Abstract
Testing for coliforms has a long history in the dairy industry and has helped to identify raw milk and dairy products that may have been exposed to unsanitary conditions. Coliform standards are included in a number of regulatory documents (e.g., the U.S. Food and Drug Administration’s Grade “A” Pasteurized Milk Ordinance). As a consequence, detection above a threshold of members of this method-defined, but diverse, group of bacteria can result in a wide range of regulatory outcomes. Coliforms are defined as aerobic or facultatively anaerobic, Gram negative, non-sporeforming rods capable of fermenting lactose to produce gas and acid within 48 h at 32–35°C; 19 genera currently include at least some strains that represent coliforms. Most bacterial genera that comprise the coliform group (e.g., Escherichia, Klebsiella, and Serratia) are within the family Enterobacteriaceae, while at least one genus with strains recognized as coliforms, Aeromonas, is in the family Aeromonadaceae. The presence of coliforms has long been thought to indicate fecal contamination, however, recent discoveries regarding this diverse group of bacteria indicates that only a fraction are fecal in origin, while the majority are environmental contaminants. In the US dairy industry in particular, testing for coliforms as indicators of unsanitary conditions and post-processing contamination is widespread. While coliforms are easily and rapidly detected, and are not found in pasteurized dairy products that have not been exposed to post-processing contamination, advances in knowledge of bacterial populations most commonly associated with post-processing contamination in dairy foods has led to questions regarding the utility of coliforms as indicators of unsanitary conditions for dairy products. For example, Pseudomonas spp. frequently contaminate dairy products after pasteurization, yet they are not detected by coliform tests. This review will address the role that coliforms play in raw and finished dairy products, their sources and the future of this diverse group as indicator organisms in dairy products.
Highlights
In microbiological testing, an “indicator organism” is defined as a marker that reflects the general microbiological condition of a food or environment (Chapin et al, 2014)
Recent work indicates that testing for EB or total Gramnegative bacteria offers a distinct advantage to coliform testing when detecting common post-processing contamination (PPC) organisms in dairy products (Hervert et al, 2016)
This study found no association between pathogen presence and coliform detection, despite an association between Listeria monocytogenes with washed rind style cheeses
Summary
An “indicator organism” is defined as a marker that reflects the general microbiological condition of a food or environment (Chapin et al, 2014). “thermophilic and ubiquitous” coliforms originate from various natural environments including soil, water, vegetation, insects, farm produce, wooden reservoirs, grass, silages, and fresh vegetables (Seidler et al, 1975) Members of this group of “ubiquitous” coliforms are found within the genera Klebsiella, Enterobacter, and Citrobacter. California has established the only regulatory limit for coliforms in raw milk intended for Grade “A” dairy products in the U.S (not to exceed 750 CFU/mL; California Department of Food and Agriculture [CDFA], 2016). Common coliform genera in raw milk include Citrobacter, Enterobacter, Escherichia, and Klebsiella (Jayarao and Wang, 1999), which can originate from a variety of sources in the dairy farm environment including water, plant materials, equipment, dirt, and fecal sources (Kagkli et al, 2007). Jackson et al (2012) examined levels of coliform bacteria in raw silo milk in correlation to the presence and levels of four pathogens of interest
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