Multidrug and heavy metal-resistant Raoultella planticola isolated from surface water

Co-occurrence of heavy metals and antibiotics resistance in bacteria isolated from metal-polluted soil

The indiscriminate deposition of metal-containing substances into the environment contributes significantly to high concentrations of metals in the soil resulting in resistance to metals and consequentially to antibiotics by inherent microbes which may eventually spread to other pathogenic microbes thereby elevating disease burden due to antibiotic resistance. The study aimed at determining the co-occurrence of resistance of bacteria isolated from metal-contaminated soil to heavy metals and subsequently, antibiotics. Metal-tolerant bacteria were randomly isolated from top soils from a battery waste site using the pour plate method. Selected isolates were identified using biochemical tests, then, subjected to elevating supplemented concentrations of different metal salts at 100-500 μg/mL to determine the minimum inhibitory concentration. Isolates tolerant to minimum three metals up to 400 μg/mL were subjected to Sulfamethoxazole-trimethoprim (25 μg), Imipenem (10 μg), Amoxicillin (30 μg), Ciprofloxacin (10 μg) and Tigecycline (15 μg) and observations interpreted using the guiding principle of the Clinical and Laboratory Standards Institute. Metal concentrations in the soils exceeded permissible limits. In total, 16 isolates were selected and identified as Proteus sp. (1), Pseudomonas spp. (5), Enterobacter spp. (2), Klebsiella spp. (2), Escherichia spp. (3), Raoultella spp. (2) and Rahnella sp. (1). Thirteen (81.25 %) of all isolates showed multi-resistance to the metals and seven exhibited multidrug-resistance, with 4 (57.1 %) showing resistance to three different classes of antibiotics and 3 (42.9 %) showed resistance to four antibiotic classes. Heavy metal-tolerant bacteria isolated from this study possess co-selection potentials as they showed resistance to different metals and antibiotics classes which is a concern to public health.

Whole Genome Sequencing of an Extensively Drug-Resistant Raoultella planticola Isolate Containing blaKPC-2, blaNDM-1, and blaCTX-M-15

Raoultella planticola harboring genes that confer resistance to antimicrobials, such as carbapenems, have been associated with severe infections in immunocompromised patients. In this study, we reported the first whole genome sequence of a Brazilian isolate of R. planticola and the genomic context of antibiotic resistance markers. By whole-genome sequencing (WGS) of a carbapenem-resistant R. planticola isolate, RpHUM1, we found 23 resistance-encoding genes belonging to 9 classes of antibiotics (aminoglycosides, β-lactams, fluoroquinolones, fosfomycin, macrolides, phenicols, sulfonamides, tetracycline, and diaminopyrimidine derivatives) and 3 plasmids (RpHUM1pEaer-4382s, RpHUM1_pFDAARGOS_440, and RpHUM1pRSF1010). This isolate coharbored the genes blaKPC-2, which is carried by the plasmid RpHUM1pEaer-4382s, and blaNDM-1 and blaCTX-M-15 all located in the accessory genome. In addition, these genes were associated with, at least, one mobile genetic element. This comprehensive knowledge is of great importance for implementation of control measures to prevent the rapid dissemination of this neglected microorganism and their genetic resistance background.

Chromate Removal by Enterobacter cloacae Strain UT25 from Tannery Effluent and Its Potential Role in Cr (VI) Remediation

An indigenous chromate-resistant bacterial strain isolated from tannery effluent was identified based on morphological, biochemical, and 16S rRNA gene sequencing, as Enterobacter cloacae UT25. It was found to resist heavy metal ions such as Cr (VI), Pb (II), Cu (II), Co (II), Ni (II), Hg (II), and Zn (II) and antibiotics. The strain was able to remove 89 and 86% chromate, after 24 h of incubation in a Luria-Bertani (LB) medium at an initial Cr (VI) concentration of 1000 and 1500 µg/ml, respectively. Minimum inhibitory concentration (MIC) was observed for chromate to be 80,000 and 1850 µg/ml, after 48 h of incubation in LB and acetate minimal media (AMM), respectively. Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) analysis showed discrete cells with intact and smooth cell walls and homogenous cytoplasm in the absence of metal stress, whereas chromate stress caused cell lysis and reduction in size, which was a characteristic response to Cr (VI) toxicity. Energy Dispersive X-Ray Spectroscopy (EDX) confirmed the adsorption of oxyanions to the cell wall which was one of the Cr (VI) removal mechanisms by the bacterium. Atomic Force Microscopy (AFM) micrographs of chromate-untreated and treated cells revealed Root Mean Square roughness (Rq) values of 16.25 and 11.26 nm, respectively, indicating less roughness in the presence of stress. The partial gene sequence of class 1 integrons (intI1) of strain UT25 showed 94% homology with intI1 gene of strain Enterobacter hormaechei strain ECC59 plasmid pECC59-1. The present analysis highlighted the potential of E. cloacae UT25 as a promissory bacterium that could be applied in removing chromate from polluted environments.

