Impacts of L1 Promoter Variation and L2 Clavulanate Susceptibility on Ticarcillin-Clavulanate Susceptibility of Stenotrophomonas maltophilia.

Inducible expression of L1 and L2 ß-lactamases is the principal mechanism responsible for ß-lactam resistance in Stenotrophomonas maltophilia Ticarcillin-clavulanate (TIM) is one of the few effective ß-lactams for S. maltophilia treatment. Clavulanate (CA) is a ß-lactamase inhibitor that specifically targets class A, C, and D ß-lactamases. In view of the presence of class B L1 ß-lactamase, it is of interest to elucidate why TIM is valid for S. maltophilia treatment. The L1-L2 allelic variation and TIM susceptibilities of 22 clinical isolates were established. Based on L1 and L2 protein sequences and TIM susceptibility, three L1-based phylogenetic clusters (L1-A, L1-B, and L1-C) and three L2-based phylogenetic clusters (L2-A, L2-B1, and L2-B2) were classified. The contribution of each L1- and L2-based phylogenetic cluster to ticarcillin (TIC) and TIM susceptibility was investigated. All the L1s and L2s tested contributed to TIC resistance. The L1s tested were inert to CA; nevertheless, the sensitivities of L2s to CA were widely different. In addition, the genetic organizations upstream of the L1 gene varied greatly in these isolates. At least three different L1 promoter structures (K279a type, D457 type, and none) were found among the 22 isolates assayed. The differences in the L1 promoter structure had a great impact on TIC-induced L1 ß-lactamase activities. Collectively, the L1 promoter activity in response to TIC challenge and L2 susceptibility to CA are critical factors determining TIM susceptibility in S. maltophilia.

Interplay among membrane-bound lytic transglycosylase D1, the CreBC two-component regulatory system, the AmpNG-AmpDI-NagZ-AmpR regulatory circuit, and L1/L2 ß-lactamase expression in Stenotrophomonas maltophilia.

Lytic transglycosylases (LTs) are an important class of enzymes involved in peptidoglycan (PG) cleavage, with the concomitant formation of an intramolecular 1,6-anhydromuramoyl reaction product. There are six annotated LT genes in the Stenotrophomonas maltophilia genome, including genes for five membrane-bound LTs (mltA, mltB1, mltB2, mltD1, and mltD2) and a gene for soluble LT (slt). Six LTs of S. maltophilia KJ were systematically mutated, yielding the ΔmltA, ΔmltB1, ΔmltB2, ΔmltD1, ΔmltD2, and Δslt mutants. Inactivation of mltD1 conferred a phenotype of elevated uninduced ß-lactamase activity. The underlying mechanism responsible for this phenotype was elucidated by the construction of several mutants and determination of ß-lactamase activity. The expression of the genes assayed was assessed by quantitative reverse transcriptase PCR and a promoter transcription fusion assay. The results demonstrate that ΔmltD1 mutant-mediated L1/L2 ß-lactamase expression involved the creBC two-component regulatory system (TCS) and the ampNG-ampDI-nagZ-ampR regulatory circuit. The inactivation of mltD1 resulted in mltB1 and mltD2 upexpression in a creBC- and ampNG-dependent manner. The overexpressed MltB1 and MltD2 activity contributed to the expression of the L1/L2 ß-lactamase genes via the ampNG-ampDI-nagZ-ampR regulatory circuit. These findings reveal, for the first time, a linkage between LTs, the CreBC TCS, the ampNG-ampDI-nagZ-ampR regulatory circuit, and L1/L2 ß-lactamase expression in S. maltophilia.

Association Between Genetic Polymorphism of the MIF Gene and Colorectal Cancer in Taiwan.

