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Overproduction of a low-affinity penicillin-binding protein and high-level ampicillin resistance in Enterococcus faecium.

Five ampicillin-resistant clinical isolates of Enterococcus faecium were analyzed for a correlation between overproduction of the low-affinity penicillin-binding protein (PBP 5) and the level of ampicillin resistance. Comparison was made with one susceptible clinical isolate and its ampicillin-resistant derivative obtained in the laboratory by selection with increasing concentrations of penicillin. Overproduction of the low-affinity PBP relative to the susceptible isolate was noted in moderately resistant strains (MIC, 32 micrograms/ml) but not in highly resistant strains (MIC, 128 micrograms/ml). Polyclonal antibodies specifically reacting with the low-affinity PBP of Enterococcus hirae, Enterococcus faecalis, and Enterococcus faecium (M. Ligozzi, M. Aldegheri, S. C. Predari, and R. Fontana, FEMS Microbiol. Lett. 83:335-340, 1991) were used to determine the amount of this PBP in the E. faecium isolates. In all strains, the antibody preparation reacted with a membrane protein of the same molecular mass as PBP 5. The amount of this protein was very small in the susceptible strain but large in all of the resistant strains. These results suggest that the highly resistant strains also overproduced the low-affinity PBP, which, compared with PBP 5 of moderately resistant strains, appeared to be modified in its penicillin-binding capability.

Ampicillin Resistance↗

Efficacies of ABT-719 and related 2-pyridones, members of a new class of antibacterial agents, against experimental bacterial infections.

The 2-pyridones are a new class of broad-spectrum orally bioavailable antibacterial agents. These compounds are potent bacterial DNA gyrase inhibitors which differ from fluoroquinolones by placement of the nitrogen atom in the ring juncture. ABT-719 is an S isomer and a representative 2-pyridone. ABT-719 administered orally or subcutaneously was 4- to 10-fold more effective than ciprofloxacin against Staphylococcus aureus, Streptococcus pneumoniae, and Streptococcus pyogenes infections in normal mice. ABT-719 was equivalent in efficacy to ciprofloxacin for treatment of gram-negative bacterial infections caused by Pseudomonas aeruginosa or Escherichia coli. The racemate and R forms of ABT-719 produced similar results against gram-positive and gram-negative bacterial infections. The 50% effective doses of ABT-719 were at least threefold lower than those of ciprofloxacin for therapy of intracellular infections caused by Salmonella typhimurium or Listeria monocytogenes. In immunosuppressed mice, ABT-719 was more effective than ciprofloxacin against quinolone-sensitive S. aureus, Enterococcus faecalis, and Enterococcus faecium. The pharmacokinetic properties of ABT-719 were consistent with its relative efficacy. The 2-pyridones are potent, orally available antibacterial agents with efficacy against gram-positive and gram-negative bacterial infections in mice.

Animals↗

Antimicrobial activity of DU-6681a, a parent compound of novel oral carbapenem DZ-2640.

The in vitro antibacterial activity of DU-6681a, a parent compound of DZ-2640, against gram-positive and -negative bacteria was compared with those of penems and cephalosporins currently available. MICs at which 90% of the isolates are inhibited (MIC90s) of the compound for clinical isolates of methicillin-susceptible and -resistant Staphylococcus aureus and Staphylococcus epidermidis, including methicillin-susceptible and -resistant strains, were 0.10, 25, and 12.5 microg/ml, respectively. DU-6681a inhibited the growth of all strains of Streptococcus pyogenes and of penicillin-susceptible and -insusceptible Streptococcus pneumoniae at 0.006, 0.025, and 0.20 microg/ml, respectively, and MIC90s of the compound were 6.25 and >100 microg/ml for Enterococcus faecalis and Enterococcus faecium, respectively. MIC90s of DU-6681a were 0.20, 0.10, and 0.025 microg/ml for Haemophilus influenzae, Moraxella catarrhalis, and Neisseria gonorrhoeae, respectively. For Pseudomonas aeruginosa, the MIC50 and MIC90 of DU-6681a were 25 and 50 microg/ml, respectively. DU-6681a activity was not affected by different media, varied inoculum size (10(4) to 10(7) CFU), or the addition of human serum but was decreased under acidic conditions against gram-negative bacteria, under alkaline conditions against gram-positive bacteria, and in human urine, as was the activity of the other antibiotics tested. The frequency of spontaneous resistance to DU-6681a was less than or equal to those of the reference compounds. Time-kill curve studies demonstrated the bactericidal action of DU-6681a against S. aureus, S. pneumoniae, Escherichia coli, and H. influenzae.