Draft genome of Raoultella planticola, a high lead resistance bacterium from industrial wastewater

Isolation of heavy metals-resistant bacteria from their original habitat is a crucial step in bioremediation. Six lead (Pb) resistant bacterial strains were isolated and identified utilizing 16S rRNA to be Enterobacter ludwigii FACU 4, Shigella flexneri FACU, Microbacterium paraoxydans FACU, Klebsiella pneumoniae subsp. pneumonia FACU, Raoultella planticola FACU 3 and Staphylococcus xylosus FACU. It was determined that all these strains had their Minimum inhibitory concentration (MIC) to be 2500 ppm except R. planticola FACU 3 has a higher maximum tolerance concentration (MTC) up to 2700 ppm. We evaluated the survival of all six strains on lead stress, the efficiency of biosorption and lead uptake. It was found that R. planticola FACU 3 is the highest MTC and S. xylosus FACU was the lowest MTC in this evaluation. Therefore, transmission electron microscopy (TEM) confirmed the difference between the morphological responses of these two strains to lead stress. These findings led to explore more about the genome of R. planticola FACU 3 using illumine Miseq technology. Draft genome sequence analysis revealed the genome size of 5,648,460 bp and G + C content 55.8% and identified 5526 CDS, 75 tRNA and 4 rRNA. Sequencing technology facilitated the identification of about 47 genes related to resistance to many heavy metals including lead, arsenic, zinc, mercury, nickel, silver and chromium of R. planticola FACU 3 strain. Moreover, genome sequencing identified plant growth-promoting genes (PGPGs) including indole acetic acid (IAA) production, phosphate solubilization, phenazine production, trehalose metabolism and 4-hydroxybenzoate production genes and a lot of antibiotic-resistant genes.

Chronic cholecystitis from Raoultella planticola infection associated with adenomyomatous hyperplasia

A 67-year-old woman presented with lower abdominal pain, diarrhea, nausea, vomiting and fatigue. Computed tomography was suggestive of cholecystitis, but neither ultrasound nor magnetic resonance cholangiopancreatography found evidence of cholecystitis or biliary ductal dilatation. The patient was started on piperacillin-tazobactam, and blood cultures revealed gram-negative-rod bacteremia. Laparoscopic cholecystectomy was performed and bile cultures grew Raoultella planticola susceptible to ciprofloxacin, which was identical to the speciation of her positive blood cultures. In addition, pathology revealed adenomyomatous hyperplasia of the gallbladder and chronic cholecystitis. Unlike other cases of R. planticola cholecystitis, our patient had no significant risk factors for the infection—no history of immunosuppression, diabetes mellitus, nor underlying malignancy. We discuss the current knowledge of R. planticola infection in the setting of chronic cholecystitis and adenomyomatous hyperplasia.

Ingestion of remediated lead-contaminated soils affects the fecal microbiome of mice

