Do intraoperative pyloric interventions predict the need for postoperative endoscopic interventions after minimally invasive esophagectomy?

Intraoperative pyloric procedures are often performed during esophagectomies to reduce the rates of gastric conduit dysfunction. They include pyloroplasty (PP), pyloromyotomy (PM), and pylorus botulinum toxin type-A injections (BI). Despite these procedures, patients frequently warrant further endoscopic interventions. The aim of this study is to compare intraoperative pyloric procedures and the rates of postoperative endoscopic interventions following minimally invasive esophagectomy (MIE). We identified patients who underwent MIE for esophageal carcinoma and grouped them as 'None' (no intervention), 'PP', 'PM', or 'BI' based on intraoperative pyloric procedure type. The rates of endoscopic interventions for the first six postoperative months were compared. To adjust for variability due to MIE type, the rates of >1 interventions were compared using a zero-inflated Poisson regression analysis. Significance was established at P < 0.05. There were 146 patients who underwent an MIE for esophageal cancer from 2008 to 2015; 77.4% were three-hole MIE, and 22.6% were Ivor- Lewis MIE. BI was most frequent in Ivor-Lewis patients (63.5%), while PP was most frequent (46.9%) in three-hole patients. Postoperative endoscopic interventions occurred in 38 patients (26.0%). The BI group had the highest percentage of patients requiring a postoperative intervention (n = 13, 31.7%). After adjusting for higher rates of interventions in three-hole MIE patients, the BI and None groups had the lowest rates of >1 postoperative interventions. Our data did not show superiority of any pyloric intervention in preventing endoscopic interventions. The patients who received BI to the pylorus demonstrated a trend toward a greater likelihood of having a postoperative intervention. However when adjusted for type of MIE, the BI and None groups had lower rates of subsequent multiple interventions. Further research is needed to determine if the choice of intraoperative pyloric procedure type significantly affects quality of life, morbidity, and overall prognosis in these patients.

Why are there no new antibiotics?

Renewed efforts are underway in the pharmaceutical industry to address the growing problem of antibiotic resistant pathogens. With this rededication to novel antibiotic discovery, new tools and technologies are being deployed to understand critical therapeutic intervention points in bacterial metabolism.

38th Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC), September 24-27, 1998, San Diego, CA, USA

This year's ICAAC meeting was dominated by exciting late-stage development antibiotics that represent breakthroughs in covering pathogens of unmet medical need, including drug-resistant pathogens. There are several exciting antibiotics in late-stage development, among them, linezolid, gatifloxacin, moxifloxacin, SB-265805, HMR 3647, SCH27899 and the resurrected daptomycin. The development of new technology for screening and the cross-application into genomics have led to numerous breakthroughs in techniques and strategies for the identification of novel prokaryotic targets.

39th Interscience Conference on Antimicrobial Agents and Chemotherapyof the American Society for Microbiology

The 39th ASM ICAAC Meeting, attended by over 16,000 delegates, highlighted numerous late-stage development antibacterials. The presentation of over 600 reports (posters, symposia and oral presentations) regarding resistance emergence underscores the evolving landscape of antibiotic susceptibility worldwide. Although bacterial genomic efforts are slowly expanding the potential sources of novel targets, the established antibacterial classes, including quinolones, beta-lactams, protein synthesis inhibitors and carbapenems, were most prevalent among the presentations. Quinolones dominated this conference, with many presentations of moxifloxacin (> 72 presentations), gatifloxacin (> 66 presentations) and gemifloxacin (> 59 presentations). The new class of antibacterials, the oxazolidinones, represented by Linezolid, was also highlighted.

98th General Meeting of the American Society for Microbiology

The 98th General Meeting of the American Society for Microbiology was held from May 17-21, 1998, in Atlanta, Georgia and was attended by well over 10,000 scientists. The theme of antibiotic resistance dominated the meeting with numerous presentations on resistance mechanisms, new targets and potential antimicrobial agents. Many new insights into the understanding of microbial physiology were provided. Microbial genomics was shown to be revolutionizing the way in which scientists can probe and explore bacteria and fungi.

Role of penicillin-binding protein 4 in expression of vancomycin resistance among clinical isolates of oxacillin-resistant Staphylococcus aureus

It has been reported that penicillin-binding protein 4 (PBP4) activity decreases when a vancomycin-susceptible Staphylococcus aureus isolate is passaged in vitro to vancomycin resistance. We analyzed the PBP profiles of four vancomycin intermediately susceptible S. aureus (VISA) clinical isolates and found that PBP4 was undetectable in three isolates (HIP 5827, HIP 5836, and HIP 6297) and markedly reduced in a fourth (Mu50). PBP4 was readily visible in five vancomycin-susceptible, oxacillin-resistant S. aureus (ORSA) isolates. The nucleotide sequences of the pbp4 structural gene and flanking sequences did not different between the VISA and vancomycin-susceptible isolates. Overproduction of PBP4 on a high-copy-number plasmid in the VISA isolates produced a two- to threefold decrease in vancomycin MICs. Inactivation of pbp4 by allelic replacement mutagenesis in three vancomycin-susceptible ORSA strains (COL, RN450M, and N315) led to a decrease in vancomycin susceptibility, an increase in highly vancomycin-resistant subpopulations, and decreased cell wall cross-linking by high-performance liquid chromatography analysis. Complementation of the COL mutant with plasmid-encoded pbp4 restored the vancomycin MIC and increased cell wall cross-linking. These data suggest that alterations in PBP4 expression are at least partially responsible for the VISA phenotype.

