Automated Scoring of Chromogenic Media for Detection of Methicillin-Resistant Staphylococcus aureus by Use of WASPLab Image Analysis Software

Abstract

Recently, systems have been developed to create total laboratory automation for clinical microbiology. These systems allow for the automation of specimen processing, specimen incubation, and imaging of bacterial growth. In this study, we used the WASPLab to validate software that discriminates and segregates positive and negative chromogenic methicillin-resistant Staphylococcus aureus (MRSA) plates by recognition of pigmented colonies. A total of 57,690 swabs submitted for MRSA screening were enrolled in the study. Four sites enrolled specimens following their standard of care. Chromogenic agar used at these sites included MRSASelect (Bio-Rad Laboratories, Redmond, WA), chromID MRSA (bioMérieux, Marcy l'Etoile, France), and CHROMagar MRSA (BD Diagnostics, Sparks, MD). Specimens were plated and incubated using the WASPLab. The digital camera took images at 0 and 16 to 24 h and the WASPLab software determined the presence of positive colonies based on a hue, saturation, and value (HSV) score. If the HSV score fell within a defined threshold, the plate was called positive. The performance of the digital analysis was compared to manual reading. Overall, the digital software had a sensitivity of 100% and a specificity of 90.7% with the specificity ranging between 90.0 and 96.0 across all sites. The results were similar using the three different agars with a sensitivity of 100% and specificity ranging between 90.7 and 92.4%. These data demonstrate that automated digital analysis can be used to accurately sort positive from negative chromogenic agar cultures regardless of the pigmentation produced.

Commentary: Automatic Digital Plate Reading for Surveillance Cultures

“…Similar results were observed previously by using the same CDM tuned to interpret chromogenic agar designed to detect methicillin-resistant Staphylococcus aureus (MRSA) (6). In that study, 57,690 nasal swabs collected for MRSA screening purposes at 4 sites were plated to one of three chromogenic screening agars The WASPLab CDM was tuned to detect colonies exhibiting the characteristic color specified for MRSA colonies in the package insert of each chromogenic agar.…”

“…This allows the technologist to group negative plates and to quickly confirm the no-growth call in a batch mode, improving efficiency. Additional advances in artificial intelligence, neural networks, and other digital interpretive techniques allow more-sophisticated automated colony analysis, including identification of organisms based on colony morphology and/or specific reactions on chromogenic or other differential agar (5,6). Additional potential benefits of digital plate reading include the possibility of telemicrobiology (i.e., remote consultation with clinical staff and/or the laboratory director that includes transmission of plate images), decreased time of physical exposure to pathogens, and improved ergonomics (7,8).…”

Automatic Digital Analysis of Chromogenic Media for Vancomycin-Resistant-Enterococcus Screens Using Copan WASPLab

“…Using the Chromogenic Detection Module (CDM) image analysis software incorporated into the WASPLab, images were automatically screened by comparing the plate at time point 0 to the plate after incubation. The CDM analysis was previously described by Faron et al (13). Briefly, the software analyzes the plates to identify differences in growth and colony color and is programmed to correspond specifically to the medium type used by the laboratory (expected colony color per package insert).…”

“…Previously, we reported on the use of the WASPLab to automatically plate and categorize chromogenic methicillin-resistant Staphylococcus aureus (MRSA) specimens as negative or "nonneg-ative" (detection of color can be performed after 24 h but requires manual examination to confirm) (13). Using specific algorithms to interpret colony growth and color, the software was highly sensitive and resulted in no false-negative specimen identifications.…”

Resistance Mechanisms, Epidemiology, and Approaches to Screening for Vancomycin-Resistant Enterococcus in the Health Care Setting

“…Compared with the previous reports, active screening alone is cost-effective if it reduces 1 to 2 VRE BSI events a year, whereas larger infection control programs may need to prevent multiple infections a year to be cost-effective. Long-term costs of specialized chromogenic VRE screening media can be offset if the laboratory adopts automated systems that can plate, incubate, and analyze media by reducing the cost of technologists' time (57).…”