Quantification of Histamine Concentration, Identification, and Antibiotic Resistance of Potential Histamine-Forming Bacteria in Bullet Tuna

Consuming scombroid fish containing high histamine levels can lead to histamine fish poisoning caused by the proliferation of histamine-forming bacteria (HFB). Interestingly, some HFB strains have developed resistance to antibiotics. This complicates efforts to control their populations in fish and aquatic environments. As these bacteria become harder to eliminate, the risk of histamine fish poisoning may increase, highlighting a concerning link between antibiotic resistance and food safety. In this study, the histamine concentration levels and the presence and antibiotic resistance of isolated HFB in bullet tuna were investigated. The fluorometric method (AOAC 977.13) showed that the average amount of histamine was 39 ppm, which was below the local regulatory limit (< 200 ppm). Ten (10) presumptive HFBs were isolated using modified Niven’s agar. However, only five of the 10 isolates were identified at the species level by molecular methods. These isolates were then identified as Proteus mirabilis (Hfb_5, Hfb_8, and Hfb_13) and Klebsiella pneumoniae (Hfb_6, and Hfb_10). These potential HFBs were subjected to antibiotic susceptibility testing. Results showed that all potential HFBs displayed multidrug resistance to the antibiotic used. Despite the occurrence of low histamine levels, it is still recommended that the proper handling and storage of fish products should be strictly practiced to mitigate the proliferation of HFB. Moreover, the presence of antibiotic-resistant bacteria on fish products should be sufficient to raise awareness about the extent of such phenomena in the aquatic environment, therefore encouraging future researchers to delve into this interesting yet concerning environmental problem.