BACKGROUND: Colorectal cancer (CRC) is the highest leading cause of cancer-related mortality in Taiwan. Macrophage migration inhibitory factor (MIF) has recently been defined as a novel protumorigenic factor that promotes cell proliferation, migration, and invasion. The aim of the present study is to identify the association between MIF gene polymorphism and CRC. METHODS: A case-control study was designed to test the hypothesis. A total of 192 biopsy-diagnosed CRC patients (CRC) and 256 healthy subjects (control) were recruited. Genotyping of four single nucleotide polymorphism (SNPs; rs755662, rs11548059, rs1049829, rs1803976) at chromosome positions 755662 (5' UTR), 11548059 (exon2), 1049829 (exon2), 1803976 (exon3) was performed using a Taqman SNP genotyping assay. RESULTS: There is a significant difference in genotype frequency distribution of rs755662 polymorphism between CRC patients and controls (P = 0.011). No significant difference was found in the frequency distribution of rs11548059, rs1049829, rs1803976 polymorphism in CRC patients and controls (P = 0.660, P = 0.700, and P = 0.959, respectively). Moreover, the MIF-173 SNP was also significantly associated with young patients (age < 50 years, P = 0.026) late stage (Stage IV, P = 0.038) and poor differentiation group (P = 0.040). Compared to the control group, the MIF-173 SNP also significantly associated with patients with stages III and IV (P = 0.034 and 0.003, respectively). CONCLUSION: The presence of MIF-173 (G/C) gene polymorphism (rs755662) was associated with susceptibility, patient age, and stages of CRC in Taiwanese.

SmeOP-TolCSm efflux pump contributes to the multidrug resistance of Stenotrophomonas maltophilia.

A five-gene cluster, tolCSm-pcm-smeRo-smeO-smeP, of Stenotrophomonas maltophilia was characterized. The presence of smeOP and smeRo-pcm-tolCSm operons was verified by reverse transcription (RT)-PCR. Both operons were negatively regulated by the TetR-type transcriptional regulator SmeRo, as demonstrated by quantitative RT-PCR and a promoter-fusion assay. SmeO and SmeP were associated with TolCSm (the TolC protein of S. maltophilia) for the assembly of a resistance-nodulation-cell-division (RND)-type pump. The compounds extruded by SmeOP-TolCSm mainly included nalidixic acid, doxycycline, amikacin, gentamicin, erythromycin, leucomycin, carbonyl cyanide 3-chlorophenylhydrazone, crystal violet, sodium dodecyl sulfate, and tetrachlorosalicylanilide.

Role of the pcm-tolCsm operon in the multidrug resistance of Stenotrophomonas maltophilia.

OBJECTIVES: To elucidate the role of the pcm-tolCsm operon in the multidrug resistance of Stenotrophomonas maltophilia. METHODS: The presence of the pcm-tolCsm operon was verified by RT-PCR. The phylogenetic relationship between the outer membrane proteins known to be involved in functional tripartite efflux in Escherichia coli, Pseudomonas aeruginosa and S. maltophilia was analysed. The contribution of TolCsm to resistance to a variety of compounds was investigated by susceptibility testing of the ΔtolCsm mutant. The role of pcm in the expression and function of tolCsm was assessed by quantitative real-time PCR and complementation assay. RESULTS: The pcm and tolCsm genes formed an operon. TolCsm of S. maltophilia, OpmH of P. aeruginosa and TolC of E. coli formed a distinguishing phylogenetic TolC-like clade. TolCsm deletion increased the susceptibility of S. maltophilia KJ2 to several antimicrobial agents (aminoglycoside, macrolide, ß-lactam, chloramphenicol, nalidixic acid, doxycycline and trimethoprim/sulfamethoxazole) and chemical compounds (acriflavine, carbonyl cyanide 3-chlorophenylhydrazone, crystal violet, fusaric acid, menadione, Paraquat, plumbagin, SDS and tetrachlorosalicylanilide). The in-frame deletion of pcm caused a polar effect on the expression of tolCsm, which compromised the resistance to amikacin and gentamicin. Nevertheless, the presence of the PCM protein made an insignificant contribution to the function of TolCsm in the resistance to amikacin and gentamicin. CONCLUSIONS: The pcm-tolCsm operon makes a significant contribution to the multidrug resistance of S. maltophilia.

Characterization of a major facilitator superfamily (MFS) tripartite efflux pump EmrCABsm from Stenotrophomonas maltophilia.

