Streptococcus infantarius is a bacterial species belonging to the Streptococcus genus. Historically, this organism was often grouped with others under the broader, older classification of Streptococcus bovis, particularly as biotype II/1. Modern molecular techniques refined the taxonomy, leading to the formal classification of S. infantarius in 2000, establishing it as its own distinct species.
Classification and Natural Habitat
Streptococcus infantarius is a member of the Streptococcus bovis/Streptococcus equinus Complex (SBSEC), a group of non-enterococcal bacteria that are part of the Lancefield group D streptococci. Within the complex, S. infantarius is closely related to species like S. gallolyticus and S. lutetiensis. The species was historically divided into two subspecies, S. infantarius subsp. infantarius and S. infantarius subsp. coli, though the latter has been reclassified as Streptococcus lutetiensis.
The natural habitat of this bacterium is the gastrointestinal tract of various mammals, where it acts as a common gut commensal. It is frequently found in the gut microbiota of livestock, including cattle, sheep, pigs, horses, and camels. Due to its presence in animal guts, it is also prevalent in associated environmental reservoirs, such as feces.
S. infantarius is also a component of the human gastrointestinal microbiota. Fecal carriage rates for the SBSEC group vary widely in healthy adults. Its presence in both humans and animals suggests it shares both commensal and food-related habitats. The high genetic diversity within the SBSEC complex necessitates molecular methods for accurate identification.
Role in Animal and Food Production
S. infantarius in livestock plays a dual role in animal health, existing as a harmless commensal or, in some circumstances, acting as a pathogen. It contributes to the overall microbial ecology of the digestive system in various farm animals. Specific strains have been associated with diseases in animals, though its full pathogenic potential is still being investigated.
In food production, S. infantarius subsp. infantarius is significant, particularly in the dairy industry. It is a predominant lactic acid bacterium found in spontaneously fermented dairy products, notably in Africa. This bacterium contributes to the fermentation process, which preserves milk and develops characteristic flavors.
African variants have adapted to the dairy environment, allowing them to metabolize lactose efficiently. The ability to thrive in milk fermentation suggests a potential technological application as a starter culture for fermented milk products. However, their close relation to pathogenic strains within the SBSEC complex means their use in food is subject to safety discussions.
Significance in Human Health
S. infantarius has a dual significance in human health, acting as both a potential beneficial colonizer and an opportunistic pathogen. As a member of the human gut flora, certain strains show characteristics suggesting a potential probiotic role. Some isolates, particularly from food sources, produce bacteriocins, compounds that inhibit the growth of potential pathogens.
The species is classified within a group known for containing opportunistic pathogens. It can cause systemic infections, especially in individuals with underlying health conditions or compromised immune systems. These infections occur when the bacterium, normally confined to the gut, enters the bloodstream or other sterile body sites.
Infections caused by S. infantarius include:
- Bacteremia (bacteria in the blood).
- Endocarditis (inflammation of the heart’s inner lining, which can be life-threatening).
- Infections of the musculoskeletal system and soft tissues.
- Abdominal and gastrointestinal tract infections.
Furthermore, like other SBSEC members, some cases of bacteremia have been linked to underlying conditions such as colorectal cancer.
Treatment generally follows the standard approach for streptococcal infections, with most isolates susceptible to penicillin. For patients with a penicillin allergy, alternative antibiotics such as clindamycin are often effective, though resistance has been reported in some strains. Accurate identification and antibiotic susceptibility testing are necessary for effective clinical management.