Streptomycin-resistant Strains Research Articles

Multisite Field Evaluation of Bacteriophages for Fire Blight Management: Incorporation of Ultraviolet Radiation Protectants and Impact on the Apple Flower Microbiome.

Fire blight, a disease of pome fruits caused by the bacterium Erwinia amylovora, has become increasingly difficult to manage after the emergence of streptomycin-resistant strains. Alternative antibiotics and copper are available; however, these chemicals have use restrictions in some countries and also can carry risks of phytotoxicity. Therefore, there is growing interest in biological-based management options, with bacteriophage (phages) showing promise, as these naturally occurring pathogens of bacteria are easy to isolate and grow. However, there are several technical challenges regarding the implementation of phage biocontrol in the field, as the viral molecules suffer from ultraviolet radiation (UVR) degradation and can die off rapidly in the absence of the host bacterium. In this work, we assessed the efficacy of Erwinia phages and a commercial phage product for blossom blight control in the field across multiple locations in the eastern United States. In these tests, disease control ranged from 0.0 to 82.7%, and addition of a UVR protectant only resulted in significantly increased disease control in 2 of 12 tests. We also analyzed microbial community population changes in response to phage application. Changes in bacterial community diversity metrics over time were not detected; however, relative abundances of target taxa were temporarily reduced after phage applications, indicating that these phage applications did not have deleterious effects on the flower microbiome. We have demonstrated that biological control of fire blight with phages is achievable, but a better understanding of phage-pathogen dynamics is required to optimize disease control efficacy.

The Proteome of Extracellular Membrane Vesicles from Bacillus pumilus 3-19

—Production of extracellular membrane vesicles plays an important role in communication in bacterial populations and in bacteria–host interactions. Vesicles as carriers of various regulatory and signaling molecules may be potentially used as disease biomarkers and promising therapeutic agents, including vaccine preparations. The composition of membrane vesicles has been deciphered for a limited number of Gram-negative and Gram-positive bacteria. In this work, for the first time, extracellular membrane vesicles of a streptomycin-resistant strain Bacillus pumilus 3-19, a producer of extracellular guanyl-preferring ribonuclease binase, are isolated, visualized, and characterized by their genome and proteome composition. It has been established that there is no genetic material in the vesicles and the spectrum of the proteins differs depending on the phosphate content in the culture medium of the strain. Vesicles from a phosphate-deficient medium carry 49 unique proteins in comparison with 101 from a medium with the high phosphate content. The two types of vesicles had 140 mutual proteins. Flagellar proteins, RNase J, which is the main enzyme of RNA degradosomes, phosphatases, peptidases, iron transporters, signal peptides, were identified in vesicles. Antibiotic resistance proteins and amyloid-like proteins whose genes are present in B. pumilus 3-19 cells are absent. Phosphate deficiency-induced binase was found only in vesicles from a phosphate-deficient medium.

Presence of genes encoding aminoglycoside-modifying enzyme (AME) and virulence factors in high-level aminoglycoside-resistant (HLAR) Enterococcus strains isolated from retail chicken meat in Turkey

In this study, the presence of aminoglycoside-modifying enzyme (AME) and virulence factor genes were investigated in previously isolated 32 high-level aminoglycoside-resistant (HLAR) Enterococcus strains isolated from retail chicken meat in Turkey. At least one AME-encoding gene was detected in HLAR enterococci by polymerase chain reaction (PCR). The ant(6ʹ)-Ia was identified as the most prevalent (87.5%, 28/32) AME gene. The aph(3ʹ)-IIIa (78.13%, 25/32), ant(4ʹ)-Ia (68.75%, 22/32), aph(2ʹʹ)-Ib (62.5%, 20/32), aac(6ʹ)-Ie-aph(2ʹʹ)-Ia (21.88%, 7/32) and aph(2ʹʹ)-Ic (9.38%, 3/32) are the other detected AME-encoding genes in strains. The aph(2ʹʹ)-Id was found in none of the HLAR strains. The aph(2ʹʹ)-Ib and ant(6ʹ)-Ia were identified as the most frequently AME-encoding genes in high-level gentamicin-resistant (HLGR) and high-level streptomycin-resistant (HLSR) strains, respectively. Among the 32 HLAR strains, only E. faecalis MSE61.1 and E. avium MSE63.1 were found capable of hydrolyzing gelatine. All HLAR strains showed α-hemolytic activity except E. durans MG13.4 and E. casseliflavus MGM111.1, which were exhibited β- and γ-hemolytic activity, respectively. It was determined that all HLAR strains, except E. durans MGE13.1 and MGE63.1, contain at least one virulence factor gene. The efaAfm (87.5%, 28/32), acm (65.63%, 21/32) and gelE (37.5%, 12/32) were found to be the most prevalent virulence factor genes. HLAR enterococci strains that have the virulence factor genes may pose a risk to consumer health.

