Microbiology: Medications + Infection by system

What organisms commonly cause community-acquired pneumonia?

Streptococcus pneumoniae, Haemophilus influenzae, atypicals, and respiratory viruses.

What organism causes pneumonia with a sweet or grape-like odor?

Pseudomonas aeruginosa.

What organism causes pneumonia with diarrhea and hyponatremia?

Legionella pneumophila.

What organism causes atypical pneumonia with cold agglutinins?

Mycoplasma pneumoniae.

What organisms commonly cause late-onset ventilator-associated pneumonia?

Pseudomonas, Klebsiella, Acinetobacter, and Staphylococcus aureus.

What organisms commonly cause catheter-associated UTIs?

Escherichia coli, Proteus, and Klebsiella.

What organism causes UTI with alkaline urine and struvite stones?

Proteus mirabilis; urease production raises urine pH.

What organisms are associated with infections of prosthetic devices?

Staphylococcus epidermidis and other biofilm-forming organisms.

What organism causes meningitis in neonates and can be acquired from unpasteurized dairy?

Listeria monocytogenes.

What organism causes meningitis in unvaccinated children and epiglottitis?

Haemophilus influenzae type b.

What organism causes meningitis with petechiae and purpura?

Neisseria meningitidis.

What organism causes meningitis in older adults and alcohol use disorder?

Streptococcus pneumoniae; Listeria risk also increases with age.

What organisms commonly cause foodborne gastroenteritis?

Salmonella, Campylobacter, Shigella, pathogenic E. coli, and Staphylococcus aureus.

What organism causes bloody diarrhea and HUS without invading intestinal cells?

Enterohemorrhagic E. coli; Shiga-like toxin causes endothelial injury.

What organism causes watery diarrhea after contaminated water exposure?

Vibrio cholerae; toxin-mediated increased cAMP causes fluid secretion.

What organism causes diarrhea after undercooked poultry?

Campylobacter jejuni; can precede Guillain-Barré syndrome.

What organism causes pseudomembranous colitis after antibiotic use?

Clostridioides difficile.

What organism causes dysentery after ingestion of contaminated food or water?

Shigella species; causes inflammatory diarrhea.

What organisms are associated with peptic ulcer disease?

Helicobacter pylori; associated with chronic gastritis and gastric malignancy.

What organism causes painless genital ulcers?

Treponema pallidum; primary syphilis produces a chancre.

What organism causes painful genital ulcers?

Haemophilus ducreyi; chancroid.

What organisms commonly cause urethritis and cervicitis?

Neisseria gonorrhoeae and Chlamydia trachomatis.

What organism causes pelvic inflammatory disease and neonatal conjunctivitis?

Chlamydia trachomatis; also causes neonatal pneumonia.

What organism causes greenish vaginal discharge and strawberry cervix?

Trichomonas vaginalis.

What organism causes genital warts?

Human papillomavirus; types 6 and 11 commonly cause condylomata acuminata.

What organism causes congenital infection with cataracts, PDA, and deafness?

Rubella virus.

What viruses cause congenital infection with hearing loss and other neurologic findings?

Cytomegalovirus is a major cause of congenital sensorineural hearing loss.

What organism causes a rash beginning on the head with Koplik spots?

Measles virus; rash spreads downward.

What organism causes rash with postauricular lymphadenopathy?

Rubella virus.

What organism causes croup?

Parainfluenza virus; causes barking cough and inspiratory stridor.

What organism causes bronchiolitis in infants?

Respiratory syncytial virus.

What organism causes epiglottitis with drooling and stridor?

Haemophilus influenzae type b is classic, though other bacteria can cause it.

What are the main mechanisms of beta-lactam antibiotics?

Inhibit penicillin-binding proteins and cross-linking of peptidoglycan.

Which antibiotics inhibit bacterial cell-wall synthesis?

Penicillins, cephalosporins, carbapenems, and monobactams.

What is the mechanism of vancomycin?

Binds D-Ala-D-Ala, inhibiting peptidoglycan synthesis.

What are major adverse effects of vancomycin?

Nephrotoxicity and infusion-related flushing (red-man syndrome).

What is the mechanism of aminoglycosides?

