Taxonomy
Family: Streptococcaceae

Streptococcus anginosus group / “S. milleri” / Lancefield Group F
- S. anginosus
- S. constellatus
- S. intermedius

Natural habitats
They are regarded generally as harmless commensals of the oropharyngeal, urogenital and gastrointestinal microbiota.

Clinical significance
These organisms are strongly associated with abscess formation in the brain, the oropharynx, or the peritoneal cavity.

The S. anginosus group has been implicated as an emerging psathogen in the respiratory tract of cystic fibrosis patients.

Specific isolation site
- S. anginosus - urogenital or gastrointestinal tract
- S. constellatus - respiratory tract
- S. intermedius - abscesses of the brain or liver

Taxonomy
Family: Leuconostocaceae

Natural habitats
They can be isolated from plants, occasionally from milk and milk products.

Clinical significance
They can be isolated from the female genital tract, and the gastrointestinal tract.

Infectious for humans that have surgery, antibiotic therapy, or have impared immunological systems.

A. defectiva is a fastidious organism that requires a complex medium enriched with L-cysteine or vitamin B6 as well as other unique nutritional requirements that are essential for growth.

Taxonomy:
Family: Aerococcaceae
Genus: Abiotrophia and Granulicatella
Formerly: Streptococcus defective, Nutritionally Variant Streptococci or satelliting streptococci

Natural habitat
They are members of normal flora of the oral cavity or upper respiratory tract as well as the intestinal tract.

Clinical significance
They are opportunistic pathogens, and are formally known as NVS (nutritionally variant streptococci) are normal residents of the oral cavity
and are recognized as agents of endocarditis involving both native and prosthetic valves.
These organisms have also been isolated from other types of infections, including ophthalmic infections, peritonitis in patients undergoing continuous ambulatory peritoneal dialysis, musculoskeletal infection, septic arthritis, and a breast implant-associated infection.

Although it is rare for A. defectiva to cause endocarditis they have a greater morbidity and mortality than endocarditis caused by other streptococci due to its poor response to many antibiotics. Cases are rare.

Taxonomy
Family: Lactobacillaceae

Natural habitats
They are commonly found in fermented vegetables, fermented dairy products and meat.

They are being used as probiotic supplements in treating constipation, diarrhea, relieving stress, enhancing immune response among birds and small animals, human trials are still limited.

Clinical significance
P. acidilactici is the most common clinical isolate of pediococci

They have been isolate from bacteremia, sepsis and hepatic abscess in compromised patients

Taxonomy
Family: Streptococcaceae

Streptococcus mutans group / Lancefield Group F
- S. mutans
- S. sobrinus

(S.criceti, S.ratti, S.downei)

Natural habitats
Commensals of the oral cavity.

Clinical significance
Is the major cause of dental caries and endocarditis.

S. mutans metabolizes sucrose to produce polysaccharides that help them cohere to one another forming plaque.

The combination of this plaque and acids released by S. mutans leads to the breakdown / dissolve of tooth enamel resulting in dental caries.

They are easily dismissed as a common non-pathogenic skin bacterial contaminant termed “diphteroid”

Streptococcus pyogenes = Lancefield Group A

Taxonomy
Family: Streptococcaceae

Natural habitats
Colonizes the human throat and skin and has developed complex virulence mechanism to avoid host defenses.

Clinical significance
The upper respiratory tract and skin lesions serve as primary focal sites of infections and principal reservoirs of transmission.

They can cause superficial or deep infections due to toxin-mediated and immunologically mediated mechanisms of disease.

S. pyogenes is the most common cause of bacterial pharyngitis and impetigo.

In the past, S. pyogenes was a common cause of childbed fever of puerperal sepsis.

They are responsible for deep or invasive infections, especially bacteremia, sepsis, deep soft tissue infections, such as erysipelas, cellulitis, and necrotizing fasciitis.

Less common myositis, osteomyelitis, septic arthritis, pneumonia, meningitis, endocarditis, pericarditis, and severe neonatal infections following intrapartum transmission.

Taxonomy
Family: Streptococcaceae

Streptococcus salivarius group / Lancefield Group F
- S. salivarius
- S. vestibularis
- S. thermophilis (no human pathogen)

Natural habitats
Commensals of the oral cavity, and feces

Clinical significance
S. vestibularis has not been clearly associated with human infections.

Isolation of these species from blood cultures in asymptomatic patients often does not require antibiotic treatment, if it is due to a transient bacteremia.

They can also be found as transient microbiota of the normal skin and often represent contaminants when isolated from blood cultures.

At the same time these species are the most frequently isolated bacteria in bacterial endocarditis in native valve and less frequently, in prosthetic valve infections.

Careful evaluation of the clinical situation is therefore crucial to correctly interpret the clinical significance.

In neutropenic patients, streptococcal species from these groups are often responsible for life-threatening sepsis an pneumonia cases following immunosuppression by chemotherapy.

