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10100.9725The encapsulated strain TIGR4 of Streptococcus pneumoniae is phagocytosed but is resistant to intracellular killing by mouse microglia. The polysaccharide capsule is a major virulence factor of Streptococcus pneumoniae as it confers resistance to phagocytosis. The encapsulated serotype 4 TIGR4 strain was shown to be efficiently phagocytosed by the mouse microglial cell line BV2, whereas the type 3 HB565 strain resisted phagocytosis. Comparing survival after uptake of TIGR4 or its unencapsulated derivative FP23 in gentamicin protection and phagolysosome maturation assays, it was shown that TIGR4 was protected from intracellular killing. Pneumococcal capsular genes were up-regulated in intracellular TIGR4 bacteria recovered from microglial cells. Actual presence of bacteria inside BV2 cells was confirmed by transmission electron microscopy (TEM) for both TIGR4 and FP23 strains, but typical phagosomes/phagolysosomes were detected only in cells infected with the unencapsulated strain. In a mouse model of meningitis based on intracranic inoculation of pneumococci, TIGR4 caused lethal meningitis with an LD(50) of 2 × 10² CFU, whereas the LD(50) for the unencapsulated FP23 was greater than 10⁷ CFU. Phagocytosis of TIGR4 by microglia was also demonstrated by TEM and immunohistochemistry on brain samples from infected mice. The results indicate that encapsulation does not protect the TIGR4 strain from phagocytosis by microglia, while it affords resistance to intracellular killing.201020615478
616610.9714Intraperitoneal infection with Salmonella abortusovis is partially controlled by a gene closely linked with the Ity gene. The aim of the present study was to determine whether the Ity gene, which controls the resistance to S. typhimurium infection in mice, also governs the resistance to S. abortusovis, a serotype specific for goat and sheep. During either i.v. or i.p. infection, BALB/c mice (Itys) were not able to control the growth of S. abortusovis and eventually died from infection. In contrast CBA (Ityr) or (C.CB)F1 (Ityr/s) mice were able to control the growth of these bacteria. Using congenic C.D2 Ityr mice, we found that the gene controlling resistance to S. abortusovis was tightly linked to the Ity gene on chromosome 1. Furthermore, in the spleen and the liver of backcross BALB/c x (CBA x BALB/c) mice, the S. abortusovis resistance phenotype cosegregated with the two alleles of the Len-1 gene, a gene tightly linked to the Ity gene. By contrast, in these backcross mice, the level of infection of the peritoneal cavity, the site of inoculation, did not correlated with the Len-1 phenotype of the animal. These results provide evidence that after i.p. inoculation the control of S. abortusovis growth in the spleen and the liver is controlled by the Ity gene, but also suggest that additional gene(s) regulate the number of bacteria at the site of inoculation.19921544222
615920.9705Gene expression profiling of Cecropin B-resistant Haemophilus parasuis. Synthetically designed antimicrobial peptides (AMPs) present the potential of replacing antibiotics in the treatment of bacterial infections. However, microbial resistance to AMPs has been reported and little is known regarding the underlying mechanism of such resistance. The naturally occurring AMP cecropin B (CB) disrupts the anionic cell membranes of Gram-negative bacteria. In this study, CB resistance (CBR) was induced in Haemophilusparasuis SH0165 by exposing it to a series of CB concentrations. The CB-resistant H.parasuis strains CBR30 and CBR30-50 were obtained. The growth curves of SH0165 and CBR30 showed that CBR30 displayed lower growth rates than SH0165. The result of transmission electron microscopy showed cell membranes of the CB-resistant CBR30 and CBR30-50 were smoother than SH0165. Microarrays detected 257 upregulated and 254 downregulated genes covering 20 clusters of orthologous groups (COGs) of the CB-resistant CBR30 compared with SH0165 (>1.5-fold change, p < 0.05). Sixty genes were affected in CBR30-50 covering 18 COGs, with 28 upregulated and 32 downregulated genes. Under the COG function classification, the majority of affected genes in the CB-resistant CBR30 and CBR30-50 belong to the category of inorganic ion transport, amino acid transport, and metabolism. The microarray results were validated by real-time quantitative reverse transcription PCR. This study may provide useful guidance for understanding the molecular mechanism underlying H.parasuis resistance to CB.201424862339
