Evaluation of a cost effective broth and selective agar combination for the detection of MRSA and Staphylococcus aureus from surveillance specimens using regular workflow.

OBJECTIVE: To evaluate the use of selective agar and broth combination in a regular laboratory daily workflow. DESIGN: Swabs from 173 surveillance specimens were inoculated onto half of the Bio-Rad MRSASelect (M), SaSelect (S) and Sheep Blood agars (SBA) and the swab placed in the LIM broth. After overnight incubation, 10 microL of the LIM broth was inoculated onto the other half of the three agars and incubated overnight. All the and examined worked after agars were up approximate 14-18 hours of incubation for day one and two according to the regular workflow of the laboratory, without incubating for the full 24 hours for each incubation day. M agar and SBA were evaluated for Methicillin-Resistant Staphylococcus aureus (MRSA), while the S agar was evaluated for Staphylococcus aureus (SA) based on typical colony morphology development. Colonies on the SBA were picked and processed for definitive identification and cefoxitin susceptibility result. SETTING: Trinity Medical Center, a community hospital with network hospitals PATIENTS: Patient admitted to the hospital submitted swab for surveillance culture RESULTS: There were a total of 29 MRSA isolated in the study. On day one, both M agar and SBA detected 14 MRSA (48.3%) and on day two, M agar detected 10 (82.7%), while SBA detected 8 (75.8%) additional MRSA. LIM broth added 5 more MRSA to both agars on day 2, to give M agar a total of 29 (100%) and SBA agar a total of 27 (93.1%) of MRSA from the 173 specimens. There were a total of 62 SA isolated. Both the S agar and SBA isolated 34 (54.8%) on day one and 15 more (79%) on day two. The LIM broth added an additional 13 SA for both agars on day two. CONCLUSION: Using half of the agar plate for the initial swab and the other half for the broth creates an economic strategy for the detection of MRSA using the M agar and SA using the S agar. Both the M and S agars provided excellent identification and recovery of MRSA or SA based on color and colony morphology unless the colony was too young for color development. The color morphology from the M and S agars was distinguishable overnight after being subcultured from LIM broth. Working up the specimen according to the workflow of the laboratory without having to wait for each plate to incubate a full 24 hours, can still detect all the targeted organisms within 2 workdays using this cost effective strategy.

Comparing ImmunoCard with two EIA assays for Clostridium difficile toxins.

OBJECTIVE: To compare three Clostridium difficile EIA kits for the detection of C. difficile toxins from clinical specimens. DESIGN: A total of 287 fresh and stored stool specimens were tested using all three assays. Stools with discrepant results were sent to a reference laboratory for tissue cytotoxin assay. SETTING: Trinity Medical Center, a community hospital with network hospitals. PATIENTS: Patients with diarrhea submitted stools for detection of C. difficile toxins. RESULTS: Of the 287 stool specimens, 116 were positive and 171 negative for C. difficile toxins. The sensitivity, specificity, and positive and negative predictive values of Meridian EIA assay were 99.1, 97.7, 96.6, and 99.4%; ImmunoCard were 100, 98.2, 97.5, and 100%; BioStar OIA assay were 94, 98.8, 98.2, and 96% respectively. ImmunoCardprovides the best sensitivity (100%) for C. difficile toxins A and B detection. The BioStar OIA rapid test missed seven positive stool specimens possibly due to failure to detect toxin B. CONCLUSION: ImmunoCard has slightly higher predictive values, shorter turnaround time and greater convenience compared to the Meridian EIA Assay. ImmunoCard may be cost effective not only in smaller laboratories, but also in high volume laboratories, when used on a STAT basis or single request.