Isolation of histamine producing Enterococcus strains from white cheeses

Abstract

Enterococcus-associated biogenic amines are frequently found in foods such as cheese, fermented beverages, and fish. Histamine, tyramine, cadaverine, and putrescine are commonly detected biogenic amines in food items. Consumption of certain levels of biogenic amines can lead to symptoms like migraines, hypertension, nausea, and vomiting. Given these adverse health effects, our study aimed to investigate the histamine-producing capabilities of Enterococcus strains isolated from cheese using qualitative, quantitative, and molecular methods. In this study, 452 cheese samples obtained from markets and bazaars were analyzed. Suspicious Enterococcus spp. colonies were identified in 391 samples based on morphology. Amino acid decarboxylase activity test was performed to determine whether enterococci isolates were histamine producers. Of the isolates analyzed, 276 were found to produce histamine. Biochemical identification tests were performed on these histamine-producing isolates, revealing that 25 strains exhibited strong histamine production. Histamine concentrations produced by selected Enterococcus strains were determined through HPLC analysis, yielding concentrations ranging from 14,874 to 26,239 mg/L. Moreover, 16S rDNA sequence analysis was employed to identify 25 Enterococcus strains at the species level, and the presence of the amino acid decarboxylase gene region was investigated. Among these strains, 7 (28%) were identified as E. faecalis and 18 (72%) as E. faecium. The gene regions responsible for histamine production were detected in all 25 strains. These findings highlight the importance of maintaining stringent hygiene conditions during cheese production and storage, as the presence of Enterococcus strains capable of producing high levels of histamine underscores the need for increased vigilance in food safety practices.