serotype 4b strains demonstrate a fitness advantage over strains of serotypes 1/2a and 4b-v1 on cantaloupe rind and flesh at different temperatures.

is a foodborne pathogen implicated in several produce-related outbreaks. In nature, it is saprophytic and is isolated from agricultural areas and surface waters. The ability of the pathogen to grow at cold temperatures results in population growth when contaminated foods are stored in the refrigerator. Most outbreaks are caused by serotypes 1/2a and 4b. In the last decade, several produce-related outbreaks have been caused by an atypical serotype 4b subtype termed 4b-v1, specifically strains of sequence type (ST) 382. ST382 strains are overrepresented in environmental isolates. This study asked if strains of ST382 displayed better fitness on produce by growing to higher levels on cantaloupe surfaces when inoculated as strain mixtures. Strains of serotypes 1/2a, 4b, and 4b-v1 were co-inoculated onto cantaloupe rinds and flesh and incubated for 24 h at 25°C or for 7 days at 4°C. After rinsing, 30 resulting colonies were screened for serotype. Serotype 4b strains demonstrated significantly better fitness on cantaloupe rind than either serotype 1/2a or 4b-v1 strains. On cantaloupe flesh, serotypes 4b and 4b-v1 strains were statistically similar, and serotype 4b was more fit than serotype 1/2a. Serotype 4b colonies represented approximately 50% of the colonies recovered from rind and 40% of the colonies recovered from flesh. Incubation temperature was not a factor. While all the strains could grow on both cantaloupe surfaces, the data indicate that strains of ST382 did not have a fitness advantage on cantaloupe.IMPORTANCEMost outbreaks are caused by serotypes 4b and 1/2a. An atypical variant of serotype 4b, 4b-v1, specifically sequence type (ST) 382, caused three nationwide produce-related outbreaks in the last decade. To address the fitness of ST382 on produce, these strains were inoculated in mixtures including serotypes 1/2a and 4b onto cantaloupe rinds and flesh and incubated at 25°C and 4°C. Fitness was determined by measuring the percentage recovery of the individual serotypes in the mixed population recovered from cantaloupe surfaces. Serotype 4b strains were recovered consistently at higher levels than both serotypes 1/2a and 4b-v1 strains from cantaloupe rind. On cantaloupe flesh, serotypes 4b and 4b-v1 were statistically equivalent, but serotype 4b had the advantage over serotype 1/2a strains. While all the strains can reproduce on the cantaloupe surfaces, ST382 was not more fit on the cantaloupe. Furthermore, serotype 4b strains had a fitness advantage in mixed populations on cantaloupe.