American Society of Microbiology - 101st General Meeting. 20-24 May 2001, Orlando, FL, USA

Sessions on prokaryotic genomics, bioinformatics, antibiotic resistance, intrinsic antibacterial resistance, and the identification of novel targets were the main highlights of this year's American Society Microbiology (ASM) meeting. In addition, updates on the status of antimicrobial developmental candidates and recently approved agents, were also discussed.

American Society of Microbiology 101st General Meeting. 20-24 May 2001, Orlando, FL, USA

The application of sophisticated molecular biology, genetics and genomics has made possible the advanced analyses of microbial genes, the topology of DNA and chromosomes, and insight into the regulation of gene expression during all stages of the life cycle of microbes, both in vitro and in vivo. The struggle to control contagious pathogens continues world wide amidst resistance emergence to many classes of antimicrobial agents. Many hospital, research and community labs are applying themselves to a more thorough understanding of the molecular basis of this resistance. New drugs which improve on predecessor agents were presented. The following classes of antimicrobial agents were represented: quinolones, cephems, macrolides and natural products. New target opportunities against both lethal (essential) gene targets and virulence targets were presented throughout the conference. In addition, increasing attention to the involvement of microbial life forms in immune function and dysfunction were described in numerous presentations.

American Society of Microbiology - 100th General Meeting

Symposium sessions on genomics, surveillance, and pharmaceutical intervention opportunities were highlights of this annual ASM meeting. Two-component signal transduction was highlighted by both academic and industrial representatives, as was prokaryotic genomics. Recurring themes throughout the meeting were the contribution of efflux mechanisms to worldwide resistance, target modifications responsible for fluoroquinolone resistance, and the role of structural biology in the discovery and exploitation of bacterial targets.

Comparison of the D-glutamate-adding enzymes from selected gram-positive and gram-negative bacteria

The biochemical properties of the D-glutamate-adding enzymes (MurD) from Escherichia coli, Haemophilus influenzae, Enterococcus faecalis, and Staphylococcus aureus were investigated to detect any differences in the activity of this enzyme between gram-positive and gram-negative bacteria. The genes (murD) that encode these enzymes were cloned into pMAL-c2 fusion vector and overexpressed as maltose-binding protein-MurD fusion proteins. Each fusion protein was purified to homogeneity by affinity to amylose resin. Proteolytic treatments of the fusion proteins with factor Xa regenerated the individual MurD proteins. It was found that these fusion proteins retain D-glutamate-adding activity and have Km and Vmax values similar to those of the regenerated MurDs, except for the H. influenzae enzyme. Substrate inhibition by UDP-N-acetylmuramyl-L-alanine, the acceptor substrate, was observed at concentrations greater than 15 and 30 microM for E. coli and H. influenzae MurD, respectively. Such substrate inhibition was not observed with the E. faecalis and S. aureus enzymes, up to a substrate concentration of 1 to 2 mM. In addition, the two MurDs of gram-negative origin were shown to require monocations such as NH4+ and/or K+, but not Na+, for optimal activity, while anions such as Cl- and SO4(2-) had no effect on the enzyme activities. The activities of the two MurDs of gram-positive origin, on the other hand, were not affected by any of the ions tested. All four enzymes required Mg2+ for the ligase activity and exhibited optimal activities around pH 8. These differences observed between the gram-positive and gram-negative MurDs indicated that the two gram-negative bacteria may apply a more stringent regulation of cell wall biosynthesis at the early stage of peptidoglycan biosynthesis pathway than do the two gram-positive bacteria. Therefore, the MurD-catalyzed reaction may constitute a fine-tuning step necessary for the gram-negative bacteria to optimally maintain its relatively thin yet essential cell wall structure during all stages of growth.

Identification and characterization of cell wall-cell division gene clusters in pathogenic gram-positive cocci

Clusters of peptidoglycan biosynthesis and cell division genes (DCW genes) were identified and sequenced in two gram-positive cocci, Staphylococcus aureus and Enterococcus faecalis. The results indicated some similarities in organization compared with previously reported bacterial DCW gene clusters, including the presence of penicillin-binding proteins at the left ends and ftsA and ftsZ cell division genes at the right ends of the clusters. However, there were also some important differences, including the absence of several genes, the comparative sizes of the div1B and ftsQ genes, and a wide range of amino acid sequence similarities when the genes of the gram-positive cocci were translated and compared to bacterial homologs.

