A note on Streptococcus suis.

Here is my note on Streptococcus suis. These facts can be used to make a learning aid such as flashcards.

Features

Alpha-hemolytic ; in viridans group (not pneumococci)
Facultative anaerobe
Gram positive
Coccoid or ovoid (Spindle-shaped cocci in one article)
Singly, pairs (frequently) or short chain (occasionally)
20 Mbp genome
Thirty-five capsular serotypes (more in Epidemiology heading)
Lancefield's group D
- Rebecca C. Lancefield (published in 1933)
- Classified hemolytic streptococci into five groups by precipitin test
  - Prepare type-specific rabbit sera.
  - Extract (water-clear supernatant fluid) from the neutralized HCl-treated culture.
  - Layer antiserum on the extract, stand tubes for 10-30 mins (RT/37C) and observe ring formation, then shake and incubate at 37C for 2 hrs. Finally, leave them sit on ice o/n before reading.
- Nowadays, it is performed by using Streptex (Remel, USA)

The virulence differs among serotypes and between different strains of the same serotype.

Swine diseases

Disease in swine and others (boars, horses, dogs, cats, birds)
Pigs can be carriers, in upper respiratory tract of pig (tonsils, nasal cavities), genital and alimentary tract
Serotype 2 is the most pathogenic to pigs (among the capsular serotype), and was isolated in up to 50.6% of all S. suis isolates from healthy swine tonsil.

Occupational disease

1500 times higher risk in persons working in pork industry (Netherlands)
carriage rate 5.3% in high-risk group (Germany)
9% dairy farmers, 10% meat inspectors, 21% pig farmers (NZ)

Human diseases

Meningitis (72.5%), others [septicaemia and septic shock (24.2%), arthritis, endocarditis, spondylodiscitis (of spine disc), endophthamitis (of the intraocular cavities), and uveitis (of the middle layer of the eye)]
Hearing loss and vestibular dysfunction are marked sequelae
High mortality rate (average of 17.8%), and higher if septicaemia.
Recent outbreak (Sichuan, 2005) with high mortality rate, cause of dead (the cause?? toxic shock syndrome or new virulent factor)
Symptom of fatal case similar to TSS (toxic-shock syndrome---patho=superantigen) but No S. pyogenes toxin gene found.
relapse---prolong treatment required

Physicians around the world should be aware of the possibility of S. suis-associated STSS when they see patients with unexplained sepsis who had been in contact with pigs.

Epidemiology

Zoonosis
Unlikely human-to-human transmission without close contact with materials (blood)
No obvious seasonal, but two Chinese outbreaks occurred in summer.
first human (Denmark) case 1968
Three outbreaks in China; in 1998, 1999, and 2005.
spread worldwide, but three countries are comprised of almost 90% (China 69%, Thailand 11.5% [with highest mortality rate26%] and Netherlands 8.3%)
2005 outbreak in china: 204 infected and 38 deaths
Total 409 cases with 73 deaths (2007 review)
Capsular serotypes: 35 types (1-34 and ½), but types 32 and 34 proven to be S. orisratti.
In most countries, capsular type 2 is currently the cause of most S. suis infections, whereas in Denmark and Finland, capsular type 7 appears to be most prevalent.

Stability and Control

60 °C for 10 mins.
50 °C for 2 hours.
10 °C for 6 weeks (carcasses).
0 °C for 1 month (in dust), for >3 months in faeces.
25 °C for 24 hours (in dust), for 8 days in faeces.
Killed with 5% bleach (1:799 dilution)

Case report

Taiwan Case 1 (38): fever, chill, headache, hearing impairment, acute OM, CSF culture yielded S. suis. a bank clerk, no pig contact. (tx: ceftriaxone, then PenG)
Taiwan case 2 (52): fever, nausea, headache, vomiting, neck stiffness, photophobia, (tx: Amp + Ceftriaxone), blood culture: S. suis, sterile CSF, Skin itching (pen allergic → ceftriaxone alone x14d), a pultry seller with a pig farm near her home.
Taiwan case 3 (61), diarrhea, abd pain, consciousness change

Lab identification

Culture
- rapid growth
- small colony (0.5-1.0 mm)
- gray-whitish colonies, or grayish or transparent and slightly mucoid.
- alpha-hemolysis (trypticase soy agar + 5% SRBC) 5%CO2, 35°C
- type 2 produces beta-hemolysis on horse blood agar plates.
- catalase-negative
- gram-positive cocci
- No growth in 6.5% NaCl media

Biochemical test (Phenotypic reaction profiles)
- In an article, different test kits gave different results;
  - S. suis by API Rapid ID20 Strep system (bioMerieux, Fr.) [biotype profile, 0641473; identity, 99.8%],
  - S. anginosus by Vitek GPI Card (bioMerieux Vitex, USA) [biotype profile, 5166333400; identity, 95%], and
  - S. vestibularis by Phoenix System PID (Beckon Dickinson, USA) [biotype profile, 420080163621; confidence value, 97%]

Species confirmed by
- 16S rRNA sequence analysis (1475 bp) and similarity search with BLAST : (in one article found similarity with S. suis; AF009476; 99%)
- PCR
  - rapid
  - detect specific serotypes or strains of S. suis
  - in animal carriers, infected or healthy pigs, and clinical samples.
  - S. suis-specific 16S ribosomal RNA region
  - a species-specific probe (serotypes 1-31) targeting 16S rRNA gene can be used to identify S. suis strains.
  - Multiplex PCR

Capsular reaction (1990) = Quellung Reaction (used in S. pneumococci)
- Test of choice (type-specific serum + capsular polysaccharide material)
- 5-6 hr culture (to avoid aging)
- Easy, rapid, specific- technique
  - A loopful of a 5%-serum culture broth is spread over an area of 0.5 cm in diameter on a glass slide.
  - One loopful of the antiserum is then mixed thoroughly with the culture on the slide.
  - Place a coverslip
  - examined under a phase contrast microscope with 1000x magnification.
  - Capsule visible (twice as big as those of control strains, which are mixed with non-immune rabbit serum.)

- Suis Type Antisera (Statens Serum Institute, Copenhagen, Denmark) can be used in the Quellung reaction.

Other techniques
- immunocapture
- fluorescent antibody techniques
- whole-cell antigen-based indirect ELISA, and
- purified capsular polysaccharide antigen-based indirect ELISA.

Phylogenetic analysis and study of genetic diversity