Antimicrobial Resistance, Serotypes and Virulence Factors of Streptococcus suis Isolates from Diseased Pigs

Streptococcus suis isolates obtained from diseased pigs in China were found by resarchers in Guangzhou to be genetically diverse, resistant to multiple antibiotics and carry known virulence factors.
calendar icon 25 July 2012
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In a paper published in Foodborne Pathogens and Disease, Lu-Lu Li and co-authors at South China Agricultural University in Guangzhou report that they examined S. suis isolates from diseased pigs for susceptibility to nine antimicrobials, possession of virulence-associated factors (VFs) and distribution of serotypes.

The association between antimicrobial resistance (AMR) and serotypes as well as VFs was subsequently assessed.

Among the isolates investigated, serotype 2 (66.04 per cent) was mostly prevalent, followed by serotypes 1 (23.27 per cent), 9 (1.26 per cent), and 7 (0.63 per cent), whereas 14 isolates were untypable by the polymerase chain reaction (PCR) typing method used.

Analysis with pulsed-field gel electrophoresis revealed the isolates had diverse DNA macrorestriction patterns.

The frequency of antimicrobial resistance among the S. suis isolates was higher than that reported from other countries. It is notable that multiple antimicrobial resistance (three or more antimicrobials) was observed with 98.73 per cent of the S. suis isolates, and the dominant resistance phenotype was erythromycin-tilmicosin-clindamycin-chloramphenicol-levofloxacin-ceftiofur-kanamycin-tetracycline-penicillin (35.85 per cent).

The most prevalent VFs were those encoded by muramidase-released protein (61.64 per cent), followed by suilysin (56.60 per cent) and extracellular factor (46.54 per cent). Presence of VFs and the possession of certain AMR phenotypes were significantly associated as determined by statistical analysis.

Together, Li and colleagues conclude from their findings that the clinical S. suis isolates obtained from diseased pigs in China are genetically diverse, are resistant to multiple antibiotics of clinical importance, and carry known virulence factors.


Li L-L., X-P. Liao, J. Sun, Y-R. Yang, B-T. Liu, S-S. Yang, D-H. Zhao and Y-H. Liu. 2012. Antimicrobial resistance, serotypes, and virulence factors of Streptococcus suis isolates from diseased pigs. Foodborne Pathogens and Disease, 9(7):583-588. doi:10.1089/fpd.2011.1106.

Further Reading

You can view the full report by clicking here.

Further Reading

You can find out more about streptococcal infections in pigs by clicking here.

July 2012
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