The relationship between ingestion of diets amended with a Pb-contaminated soil and the composition of the fecal microbiome was examined in a mouse model. Mice consumed diets amended with a Pb-contaminated soil in its native (untreated) state or after treatment for remediation with phosphoric acid or triple superphosphate alone or in combination with iron-waste material or biosolids compost. Subacute dietary exposure of mice receiving treated soil resulted in modulation of the fecal intestinal flora, which coincided with reduced relative Pb bioavailability in the bone, blood and kidney and differences in Pb speciation compared to untreated soil. Shifts in the relative abundance of several phyla including Verrucomicrobia, Tenericutes, Firmicutes, Proteobacteria, and TM7 (Candidatus Saccharibacteria) were observed. Because the phyla persist in the presence of Pb, it is probable that they are resistant to Pb. This may enable members of the phyla to bind and limit Pb uptake in the intestine. Families Ruminococcaceae, Lachnospiraceae, Erysipelotrichaceae, Verrucomicrobiaceae, Prevotellaceae, Lactobacilaceae, and Bacteroidaceae, which have been linked to health or disease, also were modulated. This study is the first to explore the relationship between the murine fecal microbiome and ingested Pb contaminated soils treated with different remediation options designed to reduce bioavailability. Identifying commonalities in the microbiome that are correlated with more positive health outcomes may serve as biomarkers to assist in the selection of remediation approaches that are more effective and pose less risk.

Insights to antimicrobial resistance: heavy metals can inhibit antibiotic resistance in bacteria isolated from wastewater

The alarming upsurge in the co-existence of heavy metal and antibiotic resistance may have a devastating impact on humans, animals, and the environment. Four metal-resistant bacteria were isolated from hospital effluents and industrial drain. Heavy metal resistance and antimicrobial resistance were examined in the isolates followed by identification through 16S rRNA gene sequencing. Delftia tsuruhatensis strain FK-01 and Carnobacterium inhibens strain FK-02 tolerated arsenic with maximal tolerated concentration (MTC) of 30 mM and 10 mM, respectively. Staphylococcus hominis strain FK-04 tolerated copper up to 4 mM and lead-resistant Raoultella ornithinolytica strain FK-05 exhibited tolerance to 1 mM lead. The growth kinetics of bacteria were monitored in the presence of metals and the following antibiotics, tetracycline, chloramphenicol, and kanamycin. The presence of arsenate significantly enhanced tetracycline resistance in C. inhibens. Heavy metal-induced antibiotic resistance was also observed in S. hominis and R. ornithinolytica, against chloramphenicol and tetracycline respectively. D. tsuruhatensis showed resistance to kanamycin but when grown in the presence of arsenic and kanamycin, bacteria lost resistance to the antibiotic. Therefore, it is suggested that the novel arsenate-resistant strain Delftia tsuruhatensis FK-01 has a unique ability to inhibit antimicrobial resistance that can be harnessed in bioremediation.

The role of antibiotics and heavy metals on the development, promotion, and dissemination of antimicrobial resistance in drinking water biofilms

Antimicrobial resistance (AMR), as well as the development of biofilms in drinking water distribution systems (DWDSs), have become an increasing concern for public health and management. As bulk water travels from source to tap, it may accumulate contaminants of emerging concern (CECs) such as antibiotics and heavy metals. When these CECs and other selective pressures, such as disinfection, pipe material, temperature, pH, and nutrient availability interact with planktonic cells and, consequently, DWDS biofilms, AMR is promoted. The purpose of this review is to highlight the mechanisms by which AMR develops and is disseminated within DWDS biofilms. First, this review will lay a foundation by describing how DWDS biofilms form, as well as their basic intrinsic and acquired resistance mechanisms. Next, the selective pressures that further induce AMR in DWDS biofilms will be elaborated. Then, the pressures by which antibiotic and heavy metal CECs accumulate in DWDS biofilms, their individual resistance mechanisms, and co-selection are described and discussed. Finally, the known human health risks and current management strategies to mitigate AMR in DWDSs will be presented. Overall, this review provides critical connections between several biotic and abiotic factors that influence and induce AMR in DWDS biofilms. Implications are made regarding the importance of monitoring and managing the development, promotion, and dissemination of AMR in DWDS biofilms.

Raoultella terrigena: Current state of knowledge, after two recently identified clinical cases in Eastern Europe

Raoultella terrigena is a rarely found opportunistic pathogen that can cause healthcare-associated infections with high mortality. It is important to differentiate it from Klebsiella species.

