Analysis of a gene cluster of Enterococcus faecalis involved in polysaccharide biosynthesis

Previously, we described a gene cluster of Enterococcus faecalis OG1RF that produced an antigenic polysaccharide when cloned in Escherichia coli. The polysaccharide antigen was not detectable in E. faecalis strains, however. Here, we show by reverse transcriptase-PCR that the 16 genes in this region are transcribed in OG1RF. Gene disruption of orfde4, encoding a putative glycosyl transferase, and orfde6, a putative dTDP-rhamnose biosynthesis gene, generated two OG1RF mutants. The mutants showed delayed killing and a higher 50% lethal dose in a mouse peritonitis model. In addition, two mucoid E. faecalis isolates from patients with chronic urinary tract infections were found to produce the polysaccharide antigen.

In vitro activity of moxifloxacin, a new 8-methoxyquinolone, against gram-positive bacteria

The in vitro activity of moxifloxacin, formerly BAY 12-8039, against gram-positive bacteria was tested by the agar dilution method. A total of 189 isolates that included Staphylococcus aureus, Enterococcus faecalis, Enterococcus faecium, streptococci, rhodococci, leuconostocs, pediococci, lactobacilli, and diphtheroids were tested. Moxifloxacin showed greater potency than ciprofloxacin against S. aureus, streptococci, and enterococci, having Minimal Inhibitory Concentrations (MICs) lower than those of ciprofloxacin by 2- to 64-fold. This improved activity was most prominent for S. aureus. Moxifloxacin was active against Leuconostoc and Rhodococcus species. Time-kill studies using moxifloxacin at a concentration of 3 micrograms/mL against one isolate each of methicillin-resistant S. aureus (MSSA) (MIC, 0.031 microgram/mL), MRSA (MIC, 1 microgram/mL), two isolates of E. faecalis (MICs, 0.25 and 2 micrograms/mL), and two isolates of vancomycin-resistant E. faecium (MICs, 0.25 and 2 micrograms/mL) revealed an average decrease in colony forming unit (CFU) by 3.8, 0.4, 4.0, 2.0, 4.2, and 1.8 log10 CFU/mL at 24 h, respectively. Moxifloxacin is a new 8-methoxyquinolone with improved in vitro activity against gram-positive bacteria. Further studies of the in vivo activity of this compound appear warranted.

From vanA Enterococcus hirae to vanA Enterococcus faecium: a study of feed supplementation with avoparcin and tylosin in young chickens

Fifteen newborn chickens were isolated in separate cages after 1 month of living together, divided into three groups, and challenged for 5 weeks with seed food which either was supplemented with avoparcin (10 mg/kg of animal food) or tylosin (40 mg/kg) or was nonsupplemented. At 9 weeks of age and after the 5-week challenge, all chickens received nonsupplemented feed for 4 additional weeks. At 4, 9, and 13 weeks of life, feces were collected and inoculated on M-Enterococcus agar plates with and without vancomycin (4 micrograms/ml). vanA-containing Enterococcus hirae was isolated from 11 of 15 chickens before antibiotic challenge, without detection of vancomycin-resistant Enterococcus faecium. At 9 weeks of age and after the 5-week avoparcin challenge, vanA E. hirae strains were no longer detected, but five of five chickens now had vanA E. faecium. At a lower frequency, vanA E. faecium had also displaced vanA E. hirae in both the tylosin group (one of four chickens) and the control group (two of five chickens). One month after avoparcin discontinuation, the number of chickens colonized with vanA E. faecium decreased from five to one. All vanA-containing E. hirae strains detected in the first month of life and most of the vanA-containing E. faecium strains detected in the second month of life showed identical ApaI and SmaI restriction patterns, respectively, when analyzed by pulsed-field gel electrophoresis. All vanA E. hirae isolates transferred glycopeptide and macrolide resistance to Enterococcus faecalis JH2-2 in vitro; the level of glycopeptide resistance was higher in the transconjugants than in the donor E. hirae strains. These data suggest that E. hirae may be a significant source of vanA determinants with the potential of transfer to other enterococcal species from humans or animals.

