Bloody diarrhea associated with cytotoxic Aeromonas enteropelogenes harboring act and aerA genes: A case report highlighting diagnostic pitfalls.

Aeromonas enteropelogenes (synonym Aeromonas trota) is a rare cause of human gastroenteritis and is often overlooked because of diagnostic difficulties. We report a case of bloody diarrhea associated with A. enteropelogenes in a woman in her 90s with aplastic anemia. During hospitalization, she developed bloody diarrhea. Stool cultures yielded non-hemolytic colonies on sheep blood agar and sucrose-negative colonies on DHL agar. Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) yielded high scores for both A. enteropelogenes and A. jandaei while an automated identification system identified the isolate as A. veronii complex. Definitive identification was achieved by multilocus phylogenetic analysis (MLPA) using gyrB, rpoD, and gyrA genes. The isolate harbored the cytotoxic enterotoxin (act) and aerolysin (aerA) genes, suggesting the potential to cause mucosal injury. However, the severity of the hemorrhagic symptoms was likely exacerbated by the patient's severe thrombocytopenia. Notably, the strain was susceptible to ampicillin (AMP) but resistant to cefazolin (CZO), a characteristic pattern that distinguishes it from other major Aeromonas species. This case highlights the limitations of routine diagnostic methods, which may lead to an underestimation of this species. AMP susceptibility may serve as an important phenotypic clue, and accurate identification is essential to clarify its epidemiology and pathogenic potential.