615830.9687Nitric oxide stress resistance in Porphyromonas gingivalis is mediated by a putative hydroxylamine reductase. Porphyromonas gingivalis, the causative agent of adult periodontitis, must maintain nitric oxide (NO) homeostasis and surmount nitric oxide stress from host immune responses or other oral bacteria to survive in the periodontal pocket. To determine the involvement of a putative hydroxylamine reductase (PG0893) and a putative nitrite reductase-related protein (PG2213) in P. gingivalis W83 NO stress resistance, genes encoding those proteins were inactivated by allelic exchange mutagenesis. The isogenic mutants P. gingivalis FLL455 (PG0893ermF) and FLL456 (PG2213ermF) were black pigmented and showed growth rates and gingipain and hemolytic activities similar to those of the wild-type strain. P. gingivalis FLL455 was more sensitive to NO than the wild type. Complementation of P. gingivalis FLL455 with the wild-type gene restored the level of NO sensitivity to a level similar to that of the parent strain. P. gingivalis FLL455 and FLL456 showed sensitivity to oxidative stress similar to that of the wild-type strain. DNA microarray analysis showed that PG0893 and PG2213 were upregulated 1.4- and 2-fold, respectively, in cells exposed to NO. In addition, 178 genes were upregulated and 201 genes downregulated more than 2-fold. The majority of these modulated genes were hypothetical or of unknown function. PG1181, predicted to encode a transcriptional regulator, was upregulated 76-fold. Transcriptome in silico analysis of the microarray data showed major metabolomic variations in key pathways. Collectively, these findings indicate that PG0893 and several other genes may play an important role in P. gingivalis NO stress resistance.201222247513
616740.9686Differential gene expression in Escherichia coli during aerosolization from liquid suspension. Comparative transcriptome analysis was used to determine the differentially expressed genes in Escherichia coli during aerosolization from liquid suspension. Isogenic mutant studies were then used to examine the potential part played by some of these genes in bacterial survival in the air. Bioaerosols were sampled after 3 min of nebulization, which aerosolized the bacteria from the liquid suspension to an aerosol chamber (A0), and after further 30 min of airborne suspension in the chamber (A30). Bacteria at A0 showed 65 differentially expressed genes (30 downregulated and 35 upregulated) as compared to the original bacteria in the nebulizer. Droplet evaporation models predicted a drop in temperature in the bioaerosols, which coincides with the change in the expression of cold shock protein genes-cspB and cspG in the bacteria. The most notable group of differentially expressed genes was sorbitol transport and metabolism genes (srlABDEMR). Other genes associated with osmotic stress, nutrient limitation, DNA damage, and other stresses were differentially expressed in the bacteria at A0. After further airborne suspension, one gene (ypfM, which encodes a hypothetical protein with unknown function) was downregulated in the bacteria at A30 as compared to those at A0. Finally, isogenic mutants with either the dps or srlA gene deleted (both genes were upregulated at A0) had lower survival than the parental strain, which is a sign of their potential ability to protect the bacteria in the air.201829808326