Administration, Oral↗

Antimicrobial activities of mefloquine and a series of related compounds.

Mefloquine was found to have bactericidal activity against methicillin- and fluoroquinolone-susceptible and -resistant strains of Staphylococcus aureus and Staphylococcus epidermidis and gentamicin- and vancomycin-resistant strains of Enterococcus faecalis and Enterococcus faecium. The MICs were 16 microg/ml, and the minimal bactericidal concentrations (MBCs) were 16 to 32 microg/ml. These concentrations cannot be achieved in serum. Mefloquine was active at a more achievable concentration against penicillin-susceptible and -resistant Streptococcus pneumoniae, with MICs of 0.2 to 1.5 microg/ml. Mefloquine was not active against gram-negative bacteria and yeasts. In an attempt to find more active derivatives, 400 mefloquine-related compounds were selected from the chemical inventory of The Walter Reed Army Institute of Research. We identified a series of compounds containing a piperidine methanol group attached to pyridine, quinoline, and benzylquinoline ring systems. These had activities similar to that of mefloquine against S. pneumoniae but were far more active against other gram-positive bacteria (MICs for staphylococci, 0.8 to 6.3 microg/ml). They had activities similar to that of amphotericin B against Candida spp. and Cryptococcus neoformans. Combinations of the compounds with gentamicin and vancomycin were additive against staphylococci and pneumococci. The MIC and MBC of gentamicin were decreased by four- to eightfold when this drug was combined with limiting dilutions of the compounds. There was no antagonism with other antimicrobial drugs. The compounds were rapidly bactericidal. They appear to act by disrupting cell membranes. Combinations of the compounds with aminoglycoside antibiotics may have potential for therapeutic use.

Anti-Bacterial Agents↗

In vitro antimicrobial activities of novel anilinouracils which selectively inhibit DNA polymerase III of gram-positive bacteria.

The 6-anilinouracils are novel dGTP analogs that selectively inhibit the replication-specific DNA polymerase III of gram-positive eubacteria. Two specific derivatives, IMAU (6-[3'-iodo-4'-methylanilino]uracil) and EMAU (6-[3'-ethyl-4'-methylanilino]uracil), were substituted with either a hydroxybutyl (HB) or a methoxybutyl (MB) group at their N3 positions to produce four agents: HB-EMAU, MB-EMAU, HB-IMAU, and MB-IMAU. These four new agents inhibited Staphylococcus aureus, coagulase-negative staphylococci, Enterococcus faecalis, and Enterococcus faecium. Time-kill assays and broth dilution testing confirmed bactericidal activity. These anilinouracil derivatives represent a novel class of antimicrobials with promising activities against gram-positive bacteria that are resistant to currently available agents, validating replication-specific DNA polymerase III as a new target for antimicrobial development.

Anti-Bacterial Agents↗

Nitrofurantoin is active against vancomycin-resistant enterococci.

The activity of nitrofurantoin was tested against 300 isolates of Enterococcus faecium, Enterococcus faecalis, and Enterococcus gallinarum. No isolates tested were resistant to nitrofurantoin (MIC, >/=128 microg/ml), including vancomycin-resistant E. faecium isolates with vanA- and vanB-positive genotypes and vancomycin-resistant E. gallinarum isolates. We conclude that nitrofurantoin may provide effective treatment of urinary tract infections caused by vancomycin-resistant enterococci.

Anti-Bacterial Agents↗

In vitro antibacterial activities of DQ-113, a potent quinolone, against clinical isolates.

