Natural Antibiotic Resistances of Raoultella planticola
Raoultella planticola demonstrates intrinsic resistance to ampicillin, which is a consistent characteristic across nearly all isolates and should be considered when selecting empirical antibiotic therapy. 1, 2
Intrinsic (Natural) Resistance Pattern
Ampicillin resistance is the hallmark natural resistance of R. planticola, documented in 35 of 37 isolates (94.6%) in a large retrospective study, confirming this as an intrinsic characteristic rather than acquired resistance 1
Resistance to aminopenicillins extends beyond ampicillin to include amoxicillin/clavulanic acid in environmental isolates, though clinical isolates may show variable susceptibility to beta-lactamase inhibitor combinations 2
Additional intrinsic resistances documented in environmental strains include oxacillin, penicillin, vancomycin (as expected for Gram-negative organisms), erythromycin, and rifampin 2
Antibiotics with Preserved Susceptibility
Carbapenems maintain excellent activity, with imipenem susceptibility at 99.0% and meropenem at 98.1% across tested strains, making these reliable options for serious infections 3
Fluoroquinolones remain highly effective, with ciprofloxacin susceptibility at 92.4% and documented as the most frequently prescribed antibiotic in clinical practice for R. planticola UTIs 1, 3
Aminoglycosides show strong activity, with gentamicin susceptibility at 93.3%, though resistance can develop in environmental isolates exposed to heavy metals 3, 4
Third-generation cephalosporins are generally effective, with no documented resistance in clinical bacteremia cases, though ESBL-producing strains (12.4% prevalence) would be resistant 3, 5
Important Clinical Considerations
Multidrug resistance remains uncommon but emerging, with only 2 of 37 clinical isolates showing multidrug resistance patterns, though these remained susceptible to ciprofloxacin 1
ESBL production occurs in approximately 12.4% of strains, conferring resistance to third-generation cephalosporins and aztreonam while maintaining carbapenem susceptibility 3
Environmental isolates may harbor broader resistance than clinical isolates, including resistance to piperacillin, piperacillin/tazobactam, aztreonam, imipenem, and ticarcillin combinations, suggesting potential for resistance acquisition 2
Key Pitfalls to Avoid
Never use ampicillin or other aminopenicillins as monotherapy for suspected or confirmed R. planticola infections, as intrinsic resistance renders these ineffective 1, 2
Do not assume susceptibility to beta-lactam/beta-lactamase inhibitor combinations without testing, as resistance patterns vary between clinical and environmental isolates 2
Automated identification systems may misidentify Raoultella species, requiring 16S rRNA sequencing for definitive identification when clinical significance is uncertain 4