Effect of milk bactofugation on the counts and diversity of thermoduric bacteria

Abstract

The objective of this work was to determine the effect of milk bactofugation on the counts and microbial diversity of mesophilic (MT), psychrotrophic (PT), and thermophilic (TT) thermoduric bacteria and its potential as a technological method to remove spoilage microorganisms resistant to pasteurization. Different batches of raw milk from 69 dairy farms divided into sets in 3 bulk tanks (A, B, C) were evaluated at different times during the technological process. As the raw milk was preheated (~55°C) immediately before bactofugation (10,000 × g), the effect of bactofugation was estimated by comparing the counts in raw, preheated, and bactofuged milk. This centrifugation was sufficient to reduce the isolation of 88% of the MT in preheated milk. For PT, it was possible to verify a reduction of 72.5% in batch C. The TT were not recovered at higher detection limits (<5 cfu/mL). For diversity, 310 isolates were identified using a molecular approach; 15 species of contaminating thermoduric bacteria were identified from raw and preheated milk, and only 6 species were recovered in bactofuged milk. Only MT were recovered from the bactofuged milk, mainly the species Lysinibacillus fusiformis (61.7%) and Bacillus licheniformis (12.3%). Both species are known to be endosporeforming psychrotrophs and have proteolytic or lipolytic activity. The bactofugation of raw milk reduced the number of isolates of B. licheniformis, Bacillus toyonensis, Micrococcus aloeverae, and Aestuariimicrobium kwangyangense by 33, 43, 86, and 92%, respectively, and reduced the isolates of Macrococcus caseolyticus, Lysinibacillus varians, Carnobacterium divergens, Microbacterium hominis, Kocuria indica, Micrococcus yunnanensis, Gordonia paraffinivorans, Bacillus invictae, and Kocuria kristinae to undetectable levels. The results of this study indicate that bactofugation can be applied by the dairy industry to reduce pasteurizationresistant microorganisms in combination with prophylactic measures to prevent the contamination of raw milk by spores and vegetative forms of bacteria.

Elucidating the effect of iron acquisition systems in Klebsiella pneumoniae on susceptibility to the novel siderophore-cephalosporin cefiderocol

“…DNA was extracted from pure bacterial colonies using boiling lysis method [ 21 ]. The mechanism of penetration of CFDC through the OM is described in the literature as passing through the iron transport system [ 22 , 23 ].…”

Identification and Characterisation of Spore-Forming Bacteria in Bovine Raw Milk Collected from Four Dairy Farms in New Zealand

“…Although in low numbers, these sporeforming bacteria have been isolated from raw milk and milk products elsewhere and have been associated with spoilage [66,[95][96][97][98]. Lysinibacillus fusiformis is another spore-forming bacterium which has been isolated from raw milk in a previous study [99]. In the present study, two isolates of L. fusiformis were isolated from Farm 4 raw-milk samples, one from summer and one from winter.…”

Synergistic interactions in multispecies biofilm combinations of bacterial isolates recovered from diverse food processing industries

“…B. licheniformis is one of the biggest concerns for the dairy industry throughout the world, especially for milk powder production ( Sadiq et al, 2016 ), as it is the predominant bacterial species found in raw milk and at all stages of dairy processing ( Banykó and Vyletělová, 2009 ; Gopal et al, 2015 ; Sadiq et al, 2016 , 2018 ). B. licheniformis and M. lacticum have been reported co-existing in whey protein concentrate ( Walsh et al, 2012 ) and raw milk ( Ribeiro-Júnior et al, 2020 ). These three species were shown to form synergistic biofilms in many combinations with other species like B. simplex , Kocuria salsicia , and opportunistic pathogens like Staphylococcus warneri .…”