Whole-genome sequencing and transcriptome-characterized mechanism of streptomycin resistance in Vibrio parahaemolyticus O10: K4

Streptomycin resistance in V. parahaemolyticus has been widespread in both clinical and environmental isolates. Therefore, it is of great significance to characterize the mechanism of streptomycin resistance in V. parahaemolyticus. O10:K4 has emerged and becoming the new dominant serotype since 2020. In this study, we isolated a total of 36 strains of V. parahaemolyticus O10:K4 from 2020 to 2022 and found that more than half of them were resistant to streptomycin. We obtained streptomycin resistant and sensitive strains by detecting the resistance profiles. Whole-genome sequencing showed that VP_RS10735 and VP_RS05605 were the predominant mutations in streptomycin resistant O10:K4 clinical isolates. In addition, this study provided global insight into the characteristics of the transcriptome signature of streptomycin resistance, revealing that efflux transporters play a key role in streptomycin resistance. Finally, we found that streptomycin resistant strain was more virulent than sensitive strain. The results of this study should advance our understanding of the mechanisms of aminoglycoside resistance.

A Novel IncX Plasmid Mediates High-Level Oxytetracycline and Streptomycin Resistance in Erwinia amylovora from Commercial Pear Orchards in California.

Isolates of the fire blight pathogen Erwinia amylovora with high-level resistance to oxytetracycline (minimal inhibitory concentration [MIC] > 100 μg/ml) and to streptomycin (MIC > 100 μg/ml) were recovered from four commercial pear orchards in California between 2018 and 2020. The two representative oxytetracycline- and streptomycin-resistant (OxyTcR-SmR) strains 32-10 and 33-1 were as virulent as the antibiotic susceptible strain 13-1 in causing blossom blight of pear and were recovered more than 50% of the time 7 days after co-inoculation to pear flowers with strain 13-1. In the field, inoculation of strain 32-10 to pear flowers that were pretreated with oxytetracycline at 200 μg/ml did not reduce disease compared with an untreated control. Four OxyTcR-SmR strains were subjected to draft genome sequencing to identify the genetic determinants of antibiotic resistance and their location. A 43.6-kb IncX plasmid, designated pX11-7, was detected in each of the four strains, and this plasmid encoded the tetracycline-resistance gene tetB and the streptomycin-resistance gene pair strAB within a large putatively mobile genetic element consisting of the transposon Tn10 that had inserted within the streptomycin-resistance transposon Tn6082. We also determined that pX11-7 was conjugative and was transferred at a rate that was 104 to 105 higher into an E. amylovora strain isolated in California compared with an E. amylovora strain that was isolated in Michigan. The occurrence of high levels of resistance to both oxytetracycline and streptomycin in E. amylovora strains from commercial pear orchards in California significantly limits the options for blossom blight management in these locations.

Plague Gives Surprises in the Second Decade of the Twenty-First Century.

