Post-streptococcal glomerulonephritis (PSGN) is an uncommon complication of either a strep throat or a streptococcal skin infection. It is classified as a type III hypersensitivity reaction. Symptoms of PSGN develop within 10 days following a strep throat or 3 weeks following a GAS skin infection. PSGN involves inflammation of the kidney. Symptoms include pale skin, lethargy, loss of appetite, headache, and dull back pain. Clinical findings may include dark-colored urine, swelling of different parts of the body (edema), and high blood pressure. Treatment of PSGN consists of supportive care.

A subset of children with acute, rapid-onset of tic disorders and obsessive compulsive disorder (OCD) are hypothesized to be due to an autoimmune response to group A beta-hemolytic streptococcal infection (PANDAS).

The typical signs and symptoms of streptococcal pharyngitis are a sore throat, fever of greater than , tonsillar exudates (pus on the tonsils), and large cervical lymph nodes.

Other symptoms include: headache, nausea and vomiting, abdominal pain, muscle pain, or a scarlatiniform rash or palatal petechiae, the latter being an uncommon but highly specific finding.

Symptoms typically begin one to three days after exposure and last seven to ten days.

Strep throat is unlikely when any of the symptoms of red eyes, hoarseness, runny nose, or mouth ulcers are present. It is also unlikely when there is no fever.

Streptococcal pharyngitis, also known as strep throat, is an infection of the back of the throat including the tonsils caused by "group A streptococcus" (GAS). Common symptoms include fever, sore throat, red tonsils, and enlarged lymph nodes in the neck. A headache, and nausea or vomiting may also occur. Some develop a sandpaper-like rash which is known as scarlet fever. Symptoms typically begin one to three days after exposure and last seven to ten days.

Strep throat is spread by respiratory droplets from an infected person. It may be spread directly or by touching something that has droplets on it and then touching the mouth, nose, or eyes. Some people may carry the bacteria without symptoms. It may also be spread by skin infected with group A strep. The diagnosis is made based on the results of a rapid antigen detection test or throat culture in those who have symptoms.

Prevention is by washing hands and not sharing eating utensils. There is no vaccine for the disease. Treatment with antibiotics is only recommended in those with a confirmed diagnosis. Those infected should stay away from other people for at least 24 hours after starting treatment. Pain can be treated with paracetamol (acetaminophen) and nonsteroidal anti-inflammatory drugs (NSAIDS) such as ibuprofen.

Strep throat is a common bacterial infection in children. It is the cause of 15–40% of sore throats among children and 5–15% among adults. Cases are more common in late winter and early spring. Potential complications include rheumatic fever and peritonsillar abscess.

Common signs and symptoms include:

- sore throat

- red, swollen tonsils

- pain when swallowing

- high temperature (fever)

- headache

- tiredness

- chills

- a general sense of feeling unwell (malaise)

- white pus-filled spots on the tonsils

- swollen lymph nodes (glands) in the neck

- pain in the ears or neck

- weight loss

- difficulty ingesting and swallowing meal/liquid intake

- difficulty sleeping

Less common symptoms include:

- nausea

- fatigue

- stomach ache

- vomiting

- furry tongue

- bad breath (halitosis)

- voice changes

- difficulty opening the mouth (trismus)

- loss of appetite

- Anxiety/fear of choking

In cases of acute tonsillitis, the surface of the tonsil may be bright red and with visible white areas or streaks of pus.

Tonsilloliths occur in up to 10% of the population frequently due to episodes of tonsillitis.

Tonsillitis is inflammation of the tonsils, typically of rapid onset. It is a type of pharyngitis. Symptoms may include sore throat, fever, enlargement of the tonsils, trouble swallowing, and large lymph nodes around the neck. Complications include peritonsillar abscess.

Tonsillitis is most commonly caused by a viral infection, with about 5% to 40% of cases caused by a bacterial infection. When caused by the bacterium group A streptococcus, it is referred to as strep throat. Rarely bacteria such as "Neisseria gonorrhoeae", "Corynebacterium diphtheriae", or "Haemophilus influenzae" may be the cause. Typically the infection is spread between people through the air. A scoring system, such as the Centor score, may help separate possible causes. Confirmation may be by a throat swab or rapid strep test.

