Multi-year comparison of VITEK® MS and 16S rRNA gene sequencing performance for the identification of rarely encountered anaerobes causing invasive human infections in a large Canadian region: can our laboratory abandon 16S rRNA gene sequencing?

BACKGROUND: Our large regional laboratory routinely provides a definitive identification (ID) for 800-1,200 anaerobic bacteria per annum that cause invasive human infections. An increasing number of isolates (i.e., 10 to 13%) recovered from clinical specimens from these cases were more unusual or rarely isolated genera and/or species (i.e., ≤5 individual cases/annum). METHODS: VITEK® MS (MALDI-TOF MS) is done initially on all anaerobic bacteria, but rare isolates undergo in-house PCR/sequencing when proteomics provides a wrong ID or no results despite repeat testing. A clinical microbiologist in consultation with the Infectious Diseases service approves molecular analyses. This multi-year comparison (2014-19) of the performance of MALDI-TOF MS and 16S rRNA gene sequencing using the IDNS® SmartGene bacterial dataset shows both method's abilities to provide a genus-level and/or species-level ID for rare isolates. RESULTS: 489 rare anaerobes were recovered from a variety of clinical specimens: 57% blood cultures, 19% other sterile fluids, 14% sterile tissues, 8% deep wounds/abscesses, and 2% prosthetic implants. 16S rRNA gene sequencing gave an accurate genus-vs. species level ID for 487/489 (99.6%) and 401/489 (82.0%) of isolates respectively. Accurate genus-vs species-level ID were obtained by MALDI-TOF MS for 269/489 (53.4%) and 187/489 (37.3%) of isolates respectively. MALDI-TOF MS gave wrong or no results for 35.1% of Gram-negative anaerobic cocci (GNAC), 62% of Gram-negative anaerobic bacilli (GNAB), 30.8% of Gram-positive anaerobic cocci (GPAC) and 46.3% of Gram-positive anaerobic bacilli (GPAB). Neither method gave an ID for one GNAB and one GPAC isolate. MALDI-TOF MS genus-level ID of GNAC and genus/species-level ID of GPAB improved during the study but its performance remained stable for genus- or species-level ID of other organism groups. CONCLUSIONS: MALDI-TOF MS provides accurate ID for most common anaerobes, but molecular analyses need to be available for rare isolates. Large complex laboratories should have a workflow for sending rare isolates for 16S rRNA gene sequencing in invasive cases where a definitive ID is clinically required.

Development and evaluation of a novel fast broad-range PCR and sequencing assay (FBR-PCR/S) using dual priming oligonucleotides targeting the ITS/LSU gene regions for rapid diagnosis of invasive fungal diseases: multi-year experience in a large Canadian healthcare zone.

BACKGROUND: This study evaluated the performance of a novel fast broad range PCR and sequencing (FBR-PCR/S) assay for the improved diagnosis of invasive fungal disease (IFD) in high-risk patients in a large Canadian healthcare region. METHODS: A total of 114 clinical specimens (CS) including bronchoalveolar lavages (BALs) were prospectively tested from 107 patients over a 2-year period. Contrived BALs (n = 33) inoculated with known fungi pathogens were also tested to increase diversity. Patient characteristics, fungal stain and culture results were collected from the laboratory information system. Dual-priming oligonucleotide (DPO) primers targeted to the internal transcribed spacer (ITS) (~ 350 bp) and large subunit (LSU) (~ 550 bp) gene regions were used to perform FBR-PCR/S assays on extracted BALs/CS. The performance of the molecular test was evaluated against standard microbiological methods and clinical review for the presence of IFD. RESULTS: The 107 patients were predominantly male (67, 62.6%) with a mean age of 59 years (range = 0-85 years): 74 (69.2%) patients had at least one underlying comorbidity: 19 (34.5%) had confirmed and 12 (21.8%) had probable IFD. Culture recovered 66 fungal isolates from 55 BALs/CS with Candida spp. and Aspergillus spp. being most common. For BALs, the molecular assay vs. standard methods had sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV), and efficiency of 88.5% vs.100%, 100% vs. 61.1%, 100% vs. 88.5%, 61.1% vs. 100%, and 90.2% for both. For other CS, the molecular assay had similar performance to standard methods with sensitivity, specificity, PPV, NPV and efficiency of 66.7%, 87.0%, 66.7%, 87.0% and 81.3% for both methods. Both methods also performed similarly, regardless of whether CS stain/microscopy showed yeast/fungal elements. FBR-PCR/S assays results were reported in ~ 8 h compared to fungal cultures that took between 4 and 6 weeks. CONCLUSIONS: Rapid molecular testing compared to standard methods have equivalent diagnostic efficiency but improves clinical utility by reporting a rapid species-level identification the same dayshift (~ 8 h).

