Penicillin tolerance and bacterial endocarditis

A total of 965 cultures of streptococci received at a reference unit for identification were examined with API-20 Strep kits and also by established methods. The API method, although it needed to be supplemented with additional tests, largely overcame the difficulty that pyogenic streptococci are usually identified by their serological reactions and that biochemical tests are used for the identification of the other streptococci. Representatives of at least 24 established or possible species were identified.

Identification of streptococci in a medical laboratory.

The bacteria responsible for ureolysis in artificial dental plaque.

Routine identification of Streptococcus mutans and Streptococcus sobrinus is generally based upon growth on various selective media, colony morphology and biochemical characteristics. We examined various approaches of differentiating these two species through a combination of the conventional phenotypic methodology with chromosomal DNA fingerprint (CDF) and arbitrarily primed polymerase chain reaction (AP-PCR) methods. Initially, ten ATCC type strains and 20 randomly selected clinical isolates of mutans streptococci (MS) were characterized and grouped into two major types based on patterns generated by the CDF using HaeIII digestion. The CDF's patterns with restriction fragments equal to or greater than 6.6 kb were defined as the CDF-1 group. The CDF's patterns with restriction fragments less than 6.6 kb were defined as the CDF-2 group. Both groups were then examined for biotype, serotype, and composition of DNA via thermal denaturation. AP-PCR was applied and evaluated for the capability of delineating S. mutans from S. sobrinus strains. Results of this study showed that all CDF-1 strains fit within a G+C range of 36.2% to 42.2%, whereas the CDF-2 strains had a G+C range of 45.8% to 47.0%. The serotyping assay exhibited 100% sensitivity, 90% specificity and 86.7% agreement with the CDF. The biotyping assay presented the poorest specificity (38.5%), indicating the highest variability. The capability of AP-PCR in differentiation of S. mutans from S. sobrinus was comparable to the CDF method, suggesting that either of these two approaches can and may serve as a viable alternative method to serotyping or biotyping of MS.

Differentiation of Streptococcus mutans and Streptococcus sobrinus via genotypic and phenotypic profiles from three different populations.

The API 20S system (Analytab Products, Plainview, N.Y.) and the AutoMicrobic Gram-Positive Identification system (GPI; Vitek Systems, Hazelwood, Mo.) were evaluated for their capacity to identify the non-beta-hemolytic streptococci and aerococci to the species level. The 20S system identified 86% (six of seven strains) of nonhemolytic group B streptococci, whereas 100% of the same group B streptococcal strains were correctly identified by the GPI system. With both systems 99% (134 of 135 strains) of four species of group D enterococcus strains and 92% (24 of 26 strains) of the Aerococcus spp. strains were identified. The 20S system identified 84% (41 of 49 strains) of three species of group D non-enterococcus strains. The GPI system identified 96% of the same group D non-enterococcus strains. The 20S system identified 84% (190 of 226 strains) of 10 species of viridans streptococci; however, supplemental conventional tests were required to identify 49% (110 of the 226 strains) of the viridans strains to the species level. The GPI system identified 79% of the same viridans streptococci without the need for supplemental tests. Both systems identified 84% (161 of 192 strains) of the seven most commonly occurring viridans Streptococcus spp. The 20S system identified 82% (75 of 92 strains) and the GPI system identified 84% (54 of 64 strains) of Streptococcus pneumoniae.

Comparative evaluation of the API 20S and AutoMicrobic gram-positive identification systems for non-beta-hemolytic streptococci and aerococci.

A total of 227 strains of viridans streptococci were simultaneously identified on the Minitek Miniaturised System (BBL) and by a conventional method according to Colman and Williams. The Minitek discs were each overlaid with a drop of sterile liquid paraffin, and the trays were incubated in GaSPak jars (BBL) with CO2 generator envelopes. Identification was possible three to four days earlier than with the conventional method. The results were found to be in agreement with the conventional method. Compared to the identification schemes of Cowan and Steel and of Facklam, the results were also in good agreement. Minor differences were found in the number of positive and negative results in those reactions that are variable in all three schemes.

https://jcp.bmj.com/content/jclinpath/32/11/1168.full.pdf

M Schaareman

Papers

Identification of viridans streptococci on the Minitek Miniaturised Differentiation System.