Robert Rennie

Characterization of Pseudomonas aeruginosa Isolates: Occurrence Rates, Antimicrobial Susceptibility Patterns, and Molecular Typing in the Global SENTRY Antimicrobial Surveillance Program, 1997–1999

During 1997-1999, a total of 70,067 isolates (6631 Pseudomonas aeruginosa isolates) were analyzed in the SENTRY program by geographic region and body site of infection. The respiratory tract was the most common source of P. aeruginosa. P. aeruginosa isolation rates increased during the study interval. Europe was the only region to show a significant decline in beta-lactam and aminoglycoside susceptibility rates. There was a reduction in the rates of susceptibility of Canadian isolates to imipenem and of Latin American isolates to meropenem. A total of 218 multidrug-resistant P. aeruginosa isolates (MDR-PSA; resistant to piperacillin, ceftazidime, imipenem, and gentamicin) were observed; MDR-PSA occurrence rates (percentages of all isolates) ranged from 8.2% (Latin America) to 0.9% (Canada). No antimicrobial inhibited >50% of MDR-PSA strains. Molecular characterization of selected, generally resistant strains was performed. Isolates showing unique ribogroups were found in Europe, Latin America, and the United States, but clonal spread was documented in several medical centers.

Sputum isolation of Wangiella dermatitidis in patients with cystic fibrosis.

We report a case of invasive fungal pulmonary infection in a cystic fibrosis patient. Clinical deterioration coincided with isolation of Wangiella dermatitidis from her sputum, and treatment with amphotericin B followed by voriconazole resulted in clinical improvement and sterilization of the sputum. This case suggests that W. dermatitidis may be an etiologic agent of invasive pulmonary disease in the cystic fibrosis population.

Evaluation of CHROMagar Candida for presumptive identification of clinically important Candida species

CHROMagar Candida is a recently described and differential medium for the isolation and the presumptive identification of clinically important yeasts. We evaluated it with 262 yeast strains from clinical specimens, including 173 Candida albicans, 21 Candida tropicalis, 8 Candida krusei, 49 Candida glabrata, and 12 strains of other yeast species. Strains were presumptively identified on the basis of colony color and texture. These observations were compared with conventional identification results. Candida albicans was identified correctly in 170 (98%) of the 173 strains. A total of 46 of the 205 specimens that were plated on CHROMagar contained mixed cultures of yeast. Thirty-seven (80%) of these mixed cultures were not detected in the original specimens. CHROMagar Candida was useful for the rapid presumptive identification of Candida albicans and facilitated the recognition of mixed cultures. For other yeast species, it may provide additional information to laboratories that do not regularly perform identifications beyond the germ tube test.

First Comprehensive Evaluation of the M.I.C. Evaluator Device Compared to Etest and CLSI Reference Dilution Methods for Antimicrobial Susceptibility Testing of Clinical Strains of Anaerobes and Other Fastidious Bacterial Species

ABSTRACT The new M.I.C. Evaluator strip uses test methodology and the recording of results that are similar to those of Etest. For this first assessment, 102 clinical strains of anaerobic bacteria from 12 genera and 155 strains from 7 genera and 8 species of fastidious bacteria were tested by M.I.C. Evaluator, Etest, and agar dilution or broth microdilution as a reference standard. Ampicillin, amoxicillin, amoxicillin-clavulanate, cefotaxime, ciprofloxacin, erythromycin, imipenem, levofloxacin, metronidazole, penicillin, and tetracycline were tested depending on the species. Agar dilution for anaerobes was performed according to CLSI document M11-A7. For the fastidious bacteria, CLSI document M45-A2 was followed. For the anaerobes, essential and categorical agreement between M.I.C. Evaluator and Etest was >90%. Compared to agar dilution, essential agreement was low for both strip tests, and many very major errors were observed for metronidazole (13 to 14%) and penicillin (8 to 9%) with isolates from the Bacteroides fragilis group and Clostridium species. For fastidious species, essential agreements for M.I.C. Evaluator and Etest plus or minus one doubling dilution were >95%. Compared to broth microdilution, essential agreements were low (40 to 90%) plus or minus one dilution and were >90% plus or minus two dilutions, with high overall category agreement (CA). Major and minor errors were within established parameters for all strains tested. The M.I.C. Evaluator strips were equivalent to Etest for anaerobes and fastidious species. These observations require further investigation to determine which methods provide the most accurate MIC for clinical utility. The further evaluation of additional M.I.C. Evaluator agents will be performed as they become available.

Antimicrobial Resistance in Haemophilus influenzae: How Can We Prevent the Inevitable? Commentary on Antimicrobial Resistance in H. influenzae Based on Data from the TARGETed Surveillance Program

Haemophilus influenzae is an important cause of respiratory tract infections, particularly in elderly persons. It is the major bacterial pathogen in acute exacerbations of chronic bronchitis (AECB) and also causes otitis media and sinusitis. In many cases, treatment is empiric, and there is a lack of understanding of resistance issues with this bacterium. There is little understanding of the epidemiology of H. influenzae respiratory infections, although some strains may be replaced by new strains that cause more severe infections. There is almost no information on how these bacteria may spread in the community. Ampicillin resistance is significant (it may be >30%), and there are few oral agents capable of reducing organism burden. There is little understanding of the epidemiology of H. influenzae respiratory infections, and almost no information on how these bacteria may spread in the community. Recent evidence suggests that these bacteria may behave in a similar way to Streptococcus pneumoniae. If that proves correct, then it will be important to follow these organisms in the community to determine if resistance determinants may spread more widely than we have thus far believed. The implications for treatment, infection prevention and control, and public health should not be underestimated as it has been with other organisms such as S. pneumoniae and Staphylococcus aureus.