The 97th Annual Meeting of the American Society for Microbiology

The Annual Meeting of the American Society for Microbiology took place in Miami Beach, Florida, from May 4-8, 1997. Over 9000 scientists attended this meeting, which covers all major aspects of prokaryotic research (basic, applied, medical, and diagnostic). Genomics discussions were a major part of the meeting agenda, with scientists detailing both basic and applied research effort using genomics and bioinformatics. New ideas for potential novel antimicrobials have also surfaced as the tools to pursue Drug Discovery have fallen into place and pharmaceutical companies have ;rediscovered' anti-infectives.

Direct quantitation of the number of individual penicillin-binding proteins per cell in Escherichia coli

The penicillin-binding proteins (PBPs) are a set of enzymes that participate in the terminal stages of bacterial peptidoglycan assembly. As their name implies, these proteins also covalently bind and are inhibited by beta-lactam antibiotics. Although many studies have examined the relative binding affinities of a number of beta-lactam antibiotics, a surprisingly small number of studies have addressed the absolute numbers of each of the PBPs present in the bacterial cell. In the present study, the PBP values initially reported in Escherichia coli almost 20 years ago by B. G. Spratt (Eur. J. Biochem. 72:341-352, 1977) were refined. The individual PBPs from a known number of bacteria radiolabeled with [3H]benzylpenicillin were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The radioactive bands were located, excised, and quantitatively extracted from the gel slices. The radioactivity was measured by scintillation counting, and the absolute disintegrations per minute were calculated. From the specific activity of the labeled penicillin, the absolute disintegrations per minute, and the CFU per milliliter, a determination of the number of each of the PBPs per cell was made. The measurements were performed on multiple samples to place statistical limits on the numbers obtained. The values for the individual PBPs found in E. coli deviated in several ways from the previously reported observations. Of particular significance is the higher number of molecules of PBP 2 and 3 observed, since these PBPs are known to participate in cell morphogenesis. The PBP content in both rich Luria broth medium and M9 minimal medium was determined, with the slower-growing cells in minimal medium possessing fewer of the individual PBPs per cell.

Role of mecA transcriptional regulation in the phenotypic expression of methicillin resistance in Staphylococcus aureus

The gene required for methicillin resistance in staphylococci, mecA, encodes the low-affinity penicillin-binding protein 2a (PBP2a). Transcriptional regulation of mecA is accomplished in some isolates by mecR1 and mecI, cotranscribed chromosomal genes that encode a putative signal transducer and a transcriptional repressor, respectively. Two Staphylococcus aureus strains that have identical mecR1-mecI nucleotide sequences, BMS1 and N315P, both exhibit low-level, heterotypic expression of methicillin resistance and contain no beta-lactamase coregulatory sequences. mecR1-mecI was amplified from BMS1 by PCR and was shown to be functional on a high-copy-number plasmid when introduced into an S. aureus strain with a deleted mecR1-mecI locus. Cloned mecR1-mecI repressed phenotypic expression of methicillin resistance, mecA transcription and PBP2a production and mediated PBP2a induction in response to certain beta-lactam antibiotics. However, mecR1-mecI had different regulatory activities in its native chromosomal location in N315P compared with those in BMS1. Uninduced mecA transcription was markedly repressed in N315P, and mecI inactivation increased mecA transcription and PBP2a production 5- and 40-fold, respectively. Furthermore, the N315P phenotype changed from low-level, heterotypic resistance with intact mecI to high-level, homotypic resistance in strains with disrupted mecI. In contrast, uninduced BMS1 produced abundant mecA transcript and PBP2a, while the disruption of mecI had no effect on phenotype and little effect on mecA transcription or PBP2a production. Thus, mecI-mediated repression of mecA appears to be dysfunctional in BMS1 because of the presence or absence of additional regulatory cofactors. Furthermore, heterotypic resistance expression in this strain is independent of mecA transcriptional regulation.

Mobilization of vancomycin resistance by transposon-mediated fusion of a VanA plasmid with an Enterococcus faecium sex pheromone-response plasmid

A striking feature of recent outbreaks of vancomycin-resistant (VmR) enterococci is the apparent horizontal dissemination of resistance determinants. The plasmids pHKK702 and pHKK703 from Enterococcus faecium clinical isolate R7 have been implicated in the conjugal transfer of VmR. pHKK702 is a 41-kb plasmid that contains an element indistinguishable from the glycopeptide-resistance transposon Tn1546. pHKK703 is an approx. 55-kb putative sex pheromone-response plasmid that is required for conjugative mobilization of pHKK702. During experiments in which strain R7 was used as a donor, a highly conjugative VmR transconjugant was isolated that formed constitutive cellular aggregates. Restriction analyses and DNA hybridizations revealed that the transconjugant harbored a single plasmid of approx. 92 kb and this plasmid (pHKK701) was composed of DNA from both pHKK702 and pHKK703. Results from DNA sequence analyses showed that a 39-kb composite transposon (Tn5506) from pHKK702 had inserted into pHKK703. The left end of Tn5506 contained a single insertion sequence (IS) element, IS1216V2, whereas the right end was composed of a tandem IS structure consisting of the novel 1065-bp IS1252 nested within an IS1216V1 element. Transposition of Tn5506 from pHKK702 to pHKK703 created an 8-bp target sequence duplication at the site of insertion and interrupted an ORF (ORFX) that was 91% identical to that of prgX, a gene proposed to negatively regulate sex pheromone response of the E.faecalis plasmid, pCF10. We propose that the interruption of ORFX by Tn5506 led to the constitutive cellular aggregation phenotype and thereby enhanced the efficiency with which VmR was transferred. Similar IS1216V-mediated transposition events may contribute to the horizontal spread of glycopeptide resistance among enterococci in nature.

