Streptococcus suis, a major porcine pathogen, is emerging as a zoonotic agent capable of causing severe invasive disease in humans exposed to pigs or pork products. S. suis infection is rare in industrialised countries and usually arises as sporadic cases, with meningitis the most common clinical presentation in humans. Recent reports of two cases of meningitis in Sardinia and northeastern Italy prompted this first characterisation of Italian S. suis isolates. Fifty-nine S. suis strains, the two recent human strains and 57 swine clinical isolates collected between 2003 and 2007 from different Italian herds and regions, were tested for antimicrobial susceptibility, PCR-screened for virulence and antibiotic resistance genes, and subjected to molecular typing. Phenotypic and genotypic analysis demonstrated an overall high genetic diversity among isolates, the majority of which were resistant to macrolides (78%) and tetracyclines (90%). The erm(B), tet(O), mosaic tet(O/W/32/O), tet(W), and tet(M) genes were detected. The tet(O/W/32/O) gene, the most frequent tet gene after tet(O), had never been described in the genus Streptococcus before. In addition, a virulent cps2, erm(B) tet(O) clone, belonging to sequence type 1 (ST1) of the ST1 complex, was found to be prevalent and persistent in Italian swine herds. Finally, the two human isolates (both ST1) carrying cps2, erm(B) and tet(W) were seen to be closely related to each other.

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The genetic support for tet(W), an emerging tetracycline resistance determinant, was studied in two strains of Streptococcus suis, SsCA and SsUD, both isolated in Italy from patients with meningitis. Two completely different tet(W)-carrying genetic elements, sharing only a tet(W)-containing segment barely larger than the gene, were found in the two strains. The one from strain SsCA was nontransferable, and aside from an erm(B)-containing insertion, it closely resembled a genomic island recently described in an S. suis Chinese human isolate in sequence, organization, and chromosomal location. The tet(W)-carrying genetic element from strain SsUD was transferable (at a low frequency) and, though apparently noninducible following mitomycin C treatment, displayed a typical phage organization and was named ⌽SsUD.1. Its full sequence was determined (60,711 bp), the highest BLASTN score being Streptococcus pyogenes ⌽m46.1. ⌽SsUD.1 exhibited a unique combination of antibiotic and heavy metal resistance genes. Besides tet(W), it contained a MAS (macrolide-aminoglycoside-streptothricin) fragment with an erm(B) gene having a deleted leader peptide and a cadC/cadA cadmium efflux cassette. The MAS fragment closely resembled the one recently described in pneumococcal transposons Tn6003 and Tn1545. These resistance genes found in the ⌽SsUD.1 phage scaffold differed from, but were in the same position as, cargo genes carried by other streptococcal phages. The chromosome integration site of ⌽SsUD.1 was at the 3 end of a conserved tRNA uracil methyltransferase (rum) gene. This site, known to be an insertional hot spot for mobile elements in S. pyogenes, might play a similar role in S. suis. tet(W)is an emerging tetracycline resistance determinant whose host range, including Gram-positive, Gram-negative, aerobic, and anaerobic bacteria, is second only to that of tet(M) among ribosomal protection tet genes (26). tet(W) was first identified in the rumen anaerobe Butyrivibrio fibrisolvens (3), where it was associated with a transposable chromosomal element. It was subsequently detected in several other bacteria of the animal and human gastrointestinal tract, associated with either conjugative or nonconjugative elements (1, 5, 13, 14, 19, 29-31, 33, 37).In 2008 we first described tet(W) in Streptococcus suis, in a human isolate from a sporadic case of meningitis in Italy (23). S. suis, a major swine pathogen worldwide, is emerging as a zoonotic agent, the most common human clinical manifestations being meningitis and sepsis (20,39). Most cases of human S. suis infection have originated in Southeast Asia, where pig rearing is widespread, and large outbreaks have occurred in China (20). In industrialized countries human infections are rare, albeit probably underdiagnosed, and usually arise as sporadic cases. The growing interest in this emerging pathogen is reflected by recent whole-genome sequencing studies of selected isolates directed at elucidating the occurrence and evolution of the genetic determinants of its pathogenicity and dru...

The study was undertaken to investigate vancomycin-resistant (vanA) Enterococcus faecalis isolates carrying aggregation substance (AS) gene(s) for their ability to co-transfer vanA and AS genes. Methods: Six vanA clumping-positive E. faecalis isolates (five human and one food sample) carrying one or more AS genes (prgB, asa1, asa373) were analysed for co-transfer of vanA and AS genes to E. faecalis JH2-2 and Enterococcus faecium 64/3. Results: E. faecalis isolates harboured one or multiple plasmids carrying vanA, one or more AS gene(s) or both. vanA was transferred to JH2-2 (frequencies of 10 23-10 26) from all donors and to 64/3 (10 2 6-10 2 8) only from donors from humans. AS genes were detected in 51/60 (85%) of JH2-2 and in 20/50 (40%) of 64/3 vanA transconjugants (prgB, asa1, asa373 or prgB asa373), of which a total of 53.6% were clumping-positive. The plasmid content of JH2-2 transconjugants from the same donor was either identical to that of the donor or it was completely different, suggesting different mechanisms for co-transfer (location on the same pheromone plasmid, mobilization of vanA plasmids by the pheromone-inducible conjugation system, rearrangement of plasmid content during matings). After induction with pheromones, a marked increase in adhesion to Caco-2 cells was observed in four isolates and in some JH2-2 transconjugants, all clumping-positive. Conclusions: Findings suggest that co-transfer of vanA and AS genes may be a common feature of E. faecalis isolates. Since AS is recognized as a virulence factor, this feature might contribute to the emergence of strains with enhanced ability to cause infection and disease in humans.

Aims:  This study was designed to determine whether the probiotic strain Lactobacillus GG, which is extensively used in the treatment and prevention of intestinal disorders, is able to inhibit invasion of cultured human respiratory cells by macrolide‐resistant group A streptococci (GAS) carrying the prtF1 gene, which encodes the fibronectin (Fn)‐binding invasin F1. Methods and Results:  Eight prtF1‐positive erythromycin‐resistant GAS strains were used to infect A549 monolayers in competition and displacement assays with Lactobacillus GG. Live (L‐LGG) and heat‐killed (HK‐LGG) lactobacilli and their spent culture supernatant (SCS) significantly reduced (P < 0·001) GAS invasion efficiency in both assays. No antibacterial activity of Lactobacillus GG against GAS was detected. Both L‐LGG and HK‐LGG and all prtF1‐positive GAS induced a strong agglutination reaction using Fn‐coated particles. Conclusions:  Lactobacillus GG exerts an antagonistic action against GAS by inhibiting cell invasion. Competitive binding of Lactobacillus GG and GAS to Fn might be involved in the inhibition process. Significance and Impact of the Study:  The finding that Lactobacillus GG can prevent in vitro invasion of respiratory cells by GAS suggests new applications for this probiotic strain and warrants further studies of its capacity to prevent GAS throat infections.