We describe here the development and evaluation of MRSA ID, a new chromogenic agar medium for the specific isolation and identification of methicillin-resistant Staphylococcus aureus (MRSA). We used S. aureus ID (bioMérieux, La Balme Les Grottes, France) and supplemented it with various antimicrobials, including cefoxitin, ciprofloxacin, oxacillin, and methicillin. Cefoxitin proved to be superior to the other antimicrobials for the selection of MRSA from other strains of S. aureus. MRSA ID (consisting of S. aureus ID supplemented with 4 mg of cefoxitin/liter) was evaluated by the use of 747 swabs from various clinical sites. All specimens were also cultured on CHROMagar MRSA and oxacillin resistance screening agar base (ORSAB) and in selective mannitol broth (SMB). A total of 85 MRSA strains were isolated by a combination of all methods. After 22 to 24 h of incubation, 80% of the MRSA strains were isolated as green colonies on MRSA ID, compared with 59 and 62% of the strains that were isolated as colored colonies on CHROMagar MRSA and ORSAB, respectively. After 48 h of incubation, 89, 72, and 78% of the MRSA strains were isolated on MRSA ID, CHROMagar MRSA, and ORSAB, respectively. Sixty-five percent of the strains were isolated by growth in SMB. The specificities of MRSA ID, CHROMagar MRSA, ORSAB, and SMB were 99.5, 99.3, 97.9, and 92.8%, respectively, after 22 to 24 h of incubation. We conclude that MRSA ID is a sensitive and specific medium for the isolation and identification of MRSA.

S. aureus ID (bioMérieux, La Balme Les Grottes, France) is a new chromogenic agar medium designed to enable the isolation of staphylococci and the specific identification of Staphylococcus aureus. S. aureus produces green colonies on this medium due to production of ␣-glucosidase. To evaluate this medium, a total of 350 wound swabs were cultured onto S. aureus ID, CHROMagar Staph. aureus, and conventional media routinely used in our laboratory. After 18 to 20 h of incubation, 96.8% of strains formed green colonies on S. aureus ID compared with 91.1% of strains forming mauve colonies on CHROMagar Staph. aureus. A total of 94.3% of strains were recovered within 18 to 20 h with conventional media. The sensitivity was increased after 48 h of incubation to 98.7, 96.2, and 95.6% with S. aureus ID, CHROMagar Staph. aureus, and conventional media, respectively. A total of 97.4% of green colonies on S. aureus ID were confirmed as S. aureus compared with 94.4% of mauve colonies on CHROMagar Staph. aureus. We conclude that S. aureus ID is a highly sensitive and specific medium for the isolation and identification of S. aureus from wound swabs.Staphylococcus aureus is an important and frequent cause of wound infection and is consequently one of the most common pathogens sought in clinical microbiology laboratories. Diagnosis of S. aureus infection is generally performed by culture of wound swabs onto nonspecific media and confirmation of suspect colonies by biochemical and/or serological tests. Most commonly, this involves testing colonies of staphylococci for agglutination with sensitized latex particles to detect bound coagulase, protein A, and/or specific capsular antigens (12, 13). Colonies of S. aureus may be atypical and difficult to differentiate from coagulase-negative staphylococci (3); hence, a large number of agglutination tests may be required to rule out the presence of S. aureus. A number of culture media have been developed to increase the specificity of S. aureus detection, including mannitol-salt agar and Baird-Parker medium (2, 6, 7). A more recent approach has been the use of CHROMagar Staph. aureus, which employs chromogenic enzyme substrates in a selective agar medium, allowing the detection of S. aureus with a high degree of sensitivity and specificity (8). S. aureus ID is another recently described chromogenic medium for the specific detection of S. aureus, but there are no reports of the efficacy of this medium with clinical samples (C. Cotte, N. Fanjat, C. Ilter, D. Monget, S. Orenga, D. Robichon, and C. Roger-Dalbert, Abstr. 102nd Gen. Meet. Am. Soc. Microbiol., abstr. C23, 2002). On S. aureus ID, S. aureus forms distinctive green colonies due to production of ␣-glucosidase. Other staphylococci generally form white colonies but occasionally produce pink colonies due to the hydrolysis of a second chromogenic substrate for ␤-glucosidase.We performed a comparison of S. aureus ID and CHROMagar Staph. aureus for the detection of S. aureus with 350 clinical samples. These media were compared with nonspec...

Aims: To compare the performance of a new chromogenic medium, Uriselect 4, with cystine lactose electrolyte deficient (CLED) agar and an established chromogenic agar, CPS ID 2 medium, for detection of urinary tract pathogens. Methods: Using a semiquantitative culture method, 777 samples were inoculated on to the three test media in duplicate. All bacterial strains that yielded a potentially significant growth were observed for colony colour and identified using standard methods. Results: Of the 777 samples tested, 589 urine samples yielded potentially significant growth of at least one strain. A total of 811 strains were isolated on at least one of the three media. A total of 168 urine samples yielded a mixture of at least two strains. Uriselect 4 medium showed the best sensitivity of the three media and only failed to recover 14 strains (1.7%). CPS ID 2 medium failed to recover 22 strains (2.7%). CLED medium showed the worst recovery and failed to recover 74 strains (9.1%). Both chromogenic media allowed for identification of Escherichia coli with a high degree of specificity (98% for Uriselect 4, 99.7% for CPS ID 2). Inclusion of a spot indole test increased the specificity of both chromogenic media to 100% for E coli. Conclusions: Uriselect 4 and CPS ID 2 were superior to CLED medium for the isolation of urinary tract pathogens mainly because of their ability to discriminate mixed cultures. Both chromogenic media were also useful for the preliminary identification of the most common urinary tract pathogens.

Aims: To synthesize novel substrates for the detection of b-ribosidase and assess their potential for the differentiation of Gram-negative bacteria. Methods and Results: Two novel chromogenic substrates, 3¢,4¢-dihydroxyflavone-4¢-b-D-ribofuranoside (DHFriboside) and 5-bromo-4-chloro-3-indolyl-b-D-ribofuranoside (X-riboside) were evaluated along with a known fluorogenic substrate, 4-methylumbelliferyl-b-D-ribofuranoside (4MU-riboside). A total of 543 Gram-negative bacilli were cultured on media containing either DHF-riboside or X-riboside. Hydrolysis of DHF-riboside or X-riboside resulted in the formation of clearly distinguishable black or blue-green colonies, respectively. Hydrolysis of 4MU-riboside was evaluated in a liquid medium in microtiter trays and yielded blue fluorescence on hydrolysis which was measured using fluorimetry. b-Ribosidase activity was widespread with 75% of strains, including 85AE6% of Enterobacteriaceae, showing activity with at least one substrate. Genera that demonstrated b-ribosidase activity included Aeromonas, Citrobacter, Enterobacter, Escherichia, Hafnia, Klebsiella, Morganella, Providencia, Pseudomonas, Salmonella and Shigella. In contrast, strains of Proteus spp., Acinetobacter spp., Yersinia enterocolitica, Vibrio cholerae and Vibrio parahaemolyticus generally failed to demonstrate b-ribosidase activity. Conclusions: The novel substrates DHF-riboside and X-riboside are effective for the detection of b-ribosidase in agar-based media and may be useful for the differentiation and identification of Gram-negative bacteria. Significance and Impact of the Study: This is the first report describing the application and utility of chromogenic substrates for b-ribosidase. These substrates could be applied in chromogenic media for differentiation of Gram-negative bacteria.

No abstract