Streptococcus zooepidemicus

Hemolysis on blood agar is beta-hemolytic. It ferments D-glucose, lactose, maltose, sucrose, salicin, D-sorbitol, and starch, but is negative for others like D-mannitol, glycerol, and inulin. S. zooepidemicus is also positive for Ala-Phe-Pro, Leucine, and Tyrosine arylamidase, all of which catalyze hydrolysis of amino acid residues from amino terminus of polypeptide chains. Antibiotic wise, S. zooepidemicus is highly susceptible to Penicillin, usually give for treatment, as well as Ampicillin and Erythromycin, but is extremely resistant to Novobiocin, Optochin, and Tribrissen.[4]

Known strains include:[6]

• ATCC 43079
• CCUG 23256
• CIPP 103228
• DSM 20727
• LMG 16030
• NCDO 1358
• NCIMB 701358
• NCTC 4676

Some cell-surface virulence factors, which all contribute to the pathogenicity of S. zooepidemicus, include:

• SzP proteins: similar to a surface M-protein, this protein is anti-phagocytic and anti-opsonization, with impairs with host protection. This is one of the most important virulence factors.[10]
• FNZ protein: binds specifically to fibronectin, which is present on most host cell walls. This allows it to easily bind to and enter cells.[10]
• FNZ2 protein: binds to collagen, also present on host cell walls, and fibronectin (similar to FNZ).[10]
• SodA protein: destroys toxic free radicals, which are made by the host as a defensive mechanism.[11]
• SeM: produces enterotoxins.[11]

S. zooepidemicus, which is considered a zoonotic pathogen, has rarely been isolated in humans, and infection is usually very rare. Infections are only known to be severe in immunocompromised people, namely the elderly who spent time around horses. There has also been cases of people acquiring the pathogen from homemade or unpasteurized milk or cheese.[2] Most common symptoms of glomerulonephritis, rheumatic fever, meningitis, arthritis and more, leading to the death of several patients.[2]

Before 2017, there has been 32 reported cases of infections due to Streptococcus zooepidemicus.[13]

In 2004, a 63-year-old man developed left thigh pain and swelling, which evolved into fevers, rigors, and skin rash. Two days, he experienced vertigo and vomiting, and was emitted into the hospital where he was treated with acute labyrinthitis, followed by meningococcal sepsis. Hypertension ensued, and edema of the left thigh muscle was discovered during surgery. These treatments were continued, but the patient went into progressive organ failure, followed by muscle necrosis, and ventricular tachycardia. The patient later went into circulatory and respiratory failure, before passing away less than 48 hours after being emitted into the hospital.[14]

Muscle biopsies determined S. zooepidemicus, as well as evidence of an unidentified superantigen exotoxin, to be the cause of infection, and toxic-shock like syndrome to be the cause of death. It was always noteworthy that the patient had frequent contact with horses, pigs, and cattle. This case study specifically is interesting as it strongly suggests an unidentified novel exotoxin, possibly produced by S. zooepidemicus.

In 2008, a 59-year-old woman was admitted to the emergency room due to body weakness and lightheadedness when standing, which starting three weeks prior. Over the past couple of days before being emitted she also reported shortness of breath, as well as resting tremors, rhinorrhea, and a chronic cough. She had a vast medicine history including hypertension, diabetes, obesity, chronic kidney failure, and more. She was treated for severe orthostatic hypo-tension, but in the following days complained of symptoms, and had test results that suggested meningitis. Various symptoms continued for almost a month until a blood culture tested positive for Streptococcus zooepidemicus. The patient was treated with intravenous antibiotics for six weeks, and her condition gradually improved. The patient stated there was a horse stable on her property, but she only visited it occasionally.[15]