Moving towards a standardized definition of antimicrobial resistance: a comparison of the antimicrobial susceptibility profile of difficult-to-treat resistance (DTR) versus multidrug-resistant (MDR) Pseudomonas aeruginosa clinical isolates (CANWARD, 2016-2021).

Pseudomonas aeruginosa clinical isolates demonstrating difficult-to-treat resistance (DTR) and multidrug-resistant (MDR) phenotypes were evaluated by broth microdilution. Susceptibility was lower for all antimicrobials versus DTR relative to MDR isolates. Ceftazidime-avibactam, ceftolozane-tazobactam, and imipenem-relebactam susceptibility was 35.9%, 64.5%, and 47.0% for DTR isolates and 60.5%, 80.6%, and 71.5% for MDR isolates.

Canadian recommendations for laboratory interpretation of multiple or extensive drug resistance in clinical isolates of Enterobacteriaceae, Acinetobacter species and Pseudomonas aeruginosa.

The goal of this document was to provide Canadian laboratories with a framework for consistent reporting and monitoring of multidrug resistant organisms (MDRO) and extensively drug resistant organisms (XDRO) for common gram-negative pathogens. This is the final edition of the interim recommendations, which were modified after one year of broad consultative review. This edition represents a consensus of peer-reviewed information and was co-authored by the Canadian Public Health Laboratory Network and the Canadian Association of Clinical Microbiology and Infectious Diseases. There are two main recommendations. The first recommendation provides standardized definitions for MDRO and XDRO for gram-negative organisms in clinical specimens. These definitions were limited to antibiotics that are commonly tested clinically and, to reduce ambiguity, resistance (rather than non-susceptibility) was used to calculate drug resistance status. The second recommendation identifies the use of standardized laboratory reporting of organisms identified as MDRO or XDRO. Through the broad consultation, which included public health and infection prevention and control colleagues, these definitions are ready to be applied for policy development. Both authoring organizations intend to review these recommendations regularly as antibiotic resistance testing evolves in Canada.

Antimicrobial susceptibility of clinical isolates of Neisseria gonorrhoeae to alternative antimicrobials with therapeutic potential.

Background: The prevalence of MDR Neisseria gonorrhoeae is increasing globally and represents a public health emergency. Development and approval of new anti-gonococcal agents may take years. As a concurrent approach to developing new antimicrobials, the laboratory and clinical evaluation of currently licensed antimicrobials not widely used for the treatment of gonorrhoea may provide new options for the treatment of gonococcal infections. Objectives: To determine the in vitro activity of nine alternative, currently licensed and late-development antimicrobials with the potential to treat gonococcal infections against 112 clinical isolates of N. gonorrhoeae resistant to one or multiple antimicrobials. Methods: The MICs of conventional anti-gonococcal antimicrobials (penicillin, ceftriaxone, cefixime, azithromycin, ciprofloxacin, tetracycline and spectinomycin) and alternative antimicrobials (ertapenem, gentamicin, netilmicin, tigecycline, eravacycline, fosfomycin, linezolid, ceftazidime/avibactam and ceftaroline) were determined by agar dilution. Results: Ertapenem and the novel cephalosporins demonstrated similar MIC values to the third-generation cephalosporins, but increased MICs were observed for isolates with increased cefixime and ceftriaxone MICs. Tigecycline and eravacycline had MIC values below expected serum concentrations for all isolates tested. The aminoglycosides gentamicin and netilmicin were generally more potent than spectinomycin, with netilmicin demonstrating the greatest potency. Fosfomycin MICs were elevated compared with other agents, but remained within the MIC range for susceptible organisms, while linezolid MICs were generally higher than those for organisms considered resistant. Conclusions: Among potentially therapeutically useful alternative agents, the aminoglycosides, eravacycline, tigecycline and fosfomycin had good in vitro activity. The novel cephalosporins and ertapenem had comparable activity to cefixime and ceftriaxone.

In vitro activity of oritavancin against Gram-positive pathogens isolated in Canadian hospital laboratories from 2011 to 2013.

Gram-positive pathogens isolated in 15 Canadian hospital laboratories between 2011 and 2013 were tested for susceptibility to oritavancin and comparative antimicrobial agents using the Clinical and Laboratory Standards Institute broth microdilution method. Oritavancin demonstrated in vitro activity equivalent to, or more potent than, vancomycin, daptomycin, linezolid, and tigecycline against the isolates of methicillin-susceptible Staphylococcus aureus (n=1460; oritavancin MIC90, 0.06 µg/mL; 99.7% oritavancin-susceptible), methicillin-resistant S. aureus (n=427; oritavancin MIC90, 0.06 µg/mL; 99.5% oritavancin-susceptible), Streptococcus pyogenes (n=132; oritavancin MIC90, 0.25 µg/mL; 99.2% oritavancin-susceptible), Streptococcus agalactiae (n=156; oritavancin MIC90, 0.12 µg/mL; 100% oritavancin-susceptible), and Enterococcus faecalis (n=304; oritavancin MIC90, 0.06 µg/mL; 98.7% oritavancin-susceptible) tested.

Genotypic characterization of tuberculosis transmission within Toronto's under-housed population, 1997-2008.

Toronto has been the site of a recent extended tuberculosis (TB) outbreak in the homeless or under-housed population. Genotyping has identified a unique strain that continues to circulate within this population, with spread to individuals with no links to the shelter system, and anecdotally appears to progress rapidly from infection to active disease in some cases. The recent appearance and transmission of another unique strain was also identified, indicating that TB transmission continues to be a problem within the under-housed population. Enhanced surveillance utilizing molecular epidemiology is a useful tool to assist in TB control in vulnerable populations.

Changing epidemiology of invasive Haemophilus influenzae in Ontario, Canada: evidence for herd effects and strain replacement due to Hib vaccination.

The epidemiology of invasive Haemophilus influenzae infections was evaluated in Ontario between 1989 and 2007 to assess the impact of the introduction of the conjugate H. influenzae serotype b (Hib) vaccine in the early 1990 s on Hib and non-Hib serotypes in both vaccinated and unvaccinated cohorts as well as the possibility of "strain replacement" with non-vaccine H. influenzae strains. Data were collected by the provincial Public Health Laboratories-Toronto, Ontario Agency for Health Protection and Promotion, which performed almost all serotyping on invasive (blood, CSF, other sterile sites) H. influenzae strains isolated in the province during the study period. Temporal trends for Hib, other typeable strains, and non-typeable H. influenzae were evaluated by Poisson regression, controlling for the specimen submissions. Prior to infant Hib vaccination, the most commonly observed serotype was serotype b (64.9%). Subsequently, 70.3%, 13.6%, and 9.4% of isolates were non-typeable, serotype f, and serotype b, respectively. Infant Hib vaccination resulted in a decrease in Hib incidence in all age groups (pooled IRR 0.432) and marked increases of non-typeable and serotype f H. influenzae in children aged <5 years (IRR 2.4 and 3.0, respectively). Vaccination against Hib has altered the epidemiology of invasive H. influenzae infections in Ontario. Prevention of invasive Hib disease was observed in both vaccinated and unvaccinated age groups. Invasive H. influenzae infection now commonly presents as sepsis due to non-typeable H. influenzae in older individuals. However, strain replacement of Hib with serotype f and non-typeable strains in children under 5 years was documented.