Patterns of antimicrobial resistance observed in the Middle East: Environmental and health care retrospectives

Antimicrobial resistance is one of the biggest worldwide challenging problems that associates with high morbidity and mortality rates. The resistance of bacteria to various antibiotic classes results in difficulties in the treatment of infectious diseases caused by those bacteria. This paper highlights and provides a critical overview of observational and experimental studies investigating the presence of antibiotic resistant bacteria in different environments in Middle East countries and the mechanisms by which bacteria acquire and spread resistance. The data of this research considered the published papers within the last ten years (2010-2020) and was carried out using PubMed. A total of 66 articles were selected in this review. This review covered studies done on antibiotic resistant bacteria found in a wide range of environments including foods, animals, groundwater, aquatic environments as well as industrial and hospital wastewater. They acquire and achieve their resistance through several mechanisms such as antibiotic resistant genes, efflux pumps and enzymatic reactions. However, the dissemination and spread of antibiotic resistant bacteria is affected by several factors like anthropogenic, domestic, inappropriate use of antibiotics and the expulsion of wastewater containing antibiotic residues to the environments. Therefore, it is important to increase the awareness regarding these activities and their effect on the environment and eventually on health.

Carbapenem resistant Enterobacteriaceae from port areas in São Paulo State (Brazil): Isolation and molecular characterization

Coastal areas with important economic activities have high levels of contamination by metals, pathogenic bacteria, among other contaminants. The emergence of antibiotic-resistant bacteria is a global problem of public health. Carbapenem resistant Enterobacteriaceae (CRE) are a serious threat. The occurrence of carbapenem resistant bacteria was investigated in waters and sediments of a Brazilian coastal area, characterized by high levels of contamination. The samples of water and sediment were collected in two areas of the coast of São Paulo (Brazil). The study involved the characterization of the molecular mechanisms associated with the carbapenem resistance phenotype. No genes were detected for β-lactamases but the absence and/or presence of mutations in outer membrane proteins (OMPs) may justify the detected phenotype. The presented results show the need for further studies that allow a review of the current legislation and the importance of the reevaluation of monitoring policies of these environments.

Neonatal septicemia caused by a rare pathogen: Raoultella planticola - a report of four cases

Background

Raoultella planticola(R.planticola) is a very rare opportunistic pathogen and sometimes even associated with fatal infection in pediatric cases. Recently,the emergence of carbapenem resistance strains are constantly being reported and a growing source of concern for pediatricians.

Case presentation

We reported 4 cases of neonatal septicemia caused by Raoultella planticola. Their gestational age was 211 to 269 days, and their birth weight was 1490 to 3000 g.The R. planticola infections were detected on the 9th to 27th day after hospitalization and occured between May and June. They clinically manifested as poor mental response, recurrent cyanosis, apnea, decreased heart rate and blood oxygen, recurrent jaundice, fever or nonelevation of body temperature. The C-reactive protein and procalcitonin were elevated at significantly in the initial phase of the infection,and they had leukocytosis or leukopenia. Prior to R.planticola infection,all of them recevied at least one broad-spectrum antibiotic for 7-27d.All the R.planticola strains detected were only sensitive to amikacin, but resistant to other groups of drugs: cephalosporins (such as cefazolin, ceftetan,etc) and penicillins (such as ampicillin-sulbactam,piperacillin,etc),and even developed resistance to carbapenem. All the infants were clinically cured and discharged with overall good prognosis.

Conclusion

Neonatal septicemia caused by Raoultella planticola mostly occured in hot and humid summer, which lack specific clinical manifestations. Pediatricians should keep in mind that R. planticola can be a potential source of neonatal sepsis and even has the potential to acquire carbapenem-resistance. Preventing outbreaks of epidemics requires early detection, timely diagnosis and treatment, and active isolation.

CTX-M-9 group ESBL-producing Raoultella planticola nosocomial infection: first report from sub-Saharan Africa

BACKGROUND

Raoultella are Gram-negative rod-shaped aerobic bacteria which grow in water and soil. They mostly cause nosocomial infections associated with surgical procedures. This case study is the first report of a Raoultella infection in Africa. Case presentation We report a case of a surgical site infection (SSI) caused by Raoultella planticola which developed after caesarean section (CS) and surgery for secondary small bowel obstruction. The patient became febrile with neutrophilia (19,157/µL) 4 days after laparotomy and started to develop clinical signs of a SSI on the 8^th day after laparotomy. The patient continued to be febrile and became critically ill despite empirical treatment with ceftriaxone and vancomycin. Raoultella species with extended antimicrobial resistance (AMR) carrying the CTX-M-9 β-lactamase was isolated from the wound discharge. Considering the antimicrobial susceptibility test, ceftriaxone was replaced by ceftazidime. The patient recovered and could be discharged on day 29 after CS.

