G Model ANTAGE-4308; No. of Pages 2
ARTICLE IN PRESS International Journal of Antimicrobial Agents xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
International Journal of Antimicrobial Agents journal homepage: http://www.elsevier.com/locate/ijantimicag
Letter to the Editor
Surveillance of antimicrobial resistance in contemporary clinical isolates of Bordetella pertussis in Ontario, Canada Sir, The Gram-negative bacterium Bordetella pertussis causes respiratory infections in humans. Despite decreasing numbers of reported cases in Canada since the introduction of the whole-cell pertussis vaccine in 1943 and the acellular vaccine in 1997/1998, periodic outbreaks have continued to occur in the province of Ontario over the last decade. Possible contributing factors to these outbreaks have been hypothesised to be waning immunity in vaccinated individuals, more sensitive laboratory detection methods, undervaccinated subpopulations and the emergence of new strains [1]. Most recently in 2012/2013, an outbreak in southwestern Ontario involving 443 cases was monitored by local and provincial public health authorities. Case management guidelines recommended treatment with antibiotics at the discretion of the attending healthcare provider with azithromycin, clarithromycin or erythromycin as indicated by the guidelines from the Public Health Agency of Canada [2]. Since treatment of B. pertussis infection is primarily mediated by antibiotics, it is important to monitor antimicrobial susceptibility profiles in order to provide effective treatment guidance. The possibility of new strains as well as overall uncertainty about the cause and implications of the reemergence of pertussis also make the need for good surveillance of the organism a high priority, including baseline levels of antimicrobial susceptibility, which has not previously been done in Ontario. Here we investigated the antibiotic susceptibility profiles of B. pertussis isolates collected before and during an outbreak in Ontario that occurred between November 2011 and April 2013. In addition to susceptibility testing, all isolates were investigated for macrolide resistance by molecular methods. Culture-positive isolates (only PCR-positive specimens as previously described [3] were plated on charcoal media and incubated at 37 ◦ C for 7 days) were tested for antimicrobial susceptibility and mutations known to cause macrolide resistance as follows. Isolates were cultured on plain charcoal agar plates (Public Health Ontario Laboratories, Toronto, Ontario, Canada) incubated at 37 ◦ C and Etest was performed for phenotypic susceptibility as previously described [4] with the following modifications. The cell concentration was adjusted to obtain a 0.5 McFarland standard, only azithromycin and trimethoprim/sulfamethoxazole (SXT) Etest strips (bioMérieux, St-Laurent, Quebec) were used, and minimum inhibitory concentrations (MICs) were recorded after 4 days. PCR amplification was performed on a 521-bp region in domain V of 23S rRNA centred on the peptidyl transferase region (the target
for macrolide class antimicrobial agents) where a G→A nucleotide mutation at position 2058 (Escherichia coli numbering) confers macrolide resistance in B. pertussis. Sequence analysis was conducted using Vector NTI software (Life Technologies Inc., Carlsbad, CA). From September 2011 to December 2012, 8082 specimens were received by Public Health Ontario Laboratories for detection of B. pertussis, of which 720 (8.9%) were positive by PCR and 295 (3.7%) were also positive by culture. A total of 275 viable isolates (275/295; 93.2%) were tested for antimicrobial susceptibility; 112 were from the regions affected by the outbreak. All isolates were found to be susceptible to both antibiotics (azithromycin range,
ARTICLE IN PRESS International Journal of Antimicrobial Agents xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
International Journal of Antimicrobial Agents journal homepage: http://www.elsevier.com/locate/ijantimicag
Letter to the Editor
Surveillance of antimicrobial resistance in contemporary clinical isolates of Bordetella pertussis in Ontario, Canada Sir, The Gram-negative bacterium Bordetella pertussis causes respiratory infections in humans. Despite decreasing numbers of reported cases in Canada since the introduction of the whole-cell pertussis vaccine in 1943 and the acellular vaccine in 1997/1998, periodic outbreaks have continued to occur in the province of Ontario over the last decade. Possible contributing factors to these outbreaks have been hypothesised to be waning immunity in vaccinated individuals, more sensitive laboratory detection methods, undervaccinated subpopulations and the emergence of new strains [1]. Most recently in 2012/2013, an outbreak in southwestern Ontario involving 443 cases was monitored by local and provincial public health authorities. Case management guidelines recommended treatment with antibiotics at the discretion of the attending healthcare provider with azithromycin, clarithromycin or erythromycin as indicated by the guidelines from the Public Health Agency of Canada [2]. Since treatment of B. pertussis infection is primarily mediated by antibiotics, it is important to monitor antimicrobial susceptibility profiles in order to provide effective treatment guidance. The possibility of new strains as well as overall uncertainty about the cause and implications of the reemergence of pertussis also make the need for good surveillance of the organism a high priority, including baseline levels of antimicrobial susceptibility, which has not previously been done in Ontario. Here we investigated the antibiotic susceptibility profiles of B. pertussis isolates collected before and during an outbreak in Ontario that occurred between November 2011 and April 2013. In addition to susceptibility testing, all isolates were investigated for macrolide resistance by molecular methods. Culture-positive isolates (only PCR-positive specimens as previously described [3] were plated on charcoal media and incubated at 37 ◦ C for 7 days) were tested for antimicrobial susceptibility and mutations known to cause macrolide resistance as follows. Isolates were cultured on plain charcoal agar plates (Public Health Ontario Laboratories, Toronto, Ontario, Canada) incubated at 37 ◦ C and Etest was performed for phenotypic susceptibility as previously described [4] with the following modifications. The cell concentration was adjusted to obtain a 0.5 McFarland standard, only azithromycin and trimethoprim/sulfamethoxazole (SXT) Etest strips (bioMérieux, St-Laurent, Quebec) were used, and minimum inhibitory concentrations (MICs) were recorded after 4 days. PCR amplification was performed on a 521-bp region in domain V of 23S rRNA centred on the peptidyl transferase region (the target
for macrolide class antimicrobial agents) where a G→A nucleotide mutation at position 2058 (Escherichia coli numbering) confers macrolide resistance in B. pertussis. Sequence analysis was conducted using Vector NTI software (Life Technologies Inc., Carlsbad, CA). From September 2011 to December 2012, 8082 specimens were received by Public Health Ontario Laboratories for detection of B. pertussis, of which 720 (8.9%) were positive by PCR and 295 (3.7%) were also positive by culture. A total of 275 viable isolates (275/295; 93.2%) were tested for antimicrobial susceptibility; 112 were from the regions affected by the outbreak. All isolates were found to be susceptible to both antibiotics (azithromycin range,