In vitro activities of two ketolides, HMR 3647 and HMR 3004, against gram-positive bacteria

The in vitro activities of two new ketolides, HMR 3647 and HMR 3004, were tested by the agar dilution method against 280 strains of gram-positive bacteria with different antibiotic susceptibility profiles, including Staphylococcus aureus, Enterococcus faecalis, Enterococcus faecium, Streptococcus spp. (group A streptococci, group B streptococci, Streptococcus pneumoniae, and alpha-hemolytic streptococci). Seventeen erythromycin-susceptible (EMs), methicillin-susceptible S. aureus strains were found to have HMR 3647 and HMR 3004 MICs 4- to 16-fold lower than those of erythromycin (MIC at which 50% of isolates were inhibited [MIC50] [HMR 3647 and HMR 3004], 0.03 microgram/ml; range, 0.03 to 0.06 microgram/ml; MIC50 [erythromycin], 0.25 microgram/ml; range, 0.25 to 0.5 microgram/ml). All methicillin-resistant S. aureus strains tested were resistant to erythromycin and had HMR 3647 and HMR 3004 MICs of > 64 micrograms/ml. The ketolides were slightly more active against E. faecalis than against E. faecium, and MICs for individual strains varied with erythromycin susceptibility. The MIC50s of HMR 3647 and HMR 3004 against Ems enterococci (MIC < or = 0.5 microgram/ml) and those enterococcal isolates with erythromycin MICs of 1 to 16 micrograms/ml were 0.015 microgram/ml. E. faecalis strains that had erythromycin MICs of 128 to > 512 micrograms/ml showed HMR 3647 MICs in the range of 0.03 to 16 micrograms/ml and HMR 3004 MICs in the range of 0.03 to 64 micrograms/ml. In the group of E. faecium strains for which MICs of erythromycin were > or = 512 micrograms/ml, MICs of both ketolides were in the range of 1 to 64 micrograms/ml, with almost all isolates showing ketolide MICs of < or = 16 micrograms/ml. The ketolides were also more active than erythromycin against group A streptococci, group B streptococci, S. pneumoniae, rhodococci, leuconostocs, pediococci, lactobacilli, and diphtheroids. Time-kill studies showed bactericidal activity against one strain of S. aureus among the four strains tested. The increased activity of ketolides against gram-positive bacteria suggests that further study of these agents for possible efficacy against infections caused by these bacteria is warranted.

Characterization of dihydrofolate reductase genes from trimethoprim-susceptible and trimethoprim-resistant strains of Enterococcus faecalis

Enterococci are usually susceptible in vitro to trimethoprim; however, high-level resistance (HLR) (MICs, >1,024 microg/ml) has been reported. We studied Enterococcus faecalis DEL, for which the trimethoprim MIC was >1,024 microg/ml. No transfer of resistance was achieved by broth or filter matings. Two different genes that conferred trimethoprim resistance when they were cloned in Escherichia coli (MICs, 128 and >1,024 microg/ml) were studied. One gene that coded for a polypeptide of 165 amino acids (MIC, 128 microg/ml for E. coli) was identical to dfr homologs that we cloned from a trimethoprim-susceptible E. faecalis strain, and it is presumed to be the intrinsic E. faecalis dfr gene (which causes resistance in E. coli when cloned in multiple copies); this gene was designated dfrE. The nucleotide sequence 5' to this dfr gene showed similarity to thymidylate synthetase genes, suggesting that the dfr and thy genes from E. faecalis are located in tandem. The E. faecalis gene that conferred HLR to trimethoprim in E. coli, designated dfrF, codes for a predicted polypeptide of 165 amino acids with 38 to 64% similarity with other dihydrofolate reductases from gram-positive and gram-negative organisms. The nucleotide sequence 5' to dfrF did not show similarity to the thy sequences. A DNA probe for dfrF hybridized under high-stringency conditions only to colony lysates of enterococci for which the trimethoprim MIC was >1,024 microg/ml; there was no hybridization to plasmid DNA from the strain of origin. To confirm that this gene causes trimethoprim resistance in enterococci, we cloned it into the integrative vector pAT113 and electroporated it into RH110 (E. faecalis OG1RF::Tn916DeltaEm) (trimethoprim MIC, 0.5 microg/ml), which resulted in RH110 derivatives for which the trimethoprim MIC was >1, 024 microg/ml. These results indicate that dfrF is an acquired but probably chromosomally located gene which is responsible for in vitro HLR to trimethoprim in E. faecalis.

