Bovine mastitis is often taken as one of the most common diseases in dairy farms, which its pathophysiology leads to a reduction of milk production and its quality. The penetration of pathogenic bacteria into the mammary gland, through either a contagious or environmental approach, has been determined the way of infection. The mastitis derived bacteria have become a challenge in practice, since the increasing exposure of antimicrobial. In order to identify characteristics of the epidemiological regulation and drug resistance of the pathogenic bacteria of bovine mastitis in northern Jiangsu, 156 clinical mastitis milk samples were collected from 3 large-scale farms for the epidemiological investigation and analysis of the drug resistance of E. coli. The bacteria were positively isolated in a total of 143 milk samples. The results showed that 78 strains of E. coli were detected, with a prevalence rate of 26.99%, followed by 67 strains of K. pneumoniae, with a prevalence of 23.19%, and 38 strains of Staphylococcus, with a prevalence of spp. 13.15%. In addition, 78 strains of E. coli isolated from bovine mastitis were tested for susceptibility to 8 kinds of antibiotics. It was shown that gentamicin and tetracycline were the most effective against E. coli, with the susceptibility rate of 83.3%, followed by streptomycin and ciprofloxacin, with 73.1% and 71.8% respectively. However, β-lactams including penicillin, cefothiophene, and amoxicillin showed serious resistance to E. coli isolates. There were 12 drug resistance genes detected by PCR, including β-lactam (blaTEM, blaCTX-M, and blaSHV), aminoglycoside (armA and armB), tetracycline (tetA, tetB, and tetC), and quinolone (qnrS, qepA, oqxA, and oqxB) related genes. Notably, all E. coli isolates carried blaTEM gene (100%). The detection rate of blaCTX-M was 53.8%, followed by the detection of blaSHV (20.5%), armA (9.0%), tetA (26.9%), tetB (2.6%), tetC (20.5%), qnrS (29.5%), oqxA (37.2%) and oqxB (1.3%). The present study provides crucial information on the distribution of bovine mastitis derived bacterial pathogens in Jiangsu province, as well as highlighting the antimicrobial resistance which might help to improve the efficiency of antibiotics treatment on bovine mastitis.

This study aimed to provide experimental support for the prevention and treatment of Pseudomonas aeruginosa infections and to elucidate the epidemiological distribution of resistance and virulence genes of Pseudomonas aeruginosa from mastitis in dairy cows in the northern part of Jiangsu Province and their relationship with the biofilm-forming ability of the strains. Mastitis presents a significant challenge within dairy farming, adversely impacting the health of dairy cows and precipitating substantial economic losses in milk production. In this study, Pseudomonas aeruginosa (PA) was isolated and identified from mastitis milk samples in Jiangsu Province, China. In order to characterize the isolates, multilocus sequence typing (MLST), drug resistance phenotypes, virulence genes, and biofilm formations were detected. The isolation and identification of pathogenic bacteria from 168 clinical mastitis milk samples using 16S rRNA and PCR revealed 63 strains of Pseudomonas aeruginosa, which were determined to be highly homologous according to phylogenetic tree analysis. In addition, the MLST indicated five major ST types, namely ST277, ST450, ST571, ST641, and ST463. The susceptibility to 10 antimicrobials was determined, and it was found that 63 strains of Pseudomonas aeruginosa did not have a strong resistance to the antimicrobials in general. However, there were differences in the phenotypes’ resistance to antimicrobials among the different ST types. It was also found that the more resistant the strains were to antimicrobials, the lower the carriage of virulence genes detected. The biofilm content was measured using the semi-quantitative crystal violet method. It was found that there were a few strains with medium or strong biofilm-forming abilities. However, the number of virulence genes carried by the 63 strains of Pseudomonas aeruginosa was inversely proportional to the biofilm-forming ability. It was also found that there were significantly more Pseudomonas aeruginosa in the biofilm state than in the planktonic state and that strains with strong biofilm-forming abilities were more resistant to antimicrobials.

According to recent investigations, the proportion of mastitis caused by environmental pathogens, such as K. pneumoniae, has increased. In this research, the epidemiology of pathogens in milk samples collected from four farms in the Jiangsu Province was carried out. The results show that 16 pathogens were detected in 186 positive milk samples. It was found that K. pneumoniae had the lowest sensitivity to penicillin (0%) and amoxicillin (4%) compared to its sensitivity to gentamicin (92%) and piperacillin (89%). A total of eight ESBL-producing strains were detected. Crystal violet staining showed that 46 of the 68 isolates of K. pneumoniae had strong biofilm-forming ability, which was related to the tetracycline resistance phenotype (p < 0.05). The detection rate of the ESBL-resistant gene (bla_SHV) reached 100%. The results show that resistance genes bla_VIM, bla_OXA-10, and bla_TEM were correlated with drug-resistance phenotypes to varying degrees. The present study indicates the prevalence of bovine mastitis-derived pathogens in part of Jiangsu Province and reveals the distribution of β-lactam resistance genes and the strong biofilm-forming ability of K. pneumoniae and its relationship with tetracycline resistance. This study provided theoretical support and guidance for rational drug use and disease prevention and control on farms.

Pyocyanin (PCN) is an extracellular toxin secreted by Pseudomonas aeruginosa (PA), which has redox capacity and disrupts the redox balance of host cells, affecting cell function and leading to cell death. The aim of this experiment was to compare the degree of apoptosis, inflammation, and oxidative stress of bovine mammary epithelium cells (bMECs) induced by lipopolysaccharide (LPS) and pyocyanin (PCN) and to examine whether PCN can promote the apoptosis, inflammation, and oxidative stress of bMECs induced by LPS. In this study, 1 µg/mL LPS and 1 µg/mL PCN were finally selected for subsequent experiments through dose-dependent experiments. In this study, cells were not given any treatment and were used as the control group (NC). The cells were treated with PCN or LPS individually for 6 h as the PCN group (PCN) or the LPS group (LPS), and the combination of LPS and PCN challenge for 6 h as the LPS + PCN (LPS + PCN) group. Compared with the control and LPS groups, PCN resulted in a significantly upregulated expression of genes related to pro-inflammatory (IL-6, TNF-α, MyD88), apoptotic (Bax, Caspase3, Caspase9), as well as protein expression of components in the TLR4/NF-κB signaling pathway (TLR4, p-p65, p65), and p53 signaling pathway (p-p53, p53, Caspase9) (p < 0.05). Moreover, the expression of genes and proteins was significantly upregulated after PCN treatment combined with LPS compared to either LPS or PCN challenge alone (p < 0.05). The stimulation of PCN combined with LPS significantly increased reactive oxygen species (ROS) and malondialdehyde (MDA) production in bovine mammary epithelial cells (bMECs), as well as decreased glutathione peroxidase (GSH-Px) and total antioxidant capacity (T-AOC). Moreover, cells in the LPS + PCN group aggravated oxidative stress and antioxidant inhibition in cells. In addition, the expression of the corresponding genes and proteins related to the Nrf2 pathway (Nrf2, HO-1) was significantly down-regulated in the PCN group as compared to the control group (p < 0.05). Altogether, PCN stimulation exacerbates inflammatory reactions, apoptosis, and oxidative stress reactions, as well as when combined with LPS challenge in bMECs. Therefore, this study indicates that PCN manifests a role in promoting apoptosis, inflammation, and oxidative stress and interacting with LPS to enhance more serious biological stress responses.