Molecular epidemiology of Escherichia coli causing bloodstream infections in a centralized Canadian region: a population-based surveillance study.

OBJECTIVES: Escherichia coli is a leading cause of bloodstream infections worldwide, and is responsible for substantial patient morbidity, mortality and healthcare expenditure. Understanding the molecular epidemiology of E. coli will aid in designing superior treatment and prevention strategies. METHODS: We undertook a population-based surveillance study describing the clinical factors, susceptibility patterns, incidence rates and geographical distribution of sequence types (STs) among E. coli isolates (n = 686) causing incident bloodstream infections in a centralized Canadian region during 2016. STs were identified using a seven-single-nucleotide-polymorphism quantitative PCR (n = 422) and sequencing of certain house-keeping genes (n = 249). RESULTS: The annual population incidence rate of E. coli bloodstream infections was 48.8/100 000 patient years, and five dominant clones (ST131, ST73, ST69, ST95 and ST1193) accounting for 55% (378/686) of the population were identified, each with a specific geographical distribution within Calgary. ST131 was the most common (overall incidence rate of 10.4/100 000 patient years), an antimicrobial-resistant (AMR) clone affecting mainly the elderly and the very young. ST131 was common among residents in long-term care with an incidence rate of 312.5/100 000 patient years. ST73 was associated with community infections in the elderly, while ST69 and ST95 had increased incidence rates among females. ST1193 was the second most AMR clone and was associated with bloodstream infections in elderly males. CONCLUSIONS: This study showed that E. coli clones have unique characteristics in a well-defined human population. The elimination of ST131 would substantially decrease the overall incidence rate and AMR burden among E. coli bloodstream infections in the Calgary region, leading to considerable public health benefits.

Colistin-Nonsusceptible Pseudomonas aeruginosa Sequence Type 654 with blaNDM-1 Arrives in North America.

This study describes 3 different blaNDM-1 genetic platforms in 3 different species obtained from the same patient who was directly transferred to an institution in Calgary, Alberta, Canada, following a prolonged hospital stay in India. The blaNDM-1 in the Escherichia coli isolate was located on a 176-kb IncA/C plasmid contained within an ISCR1 region. The blaNDM-1 in the Providencia rettgeri isolate was located on a 117-kb IncT plasmid contained within Tn3000, while the blaNDM-1 in the Pseudomonas aeruginosa isolate was located on the chromosome within an ISCR3 region. This report highlights the plasticity of the genetic regions and environments associated with blaNDM-1. To the best of our knowledge, this is the first report of P. aeruginosa with blaNDM-1 identified in North America and the first report of blaOXA-181 in P. rettgeri. The P. aeruginosa isolate belonged to the international high-risk sequence type 654 clone and was nonsusceptible to colistin. This case emphasizes the need for the use of appropriate infection prevention and control measures and vigilant screening for carbapenem-resistant Gram-negative bacteria in patients with a history of travel to areas of endemicity, such as the Indian subcontinent.

Species-Level Identification of Actinomyces Isolates Causing Invasive Infections: Multiyear Comparison of Vitek MS (Matrix-Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry) to Partial Sequencing of the 16S rRNA Gene.

