Page 192 - First Aid for the USMLE Step 1 2020, Thirtieth edition [MedicalBooksVN.com]_Neat

148 SEcTioN ii Microbiology ` microbiology—cliNical bacteriology Microbiology ` microbiology—cliNical bacteriology

VDRL false positives VDRL detects nonspecific antibody that False-Positive results on VDRL with:
reacts with beef cardiolipin. Quantitative, Pregnancy
inexpensive, and widely available test for Viral infection (eg, EBV, hepatitis)
syphilis (sensitive but not specific). Drugs (eg, chlorpromazine, procainamide)
Rheumatic fever (rare)
Lupus and leprosy

Serologic testing Direct testing

Nontreponemal Treponemal
(nonspecific) (specific) Darkfield PCR
microscopy

RPR VDRL FTA-ABS TPPA

Jarisch-Herxheimer Flu-like syndrome (fever, chills, headache, myalgia) after antibiotics are started; due to killed
reaction bacteria (usually spirochetes) releasing toxins.

Gardnerella vaginalis A pleomorphic, gram-variable rod involved in I don’t have a clue why I smell fish in the vagina
bacterial vaginosis. Presents as a gray vaginal garden!
A
discharge with a fishy smell; nonpainful (vs Amine whiff test—mixing discharge with 10%
vaginitis). Associated with sexual activity, but KOH enhances fishy odor.
not sexually transmitted. Bacterial vaginosis Treatment: metronidazole or clindamycin.
is also characterized by overgrowth of
certain anaerobic bacteria in vagina (due to
 lactobacilli). Clue cells (vaginal epithelial
cells covered with Gardnerella) have stippled
appearance along outer margin (arrow in A ).

Chlamydiae Chlamydiae cannot make their own ATP. They Chlamydial cell wall lacks classic peptidoglycan
A are obligate intracellular organisms that cause (due to reduced muramic acid), rendering
mucosal infections. 2 forms: β-lactam antibiotics ineffective.
ƒ Elementary body (small, dense) Chlamys = cloak (intracellular).
is “Enfectious” and Enters cell via C psittaci—has an avian reservoir (parrots),
Endocytosis; transforms into reticulate body. causes atypical pneumonia.
ƒ Reticulate body Replicates in cell by fission; Lab diagnosis: PCR, nucleic acid amplification
Reorganizes into elementary bodies. test. Cytoplasmic inclusions (reticulate bodies)
Chlamydia trachomatis causes neonatal seen on Giemsa or fluorescent antibody–
and follicular adult conjunctivitis A , stained smear.
nongonococcal urethritis, PID, and reactive Treatment: azithromycin (favored because
arthritis. one-time treatment) or doxycycline. Add
Chlamydophila pneumoniae and Chlamydophila ceftriaxone for possible concomitant
psittaci cause atypical pneumonia; transmitted gonorrhea.
by aerosol.

FAS1_2019_03-Microbiology.indd 148 11/14/19 12:20 PM