OBJECTIVES: To characterize the emrRCABsm operon of Stenotrophomonas maltophilia. METHODS: The presence of the emrRCABsm operon was verified by RT-PCR. The regulatory role of EmrRsm was investigated by ΔemrRsm mutant construction and promoter transcriptional fusion assay. A susceptibility test was employed to assess the substrate spectrum of the EmrCABsm efflux pump. The requirement for each component of the EmrCABsm pump was assessed by individual mutant construction and susceptibility testing. The expression of the emrRCABsm operon was evaluated by an induction assay, using different compounds as inducers. RESULTS: emrRsm, emrCsm, emrAsm and emrBsm formed a four-member operon that was negatively regulated by the MarR-type transcriptional regulator EmrRsm. The emrRCABsm operon was intrinsically poorly expressed and the EmrCAB pump favoured extrusion of the uncoupling agents carbonyl cyanide 3-chlorophenylhydrazone (CCCP) and tetrachlorosalicylanilide (TCS), and the hydrophobic antibiotics nalidixic acid and erythromycin. However, the emrRCABsm operon could not be derepressed by CCCP, nalidixic acid, TCS, 2-chlorophenylhydrazine hydrochloride or salicylate, which are known to be possible inducers for MarR-type regulons. Each component of the EmrCABsm pump was apparently essential for pump function. CONCLUSIONS: The EmrRsm-regulated EmrCABsm efflux pump is involved in the extrusion of hydrophobic compounds.

CA125 for the Diagnosis of Advanced Urothelial Carcinoma of the Bladder: A Systematic Review and Meta-Analysis.

BACKGROUND: Urothelial carcinoma of the bladder (UCB) is the second most common genitourinary cancer. This study aims to assess the diagnostic accuracy of CA125 in advanced UCB. METHODS: We searched prevalent studies in PubMed, the Cochrane Library, Scopus, Embase, the Web of Science China National Knowledge Infrastructure database, and Wanfang data before October 2022. Pooled sensitivity, specificity, and summary receiver operating characteristics were used to assess the diagnostic value of CA125. RESULTS: One thousand six hundred forty-one patients from 14 studies were analyzed. UCB stage T3-4N1 was defined as advanced UCB in ten studies; T2-4 was used in three studies; and N1M1 in one study. Patients' age was between 21 to 92, and 21% to 48.6% of patients were female. The pooled sensitivity was 0.695 (95% confidence interval (CI): 0.426-0.875). The pooled specificity was 0.846 (95% CI: 0.713-0.924). The diagnostic odds ratio was 8.138 (95% CI: 4.559-14.526). The AUC was 0.797. CONCLUSION: CA125 may provide significant diagnostic accuracy in identifying muscle-invasive, lymph node-involved, and distant metastatic tumors in patients with urothelial carcinoma of the bladder. Limited studies have been conducted on the prognostic role of CA125. More studies are needed for a meta-analysis on the prognostic role of CA125 in UCB.

NagZ-dependent and NagZ-independent mechanisms for ß-lactamase expression in Stenotrophomonas maltophilia.

ß-N-Acetylglucosaminidase (NagZ), encoded by the nagZ gene, is a critical enzyme for basal-level ampC derepression (ampC expression in the absence of ß-lactam challenge) in ampD and dacB mutants of Pseudomonas aeruginosa. Three mutants with a phenotype of basal-level L1 and L2 ß-lactamase derepression in Stenotrophomonas maltophilia have been reported, including KJΔDI (ampD(I) mutant), KJΔmrcA (mrcA mutant), and KJΔDIΔmrcA (ampD(I) and mrcA double mutant). In this study, nagZ of S. maltophilia was characterized, and its roles in basal-level ß-lactamase derepression, induced ß-lactamase activities, and ß-lactam resistance of KJΔDI, KJΔmrcA, and KJΔDIΔmrcA were evaluated. Expression of the nagZ gene was constitutive and not regulated by AmpR, AmpD(I), AmpN, AmpG, PBP1a, and NagZ. Introduction of ΔnagZ into KJΔDI nearly abolished basal-level derepressed ß-lactamase activity; conversely, introduction of ΔnagZ into KJΔmrcA did not affect it. At least two activator ligands (ALs) are thus considered responsible for ß-lactamase expression in the S. maltophilia system, specifically, the NagZ-dependent (AL1) and NagZ-independent (AL2) ligands responsible for the basal-level derepressed ß-lactamase activities of KJΔDI and KJΔmrcA, respectively. The contributions of AL1 and AL2 to the induced ß-lactamase activities may vary with the types of ß-lactams. nagZ inactivation did not affect aztreonam-, cefoxitin-, and carbenicillin-induced ß-lactamase activities, but it attenuated cefuroxime- and piperacillin-induced ß-lactamase activities. Introduction of ΔnagZ into KJ, KJΔDI, KJΔmrcA, and KJΔDIΔmrcA did not significantly change the MICs of the ß-lactams tested except that the MICs of cefuroxime and piperacillin moderately decreased in strains KJΔZ and KJΔDIΔZ (nagZ mutants).

