called a morulae) in a PMN in the picture combined with the link to a deer tick. Borrelia burgdorferi, the agent of Lyme Disease, has the same vector but would not cause inclusions in PMNs. The vector of B. henselae is a flea, and rash is not part of the presentation of cat scratch fever. In Erlichia infections, the inclusion would be in a monocyte or macrophage and the vector is the Lone Star tick. Erlichia causes human monocytic ehrlichiosis. Rocky Mountain spotted fever is caused by Rickettsia rickettsii, would cause a more fulminate rash, and the vector is the dog tick.
A 36-year-old returned Peace Corps volunteer from Ghana returns to the US for an extended family visit. While at home, he complains of not feeling well. During the course of one week, he develops symptoms of severe myalgias, abdominal discomfort, vomiting, diarrhea, fever, chills, and sweats. Because his symptoms are not improving, he goes to the local university hospital. On physical exam, enlarged lymph nodes are noted. Blood cultures are drawn, and thin/thick smears are prepared for Giemsa staining. A lymph node aspirate is also performed, and the fluid is sent for Gram staining, culture, and Giemsa staining. All cultures are negative, but the Giemsa stained peripheral blood smear shows the following results. Which organism is most likely to be the cause of this patient’s illness?
- Trypanosoma cruzi
- Toxoplasma gondii
- Plasmodium falciparum
- Trypanosoma brucei gambiense
- Trypanosoma brucei rhodesiense
Answer: Trypanosoma brucei gambiense
Explanation: The picture shows an extracellular hemoflagellate protozoan, morphology typical of the genus Trypanosoma. The patient history tells us the patient has lived in West Africa, and the presentation of a sytemically ill patient with large lymph nodes (Winterbottom’s sign) is consistent with T. brucei gambiense. Subspecies rhodesiense causes a more acute and debilitating form of “sleeping sickness” and is endemic to East Africa. The South American T. cruzi is more often asymptomatic until later in life when one may experience cardiomyopathy, megacolon or megaesophagus. Anyone returning from a malaria endemic area with fever should be tested for malaria, but this blood film does not show any malarial parasites are present. T. gondii is generally diagnosed in tissue, esp. brain, or by serological means.
