Enterococcus hirae is a species of bacteria belonging to the Enterococcus genus, known for its resilience. This microbe commonly inhabits the gastrointestinal tracts of many animals, including livestock and poultry. While usually harmless, E. hirae can cause disease, particularly in animals, and its presence contributes to public health concerns. The bacterium’s ability to acquire antibiotic resistance genes makes it an organism of significant interest in both veterinary and human medicine.
Basic Identity and Environmental Presence
Enterococcus hirae is classified as a Gram-positive coccus, meaning it is a spherical bacterium that retains the crystal violet stain used in laboratory testing. Like other members of its genus, it is a facultative anaerobe, capable of surviving in environments both with and without oxygen. This adaptability allows it to thrive in natural settings, including soil, water, food products, and wastewater. E. hirae is distinct from the more common human pathogens E. faecalis and E. faecium, requiring specific biochemical tests or DNA analysis for identification. For example, E. hirae is often the predominant Enterococcus species found in cattle, while the other two species are more frequently associated with humans.
Primary Role in Animal Health
The greatest impact of E. hirae is observed in veterinary medicine, where it is a recognized pathogen, particularly in agricultural settings. The bacterium commonly causes infectious disease in livestock and poultry, including chickens, turkeys, pigs, and cattle, often manifesting as systemic illnesses. In young animals, such as piglets and poultry, infection can cause septicemia, a severe bloodstream infection, or localized issues like diarrhea. It is also a causative agent of endocarditis in chickens and mastitis in dairy cattle. The widespread use of antibiotics in animal husbandry has contributed to the selection of drug-resistant strains, complicating effective treatment.
Clinical Relevance in Humans and Treatment Challenges
E. hirae is less frequently isolated from human clinical samples than E. faecalis and E. faecium, but it is an opportunistic pathogen that causes serious infections in vulnerable individuals. Cases typically occur in those who are immunocompromised, have underlying illnesses, or are neonates. Reported human infections include bacteremia, urinary tract infections (UTIs), and more severe conditions like endocarditis and meningitis.
A significant challenge in treatment is the inherent and acquired resistance mechanisms present in the bacteria. E. hirae possesses intrinsic resistance to several antibiotic classes, including cephalosporins, and can acquire genes that confer vancomycin resistance (VRE).
When infection is suspected, laboratory testing is crucial to determine the antibiotic susceptibility profile of the isolated strain. Ampicillin is often the first-line treatment if the strain is susceptible, but multidrug resistance limits options, forcing reliance on alternatives like linezolid or daptomycin.