Research Of Bacterial Diversity And Antibiotic Resistance In Bulk Tank Milk From Dairy Farms In Parts Of Shandong Province

Dairy products are an important part of people’s daily diet because of their rich nutritional content.Dairy products are prepared from raw cow’s milk after a series of processing,so the quality of raw cow’s milk has an important impact on the quality of dairy products.However,the raw cow’s milk is easily contaminated in the various stages of processing.The bacteria have a great impact on the storage and production of raw cow’s milk.These bacteria can infect raw cow milk in various ways,affecting the quality of raw milk.Due to the use of antibiotics in the dairy production,It can lead to antibiotic resistance thus causing public health and safety problems.A total of 30 raw cow milk samples were collected from Taian City,Dongying City and Qingdao City,Shandong Province in this paper.6 samples were collected from each cattle farm.Total bacterial counts,bacterial diversity and antibiotic resistance in raw cow milk samples from different cattle farms were investigated.The total number of bacteria in those samples was calculated by plate scribe counting.In this study,the bacterial counts of raw cow’s milk samples ranged from 4.08 to 6.56 log CFU/m L.The results showed that Taian cattle farm had the lowest total bacterial counts and QD1 cattle farm had the highest total bacterial counts.The total bacterial counts of QD2 was more discrete.It was different in total bacterial counts between different dairy farms.Blood plate scribing culture combined with the matrix-assisted laser desorption ionization time-of-flight mass spectrometry（MALDI-TOF MS）was used to compare the bacterial diversity and the correlation of bacterial species between different cattle farms.Thirty samples were isolated with 129 bacterial strains belonging to 18 genera and 37 species.The dominant species were Lactococcus lactis and Acinetobacter johnsonii as well as the dominant genera were Acinetobacter,Pseudomonas and Lactococcus.The bacteria in Taian City belonged to 6 genera and 13 species with Bacillus marisflavi and Staphylococcus xylosus as the dominant species.the dominant genera were Bacillus and Staphylococcus.The bacteria in Dongying city identified as 15 species in nine genera.Lactococcus lactis and Pseudomonas gessardii were the dominant species.the dominant genera were Pseudomonas,Lactococcus and Acinetobacter.The bacteria in Qingdao city belonged to 11 genera and 17 species,of which the dominant species were Acinetobacter johnsonii and Lactococcus lactis.the dominant families were Acinetobacter,Lactococcus and Macrococcus.The results showed that the bacterial diversity in Taian city was different from that in Dongying and Qingdao,and the bacterial diversity in Dongying was somewhat different from that in Qingdao city.The presence of some conditionally pathogenic bacteria such as Staphylococcus chromogenes and some bacteria causing spoilage of raw cow milk such as Pseudomonas fragi were found in some samples.Rothia endophytica was detected in Taian city,Dongying and Qingdao city.Then,antibiotic resistance in raw cow’s milk bacterial isolates was detected using a 96-well plate micro-broth dilution method.Antibiotic resistance genes of bacterial isolates were detected by PCR and Agarose gel electrophoresis.10 antibiotics were tested and bacterial strains were found to have high resistance to sulfadiazine and streptomycin at 53.2%and 50.6%,respectively.The antibiotic resistance rates of ampicillin,mucomycin sulfate,ceftriaxone sodium and lincomycin were 29.0%,24.3%,20.2%and 11.8%.The antibiotic resistance of bacterial strains to neomycin,doxycycline,gentamicin,and levofloxacin was low at 8.6%,8.2%,6.2%,and 6.0%,respectively.The antibiotic resistance pattern showed that there was a total of 22 multi-drug resistant strains,among which triple and quadruple resistant were more frequent.The results indicate that the choice of antibiotics should be strictly controlled.7 categories of 9 drug resistance genes were screened for testing.The highest positivity rates were observed for the sulfonamide resistance gene sulⅠ and the aminoglycoside resistance gene ant（4′）-Ⅰa.The positive rates of tetracycline resistance gene tetM,quinolone resistance gene qnrS,β-lactam resistance gene bla _KPC,and aminoglycoside resistance gene aph（2′′）-Ⅰc were low.Polymyxin resistance gene mcr-1,β-lactam resistance gene bla _NDM-1,and lincomycin resistance gene lnuB were not detected.In this study,we research the bacterial diversity and antibiotic resistance in raw cow milk in parts of Shandong Province.The monitoring data of microorganisms in bulk tank milk from dairy farms in Shandong Province was improved,laying the foundation for quality control and risk warning of raw cow milk.