Treatment efforts involve improving symptoms and decreasing complications. Paracetamol (acetaminophen) and ibuprofen may be used to help with pain. If strep throat is present the antibiotic penicillin by mouth is generally recommended. In those who are allergic to penicillin, cephalosporins or macrolides may be used. In children with frequent episodes of tonsillitis, tonsillectomy modestly decreases the risk of future episodes.

About 7.5% of people have a sore throat in any three-month period and 2% of people visit a doctor for tonsillitis each year. It is most common in school aged children and typically occurs in the fall and winter months. The majority of people recover with or without medication. In 40% of people, symptoms resolve within three days, and in 80% symptoms resolve within one week, regardless of if streptococcus is present. Antibiotics decrease symptom duration by approximately 16 hours.

Affected individuals typically develop symptoms including high fevers, shaking, chills, fatigue, headaches, vomiting, and general illness within 48 hours of the initial infection. The erythematous skin lesion enlarges rapidly and has a sharply demarcated, raised edge. It appears as a red, swollen, warm, and painful rash, similar in consistency to an orange peel. More severe infections can result in vesicles (pox or insect bite-like marks), blisters, and petechiae (small purple or red spots), with possible skin necrosis (death). Lymph nodes may be swollen, and lymphedema may occur. Occasionally, a red streak extending to the lymph node can be seen.

The infection may occur on any part of the skin, including the face, arms, fingers, legs, and toes; it tends to favour the extremities. Fat tissue and facial areas, typically around the eyes, ears, and cheeks, are most susceptible to infection. Repeated infection of the extremities can lead to chronic swelling (lymphangitis).

Erysipelas is an acute infection typically with a skin rash, usually on any of the legs and toes, face, arms, and fingers. It is an infection of the upper dermis and superficial lymphatics, usually caused by beta-hemolytic group A "Streptococcus" bacteria on scratches or otherwise infected areas. Erysipelas is more superficial than cellulitis, and is typically more raised and demarcated. The term is from Greek ἐρυσίπελας, meaning "red skin".

Epiglottitis is associated with fever, difficulty in swallowing, drooling, hoarseness of voice, and typically stridor. Stridor is a sign of upper airways obstruction and is a surgical emergency. The child often appears acutely ill, anxious, and has very quiet shallow breathing with the head held forward, insisting on sitting up in bed. The early symptoms are insidious but rapidly progressive, and swelling of the throat may lead to cyanosis and asphyxiation.

Since the introduction of the "Hemophilus influenzae" (Hib) vaccination in many Western countries, childhood incidence has decreased while adult incidence has remained the same; the disease is thus becoming "relatively" more common in adults than children.

Pharyngitis is a type of inflammation, most commonly caused by an upper respiratory tract infection. It may be classified as acute or chronic. Acute pharyngitis may be catarrhal, purulent or ulcerative, depending on the causative agent and the immune capacity of the affected individual. Chronic pharyngitis may be catarrhal, hypertrophic or atrophic.

Tonsillitis is a sub type of pharyngitis. If the inflammation includes both the tonsils and other parts of the throat, it may be called pharyngotonsillitis. Another sub classification is nasopharyngitis (the common cold).

The term "penicillin" is often used generically to refer to benzylpenicillin (penicillin G, the original penicillin found in 1928), procaine benzylpenicillin (procaine penicillin), benzathine benzylpenicillin (benzathine penicillin), and phenoxymethylpenicillin (penicillin V). Procaine penicillin and benzathine penicillin have the same antibacterial activity as benzylpenicillin but act for a longer period of time. Phenoxymethylpenicillin is less active against gram-negative bacteria than benzylpenicillin. Benzylpenicillin, procaine penicillin and benzathine penicillin can be given by intravenous or intramuscular injections, but phenoxymethylpenicillin can be given by mouth because of its acidic stability.