Effect of disruption of a gene encoding an autolysin of Enterococcus faecalis OG1RF

A mutant (TX5127) of Enterococcus faecalis OG1RF was generated by disruption mutagenesis of a previously described autolysin gene. TX5127 formed longer chains (2 to 10 cells per chain) than wild-type OG1RF (mainly single cells) during growth in broth even though it had a growth rate similar to that of the parental strain as measured by turbidity and cell count. Autolysin activity, as defined by the ability to lyse heat-killed Micrococcus lysodeikticus cells, was absent in TX5127, while this activity was easily detectable in OG1RF. However, disruption of this autolysin gene did not block the ability of TX5127 to hydrolyze E. faecalis cell walls compared to that of OG1RF. The autolysis rate of cells of TX5127 in 10 mM sodium phosphate buffer (pH 6.8) was slower than that of wild-type OG1RF. TX5127 also showed a decreased rate of lysis in the presence of penicillin, as measured by changes in the turbidity of the culture during 24 h of incubation at 37 degrees C and a slightly decreased effect of penicillin as measured by time-kill curves. The virulence of TX5127 was similar to that of OG1RF in the mouse peritonitis model, indicating that the autolysin of E. faecalis is not important for infection in this model.

Generation and testing of mutants of Enterococcus faecalis in a mouse peritonitis model

A previously described mouse peritonitis model was used to study derivatives of Enterococcus faecalis strain OG1RF. The addition of sterile rat fecal extracts (SRFE) lowered the LD50 of OG1RF >10-fold. Hemolysin production caused a 35-fold lower LD50 and a much shorter survival, similar to previous results using a peritonitis model without SRFE. A purine (but not a pyrimidine) auxotroph was considerably less lethal than wild type; gelatinase mutants were also attenuated. A suicide vector was generated with an enterococcal selectable marker in order to disrupt a gene encoding an E. faecalis antigen; the resulting mutant was not attenuated despite a slower growth rate. In conclusion, this model allows attenuated mutants to be detected, corroborates prior reports that hemolysin is a virulence factor, and suggests a role for gelatinase in virulence of E. faecalis in mice; the attenuated purine auxotroph may provide a system for developing vectors for in vivo expression systems.

In vivo testing of an Enterococcus faecalis efaA mutant and use of efaA homologs for species identification

Disruption of the previously described efaA (from Enterococcus faecalis antigen A) gene was generated in E. faecalis strain OG1RF and loss of an 37-kDa immunoreactive band from the mutant was demonstrated in Western blots. In a mouse peritonitis model, mice infected with the efaAfs (fs=from Enterococcus faecalis) mutant showed more prolonged survival than mice infected with the parent strain OG1RF. These results suggest that efaAfs encodes a function important for infection of mice by enterococci. An efaA-like gene was also identified in E. faecium DNA libraries and its deduced amino acid sequence showed 73% similarity to EfaA of E. faecalis and 42-63% similarities to a group of streptococcal virulence and adhesion associated proteins that are components of ATP-binding cassette transport systems. Intragenic probes representing efaAfs, recAfs, efaAfm (fm=from E. faecium) and gyrAfm were tested for their ability to identify E. faecalis and E. faecium using colony lysates of 133 enterococci and one Streptococcus sp. Probes of E. faecium and E. faecalis origin hybridized to all isolates of E. faecium and E. faecalis, respectively, regardless of their clinical source but not to any of 29 other enterococci. These results suggest that the use of gene probes may prove helpful in identification of isolates of E. faecium and E. faecalis.

