Differentiation of Highly Virulent Strains of Streptococcus suis Serotype 2 According to Glutamate Dehydrogenase Electrophoretic and Sequence Type

Abstract

The glutamate dehydrogenase (GDH) enzymes of 19 Streptococcus suis serotype 2 strains, consisting of 18 swine isolates and 1 human clinical isolate from a geographically varied collection, were analyzed by activity staining on a nondenaturing gel. All seven (100%) of the highly virulent strains tested produced an electrophoretic type (ET) distinct from those of moderately virulent and nonvirulent strains. By PCR and nucleotide sequence determination, the gdh genes of the 19 strains and of 2 highly virulent strains involved in recent Chinese outbreaks yielded a 1,820-bp fragment containing an open reading frame of 1,344 nucleotides, which encodes a protein of 448 amino acid residues with a calculated molecular mass of approximately 49 kDa. The nucleotide sequences contained base pair differences, but most were silent. Cluster analysis of the deduced amino acid sequences separated the isolates into three groups. Group I (ETI) consisted of the seven highly virulent isolates and the two Chinese outbreak strains, containing Ala 299 -to-Ser, Glu 305 -to-Lys, and Glu 330 -to-Lys amino acid substitutions compared with groups II and III (ETII). Groups II and III consisted of moderately virulent and nonvirulent strains, which are separated from each other by Tyr 72 -to-Asp and Thr 296 -to-Ala substitutions. Gene exchange studies resulted in the change of ETI to ETII and vice versa. A spectrophotometric activity assay for GDH did not show significant differences between the groups. These results suggest that the GDH ETs and sequence types may serve as useful markers in predicting the pathogenic behavior of strains of this serotype and that the molecular basis for the observed differences in the ETs was amino acid substitutions and not deletion, insertion, or processing uniqueness.Streptococcus suis is a world-wide pathogen of swine and an important zoonotic agent (21,22,24,26,27). Strains of this bacterium are divided into 35 serotypes (types 1/2 and 1 through 34) according to polysaccharide capsular antigens. Type 2 is the type most frequently associated with disease and also the type most often isolated. The disease conditions in swine include meningitis, arthritis, septicemia, endocarditis, encephalitis, abortions, polyserositis, and bronchopneumonia (22). S. suis has been isolated from other animal species, including horses, dogs, cats, birds, and wild boars, suggesting that it may be pathogenic for more than one animal species (22). In infected humans, S. suis type 2 can cause meningitis, endocarditis, septicemia, toxic shock, and permanent hearing loss (21,22,24,26,27). A recent outbreak in China, which involved 39 human and Ͼ200 swine deaths, has caused elevated concern (27). Attempts to effectively control S. suis infection have been problematic due to genetic heterogeneity within and between serotypes, a lack of effective vaccine and diagnostic reagents, inability to effectively distinguish virulent from nonvirulent isolates, a paucity of information on the genetics of S. suis relative to its mechanism of pathogen...

Güney Çin’de Hastalıklı ve Sağlıklı Domuzlarda Streptococcus suis’in Antimikrobiyal Direnci, Serotipleri ve Genetik Çeşitliliği

“…Highly virulent strains of S. suis serotype 2 can be distinguished from moderately virulent and nonvirulent strains on the basis of their GDH [26,27] . The isolates of S. suis serotype 2 were divided into 3 groups according to deduced GDH amino acid sequence.…”

“…Group I consisted of highly virulent isolates, containing Ala299-to-Ser, Glu305-to-Lys, and Glu330-to-Lys amino acid substitutions compared with groups II and III. Groups II and III consisted of moderately virulent and nonvirulent strains, which are separated from each other by Tyr72-to-Asp and Thr296to-Ala substitutions [27] . In this study, the GDH gene of 36 strains of S. suis serotype 2 obtained a 1.500-bp fragment containing an open reading frame of 1.344 nucleotides by PCR and nucleotide sequence determination.…”

“…Subsequently, the PCR product obtained from each isolate was sub-cloned into the pUCm-T vector and sequenced using the dideoxy chain-termination method (Sangon Biotech Ltd., Shanghai, China). GDH sequence types of the S. suis isolates were analyzed using the method described by Kutz et al [27] .…”

Genetic and virulence characterization of Streptococcus suis type 2 isolates from swine in the provinces of Zhejiang and Henan, China

“…There are a number of approaches to differentiate pathogenic isolates from low virulent or avirulent ones such as virulotyping and MLST. Several putative virulence factors such as GDH, MRP, EF, CPS, SLY, and 89K have been used as virulence-associated markers for virulotyping of SS2 isolates (Baums and Valentin-Weigand 2009;Lun et al 2007;Kutz and Okwumabua 2008). MLST has been used for the typing of more than 400 SS2 isolates, and those belonging to ST1 and ST27 complexes are considered Zhejiang, lung lesion as more pathogenic (King et al 2002;Takamatsu et al 2008).…”

Impact of gene modification of phosphotransferase system on expression of glutamate dehydrogenase protein of Streptococcus suis in Escherichia coli

“…The glutamate dehydrogenase (GDH) of Streptococcus suis is conserved and antigenic, as it reacts with serum from animals with S. suis type 2 infection, leading to it being utilized as a serological assay for diagnosis of S. suis infection [1,2]. It has been reported that the subunit vaccination based on GDH protein of S. suis is an effective strategy for protecting pigs against S. suis infection [3] but its market is limited because of the high cost.…”