CONCLUSIONS

Raoultella planticola was isolated from an infected surgical site after repeated abdominal surgery. Due to the infection the patient's stay in the hospital was prolonged for a total of 4 weeks. It is noted that patients undergoing surgical and prolonged inpatient treatment are at risk for infections caused by Raoultella. The development of a SSI caused by Raoultella planticola with extended AMR has to be assumed to be a consequence of ineffective antibiotic utilization. The presented case advices that rare bacteria as Raoultella should be considered as potential cause of nosocomial SSI with challenging treatment due to high levels of AMR.

Advances in characterizing microbial community change and resistance upon exposure to lead contamination: Implications for ecological risk assessment

Recent advancement in molecular techniques has spurred waves of studies on responses of microorganisms to lead contamination exposure, leveraging detailed phylogenetic analyses and functional gene identification to discern the effects of lead toxicity on microbial communities. This work provides a comprehensive review of recent research on (1) microbial community changes in contaminated aquatic sediments and terrestrial soils; (2) lead resistance mechanisms; and (3) using lead resistance genes for lead biosensor development. Sufficient evidence in the literature, including both in vitro and in situ studies, indicates that exposure to lead contamination inhibits microbial activity resulting in reduced respiration, suppressed metabolism, and reduced biomass as well as altered microbial community structure. Even at sites where microbial communities do not vary compositionally with contamination levels due to extremely long periods of exposure, functional differences between microbial communities are evident, indicating that some microorganisms are susceptible to lead toxicity as others develop resistance mechanisms to survive in lead contaminated environments. The main mechanisms of lead resistance involve extracellular and intracellular biosorption, precipitation, complexation, and/or efflux pumps. These lead resistance mechanisms are associated with suites of genes responsible for specific lead resistance mechanisms and may serving as indicators of lead contamination in association with dominance of certain phyla. This allows for development of several lead biosensors in environmental biotechnology. To promote applications of these advanced understandings, molecular techniques, and lead biosensor technology, perspectives of future work on using microbial indicators for site ecological assessment is presented.

Comparative genomics analysis of Raoultella planticola S25 isolated from duck in China, with florfenicol resistance

To characterize the florfenicol resistance gene and analyze the structure of the resistance gene-related sequence of an Raoultella planticola strain S25 isolated from a duck fecal sample from a farm in South China. Molecular cloning was performed to clone the resistance genes such as mdfA, floR and so on, and the minimum inhibitory concentrations (MICs) were quantified to determine the resistance levels generated by the cloned genes and the related strains. Sequencing and comparative genomics methods were used to analyze the structure of the resistance gene-related sequence. The result showed that the genome of R. planticola S25 consists of a 5.47 Mb chromosome encoding 4962 predicted coding sequence (CDS) and a 68,566 bp plasmid, pS25-68, encoding 84 ORFs. The plasmid sharing the greatest sequence identity with the floR-carrying plasmid pS25-68 is plasmid1 in Klebsiella pneumoniae strain blaNDM-1, which was isolated from a patient in Canada. The mdfA1 gene encoded on the chromosome generated resistance to florfenicol in addition to chloramphenicol. Comparative genomic analysis of the floR-related transposon-like fragment of pS25-68 showed that an approximately 3 kb sequence encoding IS91-virD2-floR-lysR was conserved and presented in the majority of the sequences (84.5 %, 169/200) collected from the database. The results of this work demonstrated that horizontal transfer of the florfenicol resistance gene floR occurred widely between the bacteria of different species and with different origins and that additional florfenicol resistance genes may be present in the bacterial population.

