Streptococcus, Enterococcus

Question 1

What are the microbiological characteristics of Streptococcus?

Answer 1

• gram (+) cocci
• aerobic or facultatively anaerobic
• commonly grouped by: (hemolysis (a, B, gamma); Lancefield group (surface antigens identified serologically)
• can be fastidious - requires blood or serum in media to grow
• differentiate from Staphylococcus (other Gram (+) cocci) using catalase test (also staph forms clusters where strep forms chains)

Question 2

What is the biocontainment level of Streptococcus?

Answer 2

2

Question 3

What is Streptococcus’s/ Enterococcus’s natural host or habitat?

Answer 3

• host associated, part of the normal microbiota (mucous membranes & respiratory tract (Streptococci); intestinal tract (Enterococci))
• carriers of these organisms are the primary source
• environmental contamination w/ Enterococcus sp associated w/ nosocomial infections

Question 4

What are options for biochemical identification?

Answer 4

• commercial biochemical strip test (each well of the strip contains a reagent that the bacteria can react with producing a colourimetric change
• CAMP test

Question 5

What is Lancefield grouping?

Answer 5

• named after Rebecca Lancefield who developed this
• Groups A, B, C, F, & G are polysaccharides
• Group D is a lipoteichoic acid
• some organisms fail to group w/ Lancefield antisera (S. suis)

Question 6

What virulence factors does Streptococcus have?

Answer 6

• MSCRAMMs
• exotoxins (superantigen - Streptococcus pyogenes)
• phage mediated superantigen (some Streptococcus canis)
• capsule (prevents phagocytosis, some capsules composed of hyaluronic acid are indistinguishable from some host tissues - may explain post-infection autoimmunity)
• hemolysins (cytotoxic to eukaryotic cells)
• CAMP factor (pore forming toxin)

Question 7

How may Mozart have died?

Answer 7

• Dec 5, 1791
• evidently, he was working on his Requiem on his death bed
• records from the time describe a localized epidemic of deaths involving “edema”
• Mozart reportedly had an “inflammatory fever” earlier that fall
• speculation that Mozart may have suffered from Strep throat (Streptococcus pyogenes), followed by post-streptococcal glomerulonephritis (infection may stimulate production of cross-reactive antibodies)

Question 8

What is the clinical significance of Streptococcus agalactiae?

Answer 8

• contagious mastitis (infected cows are the source)
• mainly subclinical disease w/ bouts of illness (not systemically ill)
• disease suggests breakdown of biosecurity (teat hygiene, cleaning milk equipment, handwashing)
• intra-mammary antibiotics (unlike staph, many strep remain penicillin susceptible)

Question 9

What is the clinical significance of Streptococcus dysgalactiae?

Answer 9

• environmental mastitis (contamination of teats from environment/bedding)
• often subclinical
• suggests management issue (improve cleanliness, better bedding, access to shelter)
• treatment (dry cow treatment & teat sealer)

Question 10

What is the clinical significance of Streptococcus equi subsp equi?

Answer 10

• normal inhabitant of upper respiratory tract
• strangles (abscessation of submandibular & retropharyngeal lymph nodes)
• transmitted by contact w/ nasal secretions/discharge from abscesses; either direct contact or fomites; very contagious (high morbidity, low mortality) - ISOLATION IS KEY - prevent transmission)
• 2-6 day incubation period
• penicillin is treatment of choice
• long term sequelae following infection possible: metastatic abscesses “bastard strangles” (hematogenous spread to lung, liver, mesentery, spleen, kidneys, & brain); purpura hemorrhagica (vasculitis secondary to deposition of immune complexes (type III hypersensitivity)); guttural pouch empyema
• transfer of immunity in colostrum - protects foals until weaned
• vaccines are available