Drug resistance in Salmonella strains isolated from domestic wastewater before and after treatment in stabilization ponds in an arid region (Marrakech,Morocco)

Some 118 Salmonella strains isolated before and after treatment in stabilization ponds were tested for antimicrobial resistance. In the treatment plant, which decreases the abundance of Salmonella by 99%, a significantly lower level of antibiotic resistance (P<0.01) was identified at the system's inflow point (19%) than at its outflow (29%). The serotypes most frequently identified as having multiple antibiotic resistance were Salmonella paratyphi B and S. typhimurium. High tetracycline resistance was observed at all sampling points, followed by resistance to ampicillin and streptomycin. Antibiotic resistance can be transferred from Salmonella to other members of the Enterobacteriaceae family, such as Escherichia coli K12; transfer frequencies in nutrient broth and filtered sewage water were 4.5×10^-4 and 7×10^-7, respectively.The authors are with the Université CADI AYYAD, Faculté des Sciences—Semlalia, Département de Biologie, Laboratoire de Microbiologie, Bd Le Prince My Abdallah, BP. S.15, Marrakech, Morocco.     

克雷伯氏菌属(Klebsiella)细菌比较基因组学分析揭示多复制子抗性质粒介导广泛的抗性基因传播

[目的] 研究克雷伯氏菌与多复制子抗性质粒间的关系,分析细菌携带多复制子质粒对抗生素环境的响应机制。[方法] 以2018-2020年分离的56株不同来源克雷伯氏菌（Klebsiella sp.）分离株为研究对象,利用微量肉汤稀释法评估其多重耐药表型,对分离菌株进行全基因组测序（WGS）,通过细菌全基因组关联分析（BGWAS）技术和比较基因组学方法深入解析多复制子抗性质粒形成的机制。[结果] 耐药表型分析发现野生动物来源的菌株具有更广的耐药谱系,总体Klebsiella sp.对氨苄西林表现出很高的耐药率（80.36%）,尤其是马来穿山甲来源菌株对头孢类抗生素高度耐受,同时对氯霉素、左氧氟沙星和复方新诺明等药物耐受,基因组分析发现这些菌株携带了抗性质粒和更多的抗生素抗性基因。进一步对69个质粒序列分析,发现有28个质粒为多复制子质粒,主要携带bla_CTX-M-15、bla_CTX-M-14、bla_CTX-M-55、bla_OXA-1和bla_TEM-1等β-内酰胺酶基因。细菌携带质粒类型分析认为Klebsiella pneumoniae可能是多复制子质粒的重要宿主,质粒骨架与结构分析发现多复制子质粒多由2个或2个以上单个质粒融合而成,携带此类质粒的菌株不仅获得了更广的耐药表型,而且在全球传播扩散分布逐年增加,因此产生对抗生素环境更强的适应性。[结论] 多重耐药性细菌呈现的表型与携带的多复制子质粒有关,相比较下多复制子质粒比非多复制子质粒有更强的抗性基因携带能力,或许是细菌在强大的抗生素压力下产生的重要响应机制。本研究对于未来探索细菌抗性基因的传播扩散机制具有重要意义。     

Studies of two Frankia strains isolated from Trevoa trinervis Miers

The Frankia strains TtI 11 and TtI 12 isolated from T. trinervis Miers were characterized regarding their carbon source utilization, intrinsic antibiotic resistance, infectivity, and effectivity on the original host. Both strains grew on BAP medium supplemented with glucose, maltose, and sucrose, but differed in their ability to use other carbon sources such as propionate, pyruvate, acetate, succinate, citrate, and mannitol. The isolates were sensitive to five of the twelve antibiotics tested at 1 μg mL⁻¹ concentration: chloramphenicol, tobramycin, eritromycin, streptomycin, and rifampicin. They exhibited a variable degree of resistance at 1 μg mL⁻¹ concentraction to penicillin G, 4-fluorouracil, oleandomycin, and lincomycin. Both isolates were able to infect and nodulate the original host plant, and thus represent the first reported infective and effective microsymbionts for T. trinervis Miers, a rhamnaceous actinorhizal host. R O D Dixon Section editor     