Actinomyces species are uncommon but important causes of invasive infections. The ability of our regional clinical microbiology laboratory to report species-level identification of Actinomyces relied on molecular identification by partial sequencing of the 16S ribosomal gene prior to the implementation of the Vitek MS (matrix-assisted laser desorption ionization-time of flight mass spectrometry [MALDI-TOF MS]) system. We compared the use of the Vitek MS to that of 16S rRNA gene sequencing for reliable species-level identification of invasive infections caused by Actinomyces spp. because limited data had been published for this important genera. A total of 115 cases of Actinomyces spp., either alone or as part of a polymicrobial infection, were diagnosed between 2011 and 2014. Actinomyces spp. were considered the principal pathogen in bloodstream infections (n = 17, 15%), in skin and soft tissue abscesses (n = 25, 22%), and in pulmonary (n = 26, 23%), bone (n = 27, 23%), intraabdominal (n = 16, 14%), and central nervous system (n = 4, 3%) infections. Compared to sequencing and identification from the SmartGene Integrated Database Network System (IDNS), Vitek MS identified 47/115 (41%) isolates to the correct species and 10 (9%) isolates to the correct genus. However, the Vitek MS was unable to provide identification for 43 (37%) isolates while 15 (13%) had discordant results. Phylogenetic analyses of the 16S rRNA sequences demonstrate high diversity in recovered Actinomyces spp. and provide additional information to compare/confirm discordant identifications between MALDI-TOF and 16S rRNA gene sequences. This study highlights the diversity of clinically relevant Actinomyces spp. and provides an important typing comparison. Based on our analysis, 16S rRNA gene sequencing should be used to rapidly identify Actinomyces spp. until MALDI-TOF databases are optimized.

Molecular Characterization by Using Next-Generation Sequencing of Plasmids Containing blaNDM-7 in Enterobacteriaceae from Calgary, Canada.

Enterobacteriaceae with blaNDM-7 are relatively uncommon and had previously been described in Europe, India, the United States, and Japan. This study describes the characteristics of Enterobacteriaceae (Klebsiella pneumoniae [n = 2], Escherichia coli [n = 2], Serratia marcescens [n = 1], and Enterobacter hormaechei [n = 1] isolates) with blaNDM-7 obtained from 4 patients from Calgary, Canada, from 2013 to 2014. The 46,161-bp IncX3 plasmids with blaNDM-7 are highly similar to other blaNDM-harboring IncX3 plasmids and, interestingly, showed identical structures within the different isolates. This finding may indicate horizontal transmission within our health region, or it may indicate contact with individuals from areas of endemicity within the hospital setting. Patients infected or colonized with bacteria containing blaNDM-7 IncX3 plasmids generate infection control challenges. Epidemiological and molecular studies are required to better understand the dynamics of transmission, the risk factors, and the reservoirs for bacteria harboring blaNDM-7. To the best of our knowledge, this is the first report of S. marcescens and E. hormaechei with blaNDM-7.

Incidence, risk factors, and outcomes for Enterococcus spp. blood stream infections: a population-based study.

BACKGROUND: Enterococci are a clinically significant cause of bloodstream infections (BSI), particularly in the nosocomial setting. The purpose of this study was to characterize the incidence, risk factors for acquisition, microbiological characteristics and mortality of enterococcal BSI within the well-defined population of a large Canadian health region. METHODS: Surveillance for all episodes of enterococcal BSI occurring among residents of the Calgary Health Zone (population 1.2 million) between 2000 and 2008 was conducted using an electronic surveillance system. Clinical features, microbiology, and outcomes were obtained. RESULTS: A total of 710 incident episodes of enterococcal BSI were identified for an annual incidence of 6.9 episodes per 100,000; the incidences of E. faecalis and E. faecium BSI were 4.5, and 1.6 per 100,000, respectively. Enterococcus faecalis infections were associated with a urinary focus, genitourinary malignancy, and abnormal genitourinary anatomy. E. faecium infections were associated with a gastrointestinal focus. Resistance to ampicillin, vancomycin and ciprofloxacin was higher in E. faecium infection. The overall case fatality rate was 22.8%, and was higher for E. faecium infection. CONCLUSIONS: This is the second population-based study to assess the risk factors for enterococcal BSI and compare the characteristics of infection with E. faecalis and E. faecium. Results suggest that BSI with E. faecalis and E. faecium should be regarded as two clinically different entities with unique sets of risk factors and microbiologic characteristics.

Identification by 16S rRNA gene sequencing of an Actinomyces hongkongensis isolate recovered from a patient with pelvic actinomycosis.

A case of Actinomyces hongkongensis pelvic actinomycosis in an adult woman is described. Conventional phenotypic tests failed to identify the Gram-positive bacillus isolated from a fluid aspirate of a pelvic abscess. The bacterium was identified by 16S rRNA gene sequencing and analysis using the SmartGene Integrated Database Network System software.

Population-based assessment of the incidence, risk factors, and outcomes of anaerobic bloodstream infections.

