High Prevalence and Molecular Analysis of Macrolide-NonsusceptibleMoraxella catarrhalisIsolated from Nasopharynx of Healthy Children in China

Abstract

Three hundred eighty-three isolates of Moraxella catarrhalis were collected from healthy children aged less than 2 years in China and assessed for antimicrobial resistance. We found that 92.2% (n=353) produced a β-lactamase. Nonsusceptibility rates to erythromycin and azithromycin, determined using Clinical Laboratory Standards Institute (CLSI) breakpoints, were 40.3% and 22.5%, respectively; nonsusceptibility rates determined using pharmacokinetics/pharmacodynamics breakpoints, however, were 59% and 60.1%. The minimal inhibitory concentration (MIC)(90) values were >256 μg/ml. Nonsusceptibility rates varied by region from 9.7% in Dongguan to 75.9% in Jinan. Further, concomitant resistance to β-lactam antibiotics was also observed. Pulsed-field gel electrophoresis analysis of 27/37 high-level macrolide-resistant M. catarrhalis isolates showed that closely related pulsotypes dominated, with a total of 11 different pulsotypes being observed. The closely related pulsotypes were observed in isolates originating from all six Chinese cities investigated, possibly as a consequence of the mobility of the Chinese population. Sixteen patterns of 23S rRNA mutations were found among 97 selected isolates using polymerase chain reaction and sequencing, but no known ermA, ermB, mefA, or mefE genes could be detected. Mutations A2982T and A2796T in 23S rRNA were related to high-level macrolide resistance (MICs ranging from 24 to >256 μg/ml), while an A2983T mutation was associated with low-level macrolide resistance (MICs ranging from 0.19 to 16 μg/ml).

Use of next generation sequence to investigate potential novel macrolide resistance mechanisms in a population of Moraxella catarrhalis isolates

“…Pulsed-field gel electrophoresis (PFGE) and copB polymerase chain reaction–restriction fragment length polymorphisms were performed on the four isolates as previously described 10 .…”

“…For the rpIF gene, a standard PCR protocol comprising 94 °C for 5 min, followed by 35 cycles of 94 °C for 30 sec, 50 °C for 30 sec, 72 °C for 90 sec, and an extension time of 7 min at 72 °C, was used. We further investigated the 23S rRNA gene sequence changes in a 934-bp region in all the 73 M. catarrhalis isolates as per our previous study 10 . Due to limited budget, only 73 isolates instead of the 188 were tested for the presence of the identified informative candidate SNPs ( Fig.…”

“…Interestingly and in contrast to M. catarrhalis , mutation of the 23S rRNA gene is usually not the main reason for macrolide-resistance in other bacterial species (such as Streptococcus pneumoniae, Streptococcus pyogenes , etc 15 16 17 ). Moreover, multilocus sequence typing (MLST) results from our previous study showed a very high level of heterogeneity among M. catarrhalis isolates 10 13 . Given the above background, it is possible that several mechanisms are involved in M. catarrhalis macrolide resistance.…”

“…Although most M. catarrhalis isolates are still susceptible to macrolide in many countries 4 5 6 , with a minimal inhibitory concentration (MIC) 90 of 0.25 g/L, macrolide-resistant M. catarrhalis have been reported in several studies worldwide 7 8 9 . In 2012, we reported for the first time that ribosomal mutation was crucial for creating macrolide-non-susceptible M. catarrhalis , and that A2330T (position referring to M. catarrhalis 23S rRNA gene, GenBank number NR_103214.1) mutation was related to high-level macrolide-resistance 10 . In the following three years, several studies confirmed that indeed A2330T mutation of the 23S rRNA gene could lead to isolates with high-level macrolide resistance (MIC > 256 g/L) 11 12 13 14 .…”

Bronchiectasis in Children: Current Concepts in Immunology and Microbiology

“…Most M. catarrhalis strains produce β-lactamase; 92% in the PROTEKT study (87). In contrast, M. catarrhalis is almost universally susceptible to azithromycin (87,95,107,108), although macrolide resistance has recently been reported in China (109,110), Japan (111,112), and Pakistan (113). In Australian Indigenous children with bronchiectasis, most M. catarrhalis isolates from the NP (91%) and BAL (100%) were β-lactamase positive; however, azithromycin resistance was not tested (89).…”