872250.9684Symbiotic Fungus Affected the Asian Citrus Psyllid (ACP) Resistance to Imidacloprid and Thiamethoxam. The Asian citrus psyllid (ACP), Diaphorina citri (Kuwayama) (Hemiptera: Liviidae), is a notorious Rutaceae plant pest. Frequent and extensive use of pesticides has resulted in severe insecticide resistance in ACP populations. Fully understanding the mechanism of ACP resistance to pesticides is vital for us to control or delay the development of resistance. Therefore, we compared the difference in resistance to imidacloprid and thiamethoxam between Hunan (Yongzhou, Chenzhou) and Guangdong (Guangzhou) ACP populations and analyzed the correlations between the resistance level and genes and symbiotic fungi. The results showed that the resistance of the Guangdong ACP population to imidacloprid and thiamethoxam was lower than that of Hunan ACP population, and the relative expression of genes associated with P450 mono-oxygenase and acetylcholinesterase was significantly lower in the Guangdong ACP population than in Hunan ACP population. The differences of mean relative abundances of four symbiotic bacteria among three populations were marginally significant; however, the mean relative abundance of 16 fungi among three populations was significantly different, and positive linear correlations were observed between the resistance level and two fungi (Aspergillus niger and Aureobasidium pullulans) and two genes (CYP4C70 and CYP4DB1). Negative correlations were only observed between the resistance level and two fungi (Golubevia pallescens and Acremonium sclerotigenum). Moreover, four fungi were unique to the Chenzhou population which was the highest resistance to imidacloprid and thiamethoxam. These findings suggested the P450 mono-oxygenase and symbiotic fungi together affected ACP resistance to imidacloprid and thiamethoxam. In the future, we may use environmental G. pallescens and A. sclerotigenum to control or delay ACP resistance.202033391190
616060.9678Comparative transcriptional profiling of tildipirosin-resistant and sensitive Haemophilus parasuis. Numerous studies have been conducted to examine the molecular mechanism of Haemophilus parasuis resistance to antibiotic, but rarely to tildipirosin. In the current study, transcriptional profiling was applied to analyse the variation in gene expression of JS0135 and tildipirosin-resistant JS32. The growth curves showed that JS32 had a higher growth rate but fewer bacteria than JS0135. The cell membranes of JS32 and a resistant clinical isolate (HB32) were observed to be smoother than those of JS0135. From the comparative gene expression profile 349 up- and 113 downregulated genes were observed, covering 37 GO and 63 KEGG pathways which are involved in biological processes (11), cellular components (17), molecular function (9), cellular processes (1), environmental information processing (4), genetic information processing (9) and metabolism (49) affected in JS32. In addition, the relative overexpression of genes of the metabolism pathway (HAPS_RS09315, HAPS_RS09320), ribosomes (HAPS_RS07815) and ABC transporters (HAPS_RS10945) was detected, particularly the metabolism pathway, and verified with RT-qPCR. Collectively, the gene expression profile in connection with tildipirosin resistance factors revealed unique and highly resistant determinants of H. parasuis to macrolides that warrant further attention due to the significant threat of bacterial resistance.201728790420
872470.9678Effects of different salinity on the transcriptome and antibiotic resistance of two Vibrio parahaemolyticus strains isolated from Penaeus vannamei cultured in seawater and freshwater ponds. The transcriptome and antibiotic resistance of Vibrio parahaemolyticus isolated from Penaeus vannamei cultured in seawater (strain HN1)and freshwater (strain SH1) ponds were studied at different salinity (2‰ and 20‰). At different salinity, 623 differentially expressed genes (DEGs) significantly upregulated and 1,559 DEGs significantly downregulated in SH1. In HN1, 466 DEGs significantly upregulated and 1,930 DEGs significantly downregulated, indicating high salinity can lead to the downregulation of most genes. In KEGG analysis, the expression of DEGs annotated to starch and sucrose metabolism pathway was higher at 2‰ salinity than at 20‰ salinity in HN1 and SH1, implying salinity affected bacterial growth mainly through this pathway. In the enrichment analysis of upregulated DEGs, two pathways (Valine, leucine, and isoleucine degradation, and Butanoate metabolism) were significantly enriched at different salinity. Antibiotic-susceptibility test discovered that SH1 isolated from P. vannamei cultured in freshwater was resistant to multiple drugs, including kanamycin, gentamicin, medemycin, and azithromycin, at a salinity of 2‰, whereas at 20‰ salinity, SH1 was not resistant to the drugs. The HN1 strain isolated from P. vannamei cultured in mariculture was resistant to polymyxin B and clindamycin at 20‰ salinity. Whereas, HN1 was intermediately susceptible to these two antibiotics at 2‰ salinity. These results indicate that the drug resistance of bacteria was affected by salinity. Furthermore, beta-lactam resistance was significantly enriched in SH1 at different salinity, and the inhibition zone of penicillin G was consistent with the results of a beta-lactam resistance pathway.202134496040
