Marc Desjardins

Evaluation of the IDI-MRSA Assay for Detection of Methicillin-Resistant Staphylococcus aureus from Nasal and Rectal Specimens Pooled in a Selective Broth

ABSTRACT Rapid detection of methicillin-resistant Staphylococcus aureus (MRSA) by PCR can be performed directly from nasal specimens with the IDI-MRSA assay. To improve the efficiency of screening, we evaluated the performance of the IDI-MRSA assay for the detection of MRSA from pooled and unpooled specimens cultured in a selective broth. Of the 287 specimens evaluated, 71 were culture and PCR positive, 203 were culture and PCR negative, 3 were culture positive and PCR negative, 8 were culture negative and PCR positive, and 2 remained inhibited. A methicillin-susceptible Staphylococcus aureus isolate was recovered from five of the eight specimens with false-positive PCR results. Compared to the results of culture, the sensitivity, specificity, and negative and positive predictive values of the IDI-MRSA assay for detection of MRSA from broth were 96%, 96%, 90%, and 98%, respectively. Following implementation of the IDI-MRSA assay, PCR-positive broths were subcultured for evaluation of assay performance. Of the 298 IDI-MRSA assay-positive broths, the results for 103 could not be confirmed by culture. A methicillin-susceptible S. aureus (MSSA) isolate was recovered from 77 of these 103 broths. Repeat testing by the IDI-MRSA assay directly with the MSSA isolates confirmed the original positive PCR result. The positive predictive value of the IDI-MRSA assay fell from 90% during the evaluation phase to 65% postimplementation. The IDI-MRSA assay performed well for the detection of MRSA from a selective broth compared to the performance of the detection of MRSA from culture. However, because of the burden associated with implementation of infection control precautions, cultures remain essential in confirming positive IDI-MRSA results.

Prevalence and Mechanisms of Erythromycin Resistance in Group A and Group B Streptococcus: Implications for Reporting Susceptibility Results

ABSTRACT Increased rates of erythromycin resistance among group B Streptococcus (GBS) and group A Streptococcus (GAS) have been reported. Cross-resistance to clindamycin may be present, depending on the mechanism of resistance. We determined the prevalence of macrolide-resistant determinants in GBS and GAS isolates to guide the laboratory reporting of erythromycin and clindamycin susceptibility. Susceptibilities were determined by the disk diffusion and broth microdilution methods. Inducible and constitutive resistance to clindamycin was determined by the double-disk diffusion method. The presence of the ermTR, ermB, and mefA genes was confirmed by PCR. Of the 338 GBS isolates, 55 (17%) were resistant to erythromycin, whereas 26 (8%) were resistant to clindamycin. The erm methylase gene was identified in 48 isolates, 22 of which had inducible resistance to clindamycin and 26 of which had constitutive resistance to clindamycin. The remaining seven resistant isolates had mefA. Of the 593 GAS isolates, 49 (8%) and 6 (1%) isolates were resistant to erythromycin and clindamycin, respectively. Erythromycin resistance was due to mefA in 33 isolates, whereas 14 isolates had erm-mediated resistance (9 isolates had inducible resistance and 5 isolates had constitutive resistance). In our population, erythromycin resistance in GAS was predominantly mediated by mefA and erythromycin resistance in GBS was predominantly mediated by erm. Regional differences in mechanisms of resistance need to be taken into consideration when deciding whether to report clindamycin susceptibility results on the basis of in vitro test results. Testing by the double-disk diffusion method would be an approach that could be used to address this issue, especially for GAS.

Detection of Plasmid-Mediated KPC-Producing Klebsiella pneumoniae in Ottawa, Canada: Evidence of Intrahospital Transmission

ABSTRACT Klebsiella pneumoniae isolates from three patients admitted to the Ottawa Hospital, a 1,040-bed teaching hospital, were found to contain the plasmid-borne K. pneumoniae carbapenemase (KPC)-producing bla gene (blaKPC). There was evidence of person-to-person transmission for two patients. Screening of 186 clinical isolates revealed no additional blaKPC-containing isolates.

A 7-year retrospective review from 2005 to 2011 of Propionibacterium acnes shoulder infections in Ottawa, Ontario, Canada.

This study evaluated the clinical factors associated with Propionibacterium acnes shoulder infection and the standard culture procedures for isolating P. acnes from shoulder specimens by a 7-year retrospective analysis. P. acnes was incriminated as the second most common pathogen in 17 of 80 patients with positive shoulder cultures. All of the 17 patients had prior shoulder implant. The cumulative rates for isolating P. acnes were 1.9%, 1.9%, 41.9%, 96.4%, and 100% at day 1 to day 5 of incubation, respectively. The standard practice of anaerobic culture was able to detect P. acnes from shoulder specimens in patients with a clinical suspicion of infection. The sensitivity and specificity of prolonged incubation remain to be determined.

Changes in fluoroquinolone resistance over 5 years (CANWARD 2007–11) in bacterial pathogens isolated in Canadian hospitals

