Enterobacter hormaechei

Enterobacter hormaechei is Gram-negative bacterial species in the family Enterobacteriaceae and a member of the Enterobacter cloacae complex. It is an opportunistic pathogen associated mainly with healthcare-associated infections, particularly in hospitalized or immunocompromised patients.

Taxonomy

Enterobacter hormaechei was first described in 1989 and was originally known as Enteric Group 75. The type strain is ATCC 49162. The species was named after Estenio Hormaeche, a microbiologist from Uruguay.

Enterobacter hormaechei is part of the Enterobacter cloacae complex. This complex includes several closely related Enterobacter species that can be hard to tell apart using standard laboratory tests. Several subspecies have been described, including E. hormaechei subsp. hormaechei, oharae, steigerwaltii, hoffmannii, and xiangfangensis.

Characteristics

Enterobacter hormaechei is a Gram-negative, oxidase-negative, fermentative, non-pigmented rod-shaped bacterium with the general characteristics of the family Enterobacteriaceae and the genus Enterobacter.

Clinical significance

Enterobacter hormaechei is an opportunistic pathogen associated mainly with healthcare-associated infections. It has been isolated from clinical specimens including blood, sputum, urine, bile, stool, wounds, and other body sites. Reported infections include bacteraemia, pneumonia, urinary tract infections, biliary tract infections, colitis, and cellulitis.

Antimicrobial resistance is a major concern in E. hormaechei. Resistant isolates producing extended-spectrum β-lactamases, AmpC β-lactamases, and carbapenemases have been reported in several countries. Whole-genome sequencing has improved the identification of E. hormaechei within the Enterobacter cloacae complex and has helped clarify its role in multidrug-resistant hospital-associated infections.

Carbapenem-resistant strains of E. hormaechei have been implicated in healthcare-associated outbreaks. In 2026, a multicountry outbreak of E. hormaechei sequence type 1344 carrying blaNDM-5 was reported in the European Union and European Economic Area. The outbreak involved 57 cases detected between March 2025 and April 2026 in seven EU/EEA countries; many patients were hospitalized, and the source had not been identified at the time of publication.