Characterization of IS1272, an insertion sequence-like element from Staphylococcus haemolyticus

We have previously shown (G. L. Archer, D. M. Niemeyer, J. A. Thanassi, and M. J. Pucci, Antimicrob. Agents Chemother. 38:447-454, 1994) that some methicillin-resistant staphylococcal isolates contain a partial deletion of the genes (mecR1 and mecI) that regulate the transcription of the methicillin resistance structural gene (mecA). When a fragment of DNA inserted at the point of the mecR1 deletion was used as a probe, hybridization with multiple bands was detected for Staphylococcus haemolyticus genomic DNA. In the present study, DNA sequencing of four unique clones recovered from a lambda library of S. haemolyticus revealed identical 1,934-bp elements. Each element, designated IS1272, contained 16-bp terminal inverted repeats (sequence identity, 15 of 16 bp) and two open reading frames of 819 and 687 bp; there were no flanking target site duplications. Database searches yielded amino acid homology with proteins predicted to be encoded by open reading frames from a putative insertion sequence element from Enterococcus hirae. DNA probes from each end and the middle of IS1272 were hybridized with restriction endonuclease-digested genomic DNA from clinical S. haemolyticus, Staphylococcus epidermidis, and Staphylococcus aureus isolates. Each of the 20 or more copies of the element found in S. haemolyticus isolates was intact, and copies were found in most chromosomal SmaI fragments. S. aureus and S. epidermidis isolates contained mostly incomplete fragments of the element, and there were many more hybridizing fragments in methicillin-resistant than in methicillin-susceptible isolates. IS1272, which appears to be primarily resident in S. haemolyticus, has disseminated to multiple staphylococcal species and is prevalent in multiresistant isolates.

UDP-N-acetylmuramyl-L-alanine functions as an activator in the regulation of the Escherichia coli glutamate racemase activity

D-Glutamate is an essential component of the bacterial peptidoglycan. In Escherichia coli, the biosynthesis of D-glutamate is catalyzed by a glutamate racemase (encoded by the dga gene) and is regulated by UDP-N-acetylmuramyl-L-alanine [Doublet et al. (1994) Biochemistry 33, 5285], a bacterial peptidoglycan subunit precursor. Investigation was conducted to elucidate the interaction between the enzyme and its regulator. Whole and N-terminal truncated enzymes, encoded by individual constructs containing either a full-length or an N-terminal truncated dga gene, were evaluated. In the absence of the regulator, the purified whole enzyme showed a low-level basal racemase activity for which a Km value of 18.9 mM and a Vmax of 0.4 mumol/(min.mg) were determined, using D-glutamate as the substrate. Using the same substrate, in the presence of 6.5 microM UDP-N-acetylmuramyl-L-alanine, a Km value of 4.2 mM and a Vmax of 34 mumol/(min.mg) were measured. Similar kinetic parameters for the activated enzyme were obtained using L-glutamate as the substrate. The N-terminal truncated E. coli enzyme, with a 21 amino acid region removed, is similar in size to the Pediococcus pentosaceus glutamate racemase. Effects of the regulator on the full-length and the N-terminal truncated enzyme in the dialyzed cell lysate were compared. A host cell line, E. coli WM335 delta recA, containing a nonfunctional chromosomal dga gene was used to minimize the background interference. With 6.5 microM regulator added, the N-terminal truncated enzyme displayed a loss of more than 80% of the activity compared to the full-length enzyme.(ABSTRACT TRUNCATED AT 250 WORDS)

Heterogeneity of the vanA gene cluster in clinical isolates of enterococci from the northeastern United States

In several strains of Enterococcus faecium isolated in Europe, the cluster of genes encoding high-level resistance to vancomycin (VanA phenotype) resides on a 10.85-kb transposon, Tn1546, or closely related elements. To determine whether Tn1546 was conserved in recent enterococcal isolates from the northeastern United States, seven strains were compared by restriction mapping and DNA hybridization with probes from within the van cluster. Two of the seven strains contained intact Tn1546-like sequences; however, in five of the strains, the organization of the van cluster differed from that of Tn1546. Three of the five strains with variations harbored a novel DNA segment within the van gene cluster. This 1,496-bp segment was similar to IS1165 of Leuconostoc mesenteroides and IS1181 of Staphylococcus aureus and was flanked by 24- and 23-bp imperfect inverted repeats and 8-bp direct repeats. On the basis of these findings, we propose that this element comprises a novel insertion-like sequence, IS1251. Multiple copies of IS1251 were also present at other sites in both resistant and susceptible clinical isolates. Our findings suggest that the van cluster in recent isolates from the northeastern United States differs from that present in the early European VanA phenotype strains.

