Mechanisms, molecular and sero-epidemiology of antimicrobial resistance in bacterial respiratory pathogens isolated from Japanese children

Abstract

Background: The clinical management of community-acquired respiratory tract infections (RTIs) is complicated by the increasing worldwide prevalence of antibacterial resistance, in particular, beta-lactam and macrolide resistance, among the most common causative bacterial pathogens. This study aimed to determine the mechanisms and molecular- and sero-epidemiology of antibacterial resistance among the key paediatric respiratory pathogens in Japan.

Methods: Isolates were collected at 18 centres in Japan during 2002 and 2003 from children with RTIs as part of the PROTEKT surveillance programme. A proportion of Haemophilus influenzae isolates was subjected to sequencing analysis of the ftsI gene; phylogenetic relatedness was assessed using multilocus sequence typing. Streptococcus pneumoniae isolates were screened for macrolide-resistance genotype by polymerase chain reaction and serotyped using the capsular swelling method. Susceptibility of isolates to selected antibacterials was performed using CLSI methodology.

Results and discussion: Of the 557 H. influenzae isolates collected, 30 (5.4%) were beta-lactamase-positive [BL+], 115 (20.6%) were BL-nonproducing ampicillin-resistant (BLNAR; MIC >or= 4 mg/L) and 79 (14.2%) were BL-nonproducing ampicillin-intermediate (BLNAI; MIC 2 mg/L). Dabernat Group III penicillin binding protein 3 (PBP3) amino acid substitutions in the ftsI gene were closely correlated with BLNAR status but phylogenetic analysis indicated marked clonal diversity. PBP mutations were also found among BL+ and BL-nonproducing ampicillin-sensitive isolates. Of the antibacterials tested, azithromycin and telithromycin were the most active against H. influenzae (100% and 99.3% susceptibility, respectively). A large proportion (75.2%) of the 468 S. pneumoniae isolates exhibited macrolide resistance (erythromycin MIC >or= 1 mg/L); erm(B) was the most common macrolide resistance genotype (58.8%), followed by mef(A) (37.2%). The most common pneumococcal serotypes were 6B (19.7%), 19F (13.7%), 23F (13.5%) and 6A (12.8%). Telithromycin and amoxicillin-clavulanate were the most active antibacterials against S. pneumoniae (99.8% and 99.6% susceptibility, respectively).

Conclusion: Approximately one-third of H. influenzae isolates from paediatric patients in Japan are BLNAI/BLNAR, mainly as a result of clonally diverse PBP3 mutations. Together with the continued high prevalence of pneumococcal macrolide resistance, these results may have implications for the clinical management of paediatric RTIs in Japan.

Figure 1

Phylogenetic relationships based on sequence-type variations found in Haemophilus influenzae that were β-lactamase nonproducing ampicillin-resistant with β-lactamase nonproducing ampicillin-sensitive (BLNAS; n = 14).

Figure 2

Phylogenetic relationships based on sequence-type variations found in Haemophilus influenzae that were β-lactamase nonproducing ampicillin-resistant with βlactamase positive (BL+; n = 27).

Figure 3

Serotype distribution of 468 isolates of Streptococcus pneumoniae collected from Japanese children (aged < 16 years) with community-acquired respiratory tract infections (combined data for all four 1-week study periods).