Prevalence of antimicrobial resistant pathogens from blood cultures from Canadian hospitals: results of the CANWARD 2007–2009 study

This study assessed the epidemiology and antimicrobial resistance of pathogens associated with bloodstream infections in Canadian hospitals between 2007 and 2009. Tertiary-care medical centers representing 8 of 10 Canadian provinces submitted bloodstream infection pathogens from patients attending hospital clinics, emergency rooms, medical/surgical wards, and intensive care units. Over 8,000 blood culture pathogens were collected. The 10 most common pathogens (representing 80.9% of all isolates) were Escherichia coli (1856 [22.6%]), Staphylococcus aureus (1457 [17.7%] including 1101 methicillin-susceptible Staphylococcus aureus and 356 methicillin-resistant Staphylococcus aureus), coagulase-negative staphylococci (907 [11.0%]), Klebsiella pneumoniae (600 [7.3%]), Streptococcus pneumoniae (470 [5.7%]), Enterococcus faecalis (360 [4.4%]), Pseudomonas aeruginosa (333 [4.0%]), viridans group streptococci (321 [3.9%]), Enterobacter cloacae (193 [2.3%]), and Streptococcus pyogenes (159 [1.9%]). The most active agents against Gram-negative bacilli were carbapenems (e.g., meropenem and ertapenem) and piperacillin-tazobactam, while for Gram-positive cocci, they were vancomycin, linezolid, and daptomycin.

Evaluation of E Test, disk diffusion and broth microdilution to establish tentative quality control limits and review susceptibility breakpoints for two aerobic actinomycetes

A single laboratory study was carried out to compare E Test with broth microdilution and disk diffusion to establish tentative quality control ranges for Nocardia asteroides ATCC 19247 and Rhodococcus equi ATCC 6939 against a panel of eight antimicrobial agents. Reproducibility testing was performed on 12 consecutive days to establish tentative quality control ranges. A total of 36 clinical strains of the Nocardia asteroides complex and 5 Rhodococcus strains were used in the study. Both candidate control strains and clinical strains grew well on cation-adjusted Mueller-Hinton agar. Adequate growth occurred at 48 to 72 h for the Nocardia isolates and 24 to 48 h for Rhodococcus. A standardized primary inoculum of 5 x 10(4) CFU/mL was used for performance of E Test and disk diffusion for the Nocardia isolates. Tentative population-based error rates were calculated using current breakpoints for Enterobacteriaceae for E Test compared with disk diffusion for the 36 clinical strains of Nocardia species. Significant very major error rates were observed for imipenem (22%) and minor error rates varied from 2.7% to 50%. These methods require more extensive validation before definitive breakpoint criteria can be established.

Evaluation of a no-dressing intervention for tunneled central venous catheter exit sites.

This study tested whether central venous catheter (CVC)-related sepsis could be reduced by removing a hypothesized reservoir for pathogens, the CVC exit site dressing. Seventy-eight individuals with cancer, stratified for gender (37 men and 41 women) and transplant status, with newly inserted CVCs were recruited and randomly assigned to receive either a gauze dressing or no dressing, once their catheter insertion site had healed (3 weeks). Because there was no difference in CVC-related septic episodes based on gender or transplant status, the stratification was not maintained for remaining analyses. Although there was no significant difference in CVC-related septic episodes (P = .28) or rehospitalization rates (P = .41) because of CVC-related sepsis between the dressing and no-dressing group, individuals in the dressing group developed CVC-related sepsis sooner (P = .02) than did individuals in the no-dressing group.

Susceptibility of Staphylococcus aureus to fusidic acid: Canadian data.

Background: Ongoing antimicrobial surveillance is important to ensure proper management of infectious diseases. There are inherent issues in estimating the relevant incidence of antimicrobial resistance from surveillance data and special issues for topical preparations. Objective: To perform semiannual surveillance of fusidic acid susceptibility of Staphylocccus aureus strains in a Canadian tertiary care hospital. Methods: S. aureus strains were collected twice yearly from routine cultures. Routine antimicrobial susceptibility testing was performed by an automated method. Fusidic acid susceptibility testing was performed by disk diffusion. Results: Between 1999 and 2005, 2,302 S. aureus strains were tested, of which 240 were methicillin resistant (MRSA). Among all strains tested, 65 (2.8%) were resistant to fusidic acid. Ten of the MRSA strains (4.2%) were resistant to fusidic acid. Although from different patients, these were shown to be part of a hospital outbreak and were epidemiologically linked. Conclusions: There has been no trend toward increasing fusidic acid resistance in our hospital over this period.

Comparison of three commercial systems for the identification of germ-tube negative yeast species isolated from clinical specimens

Three commercial systems were evaluated for their ability to identify 171 germ-tube negative yeasts isolated from clinical specimens. The Yeast Biochemical Card and Analytical Profile Index 20 AUX identified 97% of 171 strains tested. The Biolog system had poor clinical utility: only 48% of strains were identified. For Yeast Biochemical Card and Analytical Profile Index 20 AUX, 9% and 6%, respectively, required repeat testing and both systems required supplemental tests for 28% of the strains. These observations indicate that considerable expertise and a battery of reagents in addition to the basic systems are required for accurate identification of germ-tube negative yeasts.