521780.9674UV Resistance of bacteria from the Kenyan Marine cyanobacterium Moorea producens. UV resistance of bacteria isolated from the marine cyanobacterium Moorea producens has not been observed previously, findings which highlight how unsafe germicidal UV irradiation for sterilization of air, food, and water could be. Further, UV resistance of Bacillus licheniformis is being observed for the first time. This study focused on bacteria isolated from the marine cyanobacterium M. producens collected off the Kenyan coast at Shimoni, Wasini, Kilifi, and Mida. UV irradiance of isolates (302 nm, 70 W/m(2) , 0-1 hr) established B. licheniformis as the most UV resistant strain, with the following order of taxon resistance: Bacilli> γ proteobacteria > Actinobacteria. UV resistance was independent of pigmentation. The maximum likelihood phylogenetic distance determined for both B. licheniformis and Bacillus aerius relative to M. producens CCAP 1446/4 was 2.0. Survival of B. licheniformis upon UV irradiance followed first-order kinetics (k = 0.035/min, R(2)  = 0.88). Addition of aqueous extracts (2, 10, 20 and 40 mg/ml) of this B. licheniformis strain on the less resistant Marinobacterium stanieri was not significant, however, the commercial sunscreen benzophenone-3 (BP-3) positive control and the time of irradiance were significant. Detection of bacteria on M. producens filaments stained with acridine orange confirmed its nonaxenic nature. Although the chemistry of UV resistance in cyanobacteria has been studied in depth revealing for example the role of mycosporine like amino acids (MAAs) in UV resistance less is known about how bacteria resist UV irradiation. This is of interest since cyanobacteria live in association with bacteria.201930123980
616490.9672Genetic factors involved in murine resistance to experimental brucellosis. C57 B1/6 are more resistant than DBA2 mice to IV inoculation of Brucella suis 1330. This difference does not concern the blood clearance of the injected bacteria or the number of infective colonies in the spleen at very early (less than 24 h) or at late (greater than 2 months) stages but the splenic infection at intermediate stages with maximal differences between days 7 and 14. The "resistance" character is inherited by F1 and backcrosses as a partially dominant character with polygenic control and a better expression of resistance factor(s) in females, independently of male-female matings. Association of the "resistance" character with known genetic markers was investigated using (B6 X DB) X DB backcrosses, BALB/B, BALB/c, C3H/eb and C3H/HeJ mice. No correlation of "resistance" with Ig allotypes, the "d" coat colour or the LPS genes was evidenced. On the other hand significant differences in the number of splenic colonies on day 7 were observed according to the H-2 haplotype or the "b" coat colour phenotypes. These results are discussed in terms of a comparison with the genetics of other facultative intracellular bacteria and of the partially common and partially independent genetic regulation of the functional components of anti-Brucella resistance.19846593265
398100.9670The chloramphenicol-inducible catB gene in Agrobacterium tumefaciens is regulated by translation attenuation. Agrobacterium tumefaciens strains C58, A136, and BG53 are chloramphenicol resistant, and each contains the catB gene originally identified by Tennigkeit and Matzuran (Gene 99:113-116, 1991). The chloramphenicol acetyltransferase activity in all of the strains is chloramphenicol inducible. Examination of the catB gene in strain BG53 indicates that it is regulated by an attenuation mechanism similar to translation attenuation that regulates inducible catA genes resident in gram-positive bacteria and the inducible cmlA gene that confers chloramphenicol resistance in Pseudomonas spp.200212107148
