Objectives:

Nutritionally variant Streptococci (NVS) were described as a major causative agent of septicaemia in neutropenic cancer patients and accounted for serious cases of infective endocarditis. In clinical laboratories, the identification of NVS is often dependent upon their phenotypic characterisation. An overlap in physiologic characteristics between NVS and other Gram-positive catalase-negative cocci is known.

Methods:

Our study examined, if it is possible to confirm preliminary phenotypical identification as NVS by fatty acid analysis based on whole cell fatty acid methyl esters (MIS Sherlock, MIDI, Inc., USA). Two years of study on Gram-positive catalase-negative cocci recovered from blood cultures yielded nine isolates of NVS. According to the analysis of partial 16S rRNA gene sequence, NVS-isolates were identified as Granulicatella adiacens (7) and Abiotrophia defectiva (2). To confirm correct interpretation of fatty acid results, NVS reference strains and ‘viridans streptococci’ isolates, which were identified as Streptococcus spp. and phenotypically resembled NVS, were also included in the study. The obtained fatty acid compositions of our isolates were also compared with the phenotypically similar Gemella morbillorum.

Results:

All Streptococcus spp. significantly differed from other strains tested by lower amount of both C16: 1w9c and C18: 1w9c. In comparison with other NVS, only G. elegans showed unique fatty acid composition, the amount of C18: 2w6,9c was almost three times higher and C16: 1w9c was not detected at all. For further differentiation of A. defectiva, G. adiacens and G. morbillorum, three fatty acids were chosen – C16: 0, C18: 1w9c and C18: 2w6,9c. Unlike G. adiacens and G. morbillorum, the amount of C16: 0 lower than 30% and simultaneously the amount of C18: 1w9c higher than 20% were detected in A. defectiva. G. adiacens differed from G. morbillorum by the amount of C18: 2w6,9c being lower than 3%.

Conclusions:

(1) The fatty acid composition of phenotypically similar Streptococcus spp. differs significantly from all tested NVS. (2) Fatty acid analysis could be an useful tool for the discrimination of G. elegans from G. adiacens and A. defectiva. (3) In case of failure of satelitism behaviour, the found differences in fatty acid composition could help to distinguish G. morbillorum from NVS.

Acknowledgement:

Our work was supported by the Ministry of Health of the Czech Republic, Id.code: MZO/ZA/00538.