In adolescence and young adulthood, the disease presents with a characteristic triad:

- Fever – usually lasting 14 days; often mild

- Sore throat – usually severe for 3–5 days, before resolving in the next 7–10 days.

- Swollen glands – mobile; usually located around the back of the neck (posterior cervical lymph nodes) and sometimes throughout the body.

Another major symptom is feeling tired. Headaches are common, and abdominal pains with nausea or vomiting sometimes also occur. Symptoms most often disappear after about 2–4 weeks. However, fatigue and a general feeling of being unwell (malaise) may sometimes last for months. Fatigue lasts more than one month in an estimated 28% of cases. Mild fever, swollen neck glands and body aches may also persist beyond 4 weeks. Most people are able to resume their usual activities within 2–3 months.

The most prominent sign of the disease is often the pharyngitis, which is frequently accompanied by enlarged tonsils with pus—an exudate similar to that seen in cases of strep throat. In about 50% of cases, small reddish-purple spots called petechiae can be seen on the roof of the mouth. Palatal enanthem can also occur, but is relatively uncommon.

Spleen enlargement is common in the second and third weeks, although this may not be apparent on physical examination. Rarely the spleen may rupture. There may also be some enlargement of the liver. Jaundice occurs only occasionally.

A small minority of people spontaneously present a rash, usually on the arms or trunk, which can be macular (morbilliform) or papular. Almost all people given amoxicillin or ampicillin eventually develop a generalized, itchy maculopapular rash, which however does not imply that the person will have adverse reactions to penicillins again in the future. Occasional cases of erythema nodosum and erythema multiforme have been reported.

Infectious mononucleosis mainly affects younger adults. When older adults do catch the disease, they less often have characteristic signs and symptoms such as the sore throat and lymphadenopathy. Instead, they may primarily experience prolonged fever, fatigue, malaise and body pains. They are more likely to have liver enlargement and jaundice. People over 40 years of age are more likely to develop serious illness. (See Prognosis.)

Strangles (equine distemper) is a contagious upper respiratory tract infection of horses and other equines caused by a gram-positive bacterium, "Streptococcus equi". As a result the lymph nodes swell, compressing the pharynx, larynx and trachea and can cause airway obstruction leading to death, hence the name Strangles. Strangles is enzootic in domesticated horses worldwide. The contagious nature of the infection has at times led to limitations on sporting events.

Common (≥ 1% of people) adverse drug reactions associated with use of the penicillins include diarrhoea, hypersensitivity, nausea, rash, neurotoxicity, urticaria, and superinfection (including candidiasis). Infrequent adverse effects (0.1–1% of people) include fever, vomiting, erythema, dermatitis, angioedema, seizures (especially in people with epilepsy), and pseudomembranous colitis. Penicillin can also induce serum sickness or a serum sickness-like reaction in some individuals. Serum sickness is a type III hypersensitivity reaction that occurs one to three weeks after exposure to drugs including penicillin. It is not a true drug allergy, because allergies are type I hypersensitivity reactions, but repeated exposure to the offending agent can result in an anaphylactic reaction. Anaphylaxis will occur in approximately 0.01% of patients.

Pain and inflammation at the injection site is also common for parenterally administered benzathine benzylpenicillin, benzylpenicillin, and, to a lesser extent, procaine benzylpenicillin.

Anaerobes can be isolated from most types of upper respiratory tract and head and neck and infection and are especially common in chronic ones. These include tonsillar, peritonsillar and retropharyngeal abscesses, chronic otitis media, sinusitis and mastoiditis, eye ocular) infections, all deep neck space infections, parotitis, sialadenitis, thyroiditis, odontogenic infections, and postsurgical and nonsurgical head and neck wounds and abscesses., The predominant organisms are of oropharyngeal flora origin and include AGNB, "Fusobacterium" and Peptostreptococcus spp.

Anaerobes involve almost all dental infections. These include dental abscesses, endodontal pulpitis and periodontal (gingivitis and periodontitis) infections, and perimandibular space infection. Pulpitis can lead to abscess formation and eventually spread to the mandible and other neck spaces. In addition to strict anaerobic bacteria, microaerophilic streptococci and "Streptococcus salivarius" can also be present.