536110.9670Thymidylate synthase gene from Lactococcus lactis as a genetic marker: an alternative to antibiotic resistance genes. The potential of the thymidylate synthase thyA gene cloned from Lactococcus lactis subsp. lactis as a possible alternative selectable marker gene to antibiotic resistance markers has been examined. The thyA mutation is a recessive lethal one; thyA mutants cannot survive in environments containing low amounts of thymidine or thymine (such as Luria-Bertani medium) unless complemented by the thyA gene. The cloned thyA gene was strongly expressed in L. lactis subsp. lactis, Escherichia coli, Rhizobium meliloti, and a fluorescent Pseudomonas strain. In addition, when fused to a promoterless enteric lac operon, the thyA gene drove expression of the lac genes in a number of gram-negative bacteria. In transformation experiments with thyA mutants of E. coli and conjugation experiments with thyA mutants of R. meliloti, the lactococcal thyA gene permitted selection of transformants and transconjugants with the same efficiency as did genes for resistance to ampicillin, chloramphenicol, or tetracycline. Starting from the broad-host-range plasmid pGD500, a plasmid, designated pPR602, was constructed which is completely free of antibiotic resistance genes and has the lactococcal thyA gene fused to a promoterless lac operon. This plasmid will permit growth of thyA mutant strains in the absence of thymidine or thymine and has a number of unique restriction sites which can be used for cloning.19902117883
6211120.9670Natural resistance to salmonellae in mice: control by genes within the major histocompatibility complex. Determinations of 50% lethal dose (LD50) values in H-2 congenic B10 lines showed that late-emerging resistance (postimmune response phase) to salmonellae of intermediate virulence was less in H-2b and H-2d than in H-2a, H-2k, and H-2f mice. Association of resistance to H-2 was confirmed by backcross analysis, and LD50 determinations on H-2 recombinant haplotype strains showed that resistance maps to the I-E subregion. Bacterial growth curves in liver and spleen showed that susceptible mice carried bacteria for longer in the reticuloendothelial system than did resistant mice and that susceptible mice showed greater splenomegaly. Association of resistance and susceptibility to H-2 was not different when sister transductant salmonellae expressing somatic antigens O4 and O9 were used. Thus a gene(s) within the major histocompatibility complex controls natural resistance to salmonellae in mice by influencing the ability to clear bacteria from the reticuloendothelial system in the later phase of the infection, and the immunodominant O antigen cannot be solely involved.19852413142
8132130.9668Autoclave treatment of pig manure does not reduce the risk of transmission and transfer of tetracycline resistance genes in soil: successive determinations with soil column experiments. The increasing use of antibiotics, especially tetracycline, in livestock feed adversely affects animal health and ecological integrity. Therefore, approaches to decrease this risk are urgently needed. High temperatures facilitate antibiotic degradation; whether this reduces transmission risk and transfer of tetracycline-resistant bacteria (TRBs) and tetracycline resistance genes (TRGs) in soil remains unknown. Successive experiments with soil columns evaluated the effects of autoclaving pig manure (APM) on soil TRB populations and TRGs over time at different soil depths. The data showed sharp increases in TRB populations and TRGs in each subsoil layer of PM (non-APM) and APM treatments within 30 days, indicating that TRBs and TRGs transferred rapidly. The level of TRBs in the upper soil layers was approximately 15-fold higher than in subsoils. TRBs were not dependent on PM and APM levels, especially in the late phase. Nevertheless, higher levels of APM led to rapid expansion of TRBs as compared to PM. Moreover, temporal changes in TRB frequencies in total culturable bacteria (TCBs) were similar to TRBs, indicating that the impact of PM or APM on TRBs was more obvious than for TCBs. TRBs were hypothesized to depend on the numbers of TRGs and indigenous recipient bacteria. In the plough layer, five TRGs (tetB, tetG, tetM, tetW, and tetB/P) existed in each treatment within 150 days. Selective pressure of TC may not be a necessary condition for the transfer and persistence of TRGs in soil. High temperatures might reduce TRBs in PM, which had minimal impact on the transmission and transfer of TRGs in soil. Identifying alternatives to decrease TRG transmission remains a major challenge.201626517996
