Morganella morganii Susceptible Antibiotics
First-Line Antibiotic Therapy
For invasive Morganella morganii infections, gentamicin combined with a third-generation cephalosporin (such as ceftazidime) represents the most evidence-based treatment approach, with carbapenems (imipenem or meropenem) reserved for documented resistance or critically ill patients. 1, 2
Primary Treatment Regimen
Gentamicin plus third-generation cephalosporin is the most frequently successful combination for M. morganii invasive infections, based on systematic review evidence showing complete recovery in the majority of treated patients 2
Ceftazidime demonstrates high susceptibility rates and should be the preferred third-generation cephalosporin when available 2
Amikacin shows excellent activity against M. morganii isolates and represents an alternative aminoglycoside option 2
The combination approach is critical because M. morganii possesses inducible beta-lactamase (AmpC), which can lead to treatment failure with monotherapy and requires dual coverage to ensure bactericidal activity and prevent resistance induction 2, 3, 4
Carbapenem Therapy
Imipenem and meropenem demonstrate the highest activity against M. morganii isolates, including multidrug-resistant strains 1, 2, 5
Carbapenems should be reserved for documented resistance to first-line agents or critically ill patients, following carbapenem-sparing principles to preserve these agents 1
All M. morganii isolates in one study were susceptible to meropenem and imipenem, making them reliable options when first-line therapy fails 5
Fluoroquinolone Options
Ciprofloxacin shows activity against M. morganii with FDA labeling indicating susceptibility for most strains 6
Levofloxacin is active in vitro against M. morganii with MIC values ≤2 mcg/mL for most isolates 7
However, fluoroquinolone resistance is increasingly common, with recent multicenter data showing ciprofloxacin resistance in M. morganii bloodstream infections 8
Fluoroquinolones should not be used as monotherapy due to the risk of mutational resistance development 6
Antibiotics to Avoid
Trimethoprim/sulfamethoxazole shows high resistance rates in recent surveillance data and should be avoided 8
Colistin resistance has been documented in M. morganii isolates 8
Nitrofurantoin and amoxicillin demonstrate poor activity and should not be used 8
Tigecycline should never be used for M. morganii infections due to intrinsic resistance 1
Treatment Duration and Surgical Considerations
Complicated skin and soft tissue infections require a minimum of 4 months of therapy 1
Bone infections require 6 months of antimicrobial therapy 1
Surgical source control is essential for treatment success in invasive infections, including debridement, drainage, or removal of infected foreign material such as catheters 1
Medical therapy alone has high failure rates when adequate source control is not achieved 1
Critical Clinical Pitfalls
M. morganii is often multidrug-resistant, particularly in nosocomial settings, making empiric therapy challenging 8, 2, 5
All M. morganii isolates should be tested for ESBL production, as all isolates in one study were ESBL producers 5
Mortality rates approach 41% in bloodstream infections, with higher risk in ICU patients, those >65 years, and patients with Klebsiella pneumoniae co-infection 8
Resistance can develop during therapy due to inducible AmpC beta-lactamase, necessitating combination therapy from the outset 2, 3, 4
Susceptibility testing is mandatory for all clinically significant isolates to guide definitive therapy, as resistance patterns vary significantly 2, 5