Recent developments in antibiotic treatment

In vivo activity of mutacin B-Ny266

OBJECTIVES

The objective of this study was to assess the in vivo activity of mutacin B-Ny266 (a bacteriocin produced by Streptococcus mutans) in order to eventually use it as an antibiotic.

METHODS

Intraperitoneal infection was induced with a methicillin-susceptible Staphylococcus aureus strain in mice. Some of the mice were simultaneously injected intraperitoneally with mutacin B-Ny266, some with the vehicle only and some with vancomycin.

RESULTS

While there was 70 and 100% mortality in the control groups of mice, no mortality was observed in the mice injected with vancomycin or mutacin B-Ny266.

CONCLUSIONS

The results presented here show, for the first time, the in vivo efficacy of a mutacin (B-Ny266) against an experimental intraperitoneal infection by S. aureus in a mouse model.

Antifolate activity of epigallocatechin gallate against Stenotrophomonas maltophilia

The catechin epigallocatechin gallate, one of the main constituents of green tea, showed strong antibiotic activity against 18 isolates of Stenotrophomonas maltophilia (MIC range, 4 to 256 microg/ml). In elucidating its mechanism of action, we have shown that epigallocatechin gallate is an efficient inhibitor of S. maltophilia dihydrofolate reductase, a strategic enzyme that is considered an attractive target for the development of antibacterial agents. The inhibition of S. maltophilia dihydrofolate reductase by this tea compound was studied and compared with the mechanism of a nonclassical antifolate compound, trimethoprim. Investigation of dihydrofolate reductase was undertaken with both a trimethoprim-susceptible S. maltophilia isolate and an isolate with a high level of resistance. The enzymes were purified using ammonium sulfate precipitation, gel filtration, and methotrexate affinity chromatography. The two isolates showed similar levels of dihydrofolate reductase expression and similar substrate kinetics. However, the dihydrofolate reductase from the trimethoprim-resistant isolate demonstrated decreased susceptibility to inhibition by trimethoprim and epigallocatechin gallate. As with other antifolates, the action of epigallocatechin gallate was synergistic with that of sulfamethoxazole, a drug that blocks folic acid metabolism in bacteria, and the inhibition of bacterial growth was attenuated by including leucovorin in the growth medium. We conclude that the mechanism of action of epigallocatechin gallate on S. maltophilia is related to its antifolate activity.

Influence of antibiotic therapy on mortality of critical surgical illness caused or complicated by infection

BACKGROUND

Conceptually, appropriateness of antibiotic therapy includes choice of agent relative to susceptibility of pathogens as well as dosing, timing of onset, and duration of therapy, but is most commonly considered in terms of choice of antibiotic. It has been suggested that inappropriate antibiotic selection can result in increased mortality. This study was performed to elucidate the role of scheduled, rotating antibiotic therapy in defining mortality among febrile, infected surgical ICU patients.

METHODS

Prospective inception-cohort study of 356 patients during their initial episode of fever (temperature > 38.2 degrees C), caused by infection diagnosed by positive cultures or direct inspection (some cases of peritonitis). Collected data included age, gender, admission APACHE III score, peak temperature, microbial isolates and susceptibility, source of infection, multiple organ dysfunction score, mortality, and several time intervals (time that cultures were collected, time from collection to antibiotic prescription, time from collection to antibiotic administration, duration of therapy).

RESULTS

The mean age was 63 +/- 1 years, the mean APACHE III score was 74 +/- 2 points, the mean multiple organ dysfunction score was 8 +/- 1 points, and overall mortality was 31%. Neither the source of infection nor the specific isolate influenced mortality. Antibiotic therapy was appropriate (covered the isolates) in 94% of cases, and did not influence mortality. Duration of therapy was identical between groups (5.1 +/- 0.3 vs. 5.4 +/- 0.3 days, p = 0.61). By logistic regression (dependent variable = mortality), APACHE III score OR 1.025, 95% C.I. 1.021-1.04) and delayed antibiotic administration (30-min intervals, OR 1.021, 95% C.I. 1.003-1.038) were independent predictors of mortality.

CONCLUSIONS

The use of scheduled monthly antibiotic cycling in the surgical ICU is associated with a high rate of "appropriate" antibiotic therapy, and appears to maintain or improve resistance patterns. Because antibiotic therapy was mostly appropriate for isolates, initial inappropriate therapy could not be identified as a risk factor for mortality. However, in the setting of appropriate antibiotic choice, the prompt initial administration of antibiotics appears to be crucial for survival, but neither site of infection nor specific pathogen are influential.

Homology model of the multidrug transporter LmrA from Lactococcus lactis

LmrA is an ATP dependent multidrug transporter from Lactococcus lactis conferring antibiotic resistance to 17 out of 21 most frequently administered antibiotics. Starting from the dimeric crystal structure of Vc-MsbA, we built two homology models, with NBD:NBD interfaces reflecting the nonenergized and energized state, respectively. The TMD:TMD topology of the dimer is consistent with the previously obtained substrate photoaffinity labeling pattern suggesting binding of substrates at the TMD:TMD interface involving helix 3 of one monomer and helices 5 and 6 of the other monomer.