Introduction.
The bacteriocin, Lacticin 3147 has been shown to be highly effective in controlling the growth of Gram positive pathogens such as Listeria monocytogenes and Staphylococcus aureus. Lacticin is a dipeptide produced by Lactococcus lactis which attaches to microbial cell walls creating pores in the cytoplasmic membrane leading to cell death. The purpose of this study was to determine if MAP, with its resistant cell wall was susceptible to inactivation by lacticin.
Materials and methods.
MAP (ATCC 19698) was grown in static and stirred culture at 37ºC in 7 ml bijou containers. 3 ml volumes (in triplicate) of Middlebrook medium were inoculated with MAP (10
5-10
6 cfu/ml) in the presence and absence of lacticin (1280 AU/ml). Negative controls containing lacticin but no inoculum were also included. At selected time intervals 0.1ml was pipetted to the wells of a microtitre plate and the absorbance at 620nm measured.
Results.
In stirred culture and in the absence of lacticin there was no evidence of growth of MAP up to day 11. Growth was detected when measured on day 21 and increased steadily thereafter resulting in a fine suspension with a minimum of deposit. Comparable data generated in the presence of lacticin indicated absence of growth under these conditions. The growth curve for the organism was less uniform in static culture a reflection of the pellicle nature of growth under these conditions and in this instance lacticin appears to retard rather than prevent growth.
Discussion.
Mycobacteria have a complex exterior making them resistant to many antimicrobial agents including antibiotics whose action is usually species specific. Some mycobacteria have a tendency to form clumps and in this form they may have increased resistance to inhibitors. It is possible that reduced clumping of cells in stirred culture makes MAP more susceptible to inhibition by the bacteriocin.