BACKGROUND: Anaerobes are a relatively uncommon but important cause of bloodstream infection. However, their epidemiology has not been well defined in non-selected populations. We sought to describe the incidence of, risk factors for, and outcomes associated with anaerobic bacteremia. METHODS: Population-based surveillance for bacteremia with anaerobic microorganisms was conducted in the Calgary area (population 1.2 million) during the period from 2000 to 2008. RESULTS: A total of 904 incident cases were identified, for an overall population incidence of 8.7 per 100,000 per year; 231 (26 %) were nosocomial, 300 (33 %) were healthcare-associated community-onset, and 373 (41 %) were community-acquired. Elderly males were at the greatest risk. The most common pathogens identified were: Bacteroides fragilis group (3.6 per 100,000), Clostridium (non-perfringens) spp. (1.1 per 100,000), Peptostreptococcus spp. (0.9 per 100,000), and Clostridium perfringens (0.7 per 100,000). Non-susceptibility to metronidazole was 2 %, to clindamycin 17 %, and to penicillin 42 %. Relative to the general population, risk factors for anaerobic bloodstream infection included: male sex, increasing age, a prior diagnosis of cancer, chronic liver disease, heart disease, diabetes mellitus, stroke, inflammatory bowel disease, human immunodeficiency virus (HIV) infection, chronic obstructive pulmonary disease (COPD), and/or hemodialysis-dependent chronic renal failure (HDCRF). The 30-day mortality was 20 %. Increasing age, nosocomial acquisition, presence of malignancy, and several other co-morbid illnesses were independently associated with an increased risk of death. CONCLUSION: Anaerobic bloodstream infection is responsible for a significant burden of disease in general populations. The data herein establish the extent to which anaerobes contribute to morbidity and subsequent mortality. This information is key in developing preventative, empiric treatment and research priorities.

Pyrosequencing reveals the complex polymicrobial nature of invasive pyogenic infections: microbial constituents of empyema, liver abscess, and intracerebral abscess.

The polymicrobial nature of invasive pyogenic infections may be underestimated by routine culture practices, due to the fastidious nature of many organisms and the loss of viability during transport or from prior antibacterials. Pyrosequencing was performed on brain and liver abscesses and pleural fluid and compared to routine culture data. Forty-seven invasive pyogenic infection samples from 44 patients [6 intracerebral abscess (ICA), 21 pyogenic liver abscess (PLA), and 18 pleural fluid (PF) samples] were assayed. Pyrosequencing identified an etiologic microorganism in 100 % of samples versus 45 % by culture, p <0.01. Pyrosequencing was also more likely than traditional cultures to classify infections as polymicrobial, 91 % versus 17 %, p <0.001. The median number of genera identified by pyrosequencing compared to culture was 1 [interquartile range (IQR) 1-3] versus 0 (IQR 0-1) for ICA, 7 (IQR 1-15) versus 1 (IQR 0-1) for PLA, and 15 (IQR 9-19) versus 0 (IQR 0-1) for PF. Where organisms were cultured, they typically represented the numerically dominant species identified by pyrosequencing. Complex microbial communities are involved in invasive pyogenic infection of the lung, liver, and brain. Defining the polymicrobial nature of invasive pyogenic infections is the first step towards appreciating the clinical and diagnostic implications of these complex communities.

Long-term mortality associated with community-onset bloodstream infection.

PURPOSE: Although bloodstream infection is widely recognized as an important cause of acute morbidity and mortality, long-term mortality outcomes are less well defined. The objective of this study was to define the early (≤28 days) and late (>28 days) mortality and assess determinants of late death following community-onset bloodstream infection. METHODS: All adult residents of the Calgary Zone who had community-onset bloodstream infections during the period 1 January 2003 and 31 December 2007 were included. The mortality outcome was assessed through to 31 December 2008. RESULTS: A total of 4,553 cases were identified, of which 2,105 (46%) were healthcare-associated and 2,448 (54%) were community-acquired. The 28-day, 90-day, and 365-day all-cause case-fatality rates were 561/4,553 (12%), 780/4,553 (17%), and 1,131 (25%), respectively. Within the first 28 days, the median time to death was 4 (interquartile range [IQR] 1-12) days, with 158 (28%) and 212 (38%) of early (≤28-day) deaths occurring by days 1 and 2, respectively. Among survivors to 28 days (n = 3,992), 570 (14%) suffered late 1-year mortality (i.e., death occurred between 29 and 365 days postinception). The most common causes of death in this cohort as listed by the vital statistics data were malignancy in 220 (39%), cardiovascular in 135 (24%), and infection-related in 37 (7%). Older age, higher Charlson score, prolonged initial admission duration, and healthcare-associated and polymicrobial infections were independently associated with late 1-year mortality. CONCLUSIONS: Community-onset bloodstream infection is associated with major early and late mortality.