Impact of heavy metals on inhibitory concentration of Escherichia coli-a case study of river Yamuna system, Delhi, India

The occurrence of resistant bacteria to specific heavy metals can be associated with increasing load of the metals in the environment. River Yamuna is polluted by various toxic heavy metals discharged by several industrial and agricultural sources. Therefore, the use of heavy metal-resistant bacteria as an indicator of metal pollution was tested in the present study. For the purpose of the study, the heavy metal resistance status of 42 Escherichia coli strains isolated from River Yamuna water from 7 sampling sites within a span of 2 years was determined using growth curves and plate dilution method in terms of minimum inhibitory concentration (MIC) values by comparing with MIC value of control strain. Seasonally, the lowest mean MIC value was observed for bacterial strains isolated in post-monsoon (December) 2013 and highest mean MIC value was observed for bacterial strains isolated in monsoon (August) 2015. Site-wise analysis of the maximum mean MIC values for all the isolated strains showed the highest mean Ni MIC value for the bacterial strains isolated from site S4 (ITO), highest mean Cu MIC, Cr MIC, and Fe MIC values for the bacterial strains isolated from site S2 (Najafgarh drain intermixing zone) and highest mean Cd MIC, Pb MIC, and Zn MIC values for the bacterial strains isolated from site S7 (Shahdara drain intermixing zone). Correlation analysis between mean MIC site-wise results with mean heavy metal site-wise concentrations showed significant positive correlation indicating that the higher the mean concentration of a given heavy metal at a given site, the higher the mean MIC value for the strains isolated from the same site indicating higher level of resistance. Overall, the present study has shown that the presence of heavy metals in River Yamuna caused due to indiscriminate discharge of various effluents from different kind of sources as well as due to insufficient treatment capacity of sewage treatment plants as well as common effluent treatment plants, has serious impacts on its bacterial microflora as it leads to the development of resistant strains.

A Rare Case of Raoultella planticola Urinary Tract Infection in a Patient With Immunoglobulin A Nephropathy

Raoultella planticola is a gram-negative, aerobic, nonmotile mostly found in environments with high prevalence in soil and water. This organism is a very rare human pathogen as only 29 cases of Raoultella planticola–related infections have been reported until 2017, with only 7 cases in the United States. Only 3 cases of urinary tract infection secondary to R planticola have been reported, 1 in a pediatric patient and 2 in adults. In this article, we present a case of R planticola urinary tract infection in a 65-year-old male with immunoglobulin A nephropathy. On investigation, the patient was found to be septic and empirical antibiotic was started for gram-negative coverage. The patient showed remarkable improvement and discharged on oral antibiotic for 7 days. R planticola rarely cause infection in humans, with overall good prognosis.

Long-term industrial metal contamination unexpectedly shaped diversity and activity response of sediment microbiome

Metal contamination poses serious biotoxicity and bioaccumulation issues, affecting both abiotic conditions and biological activity in ecosystem trophic levels, especially sediments. The MetalEurop foundry released metals directly into the French river "la Deûle" during a century, contaminating sediments with a 30-fold increase compared to upstream unpolluted areas (Férin, Sensée canal). Previous metaproteogenomic work revealed phylogenetically analogous, but functionally different microbial communities between the two locations. However, their potential activity status in situ remains unknown. The present study respectively compares the structures of both total and active fractions of sediment prokaryotic microbiomes by coupling DNA and RNA-based sequencing approaches at the polluted MetalEurop site and its upstream control. We applied the innovative ecological concept of Functional Response Groups (FRGs) to decipher the adaptive tolerance range of the communities through characterization of microbial lifestyles and strategists. The complementing use of DNA and RNA sequencing revealed indications that metals selected for mechanisms such as microbial facilitation via "public-good" providing bacteria, Horizontal Gene Transfer (HGT) and community coalescence, overall resulting in an unexpected higher microbial diversity at the polluted site.