The gene <Emphasis Type="Italic">bap</Emphasis>, involved in biofilm production,is present in <Emphasis Type="Italic">Staphylococcus</Emphasis> spp. strains from nosocomial infections

This study analyzed ten strains of coagulase-negative staphylococci (CNS) involved in nosocomial infections in three Brazilian hospitals. Their antibiotic susceptibility profile showed that most strains exhibited multiple antibiotic resistance and possessed the mecA gene. The ability of these strains to adhere to polystyrene microtiter plates was also tested and nine of them proved to be biofilm producers at least in one of the three conditions tested: growth in TSB, in TSB supplemented with NaCl, or in TSB supplemented with glucose. The presence of the bap gene, which codes for the biofilm-associated protein (Bap), was investigated in all ten strains by PCR. AU strains were bop-positive and DNA sequencing experiments confirmed that the fragments amplified were indeed part of a bap gene. The presence of the icaA gene, one of the genes involved in polysaccharide intercellular adhesin (PIA) formation, was also detected by PCR in eight of the ten strains tested. The two icaA-negative strains were either weak biofilm producer or no biofilm producer, although they were bop-positive. To our knowledge, this is the first report demonstrating the presence of the bap gene in nosocomial isolates of CNS, being also the first report on the presence of this gene in Staphylococcus haemolyticus and S. cohnii. Electronic Supplementary Material  Supplementary material is available for this article at and is accessible for authorized users.     

Antimicrobial susceptibility and molecular characterization of <Emphasis Type="Italic">Vibrio cholerae</Emphasis> from cholera outbreaks in Chennai

The genotype and antibiotic resistance pattern of the toxigenic Vibrio cholerae strains associated with cholera outbreaks vary frequently. Fifty-one V. cholerae strains isolated from cholera outbreaks in Chennai (2002–2005) were screened for the presence of virulence and regulatory genes by multiplex polymerase chain reaction (PCR) assay. Genotyping of the isolates was done by VC1 primers derived from enterobacterial repetitive intergenic consensus (ERIC)-related sequence in V. cholerae. All the isolates possessed toxigenic genes, such as ctxA, ctxB, tcpA, ace, ompU, toxR and zot. Two different El Tor genotypes and one O139 genotype could be delineated by VC1-PCR. One of the El Tor genotypes was similar to the El Tor strains isolated from Bhind district and Delhi during 2004. Antibiotic susceptibility testing revealed greater variability among the isolates tested. All the isolates were found to be susceptible to norfloxacin, ciprofloxacin and tetracycline. Thiry-three per cent of the isolates were found to be resistant to more than 4 antibiotics and could be termed as multiple antibiotic resistant. Coexistence of O139 serogroup along with the El Tor biotype could be identified among the strains recovered during the period 2002–2004. The O139 isolates were found to be more susceptible to the antibiotics tested when compared to the El Tor isolates.     

Virulence and antibiotic susceptibility of Aeromonas spp. isolated from drinking water

Aeromonas isolates from tap water, mineral water, and artesian well water were investigated for their ability to produce different potential virulence factors or markers such as hemolysins, cytotoxins, phospholipase, DNase, hydrophobicity and their ability to adhere to epithelial cells and to abiotic surfaces. The susceptibility to antibiotics of Aeromonas isolates was also examined. Majority of the isolates displayed hemolytic activity against sheep erythrocytes, while only 7 of the 23 Aeromonas strains displayed DNase activity and 4 of the 23 Aeromonas strains tested were regarded as positive for phospholipase production. Most of the isolates showed cytotoxic activities in culture filtrate dilutions at titer of 1/8 or lower. No general relation between the strain isolated and the ability to interact with epithelial cells could be established. Using the bacterial adherence to hydrocarbons method, most of the strains were classified as highly hydrophilic. All five Aeromonas jandaei strains isolates, 9 of the 12 Aeromonas sp strains and four of the five Aeromonas hydrophila were multidrug resistant. The most active antimicrobial was ciprofloxacin (susceptible in 100% of the isolates), and the least active antibiotic was ampicillin (resistance in 92% of the isolates). The majority of the isolates tested were not killed by chlorine at 1.2 mg/l. Whether the high tolerance to chlorine of Aeromonas isolates can be linked to greater virulence is not know.     