Vancomycin resistance factor of Lactobacillus rhamnosus GG in relation to enterococcal vancomycin resistance (van) genes

Lactobacillus rhamnosus GG (ATCC 53103) is a probiotic strain used in fermented dairy products in many countries and is also used as a food supplement in the form of freeze-dried powder. The relationship of the vancomycin resistance factor in L. rhamnosus GG and the vancomycin resistance (van) genes of Enterococcus faecalis and E. faecium were studied using polymerase chain reaction (PCR), Southern hybridization and conjugation methods. Our results show that the vancomycin resistance determinant in L. rhamnosus GG is not closely related to enterococcal van genes, since no PCR product was amplified in L. rhamnosus GG with any of the three sets of vanA primers used, and enterococcal vanA, vanB, vnH, vanX, vanZ, vanY, vanS and vanR genes did not hybridize with DNA of L. rhamnosus GG. This strain does not contain plasmids and transfer of chromosomal vancomycin resistance determinant from L. rhamnosus GG to enterococcal species was not detected. Our results are in accordance with previous findings of intrinsically vancomycin-resistant lactic acid bacteria.

Application of molecular techniques to the study of nosocomial infections caused by enterococci

Enterococci are components of the normal bowel flora of humans and other animals, and have traditionally been considered to be of relatively low virulence in healthy individuals. However, they are increasingly important nosocomial pathogens and have been cited as the leading organism isolated from hospital-acquired infections, and the third leading cause of nosocomial bacteremia in the United States in a recent National Nosocomial Infection Surveillance (NNIS) system report of the Centers for Disease Control (1). The increase in enterococcal infections has been associated with the emergence of resistance to multiple antibiotics, in particular resistance to B-lactams, high-level aminoglycoside resistance, and resistance to glycopeptides. Concern that antibiotic resistance will continue to spread and will increasingly render conventional antimicrobial chemotherapy inadequate for serious enterococcal infections has stimulated interest in methods to improve the diagnosis and epi-demiologic investigation of infections caused by enterococci.

Repetitive sequence-based PCR versus pulsed-field gel electrophoresis for typing of Enterococcus faecalis at the subspecies level

Repetitive sequence-based PCR was compared to pulsed-field gel electrophoresis (PFGE) for the ability to discriminate Enterococcus faecalis isolates at the subspecies level. The BOXA2R primer, derived from repetitive sequences in Streptococcus pneumoniae, was applied to 41 isolates of E. faecalis collected from various sources. The REP1R-Dt and REP2-Dt primers, derived from the gram-negative repetitive extragenic palindromic element, were also applied to 18 selected isolates. Of the 41 isolates examined, 7 were beta-lactamase producing and 8 were vancomycin resistant. By PFGE, 17 isolates had distinct patterns; the other 24 were classified into eight different clonal groups. By PCR using the BOXA2R primer, 16 isolates generated distinct patterns; the other 25 were classified into nine different clonal groups. There were only minor differences in the PCR results obtained by using the BOXA2R primer and the REP1R-Dt and REP2-Dt primers. Two isolates among vancomycin-resistant enterococci from the greater Houston, Tex., area were related by PFGE, distinct by PCR with the BOXA2R primer, and related by PCR with the REP1R-Dt and REP2-Dt primers. Clonal relationships among the remaining 39 isolates were similar by both PFGE and PCR. PCR reliably discriminated all epidemiologically unrelated isolates. Although PCR is less time consuming than PFGE, PCR results were more difficult to interpret than PFGE results, perhaps because fewer bands were generated by PCR than by PFGE and some PCR products were inconsistently seen.

Serological investigation of enterococcal infections using western blot

To assess the usefulness of Western blot in the diagnosis of enterococcal infections, a pilot study was conducted with a newly developed Western blot using sera from patients with confirmed enterococcal infections. Sera from 17 of 19 patients with enterococcal endocarditis reacted strongly to enterococcal antigens on the Western blot, and most produced specific bands at molecular weights 98 kDa and 54 kDa. Sera from patients with bacteremic cholangitis and pyelonephritis reacted frequently as well, but the pattern of bands was different from that observed with endocarditis. Eighty-five percent of 26 sera tested from patients with bacteremia and associated deep-seated infections (endocarditis, cholangitis, and pyelonephritis) were positive on Western blot, compared to 30% of sera from bacteremic patients with no clinically determined deep focus of infection (p < 0.001).