"Fusobacterium" spp. and anaerobic spirochetes are often the cause of acute necrotizing ulcerative gingivitis (or Vincent's angina) which is a distinct form of ulcerative gingivitis.

Deep neck infections that develop as a consequence of oral, dental and pharyngeal infections are generally polymicrobial in nature. These include extension of retropharyngeal cellulitis or abscess, mediastinitis following esophagus perforation, and dental or periodontal abscess.

A horse with strangles will typically develop abscesses in the lymph nodes of the head and neck causing coughing fits and difficulty swallowing. Clinical signs include fever up to 106 °F and yellow coloured nasal discharge from both the nose and eyes.

Abscesses may form in other areas of the body, such as the abdomen, lungs and brain. This is considered a chronic form of strangles called "bastard strangles" and can have serious implications if the abscesses rupture. Horses develop this form of strangles when their immune systems are compromised or if the bacteria rapidly invades the body.

Strangles has a 8.1% mortality rate. Mortality is lower in cases without complications than it is in cases of bastard strangles. The disease is very contagious and morbidity is high. Precautions to limit the spread of the illness are necessary and those affected are normally isolated. An isolation period of 4–6 weeks is usually necessary to ensure that the disease is not still incubating before ending the quarantine.

The majority of cases are due to an infectious organism acquired from close contact with an infected individual.

Anaerobes are able to cause all types of intracranial infections. These often cause subdural empyema, and brain abscess, and rarely cause epidural abscess and meningitis. The origin of brain abscess is generally an adjacent chronic ear, mastoid, or sinus infection oropharynx, teeth or lungs. Mastoid and ear or infections generally progress to the temporal lobe or cerebellum, while facial sinusitis commonly causes frontal lobe abscess. Hematogenous spread of the infection into the CNS often occurs after oropharyngeal, dental, or pulmonary infection. Infrequently bacteremia originating of another location or endocarditis can also cause intracranial infection.

Meningitis due to anaerobic bacteria is infrequent and may follow respiratory tract infection or complicate a cerebrospinal fluid shunt. Nerological shunt infections are often caused by skin bacteria such as "Propionibacterium acnes", or in instances of ventriculoperitoneal shunts that perforate the gut, by anaerobes of enteric origin (i.e. "Bacteroides fragilis")."Clostridium perfringens" can cause of brain abscesses and meningitis following intracranial surgery or head trauma.

The anaerobes often isolated from brain abscesses complicating respiratory and dental infections are anaerobic Gram-negative bacilli (AGNB, including Prevotella, "Porphyromonas", Bacteroides), "Fusobacterium" and Peptostreptococcus spp. Microaerophilic and other streptococci are also often isolated. Actinomyces are rarely isolated.

At the stage of encephalitis, antimicrobial therapy and utilization of measures to lower the increase in the intracranial pressure can prevent the formation of an intracranial abscess However, after an abscess has emerged, surgical removal or drainage may be necessary, along with an extended course of antimicrobial therapy (4–8 weeks). Some advocate complete drainage of intracranial abscess, while others use repeated aspirations of the abscess., Repeated aspirations of an abscess are preferable in those with multiple abscesses or when the abscess is located in a predominate brain site. Administration of antimicrobials in a high-dose for an extended period of time can offer an alternative treatment strategy in this type of patients and may substitute for surgical evacuation of an abscess.

Because of the poor penetration of many antimicrobial agents through the blood–brain barrier, there are few agents available for the treatment of intracranial infections. The antimicrobials with good intracranial penetration are metronidazole, chloramphenicol, penicillins, and meropenem. Optimally, the selection of antimicrobial is done according to the recovered isolates and their antimicrobial susceptibilities. A substantial improvement in patients' survival rate has occurred after the introduction of computed tomography (CT) and other scans and utilization of metronidazole therapy.

GBS is found in the gastrointestinal and genitourinary tract of humans. In different studies, GBS vaginal colonization rate ranges from 4 to 36%, with most studies reporting rates over 20%. These variations in the reported prevalence of asymptomatic (presenting no symptoms of disease) colonization could be related to the different detection methods used, and differences in populations studied.