Contribution of resistance-nodulation-division efflux pump operon smeU1-V-W-U2-X to multidrug resistance of Stenotrophomonas maltophilia.

KJ09C, a multidrug-resistant mutant of Stenotrophomonas maltophilia KJ, was generated by in vitro selection with chloramphenicol. The multidrug-resistant phenotype of KJ09C was attributed to overexpression of a resistance nodulation division (RND)-type efflux system encoded by an operon consisting of five genes: smeU1, smeV, smeW, smeU2, and smeX. Proteins encoded by smeV, smeW, and smeX were similar to the membrane fusion protein, RND transporter, and outer membrane protein, respectively, of known RND-type systems. The proteins encoded by smeU1 and smeU2 were found to belong to the family of short-chain dehydrogenases/reductases. Mutant KJ09C exhibited increased resistance to chloramphenicol, quinolones, and tetracyclines and susceptibility to aminoglycosides; susceptibility to ß-lactams and erythromycin was not affected. The expression of the smeU1-V-W-U2-X operon was regulated by the divergently transcribed LysR-type regulator gene smeRv. Overexpression of the SmeVWX pump contributed to the acquired resistance to chloramphenicol, quinolones, and tetracyclines. Inactivation of smeV and smeW completely abolished the activity of the SmeVWX pump, whereas inactivation of smeX alone decreased the activity of the SmeVWX pump. The enhanced aminoglycoside susceptibility observed in KJ09C resulted from SmeX overexpression.

An updated review on pharmacological properties of neferine-A bisbenzylisoquinoline alkaloid from Nelumbo nucifera.

Phytochemicals have recently received a lot of recognition for their pharmacological activities such as anticancer, chemopreventive, and cardioprotective properties. In traditional Indian and Chinese medicine, parts of lotus (Nelumbo nucifera) such as lotus seeds, fruits, stamens, and leaves are used for treating various diseases. Neferine is a bisbenzylisoquinoline alkaloid, a major component from the seed embryos of N. nucifera. Neferine is effective in the treatment of high fevers and hyposomnia, as well as arrhythmia, platelet aggregation, occlusion, and obesity. Neferine has been found to have a variety of therapeutic effects such as anti-inflammatory, anti-oxidant, anti-hypertensive, anti-arrhythmic, anti-platelet, anti-thrombotic, anti-amnesic, and negative inotropic. Neferine also exhibited anti-anxiety effects, anti-cancerous, and chemosensitize to other anticancer drugs like doxorubicin, cisplatin, and taxol. Induction of apoptosis, autophagy, and cell cycle arrest are the key pathways that underlying the anticancer activity of neferine. Therefore, the present review summarizes the neferine biosynthesis, pharmacokinetics, and its effects in myocardium, cancer, chemosensitizing to cancer drug, central nervous system, diabetes, inflammation, and kidney diseases. PRACTICAL APPLICATIONS: Natural phytochemical is gaining medicinal importance for a variety of diseases like including cancer, neurodegenerative disorder, diabetes, and inflammation. Alkaloids and flavonoids, which are abundantly present in Nelumbo nucifera have many therapeutic applications. Neferine, a bisbenzylisoquinoline alkaloid from N. nucifera has many pharmacological properties. This present review was an attempt to compile an updated pharmacological action of neferine in different disease models in vitro and in vivo, as well as to summarize all the collective evidence on the therapeutic potential of neferine.

