An organism isolated from a urine culture has a Gram-negative rod with specific IMViC results. What is the likely organism?

The identification of the organism as Escherichia coli in this scenario is supported by its characteristic features. E. coli is a Gram-negative rod, which aligns with the initial observation of the organism’s morphology from the urine culture.

The IMViC test results—representing Indole, Methyl Red, Voges-Proskauer, and Citrate tests—are particularly helpful for differentiating E. coli from other Enterobacteriaceae. E. coli typically tests positive for indole and methyl red and negative for Voges-Proskauer and citrate utilization, resulting in a distinctive pattern. This set of results is a strong indicator of E. coli, especially in the context of urinary tract infections, where it is a common pathogen.

In contrast, the other organisms listed have different IMViC profiles. For example, Enterobacter cloacae would typically show a negative result for indole and a positive result for the Voges-Proskauer test. Similarly, Klebsiella pneumoniae is also indole negative and generally shows different fermentation characteristics. Serratia marcescens exhibits a positive result for the Voges-Proskauer test, setting it apart from E. coli.

Thus, the specific IMViC pattern observed in