Though GBS is an asymptomatic colonizer of the gastrointestinal human tract in up to 30% of otherwise healthy adults, including pregnant women,

this opportunistic harmless bacterium can, in some circumstances, cause severe invasive infections.

Post-mortem findings include friable internal organs, abdominal effusion and evidence of sepsis in the joints, heart valves and brain.

Bacteria can usually be cultured from tissues collected at necropsy or identified by microscope examination.

Group B streptococcus infection, also known as Group B streptococcal disease, is the infection caused by the bacterium "Streptococcus agalactiae" ("S. agalactiae") (also known as group B streptococcus or GBS). Group B streptococcal infection can cause serious illness and sometimes death, especially in newborns, the elderly, and people with compromised immune systems.

GBS was recognized as a pathogen in cattle by Edmond Nocard and Mollereau in the late 1880s, but its significance as a human pathogen was not discovered before 1938, when Fry described three fatal cases of puerperal infections caused by GBS. In the early 1960s, GBS was recognized as a main cause of infections in newborns.

In general, GBS is a harmless commensal bacterium being part of the human microbiota colonizing the gastrointestinal and genitourinary tracts of up to 30% of healthy human adults (asymptomatic carriers).

"S. agalactiae" is also a common veterinary pathogen, because it can cause bovine mastitis (inflammation of the udder) in dairy cows. The species name "agalactiae" meaning "no milk", alludes to this.

"S. agalactiae" is a Gram-positive coccus (spherical bacterium) with a tendency to form chains (streptococcus), beta-haemolytic, catalase-negative, and facultative anaerobe.

"S. agalactiae" is the species designation for streptococci belonging to the group B of the Rebecca Lancefield classification of streptococci (Lancefield grouping). GBS is surrounded by a bacterial capsule composed of polysaccharides (exopolysaccharides). GBS are subclassified into 10 serotypes (Ia, Ib, II–IX) depending on the immunologic reactivity of their polysaccharide capsule.

As other virulent bacteria, GBS harbours an important number of virulence factors,

the most important are the capsular polysaccharide (rich in sialic acid), and a pore-forming toxin, β-haemolysin.

The GBS capsule is probably the key virulence factor because it helps GBS escape from the host defence mechanisms interfering with phagocytic killing of GBS by human phagocytes.

The GBS β-haemolysin is considered identical to the GBS pigment.

The typical signs and symptoms of cellulitis is an area which is red, hot, and painful. The photos shown here of are of mild to moderate cases, and are not representative of earlier stages of the condition.

Streptococcus species are the cause of opportunistic infections in poultry leading to acute and chronic conditions in affected birds. Disease varies according to the Streptococcal species but common presentations include septicaemia, peritonitis, salpingitis and endocarditis.

Common species affecting poultry include:

- "S. gallinaceus" in broiler chickens

- "S. gallolyticus" which is a pathogen of racing pigeons and turkey poults

- "S. dysgalactiae" in broiler chickens

- "S. mutans" in geese

- "S. pluranimalium" in broiler chickens

- "S. equi subsp. zooepidemicus" in chickens and turkeys

- "S. suis" in psittacine birds

Unlike tonsillitis, which is more common in the children, PTA has a more even age spread, from children to adults. Symptoms start appearing two to eight days before the formation of an abscess. A progressively severe sore throat on one side and pain during swallowing (odynophagia) usually are the earliest symptoms. As the abscess develops, persistent pain in the peritonsillar area, fever, a general sense of feeling unwell, headache and a distortion of vowels informally known as "hot potato voice" may appear. Neck pain associated with tender, swollen lymph nodes, referred ear pain and foul breath are also common. While these signs may be present in tonsillitis itself, a PTA should be specifically considered if there is limited ability to open the mouth (trismus).

Physical signs of a peritonsillar abscess include redness and swelling in the tonsillar area of the affected side and swelling of the jugulodigastric lymph nodes. The uvula may be displaced towards the unaffected side.