USMLE NBME Step 1 - Annotated Correct Answers

USMLE NBME Step 1 - Annotated Correct Answers Formation of hypnozoites -Pt has *malaria* → one of the features is that it forms hypnozoites and has the PBS shown Transduction -Transfer of genetic material via a bacterial phage → Lytic page infects a bacterium, leading to cleavage of bacterial DNA → Parts of bacterial chromosomal DNA then b/c packaged in capsid → *phage infects another bacteria* - ANSWER-In a study of antibiotic resistance, a strain of E.coli resistant to ampicillin but sensitive to streptomycin is cultured w/a strain of salmonella enteritidis sensitive to ampicillin but resistant to streptomycin. After 4 hrs of co-cultivation. the broth is plated onto a solid medium containing both ampicillin & streptomycin. S.enteritidis bacteria that are resistant to both antibiotics grow at a frequency rate of 1 per 100 cells. Which of the following is the most likely mechanism of the acquisition of ampicillin resistance by S.enteritidis? (Conjugation OR Transduction) 20 -Vd is calculated two ways 1-t1/2 = (0.7xVd)/CL OR VD=(C-initial)/Plasma conc We use the second eq so VD = 80mg/(4ug/mL) -but we must convert 4ug to mg so Vd = 80mg/(.004mg/mL) = 20,000mL -then convert to Liters 20,000mL/(1L/1000mL) = *20L* - ANSWER-An 80M is admitted to the hospital b/c of a 2 wks Hx of severe, persistent UTI. An 80-mg dose of Drug X is administered IV. Chloroquine resistance -Can happen but it is *not a feature* - ANSWER-A 30M, who is a migrant farm worker presents to the ED b/c of a 1-wk Hx of fever, chills, & severe headache. He immigrated to the midwestern USA from Honduras 1 year ago. He is alert. Temp is 104F, pulse is 101/min, RR are 20/min, BP is 105/62. The lungs are clear to auscultation. Cardiac exam is normal. The abd is soft w/active bowel sounds. Neuro exam shows a supple neck; there is nu nuchal rigidity. He is oriented to person, place, & time. Labs show: -Hb---------------14 -Hct---------------42% -Leuko's----------4,6K -Neutro's----------57% -Lymph's-----------33% -Monocytes-------10% Urine -Color------clear yellow -Blood-------------1+ -Urobilinogen-----trace A pictomicrograph of a PBS is shown. This pt's overall condition is most likely caused by an infectious agent w/which of the following features? (Formation of hypnozoites OR Chloroquine resistance) Conjugation -Allows for transfer of DNA *high frequency transfer* via: 1-direct cell-to-cell contact 2-via a bridge-like connection *pilus* between two cells -*Classically E.coli* allows antibiotic resistance transfer to another species Thirty mins after the infusion is complete, his serum conc of Drug X is 4ug/mL. Assuming a distribution t1/2 life of 3 mins & an elimination t1/2 of 24 hrs, the volume of distribution of this drug (in L) in the peripheral compartment is closest to which of the following? (2 OR 20) Negative strand RNA Also:*P*a*R*a*MM*yxovirus 1-Mumps & Measles