Effect of Efflux on Telithromycin and Macrolide Susceptibility in Haemophilus influenzae

Abstract

This study investigated the presence of telithromycin and azithromycin efflux in 58 clinical strains of Haemophilus influenzae with various susceptibilities to macrolides, azalides, and ketolides. Efflux pumps were studied by measuring accumulation of radioactive [ 3 H]telithromycin and [N-methyl-3 H]azithromycin in the presence and absence of carbonyl m-chlorophenylhydrazone (CCCP), a protonophore. In 17 strains for which the telithromycin MICs were 0.06 to 0.5 g/ml (azithromycin MICs, <0.06 to 0.125 g/ml; clarithromycin MICs, <0.06 to 2 g/ml), telithromycin and azithromycin accumulations were high without CCCP and not affected by its addition, which indicates absence of efflux. In 22 strains for which the telithromycin MICs were 0.25 to 4 g/ml (azithromycin MICs, 0.25 to 1 g/ml; clarithromycin MICs, 1 to 8 g/ml), initially low levels of telithromycin accumulation became higher after addition of CCCP, indicating a functioning efflux pump. Nineteen strains for which the telithromycin MICs were >2 g/ml had efflux as well as various mutations in ribosomal proteins L4, L22, and/or 23S rRNA (domains II and V). Of these 19 strains, the telithromycin MICs (>8 g/ml) for 17 of them were significantly raised (azithromycin, MICs 4 to >32 g/ml; clarithromycin MICs, 8 to >32 g/ml). From these results we conclude that telithromycin efflux with or without additional ribosomal alterations is present in all H. influenzae strains, except for those for which the telithromycin MICs were very low.Haemophilus influenzae is one of the most common pathogens causing community-acquired respiratory tract infections, including community-acquired pneumonia and acute exacerbation of chronic bronchitis, which are associated with considerable morbidity, mortality, and high financial burden (1,22,17). H. influenzae is also frequently implicated in sinusitis and acute otitis media, which are usually less severe and non-lifethreatening but have potential for serious complications if not treated properly (12,7,9). Macrolides, azalides, and ketolides are currently recommended for treatment of community-acquired pneumonia and acute exacerbations of chronic bronchitis, with quinolones such as levofloxacin and moxifloxacin being alternative agents (15,16,19).H. influenzae demonstrates relatively good in vitro susceptibility to macrolides and azalides, which have a unimodal MIC distribution and low prevalence of high-level resistance when defined by current Clinical and Laboratory Standards Institute (CLSI) standards. Telithromycin appears to have less optimal and more variable activity against H. influenzae compared to azithromycin. Several in vitro studies have demonstrated that telithromycin MICs were equal to or at least 1 dilution higher than those of azithromycin (24). Telithromycin activity against H. influenzae is, however, superior to that of erythromycin and clarithromycin (14). MICs and breakpoints of macrolides, azalides, and ketolides against this organism must be considered together with their raised levels in tissue and epithelial linin...

Effect of Fluoroquinolones and Macrolides on Eradication and Resistance of Haemophilus influenzae in Chronic Obstructive Pulmonary Disease

“…The study participant received four courses of macrolides during 819 days of strain carriage. We identified a known macrolide resistance mutation in L22 in isolate 5P54H1, a switch from glycine to aspartic acid at amino acid 91 (G91D) (25). In four instances, the azithromycin MIC increased 4-fold during persistence and reached the CLSI breakpoint of 4 g/ml (Table 3).…”

“…influenzae resistance to macrolides has been linked to chromosomal mutations in genes encoding L4 and L22 ribosomal proteins and in 23S rRNA (24,25). The sequences of L4, L22, and domains II and V of 23S rRNA were determined by mapping reads to H. influenzae 86-028NP.…”

“…The sequences of L4, L22, and domains II and V of 23S rRNA were determined by mapping reads to H. influenzae 86-028NP. Macrolide resistance has also been associated with horizontally transferred erm genes, which encode rRNA methylases that inhibit macrolide binding of the 23S rRNA target, as well as mef genes, which encode alternate efflux pumps (24,25). Resistance genes mefA, ermA, ermB, ermC, and ermF were mapped to GenBank accession numbers NC_023287.1, CP003585.1, NC_014959.1, AJ888003.1, and JQ707297, respectively.…”

Emergence of telithromycin resistance in Haemophilus influenzae in Japan

“…telithromycin resistance in H. influenzae is an important clinical problem, although reports concerning resistance to telithromycin in clinical isolates of H. influenzae are few (Bogdanovich et al, 2006).…”

“…In recent studies (Bogdanovich et al, 2006), H. influenzae isolates showing MICs ¢0.5 mg telithromycin ml 21 , which include those 'susceptible' according to CLSI (2006) categories, had telithromycin efflux mechanisms. High-level telithromycin resistance in H. influenzae is rare, but has been characterized by alterations of ribosomal proteins and/or 23S rDNA, as well as efflux mechanisms (Bogdanovich et al, 2006).…”