Identification of gram-positive coccal and coccobacillary vancomycin-resistant bacteria

Abstract

A total of 84 of 150 vancomycin-resistant (defined as no inhibition of bacterial growth around a 30-μg vancomycin disk placed on 5% sheep blood-Trypticase soy agar [BBL Microbiology Systems, Cockeysville, Md.]) bacteria were definitively identified by determining the phenotypic criteria. The identity of representatives was also confirmed by DNA-DNA hybridizations. The following strains were identified: 1 Enterococcus faecium, 18 Leuconostoc mesenteroides, 15 Leuconostoc citreum, 9 Leuconostoc pseudomesenteroides, 2 Leuconostoc lactis, 20 Pediococcus acidilactici, 5 Pediococcus pentosaceus, and 14 Lactobacillus confusus. The remaining vancomycin-resistant strains were identified as probable Leuconistoc (6 strains), probable Pediococcus (1 strain), and probable lactobacilli (28 strains). A total of 32 strains of gram-positive coccobacillary bacteria remained unidentified. Test used for the phenotypic identification of strains to the genus level included a Gram stain bacteria grown in thioglycolate broth, gas production in Lactobacillus Mann, Rogosa, and Sharpe broth, hydrolysis of pyrrolidonyl-β-naphthylamide, bile-esculin reaction, demonstration of streptococcal group D antigen, and growth at 10 and 45°C and in 6.5% NaCl broth. Strains were identified to the species level by hydrolysis of esculin, reactions in litmus milk, slime production on 5% sucrose agar, acidification of maltose, melibiose, and raffinose broths, deamination of arginine, and growth at 42°C and in 6.5% NaCl broth.