Analysis of Antimicrobial Resistance and Genetic Correlations of Escherichia Coli in Dairy Cow Mastitis

Introduction

Escherichia coli is a widespread environmental pathogen frequently causing dairy cow mastitis. This bacterium is particularly capable of acquiring antimicrobial resistance, which can have severe impacts on animal food safety and human health. The objective of the study was to investigate antimicrobial resistance and genetic correlations of E. coli from dairy cow mastitis cases in northern China.

Material and Methods

Forty strains of E. coli from 196 mastitis milk samples were collected, susceptibility to 13 common antibiotics and the prevalence of resistance genes were tested in these strains, and the genetic characteristics were identified by multilocus sequence typing.

Results

The results showed that most isolates were multidrug resistant (MDR) (75%), and the resistance rates to cefazolin, trimethoprim-sulfamethoxazole and ampicillin were 77.5%, 55.0%, and 52.5%, respectively. The representative genes of the isolates were aadA (62.5%) and tet(B) (60.0%). Multilocus sequence typing showed 19 different sequence types (STs) and 5 clonal complexes (CCs) in the 40 isolates, mainly represented by ST10 and CC10. The strains of the same ST or CC showed a high level of genetic relatedness, but the characteristics of their antimicrobial resistance were markedly different.

Conclusion

Most E. coli isolates in the study were MDR strains. Some strains of the same ST or CC showed diverse resistance characteristics to common antimicrobials. Therefore, E. coli from dairy cow mastitis in northern China should be investigated to elucidate its antimicrobial resistance and genotypes.

Effect of therapeutic administration of β-lactam antibiotics on the bacterial community and antibiotic resistance patterns in milk

Dairy cows with mastitis are frequently treated with antibiotics. The potential effect of antibiotics on the milk microbiome is still not clear. Therefore, the objective of this research was to investigate the effect of 2 commonly used cephalosporins on the milk microbiota of dairy cows and the antibiotic resistance genes in the milk. The milk samples were collected from 7 dairy cows at the period before medication (d 0), medication (d 1, 2, 3), withdrawal period (d 4, 6, 8), and the period after withdrawal (d 9, 11, 13, 15). We applied 16S rRNA sequencing to explore the microbiota changes, and antibiotic resistance patterns were investigated by quantitative PCR. The microbiota richness and diversity in each sample were calculated using the Chao 1 (richness), Shannon (diversity), and Simpson (diversity) indices. The cephalosporins treatment lowered the Simpson diversity value at the period of withdrawal. Members of the Enterobacter genera were the most affected bacteria associated with mastitis. Meanwhile, antibiotic resistance genes in the milk were also influenced by antibiotic treatment. The cephalosporins treatment raised the proportion of bla_TEM in milk samples at the period of withdrawal. Therefore, the treatment of cephalosporins led to change in the milk microbiota and increase of β-lactam resistance gene in the milk at the time of withdrawal period.

Structural and functional analysis of the signaling lymphocytic activation molecule family 7 (SLAMF7) gene in response to infection with coagulase-negative and coagulase-positive staphylococci

Splice variants of the signaling lymphocytic activation molecule family 7 (SLAMF7) gene have been identified, and differences in the expression of this gene have been demonstrated at the mRNA level in the mammary glands of healthy and mastitis-infected dairy cows. At the same time, significant associations have been found between a deletion in the SLAM7 gene exon, the occurrence of different splice variants, and the occurrence of mastitis in one group of dairy cows. An expression study was conducted on 40 Polish Holstein-Friesian dairy cows of the Black and White variety (group I). Milk samples were taken for microbiological analysis 2 d before slaughter and examined for the presence of bacteria. Immediately after slaughter, mammary tissue samples were taken and divided into 3 groups according to the health status of the mammary gland: healthy (without pathogenic bacteria in milk), coagulase-negative staphylococci (CNS), and coagulase-positive staphylococci (CPS). Based on different SLAMF7 gene DNA fragments, 2 alternative variants of this gene (V1 and V2) and complete gene expression were identified. Separate analyses performed for each isoform showed that the health status of the cow was strongly associated with the expression level of individual variants. The highest expression was detected for the SLAMF7 complete amplicon in healthy cows, and in the CNS and CPS cows the expression of this variant was also higher than V1 and V2. Sanger sequencing was applied to detect the polymorphism/indel variant in the second exon of the SLAMF7 gene probably having the greatest effect on the protein structure and function of SLAMF7. Two genotypes were detected: AA (wild-type) and AB (insertion A). In healthy cows, the frequency of homozygotes AA was higher than the heterozygotes, whereas in the infected animals, the genotypic distribution was the opposite. An association analysis between the identified polymorphism and production traits-including somatic cell count, as well as lactose, protein, and casein content and yield as indicators of subclinical mastitis occurrence-was performed on the group II cows (166 Polish Holstein-Friesian dairy cows). Unfortunately, due to the low number of AB animals, no relationship was demonstrated between genotype in the second exon and the health status of cows. Additionally, the difference in the percentage of SLAMF7-targeted DNA methylation between the groups of animals was not significant, with an average of ∼66 to 68%.