Importance of the E-46-D-160 polypeptide segment of the non-penicillin-binding module for the folding of the low-affinity, multimodular class B penicillin-binding protein 5 of Enterococus hirae.

Compared with the other class B multimodular penicillin- binding proteins (PBPs), the low-affinity PBP5 responsible for penicillin resistance in Enterococcus hirae R40, has an extended non-penicillin-binding module because of the presence of an approximately 110-amino-acid E-46(-)D-160 insert downstream from the membrane anchor. Expression of pbp5 genes lacking various parts of the insert-encoding region gives rise to proteins that are inert in terms of penicillin binding, showing that during folding of the PBP, the insert plays a role in the acquisition of a correct penicillin-binding configuration by the G-364(-)Q-678 carboxy-terminal module.

Participation of PBP 3 in the acquisition of dicloxacillin resistance in Listeria monocytogenes.

Purified membranes of Listeria monocytogenes ATCC 15313 contain at least five penicillin-binding proteins. In two dicloxacillin-resistant mutants, derived from a sensitive parent strain, a 16-fold increase in the MIC of dicloxacillin was observed. A less-significant increase was detected in the MICs of other beta-lactam drugs. In the mutants, PBP 3 lost its strong affinity for dicloxacillin, but remained fully susceptible to binding of 125I-penicillin X, as compared with the wild-type strain. PBP 2 could not be detected in one of the mutants. No decrease in affinity for the radioactive tracer or dicloxacillin was detected in any other PBP of the resistant mutants.

Penicillin-binding proteins in Listeria monocytogenes.

The Penicillin-Binding Proteins (PBP) of Listeria monocytogenes 29-CCM-A: 454 (ATCC 15313) are described by the use of 125I-Penicillin X as radiotracer. The membranes of this tolerant bacilli contained at least five proteins with different affinities for the radiotracer or Dicloxacillin. The molecular weights of these proteins were estimated as 76, 74, 67, 66 and 47 KDa. Dicloxacillin induced the formation of straight filaments when present at sub-inhibitory concentrations, while Penicillin G did not induce any visible alteration in the morphology of this microorganism.

Production of Linnocuicina 819, a bacteriocin produced by Listeria innocua.

We studied the reciprocal antagonistic properties of 14 Listeria strains. Listeria innocua 29-CCM-A 819 (CIP 8011) produces a bacteriocin named Linnocuicina 819. This substance is mainly released in the exponential phase of growth and was isolated from the supernatant of TPB cultures. Thermal resistance and sensitivity to proteolytic enzymes was assayed. Linnocuicina 819 has a bactericidal mode of action producing a lytic effect.

[Obtaining dicloxacillin-resistant mutants in Listeria monocytogenes]. / Obtención de mutantes dicloxacilina resistentes en Listeria monocytogenes.

We obtained ten Dicloxacillin resistant mutants from Listeria monocytogenes ATCC: 15313 (29-CCM-A: 454). None of the mutants could be differentiated from the parental strain (except for their increased resistance) neither using conventional biochemical assays nor by analysis of the electrophoretic pattern of their detergent-soluble proteins (Figure 1). The wild type strain and some of these mutants were tolerant for Dicloxacillin and/or Penicillin G, but no rigorous correlation with each decrease in their susceptibility was observed (Table 1). Morphological studies showed that some of the resistant strains (growing at subinhibitory concentrations of Dicloxacillin) presented differences, including the formation of helical structures (Figures 2-5).

Obtención de mutantes dicloxacilina resistentes en Listeria monocytogenes. / [Obtaining dicloxacillin-resistant mutants in Listeria monocytogenes]

We obtained ten Dicloxacillin resistant mutants from Listeria monocytogenes ATCC: 15313 (29-CCM-A: 454). None of the mutants could be differentiated from the parental strain (except for their increased resistance) neither using conventional biochemical assays nor by analysis of the electrophoretic pattern of their detergent-soluble proteins (Figure 1). The wild type strain and some of these mutants were tolerant for Dicloxacillin and/or Penicillin G, but no rigorous correlation with each decrease in their susceptibility was observed (Table 1). Morphological studies showed that some of the resistant strains (growing at subinhibitory concentrations of Dicloxacillin) presented differences, including the formation of helical structures (Figures 2-5).