The antibacterial activity of DQ-113, formerly D61-1113, was compared with those of antibacterial agents currently available. MICs at which 90% of the isolates tested are inhibited (MIC90s) of DQ-113 against clinical isolates of methicillin-susceptible and -resistant Staphylococcus aureus and methicillin-susceptible and -resistant coagulase-negative staphylococci were 0.03, 0.008, 0.03, and 0.06 microg/ml, respectively. Moreover, DQ-113 showed the most potent activity against ofloxacin-resistant and methicillin-resistant S. aureus, with a MIC90 of 0.25microg/ml. DQ-113 inhibited the growth of all strains of Streptococcus pneumoniae, including penicillin-resistant strains, and Streptococcus pyogenes at 0.06 microg/ml, and DQ-113 was more active than the other quinolones tested against Enterococcus faecalis and Enterococcus faecium with MIC90s of 0.25 and 2 microg/ml, respectively. Against vancomycin-resistant enterococci, DQ-113 showed the highest activity among the reference compounds, with a MIC range from 0.25 to 2 microg/ml. DQ-113 also showed a potent activity against Haemophilus influenzae, including ampicillin-resistant strains (MIC90, 0.015 microg/ml), and Moraxella catarrhalis (MIC90, 0.03 microg/ml). The activity of DQ-113 was roughly comparable to that of levofloxacin against all species of ENTEROBACTERIACEAE: The MICs of DQ-113 against ofloxacin-susceptible Pseudomonas aeruginosa ranged from 0.25 to 2 microg/ml, which were four times higher than those of ciprofloxacin. From these results, DQ-113 showed the most potent activity against gram-positive pathogens among antibacterial agents tested.

Anti-Infective Agents↗

Heterogeneity of macrolide-lincosamide-streptogramin B resistance phenotypes in enterococci.

We determined the macrolide resistance phenotypes of 241 clinical isolates of erythromycin-resistant enterococci (MICs, > or = 1 microg/ml), including 147 Enterococcus faecalis strains and 94 Enterococcus faecium strains, collected from a hospital in Seoul, Korea, between 1999 and 2000. By the erythromycin (40 micro g)-josamycin (100 microg) double-disk test, 93 strains were assigned to the constitutive macrolide, lincosamide, and streptogramin B (MLS(B)) resistance (cMLS(B)) phenotype, and the remaining 148 strains were assigned to the inducible MLS(B) resistance (iMLS(B)) phenotype. Of the strains with the iMLS(B) phenotype, 36 exhibited a reversibly inducible MLS(B) (riMLS(B)) phenotype, i.e., blunting of the erythromycin zone of inhibition, which indicates that the 16-membered-ring macrolide josamycin is a more effective inducer than the 14-membered-ring macrolide erythromycin. Sequence analysis of the regulatory regions of the erm(B) genes from all of the strains exhibiting the riMLS(B) phenotype revealed not only erm(Bv) [where v represents variant; previously erm(AMR)] (n = 13), as reported previously, but also three kinds of erm(B) variants, which were designated erm(Bv1) (n = 17), erm(Bv2) (n = 3), and erm(Bv3) (n = 3), respectively. In lacZ reporter gene assays of these variants, the 16-membered-ring macrolide tylosin had stronger inducibility than erythromycin at > or = 0.1 microg/ml. These findings highlight the versatility of erm(B) in induction specificity.

Anti-Bacterial Agents↗

Usnic acid, a natural antimicrobial agent able to inhibit bacterial biofilm formation on polymer surfaces.

In modern medicine, artificial devices are used for repair or replacement of damaged parts of the body, delivery of drugs, and monitoring the status of critically ill patients. However, artificial surfaces are often susceptible to colonization by bacteria and fungi. Once microorganisms have adhered to the surface, they can form biofilms, resulting in highly resistant local or systemic infections. At this time, the evidence suggests that (+)-usnic acid, a secondary lichen metabolite, possesses antimicrobial activity against a number of planktonic gram-positive bacteria, including Staphylococcus aureus, Enterococcus faecalis, and Enterococcus faecium. Since lichens are surface-attached communities that produce antibiotics, including usnic acid, to protect themselves from colonization by other bacteria, we hypothesized that the mode of action of usnic acid may be utilized in the control of medical biofilms. We loaded (+)-usnic acid into modified polyurethane and quantitatively assessed the capacity of (+)-usnic acid to control biofilm formation by either S. aureus or Pseudomonas aeruginosa under laminar flow conditions by using image analysis. (+)-Usnic acid-loaded polymers did not inhibit the initial attachment of S. aureus cells, but killing the attached cells resulted in the inhibition of biofilm. Interestingly, although P. aeruginosa biofilms did form on the surface of (+)-usnic acid-loaded polymer, the morphology of the biofilm was altered, possibly indicating that (+)-usnic acid interfered with signaling pathways.