广州南沙湿地公园候鸟源肠杆菌科耐药性及产超广谱β-内酰胺酶基因监测调查

[背景]耐药基因可通过水平转移在环境、动物和人体间发生转移,而远距离传播则主要通过候鸟的迁徙.耐药基因可通过水平转移和候鸟迁徙跨地区传播至禽畜和人类,引起公共卫生问题.[目的]分离广州南沙湿地公园候鸟粪便中肠杆菌科细菌,并鉴定菌种类别,研究其对常见抗生素的耐药性及携带的主要超广谱β-内酰胺酶(extended-spec...     

Antibiotic resistance and molecular characterization of poultry isolates of Salmonella by RAPD-PCR

The antibiotic resistance profile of 17 poultry isolates of Salmonella was studied against 24 different antibiotics. 69–88% of the Salmonella isolates displayed a high level of resistance, particularly against penicillin, rifampicin, erythromycin, clarithromycin, clindamycin, sulphamethoxazole and vancomycin. In contrast, a relatively low or moderate level of resistance was observed against furazolidone, spectinomycin, ciprofloxacin, chloramphenicol, cefepime, carbenicillin, nalidixic acid, streptomycin, oxacillin and cephalothin (11–59%). Moreover, resistance to multiple antibiotics (2–5) was also observed among the Salmonella strains, and none of the isolates was found susceptible to all the antibiotics used. Similarity coefficient among Salmonella strains by RAPD-PCR analysis varied from 0.60 to 0.86, and all the salmonellae could be classified into seven groups on the basis of dendrogram analysis. Generally, a very high level of concordance between RAPD-PCR profile and antibiotic profile was not observed, which indicates that genes for antibiotic resistance may not always be present on genomic DNA rather may be plasmid-borne.     

Incidence of diverse integrons and β-lactamase genes in environmental <Emphasis Type="Italic">Enterobacteriaceae</Emphasis> isolates from Jiaozhou Bay,China

Environmental microbiology investigation was performed to determine the molecular diversity of β-lactamase genes among ampicillin-resistant bacteria from Jiaozhou Bay. β-lactamase genes were detected in 93.8% of the bacterial isolates identified as Enterobacteriaceae. The most frequently detected gene was bla _TEM, followed by bla _SHV, bla _OAX-1, bla _MOX and bla _CMY. Most of the isolates (68.8%) were positive for the intI1 integrase gene, and two isolates were also found for the intI2 gene. The dfr and aadA gene cassettes were predominant. Anthropogenic contamination from onshore sewage processing plants might contribute predominantly to the β-lactamase gene reservoir in the studied coastal waters. Environmental antibiotic-resistant bacteria and resistance genes may serve as bioindicators of coastal environmental quality or biotracers of the potential contamination sources. This is the first report of the prevalence and characterization of β-lactamase genes and integrons in coastal Enterobacteriaceae from China.     

Detection of streptomycin resistance in Mycobacterium tuberculosis clinical isolates from China as determined by denaturing HPLC analysis and DNA sequencing

China is regarded by the World Health Organization as a major hot-spot region for Mycobacterium tuberculosis infection. Streptomycin has been deployed in China for over 50 years and is still widely used for tuberculosis treatment. We have developed a denaturing HPLC (DHPLC) method for detecting various gene mutations conferring drug resistance in M. tuberculosis. The present study focused on rpsL and rrs mutation analysis. Two hundred and fifteen M. tuberculosis clinical isolates (115 proved to be streptomycin-resistant and 100 susceptible by a routine proportional method) from China were tested to determine the streptomycin minimal inhibitory concentration (MIC), and subjected to DHPLC and concurrent DNA sequencing to determine rpsL and rrs mutations. The results showed that 85.2% (98/115) of streptomycin-resistant isolates harbored rpsL or rrs mutation, while rpsL mutation (76.5%, 88/115) dominated. MIC of 98 mutated isolates revealed no close correlation between mutation types and levels of streptomycin resistance. No mutation was found in any of the susceptible isolates. The DHPLC results were completely consistent with those of sequencing. The DHPLC method devised in this study can be regarded as a useful and powerful tool for detection of streptomycin resistance. This is the first report to describe DHPLC analysis of mutations in the rpsL and rrs genes of M. tuberculosis in a large number of clinical isolates.     