From 2010 through 2019, the six leading countries by numbers of human plague cases reported to the WHO were, in order from highest to lowest, Madagascar, Congo, Uganda, Peru, Tanzania, and the United States. From these countries, there was a total of 4,547 cases, of whom 786 (17%) died. Top plague events were four outbreaks of primary pneumonic plague in Madagascar that affected 1,936 persons, including index cases, of whom 137 died. One of the outbreaks was caused by a streptomycin-resistant strain of Yersinia pestis. Person-to-person transmission occurred in a taxi, in households with family caregivers, at burial ceremonies and wakes for victims, and at a hospital where cases were treated. Unique clinical presentations in the United States included a dog owner who acquired pneumonic plague from his sick dog, a boy with septicemic plague who developed complications of osteomyelitis and arthritis that required surgery for bone removal and bone grafting, and a prairie dog handler who acquired bubonic plague from a bite by a sick prairie dog. Efficacy of antibiotics in a model of pneumonic plague in African green monkeys for use in bioterrorism revealed the most effective drugs to be gentamicin, ciprofloxacin, and levofloxacin. A recombinant vaccine containing Fraction 1 antigen and V antigen of Y. pestis designed for first responders during a bioterrorism attack and military personnel was tested for safety and immunogenicity but was not licensed for use by the end of the decade.

Evaluation of systemic acquired resistance inducers for the management of copper and streptomycin resistant strains of Xanthomonas perforans on tomato

Bacterial spot (Xanthomonas spp.) is one of the most detrimental diseases of tomato (Solanum lycopersicum L.) worldwide. Bacterial spot Xanthomonads are either endemic or spread by contaminated seed or transplant material into tomato production areas. Due to limited disease management options, transplant producers rely on copper- and streptomycin-based bactericides that are often ineffective due to the predominance of resistant Xanthomonas strains. In this study, transplant production facilities located across eight counties in western North Carolina were surveyed for bacterial spot symptoms from 2018 to 2019. In total, 29 strains (n = 6 in 2018 and n = 23 in 2019) were isolated and identified as Xanthomonas perforans. All strains were resistant to copper, while only 24% of the strains were resistant to streptomycin. Therefore, the ability of three systemic acquired resistance (SAR) inducers, methyl salicylate, Bacillus mycoides isolate J, and acibenzolar-S-methyl (ASM), alone or in combination with copper or streptomycin were evaluated as potential alternatives to copper-mancozeb (grower standard) to manage bacterial spot under greenhouse and field conditions. Under greenhouse conditions, applications of ASM at 0.4 g/L alone, or in combination with copper or streptomycin, significantly reduced bacterial spot disease severity when compared to the grower standard and nontreated controls (P < 0.05). However, none of the SAR inducers significantly reduced disease severity or improved yield when compared to copper-mancozeb-ASM under field conditions (P < 0.05). This study highlights the potential of using ASM for the management of bacterial spot of tomato transplant production to reduce bacterial spot introduction into the field.

Biopesticides provide inadequate control of three foliar bacterial diseases of tomato transplants

There are three important diseases caused by bacterial pathogens affecting tomato foliage on seedlings in the greenhouse and on mature plants in the field: bacterial canker, bacterial spot, and bacterial speck. Their causal agents are seedborne and the greenhouse environment is conducive for their multiplication and spread; therefore, control measures should be targeted to transplant production to reduce the risk of epidemics in the field. A tank-mix of copper and mancozeb or streptomycin are standard treatments to prevent or manage these diseases in the greenhouse, but the presence of copper and/or streptomycin resistant strains makes it difficult to achieve consistent control. Increasing demand for biopesticides to avoid control failure due to pesticide resistance and reduce the use of conventional pesticides has led to many products being developed. We evaluated three registered biopesticides (Regalia, Stargus, and TerraGrow) and five products in development: three botanicals (AOMMA-Agro, CranShield Plus, and CranProtect), a biological bacterial biofilm inhibitor (SP8010), and Zinkicide. Products were applied singly or in combination to assess their efficacy against three bacterial diseases of tomato seedlings caused by four pathogens, compared to a tank mixture of copper plus mancozeb alternated with streptomycin (grower standard) and a non-treated control. The grower standard provided the best control in three of the four experiments, while the biopesticides were inconsistent or ineffective in controlling each of the four pathogens in this study.