In vitro activity of the trinem sanfetrinem (GV104326) against gram-positive organisms

The in vitro activity of the trinem sanfetrinem (formerly GV104326) (GV) was compared with that of vancomycin, ampicillin, and/or nafcillin against 287 gram-positive bacteria, including methicillin-resistant Staphylococcus aureus and multiresistant enterococci, by the agar and microbroth dilution methods. GV demonstrated 2 to 16 times more activity than ampicillin and nafcillin against the majority of these organisms. The MIC range of GV was 16 to 64 micrograms/ml for 19 Enterococcus faecium strains that were highly resistant to ampicillin (ampicillin MIC range, 64 to 512 micrograms/ml) and vancomycin resistant and 0.25 to 32 micrograms/ml for resistant Rhodococcus spp. Similar activities (+/-1 dilution) were observed by either the agar or the broth microdilution method. GV demonstrated bactericidal activity against a beta-lactamase-producing Enterococcus faecalis strain and against two methicillin-susceptible Staphylococcus aureus strains in 10(5)-CFU/ml inocula. Synergy between GV and gentamicin was observed against an E. faecalis strain that lacked high-level gentamicin resistance. The activity of GV suggests this compound warrants further study.

Chromosomal DNA restriction endonuclease digestion patterns of beta-lactamase-producing Enterococcus faecalis isolates collected from a single hospital over a 7-year period

Twenty-three beta-lactamase (beta-lac)-producing, highly gentamicin-resistant Enterococcus faecalis isolates collected over a 7-year period from the same hospital were examined by pulsed-field gel electrophoresis of SmaI-digested genomic DNA. The beta-lac+ isolates appeared to form a single clonal group, which had been previously designated the mid-Atlantic pattern. Eleven variations of the mid-Atlantic clone, differing by one to six bands, were identified; some of the changes were likely due to plasmid bands. However, a number of isolates had indistinguishable patterns, including some recovered over a 4-year period. There was a surprising lack of movement of the beta-lac determinant to other strains, although this trait was transferable in vitro by conjugation. We conclude that a single clone (the mid-Atlantic clone) of beta-lac+ E. faecalis has remained endemic in this hospital for at least 7 years. The reason(s) for the apparent lack of spread to other strains of E. faecalis is unknown.

Current status of Anopheles stephensi response to various insecticides in some areas of the Thar desert

Investigations on the current response of A. stephensi. to six insecticides viz. DDT, dieldrin, malathion, fenitrothion, propoxur and permethrin, were carried out in 3 districts i.e. Barmer, Jodhpur and Pali, of the Thar desert. The species was found resistant to DDT and dieldrin, partially resistant to malathion and susceptible to fenitrothion, propoxur and permethrin. Dieldrin and malathion resistance has been detected for the first time in the Thar desert. Lethal concentrations (LC50 & LC95) of DDT and dieldrin and lethal exposure times (LT50 & LT95) of malathion, fenitrothion, propoxur and permethrin have been determined. In some areas, the differences in LC50 and LT50 values of tested insecticides, except fenitrothion, were found statistically significant. Chi-square and regression tests have revealed the homogeniety and linear trend respectively in the response of A. stephensi to insecticides. The findings of the study indicate that organochlorine compounds can be used alternately in the spray operations.

Comparison of the beta-lactamase gene cluster in clonally distinct strains of Enterococcus faecalis

Ten beta-lactamase-producing Enterococcus faecalis isolates were examined for the presence of the staphylococcal beta-lactamase repressor and antirepressor genes. Four isolates, previously shown to be unrelated to each other by pulsed-field gel electrophoresis analysis, were positive for both genes by PCR, although beta-lactamase production was not induced with methicillin. Six isolates, previously shown to be clonally related, were negative for both genes by PCR. The blaZ sequences of eight beta-lactamase-producing E. faecalis isolates were determined. Seven isolates from five distinct clones had sequences identical to that previously reported for E. faecalis HH22, regardless of whether the repressor or antirepressor was demonstrated by PCR. However, blaZ from one isolate differed from those of the other enterococci by 11 nucleotides; this isolate is part of the large clone, as defined by pulsed-field gel electrophoresis and multilocus enzyme analysis, that includes HH22. These findings suggest either that enterococci have acquired the bla gene cluster from more than one source or that the gene cluster has undergone considerable change since acquisition by this clone.