Characterization ofBradyrhizobium sp. (Astragalus sinicus L.) using serological agglutination,intrinsic antibiotic resistance,plasmid visualization,and field performance

Eleven isolates ofBradyrhizobium sp. (Astragalus sinicus L.), originating from plants ofAstragalus sinicus (Chinese milkvetch) in China and Japan, were characterized using serological agglutination, intrinsic antibiotic resistance, and plasmid visualization. Serological agglutination, using antisera against three isolates effective onA. sinicus and two isolates effective on otherAstragalus spp., showed that there may be two serogroups among the eleven isolates effective onA. sinicus, and that the antigenic components are heterogeneous. Results of both intrinsic antibiotic resistance and plasmid visualization demonstrated similarities between four of the isolates.Ten isolates were further evaluated for effectiveness on the host,A. sinicus, in a field study in Puyallup, Washington (47°N, 122°W). This study showed that the Chinese commercial inoculum and one field isolate were about ten times more effective than the control based on plant dry weight and seed yield. Eight other isolates were less effective.     

Antibiotic resistance of Salmonella strains isolated from children living in the wastewater-spreading field of Marrakesh city (Morocco)

A total of 813 Salmonella strains isolated from raw wastewater and stool specimens of inpatient children, living in the wastewater-spreading field of Marrakesh city, were examined for their susceptibility to 15 antimicrobial agents. All the isolates were susceptible to cefotaxime, and almost of them showed susceptibility to gentamicin (99.88%), trimethoprim-sulphamethoxazole (98.04%), nalidixic acid (98.04%), kanamycin (97.30%), trimethoprim (97.18%), and chloramphenicol (96.07%). The highest levels of antibiotic resistance were obtained for cephalothin (29.27%), amoxicillin (26.44%), sulphamethoxazole (26.07%), and ampicillin (25.21%). The strains from the serogroup B showed the highest antibiotic resistance frequencies. The percentage of polyresistant strains (36.09%) was significantly higher than that of monoresistant isolates (15.49%). The incidence of drug resistance in Salmonella isolates from stools was significantly higher than in those isolated from wastewater.     

Antibiotic resistance and detection of β-lactamase in bacterial strains of Staphylococci and Escherichia coli isolated from foodstuffs

Seventy strains of Staphylococcus spp. and Escherichia coli (35 each) were isolated from various foodstuffs and identified on the basis of cultural, morphological and biochemical characteristics and were further tested for their antibiotic susceptibility with commonly used antibiotics/drugs. 69.2% of the strains of Staphylococci were resistant to co-trimazine and 34.6% were resistant to penicillin-G. 19.2% of the staphylococcal isolates exhibited resistance to cloxacillin, nalidixic acid, methicillin and tetracycline whereas 15.3% of the staphylococcal isolates were resistant to amoxycillin and nitrofurantoin. The isolated E. coli strains exhibited sharp peaks of resistance to antimicrobial agents such as tetracycline (72%), doxycycline (60%) and nalidixic acid (48%). Forty-four percent of the E. coli strains were resistant to nitrofurantoin and penicillin-G respectively. Among the 13 antibiotics/drugs tested for resistance, six different resistance patterns were observed in staphylococcal isolates and seven different resistance patterns were observed in the E. coli isolates from various foodstuffs. Bacterial strains exhibiting MIC values 100 g/ml for ampicillin and cloxacillin were screened for -lactamase activity and out of 10 staphylococcal isolates, seven were found to be positive for -lactamase, whereas out of 13 E. coli isolates tested for -lactamase production, only three were found to be positive.     

