E. coli O157:H7 is a Shiga toxin-producing pathogenic strain causing severe bloody diarrhoea, hemolytic uremic syndrome (HUS), and death, especially in children and elderly. Unlike normal E.coli, O157:H7 cannot ferment sorbitol. HiCrome E. coli O157:H7 Agar exploits this: O157:H7 produces mauve/purple colonies while other E. coli produce blue-green colonies. Heavily regulated in food industry - ground beef, produce, unpasteurized juice testing required. Environmental monitoring of cattle operations also critical.
Listeria monocytogenes causes listeriosis, a serious foodborne illness with 20-30% mortality in high-risk populations (pregnant women, elderly, immunocompromised). Unlike most pathogens, L.monocytogenes grows at refrigeration temperatures (4°C). Found in: ready-to-eat foods, deli meats, soft cheeses, smoked seafood, produce. FDA and USDA enforce zero-tolerance policies for L. monocytogenes in RTE foods. Environmental monitoring in food facilities is critical to prevent contamination. Regular testing of drains, floors, equipment prevents outbreaks. This media composition is recommended by FDA BAM for Listeria detection.
HiCrome Listeria Agar is a chromogenic selective medium for detection and differentiation of Listeria species from food and environmental. L. monocytogenes and L. innocua appears bluish green without a yellow background. Listeria ivanovii appears bluish green with a yellow background. Most non-Listeria organisms are inhibited. Used in food safety programs, FDA BAM methods, and USDA protocols.
Chromogenic advantages: (1) Easier interpretation - distinct colors vs subtle differences on XLD/HE, (2) Faster presumptive results - 24 hours vs 48+ hours, (3) Improved selectivity - fewer false positives, (4) Better differentiation - simultaneous detection of multiple species, (5) Reduced technician training time (6) Improved accuracy in mixed cultures, (7) Less confirmation testing needed. Disadvantages: higher cost per plate, some strains may show atypical colors, not all regulatory agencies accept for official testing.
In FDA BAM Chapter 5 (Salmonella), use HiCrome as a plating medium: (1) Pre-enrichment: 25g sample in 225mL Buffered Peptone Water, incubate 18-24h at 35°C, (2) Selective enrichment: 0.1mL to 10mL Rappaport-Vassiliadis (RV) broth, incubate 18-24h at 42°C, (3) Plating: Streak RV broth onto HiCrome Salmonella Agar, incubate 18-24h at 35-37°C, (4) Presumptive positive: purple/mauve colonies, (5) Confirmation: biochemical tests and serology. HiCrome can replace or supplement XLD, HE, and BS Agar.
HiCrome Salmonella Agar is validated for food testing and is included in AOAC Performance Tested Methods. It can be used in FDA BAM and ISO 6579 protocols as a plating medium after selective enrichment. Many food laboratories have validated HiCrome as equivalent or superior to traditional XLD and HE Agar. Benefits: reduced confirmation testing, easier colony recognition, faster results. Some regulatory agencies require traditional media for official testing; check local requirements. Excellent for screening and research applications.
Salmonella colonies appear purple to mauve (pink-purple) on HiCrome Salmonella Agar after 18-24 hours at 35-37°C. Colony size is typically 1-3mm. Other organisms: E. coli (blue colonies), Proteus spp. (brown/cream with swarming), Pseudomonas (colorless/cream), Citrobacter (may show light purple but distinguishable from Salmonella), Other coliforms (blue-green). The distinctive purple color allows rapid presumptive identification without biochemical testing. Confirmation still required by serology or molecular methods.
HiCrome Salmonella Agar is a chromogenic differential medium for rapid detection and presumptive identification of Salmonella species. It contains enzyme substrates that produce distinctive purple/mauve colonies when cleaved by Salmonella-specific enzymes (caprylate esterase). Most other enteric bacteria produce blue, cream, or inhibited colonies. This allows: (1) Faster presumptive identification (24 hours vs 48 hours for traditional media), (2) Easier interpretation than XLD or HE Agar, (3) Improved selectivity with fewer false positives.
HiCrome MRSA Agar is selective chromogenic medium for detection of methicillin-resistant Staphylococcus aureus (MRSA) from nasal swabs and other clinical specimens. Contains: (1) Cefoxitin - selects for methicillin resistance, (2) Chromogenic substrate - produces distinctive green/teal colonies for S. aureus. Only MRSA grows. MRSA screening applications: (1) Hospital admission surveillance, (2) Healthcare worker screening, (3) Contact tracing in outbreaks, (4) ICU/high-risk unit monitoring. Direct plating method - results in 18-24 hours vs 3-4 days for traditional culture. Critical for infection prevention.
HiCrome ESBL Agar is selective chromogenic medium for detection of Extended-Spectrum Beta-Lactamase (ESBL) producing Enterobacteriaceae. Contains cefpodoxime (3rd generation cephalosporin) - only ESBL-producing organisms resistant to it can grow. Different organisms produce different colors: E. coli (pink), Klebsiella (blue), Enterobacter (blue-green). Used for: (1) ESBL surveillance screening, (2) Infection control in hospitals, (3) Outbreak investigations, (4) Rectal/stool screening for ESBL carriers. Growing public health concern - ESBL organisms resistant to many antibiotics, important for infection prevention programs.
Enterobacter screening important for: (1) Hospital-acquired infections (HAI) monitoring, (2) ICU surveillance (common opportunistic pathogen), (3) Carbapenem resistance detection. HiCrome Enterobacter allows rapid presumptive ID with distinctive colony colors distinguishing Enterobacter cloacae (blue-green) from other species. Growing concern as multi-drug resistant pathogen in healthcare.
HiCrome Klebsiella Agar selectively isolates Klebsiella pneumoniae (blue-green colonies) and K. oxytoca (blue colonies) from mixed cultures. Contains antibiotics inhibiting most other bacteria plus chromogenic substrates. Used for: (1) Hospital infection control surveillance, (2) Rectal screening for KPC-producing Klebsiella, (3) Outbreak investigations. Klebsiella increasingly important as carbapenem-resistant organisms. Recommended for detection of Gram-negative bacteria with a reduced susceptibility to carbapenem agents.
HiCrome Candida Agar differentiates Candida species by colony color: C. albicans (light green), C. tropicalis (blue -purple), C. krusei (purple, fuzzy), C. glabrata (cream to mauve). Used for presumptive ID from clinical specimens, reducing time to identification from 72 hours to 24-48 hours. Contains chromogenic substrates cleaved by species-specific enzymes plus chloramphenicol to inhibit bacteria. Recommended for rapid isolation and identification of Candida species from mixed cultures in clinical and non-clinical samples.
Traditional culture-based methods typically require 3-5 business days for complete results, as microbial enumeration requires incubation periods for growth and identification. Molecular methods like qPCR can provide faster results (24-48 hours) but may have higher costs. Some laboratories offer expedited services for rush samples, though this may affect pricing and availability
Acceptable limits vary by state and product type. Common ranges include TAMC 10,000-100,000 CFU/g, TYMC 1,000-10,000 CFU/g, pathogenic E. coli and Salmonella typically must be absent in 1 gram, and Aspergillus species limits range from absent to 1,000 CFU/g depending on the jurisdiction. Inhalable products generally have stricter limits than edibles or topicals.
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