Different loci and mRNA copy number of the increased serum survival gene of Escherichia coli.

The increased serum survival gene (iss) has been identified as a virulence trait associated with the virulence of Escherichia coli, causing colibacillosis in poultry. However, it remains unclear as to whether iss mRNA copy number and sequence affect virulence. To examine these influences, we assessed the presence of iss, sequence analysis, iss mRNA copy number, and serum resistance. The iss gene was detected in 88 (all) E. coli isolates from different sources, and sequencing identified 16 alleles (32 different loci) and 10 amino acid sequences (10 different loci). Nested polymerase chain reaction improved iss detection. The isolates from sick chickens had >68% livability in serum resistance tests and higher iss mRNA copy number. The iss mRNA copy number highly correlated with mortality and E. coli livability. Student's t tests confirmed the relationship between the different loci to iss transcription, serum resistance, and virulence. These data suggest that iss mRNA copy number and different loci affect the virulence and serum resistance. These findings could be useful in further studies on the prevalence of iss among E. coli isolates and other virulence factors.