Staphylococcus haemolyticus contains two D-glutamic acid biosynthetic activities, a glutamate racemase and a D-amino acid transaminase

Two D-glutamic acid biosynthetic activities, glutamate racemase and D-amino acid transaminase, have been described previously for bacteria. To date, no bacterial species has been reported to possess both activities. Genetic complementation studies using Escherichia coli WM335, a D-glutamic acid auxotroph, and cloned chromosomal DNA fragments from Staphylococcus haemolyticus revealed two distinct DNA fragments containing open reading frames which, when present, allowed growth on medium without exogenous D-glutamic acid. Amino acid sequences of the two open reading frames derived from the DNA nucleotide sequences indicated extensive identity with the amino acid sequence of Pediococcus pentosaceous glutamate racemase in one case and with that of the D-amino acid transaminase of Bacillus spp. in the second case. Enzymatic assays of lysates of E. coli WM335 strains containing either the cloned staphylococcal racemase or transminase verified the identities of these activities. Subsequent DNA hybridization experiments indicated that Staphylococcus aureus, in addition to S. haemolyticus, contained homologous chromosomal DNA for each of these genes. These data suggest that S. haemolyticus, and probably S. aureus, contains genes for two D-glutamic acid biosynthetic activities, a glutamate racemase (dga gene) and a D-amino acid transaminase (dat gene).

Dissemination among staphylococci of DNA sequences associated with methicillin resistance

DNA probes consisting of pUC19 containing cloned Staphylococcus aureus chromosomal fragments were constructed from two methicillin-resistant S. aureus strains with different DNA sequences 5' to mecA, the gene that mediates methicillin resistance. The probe from one strain, BMS1, contained a portion of the regulatory sequences (the terminal 641 bp of mecR1 and all of mecI) associated with the induction and repression of mecA transcription (pGO195). The second probe, from strain COL (pGO198), contained DNA not found in strain BMS1. This DNA was within the sequences added at the site of a mecR1 deletion. Genomic digests of 14 S. aureus isolates recovered between 1961 and 1969 all hybridized with pGO198. In contrast, 78% (36 of 46) of the S. aureus organisms isolated since 1988 hybridized with pGO195 but not with pGO198; the remainder hybridized with pGO198. No S. aureus isolates hybridized with both probes. Staphylococcus epidermidis digests hybridized with pGO198 (46%), pGO195 (14%), or both probes (35%); all 20 Staphylococcus haemolyticus isolates hybridized with pGO198. The restriction fragment length polymorphism patterns of all pGO198-hybridizing regions in S. aureus were identical to those in strain COL. In addition, the mecR1 deletion junction nucleotide sequences of eight S. aureus and six S. epidermidis isolates were identical. However, 21 of 23 S. epidermidis and all 20 S. haemolyticus isolates had from 5 to more than 20 additional chromosomal bands that hybridized with pGO198; none of 21 S. aureus isolates had additional hybridizing bands. These data suggest that the additional DNA responsible for the mecR1 deletion was part of a repetitive, and possibly mobile, element resident in coagulase-negative staphylococci but not in S. aureus. These data also support a hypothesis that the deletion event occurred in a coagulase-negative staphylococcus with subsequent acquisition of the interrupted sequences by S. aureus.

Penicillin-binding proteins are regulated by rpoS during transitions in growth states of Escherichia coli

Attention has been recently focused on the role of the rpoS (formerly katF) gene product as a regulator during the transition from the exponential growth phase to the stationary phase as well as during nutritional starvation. It has been demonstrated that RpoS is an alternate sigma factor which would bind to promoters of genes induced at these times. It was previously noted that rpoS mutants do not undergo a transition to short rods during entry into the stationary phase. Because of their well-established role in morphogenesis, we investigated the status of the penicillin-binding proteins (PBPs) in Escherichia coli wild-type and isogenic rpoS mutants. Samples from cultures of E. coli ZK126 and ZK1000 (rpoS::kan) were taken in the midlogarithmic, early stationary, and late (24 h) stationary phases. The increase in PBP 6 seen upon entry of the wild-type strain into the stationary phase was not observed with the rpoS::kan cells, even after 24 h. There was also a marked decrease of PBP 3 in wild-type stationary-phase cells; PBP 3 has a known influence on morphogenesis. This decrease in PBP 3 was found to be markedly affected by the disruption of rpoS. Similar observations were made after prolonged starvation of the two strains for either glucose or a required amino acid. Inasmuch as PBPs are involved in peptidoglycan synthesis, we also examined two properties of peptidoglycan, autolysis and cross-linkage, that might be altered by the PBP differences. However, neither of these properties, which are known to undergo changes in the stationary phase, appeared to be influenced by the status of RpoS.

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.

The Escherichia coli Dga (MurI) protein shares biological activity and structural domains with the Pediococcus pentosaceus glutamate racemase

The Pediococcus pentosaceus glutamate racemase gene product complemented the D-glutamate auxotrophy of Escherichia coli WM335. Amino acid sequence analysis of the two proteins revealed 28% identity, primarily in six clusters scattered throughout the sequence. Further analyses indicated secondary structure similarities between the two proteins. These data support a recent report that the dga (murI) gene product is a glutamate racemase.