Anti-Bacterial Agents↗

Acquisition of resistant bowel flora during a double-blind randomized clinical trial of ertapenem versus piperacillin-tazobactam therapy for intraabdominal infections.

Bowel colonization with resistant bacteria can develop in patients receiving broad-spectrum antimicrobial therapy. We compared the impact of two antimicrobial regimens often used to treat intraabdominal infections on susceptibility patterns of bowel flora at the end of therapy. In a double-blind clinical trial, adults with complicated intraabdominal infection requiring surgery were randomized to receive piperacillin-tazobactam (3.375 g every 6 h) or ertapenem (1 g once a day) for 4 to 14 days. Rectal swabs were obtained at baseline and at the end of study therapy to determine the acquisition rates of Enterobacteriaceae resistant to the study drug, extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli or Klebsiella species, Pseudomonas aeruginosa resistant to imipenem or piperacillin-tazobactam, and vancomycin-resistant Enterococcus faecalis or Enterococcus faecium. Treated patients were assessable for the acquisition of resistant bacteria if appropriate specimens were obtained at both time points. Enterobacteriaceae resistant to the treatment received were acquired during study therapy by 8/122 assessable piperacillin-tazobactam recipients (6.6%) compared to 0/122 assessable ertapenem recipients (P = 0.007). Neither ESBL-producing E. coli or Klebsiella species nor P. aeruginosa resistant to piperacillin-tazobactam was isolated from patients in either treatment group. Imipenem-resistant P. aeruginosa was acquired by two of the ertapenem recipients (1.6%) versus zero of the piperacillin-tazobactam recipients (P = 0.50). Vancomycin-resistant enterococci were acquired during therapy by 8/125 assessable ertapenem recipients (6.4%) versus 2/123 assessable piperacillin-tazobactam recipients (1.6%; P = 0.10). In this study, the acquisition of resistant Enterobacteriaceae occurred significantly more often in patients treated with piperacillin-tazobactam than in those treated with ertapenem.

Abdominal Abscess↗

Macrophage response to bacteria: induction of marked secretory and cellular activities by lipoteichoic acids.

Lipoteichoic acids (LTAs) from various bacterial species, including Staphylococcus aureus, Streptococcus pyogenes, Streptococcus pneumoniae, Enterococcus faecalis, and Listeria monocytogenes, were examined for the ability to induce secretory and cellular responses in a pure population of bone marrow-derived mononuclear phagocytes. Some of the highly purified LTAs, in particular LTAs from Bacillus subtilis, S. pyogenes, E. faecalis, and Enterococcus hirae, were able to affect each of the macrophage parameters measured, i.e., reductive capacity, secretion of tumor necrosis factor and nitrite, and tumoricidal activity. As after stimulation with whole organisms or other bacterial products, secretion of tumor necrosis factor induced by these LTAs reached its maximum within the first few hours of the interaction, while secretion of nitrite and tumoricidal activity required 24 to 36 h for full expression. Other purified LTAs, i.e., LTAs from Streptococcus sanguis, S. pneumoniae, and L. monocytogenes, as well as lipomannan from Micrococcus luteus affected only some of these parameters, while native LTA from S. aureus was inactive. There was no obvious correlation between biological activity and chain length, kind of glycosyl substituents, glycolipid structures, or fatty acid composition of LTAs. Deacylation of LTAs resulted in a complete loss of activity, and deacylated LTAs did not impair the activity of their acylated counterparts, suggesting that acyl chains may be essential for binding of LTA to the cell surface. The results demonstrate that some LTA species are potent inducers of macrophage secretory and cellular activities.

Animals↗

Vancomycin-resistant Leuconostoc mesenteroides and Lactobacillus casei synthesize cytoplasmic peptidoglycan precursors that terminate in lactate.