Co-Expression of Transcriptional Regulators and Housekeeping Genes in Streptomyces spp.: A Strategy to Optimize Metabolite Production.

The search for novel bioactive compounds to overcome resistance to current therapeutics has become of utmost importance. Streptomyces spp. are one of the main sources of bioactive compounds currently used in medicine. In this work, five different global transcriptional regulators and five housekeeping genes, known to induce the activation or overproduction of secondary metabolites in Streptomyces coelicolor, were cloned in two separated constructs and expressed in 12 different strains of Streptomyces spp. from the in-house CS collection. These recombinant plasmids were also inserted into streptomycin and rifampicin resistant Streptomyces strains (mutations known to enhance secondary metabolism in Streptomyces). Different media with diverse carbon and nitrogen sources were selected to assess the strains' metabolite production. Cultures were then extracted with different organic solvents and analysed to search for changes in their production profiles. An overproduction of metabolites already known to be produced by the biosynthesis wild-type strains was observed such as germicidin by CS113, collismycins by CS149 and CS014, or colibrimycins by CS147. Additionally, the activation of some compounds such as alteramides in CS090a pSETxkBMRRH and CS065a pSETxkDCABA or inhibition of the biosynthesis of chromomycins in CS065a in pSETxkDCABA when grown in SM10 was demonstrated. Therefore, these genetic constructs are a relatively simple tool to manipulate Streptomyces metabolism and explore their wide secondary metabolites production potential.

154. Prevalence and Antimicrobial Resistance of Enterococcus species in a Tertiary Center Children’s Hospital in Korea

Abstract Background Increasing prevalence of Enterococcus spp. as a nosocomial pathogen with high-level resistance to multiple antimicrobials has been a challenge throughout the years, and now, even to the pediatric age. This study is a pioneer research which was designed to determine the prevalence of different antibiogram patterns of enterococcal strains in the pediatric age. Methods In this retrospective review, we included Enterococcus species isolated from normal body fluid including blood and CSF from March 2014 through September 2020 at Asan Medical Center Children`s Hospital. Electronic Medical Records (EMR) was reviewed for clinical and demographic data. Results A total of 205 different clinical strains of Enterococcus species were collected. Isolated strains were E. faecalis (47.3%), E. faecium (41.5%), E. avium (4.9%), E. gallinarum (2.9%), E. raffinosus (2.0%) and others (1.5%). No strains were resistant to linezolid. Vancomycin or teicoplanin resistant strains were 26.3% (vancomycin 17.1%, teicoplanin 9.3%), most of which were E. faecium (vancomycin 13.7%, teicoplanin 9.3%). Ampicillin or penicillin resistant strains were 82.9% (ampicillin 39.0%, penicillin 43.9%), most of which were also E. faecium (ampicillin 35.1%, penicillin 36.1%). High-level streptomycin or gentamicin resistant strains were 46.8% (streptomycin 13.2%, gentamicin 33.7%), mostly E. faecalis (streptomycin 7.8%, gentamicin 19.0%). The prevalence of antimicrobial resistance differed significantly between E. faecalis and E. faecium; E. faecalis being nearly all susceptible to ampicillin and penicillin except 6 strains which was an interesting finding because ampicillin-susceptible, penicillin-resistant E. faecalis strains were found. Antibiotic Resistance Pattern of Enterococcal Strains MIC of ASPR Enterococcus species by Etest Conclusion Consistent findings with previous studies based on adults are that E. faecalis and E. faecium were the predominant strains causing infection in children as well. There are reports about currently emerging ampicillin-susceptible but penicillin-resistant(ASPR) E. faecalis strains which were also found in this study and so therefore further molecular studies about this newly emerging ASPR E. faecalis is in progress. Disclosures All Authors: No reported disclosures.

