What are Optimal Bacteriological Screening Test Cut-Offs for Pasteurized Donor Human Milk Intended for Feeding Preterm Infants?

BACKGROUND: Definitive criteria for microbial screening of pasteurized donor human milk are not well established and international recommendations vary. AIMS: (1) To review pasteurized donor human milk batch discard due to failed microbial screening criteria at our milk bank (following United Kingdom National Institute of Clinical Excellence guidelines), and (2) to compare our known milk discard proportion with estimated milk discard proportions that would be required by other international milk bank guidelines. METHODS: We reviewed our microbial screening results (N = 783) over 18-months (July 2018-December 2019) and compared our known milk discard proportion with estimated milk discard proportions using other international milk bank guidelines. RESULTS: Of samples, n = 50 (6.4%) failed pre-pasteurization screening, most commonly due to the presence of >104 CFU/mL Enterobacterales in the pre-pasteurization sample (n = 30; 3.8%). Two (0.3%) samples failed post-pasteurization screening, with Bacillus cereus identified in both cases, resulting in total discard proportion of 6.7% (n = 52) of batches. Applying European Milk Bank Association recommended bacterial screening criteria, approximately 23.3% (n = 183) of milk batches would have been discarded. CONCLUSIONS: Further research is required to justify the stringent European Milk Bank Association recommendations for pre-pasteurization discard criteria, although we believe that a post-pasteurization acceptance criterion of <1 CFU/mL is appropriate and aligns with international guidance. Further work is needed to understand pasteurized donor human milk microbiological safety risks, to better integrate screening criteria within current food standards regulation, and to consider risk-based assessment including the impact on availability and affordability.

Validation of low-volume enrichment protocols for detection of Escherichia coli O157 in raw ground beef components, using commercial kits.

Testing of beef destined for use in ground beef products for the presence of Escherichia coli O157:H7 has become an important cornerstone of control and verification activities within many meat supply chains. Validation of the ability of methods to detect low levels of E. coli O157:H7 is critical to confidence in test systems. Many rapid methods have been validated against standard cultural methods for 25-g samples. In this study, a number of previously validated enrichment broths and commercially available test kits were validated for the detection of low numbers of E. coli O157:H7 in 375-g samples of raw ground beef component matrices using 1 liter of enrichment broth (large-sample:low-volume enrichment protocol). Standard AOAC International methods for 25-g samples in 225 ml of enrichment broth, using the same media, incubation conditions, and test kits, were used as reference methods. No significant differences were detected in the ability of any of the tests to detect low levels of E. coli O157:H7 in samples of raw ground beef components when enriched according to standard or large-sample:low-volume enrichment protocols. The use of large-sample:low-volume enrichment protocols provides cost savings for media and logistical benefits when handling and incubating large numbers of samples.