Evaluation of a Chromogenic Medium for the Identification and Isolation of MRSA
Ede Tyrell1*, Lorenzo Richards1, Tanesha Mentore1, Shemuel Ben Lewi1 and Nazara Roach2
1School of Allied Health, College of Medical Sciences, University of Guyana, Guyana
2Eureka Medical Labs, Guyana
*Corresponding Author: Ede Tyrell, Lecturer, School of Allied Health, College of Medical Sciences, University of Guyana, Guyana.
April 18, 2022; Published: May 20, 2022
Introduction: We sought to evaluate the screening ability of the chromogenic medium, HardyCHROMTM MRSA, for the identification of Methicillin Resistant Staphylococcus aureus (MRSA) from clinical specimens at 24 hours and 48 hours of incubation.
Materials and Methods: 100 Staphylococcus aureus isolates were obtained from 162 non-repetitive clinical specimens which included: pus aspirates, blood cultures, urine; ear, wound and vaginal swabs. Stool specimens were excluded due to the possible interference of commensals. Suspected isolates of S. aureus were confirmed using Mannitol Salt Agar (MSA) and the coagulase test.
Two methods were compared for the detection of MRSA: (1) The Reference method -Kirby-Bauer disk diffusion method with a 30 (µg) cefoxitin disk on Mueller Hinton Agar (MHA) and (2) The Test method – observation of HardyCHROM™ MRSA after 24 and 48 hours. For the Reference method, a zone diameter zone diameter of ≤21 mm was an indication that the isolate was MRSA, while ≥22 mm was identified as Methicillin Sensitive Staphylococcus aureus (MSSA). Pink to magenta colonies on HardyCHROM™ MRSA were interpreted as MRSA. No growth after 48 hours was documented as MSSA.
Results: A total of 100 Staphylococcus aureus isolates, obtained from 162 non-repetitive clinical specimens were processed. The specimens were mainly pus aspirates (36%), blood cultures (27%) and wound swabs (13%). After 24 hours, the sensitivity, specificity, PPV and NPV of HardyCHROM™ MRSA were 96.9%, 5.6%, 64.6% and 50.0% respectively. At 48 hours, the sensitivity, specificity, PPV and NPV of HardyCHROM™ MRSA were 96.9%, 0%, 63.3% and 0%, respectively. Using McNemar’s test, to compare the two tests, a significant difference (p value <0.05) was found at 24 hours and 48 hours incubation
Conclusions: We concluded that because of the high sensitivity of HardyCHROM™ MRSA, this medium would be effective in the screening of patients or staff to identify persons with an MRSA infection or those carrying MRSA.
Keywords: Methicillin Resistant; Staphylococcus aureus; Chromogenic Media; Screening; Clinical Specimens; Identification
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