Characterization of BRO Enzymes and Beta-Lactamase Transfer of <i>Moraxella (Branhamella)</i><i>catatrhalis</i> Isolated in Japan

Abstract

Of the 68 strains of β-lactamase-producing Moraxella (Branhamella) catarrhalis isolated in J apan that were studied, 62 (91%) produced the BRO-1-type β-lactamase and 6 (9%) produced the BRO-2 type. There were no strains containing the BRO-3-type β-lactamase. We compared the susceptibility of BRO-1- and BRO-2-producing strains to various oral β-lactam antibiotics. We found that the BRO-1-producing strains were less susceptible than the BRO-2-producing strains. Although the BRO-1 and BRO-2 types showed a similar hydrolysis pattern, the specific activity of BRO-1 was 3-fold that of BRO-2. We examined the transfer of the BRO-1 and BRO-2 genes to non-β-lactamase-producing M. catarrhalis No. 4020 and found that of the 13 donor strains producing BRO-1,11 (85%) were able to transfer the gene for BRO-1 production by conjugation. Of the 6 donor strains producing BRO-2, 2 (33%) were able to transfer the gene for BRO-2 production by conjugation. For 3 of the 13 (23%) BRO-1-producing strains and 1 of the 6 (17%) BRO-2-producing strains, about 13 Mdal-ton of plasmids were detected. These plasmid-containing strains were used as donors, and in fi-lactamase-producing transconjugants the same size of plasmids was detected. However, when the total DNA is extracted from strains with the ability to transfer by conjugation, the transformation of the β-lactamase-producing gene can occur regardless of the presence or absence of plasmids. Furthermore, even if purified plasmids are transformed, β-lactamase-producing transformants are not obtained. In this study, we found that β-lactamase-producing ability was not related to the plasmids we detected and that the gene for β-lactamase may be in the chromosomes.

Genesis of BRO β‐lactamase‐producing Moraxella catarrhalis: evidence for transformation‐mediated horizontal transfer

“…These differences were found to affect promoter strength, resulting in a bro1 promoter that was approximately twice as strong as the bro2 promoter. The changes in the promoter region, resulting in increased resistance to β‐lactam antibiotics, have probably increased the fitness of BRO‐1‐producing strains relative to BRO‐2 producers, explaining why nowadays bro1 strains predominate (Ikeda et al ., 1993; Fung et al ., 1994; Ejlertsen and Skov, 1996).…”

“…M. catarrhalis strains produce either BRO‐1 or BRO‐2 β‐lactamase, which can be distinguished on the basis of production level and isoelectric‐focusing pattern (Wallace et al ., 1989). BRO‐1 type strains represent the majority of β‐lactamase‐producing M. catarrhalis and express higher levels of resistance to ampicillin (Wallace et al ., 1989; Ikeda et al ., 1993; Fung et al ., 1994; Bootsma et al ., 1996). Previously, we showed that the bro1 and bro2 genes were located at the same chromosomal locus.…”

“…The first two types of transfer tend to occur mainly between members of the same species, while broad host range gene transfer is most likely mediated by conjugation. Although conjugation is generally believed to mediate the transfer of BRO β‐lactamase (Kamme et al ., 1984; Wallace et al ., 1989; Ikeda et al ., 1993), transformation has been proposed as an alternative mechanism (Catlin, 1990). However, definite proof for the involvement of these processes in the transmission of bro has yet to be provided.…”