Using sequencing, researchers from the University of California, Davis, and the California Department of Public Health examined the virulence and antibiotic resistance of Shigella sonnei strains behind a 2014 and 2015 outbreak in the state, UPI reports.
As they reported last week in mSphere, the health department's Vishnu Chaturvedi and his colleagues analyzed the whole genomes and antibiotic susceptibility of 68 outbreak and archival isolates of S. sonnei. The California strains fell into two populations, one from San Diego and San Joaquin and one from the San Francisco Bay area, but both of those populations and many of the archival samples belonged to sequence type 152. Some of the San Diego/San Joaquin strains at some point obtained a lambdoid bacteriophage that housed Shiga toxin genes that likely originated from E. coli or other Shigella species that made them more virulent.
Meanwhile the San Francisco strains had point mutations in the gyrA and parC genes that bestowed ciprofloxacin resistance upon them. Those mutations, the researchers note, are often found in South Asian strains of the bacteria.
"If you have an outbreak and you want to know what is causing a particular problem, like antibiotic resistance, sequencing the genome can identify the genes involved," says Davis' Jonathan Eisen, a study co-author, in a statement. "Eventually, we should be able to sequence whole genomes of bacteria to support patient care."