The MLG: USDA’s Methods for Meat and Poultry Testing

The study: U.S. Department of Agriculture, Food Safety and Inspection Service. Microbiology Laboratory Guidebook (MLG) — reference methods for meat, poultry, and egg product testing (continuously updated).

If the BAM is FDA’s playbook, the MLG is FSIS’s — the validated methods behind meat and poultry testing: Salmonella, Campylobacter, O157:H7 and non-O157 STEC, Listeria, indicator organisms. When FSIS samples your plant’s product, MLG methods generate the results that determine compliance.

Why the MLG matters to plants

FSIS uses these methods for regulatory verification testing — the samples that can trigger enforcement. Your internal testing should be comparable: methods validated as equivalent, or the MLG methods themselves. The MLG chapters detail enrichment, screening (including molecular screens), isolation, and confirmation — and they’re updated as science advances (the non-O157 STEC methods, for example, evolved significantly).

The practical implications

Know which MLG chapter covers your product-pathogen combination, and make sure your lab (in-house or contract) can defend its methods as equivalent where they differ. Pay attention to updates — when FSIS revises a method, the regulatory bar moves with it. And understand the screening-versus-confirmation structure: molecular screens are fast but presumptive; culture confirmation is definitive. The published record shows plants panic over presumptive screen positives that never confirmed — and the published record shows plants ignore screens that later confirmed. Treat screens as what they are: early warning, not verdicts. Respond proportionally, investigate promptly.

The regulatory laboratory’s playbook

The FSIS Microbiology Laboratory Guidebook (MLG) — the continuously updated reference methods for the meat, poultry, and egg products — is the regulatory laboratory’s playbook: the Salmonella, the Campylobacter, the STEC (the MLG 5C), the Listeria, the methods the FSIS laboratories use and the industry’s laboratories follow for the regulatory testing. The MLG’s authority: the method the regulator uses is the method the regulated should match.

The MLG’s evolution (the method updates — the molecular screenings added, the cultural confirmations refined, the STEC methods expanded to the non-O157) tracks the science: the guidebook as the living document, the chapters revised as the methods improve. The laboratory working from the outdated MLG chapter risks the superseded method — the online edition as the current authority.

The MLG’s practical significance for the industry: the regulatory testing (the FSIS sampling programs — the Salmonella performance standards, the STEC testing) uses the MLG methods — and the industry’s internal testing aligned to the MLG ensures the comparability (the establishment’s results versus the regulator’s). The method differences (the enrichment variations, the detection endpoints) can explain the result discrepancies — the alignment prevents the disputes. The MLG’s message: the reference method, current edition, consistently applied — the regulatory laboratory’s discipline as the industry’s standard.

The MLG’s international influence

The MLG’s international influence — the methods referenced in the Codex discussions, the trading-partner laboratories, the global meat trade — extends the guidebook’s reach beyond the American regulation: the reference method as the trade’s common language. The countries aligning their meat-testing to the MLG (the exporters to the American market) adopt the methods for the market access. The reference method’s authority follows the market’s gravity.

Source: USDA-FSIS. Microbiology Laboratory Guidebook (MLG), current edition.