Evaluation of Methods for Identification and Determination of the Taxonomic Status of Strains Belonging to the Streptococcus porcinus-Streptococcus pseudoporcinus Complex Isolated from Animal, Human, and Dairy Sources

Centers for Disease Control and Prevention, Atlanta, Georgia, USA.
Journal of clinical microbiology (Impact Factor: 4.23). 08/2012; 50(11):3591-7. DOI: 10.1128/JCM.01481-12
Source: PubMed

ABSTRACT Ninety-seven animal, human, and dairy Streptococcus porcinus or Streptococcus pseudoporcinus isolates in the CDC Streptococcus strain collection were evaluated on the basis of DNA-DNA reassociation, 16S rRNA and rpoB gene sequencing, conventional biochemical and Rapid ID 32 Strep identification methods, and antimicrobial susceptibility testing to determine their taxonomic status, characteristics for species differentiation, antimicrobial susceptibility, and relevance of clinical source. Nineteen of the 97 isolates (1 human, 18 swine) were identified as S. porcinus. The remaining 72 human isolates and 6 dairy isolates were identified as S. pseudoporcinus. The use of 16S rRNA or rpoB gene sequencing was required to differentiate S. porcinus from S. pseudoporcinus. The human and dairy S. pseudoporcinus isolates were biochemically distinct from each other as well as distinct by 16S rRNA and rpoB gene sequencing. Therefore, we propose the subspecies denominations S. pseudoporcinus subsp. hominis subsp. nov. for the human isolates and S. pseudoporcinus subsp. lactis subsp. nov. for the dairy isolates. Most strains were susceptible to the antimicrobials tested, with the exception of tetracycline. Two strains of each species were also resistant to clindamycin and erythromycin and carried the erm(A) (S. pseudoporcinus) or the erm(B) (S. porcinus) gene. S. porcinus was identified from a single human isolate recovered from a wound in an abattoir worker. S. pseudoporcinus was primarily isolated from the genitourinary tract of women but was also associated with blood, placental, and wound infections. Isolates reacting with group B antiserum and demonstrating wide beta-hemolysis should be suspected of being S. pseudoporcinus and not S. agalactiae.

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    ABSTRACT: Three vancomycin-resistant streptococcal strains carrying vanG elements (two invasive Streptococcus agalactiae isolates [GBS-NY and GBS-NM, both serotype II and multilocus sequence type 22] and one Streptococcus anginosus [Sa]) were examined. The 45,585-bp elements found within Sa and GBS-NY were nearly identical (together designated vanG-1) and shared near-identity over an ~15-kb overlap with a previously described vanG element from Enterococcus faecalis. Unexpectedly, vanG-1 shared much less homology with the 49,321-bp vanG-2 element from GBS-NM, with widely different levels (50% to 99%) of sequence identity shared among 44 related open reading frames. Immediately adjacent to both vanG-1 and vanG-2 were 44,670-bp and 44,680-bp integrative conjugative element (ICE)-like sequences, designated ICE-r, that were nearly identical in the two group B streptococcal (GBS) strains. The dual vanG and ICE-r elements from both GBS strains were inserted at the same position, between bases 1328 and 1329, within the identical RNA methyltransferase (rumA) genes. A GenBank search revealed that although most GBS strains contained insertions within this specific site, only sequence type 22 (ST22) GBS strains contained highly related ICE-r derivatives. The vanG-1 element in Sa was also inserted within this position corresponding to its rumA homolog adjacent to an ICE-r derivative. vanG-1 insertions were previously reported within the same relative position in the E. faecalis rumA homolog. An ICE-r sequence perfectly conserved with respect to its counterpart in GBS-NY was apparent within the same site of the rumA homolog of a Streptococcus dysgalactiae subsp. equisimilis strain. Additionally, homologous vanG-like elements within the conserved rumA target site were evident in Roseburia intestinalis.
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