Identification by 16S rRNA gene sequencing of Negativicoccus succinicivorans recovered from the blood of a patient with hemochromatosis and pancreatitis.

We describe a case of Negativicoccus succinicivorans bacteremia in an adult man with hemochromatosis and acute pancreatitis. Conventional phenotypic tests and commercial identification systems failed to definitively identify the tiny anaerobic Gram-negative coccus isolated from two sets of blood cultures. The bacterium was identified by 16S rRNA gene sequencing and analysis using the SmartGene Integrated Database Network System software. This is the first published report of the recovery of this organism from a patient with invasive infection.

Detection of AmpC beta-lactamases in Escherichia coli, Klebsiella spp., Salmonella spp. and Proteus mirabilis in a regional clinical microbiology laboratory.

There are currently no standardized diagnostic tests available for the reliable detection of AmpC beta-lactamases in Klebsiella spp., Escherichia coli, Proteus mirabilis and Salmonella spp. A study was designed to evaluate a confirmation disk test using cefotetan (CTT) and cefoxitin (FOX) with phenylboronic acid (PBA). It also investigated the most suitable screening concentrations of FOX, ceftriaxone (CRO) and ceftazidime (CAZ) for the detection of AmpC beta-lactamases. A total of 126 control (consisting of 11 laboratory and 115 well-characterized clinical strains) and 29,840 non-repeat clinical isolates were included. FOX with PBA used in a confirmation test and CRO and CAZ as screening agents were found to be unreliable. FOX at >or= 32 mg/L was the best screening agent and CTT with PBA was the best confirmation test. Of the clinical isolates 635 (2%) were found to be resistant to cefoxitin (MIC >or= 32 ug/mL) and 332 (52%) were AmpC positive. E. coli was the most common organism with AmpC beta-lactamases and was mostly present in urines from community patients. It is recommended that laboratories use FOX at 32 mg/L as a screening agent and perform a disk test with CTT and PBA to confirm the presence of an AmpC cephalosporinase in isolates of Klebsiella spp., E. coli, Salmonella spp. and P. mirabilis. This approach is convenient, practical and easy to incorporate into the workflow of a clinical laboratory. False-positive AmpC detection may occur with KPC-producing bacteria when inhibitor-based methods are used.

Incidence, risk factors and outcomes of Escherichia coli bloodstream infections in a large Canadian region.

Although Escherichia coli is the most common cause of bloodstream infection, its epidemiology has not been well defined in non-selected populations. We sought to describe the incidence of risk factors for, and outcomes associated with, E. coli bacteraemia. Population-based surveillance for E. coli bacteraemia was conducted in the Calgary Health Region (population 1.2 million) during the period 2000-2006. In total, 2368 episodes of E. coli bacteraemia were identified for an overall annual population incidence of 30.3/100 000; 15% were nosocomial, 32% were healthcare-associated community-onset and 53% were community-acquired bacteraemias. The very young and the elderly were at highest risk for E. coli bacteraemia. Sixty per cent of the episodes occurred in females (relative risk 1.5; 95% CI 1.4-1.6). Dialysis, solid organ transplantation and neoplastic disease were the most important risk factors for acquiring E. coli bacteraemia. Rates of resistance to ampicillin, trimethoprim-sulphamethoxazole, gentamicin, ciprofloxacin, cefazolin and ceftriaxone increased significantly during the period 2000-2006. The case-fatality rate was 11% and the annual population mortality rate was 2.9/100 000. Increasing age, ciprofloxacin resistance, non-urinary focus and a number of comorbid illnesses were independently associated with an increased risk of death, and community acquisition and urinary focus were associated with a lower risk of death. This study documents the major burden of illness associated with E. coli bacteraemia and identifies groups at increased risk for acquiring and dying from these infections. The emergence of ciprofloxacin resistance and its adverse effect on patient outcome is a major concern.

Epidemiology of Clostridium species bacteremia in Calgary, Canada, 2000-2006.

