Streptococcus is a genus of gram-positive coccus or spherical bacteria that belongs to the family Streptococcaceae, within the order Lactobacillales, in the phylum Bacillota. Cell division in streptococci occurs along a single axis, so as they grow, they tend to form pairs or chains that may appear bent or twisted. This differs from staphylococci, which divide along multiple axes, thereby generating irregular, grape-like clusters of cells. Most streptococci are oxidase-negative and catalase-negative, and many are facultative anaerobes.
Group A streptococcal infections are a number of infections with Streptococcus pyogenes, a group A streptococcus (GAS). S. pyogenes is a species of beta-hemolytic Gram-positive bacteria that is responsible for a wide range of infections that are mostly common and fairly mild. If the bacteria enter the bloodstream an infection can become severe and life-threatening, and is called an invasive GAS (iGAS).
Streptococcus pyogenes is a species of Gram-positive, aerotolerant bacteria in the genus Streptococcus. These bacteria are extracellular, and made up of non-motile and non-sporing cocci that tend to link in chains. They are clinically important for humans, as they are an infrequent, but usually pathogenic, part of the skin microbiota that can cause Group A streptococcal infection. S. pyogenes is the predominant species harboring the Lancefield group A antigen, and is often called group A Streptococcus (GAS). However, both Streptococcus dysgalactiae and the Streptococcus anginosus group can possess group A antigen as well. Group A streptococci, when grown on blood agar, typically produce small (2–3 mm) zones of beta-hemolysis, a complete destruction of red blood cells. The name group A (beta-hemolytic) Streptococcus (GABHS) is thus also used.
Streptococcus pneumoniae, or pneumococcus, is a Gram-positive, spherical bacteria, alpha-hemolytic member of the genus Streptococcus. They are usually found in pairs (diplococci) and do not form spores and are non motile. As a significant human pathogenic bacterium S. pneumoniae was recognized as a major cause of pneumonia in the late 19th century, and is the subject of many humoral immunity studies.
Erysipelothrix rhusiopathiae is a Gram-positive, catalase-negative, rod-shaped, non-spore-forming, nonacid-fast, nonmotile bacterium. Distributed worldwide, E. rhusiopathiae is primarily considered an animal pathogen, causing the disease known as erysipelas that may affect a wide range of animals. Pigs, turkeys and laying hens are most commonly affected, but cases have been reported in other mammals, birds, fish, and reptiles. In pigs, the disease is known as diamond skin disease. The bacterium can also cause zoonotic infections in humans, called erysipeloid. The human disease called erysipelas is not caused by E. rhusiopathiae, but by various members of the genus Streptococcus.
An opportunistic infection is an infection caused by pathogens that take advantage of an opportunity not normally available. These opportunities can stem from a variety of sources, such as a weakened immune system, an altered microbiome, or breached integumentary barriers. Many of these pathogens do not necessarily cause disease in a healthy host that has a non-compromised immune system, and can, in some cases, act as commensals until the balance of the immune system is disrupted. Opportunistic infections can also be attributed to pathogens which cause mild illness in healthy individuals but lead to more serious illness when given the opportunity to take advantage of an immunocompromised host.
Streptococcus bovis is a species of Gram-positive bacteria that in humans is associated with urinary tract infections, endocarditis, sepsis, and colorectal cancer. S. gallolyticus is commonly found in the alimentary tract of cattle, sheep, and other ruminants, and may cause ruminal acidosis or feedlot bloat. It is also associated with spontaneous bacterial peritonitis, a frequent complication occurring in patients affected by cirrhosis. Equivalence with Streptococcus equinus has been contested.
Fusobacterium necrophorum is a species of bacteria responsible for Lemierre's syndrome. It has also been known to cause sinusitis, mastoiditis, and odontogenic infections.
Arcanobacterium haemolyticum is a species of bacteria classified as a gram-positive bacillus. It is catalase-negative, facultative anaerobic, beta-hemolytic, and not motile. It has been known to cause head and neck infections, pharyngitis, and sinusitis.
Pathogenic bacteria are bacteria that can cause disease. This article focuses on the bacteria that are pathogenic to humans. Most species of bacteria are harmless and are often beneficial but others can cause infectious diseases. The number of these pathogenic species in humans is estimated to be fewer than a hundred. By contrast, several thousand species are part of the gut flora present in the digestive tract.
Pneumococcal infection is an infection caused by the bacterium Streptococcus pneumoniae.