Antibiotic Resistance of Pectobacterium Korean Strains Susceptible to the Bacteriophage phiPccP-1

Commercial products with antibiotics like streptomycin as active ingredients have been used to control soft rot disease caused by Pectobacterium species for a long time. In this study, antibiotic resistance of twentyseven Korean strains of Pectobacterium species including P. carotovorum, P. odoriferum, P. brasiliense, and P. parmenteri, which were previously shown to be susceptible to the bacteriophage phiPccP-1 was surveyed using a disk diffusion assay. While all strains were highly susceptible to ampicillin, kanamycin, chloramphenicol, tetracycline, and rifampicin, some strains showed weak susceptibility to 300 μg/ml of streptomycin. Furthermore, some of them are partially or completely resistant to commercial pesticides—Buramycin and streptomycin at the concentration of 250 μg/ml that is recommended by the manufacturer for streptomycin- based pesticides. These results indicate the presence of streptomycin-resistant Pectobacterium strains in South Korea, and the development of antibiotic alternatives to control soft rot is needed.

Assessment of Antimicrobial Activity of Lichenic Compounds Isolated from Menegazzia terebrata (Hoffm.) A. Massal

The antibiotic activity of lichenic compounds atranorin, physodic, and stictic acid isolated from Menegazzia terebrata were analyzed. The antibiotic bioactivity was assessed against eight bacterial inoculums i.e., 3 g positive and 5 g negative by analyzing the minimal inhibitory concentrations (MICs) using the broth tube dilution method. All lichenic compounds showed antibiotic activities. The maximum bacterial growth inhibition activity was observed by atranorin (MIC, 0.030–0.5 mg/mL) and the minimum in physodic acid (MIC, 1 mg/mL). Stictic acid (MIC, 0.25–0.5 mg/mL) exhibited moderate antibiotic activity. Among the tested bacterial inoculums, all lichenic compounds reported antibacterial activity against a streptomycin-resistant strain of Pseudomonas aeruginosa. As a result, the study referred to the antibiotic potential of lichenic compounds, which could be developed further for pharmaceutical purposes.

Streptomyces sp. AN090126 as a Biocontrol Agent against Bacterial and Fungal Plant Diseases.

Bacteria and fungi are major phytopathogens which substantially affect global agricultural productivity. In the present study, Streptomyces sp. AN090126, isolated from agricultural suppressive soil in Korea, showed broad-spectrum antagonistic activity against various phytopathogenic bacteria and fungi. In the 96-well plate assay, the fermentation filtrate of Streptomyces sp. AN090126 exhibited antimicrobial activity, with a minimum inhibitory concentration (MIC) of 0.63–10% for bacteria and 0.63–3.3% for fungi. The MIC of the partially purified fraction was 20.82–250 µg/mL for bacteria and 15.6–83.33 µg/mL for fungi. Gas chromatography–mass spectrometry (GC-MS) analysis revealed that AN090126 produced various volatile organic compounds (VOCs), including dimethyl sulfide and trimethyl sulfide, which inhibited the growth of pathogenic bacteria and fungi in in vitro VOC assays. In pot experiments, the fermentation broth of Streptomyces sp. AN090126 reduced tomato bacterial wilt caused by Ralstonia solanacearum, red pepper leaf spot caused by Xanthomonas euvesicatoria, and creeping bentgrass dollar spot caused by Sclerotinia homoeocarpa in a dose-dependent manner. Moreover, the secondary metabolites derived from this strain showed a synergistic effect with streptomycin sulfate against streptomycin-resistant Pectobacterium carotovorum subsp. carotovorum, the causative agent of Kimchi cabbage soft rot, in both in vitro and in vivo experiments. Therefore, Streptomyces sp. AN090126 is a potential biocontrol agent in controlling plant diseases caused by pathogenic bacteria and fungi, specifically by the streptomycin-resistant strains.

