Pseudomonas azotoformans Belonging to Pseudomonas fluorescens Group as Causative Agent of Blue Coloration in Carcasses of Slaughterhouse Rabbits

SIMPLE SUMMARY: Bacteria belonging to the genus Pseudomonas are well known for their ubiquitous distribution and their high adaptation capability, which allows them to survive in a wide range of temperatures and other environmental conditions. Therefore, they may colonize food, and a number of cases of food contamination due to Pseudomonas spp. have been reported. Among them, in recent years, blue pigmentation due to Pseudomonas fluorescens has been widely described in mozzarella cheese, insomuch that it was dubbed the “blue mozzarella” case. Here, we report on the contamination of rabbit meat due to a member of the P. fluorescens group that conferred blue coloration to the food matrix. Specifically, colored meat was observed in the refrigeration cell of two butcher shops which had originated from the same slaughterhouse. Bacteriological sampling was performed on pigmented rabbit carcasses as well as from the labeling gun, knives, and water from the slaughterhouse. The same kind of bacterial colony was observed to grow from carcasses, labeling gun, and water. The first identification, performed using a miniaturized biochemical test, revealed it belonged to the P. fluorescens group, and further analysis of the 16S ribosomal RNA gene led to definitive identification as Pseudomonas azotoformans. These findings highlight the importance of considering the members of the genus Pseudomonas and, more specifically, of the P. fluorescens group when the microbiological quality of food is to be ascertained. ABSTRACT: The study describes the finding of an abnormal blue-tinged color found on rabbit carcasses in the refrigeration cell of two butcher shops in Apulia Region. The carcasses were from an industrial rabbitry for production of meat with a regularly authorized slaughterhouse. Pseudomonas azotoformans, a microorganism included in Pseudomonas fluorescens group, was isolated from samples collected by the altered carcasses, showing the growth of uniform bacterial colonies with fluorescent pigmentation. The bacterium was also isolated from an additional water sample and from the labelling gun collected in the slaughterhouse, whilst the knives used for slaughtering resulted negative. Chromatic alteration was experimentally reproduced on new carcasses using a 10(8) cfu/mL bacterial suspension prepared with the isolated strain. Due to their resistance characteristics, members of P. fluorescens group are very difficult to eradicate once introduced into the production environment. Therefore, their presence, even if not considered a public health problem, should be monitored by food industry operators in self-control plans.