Streptococcus canis is a group G beta-hemolytic species of Streptococcus. It was first isolated in dogs, giving the bacterium its name. These bacteria are characteristically different from Streptococcus dysgalactiae, which is a human-specific group G species that has a different phenotypic chemical composition. S. canis is important to the skin and mucosal health of cats and dogs, but under certain circumstances, these bacteria can cause opportunistic infections. These infections were known to afflict dogs and cats prior to the formal description of the species in Devriese et al., 1986. However, additional studies revealed cases of infection in other mammal species, including cattle and even humans. Instances of mortality from S. canis in humans are very low with only a few reported cases, while actual instances of infection may be underreported due to mischaracterizations of the bacteria as S. dysgalactiae. This species, in general, is highly susceptible to antibiotics, and plans to develop a vaccine to prevent human infections are currently being considered.
Streptococcus dysgalactiae is a gram positive, beta-haemolytic, coccal bacterium belonging to the family Streptococcaceae. It is capable of infecting both humans and animals, but is most frequently encountered as a commensal of the alimentary tract, genital tract, or less commonly, as a part of the skin flora. The clinical manifestations in human disease range from superficial skin-infections and tonsillitis, to severe necrotising fasciitis and bacteraemia. The incidence of invasive disease has been reported to be rising. Several different animal species are susceptible to infection by S. dysgalactiae, but bovine mastitis and infectious arthritis in lambs have been most frequently reported.
Streptococcus zooepidemicus is a Lancefield group C streptococcus that was first isolated in 1934 by P. R. Edwards, and named Animal pyogens A. It is a mucosal commensal and opportunistic pathogen that infects several animals and humans, but most commonly isolated from the uterus of mares. It is a subspecies of Streptococcus equi, a contagious upper respiratory tract infection of horses, and shares greater than 98% DNA homology, as well as many of the same virulence factors.
Streptococcus iniae is a species of Gram-positive, sphere-shaped bacterium belonging to the genus Streptococcus. Since its isolation from an Amazon freshwater dolphin in the 1970s, S. iniae has emerged as a leading fish pathogen in aquaculture operations worldwide, resulting in over US$100M in annual losses. Since its discovery, S. iniae infections have been reported in at least 27 species of cultured or wild fish from around the world. Freshwater and saltwater fish including tilapia, red drum, hybrid striped bass, and rainbow trout are among those susceptible to infection by S. iniae. Infections in fish manifest as meningoencephalitis, skin lesions, and septicemia.
Perianal cellulitis, also known as perianitis or perianal streptococcal dermatitis, is a bacterial infection affecting the lower layers of the skin (cellulitis) around the anus. It presents as bright redness in the skin and can be accompanied by pain, difficulty defecating, itching, and bleeding. This disease is considered a complicated skin and soft tissue infection (cSSTI) because of the involvement of the deeper soft tissues.
Bacteriophage T12 is a bacteriophage that infects Streptococcus pyogenes bacteria. It is a proposed species of the family Siphoviridae in the order Caudovirales also known as tailed viruses. It converts a harmless strain of bacteria into a virulent strain. It carries the speA gene which codes for erythrogenic toxin A. speA is also known as streptococcal pyogenic exotoxin A, scarlet fever toxin A, or even scarlatinal toxin. Note that the name of the gene "speA" is italicized; the name of the toxin "speA" is not italicized. Erythrogenic toxin A converts a harmless, non-virulent strain of Streptococcus pyogenes to a virulent strain through lysogeny, a life cycle which is characterized by the ability of the genome to become a part of the host cell and be stably maintained there for generations. Phages with a lysogenic life cycle are also called temperate phages. Bacteriophage T12, proposed member of family Siphoviridae including related speA-carrying bacteriophages, is also a prototypic phage for all the speA-carrying phages of Streptococcus pyogenes, meaning that its genome is the prototype for the genomes of all such phages of S. pyogenes. It is the main suspect as the cause of scarlet fever, an infectious disease that affects small children.
Lactococcus garvieae is a known fish pathogen affecting saltwater fish in the Far East, specifically in rainbow trout, Japanese yellowtail, Cobia and grey mullet. This bacteria causes lesions in the vascular endothelium, leading to hemorrhages and petechias at the surface of internal organs. As few as 10 bacterial cells per fish can cause an infection. L. garvieae is isolated in saltwater fish in the Far East and specifically in European rainbow trout.
Actinobacillus equuli is a gram-negative, non-motile rod bacteria from the family Pasteurellaceae.
