Microbiological Culture

We compared the performance of four commercial chromogenic media—namely, ABC medium (Lab M. Ltd., Bury, United Kingdom), COMPASS Salmonella agar (Biokar Diagnostics, Beauvais, France), CHROMagar™ Salmonella agar (CHROMagar Company, Paris, France), and SM ID agar (bioMerieux, Marcy l’Etoile, France)— with conventional Hektoen medium. Nine hundred sixteen stool samples from inpatients at three hospitals were cultured, in parallel, on the five media, both by direct inoculation and after selective enrichment in selenite broth. The specificity of the four chromogenic media was better than 91% after incubation for 24 h (77.7% with Hektoen agar) and better than 84% after incubation for 48 h (74.8% with Hektoen agar). This higher specificity reduces the need for confirmatory tests, thereby cutting technical time and reagent requirements. Both COMPASS agar and CHROMagar™ Salmonella, which after simple additional tests showed close efficiencies (96 and 97%, respectively), can be recommended as single-plate media of choice for the detection and presumptive identification of salmonellae in stools.

A new device Inoclic™ based on classical platinum wand-type inoculator system was studied for inoculation of a wide range of culture media. Inoclic™ device appears a convenient and valid alternative to agar diffusion or broth dilution to determine susceptibility of aerobic pathogens.

New device INOCLIC™ for inoculum preparation and standardization, and new rapid medium MHR-SIR™ were tested for Staphylococcus aureus A.S.T. Sixty five different clinical strains of S. aureus, including fifteen Methicillin-Resistant S. aureus (MRSA) strains, were tested using two different methods for inoculum standardization: Inoclic device (i2a, Montpellier, France) versus standard 0.5 McFarland suspension according to CLSI guidelines. And two different culture media: classical Mueller-Hinton medium (MH, i2a, Montpellier, France) versus fast Mueller-Hinton medium (MHR-SIR™, i2a, Montpellier, France).

The optimal method for surveillance of carbapenem-resistant Acinetobacter spp. (CRAB) is unknown. A collection of CRAB strains (n = 42), carbapenem-susceptible strains (CSAB), and non-Acinetobacter strains (n = 18) was used to evaluate six laboratory surveillance methods: MacConkey (MAC), MAC + 1 μg/ml imipenem (MAC-IPM), minimal salts agar + 1 % acetate (MSA), MSA with IPM disk (MSA-IPM), CHROMagar™ KPC and CHROMagar™ Acinetobacter with CR102 (CHROMAcineto). CHROMAcineto was 100 % sensitive and specific. CHROMagar KPC and MAC-IPM were highly sensitive (>95 %), but their specificity was substantially hampered by the breakthrough growth of CSAB. MSA was unsuitable for CRAB detection. CHROMAcineto is a promising medium for CRAB detection and warrants further clinical evaluation.