Antimicrobial Nanomaterials: Why Evolution Matters

Due to the widespread occurrence of multidrug resistant microbes there is increasing interest in the use of novel nanostructured materials as antimicrobials. Specifically, metallic nanoparticles such as silver, copper, and gold have been deployed due to the multiple impacts they have on bacterial physiology. From this, many have concluded that such nanomaterials represent steep obstacles against the evolution of resistance. However, we have already shown that this view is fallacious. For this reason, the significance of our initial experiments are beginning to be recognized in the antimicrobial effects of nanomaterials literature. This recognition is not yet fully understood and here we further explain why nanomaterials research requires a more nuanced understanding of core microbial evolution principles.

vanA Gene Harboring Enterococcal and Non-enterococcal Isolates Expressing High Level Vancomycin and Teicoplanin Resistance Reservoired in Surface Waters

Untreated wastewaters and treated effluents even after final disinfection contain antibiotic resistant bacteria and resistance genes before they are released into surface waters. A correlation between resistant bacteria and antibiotics in surface waters has been found, as have antibiotic resistance genes. Of particular interest are vancomycin-resistant enterococci harboring vanA gene that confers high level of resistance to glycopeptide antibiotics including teicoplanin. Therefore, in this study, river water samples were analysed to investigate vancomycin- and teicoplanin-resistant bacterial isolates harboring vanA gene. Out of 290, 15 surface water isolates displayed resistance to both antibiotics. These glycopeptide resistant enterococcal and non-enterococcal isolates, identified by 16S rRNA sequencing, were found to harbor vanA gene with sequence similarities of 50 % to 100 %. The presence of D-alanine-D-lactate ligase encoded by vanA gene was also shown for all vancomycin- and teicoplanin-resistant isolates through western blot analysis. Due to reuse of treated wastewater and release of untreated wastewaters to water bodies, antibiotic resistant bacteria and resistance genes are being introduced into surface waters and present human health risks. Therefore, surface waters are not only hot spots for vanA harboring enterococcal isolates but also non-enterococcal isolates due to gene dissemination and require special scientific consideration.

Raoultella spp.-clinical significance, infections and susceptibility to antibiotics

The genus Raoultella belongs to the family of Enterobacteriaceae. Raoultella spp. are Gram-negative, aerobic, non-motile rods. This genus can be distinguished from the genus Klebsiella, in that genus use histamine as the only source of carbon in the medium. Also, Raoultella grow at 4 °C and do not produce gas from lactose at 44.5 °C. Raoultella sp. is known to inhabit natural environments (water, soil, plants). The reservoir of Raoultella is the gastrointestinal tract and upper respiratory tract. Raoultella spp. are opportunistic bacteria, which usually cause infections of the biliary tract, pneumonia and bacteraemia in oncologic and with lower immunity patients. Raoultella planticola and Raoultella ornithinolytica are the most frequently encountered human pathogens among the genus Raoultella. In this review, the current knowledge on Raoultella infections is summarized.

Mercury-mediated cross-resistance to tellurite in Pseudomonas spp. isolated from the Chilean Antarctic territory

Mercury salts and tellurite are among the most toxic compounds for microorganisms on Earth.

Antioxidative responses of Pseudomonas fluorescens YZ2 to simultaneous exposure of Zn and Cefradine

Binary pollution of both heavy metals and antibiotics has received increasing attentions for their joint effects of eco-toxicity and health hazards. To reveal the effects of mixtures of different pollutants on bacterial antioxidant response system, Pseudomonas fluorescens ZY2, a new strain isolated from swine wastewater, was chosen to determinate growth (bacterial density OD600), reactive oxygen species (ROS) concentration, protein concentration and superoxide dismutase (SOD) activity under exposure treatments of Zn, Cefradine or Zn + Cefradine. Bacterial densities of all the treatment groups increased significantly over the incubation time, but those containing pollutant addition were slightly lower than the control at different times of incubation. Both ROS concentration and SOD activity increased first and then decreased (p < 0.01) over time, which was opposite to the protein concentrations (p < 0.01), showing a much significant increase by Cefradine alone. With Zn concentration increasing from 40 to 160 mg/L, the intracellular SOD activity increased as a response to the improvement of ROS (p < 0.05), while the balance between ROS and SOD was broken down due to the disproportionate change of total SOD activity and ROS concentration, the bacterial densities therefore decreased for the weak resistance. With the combined treatment of Zn (200 mg/L) and Cefradine (1 mg/L), though the toxicity of Zn caused a much significant increase of ROS, the bacterial resistance was further improved showing a more significant increase of total SOD activity and the bacterial densities therefore increased bacterial growth. Zn concentration also affected the protein synthesis. Either single or binary stress induced the bacterial resistance by regulating SOD activity to eliminate ROS. All results of the bacterial oxidant stress, SOD response and protein synthesis in the combined treatment groups were more complicated than those in single treatment groups, which depended on the properties of the single treatment as well as the interaction between the two treatments upon bacterial activity. For P. fluorescens ZY2, the mediation of SOD activity to eliminate ROS in response to the combined exposure to Zn and Cefradine was first revealed as one of the co-resistance mechanisms, which is informative to further understanding the risk of antibiotics resistant bacteria to human and environmental health more accurately.

