Infectious Diseases II

Resistance Genes

Species

Recommended Therapy

Alternative Therapy

OXA β-lactamasea

P. aeruginosa and

Enterobacterales

Colistin/polymyxin B

Carbapenemb

Ceftazidime-avibactamc

Cefiderocol

OXA β-lactamasea

A. baumannii

Minocycline + high-dose

ampicillin-sulbactam

Sulbactam/durlobactam + a

carbapenem

Cefiderocol

Colistin/polymyxin B

Tigecycline

Eravacycline

Carbapenemb

aResistance mechanisms associated with gram-negative pathogens are more complicated. Often, there is more than one resistance mechanism. Hence, the recommended

therapies represent reasonable empiric approaches before full antimicrobial susceptibility reports. However, therapy may be tailored to either a broader or a narrower

spectrum (Clin Infect Dis. 2024 Aug 7:ciae403).

bCarbapenem may have a higher MIC in the presence of OXA β-lactamase. If using carbapenem, may consider using maximal doses.

cNot active against metallo-β-lactamases.

Patient Case

A 54-year-old man is admitted to the medical ICU with acute necrotizing pancreatitis. He is found to have

an infected pancreatic abscess, which is being treated with meropenem and vancomycin. One week into

the course, the patient develops a fever and leukocytosis. He also becomes hemodynamically unstable and

oliguric. He is initiated on caspofungin empirically to cover for possible invasive candidiasis. Blood cul-

tures are obtained, which become positive with a preliminary result of yeast. This institution is equipped

with PNA FISH technology, which identifies the yeast as Candida parapsilosis on day 2 of therapy. The

patient remains hemodynamically unstable. Which is the most appropriate choice for this patient’s antifun-

gal therapy?

amplification)

Assays are targeting DNA sequence for the toxin A or toxin B gene.

Sensitivity and specificity: 90%–96%

Because of increased sensitivity, the false-positive rates may be increased.

As the prevalence of C. difficile decreases, the positive predictive value decreases, which may lead

to unnecessary overtreatment.

Educational efforts should be made to discourage the practice of over-ordering C. difficile rapid

nucleic acid amplification tests. In addition, clinicians should be discouraged from ordering

serial tests, which was a common practice when enzyme immunoassays were used. Because the

sensitivity is sufficiently high, serial ordering only furthers the chance of false positivity.

Genes from Rapid Diagnostic Tests for Positive Blood Culturesa (continued)