The Selumetinib chemical structure isolates that were not resistant to all concentrations of Vancomycin tested were from the species P. acidilactici (N = 1), P. claussenii (Ropy, N = 1; Non-ropy, N = 3), P. damnosus (N = 1), and P. parvulus
(Non-ropy, N = 2), suggesting that the phenomenon is not the product of a clonal event. It has previously been shown that intrinsic Vancomycin resistance in P. pentosaceus is due to a modified peptidoglycan precursor ending in D-Ala-D-lactate . While this may also be the mechanism used by other Vancomycin-resistant pediococci, it is likely that the eight susceptible isolates do not possess this mechanism. Because media previously used for Pediococcus antimicrobial susceptibility testing have since been shown to be inappropriate for such testing (11), it is possible that the earlier Adriamycin finding of intrinsic Pediococcus Vancomycin-resistance was an artifact of the testing Selonsertib nmr medium used, rather than reflective of pediococci genetic content. The ropy phenotype did not associate with resistance to any of the antimicrobial compounds tested. This was an unexpected result as the ropy phenotype acts to create a biofilm which is expected to act as a physical barrier for the bacteria, putatively protecting them
from the antimicrobial compounds. Why no associations were found is unclear. It may be that the type of exopolysaccharide matrix produced by these isolates did not result in a sufficiently dense matrix so as to inhibit the passage of antimicrobial selleck chemicals llc compounds. Alternatively, the amount of energy expended on the production of exopolysaccharide may have caused a decreased ability to grow in the presence of the antimicrobial compounds, despite the partial antimicrobial barrier created by the exopolysaccharide. Of particular interest to the
brewing industry is the presence in pediococci of hop-resistance or beer-spoilage correlated genes (ABC2, bsrA, bsrB, hitA, horA, and horC). Of these six genes, only horA has been conclusively shown to function as a multidrug transporter, however, the ABC2, bsrA, and bsrB genes are highly similar to known ABC MDR genes, and the hitA gene is similar to divalent cation transporters. As such, all six of these beer-spoilage or hop-resistance correlated genes were assessed for associations with antimicrobial resistance. The genes hitA, horC, and ABC2 did not occur with sufficient frequency to determine statistical correlation [Additional file 2]. It is important to note that, as was found for ability to grow in beer, the bsrA, bsrB, and horA genes did not demonstrate significant associations with resistance to any of the antibiotics tested, but rather with susceptibility.