Abstract
Streptococci, enterococci and Streptococcus-like bacteria are frequent etiologic agents of infective endocarditis and correct species identification can be a laboratory challenge. Viridans streptococci (VS) not seldomly cause contamination of blood cultures. Vitek 2 and partial sequencing of the 16S rRNA gene were applied in order to compare the results of both methods. Strains originated from two groups of patients: 149 strains from patients with infective endocarditis and 181 strains assessed as blood culture contaminants. Of the 330 strains, based on partial 16S rRNA gene sequencing results, 251 (76%) were VS strains, 10 (3%) were pyogenic streptococcal strains, 54 (16%) were E. faecalis strains and 15 (5%) strains belonged to a group of miscellaneous catalase-negative, Gram-positive cocci. Among VS strains, respectively, 220 (87,6%) and 31 (12,3%) obtained agreeing and non-agreeing identifications with the two methods with respect to allocation to the same VS group. Non-agreeing species identification mostly occurred among strains in the contaminant group, while for endocarditis strains notably fewer disagreeing results were observed.Only 67 of 150 strains in the mitis group strains obtained identical species identifications by the two methods. Most VS strains belonging to the groups of salivarius, anginosus, and mutans obtained agreeing species identifications with the two methods, while this only was the case for 13 of the 21 bovis strains. Pyogenic strains (n=10), Enterococcus faecalis strains (n=54) and a miscellaneous group of catalase-negative, Gram-positive cocci (n=15) seemed well identified by both methods, except that disagreements in identifications in the miscellaneous group of strains occurred for 6 of 15 strains.
Highlights
Viridans streptococci (VS), enterococci and Streptococcus-like bacteria are frequent etiologic agents of infective endocarditis and correct species identification can be a big laboratory challenge [1]
In total 330 strains were included; 149 strains were from patients with definite infective endocarditis, and 181 strains from the same period, which had been evaluated as blood culture contaminants
The Open Microbiology Journal, 2010, Volume 4 117 were pyogenic streptococcal strains, 54 were E. faecalis strains and 15 strains belonged to a miscellaneous group of catalase-negative Gram-positive cocci
Summary
Viridans streptococci (VS), enterococci and Streptococcus-like bacteria are frequent etiologic agents of infective endocarditis and correct species identification can be a big laboratory challenge [1]. Diagnostic tools for identification of bacteria have developed dramatically in the last decades. These techniques, especially sequencing of the genes coding for rRNA and other genes, have led to revolutionary insights into the phylogeny and taxonomy of streptococci and related taxons [2]. Accurate identification of strains belonging to viridans streptococci is prerequisite for understanding the pathogenesis of these opportunistic infections, especially with regards to infective endocarditis [3].
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