Controlling Listeria monocytogenes in Cottage cheese through heterologous production of enterocin A by Lactococcus lactis

AIMS

Enterocin A is an example of a class IIa bacteriocin with potent anti-listerial activity. This study was initiated with a view to harnessing this activity, through heterologous production by a lactococcal starter strain, to limit levels of Listeria monocytogenes in a food (Cottage cheese).

METHODS AND RESULTS

Plasmid pEnt02 (containing entA, I, T and D genes under the control of a constitutive promoter) was introduced into a Lactococcus lactis strain capable of fermenting lactose. When this bacteriocin-producing starter was used in combination with a non-enterocin A producer, thereby compensating for an associated reduction in acid production, during a Cottage cheese fermentation, a decrease in L. monocytogenes (tagged with lux genes for convenience) levels was evident.

CONCLUSIONS

Enterocin A, heterologously produced by a food grade lactic acid bacteria (LAB), was therefore shown to have potential for use as a biocontrol agent in food.

SIGNIFICANCE AND IMPACT OF THE STUDY

Many of the most active anti-listerial compounds identified to date are enterocins. However, because of Enterococcus-associated concerns, the use of these antimicrobials in a food setting has been curtailed. Although enterocins have been heterologously produced in LAB to overcome this problem, this study represents the first occasion upon which the benefits of such heterologous production have been demonstrated in a food context.

Trunk strength and lumbar paraspinal muscle activity during isometric exercise in chronic low-back pain patients and controls

The purpose of this study was to describe trunk strength and lumbar paraspinal muscle activity across five angles of flexion during isometric exercise and rest in chronic low-back pain patients and control subjects. High muscle tension as measured by surface integrated electromyography is predicted by a muscle spasm model, and low muscle tension is predicted by a muscle deficiency model. Prior lumbar surgery had no affect on peak torque or maximum surface integrated electromyography data. Both groups produced greater torque and less surface integrated electromyography in more flexed positions. Chronic low-back pain patients exhibited lower peak torque and lower maximum surface integrated electromyography bilaterally during isometric extension effort across all angles. A muscle deficiency model of chronic low back pain was supported by these data and a muscle spasm model was not supported. Discriminant analyses indicated that monitoring maximum surface integrated electromyography of lumbar muscles during isometric effort facilitates classification of chronic low-back pain patients. Future directions are discussed in terms of applying psychophysiologic methods to pain rehabilitation.

Nonspecific DNA binding of genome-regulating proteins as a biological control mechanism: measurement of DNA-bound Escherichia coli lac repressor in vivo

Binding of genome regulatory proteins to nonspecific DNA sites may play an important role in controlling the thermodynamics and kinetics of the interactions of these proteins with their specific target DNA sequences. An estimate of the fraction of Escherichia coli lac repressor molecules bound in vivo to the operator region and to nonoperator sites on the E. coli chromosome is derived by measurement of the distribution of repressor between a minicell-producing E. coli strain (P678-54) and the DNA-free minicells derived therefrom. Assuming the minicell cytoplasm to be representative of that of the parent E. coli cells, we find that less than 10% of the repressor tetramers of the average cell are free in solution; the remainder are presumed to be bound to the bacterial chromosome. The minimum in vivo value of the association constant for repressor to bulk nonoperator DNA (K(RD)) calculated from these results is about 10(3) M(-1), and analysis of the sources of error in the minicell experiment suggests that the actual in vivo value of K(RD) could be substantially greater. The value of K(RD), coupled with in vitro data on the ionic strength dependence of this parameter, can be used to estimate that the effective intracellular cation activity of E. coli is no greater than about 0.24 M (and probably no less than 0.17 M) in terms of sodium ion equivalents. The minicell distribution experiments also confirm that the association constant for the binding of inducer-repressor complex to bulk nonoperator DNA (K(RID)) is [unk] K(RD)in vivo. These results are used to calculate minimum in vivo values of K(RO) and K(RIO) (association constants for repressor and for inducer-repressor complex binding to operator) of about 10(12) M(-1) and about 10(9) M(-1), respectively. The results fit a quantitative model for operon regulation in which nonspecific DNA-repressor complexes play a key role in determining basal and constitutive levels of gene expression [von Hippel, P. H., Revzin, A., Gross, C. A. & Wang, A. C. (1974) Proc. Natl. Acad. Sci. USA 71, 4808-4812].