Abstract
Bacteriocins are antimicrobial peptides of bacterial origin that are considered as a promising alternative to the use of conventional antibiotics. Recently, our laboratory reported the purification and characterization of two lantibiotics, suicin 90–1330 and suicin 3908, produced by the swine pathogen and zoonotic agent Streptococcus suis (serotype 2). In this study, a novel bacteriocin produced by S. suis has been identified and characterized. The producing strain S. suis 65 (serotype 2) was found to belong to the sequence type 28, that includes strains known to be weakly or avirulent in a mouse model. The bacteriocin, whose production was only possible following growth on solid culture medium, was purified to homogeneity by cationic exchange and reversed-phase high-pressure liquid chromatography. The bacteriocin, named suicin 65, was heat, pH and protease resistant. Suicin 65 was active against all S. suis isolates tested, including antibiotic resistant strains. Amino acid sequencing of the purified bacteriocin by Edman degradation revealed the presence of modified amino acids suggesting a lantibiotic. Using the partial sequence obtained, a blast was performed against published genomes of S. suis and allowed to identify a putative lantibiotic locus in the genome of S. suis 89–1591. From this genome, primers were designed and the gene cluster involved in the production of suicin 65 by S. suis 65 was amplified by PCR. Sequence analysis revealed the presence of ten open reading frames, including a duplicate of the structural gene. The structural genes (sssA and sssA’) of suicin 65 encodes a 25-amino acid residue leader peptide and a 26-amino acid residue mature peptide yielding an active bacteriocin with a deducted molecular mass of 3,005 Da. Mature suicin 65 showed a high degree of identity with class I type B lantibiotics (globular structure) produced by Streptococcus pyogenes (streptococcin FF22; 84.6%), Streptococcus macedonicus (macedocin ACA-DC 198; 84.6%), and Lactococcus lactis subsp. lactis (lacticin 481; 74.1%). Further studies will evaluate the ability of suicin 65 or the producing strain to prevent experimental S. suis infections in pigs.
Highlights
Streptococcus suis is a major swine pathogen worldwide that is transmitted via the respiratory route and colonizes the palatine tonsils of pigs [1]
As a continuation of our ongoing work aimed to investigate S. suis bacteriocins, in this study, we identified and characterized a novel class I type B lantibiotic produced by S. suis
To exclude the possibility that this antibacterial activity resulted from the production of the two previously characterized S. suis lantibiotics, the presence of the structural genes suiA and sslA, coding respectively for suicin 3908 and suicin 90–1330, was investigated by PCR
Summary
Streptococcus suis is a major swine pathogen worldwide that is transmitted via the respiratory route and colonizes the palatine tonsils of pigs [1]. S. suis infections in humans remain sporadic and affect mainly individuals in close contact with sick or pig-derived products, important outbreaks that occurred in Asia modified the world viewpoint regarding the threat of S. suis for humans [4, 5]. While 35 serotypes (1 to 34 and 1/2) have been identified, serotype 2 is the most frequently associated with pathology [1, 2]. In the last decade, other serotypes with a particular geographical distribution have been identified as the source of many infections [6]. In North America, serotypes 2 and 3 show a prevalence of 24.3% and 21%, respectively, followed by serotypes 1/2, 8, and 7 [6]
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