Background: Coliform mastitis is common in dairy herds, especially in high-producing cows. The isolation rate of the increased serum survival (iss) gene from mild and severe cases is compared in this study as an indicator of Escherichia coli (E. coli) virulence factor.
Objectives: This study aimed to evaluate the importance of the iss gene and some affecting factors in bovine coliform mastitis caused by E. coli.
Methods: The milk samples of 80 clinical and 20 subclinical mastitis cases infected with E. coli were collected from Holstein dairy farms. In the laboratory, the colony-forming unit (CFU) of isolated E. coli was determined, and the presence of the iss gene in the bacteria was analyzed with polymerase chain reaction (PCR). The isolates were divided into the control (E. coli count<500 CFU) and the case (E. coli count >500 CFU) groups.
Results: Findings showed that the iss gene was isolated from 13 out of 45 (29%) in the control group and from 11 out of 55 (20%) in the case group (P>0.05). Mastitis grade, E. coli colony count, and Somatic cell count (SCC) did not show any difference between the groups with and without iss gene (P>0.05). The average milk production levels before the presence of mastitis in cases with the iss gene were lower than those without the iss gene only in the case group (P<0.05). A correlation between the expression of the iss gene and hot summer months (as a killing agent or stopping the growth of bacteria) was found in the case group (r=0.465, p=0.01). There was no correlation between the expression of the iss gene and hot summer months in the control group (r=-0.334, p=0.054).
Conclusions: From this study, it was concluded that the role of iss gene in the occurrence of severe mastitis needs further study, but the presence of the gene in the conditions of high milk production stress in cow and the endangered growth of bacteria in summer heat conditions were important in the development of mastitis cases.