Bind 30S, inhibit initiation, and cause misreading of mRNA; bactericidal.

Why are aminoglycosides ineffective against anaerobes?

Their uptake into bacteria requires oxygen.

What are major aminoglycoside adverse effects?

Nephrotoxicity, ototoxicity, and neuromuscular blockade.

What is the mechanism of tetracyclines?

Bind 30S and prevent aminoacyl-tRNA attachment; bacteriostatic.

What are major tetracycline adverse effects?

Photosensitivity, teeth discoloration, and inhibition of bone growth.

What is the mechanism of macrolides?

Bind 50S and inhibit translocation.

What are major macrolide adverse effects?

GI upset, QT prolongation, and drug interactions with some agents.

What is the mechanism of clindamycin?

Binds 50S and inhibits protein synthesis.

What serious infection is associated with clindamycin?

Clostridioides difficile-associated colitis.

What is the mechanism of chloramphenicol?

Inhibits peptidyl transferase on the 50S ribosomal subunit.

What are major chloramphenicol adverse effects?

Aplastic anemia and gray baby syndrome.

What is the mechanism of fluoroquinolones?

Inhibit DNA gyrase and topoisomerase IV.

What are major fluoroquinolone adverse effects?

Tendinopathy, cartilage toxicity, QT prolongation, and CNS effects.

What is the mechanism of trimethoprim-sulfamethoxazole?

Sequentially inhibits bacterial folate synthesis.

What are major TMP-SMX adverse effects?

Rash, bone marrow suppression, hyperkalemia, and hemolysis in G6PD deficiency.

What is the mechanism of metronidazole?

Reduced metabolites damage DNA in anaerobic organisms and certain protozoa.

What are characteristic adverse effects of metronidazole?

Metallic taste and a disulfiram-like reaction with alcohol.

What is the mechanism of rifampin?

Inhibits DNA-dependent RNA polymerase.

What are characteristic rifampin effects?

Orange-red body fluids and potent induction of hepatic drug-metabolizing enzymes.

What is the mechanism of linezolid?

Binds 50S and prevents formation of the initiation complex.

What are major linezolid adverse effects?

Thrombocytopenia, bone marrow suppression, and serotonin syndrome risk.

What is the mechanism of daptomycin?

Depolarizes bacterial cell membranes; active against many Gram-positive organisms.

Why is daptomycin not used for pneumonia?

Pulmonary surfactant inactivates it.

What is the mechanism of amphotericin B?

Binds ergosterol and forms membrane pores.

What are major amphotericin B adverse effects?

Nephrotoxicity, electrolyte wasting, and infusion reactions.

What is the mechanism of azole antifungals?

Inhibit ergosterol synthesis by blocking fungal 14-alpha-demethylase.

What is the mechanism of echinocandins?

Inhibit beta-1,3-D-glucan synthesis in the fungal cell wall.

What is the mechanism of flucytosine?

Converted within fungi to metabolites that inhibit DNA and RNA synthesis.

What is the mechanism of acyclovir?

Guanosine analog activated by viral thymidine kinase; inhibits viral DNA polymerase.

What is the mechanism of ganciclovir?

Inhibits viral DNA polymerase after activation; used against CMV.

What is the mechanism of oseltamivir?

Inhibits influenza neuraminidase, reducing viral release.

What is the mechanism of nucleoside reverse transcriptase inhibitors (NRTIs)?

Terminate viral DNA synthesis after incorporation by reverse transcriptase.

What is the mechanism of non-nucleoside reverse transcriptase inhibitors (NNRTIs)?

Allosterically inhibit HIV reverse transcriptase.

What is the mechanism of HIV integrase inhibitors?

Block integration of viral DNA into the host genome.

What is the mechanism of protease inhibitors against HIV?

Block viral polyprotein cleavage and maturation.

Which antiretroviral drug requires HLA-B*5701 screening?

Abacavir; the allele increases risk of hypersensitivity.

Which antiretroviral combination can be used for HIV pre-exposure prophylaxis?

Tenofovir plus emtricitabine.

Which antimicrobials should generally be avoided during pregnancy because of fetal risks?

Tetracyclines, fluoroquinolones, aminoglycosides, and ribavirin; consider the specific drug and clinical context.