Antimicrobial susceptibility of human blood culture isolates of Lactobacillus spp.

The clinical significance of Lactobacillus is a subject of debate, although it is evident that this genus has been implicated in various types of infections, especially in immunocompromised patients [1, 2]. Few published studies have included a sufficient number of human clinical isolates of individual Lactobacillus species in order to facilitate comparisons of antimicrobial sensitivities [2, 3]. The study presented here aimed at characterizing several Lactobacillus isolates using 16S rRNA gene sequencing for species identification, PFGE for strain identification, and susceptibility testing of 20 antimicrobial agents, including several newer antimicrobial agents. Twenty-three Lactobacillus strains were obtained from the blood culture samples of 23 patients in Arhus County, Denmark, between 1997 and 2004. Six of these strains have been characterized previously in some detail [4]. Species identification was performed using partial 16S rRNA analysis. Identification revealed one isolate of L. curvatus, one isolate of L. delbrueckii, one isolate of L. gasseri, five isolates of L. paracasei, four isolates of L. plantarum, ten isolates of L. rhamnosus and one isolate of L. salivarius. Thus, a high prevalence of L. rhamnosus (43%), L. paracasei (22%), and L. plantarum (17%) was observed in accordance with previous studies [1]. The L. plantarum species identity was confirmed using a species-specific PCR [5]. The strains were typed using pulsed-field gel electrophoresis (PFGE). Cluster analysis was performed using GelCompar II ver. 2.5, and the strains were compared in the database of Chr. Hansen A/S, which consists of several hundred strains; mainly food isolates and industrial starter cultures. Ten isolates of L. rhamnosus could be separated into two subgroups containing seven and three isolates, respectively. Each subgroup was not completely homogeneous, as the isolates showed variation of one to two bands. None of the PFGE fingerprints in this study resembled the fingerprint of the probiotic strain L. rhamnosus GG (data not shown). A Finnish study found that 22 of 46 L. rhamnosus bacteremia isolates had PFGE fingerprints identical to the GG strain [3] although they were phenotypically different [6]. The five isolates of L. paracasei had unique fingerprints, with one isolate being similar to ATCC 25598. Three of the four L. plantarum strains had similar fingerprints, with two being identical and the third strain differing by only two of 17 bands. Antimicrobial susceptibility to a total of 20 antimicrobial agents was determined using E-tests (AB Biodisk, Solna, Sweden) on ISO-sensitest agar (Oxoid, Basingstoke, UK) according to the manufacturer’s recommendation. The MIC ranges (mg/l) of antimicrobial agents for which no differences were observed between Lactobacillus spp were as follows: ampicillin (0.125–4), chloramphenicol (1–8), clindamycin (0.032–1), erythromycin (0.032–2), synercid (0.25–2) and linezolid (0.5–4). The MICs of the antimicrobial agents for which variation among the species was observed are presented in Table 1. Eur J Clin Microbiol Infect Dis (2007) 26:287–289 DOI 10.1007/s10096-007-0274-8