Treatment of Coccobacilli Infections
The treatment approach for coccobacilli infections depends critically on identifying the specific organism, as "coccobacilli" describes a morphologic appearance shared by multiple pathogens with vastly different antimicrobial susceptibilities and clinical implications.
Immediate Diagnostic Priorities
The term "coccobacilli" on Gram stain is descriptive, not diagnostic. Your immediate priority is organism identification through culture and susceptibility testing, as treatment varies dramatically:
HACEK Group Organisms (Most Common in Endocarditis)
- For infective endocarditis caused by HACEK organisms (Haemophilus, Aggregatibacter, Cardiobacterium, Eikenella, Kingella), treat with ceftriaxone or another third-generation cephalosporin alone for 4 weeks, or ampicillin plus gentamicin 1
- These fastidious gram-negative coccobacilli are the most common gram-negative cause of pediatric endocarditis 1
- This represents a Class I recommendation with Level C evidence from the American Heart Association 1
Other Gram-Negative Coccobacilli
For non-HACEK gram-negative coccobacilli causing serious infections:
- Use an extended-spectrum penicillin (piperacillin/tazobactam) or extended-spectrum cephalosporin (ceftazidime, ceftriaxone, or cefotaxime) combined with an aminoglycoside for minimum 6 weeks 1
- Choice must be guided by antibiotic susceptibility testing and infectious diseases consultation 1
- These organisms (E. coli, Pseudomonas, Serratia) may be nosocomially acquired with unpredictable resistance patterns including extended-spectrum β-lactamases 1
Acinetobacter Species
If Acinetobacter baumannii is identified (rare in community settings but possible):
- These gram-negative coccobacilli are intrinsically multidrug-resistant 2
- Community-acquired cases may respond to fluoroquinolones like levofloxacin 3
- Hospital-acquired infections often require colistimethate sodium, tigecycline, or minocycline due to extensive resistance 2
- Combination antimicrobial therapy is typically necessary for multidrug-resistant strains 2
Yersinia pestis (Bubonic Plague)
If plague is suspected based on epidemiology:
- Streptomycin 15 mg/kg IM every 12 hours or gentamicin 1.5 mg/kg IV every 8 hours for severe cases 1
- Doxycycline 100 mg twice daily orally for mild cases 1
- Diagnose by Gram stain and culture of aspirated lymph node material 1
- Notify microbiology laboratory immediately if suspected 1
Francisella tularensis (Tularemia)
If tularemia is suspected:
- Streptomycin 15 mg/kg IM every 12 hours or gentamicin 1.5 mg/kg IV every 8 hours for severe cases 1
- Tetracycline 500 mg four times daily or doxycycline 100 mg twice daily orally for mild cases 1
- Serologic tests are preferred for diagnosis 1
Burkholderia mallei (Glanders)
If glanders is suspected (rare, occupational exposure to horses):
- Ceftazidime, gentamicin, imipenem, doxycycline, or ciprofloxacin based on in vitro susceptibility 1
Critical Pitfalls to Avoid
- Never assume all gram-negative coccobacilli are the same organism - resistance patterns and optimal therapy differ dramatically between species 1, 2
- Do not use vancomycin for Erysipelothrix rhusiopathiae (another coccobacillus causing erysipeloid), as it is intrinsically resistant 1
- Always obtain infectious diseases consultation for serious infections caused by unusual gram-negative coccobacilli, especially with prosthetic material involvement 1
- Consider extended-spectrum β-lactamase production in nosocomial gram-negative coccobacilli infections, which renders many cephalosporins and penicillins ineffective 1
When to Escalate Therapy
- Prosthetic valve endocarditis from any gram-negative coccobacillus typically requires valve replacement surgery in addition to prolonged antibiotics 1
- Rapidly progressive infections warrant broader empiric coverage until organism identification 1
- Failure to improve on initial therapy within 48-72 hours mandates reassessment of organism identification and susceptibility 3