Taxonomy
Family: Streptococcaceae

Streptococcus mitis group / Lancefield Group F
- S. mitis
- S. cristatus
- S. oralis
- S. peroris

- S. pneumoniae

Natural habitats
Commensals of the oral cavity, the gastrointestinal tract, and the female genital tract.

Clinical significance
Isolation of these species from blood cultures in asymptomatic patients often does not require antibiotic treatment, if it is due to a transient bacteremia.

They can also be found as transient microbiota of the normal skin and often represent contaminants when isolated from blood cultures.

At the same time these species are the most frequently isolated bacteria in bacterial endocarditis in native valve and less frequently, in prosthetic valve infections.

Careful evaluation of the clinical situation is therefore crucial to correctly interpret the clinical significance of blood culture isolates from the S. mitis- or S. sanguinis group.

In neutropenic patients, streptococcal species from these groups are often responsible for life-threatening sepsis an pneumonia cases following immunosuppression by chemotherapy.

Taxonomy
Family: Streptococcaceae

Streptococcus sanguinis group / Lancefield Group F
- S. sanguinis
- S. parasanguinis
- S. gordonii

Natural habitats
Commensals of the oral cavity, the gastrointestinal tract, and the female genital tract.

Clinical significance
Isolation of these species from blood cultures in asymptomatic patients often does not require antibiotic treatment, if it is due to a transient bacteremia.

They can also be found as transient microbiota of the normal skin and often represent contaminants when isolated from blood cultures.

At the same time these species are the most frequently isolated bacteria in bacterial endocarditis in native valve and less frequently, in prosthetic valve infections.

Careful evaluation of the clinical situation is therefore crucial to correctly interpret the clinical significance of blood culture isolates from the S. mitis- or S. sanguinis group.

In neutropenic patients, streptococcal species from these groups are often responsible for life-threatening sepsis an pneumonia cases following immunosuppression by chemotherapy.

Taxonomy
Family: Streptococcaceae

Streptococcus sanguinis group / Lancefield Group F
- S. sanguinis
- S. parasanguinis
- S. gordonii

Natural habitats
Commensals of the oral cavity, the gastrointestinal tract, and the female genital tract.

Clinical significance
Isolation of these species from blood cultures in asymptomatic patients often does not require antibiotic treatment, if it is due to a transient bacteremia.

They can also be found as transient microbiota of the normal skin and often represent contaminants when isolated from blood cultures.

At the same time these species are the most frequently isolated bacteria in bacterial endocarditis in native valve and less frequently, in prosthetic valve infections.

Careful evaluation of the clinical situation is therefore crucial to correctly interpret the clinical significance of blood culture isolates from the S. mitis- or S. sanguinis group.

In neutropenic patients, streptococcal species from these groups are often responsible for life-threatening sepsis an pneumonia cases following immunosuppression by chemotherapy.

Taxonomy
Family: Streptococcaceae

Streptococcus dysgalactiae ssp equisimilis = Lancefield Group A, C, G or L

Natural habitats
Are normal commensal flora of the human upper airway and frequently are asymptomatic colonizers of the skin, gastrointestinal tract and female genital tract.

Clinical significance
After being considered nonpathogenic for many years, they are now recognized as an important bacterial pathogen.

The clinical spectrum of diseases caused by this species closely resembles Streptococcus pyogenes infections.

S. dysgalactiae ssp equisimilis and S.pyogenes share virulence factors.
The M protein is an important virulence factor because it confers resistance to phagocytosis

They are also implicated in mono- and polymicrobial infections of the skin and soft tissues, pharyngitis, bacteremia and endocarditis, septic arthritis and osteomyelitis, puerperal infections, and meningitis.

Taxonomy Family: Streptococcaceae Strepytococcus bovis group / Lancefield Group D

Former name Current name

S. bovis biotype I S. gallolyticus
​
S. bovis biotype II.1 S. infantarius

S. bovis biotype II.2 S. gallolyticus ssp pasteurianus

Natural habitats
Is part of the human gastrointestinal microbiota

Clinical significance
Species from this group are frequently encountered in blood cultures of patients with bacteremia, sepsis and endocarditis.

The clinical significance of blood cultures growing streptococci from the S.bovis group lies in the association of

S. gallolyticus ssp gallolyticus with gastrointestinal cancer

and of

S. gallolyticus ssp pasteurianus with meningitis.

Taxonomy
Family: Streptococcaceae

Streptococcus anginosus group / “S. milleri” / Lancefield Group F
- S. anginosus
- S. constellatus
- S. intermedius

Natural habitats
They are regarded generally as harmless commensals of the oropharyngeal, urogenital and gastrointestinal microbiota.

Clinical significance
These organisms are strongly associated with abscess formation in the brain, the oropharynx, or the peritoneal cavity.

The S. anginosus group has been implicated as an emerging psathogen in the respiratory tract of cystic fibrosis patients.