Comparative in-vitro activity of the new fluoroquinolone trovafloxacin (CP-99,219) against gram-positive cocci

The in-vitro activities of the new fluoroquinolone trovafloxacin (CP-99,219) and ciprofloxacin were determined against 225 Gram-positive cocci. Trovafloxacin was 4-32 fold more active than ciprofloxacin against staphylococci and streptococci and also showed greater activity against enterococci including vancomycin resistant Enterococcus faecium and Enterococcus faecalis that were highly resistant to aminoglycosides and/or produced beta-lactamase. Trovafloxacin was also bactericidal at 3 mg/L against enterococci except for isolates for which the MICs were > or = 2 mg/L.

Insecticide susceptibility status of some anophelines in district Bikaner, Rajasthan

Insecticide susceptibility tests were conducted on the adults of four anopheline species namely. Anopheles annularis, An. culicifacies, An. stephensi and An. subpictus against the diagnostic doses of six insecticides, viz. DDT (4.0%), dieldrin (0.4%), malathion (5.0%). fenitrothion (1.0%), propoxur (0.1%) and permethrin (0.25%) in District Bikaner (Rajasthan). A time dependent effect has been observed with each insecticide. All the four species were found resistant to DDT and dieldrin and susceptible to fenitrothion and permethrin. An culicifacies and An. subpictus showed susceptibility to malathion, while further verification for the other two species was required. However, with propoxur An. annularis showed resistance, whereas for other three species further studies are required. DDT and dieldrin, the two organochlorines, were found least effective as compared to organophosphates and carbamates.

Susceptibility status of Phlebotomus papatasi and Sergentomyia punjabaensis (Diptera:Psychodidae) to some insecticides in district Bikaner (Rajasthan)

Susceptibility tests were carried out on the females of two species of sandflies viz. Phlebotomus papatasi and Sergentomyia punjabaensis against six insecticides viz. DDT, dieldrin (organochlorines); malathion, fenitrothion (organophosphates); propoxur (carbamate) and permethrin (synthetic pyrethroid) in district Bikaner, Rajasthan. A concentration and time dependent effect was observed with insecticides for both the species. P. papatasi was found resistant to DDT, dieldrin and propoxur while susceptible to malathion, fenitrothion and permethrin. However, S. punjabensis was found susceptible to all the insecticides tested. LC50 and LT50 value estimated for DDT and dieldrin for P. papatasi and S. punjabaensis were found to be 2.2 and 0.3% x 1 hr and 1.45 and 0.032% x 15 min. respectively.

Insecticide susceptibility of Phlebotomus papatasi to organochlorine, organophosphate & carbamate compounds in some arid areas of western Rajasthan

Insecticide susceptibility status of P. papatasi to organochlorine, organophosphate and carbamate compounds has been estimated in Pali and Barmer districts of Rajasthan. Tests revealed that this species was resistant to DDT but susceptible to dieldrin, malathion, fenitrothion and propoxur. Efficacies to these compounds at 50 and 95 per cent levels have been estimated by probit-analysis. The LC50 values for both DDT and dieldrin, were found much lower than those reported from other parts of the country. Heterogeneity of the response was found highly significant [X2 = 43.8(3)] in case of propoxur only.

Susceptibility status of two species of Japanese encephalitis vectors to insecticides in the Thar desert, district Bikaner (Rajasthan)

Susceptibility tests were conducted on the adults of two species of Japanese encephalitis vectors viz., Culex pseudovishnui and C. tritaeniorhynchus against diagnostic doses of DDT, dieldrin, malathion, fenitrothion, propoxur and permethrin at different exposure duration. C. pseudovishnui was found susceptible to permethrin and resistant to dieldrin and propoxur while C. tritaeniorhynchus was found susceptible to permethrin and resistant to DDT, dieldrin, fenitrothion and propoxur. A verification, however, was required with other insecticides for both the species.

