Genetic diversity of Streptococcus suis clinical isolates from pigs and humans in Italy (2003-2007)

Abstract

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.

Antimicrobial Susceptibility, Tetracycline and Erythromycin Resistance Genes, and Multilocus Sequence Typing of <i>Streptococcus suis</i> Isolates from Diseased Pigs in China

“…The tetracycline efflux gene tet(40) was first reported to be located in tandem with tet(O/32/O) in the human gut firmicute bacterium C. saccharolyticum K10 [11]. While most previous studies found that rRNA methylase was the main mechanism involved in erythromycin resistance in S. suis [10,18], the efflux gene mef(A/E) has only occasionally been reported [3]. Thus, our study suggests that efflux could be another prevalent tetracycline and erythromycin resistance mechanism.…”

“…This outcome might be explained by the intensive use of tetracyclines, macrolides and lincosamides, alone or in combination, for prophylaxis or treatment in pig breeding in China, which could provide the selective pressure needed for antibiotic-resistant bacteria to develop and spread. Other studies also demonstrated that resistance to tetracycline, erythromycin and clindamycin was common in S. suis of animal origin [18,23,27]. Tetracycline resistance was found to be common among the human isolates obtained from the Chinese outbreak in 2005 [26], and 6/7 S. suis human isolates were resistant to both erythromycin and clindamycin in Japan [2].…”

“…Thirty-three serotypes (types 1-31, 33 and 1/2) have been described based on capsular polysaccharides, and serotype 2 is considered to be the most pathogenic as well as the most prevalent capsular type in diseased pigs. Control of the disease by antimicrobials has generally been ineffective, partly because of increased resistance by S. suis to antimicrobials.Tetracycline and erythromycin are two antimicrobials that are extensively used for therapy, prophylaxis and growth promotion, and subsequently, associated resistance has been widely reported at a high rate in S. suis strains isolated from pigs and human beings [3,10,18]. However, mechanisms, which contribute to the tetracycline and macrolide resistance in Chinese S. suis strains, are still poorly understood.…”

“…Tetracycline and erythromycin are two antimicrobials that are extensively used for therapy, prophylaxis and growth promotion, and subsequently, associated resistance has been widely reported at a high rate in S. suis strains isolated from pigs and human beings [3,10,18]. However, mechanisms, which contribute to the tetracycline and macrolide resistance in Chinese S. suis strains, are still poorly understood.…”

Prevalence of <i>Streptococcus suis</i> Genotypes in Isolates from Porcine Endocarditis in East Japan

“…suis is classified into more than 30 serotypes according to the different antigenicity of its capsular polysaccharides, and serotype 2 has been most frequently isolated from both infected pigs and humans in many countries [4,23]. Among the serotype 2 strains, muraminidase-released protein (MRP) and extracellular factor (EF), encoded by mrp and epf, respectively, are frequently associated with virulent strains [21], and thus mrp and epf are often used as virulence-associated markers for epidemiological studies of S. suis [3,6,7,12,13,15,18,20,24]. In addition to these two genes, sly encoding a cytotoxin (Suilysin) is also frequently used as a virulence-associated marker [3,6,7,12,13,15,18,20,24].…”