436140.9668The capsule is a virulence determinant in the pathogenesis of Pasteurella multocida M1404 (B:2). Capsules from a range of pathogenic bacteria are key virulence determinants, and the capsule has been implicated in virulence in Pasteurella multocida. We have previously identified and determined the nucleotide sequence of the P. multocida M1404 (B:2) capsule biosynthetic locus (J. D. Boyce, J. Y. Chung, and B. Adler, Vet. Microbiol. 72:121-134, 2000). The cap locus consists of 15 genes, which can be grouped into three functional regions. Regions 1 and 3 contain genes proposed to encode proteins involved in capsule export, and region 2 contains genes proposed to encode proteins involved in polysaccharide biosynthesis. In order to construct a mutant impaired in capsule export, the final gene of region 1, cexA, was disrupted by insertion of a tetracycline resistance cassette by allelic replacement. The genotype of the tet(M) OmegacexA mutant was confirmed by Southern hybridization and PCR. The acapsular phenotype was confirmed by immunofluorescence, and the strain could be complemented and returned to capsule production by the presence of a cloned uninterrupted copy of cexA. Wild-type, mutant, and complemented strains were tested for virulence by intraperitoneal challenge of mice; the presence of the capsule was shown to be a crucial virulence determinant. Following intraperitoneal challenge of mice, the acapsular bacteria were removed efficiently from the blood, spleen, and liver, while wild-type bacteria multiplied rapidly. Acapsular bacteria were readily taken up by murine peritoneal macrophages, but wild-type bacteria were significantly resistant to phagocytosis. Both wild-type and acapsular bacteria were resistant to complement in bovine and murine serum.200010816499
8473150.9667MHCII, Tlr4 and Nramp1 genes control host pulmonary resistance against the opportunistic bacterium Pasteurella pneumotropica. MHCII, Tlr4, and Nramp1 genes are each independently important in pulmonary immunity. To determine the effect of these genes on host resistance, mice carrying various combinations of functional alleles for these three genes were experimentally challenged with the opportunistic bacterium, Pasteurella pneumotropica. MHCII-/-, Tlr4d/d, and Nramp1s/s mice were significantly more susceptible to experimental infections by P. pneumotropica after intranasal challenge compared to mice carrying functional alleles at only one of those genes. P. pneumotropica were cultured from the lungs of challenged mice, and the severity of the pneumonia strongly correlated with the number of isolated bacteria. Mice with the genotype MHCII-/- Tlr4n/n genotype were less susceptible to pneumonia than MHCII+/+, Tlr4d/d mice. It is interesting that the Nramp1 gene contribution to host resistance was apparent only in the absence of functional MHCII or Tlr4 genes. These data suggest that MHCII, Tlr4, and Nramp1 genes are important to pulmonary bacterial resistance.200111261784
6172160.9667Resistance and susceptibility of mice to bacterial infection. IV. Genetic and cellular basis of resistance to chronic infection with Brucella abortus. The number of Brucella abortus strain 19 organisms in the spleens of CBA/H mice peaked two weeks after intravenous injection of 5 X 10(6) organisms. With the onset of specific cell-mediated immunity, 90% of the bacteria were killed, but approximately 10(6) bacteria persisted up to seven weeks after infection. In contrast, in BALB/c, C57BL/10, and B10Br mice, bacterial numbers peaked at two weeks but decreased steadily with the onset of bactericidal activity. In all strains, clearance of bacteria from the liver was relatively efficient. The course of infection in (CBA/H X BALB/c) F1 mice was similar to that in CBA/H mice, indicating that the mechanism(s) leading to slower recovery from infection was dominant. The H-2 haplotype of the mice did not influence the rate of recovery from infection. The use of backcross mice showed that multiple genes were involved. In bone marrow-chimeric mice, resistance was determined by the genome of the bone marrow donor, not that of the host.19826809847
