Isolation And Identification Of Cryophilic Bacteria In Dairy Halls In Northern And Southern Xinjiang And Evaluation Of Disinfection Effect

Objective: With the continuous pursuit of the quality and nutritional value of milk and dairy products,the improvement of raw milk quality has gradually attracted attention.A class of microorganisms dominated by cryophilic bacteria in raw milk can cause certain damage to milk quality,and cryophilic bacteria are difficult to prevent and control due to their low temperature resistance,wide variety and wide range of sources.Therefore,this study intends to collect environmental and raw milk samples from dairy halls from nine pastures in northern and southern Xinjiang,explore the main pollution sources of cryophilic bacteria in dairy halls in dairy farms,and use PCR technology to isolate,identify and screen out the dominant bacteria in the two regions.At the same time,conventional bacterial culture methods were used to explore the biofilm formation ability of dominant bacteria on different materials,and to verify the sanitize effect of different types of disinfectants,and to provide a sanitize prevention and control system for cryophilic bacteria for dairy halls in Xinjiang.It lays a foundation for the research and investigation of raw milk quality and cryophilic bacteria in Xinjiang.Methods:(1)On-site investigation: On-site investigation and sampling were carried out on 9 pastures of different sizes in northern and southern Xinjiang by on-site inquiry,record retrieval,and on-site understanding of relevant conditions.The method of NY/T1331-2007 "Determination of Cryophilic Bacteria,Aerobic Spores and Thermophilic Aerobic Spores in Milk and Dairy Products" was used to determine the cryophilic bacteria in the main production sites.(2)The method of 16 Sr DNA identification was used to identify the species of cryophilic bacteria in raw milk in northern and southern Xinjiang,and the dominant strains and genera were established according to the proportion.(3)The formation ability of dominant bacteria biofilm and the removal effect of different disinfectants were determined by plate coating method and ATP fluorescence biological detector.Results:(1)Among the 378 environmental samples collected from 9 dairy farms in northern and southern Xinjiang,it was found that the base of cryophilic bacteria in the milk nipples(before the medicinal bath),the pipeline interface and the loading line was the largest,followed by milk tanks,milkers and balance tanks.In the test of 120 raw milk from different farms,the base number of cryophilic bacteria at 8°C was larger at 8°C than at 4°C during storage.(2)216 strains were isolated and purified from raw milk samples obtained from different pastures in northern and southern Xinjiang,and after sequencing and comparison,a total of 11 strains were identified: Pseudomonas,Acinetobacter,Flavobacter,Enterobacteriaceae,Bacillus,Streptococcus,Arthrobacter,Moraxella,Cryophilus,Alkali Producing Bacillus,Micrococcus,Pseudomonas fluorescent,Acinetobacter Schindler,Bacillus licheniformis,Bacillus cereus and Aquatic Flavobacter.Among them,Pseudomonas and Bacillus account for the largest proportion in northern Xinjiang,and Pseudomonas and Flavobacterium account for the largest proportion in southern Xinjiang.(3)The biofilm formation ability of the three dominant strains on stainless steel plate was weaker than that in the rubber block,among which the biofilm formation ability of Pseudomonas fluorescent was the strongest,and the biofilm formation ability of Bacillus cereus was the weakest.(4)Among the four disinfectants,hydrogen peroxide has the strongest sanitize effect on the three dominant strains,up to 83.4%,and the sanitize effect of sodium hypochlorite is the weakest,only between 28.1～31.4%.Conclusion: The nipples,pipeline interfaces and loading pipelines of dairy cows in dairy halls in Xinjiang can be used as the main sources of pollution of cryophilic bacteria in raw milk,and transportation and storage at no higher than 4°C can effectively control the further growth and reproduction of cryophilic bacteria.The composition of cryophilic bacteria in raw milk in northern and southern Xinjiang regions was different,among which Pseudomonas was the dominant genus common to the two regions.The biofilm formation ability of different strains on rubber blocks is stronger than that on stainless steel plates,and the sanitize effect of hydrogen peroxide on biofilms is better than that of acid-alkali salt disinfectants.