Purpose: To better understand cold stress response in C. jejuni, we tested the survival rate in different media, transcription levels of outer membrane proteins, fatty acid profiles, and morphological change at a refrigerated temperature.
Methods: Direct plate counting, quantitative real time-PCR (qRT-PCR), fatty acid methyl ester (FAME) analysis, and transmission electron microscopy (TEM) and field emission scanning electron microscopy (FE-SEM) were performed to examine the survival of C. jejuni at low temperature.
Results: Survival of C. jejuni human (11168) and poultry (A74O22) isolates were tested in chicken juice (CJ), brain heart infusion (BHI), Mueller Hinton (MH), and phosphate buffered saline (PBS) at 4°C. C. jejuni A74O22 remained culturable for a longer period than did C. jejuni 11168 and the colony was culturable onto MH agar in both CJ and PBS up to 63 days. The relative gene expression levels of membrane proteins (mapA, omp50, pglF, peb4, and htrB) as revealed by qRT-PCR was decreased in both C. jejuni strains after 30 days. In addition, all tested genes were most significantly downregulated in C. jejuni A74O22 that was maintained in CJ compared to other media. Regardless of the types of suspended media, membrane fatty acid composition was found to be decreased slightly following exposure to cold stress. However, cis-9-octadecenoic acid (18:1) and cis-6,9,12,15-eicosatetraenoic acid were observed only in C. jejuni suspended in CJ. TEM and FE-SEM revealed that prolonged storage resulted in transformation of spiral cells to coccoid, condensed cytoplasm, and release of cellular contents.
Significance: This study provides useful information for understanding the role of cell membrane in C. jejuni survival mechanisms when exposed to low temperature.