分离自母婴肠道的假小链双歧杆菌的耐药性分析

【背景】由于滥用抗生素导致细菌耐药性日益严重。对于双歧杆菌,人们往往注重其益生功能的挖掘而忽视了对其耐药性的研究,存在一定的安全隐患。【目的】检测母婴肠道中假小链双歧杆菌的耐药性,探究婴儿肠道中假小链双歧杆菌耐药性的来源。【方法】利用微量肉汤稀释法测定48株分离自母婴肠道的假小链双歧杆菌对14种抗生素的耐药性,比较分离自不同家庭母婴肠道中假小链双歧杆菌的耐药性。【结果】48株母婴肠道分离株对四环素、氯霉素、新霉素、环丙沙星100%耐药,对其余10种抗生素耐药率依次为：卡那霉素98%、利福平80%、克林霉素78%、甲氧苄啶63%、红霉素59%、庆大霉素43%、链霉素16%、万古霉素14%、氨苄西林6%、利奈唑胺2%。母婴肠道分离株的耐药性无显著差异,分离自同一家庭母婴肠道的菌株具有相似的耐药表型。【结论】分离自母婴肠道的假小链双歧杆菌对多种抗生素具有耐药性,婴儿肠道中假小链双歧杆菌的耐药性可能是由母亲肠道垂直传递而来。     

Detection and characterization of natural transformation in the marine bacterium Pseudomonas stutzeri strain ZoBell

Soil isolates of Pseudomonas stutzeri have been shown previously to acquire genes by natural transformation. In this study a marine isolate, Pseudomonas stutzeri strain ZoBell, formerly Pseudomonas perfectomarina, was also shown to transform naturally. Transformation was detected by the Juni plate method and frequencies of transformation were determined by filter transformation procedures. Maximum frequencies of transformation were detected for three independent antibiotic resistance loci. Transformation frequencies were on the order of 4×10^-5 transformants per recipient, a frequency over 100 times that of spontancous antibiotic resistance. Transfer of antibiotic resistance was inhibited by DNase I digestion. Marine isolates achieved maximum competence 14 h after transfer of exponential cultures to filters on solid media, although lower levels of competence were detected immediately following filter immobilization. Like soil isolates, P. stutzeri strain ZoBell is capable of cell contact transformation, but unlike soil isolates where transformation frequencies are greater for cell contact transformation as compared to transformation with purified DNA, the maximum frequency of transformation achieved by cell contact in the marine strain was approximately 10-fold less than transformation frequencies with purified DNA. These studies establish the first marine model for the study of natural transformation.This paper is dedicated to John L. Ingraham, Professor Emeritus of Microbiology at the University of California, Davis. Professor Ingraham was the first person to recognize natural transformation in Pseudomonas stutzeri and has continued to contribute to our understanding of the process over the past eight years. This understanding of the genetics of P. stutzeri is only one of the many areas of microbiology to which Professor Ingraham has contributed in his exceptional career     

Antimicrobial resistance among Salmonella serovars isolated from different sources in Brazil during 1978–1983

A total of 748 Salmonella strains (97 serovars) isolated from human (291), animal (119), environmental (141), food (102) and animal feed (95) sources were examined for resistance to 9 antimicrobial agents. Most of the human isolates were from hospitalized patients (282). An overall resistance rate of 98.8% was determined with 100% for human and environmental isolates. Resistance to sulfadiazine (87.7%) was most common, followed by streptomycin (61.2%), ampicillin (39%) and trimethoprim-sulphamethoxazole (37.9%). Fifty one different resistance patterns were identified with Su (164 strains), Su-Sm (122) and Su-Sm-Tc-Cm-Km-Ap-Nx-Gm-Tm (95) predominating, the latter occurring only in human isolates. Multiple resistance was most frequently found among human isolates, particularly in S. derby and S. typhimurium strains. The relationship between antibiotic resistance, serovar and source of isolation of the Salmonella strains is discussed.     