Ethanolic extract of Puhuang (Pollen Typhae) modulates lipopolysaccharide-induced inflammatory response through inducible nitric oxide synthase / cyclooxygenase-2 signaling in RAW 264.7 macrophage.

OBJECTIVE: To evaluate the immune modulatory response of Puhuang (Pollen Typhae), ethanolic extract of dried pollens (TP-E) and charcoal activated pollens (CTP-E) were used for their phytochemical evaluation and their modulatory response against lipopolysaccharide (LPS) induced inflammatory activity on RAW264.7 macrophage cells. METHODS: Biochemical assays were carried out to quantify the 1,1-Diphenyl-2-picrylhydrazyl Radical Scavenging Activity, Reducing Power, Ferrous ion chelating ability and total polyphenol content and flavonoids. Non-toxic dose of the extract (TP-E and CTP-E) was chosen based on 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Effect of TP-E and CTP-E on lipopolysaccharides-induced inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) expression was measured by Western blot and quantitative PCR (qRT-PCR). Expression of inflammatory cytokines, such as interleukins (IL-1ß and IL-6) and tumor necrosis factor α (TNF-α), was quantified using qRT-PCR. Mitogen-activated protein kinase pathway was analyzed using Western blot. RESULTS: Phytochemical analysis revealed that both TP-E and CTP-E have strong antioxidant activities and high flavonoid and phenolic contents. TP-E and CTP-E effectively inhibit the expression of iNOS and COX-2, thereby inhibiting its downstream proinflammatory regulators, the extracellular signal-related kinase-1/2, that decreases the expression of IL-1ß, IL-6 and TNF-α. CONCLUSION: Phytochemical constituents present in Typha angustifolia Linn could be used for treating inflammation-related diseases.

AmpN-AmpG operon is essential for expression of L1 and L2 beta-lactamases in Stenotrophomonas maltophilia.

AmpG is an inner membrane permease which transports products of murein sacculus degradation from the periplasm into the cytosol in Gram-negative bacteria. This process is linked to induction of the chromosomal ampC beta-lactamase gene in some members of the Enterobacteriaceae and in Pseudomonas aeruginosa. In this study, the ampG homologue of Stenotrophomonas maltophilia KJ was analyzed. The ampG homologue and its upstream ampN gene form an operon and are cotranscribed under the control of the promoter P(ampN). Expression from P(ampN) was found to be independent of beta-lactam exposure and ampN and ampG products. A DeltaampN allele exerted a polar effect on the expression of ampG and resulted in a phenotype of null beta-lactamase inducibility. Complementation assays elucidated that an intact ampN-ampG operon is essential for beta-lactamase induction. Consistent with ampG of Escherichia coli, the ampN-ampG operon of S. maltophilia did not exhibit a gene dosage effect on beta-lactamase expression. The AmpG permease of E. coli could complement the beta-lactamase inducibility of ampN or ampG mutants of S. maltophilia, indicating that both species have the same precursor of activator ligand(s) for beta-lactamase induction.

Bacterial and viral vectors as vaccine delivery vehicles for breast cancer therapy.

Breast cancer is the frequently diagnosed cancer among women and it is the most lethal malignancy in women globally. With one million cases every year, breast cancer is the fast-growing cancer type that has a high prevalence rate in young women. The limitations and undesirable side effects of conventional therapies like chemotherapy and radiotherapy on malignant tumors necessitate the development of alternative therapeutic approaches. Gene therapy has emerged as a promising approach to cure a variety of malignant cancer types which involves the delivery of functional gene directly into the target tumor tissue. Efficient gene therapy approach relies on the effective delivery of therapeutic genes to the desired cell type. In this regard, biological and non-biological gene delivery vectors are used to protect the naked foreign DNA to mediate effective tissue entry of the desired gene of interest. In this review, the use of bacterial and viral vectors for breast cancer gene therapy was summarized.

Flagellar biogenesis of Xanthomonas campestris requires the alternative sigma factors RpoN2 and FliA and is temporally regulated by FlhA, FlhB, and FlgM.

