Citrobacter youngae Infection Treatment
Empiric Therapy for Serious Infections
For serious Citrobacter youngae infections requiring empiric therapy, initiate a third-generation cephalosporin (ceftriaxone 2 g IV once daily or ceftazidime 2 g IV every 8 hours) or a fluoroquinolone (ciprofloxacin 400 mg IV every 12 hours), pending susceptibility results. 1, 2
Citrobacter species, including C. youngae, are Gram-negative Enterobacteriaceae that can cause serious nosocomial infections, particularly in patients with underlying conditions or following instrumentation. 3, 4
The empiric regimen should mirror that used for other Gram-negative enteric organisms causing complicated urinary tract infections or bacteremia, with carbapenems (meropenem 1 g IV every 8 hours or imipenem 500 mg IV every 6 hours) reserved for multidrug-resistant strains or ESBL producers. 1, 2, 5
Always obtain blood and urine cultures with susceptibility testing before initiating antibiotics to enable targeted therapy, as Citrobacter species exhibit variable resistance patterns including β-lactamases, fluoroquinolone resistance, and occasionally carbapenem resistance. 1, 2, 3
Definitive Therapy Based on Susceptibility
Once susceptibility results are available, narrow therapy to the most appropriate agent: ceftazidime plus ciprofloxacin was successfully used in a documented case of C. youngae bacteremia with osteomyelitis. 4
For susceptible isolates, a fluoroquinolone (ciprofloxacin 500–750 mg PO twice daily or levofloxacin 750 mg PO once daily) or trimethoprim-sulfamethoxazole (160/800 mg PO twice daily) can be used for oral step-down therapy. 6, 2
Treatment duration should be 7–14 days for complicated urinary tract infections, with 14 days preferred when bacteremia is present, clinical response is delayed, or deep-seated infection (such as osteomyelitis or abscess) cannot be excluded. 1, 2, 4
Uncomplicated Urinary Tract Infection
For uncomplicated cystitis caused by Citrobacter youngae in otherwise healthy women, treat with a 3-day course of trimethoprim-sulfamethoxazole (160/800 mg twice daily) if local resistance is <20%, or a 5-day course of nitrofurantoin (100 mg twice daily) as an alternative. 6, 7
Although Citrobacter urinary tract infections are uncommon in the general population, they occur more frequently in children with underlying urological anomalies or neurologic impairment, and in adults with instrumentation or immunocompromise. 3, 8
Fosfomycin 3 g as a single oral dose is an acceptable alternative for uncomplicated cystitis when first-line agents cannot be used, though data specific to Citrobacter are limited. 6
Fluoroquinolones (ciprofloxacin 250 mg twice daily for 3 days) should be reserved for culture-proven resistant organisms or when first-line agents are contraindicated, given rising resistance rates and serious adverse effects. 6, 7
Critical Management Considerations
Address any underlying urological abnormalities (obstruction, foreign body, incomplete voiding, recent instrumentation) because antimicrobial therapy alone is insufficient without source control. 1, 2
Citrobacter species can acquire antimicrobial resistance through chromosomal and plasmid-mediated mechanisms, including ESBLs, AmpC β-lactamases, carbapenemases, and fluoroquinolone resistance genes, limiting empiric treatment options. 3, 5
Do not use amoxicillin or ampicillin alone for Citrobacter infections, as these organisms often produce chromosomal AmpC β-lactamases conferring resistance to these agents. 1, 5
For nosocomial or healthcare-associated Citrobacter infections, consider broader empiric coverage with piperacillin-tazobactam (3.375–4.5 g IV every 6 hours) or a carbapenem until susceptibility results guide de-escalation. 1, 2
Monitor for treatment failure at 48–72 hours; persistent fever or worsening symptoms warrant imaging to exclude abscess, osteomyelitis, or other deep-seated infection, as documented in the case of C. youngae causing postoperative spondylodiscitis. 2, 4