Mutation of rpsL Gene in Streptomycin-Resistant Pseudomonas syringae pv. actinidiae Biovar 3 Strains Isolated from Korea

Pseudomonas syringae pv. actinidiae (Psa) is the causal agent responsible for the bacterial canker disease of kiwifruit plants. Psa strains are divided into five different biovars based on genetic and biochemical characteristics. Among them, biovar 2 and 3 strains of Psa were isolated and have been causing widespread damages in Korea. One of the most effective ways to control Psa is to use an antibiotic such as streptomycin. However, Psa strains resistant to this antibiotic were isolated in Korea, and an earlier study revealed that the resistance in the biovar 2 is associated with strA-strB genes. This study aimed to determine the molecular resistance mechanism of Psa biovar 3 strains to streptomycin. Sequencing the rpsL gene encoding ribosomal protein S12 from three streptomycin-resistant strains screened in the laboratory revealed that a spontaneous mutation occurred either at codon 43 or 88. Meanwhile, in four streptomycin-resistant strains of Psa biovar 3 isolated from two kiwifruit orchards, a single nucleotide in codon 43 of the rpsL, which is AAA in streptomycin-sensitive strain, was substituted for AGA causing an amino acid change from lysine to arginine. The resistant mechanism in all biovar 3 strains obtained in Korea was identified as a mutation of the rpsL gene.

Amycolachromones A-F, Isolated from a Streptomycin-Resistant Strain of the Deep-Sea Marine Actinomycete Amycolatopsis sp. WP1.

In this study, a detailed chemical investigation of a streptomycin-resistant strain of the deep-sea marine, actinomycete Amycolatopsis sp. WP1, yielded six novel amycolachromones A–F (1–6), together with five known analogues (7–11). Amycolachromones A–B (1–2) possessed unique dimer skeletons. The structures and relative configurations of compounds 1–11 were elucidated by extensive spectroscopic data analyses combined with X-ray crystal diffraction analysis. Plausible biogenetic pathways of amycolachromones A–F were also proposed.

Class 1 In-Tn5393c array contributed to antibiotic resistance of non-pathogenic Pseudoxanthomonas mexicana isolated from a wastewater bioreactor treating streptomycin

The emergence of antibiotic resistance in retort to environmental pollutants during wastewater treatment still remains elusive. Here, we first to investigate the emergence of antibiotic resistance in an environmental non-pathogenic bacterium, Pseudoxanthomonas mexicana isolated from a lab-scale bioreactor treating wastewater containing streptomycin. The molecular mechanism of antibiotic resistance development was evaluated in its genomic, transcriptional, and proteomic levels. The streptomycin resistant (SR) strain showed strong resistance to streptomycin (MIC > 600 μg/mL) as well to sulfamethoxazole, ampicillin, and kanamycin (≥250 μg/mL). A 13.4 kb class-1-integron array consisting of a new arrangement of gene cassette (IS6100-sul1-aadA2-catB3-aacA1-2-aadB-int1-IS256-int) linked with Tn5393c transposon was identified in the SR strain, which has only been reported in clinical pathogens so far. iTRAQ-LC-MS/MS proteomics revealed 22 up-regulated proteins in the SR strain growing under 100 mg L−1 streptomycin, involving antibiotic resistance, toxin production, stress response, and ribosomal protein synthesis. At the mRNA level, elevated expressions of ARGs (strA, strB, and aadB) and 30S-ribosomal protein genes (rpsA and rpsU) were observed in the SR strain. The results highlighted the genomic plasticity and multifaceted regulatory mechanism employed by P. mexicana in adaptation to high-level streptomycin during biological wastewater treatment.

Whole-Genome Sequencing of Streptomycin-Resistant Mycobacterium tuberculosis Strain SBH145 from Sabah, Malaysia.

ABSTRACTThis paper reports on the whole-genome sequencing of a streptomycin-resistant Mycobacterium tuberculosis strain that was isolated from a patient with pulmonary tuberculosis in Sabah state of Malaysian Borneo. The strain belongs to the EAI2-Manila family of lineage 1 and is clustered with M. tuberculosis strains from the Philippines, India, and Taiwan.

Identification of strA-strB Genes in Streptomycin-Resistant Pseudomonas syringae pv. actinidiae Biovar 2 Strains Isolated in Korea.

