Antimicrobial susceptibility changes in Enterococcus faecalis following various penicillin exposure regimens.

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 regimes for penicillin in the treatment of enterococcal infections, when bactericidal synergism cannot be achieved with penicillin-aminoglycoside combinations.     

Diversity of domain V of 23S rRNA gene sequence in different Enterococcus species

The highly conserved central loop of domain V of 23S RNA (nucleotides 2042 to 2628; Escherichia coli numbering) is implicated in peptidyltransferase activity and represents one of the target sites for macrolide, lincosamide, and streptogramin B antibiotics. DNA encoding domain V (590 bp) of several species of Enterococcus was amplified by PCR. Twenty enterococcal isolates were tested, including Enterococcus faecium (six isolates), Enterococcus faecalis, Enterococcus avium, Enterococcus durans, Enterococcus gallinarum, Enterococcus casseliflavus (two isolates of each), and Enterococcus raffinosus, Enterococcus mundtii, Enterococcus malodoratus, and Enterococcus hirae (one isolate of each). For all isolates, species identification by biochemical testing was corroborated by 16S rRNA gene sequencing. The sequence of domain V of the 23S rRNA gene from E. faecium and E. faecalis differed from those of all other enterococci. The domain V sequences of E. durans and E. hirae were identical. This was also true for E. gallinarum and E. casseliflavus. E. avium differed from E. casseliflavus by 23 bases, from E. durans by 16 bases, and from E. malodoratus by 2 bases. E. avium differed from E. raffinosus by one base. Despite the fact that domain V is considered to be highly conserved, substantial differences were identified between several enterococcal species.     

Sequence Analysis of the RNA Polymerase Gene of Foot-and-Mouth Disease Virus Serotype Asia1

The complete nucleotide (nt.) sequence of the RNA polymerase (3D) gene and 81 nt. in the 3-untranslated region of foot-and-mouth disease virus (FMDV) serotype Asia1 (IND63/72) was determined and compared with the sequence of other FMDV serotypes. The 3D genomic region was 1410 nt. long encoding 470 amino acids with an inframe stop codon (TAA) at nt. position 1411–1413. The deduced amino acid sequence of the protein showed 8 conserved motifs as reported in other picornaviruses, 2 of which are 100% identical across the serotypes. Antigenic regions in the polymerase protein were predicted and found to be located at the N-terminus of the protein. The phylogenetic analysis showed that the FMD viruses were segregated into different clusters based on geographical origin; the Asia1 virus did not cluster tightly with any of the geographical groups.     

Comparison of ultrasonographic findings in spontaneous abortions with normal and abnormal karyotypes

To determine whether ultrasonographic findings can predict the karyotype of spontaneous abortions, 137 pregnancies (54 spontaneous, 83 assisted ovulatory cycles) that subsequently aborted and had chromosome analysis performed on the products of conception were studied ultrasonographically. Transvaginal ultrasound was performed using an Acuson 128XP/10 with 7.5 MHz probe. The numbers of empty gestational sacs, small and normal for gestational size, embryonic poles and embryos with documented cardiac activity were calculated. The frequency of each of these findings in pregnancies with normal and abnormal karyotypes was compared. Of the 137 spontaneous abortions, 51 had normal chromosome analyses and 86 had abnormal karyotypes (68 aneuploidies and 18 polyploidies). Ultrasonographic findings in the 51 karyotypically normal pregnancies included 16 (31%) with empty gestational sacs, and 35 (69%) with embryonic poles, of which 24 (69%) were at least 1 week smaller than expected for gestational age and 11 (31%) were the expected size. Embryonic cardiac activity was documented in 22 (63%) of the 35 embryonic poles. Amongst 86 pregnancies with abnormal karyotypes, similar frequencies of ultrasound findings were found: 23 (27%) with empty gestational sacs, 42 (67%) with embryonic poles smaller than expected for gestational age, and 50 (79%) embryos lost after documentation of embryonic cardiac activity. No differences in the frequency of ultrasonographic findings of empty gestational sacs, small embryonic pole and embryonic cardiac activity were observed between karyotypically normal and abnormal spontaneous abortions. Ultrasonographic findings cannot predict the karyotype of spontaneous abortions.