Summary auto-generated
Researchers identified nine bacterial strains (CTCBS1-CTCBS9) responsible for black spot formation on raw cured meat products. These Gram-negative, catalase-positive, strictly aerobic rod-shaped bacteria were isolated from defective meat samples and their causative role was confirmed through reinoculation experiments. The isolates showed genetic homogeneity and phylogenetic analysis of 16S rRNA genes revealed they form a distinct group within the gamma-subclass of Proteobacteria, most closely related to Zymobacter palmae (93.3% similarity) but distinct enough to constitute a new genus. Based on comprehensive characterization including biochemical profiles, fatty acid composition (notably 40% palmitic acid and 21% cyclopropanic acid 19:0), G+C content (56 mol%), and DNA homogeneity assessments using RAPD-PCR, the authors established the novel genus Carnimonas with the species Carnimonas nigrificans. A species-specific PCR assay using 16S rRNA-targeted primers successfully identified all nine strains. Toxicological evaluation confirmed no pathogenic potential in mice, making this organism safe for the food production environment despite its role in product discoloration.
Key findings
- Nine strains of a novel bacterium, Carnimonas nigrificans, were identified as the causative agent of black spot defects on cured meat products through reproducible reinoculation experiments
- Phylogenetic analysis of 16S rRNA sequences placed C. nigrificans within gamma-Proteobacteria, closest to Zymobacter palmae (93.3% similarity) but distinct enough to warrant separate genus status
- The organism is strictly aerobic, catalase-positive, contains unique fatty acid and lipoquinone profiles, and shows high genetic homogeneity across nine strains with 80% correlation by RAPD-PCR analysis
- A species-specific PCR assay using 16S rRNA-targeted primers was developed for reliable identification of C. nigrificans strains
- Pathogenicity testing in mice demonstrated no toxic or lethal effects from C. nigrificans at high inoculum levels, indicating it is non-pathogenic
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Abstract
Nine different strains, CTCBS1Tto CTCBS9, were identified to be the causative agents of black spots on the surface of raw cured meat products. The formation of black spots under aerobic conditions is reproducible upon reinoculation of meat products with any of these strains, indicating that they are the causative agent. The strains were Gram-negative, catalase-positive and obligately aerobic rods. The G+C content of DNA of strain CTCBS1Tis 56·0±0·3 mol%. The content of non-polar main fatty acids were 16:0, 16:1, 18:1 and 19:0 cyc. Its phylogenetic position was elucidated by comparative sequence analysis of the 16S rRNA gene. Overall sequence similarity to other bacteria does not exceed 93·3%. Isolate CTCBS1Tclustered phylogenetically within the γ-subclass of the Proteobacteria and is closely related to members of Halomonas (90·5–91·9%) and to Zymobacter palmae (93·3%). A genetic homogeneity of the nine strains was demonstrated by M13 random amplified polymorphic DNA-PCR, whereas differentiation from other genera, e.g. Zymobacter and Pseudomonas, could easily be achieved by their chemotaxonomic characteristics. Taxonomic data revealed the status of a separate genus for which the name Carnimonas gen. nov., sp., nov. is proposed. Despite chemotaxonomic and physiological similarities, the new genus is at present not a member of the family Halomonadaceae because of the lack of two out of 15 descriptive 16S rRNA signature sequences. The first member of the new genus is Carnimonas nigrificans. The use of a specific, 16S rRNA-targeted oligonucleotide primer allowed the identification of all nine strains of C. nigrificans in a PCR assay. Toxicological studies showed no pathogenic potential for C. nigrificans strain CTCBS1T(CECT 4437T).