Mechanisms of Resistance
Microbiology & Susceptibility Reporting Pearls
Name that bug!
Name that drug (or class of drugs)!
Viruses that are NOT COVID!
100
Penicillin, when discovered, was used routinely to treat infections caused by Staphylococcus aureus. Resistance developed quickly to penicillin via this mechanism.
What is a beta-lactamase? Or penicillinase?
100
Streptococcus pneumoniae grows from a lower respiratory culture. Based on the susceptibilities below, what antibiotic would you recommend, with the goal to target this organism with an agent with the most narrow spectrum possible?
--------
Ceftriaxone-Meningitis Susceptible
Ceftriaxone-Non-meningitis Susceptible
Levofloxacin Susceptible
Penicillin-Meningitis Resistant
Penicillin-Non-meningitis Susceptible
Penicillin-Oral Intermediate
Tetracycline Resistant
TMP/SMX Resistant
Vancomycin Susceptible
PO Amoxicillin high-dose
CLSI Breakpoints:
Penicillin nonmeningitis <2 (Intermediate=4, R>8)
Pencillin meningitis < 0.06 (no I range, R>0.12)
Penicillin oral < 0.06 (Intermediate 0.12-1, R>2)
100
Gentamicin is the preferred treatment for this infection, for which prairie dogs are a reservoir. The last urban outbreak of this disease in the United States occurred in Los Angeles in 1924-1925.
What is the plague (Yersinia pestis)?
100
This drug is associated with temporary reddish-orange discoloration of bodily fluids and skin and should never be used alone as antimicrobial therapy.
What is rifampin?
100
This highly contagious vaccine-preventable virus causes fever, cough, and coryza followed by a rash. It can also cause subacute sclerosing panencephalitis, a delayed progressive neurodegenerative disease that develops years after initial infection.
What is measles?
200
This is the chromosomally-mediated mechanism by which bacteria such as Enterobacter cloacae complex and Citrobacter freundii develop resistance to many beta-lactams including 3rd generation cephalosporins after being exposed to them (i.e. ceftriaxone). Cefepime is the drug of choice for these organisms.
What is Amp-C beta-lactamase?
200
The hemolysis pattern displayed by Group A (Streptococcus pyogenes) and Group B (Streptococcus agalactiae) strep.
What is beta-hemolysis? (AKA complete hemolysis)
Alpha: incomplete
Gamma: nonhemolytic
200
This gram-negative organism can cause ostearticular infections in babies and toddlers and is difficult to grow in culture, generally requiring a PCR for identification.
What is Kingella kingae?
200
This antibiotic is the treatment of choice for community-onset sepsis, but it was traditionally avoided in infants under one month of age due to risk of hyperbilirubinemia.
What is ceftriaxone?
Ceftriaxone can be used safely in young infants. SLCH criteria for use are:
-Gestational age: ≥ 35 weeks
-Postnatal age: ≥ 7 days
-Baseline total serum bilirubin: < 5 mg/dL
-Baseline albumin WNL for GA
-not receiving calcium-containing fluids
200
Approximately 20% of all hearing loss at birth is attributable to this herpes virus.
What is cytomegalovirus?
300
This mechanism of resistance in gram-negative organisms results in hydrolysis of most beta-lactams, except carbapenems. Therefore for severe infections, carbapenems are the drug of choice. This resistance mechanism most commonly originates in the community.
What is ESBL (extended-spectrum beta-lactamase)?
300
A drug/drug class and antibacterial combination that has a susceptible dose dependent (SDD) category that indicates susceptibility of an isolate depends on the dosing regimen that is used in the patient. Name one.
What is Enterobacterales and cefepime?
What is Staphylococcus aureus and ceftaroline?
What is Enterococcus faecium and daptomycin?
300
This bug is the one most frequently implicated in infectious caused by carbapenemase-producing carbapenem resistant Enterobacterales (CP-CRE) in the United States.
What is Klebsiella pneumoniae?
300
This drug is a broad-spectrum antifungal, but Candida lusitaniae is inherently resistant to it.
What is amphotericin B?
300
This virus can lead to hemorrhagic cystitis in patients after allogeneic bone marrow transplantation or nephropathy in renal transplant recipients.
What is BK virus?
AKA Polyomavirus hominis 1
Fun Fact: it was first isolated in 1971 from the urine of a renal transplant recipient with the initials B.K.
400
Penicillin resistance to Streptococcus pneumoniae is most commonly mediated by this mechanism of resistance.
What is reduced penicillin-binding-protein (PBP) binding affinity or alteration in PBPs?
400
Enterococcus faecalis that is reported susceptible to ampicillin can be assumed to be susceptible to this carbapenem
What is imipenem/cilastatin?
400
This organism is a filamentous gram-positive bacillus that has a positive modified acid-fast stain. It typically affects immunocompromised patients and has an affinity for the brain. The treatment of choice is sulfamethoxazole/ trimethoprim and sometimes requires combination therapy for severe disease.
What is Nocardia species?
400
This specific class of antibiotics provides broad antibacterial coverage and has a significant drug-drug interaction with valproic acid that results in a drastic decrease in valproic acid levels.
What are carbapenems?
400
This virus causes noncardiogenic pulmonary edema and hemodynamic collapse in patients with rodent exposure in the Southwestern United States.
What is hantavirus or Sin Nombre Virus?
500
This is the mechanism that mediates low-level resistance to vancomycin in Enterococcus gallinarum and E. casseliflavus. (Hint: This is not the same as the mechanism that mediates high-level vancomycin resistance in E. faecium or E. faecalis)
What is VanC?
500
The smell of this food item may be associated with Streptococcus anginosus group (AKA Streptococcus milleri group).
What is caramel or butterscotch?
500
This anaerobic gram-positive organism can be a cause of lung abscess associated with severe halitosis.
What is Finegoldia magna?
500
This antibiotic is new to the beta-lactam family, known as a siderophore. It has a unique mechanism of action that takes advantage of iron transport systems in outer membrane of gram-negative bacilli.
What is cefiderocol?
500
B cell defects can lead to recurrent or chronic central nervous system infections with this type of virus.
What is enterovirus?