Enterococci are commensal bacteria of the intestinal microbiota of humans and a wide variety of other animals, including poultry. Enterococci are generally considered opportunistic pathogens, and enterococcosis is an economically important disease in the poultry industry worldwide. The effects of infection by Enterococcus faecalis have become a substantial challenge for the broiler industry.
Enterococci are an important cause of nosocomial and community-acquired infections in humans, and antimicrobial resistance in poultry is a public health concern.
Etiology of Enterococcosis in Poultry
Enterococci are nonmotile, gram-positive, catalase-negative coccoid bacteria that appear singly, in pairs, or in short chains on stained smears.
Enterococcus spp bacteria are a normal component of the microbiota in the intestinal tract of poultry and other bird species. There is a succession of Enterococcus spp within the chicken intestinal tract that appears to be age dependent: E faecalis is usually the first species to colonize the intestines, followed by E faecium and then E cecorum.
Enterococcal bacteria isolated from birds with clinical signs include the following species of Enterococcus:
Some strains of Enterococcus have a beneficial effect on growth and feed efficiency and are used as probiotics.
Enterococcus infections in poultry usually occur secondary to another disease. However, E cecorum has emerged as a major cause of skeletal disease in poultry, especially broiler chickens. E cecorum has been associated with osteomyelitis, including femoral head necrosis, spondylitis, and arthritis in broiler chickens (see Infectious Skeletal Disorders in Poultry Infectious Skeletal Disorders in Poultry Severe enlargement of the free thoracic vertebra caused by vertebral osteomyelitis and arthritis with formation of a large vertebral abscess. Sagittal section showing compression of the spinal... read more ).
Enterococcus infections can result in an acute septicemic phase in which survivors develop subacute or chronic infection with lesions in the cardiovascular or skeletal system. Endocarditis can occur when the infection progresses to a subacute or chronic stage. Brain necrosis and encephalomalacia have been reported in young chickens.
Epidemiology of Enterococcosis in Poultry
Enterococcosis has been reported in a variety of avian species worldwide. For commercial flocks, lesions have resulted in increased condemnation losses.
E faecalis affects birds of all ages; however, infection is especially devastating for embryos and young chicks.
Pathogenic strains of E cecorum are associated with increased mortality rates, poor production, and increased condemnation rates.
Enterococcosis is transmitted via the oral or aerosol route, as well as from skin wounds.
The transmission route for E cecorum is not entirely understood; however, oral and aerosol routes have been proposed, as for other enterococcal species. The horizontal transmission of pathogenic strains of E cecorum between and within flocks is rapid in commercial operations.
Clinical Findings of Enterococcosis in Poultry
In the acute form of enterococcosis, clinical signs are related to septicemia and include listlessness, lethargy, ruffled feathers, diarrhea, and a decrease in egg production. In the subacute or chronic form, listlessness, lameness, and head tremors may be noted.
If enterococcosis is not treated, most affected birds die.
The most prominent sign of infection by the pathogenic E cecorum is paralysis. Paralysis results from compression of the thoracolumbar spinal cord by focal infection and inflammation in the spinal column, especially at the free thoracic vertebra (see ).
Chickens characteristically sit with both legs extended cranially (see ).
Because affected chickens are lame, they often become dehydrated, leading to increased mortality rates.
Egg transmission or fecal contamination of hatching eggs can often lead to late embryo death, as well as an increase in the number of hatchlings that are unable to pip through the shell at hatch.
Acute enterococcosis lesions include the following:
congestion of subcutaneous tissue
Multifocal, whitish-tan areas of necrosis may be observed on the liver and spleen. Omphalitis or enlarged yolk sacs may occur in infected chicks or poults.
In the subacute or chronic form, lesions include the following:
arthritis or tenosynovitis
osteomyelitis (including femoral head necrosis)
An enlarged, flaccid heart with pale to hemorrhagic areas in the myocardium has also been reported, along with infarcts throughout the internal organs.
Focal granulomas can be found in many tissues as a result of septic emboli. Gram-positive bacterial colonies are readily observed in thrombosed vessels and within areas of necrosis.
Diagnosis of Enterococcosis in Poultry
History, clinical signs, lesions, and demonstration of enterococci in blood or on impression smears are suggestive of enterococcosis.
Isolation of Enterococcus spp from lesions confirms the diagnosis. Enterococci can be cultured on blood agar.
Differential diagnoses include bacterial diseases that cause septicemia, such as the following:
Treatment and Prevention of Enterococcosis in Poultry
Prevention of underlying immunosuppressive disorders
Antimicrobials, including erythromycin and chlortetracycline, have been used to treat acute and subacute infections of enterococcosis. The current FDA-approved drugs for poultry should always be consulted when considering treatment.
Clinically affected birds respond well early in the course of enterococcal infection; however, treatment efficacy decreases as the disease progresses. Antimicrobial susceptibility testing should be performed to ensure that the most efficacious antimicrobial is used.
Prevention and control of enterococcosis require preventing immunosuppressive diseases and conditions because enterococcosis often occurs secondary to another disease.
In addition, ensuring proper cleaning and disinfection of facilities can decrease environmental reservoirs of the bacteria. Sanitation is particularly important in the hatchery because bacterial infections are a leading cause of embryo and neonatal chick death. Water sanitation helps to decrease the incidence of enterococcosis.
Enterococcal species are resistant to drying, so they can survive for prolonged periods in the environment.
Zoonotic Risk of Enterococcosis in Poultry
A high percentage of ready-to-eat poultry products are contaminated with Enterococcus spp. However, human cases of food poisoning due to enterococcosis have not been reported.
Vancomycin-resistant enterococci have been reported in poultry, and there is concern regarding the potential for transmission to humans from poultry.
Enterococcus spp are part of the normal microbiota in poultry; however, they can cause secondary infections. Therefore, treatment of primary diseases can prevent enterococcal infections.
Clinical signs of enterococcosis are related to septicemia, and treatment is effective if provided in early stages of the disease.
If enterococcosis becomes chronic, skeletal diseases have been reported, and treatment efficacy decreases with chronicity.
For More Information
Jung A, Chen LR, Suyemoto MM, Barnes HJ, Borst LB. A review of Enterococcus cecorum infection in poultry. 2018;62(3):261-271. doi: 10.1637/11825-030618-Review.1
Learn more about enterococcal infections in humans in the MSD Manual for medical professionals.