Endogenous nitric oxide in Pseudomonas fluorescens ZY2 as mediator against the combined exposure to zinc and cefradine

A better understanding on the mechanism involved in bacterial resistance to combined exposure to antibiotics and heavy metals is helpful in implementing practices to mitigate their ecological risk and spread of resistance genes in microbial population. Pseudomonas fluorescens ZY2, a strain isolated from swine wastewater, was chosen to study its growth (bacterial density OD600), the formation of reactive oxygen species (ROS), nitric oxide (NO) and NO synthases (NOS) under Zn, cefradine or Zn + cefradine treatments. Using Zn and cefradine as representative heavy metal and antibiotic in this investigation, respectively, the resistance of P. fluorescens ZY2 to toxic chemical exposure was investigated. Bacterial densities of treatment groups significantly increased over the time of incubation, but less than the control. ROS, NO and NOS initially increased, but then decreased after the initial 8 h of culturing, and were positively related to Zn concentrations. Moreover, the formation of ROS, NOS, and NO was activated by cefradine at Zn of up to 160 mg/L, but inhibited at Zn of 200 mg/L whether cefradine was added or not. Zn concentration affected ROS and NO concentrations between treatments and also was closely related to the variation of the relative bacterial density. For P. fluorescens ZY2, the mediation of endogenous NO to overcome ROS in response to the combined exposure of Zn and cefradine was suggested as a co-resistance mechanism, which would be beneficial to evaluate the ecological risk of heavy metals and antibiotics.

Combined toxic effects of heavy metals and antibiotics on a Pseudomonas fluorescens strain ZY2 isolated from swine wastewater

A Pseudomonas fluorescens strain ZY2, isolated from swine wastewater, was used to investigate the synergistic effects of five heavy metals (Pb, Cu, Zn, Cr(VI) and Hg) on bacterial resistance to antibiotics. Results indicate that the combined effects of antibiotic type, heavy metal type and concentration were significant (p < 0.01). Cross-resistance to Hg and antibiotics was the most noticeable. Moreover, the resistance to Hg and cefradine or amoxicillin, and Cr and amoxicillin were synergistic for low heavy metal concentrations, and turned antagonistic with increasing concentrations, while the resistances to Cr or Cu and cefradine, Pb or Cu and amoxicillin, Cu and norfloxacin showed reverse effects. In addition, resistance to Zn and amoxicillin were always synergetic, while resistance to Pb and cefradine or norfloxacin, Cr or Hg and norfloxacin as well as all the heavy metals and tetracycline were antagonistic. These results indicate that bacterial resistance to antibiotics can be affected by the type and concentration of co-exposed heavy metals and may further threaten people’s health and ecological security severely via horizontal gene transfer.

Co-occurrence of antibiotic and heavy metal resistance in Kızılırmak River isolates

Contamination of surface waters with antimicrobials has become an increasing public health concern because of the emergence of multi-resistant pathogens. For this reason, water samples collected from the Kızılırmak River-Kırıkkale, Turkey were analysed to learn more about the co-occurrence of heavy metal and antibiotic resistance in bacteria. Resistant profiles were determined by using 26 antibiotics and 17 heavy metals. Out of 290, 24 isolates with both heavy metal and antibiotic resistance were determined. Resistance to heavy metals including lead, tin, nickel, barium, aliminum, strontium, silver and lithium varied between 50 and 92 %. More than 50 % of the isolates showed resistance to cephalosporin, quinolone, sulfonamide and aminoglycoside type of antibiotics. The discharge of antimicrobials to water bodies may cause a combined effect of selection and co-selection towards resistant bacteria. Therefore, surface waters may be potential hot spots of the evolution of heavy metal- and antibiotic-resistant bacteria and require special scientific consideration.