Antibiotic resistance of Flavobacterium and related genera

The genus Flavobacterium is characterized by high levels of resistance to a wide range of antibiotics. Clinical laboratories may experience difficulty in detecting this resistance, the underlying mechanisms of which are unknown. Genetically the genus is so diverse that it may eventually be subdivided into at least four genera. Furthermore within the genus some species are genetically heterogeneous and warrant subdivision into further species. To date these taxonomic reforms have not been possible because of a lack of phenotypic markers which can be correlated with the genetic differences. An additional taxonomic problem which requires clarification is the relationship of Flavobacterium to other genera, particularly Cytophaga and Bacteroides. In this study eighty nine Flavobacterium study strains and 43 reference strains were tested to investigate the susceptibility of the genus to antibiotics. Cell-free betalactamase preparations of selected strains were used to determine the substrate profiles, inhibitor profiles, inducibility and isoelectric points of the beta-lactamases of the genus and some related organisms. Preliminary data were obtained about the roles of beta-lactamases and outer membrane permeability in resistance to beta-l actam antibiotics. Although two standardised conventional antibiotic susceptibil ity testing techniques showed poor correlation the antibiotic resistance patterns were nevertheless specific for certain species and for groups of flavobacteria, indicating that antibiotic resistance is of taxonomic utility for this genus. Flavobacterium aquatile, F· breve, F.· meningosepticum and F. odoratum could be readily delineated by their susceptibility patterns. Similarities in the antibiograms and beta-lactamases of F. multivorum, F. spiritivorum and F. thalpophilum was further evidence of the relatedness of these species and supported suggestions that they be recognised as a separate genus. The beta-lactamases of the genus Flavobacterium are characteristically chromosomally mediated beta-lactamases of Richmond and Sykes Class IV. Many Flavobacterium betalactamases were unusual in exhibiting activity against the new beta-lactamase resistant antibiotics cefoxitin and cefotaxime, and occasionally imipenem. This suggested that these enzymes are Class IV oxyiminocephalosporinases. This finding is of taxonomic significance. It is also of clinical and pharmaceutical significance in that it identifies Flavobacterium as a genus capable of inactivating the latest beta-lactam antibiotics and therefore requiring close examination by research chemists if they are to succeed in producing antibiotics which can evade the resistance mechanisms of pathogenic bacteria.