N2 Gas Flushing Limits the Rise of Antibiotic-Resistant Bacteria in Bovine Raw Milk during Cold Storage

Abstract

Antibiotic resistance has been noted to be a major and increasing human health issue. Cold storage of raw milk promotes the thriving of psychrotrophic/psychrotolerant bacteria, which are well known for their ability to produce enzymes that are frequently heat stable. However, these bacteria also carry antibiotic resistance (AR) features. In places, where no cold chain facilities are available and despite existing recommendations numerous adulterants, including antibiotics, are added to raw milk. Previously, N2 gas flushing showed real potential for hindering bacterial growth in raw milk at a storage temperature ranging from 6 to 25°C. Here, the ability of N2 gas (N) to tackle antibiotic- resistant bacteria was tested and compared to that of the activated lactoperoxidase system (HT) for three raw milk samples that were stored at 6°C for 7 days. To that end, the mesophiles and psychrotrophs that were resistant to gentamycin (G), ceftazidime (Ce), levofloxacin (L), and trimethoprim-sulfamethoxazole (TS) were enumerated. For the log10 ratio (which is defined as the bacterial counts from a certain condition divided by the counts on the corresponding control), classical Analyses of Variance (ANOVA) was performed, followed by a mean comparison with the Ryan-Einot-Gabriel-Welsch multiple range test (REGWQ). If the storage “time” factor was the major determinant of the recorded effects, cold storage alone or in combination with HT or with N promoted a sample-dependent response in consideration of the AR levels. The efficiency of N in limiting the increase in AR was highest for fresh raw milk and was judged to be equivalent to that of HT for one sample and superior to that of HT for the two other samples; moreover, compared to HT, N seemed to favor a more diverse community at 6°C that was less heavily loaded with antibiotic multi-resistance features. Our results imply that N2 gas flushing could strengthen cold storage of raw milk by tackling the bacterial spoilage potential while simultaneously hindering the increase of bacteria carrying antibiotic resistance/multi-resistance features.

Phospholipolysis Caused by Different Types of Bacterial Phospholipases During Cold Storage of Bovine Raw Milk Is Prevented by N2 Gas Flushing

“…During cold storage, the increases in TM and in G- bacteria levels were roughly equivalent and coincided with a rise in spoilage enzyme producers (Pr+, Li+, and PLa+) ( Figure 1 ), which is in agreement with previous studies ( Cousin, 1982 ; Sorhaug and Stepaniak, 1997 ; Chambers, 2002 ). The previously described inhibitory effect of N 2 gas flushing on bacterial growth ( Murray et al, 1983 ; Dechemi et al, 2005 ; Munsch-Alatossava et al, 2010a , b , c , 2017 , 2016 ; Gschwendtner et al, 2016 ) was also observed here. Cold storage combined with N 2 gas flushing prevented all considered bacterial types, including exoenzyme producers from exceeding 10 5 cfu/ml for samples M1 and M3 over the course of 7 days.…”

“…Strategies for preventing bacterial growth during cold storage should reduce the potential for bacterial spoilage and better preserve the proteins, lipids and phospholipids found in raw milk. Previously, we observed that N 2 gas flushing of raw milk strongly inhibited bacterial growth at laboratory and pilot plant scales, and Next Generation Sequencing revealed that key spoilers such as Pseudomonas were targeted by the N 2 flushing treatment; earlier studies also suggested that phospholipolytic bacteria present in bovine raw milk were particularly sensitive to N 2 flushing ( Munsch-Alatossava et al, 2010a , b , c , 2016 , 2017 ; Gschwendtner et al, 2016 ). Moreover, N 2 flushing treatment conferred a significant protective effect on the antioxidant components of raw milk, during cold storage ( Gursoy et al, 2017 ).…”

Potential of N2 Gas Flushing to Hinder Dairy-Associated Biofilm Formation and Extension

“…Food has also been identified as one main direct vehicle for the transmission of antibiotic-resistant bacteria from animals to humans and of antibiotic resistance (AR)-encoding genes carried by zoonotic bacteria ( Sørum and L’Abbé Lund, 2002 ; Wichmann et al, 2014 ). Similarly, raw milk-associated psychrotrophs and mesophiles, which frequently exhibit spoilage features, also carry AR features; strangely enough, AR was most prevalent in both population types at a stage when the total bacterial counts reached approximately 10 5 cfu/ml; notably, the raw milk samples presented simultaneously significant amounts of multiresistant bacteria ( Munsch-Alatossava and Alatossava, 2007 ; Munsch-Alatossava et al, 2012 , 2017 ).…”

Quality and Safety of Bovine Raw Milk: Present Challenges and Technological Solutions

“…Recently, a study that evaluated the efficiency of the activated lactoperoxidase system (LPS) and N 2 gas flushing to hinder bacterial growth in raw milk showed that N 2 seemed to favour a more diverse bacterial community at 6°C, less heavily loaded with antibiotic multi-resistance features, compared to LPS [42].…”

“…Impact of N 2 flushing on raw and pasteurised milk-associated bacterial populations, and on some pure strains[24,38,42,[57][58][59][60][61][62].…”