Recurrent group B streptococcal infections in infants: clinical and microbiologic aspects

OBJECTIVE

To describe the potential for recurrence of group B streptococcal (GBS) infection in infants, using pulsed-field gel electrophoresis as an epidemiologic tool.

DESIGN

Retrospective review of cases identified by laboratory records and review of the literature.

SETTING

Neonatal nurseries of a county hospital system.

METHODS

Retrospective review of infants with second episodes of GBS bacteremia or meningitis. Digestion of chromosomal DNA with the restriction enzyme Sma I and separation of fragments by use of contour-clamped homogeneous electric field.

RESULTS

Nine cases of recurrent GBS infection were identified during a 14-year period. Eight of the nine infants were born at 25 to 36 weeks of gestation, and one was born at term. The first episode of invasive GBS infection occurred at a mean age of 10.4 days (median, 3 days; range, 1 to 27 days). Parenteral antibiotic therapy was administered for a mean of 13.9 days (median, 14 days; range, 10 to 21 days). Recurrence occurred at a mean age of 42.3 days (median, 48 days; range, 23 to 68 days). One patient died during the second episode; eight infants survived to discharge home. Of seven sets of isolates analyzed from first and second GBS episodes, five were confirmed to be the same genotypically.

CONCLUSION

Recurrence of GBS disease in infants may be associated with the original infecting strain or a second acquired strain.

Revised estimates of enterococcal chromosomal sizes

We previously reported that the chromosomal sizes of four strains of enterococci ranged from 2,045 to 2,761 kb. Extensive analysis and mapping subsequently confirmed the size of Enterococcus faecalis strain OG1 as 2,825 kb (prior size estimate range, 2,750-2,761 kb) (Murray et al., J. Bacteriol. 175, 5216, 1993). However, using variable conditions of electrophoresis and additional digestions, revised size estimates for the other strains are 2,852-3,093 kb for E. faecalis strain JH2-2 (prior range, 2,008-2,135 kb), 2,910-3,065 kb for E. faecalis strain HH67 (prior range, 2,170-2,288 kb), and 2,334-2,558 for E. faecium strain GE-1 (prior range, 2,045-2,155 kb). The earlier underestimations of the chromosomal sizes were due to the inconsistent presence of a large fragment, likely caused by shearing of the DNA during handling, causing it to be considered a partial digestion product, and failure to resolve multiple fragments of the same approximate size.

Susceptibility of beta-lactamase-producing enterococci to piperacillin with tazobactam

The in vitro activity of piperacillin with and without tazobactam was evaluated against different inocula of 12 clinical isolates of beta-lactamase-producing Enterococcus faecalis obtained from different geographic areas. Minimum inhibitory concentrations (MICs) of piperacillin alone at approximately 10(3) colony-forming units (CFU)/spot ranged from 4 to 8 and from 4 to 8 micrograms/ml with piperacillin plus tazobactam. When approximately 10(7) CFU/spot was used, MICs increased to a range of 128-1024 micrograms/ml piperacillin. This inoculum effect was reversed by the addition of tazobactam to piperacillin at a fixed concentration of 1 microgram/ml or at a ratio of 8 : 1 (piperacillin relative to tazobactam) with an MIC90 of 16/2 micrograms/ml for the combination drug. In time-kill studies, four beta-lactamase-producing (Bla+) isolates were tested and demonstrated a decrease of > or = 2 log10 with 8 or 16 micrograms/ml of piperacillin in combination with 4 micrograms of tazobactam, but not with piperacillin alone. A non-beta-lactamase-producing isolate was equally inhibited by piperacillin alone and piperacillin plus tazobactam. Against a Bla+ isolate, the combination of piperacillin with tazobactam with streptomycin resulted in a synergistic effect relative to that of piperacillin with tazobactam; piperacillin plus streptomycin did not show synergism. Piperacillin in combination with tazobactam is active against enterococci that produce beta-lactamase and, in combination with an appropriate aminoglycoside, could be a viable choice for therapy of enterococci that do not have high-level resistance to all aminoglycosides.