Evaluation of methicillin resistance by cefoxitin disk diffusion and PBP2a latex agglutination test in mecA-positive Staphylococcus aureus, and comparison of mecA with femA, femB, femX positivities

Methicillin resistance in staphylococci is primarily due to the presence of a mecA gene which encodes the novel penicillin binding protein2a. Some chromosomal factors such as femA and femB also participate in the expression of methicillin resistance. This study was designed to detect methicillin resistance by cefoxitin disk diffusion and penicillin binding protein2a latex agglutination methods, and to compare mecA, femA, femB and femX gene positivities. A total of 60 MRSA isolates were included in the evaluation. PCR analysis showed that all isolates were positive for mecA and femA genes. Seven of these isolates tested negative by the latex agglutination test. Fifteen isolates were positive for femB and 28 isolates for femX gene. This study implicated that for the determination of methicillin resistance, latex agglutination test is the least reliable method when compared to PCR and cefoxitin disk diffusion test. femA gene shows more correlation than femB and femX with methicillin resistance.     

Characterization of a cryptic plasmid from a Greenland ice core Arthrobacter isolate and construction of a shuttle vector that replicates in psychrophilic high G+C Gram-positive recipients

Over 60 Greenland glacial isolates were screened for plasmids and antibiotic resistance/sensitivity as the first step in establishing a genetic system. Sequence analysis of a small, cryptic, 1,950 bp plasmid, p54, from isolate GIC54, related to Arthrobacter agilis, showed a region similar to that found in theta replicating Rhodococcus plasmids. A 6,002 bp shuttle vector, pSVJ21, was constructed by ligating p54 and pUC18 and inserting a chloramphenicol acetyl transferase (CAT) cassette conferring chloramphenicol resistance. Candidate Gram-positive recipients were chosen among glacial isolates based on phylogenetic relatedness, relatively short doubling times at low temperatures, sensitivity to antibiotics, and absence of indigenous plasmids. We developed an electroporation protocol and transformed seven isolates related to members of the Arthrobacter, Microbacterium, Curtobacterium, and Rhodoglobus genera with pSVJ21. Plasmid stability was demonstrated by successive transformation into Escherichia coli and four Gram-positive isolates, growth without antibiotic, and plasmid re-isolation. This shuttle vector and our transformation protocol provide the basis for genetic experiments with different high G+C Gram-positive hosts to study cold adaptation and expression of cold-active enzymes at low temperatures.     

Natural occurrence of Bacillus thuringiensis in leguminous phylloplanes in the New Delhi region of India

Bacillus thuringiensis (Bt) isolates were present on the phylloplanes of chickpea (Cicer arietinum), pigeon pea (Cajanus cajan), pea (Pisum sativum) and mung bean (Vigna radiata). Bt index (ratio of the number of Bt colonies to the total number of spore-forming colonies per g of leaves) differed significantly among these plants, with the highest (0.20) in the chickpea phylloplane, followed by pigeon pea (0.17). Bt population of the chickpea phylloplane varied with plant age, being maximal in 45-day-old plants. Diversity was observed among Bt isolates for growth (up to 10-fold difference), antibiotic resistance, PCR product profile and toxicity to Helicoverpa armigera. Two isolates with high activity towards H. armigera were found. This revised version was published online in July 2006 with corrections to the Cover Date.     

Concordance of antibiotic resistance and ERIC-PCR DNA fingerprint pattern in <Emphasis Type="Italic">Escherichia coli</Emphasis> isolated from farmer and broiler in the same farm

The study was conducted to quantify the concordance of antibiotic resistance and ERIC-PCR DNA fingerprint pattern in Escherichia coli (E. coli) isolated from farmers and their broilers of 95 broiler farms in Songkhla province, Thailand. Four hundred and fifty-seven and 460 E. coli isolates from both groups produced 35 patterns of antibiotics resistance. Mono-resistance to doxycycline (23.2%) in isolates from farmers and multiple resistance to doxycycline, nalidixic acid, norfloxacin and ciprofloxacin (17.8%) were the most common finding in broilers. Twenty-seven farms had 44 within-farm concordant patterns of resistance. From simulation, the frequency of concordance was significantly higher than concordance by chance alone (P < 0.05). Out of these 44 matched sets, only four had the same DNA fingerprint pattern. Concordance by DNA pattern was also not associated with phenotypic resistance. Clonal spread is therefore not a good explanation of the concordance in this population. Other mechanisms need further analysis.