The Escherichia coli mutant requiring D-glutamic acid is the result of mutations in two distinct genetic loci

D-Glutamic acid is an essential component of bacterial cell wall peptidoglycan in both gram-positive and gram-negative bacteria. Very little is known concerning the genetics and biochemistry of D-glutamate production in most bacteria, including Escherichia coli. Evidence is presented in this report for the roles of two distinct genes in E. coli WM335, a strain which is auxotrophic for D-glutamate. The first gene, which restores D-glutamate independence in WM335, was mapped, cloned, and sequenced. This gene, designated dga, is a previously reported open reading frame, located at 89.8 min on the E. coli map. The second gene, gltS, is located at 82 min. gltS encodes a protein that is involved in the transport of D- and L-glutamic acid into E. coli, and the gltS gene of WM335 was found to contain two missense mutations. To construct D-glutamate auxotrophs, it is necessary to transfer sequentially the mutated gltS locus, and then the mutated dga locus into the recipient. The sequences of the mutant forms of both dga and gltS are also presented.

The cytoplasmic peptidoglycan precursor of vancomycin-resistant Enterococcus faecalis terminates in lactate

Vancomycin resistance plasmids in enterococci carry the genes vanH and vanA, which encode enzymes catalyzing, respectively, the reduction of 2-keto acids to 2-D-hydroxy acids and the addition of D-hydroxy acids to D-alanine. It has therefore been postulated that resistant cells produce peptidoglycan precursors that terminate in the depsipeptide D-alanine-2-D-hydroxy acid rather than the dipeptide D-alanine-D-alanine, thus preventing vancomycin binding (M. Arthur, C. Molinas, T. D. H. Bugg, G. D. Wright, C. T. Walsh, and P. Courvalin, Antimicrob. Agents Chemother. 36:867-869, 1992). In the present work, a cytoplasmic peptidoglycan precursor was isolated from vancomycin-resistant Enterococcus faecalis and analyzed by mass spectrometry, which suggested the structure UDP-N-acetyl-muramyl-L-Ala-D-Glu-L-Lys-D-Ala-D-lactate.

Cloning, expression, and nucleotide sequence of genes involved in production of pediocin PA-1, and bacteriocin from Pediococcus acidilactici PAC1.0

The production of pediocin PA-1, a small heat-stable bacteriocin, is associated with the presence of the 9.4-kbp plasmid pSRQ11 in Pediococcus acidilactici PAC1.0. It was shown by subcloning of pSRQ11 in Escherichia coli cloning vectors that pediocin PA-1 is produced and, most probably, secreted by E. coli cells. Deletion analysis showed that a 5.6-kbp SalI-EcoRI fragment derived from pSRQ11 is required for pediocin PA-1 production. Nucleotide sequence analysis of this 5.6-kbp fragment indicated the presence of four clustered open reading frames (pedA, pedB, pedC, and pedD). The pedA gene encodes a 62-amino-acid precursor of pediocin PA-1, as the predicted amino acid residues 19 to 62 correspond entirely to the amino acid sequence of the purified pediocin PA-1. Introduction of a mutation in pedA resulted in a complete loss of pediocin production. The pedB and pedC genes, encoding proteins of 112 and 174 amino acid residues, respectively, are located directly downstream of the pediocin structural gene. Functions could not be assigned to their gene products; mutation analysis showed that the PedB protein is not involved in pediocin PA-1 production. The mutation analysis further revealed that the fourth gene, pedD, specifying a relatively large protein of 724 amino acids, is required for pediocin PA-1 production in E. coli. The predicted pedD protein shows strong similarities to several ATP-dependent transport proteins, including the E. coli hemolysin secretion protein HlyB and the ComA protein, which is required for competence induction for genetic transformation in Streptococcus pneumoniae.(ABSTRACT TRUNCATED AT 250 WORDS)

Insertional inactivation of a gene which controls expression of vancomycin resistance on plasmid pHKK100

Expression of inducible high level vancomycin resistance (Vmr) in enterococci appears to require other plasmid-encoded genes in addition to the previously described structural genes vanA and vanH. Tn917 mutagenesis was used to identify such a region in the Vmr plasmid pHKK100. Insertional inactivation of a 693-bp open reading frame upstream from vanH resulted in complete loss of Vmr. This putative 26,642-Da protein has been designated VanR.

Cloning and identification of the Escherichia coli murB DNA sequence, which encodes UDP-N-acetylenolpyruvoylglucosamine reductase

The murB gene, which complemented the UDP-N-acetylenolpyruvoylglucosamine reductase (EC 1.1.1.158) mutation in Escherichia coli ST5, was cloned from an E. coli chromosomal library. murB was subcloned on a 2.8-kb PvuII fragment into pUC19 and sequenced. A 1,029-bp open reading frame encoded a 342-amino-acid polypeptide of 37,859 Da. A DNA sequence homology search revealed that murB had almost 100% homology with a previously reported unidentified open reading frame, ORFII, at 89.9 min. Physical and genetic mapping results were consistent with this map position, and minicell analyses of murB subclones showed a plasmid-encoded protein of approximately 37,000 Da, which closely matched the calculated size of the murB protein.