In prokaryotes, flagellar biogenesis is a complicated process involving over 40 genes. The phytopathogen Xanthomonas campestris pv. campestris possesses a single polar flagellum, which is essential for the swimming motility. A sigma54 activator, FleQ, has been shown to be required for the transcriptional activation of the flagellar type III secretion system (F-T3SS), rod, and hook proteins. One of the two rpoN genes, rpoN2, encoding sigma54, is essential for flagellation. RpoN2 and FleQ direct the expression of a second alternative sigma FliA (sigma28) that is essential for the expression of the flagellin FliC. FlgM interacts with FliA and represses the FliA regulons. An flgM mutant overexpressing FliC generates a deformed flagellum and displays an abnormal motility. Mutation in the two structural genes of F-T3SS, flhA and flhB, suppresses the production of FliC. Furthermore, FliA protein levels are decreased in an flhB mutant. A mutant defective in flhA, but not flhB, exhibits a decreased infection rate. In conclusion, the flagellar biogenesis of Xanthomonas campestris requires alternative sigma factors RpoN2 and FliA and is temporally regulated by FlhA, FlhB, and FlgM.

AmpDI is involved in expression of the chromosomal L1 and L2 beta-lactamases of Stenotrophomonas maltophilia.

Two ampD homologues, ampD(I) and ampD(II), of Stenotrophomonas maltophilia have been cloned and analyzed. Comparative genomic analysis revealed that the genomic context of the ampD(II) genes is quite different, whereas that of the ampD(I) genes is more conserved in S. maltophilia strains. The ampD system of S. maltophilia is distinct from that of the Enterobacteriaceae and Pseudomonas aeruginosa in three respects. (i) AmpD(I) of S. maltophilia is not encoded in an ampDE operon, in contrast to what happens in the Enterobacteriaceae and P. aeruginosa. (ii) The AmpD systems of the Enterobacteriaceae and P. aeruginosa are generally involved in the regulation of ampR-linked ampC gene expression, while AmpD(I) of S. maltophilia is responsible for the regulation of two intrinsic beta-lactamase genes, of which the L2 gene, but not the L1 gene, is linked to ampR. (iii) S. maltophilia exhibits a one-step L1 and L2 gene derepression model involving ampD(I), distinct from the two- or three-step derepression of the Enterobacteriaceae and P. aeruginosa. Moreover, the ampD(I) and ampD(II) genes are constitutively expressed and not regulated by the inducer and AmpR protein, and the expression of ampD(II) is weaker than that of ampD(I). Finally, AmpD(II) is not associated with the derepression of beta-lactamases, and its role in S. maltophilia remains unclear.

The role of AmpR in regulation of L1 and L2 beta-lactamases in Stenotrophomonas maltophilia.

Stenotrophomonas maltophilia is known to produce at least two chromosomal-mediated inducible beta-lactamases, L1 and L2. Gene L2, which encodes a class A beta-lactamase, and the adjacent ampR gene form an ampR-class A beta-lactamase module. L1 belongs to the class B beta-lactamase and has no neighbor ampR-like regulatory gene. In this study, the ampR-L2 module from S. maltophilia KH was compared with ampR-beta-lactamase modules from several microorganisms with respect to the AmpR and beta-lactamase proteins and the intergenic (IG) region. S. maltophilia and Xanthomonas campestris showed the most closely phylogenetic relationship among the microorganisms considered. The regulatory role of AmpR towards L1 and L2 was further analyzed. In the absence of an inducer, AmpR acted as an activator for L1 expression and as a repressor for L2 expression, whereas AmpR was an activator for both genes in an induced state. In addition, inducibility of L1 and L2 genes depended on the presence of AmpR. The ampR transcript was weakly and constitutively expressed, but was not autoregulated.

Characterization of the charge variants of L2 beta-lactamase in Stenotrophomonas maltophilia.