The emergence of acquired high-level resistance among Enterococcus species has renewed interest in mechanisms of resistance to glycopeptide antibiotics in gram-positive bacteria. In Enterococcus faecalis and Enterococcus faecium, resistance is encoded by the van gene cluster and is due to the production of a peptidoglycan precursor terminating in D-alanyl-D-lactate, to which vancomycin does not bind. Most Leuconostoc and many Lactobacillus species are intrinsically resistant to high levels of glycopeptide antibiotics, but the mechanism of resistance has not been elucidated. To determine whether the mechanisms of resistance are similar in intrinsically resistant bacteria, cytoplasmic peptidoglycan precursors were isolated from Leuconostoc mesenteroides and Lactobacillus casei and analyzed by mass spectrometry, revealing structures consistent with UDP-N-acetylmuramyl-L-Ala-D-Glu-L-Lys-(L-Ala)-D-Ala-D-lactate and UDP-N-acetylmuramyl-L-Ala-D-Glu-L-Lys-D-Ala-D-lactate, respectively.

Amino Acid Sequence↗

DNA probe for identification of Streptococcus pneumoniae.

A total of 287 clinical isolates of Streptococcus pneumoniae (pneumococcus) were tested for their ability to undergo autolysis when treated with sodium deoxycholate. The test was positive for all but one isolate, strain DOC-1. This autolysis required the activity of an enzyme which is unique and characteristic of S. pneumoniae: a choline-dependent N-acetylmuramoyl-L-alanine amidase, the gene product of the lytA gene. We used lytA as a DNA probe to test the distribution of the autolysin gene among clinical isolates of S. pneumoniae. In dot blot hybridization experiments our probe reacted with the DNA of 60 of 60 strains tested, including the autolysis-deficient clinical isolate DOC-1. No hybridization occurred when strains of Streptococcus sanguis, Streptococcus mutans, Streptococcus pyogenes, Streptococcus (Enterococcus) faecalis, Streptococcus (Enterococcus) faecium, Streptococcus agalactiae, and Streptococcus bovis were tested. The lytA gene appears to be an ideal candidate for use as a DNA probe for the identification of S. pneumoniae.

Amidohydrolases↗

Typing of Enterococcus species by DNA restriction fragment analysis.

Enterococci are a frequent cause of hospital-acquired infection, being associated with urinary tract infections, wound sepsis, bacteremia, and endocarditis. The source of infection is usually thought to be endogenous, but some evidence points to cross-infection between patients. A better understanding of the epidemiology of enterococci has been limited by the lack of a good discriminatory typing system. This report describes the application of two DNA-based typing methods to Enterococcus faecalis and Enterococcus faecium: comparison of restriction fragments from total DNA by conventional electrophoresis and comparison of restriction fragments hybridizing to an rRNA gene probe (ribotyping). Comparison of restriction fragments (from SstI digestion) by conventional electrophoresis was simple and highly discriminatory. The results of analysis of blood culture isolates and of repeat isolates from individual patients are reported. Ribotyping (with BscI digestion) was more applicable at the level of species discrimination.

Bacteremia↗

Use of cephalexin-aztreonam-arabinose agar for selective isolation of Enterococcus faecium.

Cephalexin-aztreonam-arabinose agar (CAA), a new selective agar, was examined in comparison with nalidixic acid-colistin agar for the differentiation of Enterococcus faecium from other enterococci and the ability to isolate the organism from feces. Two hundred sixteen enterococcus isolates and a variety of gram-positive and gram-negative control strains were inoculated onto both media. All control strains of E. faecium were easily differentiated from Enterococcus faecalis and Enterococcus durans on the basis of arabinose fermentation on CAA. Differentiation of E. faecium from other enterococci or Streptococcus bovis was not possible on nalidixic acid-colistin agar. Increased isolation of E. faecium was demonstrated on CAA when both media were compared for the isolation of the organism from feces. CAA has been shown to possess excellent differential and selective features allowing the simple and effective isolation of E. faecium from heavily contaminated sites.

Agar↗

Evaluation of a new system, VITEK 2, for identification and antimicrobial susceptibility testing of enterococci.

