Effect of microbial cell-free meat extract on the growth of spoilage bacteria.

Aims: This study examined the effect of microbial cell-free meat extract (CFME) derived from spoiled meat, in which quorum sensing (QS) compounds were present, on the growth kinetics (lag phase, and growth rate) of two spoilage bacteria, Pseudomonas fluorescens and Serratia marcescens.
Methods and Results: Aliquots of CFME from spoiled meat were transferred to Brain Heart Infusion broth inoculated with 10(3) CFU ml(-1) of 18 h cultures of Ps. fluorescens or Ser. marcescens, both fresh meat isolates; CFME derived from unspoiled fresh meat ('clean' meat) served as a control. Changes in impedance measurements were monitored for 48 h, and the detection time (Tdet) was recorded. It was found that in the absence of CFME containing QS compounds the Tdet was shorter (P < 0.05) than that in broth samples with added CFME from spoiled meat. The rate of growth of Ps. fluorescens, recorded as the maximum slope rate of conductance changes (MSrCC), after Tdet, was higher (P < 0.05) in samples with CFME containing QS compounds compared to samples without CFME or CFME derived from 'clean' meat. Similar results in MSrCC of impedance changes were obtained for Ser. marcescens.
Conclusions: The study indicated that the growth rate (expressed in MSrCC units) of meat spoilage bacteria in vitro was enhanced in samples supplemented with CFME containing QS compounds compared to control samples (i.e., without CFME or with CFME from 'clean' meat). This behaviour may explain the dominant role of these two bacteria in the spoilage of meat.
Significance and Impact of the Study: These results illustrate the potential effect of signalling compounds released during storage of meat on the behaviour of meat spoilage bacteria. Understanding such interactions may assist in the control of fresh meat quality and the extension of its shelf life.