Comparison of cefepime, cefpirome, and cefaclidine binding affinities for penicillin-binding proteins in Escherichia coli K-12 and Pseudomonas aeruginosa SC8329

The relative binding affinities of the extended-spectrum cephalosporins cefepime, cefpirome, and cefaclidine for the penicillin-binding proteins (PBPs) of Escherichia coli K-12 and Pseudomonas aeruginosa SC8329 were determined. Affinities were calculated from competition experiments between these antibiotics and [3H]benzylpenicillin in isolated membrane preparations. The concentrations which reduced binding to a PBP by 50% (IC50s) were determined. For E. coli, all three antibiotics displayed good PBP 3 binding (IC50s of 0.5 microgram/ml or less), and MICs roughly correlated with these values. Cefepime had a greater than 20-fold-lower IC50 for PBP 2 of E. coli than the other antibiotics. For P. aeruginosa, all of the antibiotics bound poorly (greater than 25 micrograms/ml) to PBP 2 but showed excellent pseudomonal (less than 0.0025 microgram/ml) PBP 3 binding. No correlations were seen between IC50s and MICs for P. aeruginosa. Despite differences in PBP binding, cefepime, cefpirome, and cefaclidine all displayed similar bactericidal activity for E. coli K-12 over the initial 3 h after antibiotic addition. All three caused E. coli to form filaments at values close to the MICs. In addition, cefepime induced "bleb" formation along the filaments at concentrations greater than 10x the MIC.

Vancomycin resistance is encoded on a pheromone response plasmid in Enterococcus faecium 228

In Enterococcus faecium 228, vancomycin resistance is encoded on a 55-kilobase conjugative plasmid, pHKK100. This plasmid was transferred with high frequency into susceptible strains of Enterococcus faecalis and conferred responses to pheromones produced by E. faecalis and Streptococcus sanguis. pHKK100 is the first plasmid described that mediates both vancomycin resistance and pheromone response.

Inhibition of Listeria monocytogenes by using bacteriocin PA-1 produced by Pediococcus acidilactici PAC 1.0

The bacteriocin produced by Pediococcus acidilactici PAC 1.0, previously designated PA-1 bacteriocin, was found to be inhibitory and bactericidal for Listeria monocytogenes. A dried powder prepared from PAC 1.0 culture supernatant fortified with 10% milk powder was found to contain bacteriocin activity. An MIC against L. monocytogenes and lytic effects in broth cultures were determined. Inhibition by PA-1 powder occurred over the pH range 5.5 to 7.0 and at both 4 and 32 degrees C. In addition, inhibition of L. monocytogenes was demonstrated in several food systems including dressed cottage cheese, half-and-half cream, and cheese sauce.

Intergeneric and intrageneric conjugal transfer of plasmid-encoded antibiotic resistance determinants in Leuconostoc spp

Transfer of the broad-host-range resistance plasmids pIP501 and pAM beta 1 from Streptococcus faecalis to Leuconostoc dextranicum and Leuconostoc cremoris occurred between cells that were immobilized on nitrocellulose filters in the presence of DNase. Transfer of pIP501 to Leuconostoc spp. also occurred when Streptococcus sanguis and Streptococcus lactis were used as donors. In addition, transfer of pIP501 and pAM beta 1 was observed from L. cremoris and L. dextranicum transconjugants to S. sanguis and S. faecalis. Expression of the pAM beta 1 erythromycin and pIP501 erythromycin and chloramphenicol resistance determinants was essentially equivalent in donors and transconjugants. Frequencies of transfer generally ranged from 10(-4) to 10(-7) transconjugants per input donor cell. Intrageneric transfer of pIP501 and pAM beta 1 occurred between L. cremoris and L. dextranicum strains in the same approximate range. These data further extend the host range of pIP501 and pAM beta 1 and demonstrate another example of gene transfer in the genus Leuconostoc.

Molecular cloning and characterization of the glucosyltransferase C gene (gtfC) from Streptococcus mutans LM7

A glucosyltransferase (GTF) gene, designated gtfC, was cloned from Streptococcus mutans LM7. Its gene product was detected by screening a bacteriophage lambda library with rabbit antiserum raised against S. mutans LM7 extracellular proteins. DNA isolated from the immunopositive recombinant phage revealed two S. mutans chromosomal EcoRI fragment inserts, 8.1 and 4.7 kilobase pairs in size. Escherichia coli minicell analyses revealed the approximate position and direction of transcription of the gtfC gene. The gene product was determined to be a polypeptide of about 150 kilodaltons which synthesized a water-soluble glucan. Restriction endonuclease mapping and DNA hybridization indicated a repeated region of DNA corresponding to a portion of the coding region of gtfC immediately downstream from the intact gtfC locus on the chromosome. A 300-base-pair gtfC-specific probe showed that the gene and the putative duplicated sequence were present in S. mutans serotypes c, e, and f, but not in other related oral streptococci which had GTF activity. In addition, the gtfC determinant displayed homology to sequences corresponding to the carboxy-terminal coding region of a gene (gtfB) encoding a GTF activity that synthesized water-insoluble glucans. These data suggest that at least one class of GTF genes may be present in multiple copies in S. mutans and, further, that GTF genes may contain conserved sequences internal to their coding regions.