We evaluated the new automated VITEK 2 system (bioMérieux) for the identification and antimicrobial susceptibility testing of enterococci. The results obtained with the VITEK 2 system were compared to those obtained by reference methods: standard identification by the scheme of Facklam and Sahm [R. R. Facklam and D. F. Sahm, p. 308-314, in P. R. Murray et al., ed., Manual of Clinical Microbiology, 6th ed., 1995] and with the API 20 STREP system and, for antimicrobial susceptibility testing, broth microdilution and agar dilution methods by the procedures of the National Committee for Clinical Laboratory Standards. The presence of vanA and vanB genes was determined by PCR. A total of 150 clinical isolates were studied, corresponding to 60 Enterococcus faecalis, 55 Enterococcus faecium, 26 Enterococcus gallinarum, 5 Enterococcus avium, 2 Enterococcus durans, and 2 Enterococcus raffinosus isolates. Among those isolates, 131 (87%) were correctly identified to the species level with the VITEK 2 system. Approximately half of the misidentifications were for E. faecium with low-level resistance to vancomycin, identified as E. gallinarum or E. casseliflavus; however, a motility test solved the discrepancies and increased the agreement to 94%. Among the strains studied, 66% were vancomycin resistant (57 VanA, 16 VanB, and 26 VanC strains), 23% were ampicillin resistant (MICs, >/=16 microgram/ml), 31% were high-level gentamicin resistant, and 45% were high-level streptomycin resistant. Percentages of agreement for susceptibility and resistance to ampicillin, vancomycin, and teicoplanin and for high-level gentamicin resistance and high-level streptomycin resistance were 93, 95, 97, 97, and 96%, respectively. The accuracy of identification and antimicrobial susceptibility testing of enterococci with the VITEK 2 system, together with the significant reduction in handling time, will have a positive impact on the work flow of the clinical microbiology laboratory.

Bacterial Typing Techniques↗

Evaluation of 15 motility media and a direct microscopic method for detection of motility in enterococci.

Isolation of motile, vanC enterococci has yet to be a major infection control concern; however, rapid detection still is important. We evaluated 15 motility media from three manufacturers and a 2-h direct microscopic method for accurate detection of 89 enterococcal strains, including 72 vanC enterococcal strains. Resistance genes were confirmed by a multiplex PCR method with the vanC gene detected in all motile enterococci. Motility in the 72 vanC enterococci was detected at 30 degrees C within 72 h in BD Biosciences motility nitrate medium and in Remel motility B medium, motility B medium supplemented with methyl-alpha-D-glucopyranoside (investigational), motility S medium, motility test medium, and motility test medium with tetrazolium indicator. Motility was also observed for all vanC enterococci with the 2-h direct (30 degrees C incubation) microscopic detection method. All Enterococcus faecalis and Enterococcus faecium isolates were observed to be nonmotile in all media and by the direct microscopic method. Since differences between the various motility media tested were observed, the medium used for detection of enterococcal motility must be selected carefully.

Bacterial Proteins↗

Enterococcal meningitis caused by Enterococcus casseliflavus. First case report.

BACKGROUND: Enterococcal meningitis is an uncommon disease usually caused by Enterococcus faecalis and Enterococcus faecium and is associated with a high mortality rate. Enterococcus casseliflavus has been implicated in a wide variety of infections in humans, but never in meningitis. CASE PRESENTATION: A 77-year-old Italian female presented for evaluation of fever, stupor, diarrhea and vomiting of 3 days duration. There was no history of head injury nor of previous surgical procedures. She had been suffering from rheumatoid arthritis for 30 years, for which she was being treated with steroids and methotrexate. On admission, she was febrile, alert but not oriented to time and place. Her neck was stiff, and she had a positive Kernig's sign. The patient's cerebrospinal fluid was opalescent with a glucose concentration of 14 mg/dl, a protein level of 472 mg/dl, and a white cell count of 200/muL with 95% polymorphonuclear leukocytes and 5% lymphocytes. Gram staining of CSF revealed no organisms, culture yielded E. casseliflavus. The patient was successfully treated with meropenem and ampicillin-sulbactam. CONCLUSIONS: E. casseliflavus can be inserted among the etiologic agents of meningitis. Awareness of infection of central nervous system with Enterococcus species that possess an intrinsic vancomycin resistance should be increased.

Aged↗