3734170.9667Changes in the prevalence of resistant Escherichia coil in cattle receiving subcutaneously injectable oxytetracycline in addition to in-feed chlortetracycline compared with cattle receiving only in-feed chlortetracycline. Information about the prevalence of antibiotic resistance in commensal enteric bacteria is of interest because these bacteria are potential indicators of selection pressure on enteric bacteria and represent a reservoir of resistance genes in potentially pathogenic bacteria. This study reports changes in the prevalence of resistance to antibiotics in commensal Escherichia coli from cattle receiving either subcutaneously injectable oxytetracycline in addition to in-feed chlortetracycline or only in-feed chlortetracycline. Resistance to 19 antibiotics was examined. The use of injectable oxytetracycline in addition to in-feed chlortetracycline was significantly associated (P < 0.05) with an increase in the prevalence of resistance only to chloramphenicol and sulfisoxazole.200212146885
392180.9667Stable Tagging of Rhizobium meliloti with the Firefly Luciferase Gene for Environmental Monitoring. A system for stable tagging of gram-negative bacteria with the firefly luciferase gene, luc, is described. A previously constructed fusion constitutively expressing luc from the lambdap(R) promoter was used. Stable integration into the bacterial genome was achieved by use of mini-Tn5 delivery vectors. The procedure developed was applied for tagging of representative gram-negative bacteria, such as Escherichia coli, Rhizobium meliloti, Pseudomonas putida, and Agrobacterium tumefaciens. The system permitted the detection of tagged R. meliloti in the presence of more than 10 CFU per plate without the use of any selective markers (such as antibiotic resistance genes). No significant differences in growth rates or soil survival were found between the marked strain and the wild-type strain. Studies of bioluminescent R. meliloti also revealed a good correlation between cell biomass and bioluminescence. The firefly luciferase tagging system is an easy, safe, and sensitive method for the detection and enumeration of bacteria in the environment.199316349015
433190.9666Expression of the strA-strB streptomycin resistance genes in Pseudomonas syringae and Xanthomonas campestris and characterization of IS6100 in X. campestris. Expression of the strA-strB streptomycin resistance (SMr) genes was examined in Pseudomonas syringae pv. syringae and Xanthomonas campestris pv. vesicatoria. The strA-strB genes in P. syringae and X. campestris were encoded on elements closely related to Tn5393 from Erwinia amylovora and designated Tn5393a and Tn5393b, respectively. The putative recombination site (res) and resolvase-repressor (tnpR) genes of Tn5393 from E. amylovora, P syringae, and X. campestris were identical; however, IS6100 mapped within tnpR in X. campestris, and IS1133 was previously located downstream of tnpR in E. amylovora (C.-S Chiou and A. L. Jones, J. Bacteriol. 175:732-740, 1993). Transcriptional fusions (strA-strB::uidA) indicated that a strong promoter sequence was located within res in Tn5393a. Expression from this promoter sequence was reduced when the tnpR gene was present in cis position relative to the promoter. In X. campestris pv. vesicatoria, analysis of promoter activity with transcriptional fusions indicated that IS6100 increased the expression of strA-strB. Analysis of codon usage patterns and percent G+C in the third codon position indicated that IS6100 could have originated in a gram-negative bacterium. The data obtained in the present study help explain differences observed in the levels of SMr expressed by three genera which share common genes for resistance. Furthermore, the widespread dissemination of Tn5393 and derivatives in phytopathogenic prokaryotes confirms the importance of these bacteria as reservoirs of antibiotic resistance in the environment.19957487022