What is the appropriate treatment for a male patient with a urinary tract infection (UTI) caused by Morganella morganii, a gram-negative bacteria?

Morganella morganii in Male UTI: Bacterial Classification and Treatment

Morganella morganii is a Gram-negative, facultative anaerobic bacillus belonging to the Enterobacteriaceae family (tribe Proteeae), and represents an opportunistic uropathogen that requires targeted antibiotic therapy based on susceptibility testing due to its intrinsic and acquired resistance patterns. 1, 2, 3

Bacterial Classification and Characteristics

• M. morganii is a Gram-negative rod-shaped bacterium previously classified as Proteus morganii, divided into two subspecies (morganii and sibonii), and belongs to normal human gut commensal microbiota 4, 3
• This organism is an opportunistic pathogen that primarily causes urinary tract infections and post-operative wound infections, particularly in hospitalized patients with compromised immune systems 5, 4, 3
• The microbial spectrum in male UTIs includes M. morganii alongside E. coli, Proteus species, Klebsiella species, Pseudomonas species, and Enterococcus species, with higher rates of antimicrobial resistance compared to uncomplicated female cystitis 6, 7

Antibiotic Resistance Profile

• M. morganii demonstrates universal resistance to first-generation cephalosporins (cephalothin) and high resistance rates to cefuroxime (90.5%) and amoxicillin-clavulanate (95.9%) 8
• The organism shows intrinsic resistance to tigecycline despite its activity against other Enterobacteriaceae, making it unsuitable for M. morganii infections 9
• Susceptibility patterns show that 95.8% of isolates are susceptible to ceftazidime, though 19.4% demonstrate imipenem resistance 8
• Clinical isolates frequently exhibit resistance to ciprofloxacin, trimethoprim-sulfamethoxazole, gentamicin, amoxicillin, nitrofurantoin, and colistin, with multidrug resistance increasingly common 5, 10
• The FDA drug label confirms that trimethoprim-sulfamethoxazole is indicated for UTIs caused by M. morganii, though local resistance patterns must be considered 1

Recommended Treatment Approach for Male UTI

Obtain urine culture and susceptibility testing before initiating empiric therapy, as M. morganii resistance patterns are highly variable and inappropriate antibiotic treatment is the only independent risk factor for mortality (odds ratio 4.8). 6, 7, 8

First-Line Empiric Therapy (Pending Culture Results)

• Trimethoprim-sulfamethoxazole 160/800 mg twice daily for 14 days is the preferred first-line agent when local fluoroquinolone resistance is <10% and the patient has no recent fluoroquinolone exposure 6, 7, 1
• Ciprofloxacin 500-750 mg twice daily for 14 days is an alternative if TMP-SMX resistance exceeds 10% locally or if allergies exist, though resistance to fluoroquinolones is increasingly common in M. morganii 6, 7, 2
• Levofloxacin 750 mg once daily for 14 days provides convenient once-daily dosing with similar efficacy 7

Parenteral Therapy for Severe Presentations

• Initiate intravenous ciprofloxacin 400 mg twice daily or levofloxacin 750 mg once daily for patients with systemic symptoms, fever, or suspected pyelonephritis 7
• Ceftazidime 1-2 g three times daily is highly effective against M. morganii (95.8% susceptibility) and should be considered when fluoroquinolone resistance is suspected 7, 8
• Carbapenems (meropenem 1 g three times daily or imipenem-cilastatin 0.5 g three times daily) are the most frequently used and effective treatment for M. morganii bacteremia, with universal susceptibility reported in systematic reviews 5, 4

Culture-Directed Therapy

• Gentamicin in combination with third-generation cephalosporin (after testing for AmpC β-lactamase production) is recommended as definitive therapy based on systematic review evidence 4
• Amikacin demonstrates high susceptibility rates and should be considered for multidrug-resistant isolates 5, 4
• Ceftazidime-avibactam 2.5 g three times daily or meropenem-vaborbactam 2 g three times daily are reserved for confirmed resistant organisms 6, 7

Treatment Duration

• Standard duration is 14 days for male UTIs when prostatitis cannot be excluded, which applies to most presentations 6, 7
• A shorter duration of 7 days may be considered only if the patient becomes afebrile within 48 hours and shows clear clinical improvement, though subgroup analysis showed 7-day ciprofloxacin was inferior to 14-day therapy for clinical cure in men (86% vs 98%, p=0.025) 6

Critical Management Considerations

• Inappropriate antibiotic treatment is the only independent risk factor for mortality (odds ratio 4.8, p=0.002) in M. morganii bacteremia 8
• The in-hospital mortality rate for M. morganii bacteremia is 41%, with increased risk in ICU patients, those older than 65 years, and those with Klebsiella pneumoniae co-infection 5
• Polymicrobial bacteremia occurs in 45.2% of cases, with hepatobiliary tract being the major portal of entry in polymicrobial infections (30.3%) versus urinary tract in monomicrobial infections (47.5%) 8
• Source control measures including catheter removal, drainage, or surgical intervention are essential components of management 5

Common Pitfalls to Avoid

• Never use tigecycline for M. morganii infections despite its activity against other Enterobacteriaceae, as it lacks in vitro activity against this organism 9
• Avoid empiric use of amoxicillin-clavulanate due to 95.9% resistance rates 8
• Do not use first or second-generation cephalosporins (cephalothin, cefuroxime) due to universal or near-universal resistance 8
• Failing to obtain pre-treatment cultures complicates management if empiric therapy fails, particularly given the high rates of multidrug resistance 6, 7, 10
• Inadequate treatment duration (<7 days) leads to persistent or recurrent infection, particularly when prostate involvement cannot be excluded 6
• Avoid fluoroquinolones as first-line agents when other effective options are available, especially given FDA warnings about disabling adverse effects and increasing resistance rates in M. morganii 6, 5