Beta-lactamase diversity in Shigella spp

RESUMO

Some properties of the beta-lactamases produced by one strain of Shigella flexneri, one strain of Shigella sonnei, and one strain of Shigella boydii are studied. Susceptibility of these microorganisms to ampicillin and to cephalotin is investigated before and after a curing treatment with acridine oragne. The substrate profiles of these beta-lactamases, as well as their inducibility, their release to the extracellular environment by osmotic shcok,their susceptibility to enzime inhibitors, and their isoelectric points are also investigated. Transference of ampicillin resistance is tried by bacterial conjugation using a recipient strain of Escherichia coli K-12. The extrachromosomal DNA of the strain is also investigated. Through the analysis of the results the classification of these beta of these beta-lactamases is attempted in relation to the main groups of enzymes which are known at the present time. The three strains proved to be resistant to ampicillin and cephalotin but the transference of this resistance by conjugation was positive only for Sh. flexneri. Several bands of extrachromosomal DNA were observed in these microorganisms. It is concluded that, according to the properties of the enzymes, the beta-lactamase produced by Sh. flexneri belong to the TEM group of enzymes (plasmid-coded beta-lactamases). In relation to the beta-lactamase of Sh. sonnei, its general properties agree with those previously described for enzymes of the same bacterial species and allow the classification of this beta-lactamase as a constitutive cephalosporinase. It is also concluded that the bata-lactamase produced by Sh. boydii is plasmic-coded, since a curing effect was obtained with acridine orange and enzyme activity was released by osmotic shock procedure to the extracellualar environment in more than 80%. However, according to other properties (isolectric point and inhibition profile), this enzyme does not seem to belong to any of the know groups of plasmid-coded beta-lactamases...