OBJECTIVES The purpose of this study was to analyse Canadian national surveillance data, specifically fluoroquinolone resistance, from 2007 to 2011 inclusive, to determine trends in resistance over time and to assess correlations with patient demographic factors. METHODS All isolates of Escherichia coli, Klebsiella pneumoniae, Enterobacter cloacae, Pseudomonas aeruginosa, Staphylococcus aureus and Streptococcus pneumoniae collected by the 10 sites that participated in the annual CANWARD surveillance studies in each of the 5 years were included in this analysis. A multifactorial logistic regression model was used to determine the variables with significant impact on fluoroquinolone resistance. RESULTS The proportion of E. coli isolates resistant to ciprofloxacin increased significantly (P = 0.0005) between 2007 (20.0%) and 2011 (29.2%), although similar increases were not seen in K. pneumoniae, E. cloacae, P. aeruginosa and S. pneumoniae (tested against levofloxacin) (P > 0.05). Among isolates of S. aureus, there was a significant decrease in ciprofloxacin resistance from 34.4% in 2007 to 24.6% in 2011 (P < 0.0001). Resistance to ciprofloxacin was a component of most multidrug-resistant (MDR) phenotypes for E. coli, K. pneumoniae, E. cloacae, P. aeruginosa and S. aureus. CONCLUSIONS A significant increase in the percentage of ciprofloxacin-resistant E. coli, primarily among urine isolates, and a significant decrease in the percentage of ciprofloxacin-resistant S. aureus occurred between 2007 and 2011. Notably, MDR isolates were frequently fluoroquinolone resistant for all organisms studied, except S. pneumoniae.

Central venous catheter-associated Leifsonia aquatica bacteremia in a hemodialysis-dependent patient

Infections associated with Leifsonia aquatica are particularly uncommon. We describe a central venous catheter-associated L. aquatica bacteremia in a hemodialysis-dependent patient. A review of the literature revealed only 1 other case report involving 10 hemodialysis patients with documented L. aquatica bacteremia.

Characterization of an Enterococcus gallinarum Isolate Carrying a Dual vanA and vanB Cassette

ABSTRACT The ability of vancomycin resistance determinants to be horizontally transferred within enterococci species is a concern. Identification and characterization of vancomycin-resistant enterococci (VRE) in a clinical isolate have a significant impact on infection control practices. In this study, we describe a clinical isolate of Enterococcus gallinarum exhibiting high-level resistance to vancomycin and teicoplanin. The genetic characterization of this isolate showed the presence of vanA and vanB genes in addition to the naturally carried vanC gene. vanA was identified on pA6981, a 35,608-bp circular plasmid with significant homology to plasmid pS177. The vanB operon was integrated into the bacterial chromosome and showed a high level of homology to previously reported Tn1549 and Tn5382. To the best of our knowledge, this is the first report of E. gallinarum carrying both vanA and vanB operons, indicating the importance of identifying the vancomycin resistance mechanism in non-E. faecium and non-E. faecalis enterococcal species.

Competency Assessment of Microbiology Medical Laboratory Technologists in Ontario, Canada

ABSTRACT Accreditation in Ontario, Canada, requires that licensed clinical laboratories participate in external quality assessment (also known as proficiency testing) and perform competency evaluation of their staff. To assess the extent of ongoing competency assessment practices, the Quality Management Program—Laboratory Services (QMP-LS) Microbiology Committee surveyed all 112 licensed Ontario microbiology laboratories. The questionnaire consisted of a total of 21 questions that included yes/no, multiple-choice, and short-answer formats. Participants were asked to provide information about existing programs, the frequency of testing, what areas are evaluated, and how results are communicated to the staff. Of the 111 responding laboratories, 6 indicated they did not have a formal evaluation program since they perform only limited bacteriology testing. Of the remaining 105 respondents, 87% perform evaluations at least annually or every 2 years, and 61% include any test or task performed, whereas 16% and 10% focus only on problem areas and high-volume complex tasks, respectively. The most common methods of evaluation were review of external quality assessment (EQA) challenges, direct observation, and worksheet review. With the exception of one participant, all communicate results to staff, and most take remedial action to correct the deficiencies. Although most accredited laboratories have a program to assess the ongoing competency of their staff, the methods used are not standardized or consistently applied, indicating that there is room for improvement. The survey successfully highlighted potential areas for improvement and allowed the QMP-LS Microbiology Committee to provide guidance to Ontario laboratories for establishing or improving existing microbiology-specific competency assessment programs.

Identification of microorganisms grown on chromogenic media by MALDI-TOF MS

Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) and chromogenic media are widely used in clinical microbiology laboratories to facilitate the rapid selection and identification of pathogens. The aim of this study was to evaluate whether usage of chromogenic media limits the diagnostic performance of MALDI-TOF MS for microbial identification. A total of 386 microorganisms collected and analyzed at five laboratories were included. Isolates were cultured on relevant chromogenic media and non-selective agar plates in parallel and identified using the Bruker MALDI-TOF MS. Among the tested isolates, no misidentification was recorded and there was no medium-related difference in the identification level. However, score values were overall slightly but significantly lower for isolates grown on chromogenic media. In conclusion, the use of chromogenic culture media tested here had no relevant impact on MALDI-TOF MS performance for diagnostic purposes.

A comparison of the Allplex™ bacterial and viral assays to conventional methods for detection of gastroenteritis agents

ObjectiveMolecular methods to detect diarrheal pathogens are increasingly being used in place of conventional methods. We compared a new multiplex real-time PCR assay for detection of both bacterial and viral gastroenteritis agents, the Allplex™ Gastrointestinal Panel Assays (AGPA), to conventional methods (stool culture for bacterial pathogens and electron microscopy (EM) for viral pathogens).ResultsGastrointestinal viruses, in particular norovirus genogroup II viruses, were detected by the AGPA in a high number of specimens that were negative by EM. For bacterial pathogens, the AGPA was able to detect the organisms grown in culture with high sensitivity and additionally detected several types of E. coli, such as enteropathogenic E. coli (EPEC), enteroaggregative E. coli (EAEC), and non-O157 Shiga toxin-producing E. coli (STEC), that could not be detected with conventional culture methods. Overall, the AGPA had a > 2-fold higher detection rate than the conventional methods, with 24/135 (17.8%) samples positive by conventional methods and 60/135 (44.4%) by AGPA. Thus, diarrhea pathogen detection rates increased substantially with the use of the AGPA as compared to conventional methods.