Bacterial canker is a devastating disease of kiwifruit caused by the bacterium Pseudomonas syringe pv. actinidiae. Canker disease of kiwifruit in Korea has been controlled using streptomycin for more than two decades. Four streptomycin-resistant strains, belonging to biovar 2, which are found only in Korea, were collected between 2013 and 2014 from different orchards located in Jeju, Korea. The genetic background for streptomycin resistance among P. syringe pv. actinidiae strains were determined by examining the presence of strA-strB or aadA, which are genes frequently found in streptomycin-resistant bacteria, and a point mutation at codon 43 in the rpsL gene. All four streptomycin-resistant strains of P. syringe pv. actinidiae investigated in this study contained strA-strB as a resistant determinant. The presence of the aadA gene and a mutation in codon 43 of the rpsL gene was not identified.

Novel Small Molecule Growth Inhibitors of Xanthomonas spp. Causing Bacterial Spot of Tomato.

Bacterial spot (BS) of tomato, caused by Xanthomonas gardneri, X. perforans, X. vesicatoria, and X. euvesicatoria, is difficult to control because of the high prevalence of copper- and streptomycin-resistant strains and the lack of resistance cultivars and effective bactericides. The objective of this study was to identify novel growth inhibitors of BS-causing Xanthomonas (BS-X) species by using small molecules (SM; n = 4,182). Several SMs (X1, X2, X5, X9, X12, and X16) completely inhibited the growth of BS-X isolates (n = 68 X. gardneri, 55 X. perforans, 4 X. vesicatoria, and 32 X. euvesicatoria) at ≥12.5 µM by disrupting Xanthomonas cell integrity through weakening of the cell membrane and formation of pores. These SMs were also effective against biofilm-embedded, copper- and streptomycin-resistant Xanthomonas strains while having minimal impact on other plant pathogenic (n = 20) and beneficial bacteria (n = 12). Furthermore, these SMs displayed equivalent antimicrobial activity against BS-X in seeds and X. gardneri in seedlings compared with conventional control methods (copper sulfate and streptomycin) at similar concentrations while having no detectable toxicity to tomato tissues. SMs X2, X5, and X12 reduced X. gardneri, X. perforans, X. vesicatoria, and X. euvesicatoria populations in artificially infested seeds ≤3.4-log CFU/seed 1 day postinfection (dpi) compared with the infested untreated control (P ≤ 0.05). SMs X1, X2, X5, and X12 reduced disease severity ≤72% and engineered bioluminescent X. gardneri populations ≤3.0-log CFU/plant in infected seedlings at 7 dpi compared with the infected untreated control (P ≤ 0.05). Additional studies are needed to increase the applicability of these SMs for BS management in tomato production.

A novel mechanism of streptomycin resistance in Yersinia pestis: Mutation in the rpsL gene.

Streptomycin is considered to be one of the effective antibiotics for the treatment of plague. In order to investigate the streptomycin resistance of Y. pestis in China, we evaluated streptomycin susceptibility of 536 Y. pestis strains in China in vitro using the minimal inhibitory concentration (MIC) and screened streptomycin resistance-associated genes (strA and strB) by PCR method. A clinical Y. pestis isolate (S19960127) exhibited high-level resistance to streptomycin (the MIC was 4,096 mg/L). The strain (biovar antiqua) was isolated from a pneumonic plague outbreak in 1996 in Tibet Autonomous Region, China, belonging to the Marmota himalayana Qinghai-Tibet Plateau plague focus. In contrast to previously reported streptomycin resistance mediated by conjugative plasmids, the genome sequencing and allelic replacement experiments demonstrated that an rpsL gene (ribosomal protein S12) mutation with substitution of amino-acid 43 (K43R) was responsible for the high-level resistance to streptomycin in strain S19960127, which is consistent with the mutation reported in some streptomycin-resistant Mycobacterium tuberculosis strains. Streptomycin is used as the first-line treatment against plague in many countries. The emergence of streptomycin resistance in Y. pestis represents a critical public health problem. So streptomycin susceptibility monitoring of Y. pestis isolates should not only include plasmid-mediated resistance but also include the ribosomal protein S12 gene (rpsL) mutation, especially when treatment failure is suspected due to antibiotic resistance.