Molecular organization and expression of the gtfA gene of Streptococcus mutans LM7

The Streptococcus mutans LM7 gene gtfA was cloned in Escherichia coli along with flanking regions of the chromosome as a fragment representing 10.3 kilobases (kb) of streptococcal DNA. Restriction endonuclease mapping revealed that the cloned DNA consisted of four EcoRI fragments with gtfA sucrase activity localized to one fragment, EcoRI-B (2.4 kb). Subsequent analysis with E. coli minicells indicated that three polypeptides were encoded on the 10.3-kb insert (55 [GtfA], 45, and 35 kilodaltons). Neither the 45- nor 35-kilodalton polypeptide exhibited any detectable sucrase activity. The approximate positions and directions of transcription of the two larger proteins were determined from minicell protein profiles displaying truncated versions of these polypeptides. The restriction endonuclease data for the cloned gtfA gene were used to develop a strategy for insertional inactivation of this locus in vivo. An internal HincII fragment of the gtfA gene was removed and replaced with a DNA fragment containing a tetracycline resistance determinant. This new recombinant plasmid was linearized and then transformed into S. mutans GS5 and S. mutans V403 where it was incapable of replication. It was predicted that Tcr colonies would result from double-crossover recombinational events involving homologous regions flanking the gtfA gene. This was verified by Southern DNA hybridization analyses. The inactivation of the gtfA gene in both S. mutans GS5 and S. mutans V403 resulted in a decrease of water-soluble exopolysaccharide but no detectable changes in the amounts of water-insoluble polymers.

Inhibition of beta-lactam antibiotics at two different times in the cell cycle of Streptococcus faecium ATCC 9790

Treatment of Streptococcus faecium ATCC 9790 with sublytic concentrations of beta-lactam antibiotics revealed two different division blocks in the cell division cycle. One block, induced by N-formimidoyl thienamycin and methicillin, occurred before the completion of chromosome replication, whereas the other, induced by cefoxitin and cephalothin, took place later in the cycle. In addition, these antibiotics gave rise to distinct morphological forms; the antibiotics acting at the earlier block point produced mainly "dumbbells," whereas those affecting the later time formed "lemons." When used in combination N-formimidoyl thienamycin and cefoxitin exerted synergistic killing on this strain. These data suggest that beta-lactam antibiotics have at least two sites of action in S. faecium.

Cloned gtfA gene of Streptococcus mutans LM7 alters glucan synthesis in Streptococcus sanguis

Streptococcus mutans LM7 (Bratthall serotype e) chromosomal DNA was partially digested with EcoRI and ligated into the positive-selection plasmid vector pOP203(A2+). The ligation mixture was transformed into Escherichia coli, and transformants were selected for tetracycline resistance. Recombinant-bearing clones were screened for their ability to ferment raffinose, using the procedure of Robeson et al. (J. Bacteriol. 153:211-221, 1983). One raffinose-fermenting clone was isolated and found to contain a plasmid with an insert consisting of four EcoRI fragments totalling approximately 10.3 kilobases (kb). This strain was capable of growth on defined medium plus raffinose or sucrose and generated reducing sugars from a sucrose substrate. Southern hybridization analysis of the four EcoRI fragments revealed homology not only to S. mutans LM7 chromosomal DNA but also to S. mutans serotypes b, c, and f. Subcloning of this fragment array into a streptococcal E. coli shuttle vector indicated that a 2.4-kb EcoRI fragment was essential for sucrase activity. E. coli minicell experiments revealed a gene product of 55 kilodaltons. These data along with restriction endonuclease analysis and Southern hybridizations suggested that the cloned S. mutans LM7 gene was closely related to the gtfA gene cloned by Robeson et al. from S. mutans PS13 (Bratthall serotype c). The shuttle plasmid containing the 2.4-kb fragment was transformed into Streptococcus sanguis, which subsequently displayed increased sucrase activity in both intracellular and extracellular fractions. Elevated levels of synthesis of alcohol-insoluble and water-insoluble glucans were observed with crude extracellular fractions of the S. sanguis strain bearing the 2.4-kb fragment. An isolate cured of the shuttle plasmid plus the 2.4-kb fragment displayed wild-type S. sanguis glucan synthesis. In S. sanguis, this gtfA allele may play a role in glucan synthesis by interacting with extant high-molecular-weight glucosyltransferases.

Detergent-resistant Streptococcus faecium derivatives that display conditional penicillin lysis

Three spontaneous derivatives of Streptococcus faecium ATCC 9790, originally isolated as conditionally Triton X-100 detergent-resistant at 25 degrees C, displayed normal penicillin-induced rates of lysis at 37 degrees C but substantially reduced rates of lysis and killing at 25 degrees C. The addition of exogenous unsaturated fatty acids at 25 degrees C restored wild-type penicillin lysis rates.