Identification of Shewanella baltica as the Most Important H ₂ S-Producing Species during Iced Storage of Danish Marine Fish

Abstract

Shewanella putrefaciens has been considered the main spoilage bacteria of low-temperature stored marine seafood. However, psychrotropic Shewanella have been reclassified during recent years, and the purpose of the present study was to determine whether any of the new Shewanella species are important in fish spoilage. More than 500 H 2 S-producing strains were isolated from iced stored marine fish (cod, plaice, and flounder) caught in the Baltic Sea during winter or summer time. All strains were identified as Shewanella species by phenotypic tests. Different Shewanella species were present on newly caught fish. During the warm summer months the mesophilic human pathogenic S. algae dominated the H 2 S-producing bacterial population. After iced storage, a shift in the Shewanella species was found, and most of the H 2 S-producing strains were identified as S. baltica. The 16S rRNA gene sequence analysis confirmed the identification of these two major groups. Several isolates could only be identified to the genus Shewanella level and were separated into two subgroups with low (44%) and high (47%) G؉C mol%. The low G؉C% group was isolated during winter months, whereas the high G؉C% group was isolated on fish caught during summer and only during the first few days of iced storage. Phenotypically, these strains were different from the type strains of S. putrefaciens, S. oneidensis, S. colwelliana, and S. affinis, but the high G؉C% group clustered close to S. colwelliana by 16S rRNA gene sequence comparison. The low G؉C% group may constitute a new species. S. baltica, and the low G؉C% group of Shewanella spp. strains grew well in cod juice at 0°C, but three high G؉C Shewanella spp. were unable to grow at 0°C. In conclusion, the spoilage reactions of iced Danish marine fish remain unchanged (i.e., trimethylamine-N-oxide reduction and H 2 S production); however, the main H 2 S-producing organism was identified as S. baltica.

Bacterial Isolates from Seafood in Scotland

“…Shewanalla spp. were recovered in this study, but this is not surprising as [47] demonstrated the presence of cells on newly caught fish. It should not be overlooked that the organisms may be opportunistic human pathogens, being associated with bacteraemia and skin and soft tissue infections [48; 49].…”

The impact of environmental perturbation on microbial community structure and dynamics: Factors affecting growth ofClonothrix fuscain groundwater

“…Bath, the unique type I methanotroph in the databank, and in a number of marine bacteria. Among the marine bacteria belonging to the genus Shewanella , cls homologues were absent present in mesophylic species and absent in most of psychrotrophic species including Shewanella baltica and Shewanella putrefaciens (Fonnesbech Vogel et al 2005). This fact is noteworthy, because there is molecular evidence that C. fusca belongs to the psychrophilic group of type I methanotrophs (Vigliotta et al 2007).…”

Effects of different thawing methods on the quality of meagre fillets

“…All of the thawing treatments gave non-detectable values for H 2 S-producing bacteria. Some of these bacteria are capable of reducing trimethylamine N-oxide (TMAO) and also degrading sulphur-containing amino acids and producing volatile sulphides including H 2 S (18,33,53). A number of these bacteria, namely Shewanella putrefaciens, pose health risk and have been shown to be inversely related to the remaining shelf-life of seafood products (18).…”