Novel Chromogenic Screening Medium Developed for MRSA

By LabMedica International staff writers
Posted on 14 Aug 2014

A novel chromogenic screening agar medium for methicillin-resistant Staphylococcus aureus (MRSA) has been developed, as rapid and definite detection of MRSA is important not only diagnosis but also for preventing the spread of this bacteria.

MRSA is known as a major nosocomial pathogen, which causes a variety of clinical symptoms including septicemia, pneumonia, and postsurgical toxic shock syndrome and treatment of infections by MRSA has been problematic since MRSA is resistant to many antimicrobial agents.

Image: Typical colonies of methicillin-resistant Staphylococcus aureus (MRSA) grew and formed blue-colored colonies on MRSA-chrom media after 24 hours of incubation at 35 °C (Photo courtesy of Kohjin Bio Co., Ltd).

Scientists at the Kohjin Bio Co., Ltd. (Saitama, Japan) compared the company’s MRSA-chrom media with other commercially available media to detect MRSA. Forty-two strains of MRSA including 41 clinical isolates from nasal cavity were inoculated into the media for the inclusivity study. For the exclusivity study, 52 gram-positive strains other than MRSA, 36 gram-negative strains, and 3 yeasts were inoculated into suitable culture media.

A total of 42 MRSA strains grew and formed typical blue- and mauve-colored colonies on MRSA-chrom and CHROMagar MRSA (CHROMagar Microbiology; Paris, France) in 24 hours. Of 42 MRSA strains, 37 strains grew and formed typical yellow colonies with egg yolk turbid reaction for S. aureus on three other media in 48 hours. All of the other microbes tested including 17 methicillin-sensitive S. aureus (MSSA) strains failed to grow on MRSA-chrom. The colonies of Bacillus cereus were spread and had a frosted glass appearance and as a result, these colonies could be distinguished from MRSA easily. When the scientists tested the 50 clinical specimens, they found that both chromogenic media detected MRSA as typical colored colony from 33 specimens after 24 hours of incubation.

The authors concluded that the novel chromogenic medium, MRSA-chrom, developed for the screening of MRSA was excellent for both selectivity and detectability. Therefore, they suggested that MRSA-chrom was a useful alternative for rapid and definitely screening of MRSA. Moreover, MRSA-chrom had a good growth for MRSA since it contained no sodium chloride. The study was published in the August 2014 issue of the journal Diagnostic Microbiology and Infectious Disease.

Related Links:
Kohjin Bio Co., Ltd.
CHROMagar Microbiology