Which Enterobacteriaceae organism is characteristically INDOLE-POSITIVE and produces urease, making it a common cause of urinary tract infections and Proteus mirabilis-like swarming colonies on agar?

Explanation

## Morganella morganii: Biochemical Identification **Key Point:** Morganella morganii is an indole-positive, urease-positive Enterobacteriaceae that produces the characteristic swarming motility pattern on agar plates, similar to *Proteus* species. ### Biochemical Differentiation of Urease-Positive Enterobacteriaceae | Organism | Indole | Urease | H~2~S | Motility | Swarming | Clinical Association | |---|---|---|---|---|---|---| | *Proteus mirabilis* | **−** | **+** | **+** | **+** | **Yes** | UTI, catheter-associated | | *Morganella morganii* | **+** | **+** | **−** | **+** | **Yes** | UTI, wound/blood cultures | | *Providencia* spp. | **+** | **−** | **−** | **+** | No | Nosocomial infections | | *Klebsiella pneumoniae* | **−** | **−** | **−** | **−** | No | Pneumonia, sepsis | **High-Yield:** The combination of **indole-positive + urease-positive + swarming motility** is pathognomonic for *Morganella morganii*. This distinguishes it from *Proteus mirabilis* (indole-negative) and other Enterobacteriaceae. **Clinical Pearl:** *Morganella morganii* is an opportunistic pathogen associated with UTIs, particularly in hospitalized and catheterized patients. It can produce extended-spectrum β-lactamases (ESBLs) and is often multidrug-resistant. **Mnemonic:** **Morganella = Motile + Morgani** (indole-positive, urease-positive, swarming); **Proteus = Proteus** (urease-positive but indole-negative, H~2~S-positive).