Specific isolation site
- S. anginosus - urogenital or gastrointestinal tract
- S. constellatus - respiratory tract
- S. intermedius - abscesses of the brain or liver

Taxonomy
Family: Streptococcaceae

Streptococcus anginosus group / “S. milleri” / Lancefield Group F
- S. anginosus
- S. constellatus
- S. intermedius

Natural habitats
They are regarded generally as harmless commensals of the oropharyngeal, urogenital and gastrointestinal microbiota.

Clinical significance
These organisms are strongly associated with abscess formation in the brain, the oropharynx, or the peritoneal cavity.

The S. anginosus ​​​​​​​group has been implicated as an emerging psathogen in the respiratory tract of cystic fibrosis patients.

Specific isolation site
- S. anginosus - urogenital or gastrointestinal tract
- S. constellatus - respiratory tract
- S. intermedius - abscesses of the brain or liver

Streptococcus agalactiae = Lancefield Group B

Taxonomy
Family: Streptococcaceae

Natural habitats
Isolated from human urogenital tract and intestine

Clinical significance
They are the cause of invasive neonatal infections.

Neonatal infections present as two different clinical entities
- early onset neonatal disease, characterized by sepsis and pneumonia within the first 7 days of life
- late onset disease with meningitis and sepsis between 7 days and 3 month of age.

The most important risk factor for the development of invasive neonatal disease is the colonization, urogenital by S.agalactiae, which is found by pregnant women

Infections of adult patients may be observed as postpartum infections or in immunocompromised adult patients with alcoholism, diabetes mellitus, cancer or AID’s.

The spectrum of infections in adult patients includes pneumonia, bacteremia, endocarditis, urinary tract infections, skin and soft tissue infections and osteomyelitis

General information
S. acidominimus is a member of the viridans group streptococci and is rarely pathogenic in humans making it difficult to assess its epidemiologic and clinical significance.

Taxonomy
Family: Streptococcaceae

Natural habitats
In the bovine vagina, on the skin of calves and in raw milk.

Clinical significance
On rare occasions, it has been associated with infections in human

Taxonomy
Family: Streptococcaceae

Streptococcus mitis group / Lancefield Group F
- S. mitis
- S. cristatus
- S. oralis
- S. peroris
- S. pneumoniae

Natural habitats
Is a normal in habitant of the human upper respiratory tract, especially in children, without evidence of infection.

Clinical significance
They are the most frequently isolated respiratory pathogen in community-aquired pneumonia cases.

They can be found in peripheral blood cultures of patients. S.pneumoniae is also a major cause of meningitis, leading to high morbidity and mortality in pediatric and adult patients.

The most frequently observed infection due to S.pneumoniae is otitis media.

Other infections includes sinusitis, septic arthritis, osteomyelitis, endocarditis, peritonitis, cellulitis, brain abscesses.

G. adiacens is a fastidious organism that requires a complex medium enriched with L-cysteine or vitamin B6 as well as other unique nutritional requirements that are essential for growth.

Taxonomy:
Family: Aerococcaceae
Genus: Abiotrophia and Granulicatella
Formerly: Streptococcus defective, Nutritionally Variant Streptococci or satelliting streptococci

Natural habitat
They are members of normal flora of the oral cavity or upper respiratory tract as well as the intestinal tract.

Clinical significance
They are opportunistic pathogens, and are formally known as NVS (nutritionally variant streptococci) are normal residents of the oral cavity
and are recognized as agents of endocarditis involving both native and prosthetic valves.
These organisms have also been isolated from other types of infections, including ophthalmic infections, peritonitis in patients undergoing continuous ambulatory peritoneal dialysis, musculoskeletal infection, septic arthritis, and a breast implant-associated infection.

Although it is rare for G. adiacens to cause endocarditis they have a greater morbidity and mortality than endocarditis caused by other streptococci due to its poor response to many antibiotics.

Cases are rare.

Taxonomy
Family: Aerococcaceae

Natural habitats
They are in the air and dust and on the skin of people, and have been described as an airborn organism prevalent in occupied rooms.

Aerococci could be confused with streptococci and staphylococci since they have many characteristics in common, and this may account for the fact that the presence of A. viridans has not often been reported in the hospital environment or in clinical specimens.

Clinical significance
A. viridans has been noted as a contaminant in clinical cultures and infrequently as a clinical significant isolate from cases of endocarditis and bacteremia.

Taxonomy
Family: Aerococcaceae

Natural habitats
A. urinae is a rarely reported pathogen, possible due to the difficulties in the identification of the organism.

Clinical significance
Isolates of this species were originally isolated from the urine of (older) patients with urinary tract infections and were denoted Aerococcus-like organisms.

Infections with this bacterium has likely been underestimated.

A. urinae may also cause invasive infections including urosepsis, lymphadenitis, spondylodiscitis and infective endocarditis especially in elderly men with underlying urinary tract diseases.