For these reasons, lactic acid bacteria susceptibility test broth medium (LSM), which was recently developed by Klare et al. [11], should be considered the new testing standard for assessing the antimicrobial resistance spectra of lactic acid bacteria. Despite this medium being shown to be very effective for establishing antimicrobial susceptibilities of two species of Pediococcus, namely, P. acidilactici, and P. pentosaceus [10], it previously has not been used to study the prevalence, and spectrum, of antimicrobial resistance among other members of the genus. Overall, the use of antimicrobial compounds by industries such as animal husbandry,
brewing, and fuel ethanol to combat Pediococcus contaminants (e.g., hop-compounds, Penicillin, and Virginiamycin which is structurally similar to Synercid) is long-standing. However, knowledge about the resistance of pediococci VX-770 in vitro to antimicrobial agents is minimal [12]. As such, the focus of this research was to determine whether the use of antimicrobial hop-compounds in the brewing industry is associated with an increase in the overall antimicrobial resistance of Pediococcus isolates. Here we report on the testing of isolates from six species of the genus Pediococcus against 17 antimicrobial compounds using LSM broth in commercially available Sensititre GPN3F Gram-positive MIC plates (TREK Diagnostic
Systems, Cleveland Ceritinib ic50 OH). Results Antimicrobial susceptibility testing Twenty-nine isolates, including six species of the Pediococcus genus were tested. Distribution of isolates by species and their ability to grow in beer is given in Table 1. Antimicrobial Vorinostat resistance testing was reproducible and the LSM by itself (containing no antimicrobial compounds) was permissive to the rapid growth of all Pediococcus isolates tested. All isolates used in this study were capable of producing visible turbidity in LSM broth after an incubation period of 24 hours. Isolates were cultured for a period
of 48 hours in GPN3F plates so as to allow formation of larger bacterial pellets and thus a more accurate determination of the MIC for a given antibiotic. All control wells in the GPN3F plates produced appropriate results. Eight of the 29 isolates were randomly selected and tested in duplicate by the same method, and no variance in MICs was observed. The antimicrobial compounds and dilutions tested by the GPN3F antimicrobial susceptibility plates are listed in Additional file 1. Table 1 Pediococcus isolates. Species N Origin Growth in Beera Brewery Other b Unknown + – acidilactici 6 4 1 1 1 5 claussenii 12 12 0 0 11 1 ropyc (5) (5) (0) (0) (5) (0) non-ropyd (7) (7) (0) (0) (6) (1) damnosus 1 1 0 0 0 1 inopinatus 1 1 0 0 0 1 parvulus 5 0 5 0 1 4 ropy (1) (0) (1) (0) (0) (1) non-ropy (4) (0) (4) (0) (1) (3) pentosaceus 4 1 2 1 0 4 Total 29 19 8 2 13 16 a Previously reported by Haakensen et al. [3, 4].