No abstract

A relationship between resistance to methicillin and resistance to fluoroquinolones, rifampin, and mupirocin has been described for Staphylococcus aureus. Differences in resistance rates may be explainable by a higher spontaneous mutation rate (MR) or a faster development of resistance (DIFF) in methicillin-resistant S. aureus (MRSA). No differences in MR, DIFF, and mutations in grlA and gyrA were detected between methicillinsusceptible S. aureus and MRSA. The higher resistance rates in MRSA are not the result of hypermutability of target genes or a faster emergence of different mutations and may be the consequence of clonal spread of multiresistant MRSA.

Of the 419 Moraxella catarrhalis isolates collected during the 1997-1999 European SENTRY surveillance study, 385 (92%) were ␤-lactamase positive. Twenty-two (5.7%) produced BRO-2 ␤-lactamase. Twenty-one new mutations were found in the putative promoter region of the bro genes. Nineteen percent of all isolates tested were complement sensitive. Resistance to ␤-lactams is not linked to the phylogenetic lineages associated with susceptibility to complement.Moraxella catarrhalis was long considered a harmless commensal of the respiratory tract and uniformly susceptible to penicillins. In recent years, however, its pathogenic potential has come to light (9,20,27). The production of a new ␤-lactamase enzyme, designated BRO (from Branhamella and Moraxella), by this bacterium was an event that occurred virtually simultaneously around the world (9,13,19,20). Two distinct BRO ␤-lactamase enzymes, namely, BRO-1 and BRO-2, have since been found in strains of M. catarrhalis. These enzymes are identical in substrate and inhibition profile but differ by a single amino acid (2-5). The increased level of resistance conferred by BRO-1 compared to BRO-2 appears to be related to the relative amount of each enzyme produced by the strains (5). This difference in production may be the result of differences in the promoter strength of the two genes. Bootsma et al. (5) reported a 21-bp deletion in the promoter region of the ␤-lactamase gene from a BRO-2-producing strain. In addition, Richter et al. (22) suggested that additional mutations or deletions or insertions in the promoter sequence might explain the variations seen in antibiotic susceptibilities within the populations of BRO-1-and BRO-2-producing M. catarrhalis isolates.The first goal of this study, therefore, was to characterize the BRO ␤-lactamases and their putative promoter regions in the European M. catarrhalis isolates collected between 1997 and 1999 during the European SENTRY surveillance study. The relative percentages of the two enzyme types were also determined.Besides protecting the bacteria against ␤-lactam antibiotics, ␤-lactamase can also have indirect pathogenic effects. For example, it can block the antibiotic treatment of concomitant infections with more dangerous pathogens (e.g., pneumococci), as experimentally confirmed by . This, together with the discovery of M. catarrhalis as a pathogen in its own right, has aroused scientific interest in other possible virulence factors. One of these virulence factors is the ability of M. catarrhalis to resist the action of complement (9,12,17,20,(24)(25)(26). Based on molecular typing data, i.e., pulsed-field gel electrophoresis and PCR-restriction fragment length polymorphism analysis, it has been suggested that complement-resistant M. catarrhalis isolates form a genetically distinct lineage with a different pathogenic potential within the species (3,26,28). The second aim of this study, therefore, was to determine the percentage of complement-resistant M. catarrhalis isolates in the recent SENTRY surveillance study and t...