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Characterization of Leuconostoc species isolated from vacuum-packaged ham
Yimin Cai1, Yoshimi Benno, Akiko Takeda
1Japan Collection of Microorganisms, The Institute of Physical and Chemical Research, Wako 351-0198, Japan.
Abstract:
Thirty-six isolates of Leuconostoc spp. were isolated from yellow spots that occurred on the surface of vacuum-packaged ham. All isolates were Gram-positive, catalase-negative cocci that produced gas from glucose and formed more than 90% of their lactate as D(-) isomer. These isolates could grow at 4 degrees C but not above 30 degrees C and most strains produced yellow spots on the ham. The isolates were divided into three groups by sugar fermentation patterns. Representative strains from three groups showed intergroup DNA homology values of above 88.8%, showing that these groups were composed of a single species. This organism was positioned at a separate branch in the genus Leuconostoc on the phylogenetic tree based on 16S rRNA sequences, which was assigned to Leuconostoc gelidum on the basis of DNA-DNA relatedness.
Insights
Researchers identified Leuconostoc gelidum bacteria from yellow spots on vacuum-packaged ham. These cold-tolerant microbes are responsible for the spoilage, impacting food quality and safety.
Area of Science:
- Food Microbiology
- Bacteriology
- Food Spoilage
Background:
- Yellow spots on vacuum-packaged ham indicate microbial contamination.
- Leuconostoc species are known spoilage organisms in refrigerated foods.
Purpose of the Study:
- To identify the bacterial species responsible for yellow spots on vacuum-packaged ham.
- To characterize the isolated microorganisms and determine their taxonomic classification.
Main Methods:
- Isolation and culturing of bacteria from affected ham surfaces.
- Biochemical tests including Gram staining, catalase activity, and sugar fermentation.
- Molecular identification using 16S rRNA gene sequencing.
- DNA-DNA hybridization for species-level identification.
Main Results:
- Thirty-six Leuconostoc isolates were obtained from yellow spots.
- Isolates were Gram-positive, catalase-negative cocci, growing at 4°C but not 30°C.
- Most isolates produced yellow spots and fermented glucose, with D(-) lactate isomer production.
- Phylogenetic analysis and DNA-DNA relatedness identified the isolates as Leuconostoc gelidum.
Conclusions:
- Leuconostoc gelidum is the causative agent of yellow spots on vacuum-packaged ham.
- This psychrotolerant bacterium contributes to spoilage in refrigerated meat products.
- Understanding the microbiology of food spoilage is crucial for food safety and quality control.