Suicin 90-1330 from a Nonvirulent Strain of Streptococcus suis: a Nisin-Related Lantibiotic Active on Gram-Positive Swine Pathogens

Abstract

c Streptococcus suis serotype 2 is known to cause severe infections (meningitis, endocarditis, and septicemia) in pigs and is considered an emerging zoonotic agent. Antibiotics have long been used in the swine industry for disease treatment/prevention and growth promoters. This pattern of utilization resulted in the spread of antibiotic resistance in S. suis worldwide. Interestingly, pigs may harbor S. suis in their tonsils without developing diseases, while North American strains belonging to the sequence type 28 (ST28) are nonvirulent in animal models. Consequently, the aim of this study was to purify and characterize a bacteriocin produced by a nonvirulent strain of S. suis serotype 2, with a view to a potential therapeutic and preventive application. S. suis 90-1330 belonging to ST28 and previously shown to be nonvirulent in an animal model exhibited antibacterial activity toward all S. suis pathogenic isolates tested. The bacteriocin produced by this strain was purified to homogeneity by cationic exchange and reversed-phase fast protein liquid chromatography. Given its properties (molecular mass of <4 kDa, heat, pH and protease stability, and the presence of modified amino acids), the bacteriocin, named suicin 90-1330, belongs to the lantibiotic class. Using a DNA-binding fluorophore, the bacteriocin was found to possess a membrane permeabilization activity. When tested on other swine pathogens, the suicin showed activity against Staphylococcus hyicus and Staphylococcus aureus, whereas it was inactive against all Gram-negative bacteria tested. Amino acid sequencing of the purified bacteriocin showed homology (90.9% identity) with nisin U produced by Streptococcus uberis. The putative gene cluster involved in suicin production was amplified by PCR and sequence analysis revealed the presence of 11 open reading frames, including the structural gene and those required for the modification of amino acids, export, regulation, and immunity. Further studies will evaluate the ability of suicin 90-1330 or the producing strain to prevent experimental S. suis infections in pigs.

Distribution of Suicin Gene Clusters in Streptococcus suis Serotype 2 Belonging to Sequence Types 25 and 28

“…Pseudochromosomes and the genome sequences of reference strains NSUI002 and NSUI060 were converted into queryable BLASTN databases using BLAST+. Gene clusters encoding suicins 90-1330 (accession number: KU867866), 3908 (accession number: KU867867), and 65 (accession number: KU867868) have been described previously and are illustrated in Figure 1 [9–11]. The sequences of individual genes, as well as the full regions for each suicin cluster, were blasted against each genome and pseudochromosome database to test for the presence of genes encoding suicins 90-1330, 3908, and 65.…”

“…Recently, we purified and characterized three different lantibiotics, named suicins, produced by three distinct strains of S. suis serotype 2 [9–11]. The mature peptides corresponding to each suicin showed poor identity (≤24%) between each other, thus indicating that they are unrelated.…”

“…The mature peptides corresponding to each suicin showed poor identity (≤24%) between each other, thus indicating that they are unrelated. Suicin 90-1330 (SslA) is a type A (linear) lantibiotic secreted by a nonvirulent (in both mouse and pig infection models) isolate of S. suis (strain 90-1330) belonging to ST28 and exhibits high homology (90.9%) with nisin U produced by Streptococcus uberis [9]. The production of suicin 90-1330 involves a gene cluster comprising eleven genes [9].…”

“…Suicin 90-1330 (SslA) is a type A (linear) lantibiotic secreted by a nonvirulent (in both mouse and pig infection models) isolate of S. suis (strain 90-1330) belonging to ST28 and exhibits high homology (90.9%) with nisin U produced by Streptococcus uberis [9]. The production of suicin 90-1330 involves a gene cluster comprising eleven genes [9]. Suicin 3908 (SuiA) is a type B (N-terminal linear and C-terminal globular moieties) lantibiotic produced by a nonvirulent (newborn germ-free pig infection model) isolate of S. suis (strain 3908; unknown ST) isolated from a healthy carrier pig, and shows some identity with bovicin HJ50 ( Streptococcus bovis ; 49.2% identity) [10].…”

“…The gene cluster involved in the production of suicin 65 was found to contain ten genes, including a duplication of the structural gene. Since all three suicins were found to be bactericidal for highly virulent ST1 strains of S. suis [9–11], the use of the purified lantibiotics or the lantibiotic-producing strains may represent a valuable strategy to control S. suis infections and for reducing antibiotic use in the swine industry and consequently the spread of antibiotic resistance. However, the prevalence of the different suicin gene clusters among the circulating population of S. suis strains is not known.…”