Summary auto-generated
Researchers isolated a novel bacterium from green-discolored vacuum-packaged bologna sausage stored at refrigeration temperatures. Strain MPL-11T, designated Carnobacterium viridans sp. nov., is a facultatively anaerobic, non-motile, Gram-positive rod that causes greening by producing hydrogen peroxide when exposed to oxygen upon package opening. The organism is alkaliphilic, growing at pH 5.5–9.1 and temperatures from 2–30°C, and is catalase- and oxidase-negative. Phenotypic testing using API 50CHL and Biolog systems revealed that C. viridans differs from all seven previously described Carnobacterium species, notably by failing to produce acid from ribose—the first Carnobacterium species with this characteristic. 16S rRNA gene sequencing confirmed its placement within the genus Carnobacterium in a distinct phylogenetic clade. The organism produces predominantly L-lactic acid from glucose and contains meso-diaminopimelic acid in its peptidoglycan. While highly salt-tolerant, it does not grow in 4% NaCl. This is the first report of Carnobacterium causing green discoloration in cured meat products, previously attributed to Aerococcus viridans and other organisms.
Key findings
- Carnobacterium viridans sp. nov. is a novel bacterium isolated from green-discolored vacuum-packed bologna, causing discoloration through H₂O₂ production upon oxygen exposure
- C. viridans is the first Carnobacterium species that does not produce acid from ribose, distinguishing it from all seven previously described species
- 16S rRNA gene sequencing and phenotypic analysis confirm this is a distinct species phylogenetically separate from known Carnobacterium species
- The organism is alkaliphilic and psychrophilic, growing at pH 5.5–9.1 and temperatures from 2–30°C, with dominant growth in refrigerated meat products
- Green discoloration caused by C. viridans can be prevented by catalase treatment, confirming H₂O₂ as the causative agent
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Abstract
A facultatively anaerobic, non-spore-forming, psychrophilic, Gram-positive, non-aciduric but alkaliphilic, rod-shaped bacterium (MPL-11(T)) was found to be responsible for green discoloration of refrigerated vacuum-packaged bologna upon opening of the package. Although Aerococcus viridans, which had been implicated earlier in causing the same problem, was also found, this is the first report of discoloration caused by an organism shown to be a species of Carnobacterium. Bacterial discoloration was caused by H(2)O(2) production upon exposure of the meat to air. Strain MPL-11(T) is catalase- and oxidase-negative. It is not motile and does not reduce nitrate to nitrite or produce ammonia from arginine. It does not grow in acetate-containing broth or agar (Rogosa) or produce H(2)S. The peptidoglycan is of the meso-diaminopimelic acid type and it produces predominantly L(+)-lactic acid from glucose. It grows from at least 2 to 30 degrees C over a pH range from 5.5 to 9.1. Ribotyping suggested that strain MPL-11(T) could be a species of either Lactobacillus or Carnobacterium, but analysis using DNA sequences from the 16S rRNA gene showed conclusively that the organism belonged to the genus Carnobacterium. Since acid is not produced from amygdalin, inulin, mannitol, methyl alpha-D-glucoside or D-xylose, the organism differs from the seven described species of Carnobacterium. In addition, strain MPL-11(T) is the first member of the genus found that does not produce acid from ribose. It is capable of acid production/growth on galactose, glucose, fructose, mannose, N-acetylglucosamine, aesculin, cellobiose, maltose, lactose, sucrose, trehalose and tagatose. Although extremely salt tolerant, it does not grow in >= 4% NaCl. On the basis of phenotypic and genotypic data, it is concluded that this isolate represents a separate, novel species. Accordingly, the name Carnobacterium viridans sp. nov. is proposed. The type strain is strain MPL-11(T) (=ATCC BAA-336(T)=DSM 14451(T)).