Psychrotrophic bacteria in milk: How much do we really know?

Abstract

The occurrence of psychrotrophic bacteria in raw milk is studied worldwide due to the difficulties associated with controlling their growth during cold storage and the consequent negative effects upon fluid milk or dairy products. Among the psychrotrophic bacteria, the genus Pseudomonas (represented primarily by P. fluorescens) has been highlighted as the cause of numerous defects in dairy products. In light of its perceived predominance, this species has frequently been chosen as a model organism to assess the effects of psychrotrophic bacteria on milk or to evaluate the efficacy of control measures. However, recent findings derived from the application of molecular biological techniques have exposed a number of deficiencies in our knowledge of the biology of milk-associated psychrotrophs. Furthermore, it has been revealed that microbe to microbe communication plays a significant role in determining both the identities and the extent to which different groups of microbes develop during cold storage. The application of molecular identification methods has exposed errors in the classification of members of the genus Pseudomonas isolated from cold stored milk and has stimulated a reevaluation of the presumed status of P. fluorescens as the predominant milk-associated psychrotrophic species. This article presents a succinct review of data from studies on psychrotrophic bacteria in milk, some of which contest established theories in relation to the microbiology of cold stored raw milk, and poses the question: how much do we really know?

Raw and Heat-Treated Milk: From Public Health Risks to Nutritional Quality

“…Milk freshly drawn from the udder often does not contain detectable populations of psychrotrophic bacteria [25]. However, after milk collection psychrotrophic bacteria grow also when the cold chain is applied.…”

“…However, after milk collection psychrotrophic bacteria grow also when the cold chain is applied. Despite these microorganisms have optimal and maximal growth temperatures above 15 and 20 • C, respectively [25], they have, in fact, the ability to grow at low temperatures, such as 2-7 • C. This means that over time psychrotrophic populations can develop in cold stored raw milk and their presence in the raw milk microbiota can become a matter of concern. The drawback of psychrotroph presence in milk is their ability to produce extracellular enzymes, mainly proteases and lipases, which are responsible for spoiling milk but also dairy products, as the extracellular enzymes can resist pasteurization and even ultra-high temperature processing [26].…”

“…They are represented primarily by the Gram-negative genera Pseudomonas, Aeromonas, Serratia, Acinetobacter, Alcaligenes, Achromobacter, Enterobacter, Chryseobacterium and Flavobacterium (Table 1) [16,[25][26][27].…”

Incidence of psychrotrophs bacteria with potential public health implications in ice cream sold in Zakho markets

“…Many studies have reported the prevalence of pathogenic Psychrotrophic in ice cream. 1,[6][7][8][9][10][11][12] Despite the effective removal of Staphylococcus aureus via pasteurization in milk, its low infective dose and ability to survive unfavourable environments make this bacterium a serious risk to consumers. 10,13,14 Ice cream can be contaminated with Staphylococcus aureus by the introduction of flavourings and ingredients (nut and chocolate) during ice cream production or from the nasal cavities and hands of carriers during food production.…”

Electroceutical disinfection strategies impair the motility of pathogenicPseudomonas aeruginosaandEscherichia coli

“…This organism infects approximately one-third of all burn wounds 19 . Additionally, Pseudomonas aeruginosa has negative industrial and environmental influences, causing dairy spoilage 20 and issues in water treatment systems 21 . Therefore, applying electric potential could be a complementary approach in addition to using chemical-based drugs to overcome the issue of multi-drug resistance.…”