Alcaligenes faecalis Infection: Source and Management
Primary Infection Source
Alcaligenes faecalis is an environmental gram-negative bacterium transmitted primarily through contaminated water sources, hospital ventilation equipment, nebulizers, and direct contact with wet hospital surfaces. 1, 2
Environmental Reservoirs
- Water and soil saprophyte commonly recovered from moist hospital environments 3
- Droplet transmission occurs through ventilation systems and respiratory equipment 2
- Direct contact transmission documented through contaminated medical devices and wet surfaces 2
Clinical Presentation Patterns
Most Common Infection Sites (in descending order)
- Urinary tract infections (cystitis and acute pyelonephritis): 52.5% of cases 1
- Skin and soft tissue infections (diabetic foot, purulent wounds): 70.8% from purulent material 1, 3
- Respiratory tract infections (pneumonia, including cavitary lesions) 1, 2
- Bloodstream infections (bacteremia): rare but life-threatening 1, 4
- Other sites: meningitis, endocarditis, endophthalmitis 2, 5
High-Risk Patient Characteristics
- Recent intravenous antibiotic exposure within 3 months: 60.7% of infected patients 1
- Mixed bacterial infections: 83.6% of cases involve co-pathogens 1
- Hospitalized patients, particularly in surgical wards (30%) and dermatology units (14%) 3
- Immunocompromised hosts, though immunocompetent cases increasingly reported 5
Antimicrobial Management
First-Line Treatment Options
For susceptible isolates, carbapenems (imipenem or meropenem) remain the most reliable agents with 66.7% susceptibility rates, though resistance is rapidly emerging. 1
Preferred Antibiotics (based on 2019-2020 data)
- Carbapenems: Imipenem or meropenem (66.7% susceptibility) 1
- Ceftazidime: 66.7% susceptibility 1
- Piperacillin/tazobactam: Historically 100% sensitive, now <50% 1, 3
Antibiotics with Poor Activity
- Ciprofloxacin: <50% susceptibility 1
- Co-trimoxazole: 57.1% susceptibility 3
- Aztreonam: Only 22.2% susceptibility 3
Extensively Drug-Resistant (XDR) and Pandrug-Resistant (PDR) Infections
For pandrug-resistant A. faecalis bloodstream infections, double-dose tigecycline (200 mg loading dose, then 100 mg IV twice daily) successfully eradicated infection despite in vitro resistance. 4
Salvage Therapy Strategy
- Double-dose tigecycline maintains higher serum concentrations that overcome MIC resistance 4
- Treatment duration: Minimum 5 days for bloodstream clearance, extend based on clinical response 4
- Monitor closely: PDR strains now resistant to polymyxins, carbapenems, and standard-dose tigecycline 4, 2
Critical Clinical Pitfalls
- Never assume susceptibility patterns from older data: Resistance rates have dramatically increased since 2018, with XDR strains now common 1
- Always obtain culture and susceptibility testing: 83.6% of infections are polymicrobial, requiring tailored therapy 1
- Do not rely on fluoroquinolones empirically: Ciprofloxacin resistance is widespread 1
- Consider double-dose tigecycline early for critically ill patients with suspected PDR strains while awaiting susceptibilities 4
Site-Specific Considerations
Urinary Tract Infections
- Carbapenems or ceftazidime for susceptible strains 1
- Duration: 7-14 days for cystitis, 14-21 days for pyelonephritis
Pneumonia and Respiratory Infections
- Avoid tigecycline monotherapy at standard doses due to poor lung penetration in XDR cases 2
- Combination therapy with carbapenem plus double-dose tigecycline for cavitary lesions 2
Bloodstream Infections
- Minimum 14 days of IV therapy after blood culture clearance 4
- Source control is essential; remove infected catheters and drain abscesses 4
Emerging Resistance Patterns
Extensively drug-resistant A. faecalis emerged in 2018, with susceptibility to commonly used antibiotics declining from near-universal to 66.7% for even the most effective agents. 1