OBJECTIVES: To define the incidence, risk factors for acquisition, and outcomes associated with clostridial bacteremia in a large Canadian health region. METHODS: Retrospective population-based surveillance for clostridial bacteremia was conducted among all residents of the Calgary Health Region (population 1.2 million) during 2000-2006. RESULTS: One hundred and thirty-eight residents had incident Clostridium species bacteremia (1.8 per 100,000/year); 45 (33%) were nosocomial, 55 (40%) were healthcare-associated community onset, and 38 (28%) were community acquired. Older age and a number of underlying conditions were risk factors for acquiring Clostridium species bacteremia most importantly hemodialysis [relative risk (RR) 212.3; 95% confidence interval (CI) 106.5-385.5], malignancy (RR 40.2; 95% CI 27.6-58.1), and Crohn's disease (RR 11.2; 95% CI 3.0-29.4). Clostridium perfringens was most commonly identified with 58 (42%) isolates followed by Clostridium septicum (19; 14%), Clostridium ramosum (13; 9%), Clostridium clostridiiforme (8; 6%), and Clostridium difficile (7; 5%). Reduced susceptibility to penicillin occurred in 14/135 (10%), to metronidazole in 2/135 (1%), and to clindamycin in 36/135 (27%) isolates. The median length of stay was 12.7 days and 39/130 (30%) patients died in hospital for mortality rate of 0.5 per 100,000/year. CONCLUSIONS: Clostridium species bacteremia is associated with a significant burden of illness and hemodialysis and cancer patients are at highest risk.

Evaluation of the OSOM Trichomonas rapid test versus wet preparation examination for detection of Trichomonas vaginalis vaginitis in specimens from women with a low prevalence of infection.

The OSOM Trichomonas rapid test (OSOM Trich) was compared to the wet preparation examination (WP) for the detection of Trichomonas vaginalis vaginitis in women with a low prevalence of infection. A total of 19/1,009 (2%) women had T. vaginalis infection. OSOM Trich had very good performance, with sensitivity, specificity, efficiency, positive predictive value, and negative predictive value of 94.7, 100, 99.9, 100, and 99.9%, respectively. The implementation of OSOM Trich would decrease labor costs.

Evaluation of StrepB carrot broth versus Lim broth for detection of group B Streptococcus colonization status of near-term pregnant women.

The performance of StrepB Carrot Broth (SCB) versus group B Lim broth (LIM) for detection of group B streptococcus (GBS) colonization status in near-term pregnant women (35 to 37 weeks of gestation) was evaluated. Dually collected vaginal/rectal swabs from 279 women enrolled from a single large maternity clinic were analyzed. Fifty (18%) women were colonized by GBS according to both methods. SCB had excellent diagnostic performance compared to LIM, with sensitivity, specificity, positive predictive value, and negative predictive value of 92%, 100%, 100%, and 98.3%, respectively. Improved diagnostic efficiency due to direct reporting of GBS cases based on an orange color change in the SCB decreased overall labor and material costs.

Population-based laboratory surveillance for Serratia species isolates in a large Canadian health region.

A population-based laboratory surveillance was conducted during a six-year period to define the incidence, demographic risk factors for acquisition, and anti-microbial susceptibilities of Serratia species isolates. A total of 715 incident Serratia species isolates were identified for an annual incidence of 10.8 per 100,000 residents; bacteremic disease occurred in 0.9 per 100,000 residents annually. The incidence increased with advancing age and males were at the highest risk. Ninety-two percent of the isolates were Serratia marcescens, and the majority (65%) of incident Serratia species isolates were of community onset. Ninety-five percent of isolates were susceptible to ciprofloxacin, 98% to gentamicin, 98% to trimethoprim/sulfamethoxazole, and >99% to imipenem. No yearly increase in resistance was observed. Serratia species isolation is most commonly of community onset and older patients and males are at increased risk. Despite reports of increasing resistance among Serratia species, the incidence in our region remains at a low stable rate.

Evaluation of BBL CHROMagar O157 versus sorbitol-MacConkey medium for routine detection of Escherichia coli O157 in a centralized regional clinical microbiology laboratory.

The performance of BBL CHROMagar O157 (CHROM) versus that of sorbitol-MacConkey (SMAC) media for detection of Escherichia coli O157 was determined for a 3-month period. Results for 27/3,116 (0.9%) stool cultures were positive. CHROM had a higher sensitivity (96.30%) and negative predictive value (100%) and a better diagnostic efficiency than SMAC. Labor and material costs decreased when CHROM was used.