Use of Penicillin-binding Proteins for the Identification of Enterococci

Penicillin-"virgin" strains of Enterococcus faecalis collected from a population of individuals with no previous antibiotic exposure were subjected in vitro to penicillin delivered as repeated pulses, stepwise increasing concentrations, or sustained levels of a single concentration. Changes in resistance to penicillin were assessed by determination of MICs, and time-kill studies were performed to evaluate changes in tolerance to the bactericidal effects of penicillin. Isogenic clones, derived from various exposure regimens, which exhibited changes in either resistance or tolerance were further examined for changes in penicillin-binding proteins. Exposure to repeated pulses of penicillin resulted in the development of tolerance to penicillin without changes in the level of resistance. Clones derived from a regimen of stepwise increases in the penicillin concentration acquired both increased penicillin resistance and tolerance. Clones selected after prolonged continuous exposure to a fixed concentration of penicillin displayed minimally increased resistance to penicillin, but they retained the lytic, nontolerant response to the bactericidal effect of penicillin. Clones which acquired tolerance to the bactericidal effect of penicillin without changes in penicillin resistance exhibited a penicillin-binding protein pattern identical to that of the parental strain. Increased labeling of several penicillin-binding proteins accompanied the development of increased penicillin resistance in both penicillin-tolerant and nontolerant strains. Exposure of E. faecalis to penicillin in repeated pulses of brief duration, for prolonged periods at a constant concentration, or in stepwise graded concentrations can result in the selection of clones with increased resistance to the inhibitory or bactericidal effects of penicillin, or both. These observations may be relevant to the selection of dosing regimens for penicillin in the treatment of enterococcal infections, when bactericidal synergism cannot be achieved with penicillin-aminoglycoside combinations.

Section: Resultsmentioning

confidence: 79%

Antimicrobial susceptibility changes in Enterococcus faecalis following various penicillin exposure regimens

Hodges

Zighelboim-Daum

Eliopoulos

et al. 1992

“…E. faecalis A256 and E. faecium D366, D399, and D400 have been described previously (2,(17)(18)(19). E. faecium D359 is a vancomycin-susceptible control strain (19,20). * Corresponding author.…”

Section: Methodsmentioning

confidence: 99%

Inducible carboxypeptidase activity in vancomycin-resistant enterococci

Gutmann

Billot-Klein

Al-Obeid

et al. 1992

Vancomycin was found to coinduce DD-carboxypeptidase activity, together with resistance, in eight low-or high-level glycopeptide-resistant strains of enterococci. The constitutively resistant mutant (MT10) of a low-level-resistant strain of Enterococcus faecium (D366) spontaneously expressed a level of carboxypeptidase similar to that of the induced strain D366. Pentapeptide, UDP-MurNac-pentapeptide, as well as D-alanyl-Dalanine were in vitro substrates for the carboxypeptidase which was not inhibited by penicillin. The level of vancomycin resistance correlated roughly with the level of carboxypeptidase activity. We infer from these results that the carboxypeptidase is one component of the glycopeptide resistance mechanism.

“…Clostridium perfringens and Enterococcus faecium are considered intrinsically resistant (16,19,20), but susceptible strains of E. faecium have been reported recently (2). Differences among the PBPs in different species of enterococci might explain the different susceptibilities among enterococcal species (63). In a large collection of Staphylococcus aureus isolates from chickens and chicken slaughterers, no resistance against flavophospholipol was detected (25).…”

mentioning

confidence: 99%

Effects of Flavophospholipol on Resistance in Fecal Escherichia coli and Enterococci of Fattening P

Bogaard

Hazen

Hoyer³

et al. 2002

A "plasmid-curing effect" of multiresistant Escherichia coli by flavophospholipol, an antibiotic used as an antimicrobial growth promoter (AMGP) in animal feeds, has been reported to occur in vitro and in vivo under experimental conditions. In this study, the effect of flavophospholipol under field conditions was studied. The prevalence and degree (proportion of resistant strains to the total numbers present per gram of feces) of resistance of indicator bacteria, E. coli and enterococci, was determined in fecal samples from three groups of pigs that were fed a commercial finisher feed without any AMGP. Group A was the negative control group without any AMGP, group B received the same feed with 9 mg of flavophospholipol/kg of feed (study group), and group C received the same feed with 15 mg of avoparcin/kg (positive control). Fecal samples from each pig were collected at the start and at the end of the study and assessed for the prevalence and degree of resistance against antibiotics commonly used either for therapy in pig medicine or as an AMGP. Before the start of the study, all pigs were colonized with multiresistant E. coli by mixing three resistant pig isolates through their feed after disturbance of the colonization resistance of the intestinal flora by a 3-day course of lincomycin and spectinomycin. At the end of the study, the overall prevalence and degree of resistance of E. coli in the fecal flora had increased significantly in groups A and C but remained at the same level as at the start of the study in group B. The prevalence of vancomycin resistance was 44 and 41% in groups A and B, respectively, but only very low numbers of vancomycin-resistant enterococci (VRE) per gram of feces were found. In the avoparcinfed group, the prevalence was 72%, and in 57% of the samples, more than 50% of all enterococci present were vancomycin resistant. The prevalence of resistant Enterococcus faecalis increased only in the flavophospholipolexposed group, from 23% before the start of the study to 43% at the end of the study. It was concluded that flavophospholipol effectively suppressed the augmentation and dissemination of multiresistant E. coli in the intestinal flora of fattening pigs. Avoparcin use strongly selected for VRE carriage and excretion. Therefore, as neither flavophospholipol nor any related molecule is used therapeutically, no cross-resistance with therapeutic antibiotics exists and no transmissible resistance has been shown; the major decrease in resistance in intestinal E. coli of flavophospholipol-fed animals seemed to outweigh the small increase in the risk of transfer of flavophospholipol-resistant E. faecalis from animals to humans via the food chain.The most effective way to decrease the prevalence and degree of resistance in fecal indicator bacteria is to reduce the amount of antibiotics used in a population. In food animals, antibiotics are not only used for therapy and prevention of bacterial infections but are also added continuously to animal feeds as antimicrobial growth promoters (AMGP) t...