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Characterization of three new enterococcal species, Enterococcus sp. nov. CDC PNS-E1, Enterococcus sp. nov. CDC
Maria da Glória S Carvalho1, Arnold G Steigerwalt, Roger E Morey
1Division of Bacteria and Mycotic Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia 30333, USA.
Abstract:
As a reference laboratory, the Streptococcus Laboratory at the Centers for Disease Control and Prevention (CDC) is frequently asked to confirm the identity of unusual or difficult-to-identify catalase-negative, gram-positive cocci. In order to accomplish the precise identification of these microorganisms, we have systematically applied analysis of whole-cell protein profiles (WCPP) and DNA-DNA reassociation experiments, in conjunction with conventional physiological tests. Using this approach, we recently focused on the characterization of three strains resembling the physiological groups I (strain SS-1730), II (strain SS-1729), and IV (strain SS-1728) of enterococcal species. Two strains were isolated from human blood, and one was isolated from human brain tissue. The results of physiological testing were not consistent enough to allow confident inclusion of the strains in any of the known enterococcal species. Resistance to vancomycin was detected in one of the strains (SS-1729). Analysis of WCPP showed unique profiles for each strain, which were not similar to the profiles of any previously described Enterococcus species. 16S ribosomal DNA (rDNA) sequencing results revealed three new taxa within the genus ENTEROCOCCUS: The results of DNA-DNA relatedness experiments were consistent with the results of WCPP analysis and 16S rDNA sequencing, since the percentages of homology with all 25 known species of Enterococcus were lower than 70%. Overall, the results indicate that these three strains constitute three new species of Enterococcus identified from human clinical sources, including one that harbors the vanA gene. The isolates were provisionally designated Enterococcus sp. nov. CDC Proposed New Species of Enterococcus 1 (CDC PNS-E1), type strain SS-1728(T) (= ATCC BAA-780(T) = CCUG 47860(T)); Enterococcus sp. nov. CDC PNS-E2, type strain SS-1729(T) (= ATCC BAA-781(T) = CCUG 47861(T)); and Enterococcus sp. nov. CDC PNS-E3, type strain SS-1730(T) (= ATCC BAA-782(T) = CCUG 47862(T)).
Insights
Three novel Enterococcus species were identified from human clinical samples. These new bacterial species were characterized using whole-cell protein profiles and DNA sequencing, with one strain exhibiting vancomycin resistance.
Area of Science:
- Microbiology
- Bacteriology
- Clinical Microbiology
Background:
- Accurate identification of catalase-negative, gram-positive cocci is crucial for clinical microbiology.
- The Streptococcus Laboratory at CDC frequently encounters unusual or difficult-to-identify microorganisms.
- Enterococcal species identification can be challenging, necessitating advanced characterization methods.
Purpose of the Study:
- To precisely identify three unusual enterococcal strains isolated from human clinical sources.
- To characterize novel taxa within the genus Enterococcus using a polyphasic approach.
- To determine the taxonomic status of strains that did not conform to known enterococcal species.
Main Methods:
- Systematic application of whole-cell protein profiles (WCPP) analysis.
- DNA-DNA reassociation experiments for genetic relatedness assessment.
- Conventional physiological tests and 16S ribosomal DNA (rDNA) sequencing.
Main Results:
- Physiological testing was insufficient for confident species identification.
- WCPP analysis revealed unique profiles distinct from known Enterococcus species.
- 16S rDNA sequencing and DNA-DNA hybridization confirmed three distinct novel species within the Enterococcus genus, with <70% homology to known species.
- One isolate (SS-1729) demonstrated vancomycin resistance, associated with the vanA gene.
Conclusions:
- The three studied strains represent three new species of Enterococcus, isolated from human clinical specimens.
- These findings expand the known diversity of the Enterococcus genus.
- The identification of a vancomycin-resistant novel species highlights the importance of ongoing microbial surveillance.
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