Stenotrophomonas maltophilia KH has two acid beta-lactamases with isoelectric points (pIs) of 4.6 and 5.4, and several basic beta-lactamases (pIs >7.0) that produce a ladder-shaped pattern by IEF. An isogenic L2 mutant, KHL2(xylE), was constructed by gene replacement. From IEF and native PAGE zymograms of strains KH and KHL2(xylE), it was demonstrated that the basic beta-lactamases and the acid beta-lactamase with pI 5.4 are encoded by the same L2 gene and that the active types of these L2 charge variants were dependent on the buffer pH. The beta-lactamase activities of these L2 charge variants in phosphate buffer at pH 7.0 and 8.0 were 1075+/-29 and 1114+/-81 U mg(-1), respectively. These results indicate that L2 charge variants give S. maltophilia a better chance of adapting and surviving in response to changes in the environment.

Comparison of genomes of three Xanthomonas oryzae bacteriophages.

BACKGROUND: Xp10 and OP1 are phages of Xanthomonas oryzae pv. oryzae (Xoo), the causative agent of bacterial leaf blight in rice plants, which were isolated in 1967 in Taiwan and in 1954 in Japan, respectively. We recently isolated the Xoo phage Xop411. RESULTS: The linear Xop411 genome (44,520 bp, 58 ORFs) sequenced here is 147 bp longer than that of Xp10 (60 ORFs) and 735 bp longer than that of OP1 (59 ORFs). The G+C contents of OP1 (51%) and Xop411 and Xp10 (52% each) are less than that of the host (65%). The 9-bp 3'-overhangs (5'-GGACAGTCT-3') in Xop411 and Xp10 are absent from OP1. More of the deduced Xop411 proteins share higher degrees of identity with Xp10 than with OP1 proteins, while the right end of the genomes of Xp10 and OP1, containing all predicted promoters, share stronger homology. Xop411, Xp10, and OP1 contain 8, 7, and 6 freestanding HNH endonuclease genes, respectively. These genes can be classified into five groups depending on their possession of the HNH domain (HNN or HNH type) and/or AP2 domain in intact or truncated forms. While the HNN-AP2 type endonuclease genes dispersed in the genome, the HNH type endonuclease genes, each with a unique copy, were located within the same genome context. Mass spectrometry and N-terminal sequencing showed nine Xop411 coat proteins, among which three were identified, six were assigned as coat proteins (4) and conserved phage proteins (2) in Xp10. The major coat protein, in which only the N-terminal methionine is removed, appears to exist in oligomeric forms containing 2 to 6 subunits. The three phages exhibit different patterns of domain duplication in the N-terminus of the tail fiber, which are involved in determination of the host range. Many short repeated sequences are present in and around the duplicated domains. CONCLUSION: Geographical separation may have confined lateral gene transfer among the Xoo phages. The HNN-AP2 type endonucleases were more likely to transfer their genes randomly in the genome and may degenerate after successful transmission. Some repeated sequences may be involved in duplication/loss of the domains in the tail fiber genes.

The contribution of class 1 integron to antimicrobial resistance in Stenotrophomonas maltophilia.

Two hundred clinical isolates of Stenotrophomonas maltophilia were examined for the presence of class 1 integron and for the susceptibility to 12 different antimicrobials and detergents. The prevalence of class 1 integron in S. maltophilia isolates was 11%. The class 1 integron-positive isolates exhibited a higher resistance to kanamycin, tobramycin, and trimethoprim-sulfamethoxazole (SXT) than the class 1 integron-negative ones. Polymerase chain reaction (PCR), amplifying the variable region of the class 1 integron, showed the existence of six different amplicon sizes, indicating that there are at least six different class 1 integrons distributed in the 23 class 1 integron-positive isolates. Sequence analysis of six representative PCR amplicons revealed that qacK, aac(6')-Ib', qacK-aac(6')-Ib, qacK-aac(6')-Ib-aac(6')-Ib, and qacL-aadB-cmlA-aadA2 were identified in the 550-, 800-, 1,200-, 1,800, and 3,600-bp amplicons, respectively. The sequence analysis of the 150-bp PCR amplicon demonstrated no additional resistance-associated genes except the basic genetic elements of class 1 integron. The impact of class 1 integron acquisition on the antimicrobials susceptibility was assayed by isogenic integron deletion mutant construction and the susceptibility test. The most significant contribution of the class 1 integron acquisition to S. maltophilia is the increased resistance to SXT.