Low tyrosine content of growth media yields aflagellate Salmonella enterica serovar Typhimurium

Abstract

Identification of Salmonella serotypes is based on flagellar and somatic antigens. The absence of flagella may consequently affect complete identification of the serotype; here it is shown that Salmonella enterica serovar Typhimurium exhibits morphological differences dependent on the peptone constituents of the culture medium. Aflagellate salmonella were produced in certain media where the nutritional ingredient was casein-based peptone or gelatin-based peptone; in gelatin-based peptone, aggregates of salmonella were observed. However, in media containing soy-based peptone as the primary nutrient, salmonella displayed a normal flagellated morphology. Transfer of aflagellate salmonella from nutritionally poor media, with casein-or gelatin-based peptone, into rich nutrient broth allowed flagella synthesis, indicating that the aflagellate form is still able to produce flagella. Amino acid sequencing of the peptones producing aflagellate organisms showed a relatively low tyrosine concentration: only 0?03±0?01 g l "1 for gelatin-based buffered peptone water, compared to 0?21±0?01 for soy-based buffered peptone water. Tyrosine is essential for flagellin, which is the subunit of the salmonella flagellar filament. The addition of 200 mM tyrosine to casein-based peptone media produced flagellate salmonella; 2 mM glucose was needed in addition to tyrosine to achieve a similar morphology in gelatin-based media. Therefore, culture media containing less than 1?20 g tyrosine l "1, and of limited carbohydrate source, when used for serological testing of clinical isolates, may result in an incomplete serological identification.

Peptones from diverse sources: pivotal determinants of bacterial growth dynamics

“…Gelatin‐based peptones produced consistently poor generation times and yields with all bacteria; analyses showed low tyrosine content relative to other peptones. This and an inadequate carbohydrate source contribute to the poor growth of Salmonella, as does the tryptophan content [so low as to be undetectable by the methods employed (Gray et al. 2006)].…”

“…Calibration curves were constructed for each bacterial species after growth in each medium. Organisms exhibit various morphologies during growth in different peptones (Gray et al. 2006), and this may affect light scattering.…”