Staphylococcus aureus is a main cause of bovine mastitis and a major pathogen affecting human health. The emergence and spread of methicillin-resistant Staphylococcus aureus (MRSA) has become a significant concern for both animal health and public health. This study investigated the incidence of MRSA in milk samples collected from dairy cows with clinical mastitis and characterized the MRSA isolates using antimicrobial susceptibility tests and genetic typing methods. In total, 103 S. aureus isolates were obtained from dairy farms in 4 different provinces in China, including Gansu, Shanghai, Sichuan, and Guizhou. Antimicrobial susceptibility testing of these isolates revealed that the resistance rates to penicillin and sulfamethoxazole were high, while the resistance rates to ciprofloxacin and vancomycin were low. Among the 103 isolates, 49 (47.6%) were found to be mecA-positive, indicating the high incidence of MRSA. However, 37 of the 49 mecA-positive isolates were susceptible to oxacillin as determined by antimicrobial susceptibility assays and were thus classified as oxacillin-susceptible mecA-positive S. aureus (OS-MRSA). These isolates could be misclassified as methicillin susceptible Staphylococcus aureus (MSSA) if genetic detection of mecA was not performed. Molecular characterization of selected mecA-positive isolates showed that they were all negative with Panton-Valentine leukocidin (PVL), but belonged to different spa types and SCCmec types. These results indicate that OS-MRSA is common in bovine mastitis in China and underscore the need for genetic methods (in addition to phenotypic tests) to accurately identify MRSA.

This study aimed to investigate the antimicrobial resistance and virulence genes of Enterococcus faecalis isolated from subclinical bovine mastitis cases in China. Enterococcus faecalis isolates were identified by 16S rRNA amplification and sequencing. Antimicrobial susceptibility was determined by the disc diffusion method. Antimicrobial resistance and virulence genes were tested by PCR. Overall, E. faecalis was recovered from 81 of 1,787 (4.5%) mastitic milk samples. The isolates showed high resistance against tetracycline (87.7%) and erythromycin (79.0%). The most prevalent resistance genes found in the E. faecalis were tetK (96.3%), tetL (79.0%), and tetM (87.7%) for tetracycline and ermC (97.5%) for erythromycin. Moreover, gelE (70.4%), esp (85.2%), efaA (91.4%) were the most common virulence genes. This is the first report to characterize E. faecalis recovered from subclinical bovine mastitis cases in China.

This study provided the first attempt of grafting hydrophobic polyvinylidene fluoride (PVDF) membrane with hydrophilic hydroxyethyl acrylate (HEA) monomer via a radiation grafting method. This grafted membrane showed an enhanced hydrophilicity (10° decrease of water contact angle), water content ratio, settling ability and wettability compared to the control membrane. Interestingly, filtration tests showed an improved dependence of water flux of the grafted membrane on the solution pH in the acidic stage. Atomic force microscopy (AFM) analysis provided in-situ evidence that the reduced surface pore size of the grafted membrane with the solution pH governed such a dependence. It was proposed that, the reduced surface pore size was caused by the swelling of the grafted chain matrix, with the pH increase due to the chemical potential change. It was found that the grafted membrane showed a lower relative flux decreasing rate than the control membrane. Moreover, flux of the bovine serum albumin (BSA) solution was noticeably larger than that of pure water for the grafted membrane. Higher BSA flux than water flux can be explained by the effects of electric double layer compression on the polymeric swelling. This study not only provided a pH-sensitive PVDF membrane potentially useful for various applications, but also proposed novel mechanisms underlying the enhanced performance of the grafted membrane.

Let G be a graph of order n. Let λ1, λ2, . . . , λn be the eigenvalues of the adjacency matrix of G, and let µ1, µ2, . . . , µn be the eigenvalues of the Laplacian matrix of G. Much studied Estrada index of the graph G is defined as EE = EE(G) = n i=1 e λ i . We define and investigate the Laplacian Estrada index of the graph G, LEE = LEE(G) = n i=1 e (µ i − 2m n ) . Bounds for LEEare obtained, as well as some relations between LEE and graph Laplacian energy.

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