Short-Term prophylaxis with ceftriaxone plus metronidazole in esophageal cancer surgery.

An open prospective study was carried out in 82 consecutive patients undergoing resective surgery for esophageal cancer from January 1995 to July 1996. Antimicrobial prophylaxis was done using a single dose of ceftriaxone (2 g i.v.) given at the induction of anesthesia in combination with metronidazole (0.5 g i.v.). Two further doses of metronidazole were administered 8 and 16 hours postoperatively. Fourteen patients (17%) experienced postoperative infections. This study, even though open and non-comparative, confirms that ceftriaxone given as a single-dose plus metronidazole provides adequate prophylaxis and significant cost-savings in comparison with multiple-dose prophylactic regimens in patients undergoing major surgery for esophageal cancer. Furthermore, the single-dose regimen reduces the workload for the nursing staff, the risk of side effects, and the possibility of selecting resistant strains.

Nonradioactive DNA probe for detection of gene for methicillin resistance in Staphylococcus aureus.

A DNA probe was developed by inserting, in the SmaI site of pBluescript sK, a 528-bp fragment of the gene responsible for intrinsic resistance to beta-lactam antibiotics in Staphylococcus aureus (mec determinant). The mec probe provided a useful tool for the rapid identification of the intrinsic resistance trait and for establishing guidelines for testing the in vitro susceptibility of S. aureus to beta-lactams.

In vitro response to bactericidal activity of cell wall-active antibiotics does not support the general opinion that enterococci are naturally tolerant to these antibiotics.

The incidence of tolerance and paradoxical response to bactericidal activity of penicillin was investigated in 50 clinical isolates of Enterococcus faecalis. Of the isolates tested, 86% exhibited the paradoxical phenomenon whereby there were more survivors at high than at low concentrations above the MIC. Low penicillin concentrations caused decreases equal to or higher than 99.9% in 11 strains, from 99.9 to 99.5% in 23 strains, and lower than 99.5% in 9 strains. Of the total strains, 14% were killed to the same extent by all concentrations above the MIC. The bactericidal activities of other beta-lactams (ampicillin and piperacillin) and other cell wall inhibitors (vancomycin and daptomycin) were also tested against some of these strains. In general, beta-lactams exhibited the best bactericidal activity at 2 x MIC. Piperacillin was the most active, as at 2 x MIC it reduced the original inoculum by 99.9% or more in most of the strains. No concentration of vancomycin above the MIC caused 99.9% killing of the strains, whereas daptomycin was bactericidal at 8 x MIC in most cases. Paradoxical response to bactericidal activity of beta-lactams was abolished by incubation of the inoculum with 2 x MIC before exposure to higher antibiotic concentrations. These findings suggest that enterococci are not always tolerant to cell wall-active antibiotics and that accurate in vitro bactericidal tests may be useful for the choice of appropriate therapy for infections caused by these microorganisms.

Paradoxical response of Enterococcus faecalis to the bactericidal activity of penicillin is associated with reduced activity of one autolysin.

Ten clinical isolates of Enterococcus faecalis were examined for susceptibility to the bactericidal activity of penicillin. Four of these had MBCs of penicillin equal to 2 to 4 x the MIC, and six exhibited a paradoxical response to penicillin, i.e., the bactericidal activity of the antibiotic had a concentration optimum at 2 to 4 x the MIC and decreased significantly at concentrations above this. We found that the paradoxical response to penicillin was an intrinsic and stable property of a strain, but that its phenotypic expression was not homogeneous; only a fraction of the cell population that died at low concentrations was able to survive at high penicillin concentrations. The size of this fraction increased with increasing antibiotic concentration and reached a maximum in the late-log phase of growth. All 10 strains produced a lytic enzyme that was active on Micrococcus luteus heat-killed cells, whereas only some strains lysed E. faecalis heat-killed cells. Strains producing large amounts of the latter enzyme did not show the paradoxical response to penicillin, whereas mutants of these strains that lacked this enzymatic activity paradoxically responded to the antibiotic activity. In addition, from strains that showed paradoxical response to penicillin and produced only the enzyme that was active on M. luteus, it was possible to isolate mutants that were also capable of lysing E. faecalis cells and that were killed with similar efficiency by all concentrations above the MBC. On the basis of these findings, the paradoxical response to penicillin is explained as a property of certain strains of E. faecalis; this property is genetically characterized by alterations in synthesis or activity of one autolysin but phenotypically expressed only by a few cells that are in a particular physiological condition when exposed to high concentrations of antibiotics.

Interaction of FCE 22101 with penicillin-binding proteins of Staphylococcus aureus.

FCE 22101 is a new penem characterized by a broad spectrum of activity which includes activity against methicillin-resistant strains of Staphylococcus aureus. The interaction of FCE 22101 with penicillin-binding protein 2a of a methicillin-resistant S. aureus strain has been investigated in the present study. In competition experiments, the penem showed a very low affinity for this protein, and a concentration more than 4 times the MIC was required for penicillin-binding protein 2a saturation. When the classical competitive procedure was modified by increasing the time of incubation of either membranes or growing cells with FCE 22101, the antibiotic showed a much higher affinity for penicillin-binding protein 2a and saturated the protein at a concentration close to the MIC, with slow kinetics.