Structural characterization of a Type B chloramphenicol acetyltransferase from the emerging pathogen Elizabethkingia anophelis NUHP1

Elizabethkingia anophelis is an emerging multidrug resistant pathogen that has caused several global outbreaks. E. anophelis belongs to the large family of Flavobacteriaceae, which contains many bacteria that are plant, bird, fish, and human pathogens. Several antibiotic resistance genes are found within the E. anophelis genome, including a chloramphenicol acetyltransferase (CAT). CATs play important roles in antibiotic resistance and can be transferred in genetic mobile elements. They catalyse the acetylation of the antibiotic chloramphenicol, thereby reducing its effectiveness as a viable drug for therapy. Here, we determined the high-resolution crystal structure of a CAT protein from the E. anophelis NUHP1 strain that caused a Singaporean outbreak. Its structure does not resemble that of the classical Type A CATs but rather exhibits significant similarity to other previously characterized Type B (CatB) proteins from Pseudomonas aeruginosa, Vibrio cholerae and Vibrio vulnificus, which adopt a hexapeptide repeat fold. Moreover, the CAT protein from E. anophelis displayed high sequence similarity to other clinically validated chloramphenicol resistance genes, indicating it may also play a role in resistance to this antibiotic. Our work expands the very limited structural and functional coverage of proteins from Flavobacteriaceae pathogens which are becoming increasingly more problematic.

Comparison of three species of Elizabethkingia genus by whole-genome sequence analysis

Elizabethkingia are found to cause severe neonatal meningitis, nosocomial pneumonia, endocarditis and bacteremia. However, there are few studies on Elizabethkingia genus by comparative genomic analysis. In this study, three species of Elizabethkingia were found: E. meningoseptica, E. anophelis and E. miricola. Resistance genes and associated proteins of seven classes of antibiotics including beta-lactams, aminoglycosides, macrolides, tetracyclines, quinolones, sulfonamides and glycopeptides, as well as multidrug resistance efflux pumps were identified from 20 clinical isolates of Elizabethkingia by whole-genome sequence. Genotype and phenotype displayed a good consistency in beta-lactams, aminoglycosides and glycopeptides, while contradictions exhibited in tetracyclines, quinolones and sulfonamides. Virulence factors and associated genes such as hsp60 (htpB), exopolysaccharide (EPS) (galE/pgi), Mg2+ transport (mgtB/mgtE) and catalase (katA/katG) existed in all clinical and reference strains. The functional analysis of the clusters of orthologous groups indicated that 'metabolism' occupied the largest part in core genome, 'information storage and processing' was the largest group in both accessory genome and unique genome. Abundant mobile elements were identified in E. meningoseptica and E. anophelis. The most significant finding in our study was that a single clone of E. anophelis had been circulating within diversities of departments in a clinical setting for nearly 18 months.

Elizabethkingia anophelis Infection in Infants, Cambodia, 2012-2018

We describe 6 clinical isolates of Elizabethkingia anophelis from a pediatric referral hospital in Cambodia, along with 1 isolate reported from Thailand. Improving diagnostic microbiological methods in resource-limited settings will increase the frequency of reporting for this pathogen. Consensus on therapeutic options is needed, especially for resource-limited settings.

Early neonatal sepsis and meningitis caused by Elizabethkingia meningoseptica in Saudi Arabia

Elizabethkingia meningoseptica (E. meningoseptica ) are Gram-negative bacteria commonly associated with nosocomial infections in neonates. This is a case study of E. meningoseptica, presented as meningitis and sepsis in a term baby. The female infant was born by vaginal delivery at 37 weeks gestational age. The case was peculiar because the baby was neither premature nor immuno-compromised, which are known risk factors for E. meningoseptica infection. The onset began on the second day of the neonate’s life. On day 3, peripheral blood culture and cerebrospinal fluid findings isolated a gram-negative bacteria identified as E. meningoseptica. The first-line antibiotics therapy was changed to ciprofloxacin, vancomycin, and rifampicin, based on the laboratory determination of antimicrobial sensitivity. The patient’s clinical condition improved, although post hemorrhagic ventricular dilatation was revealed by imaging studies. Clinicians should possess proper awareness of the antibiotic sensitivity of E. meningoseptica, as it is important in preventing high rates of morbidity and mortality.

Molecular diversity of chromosomal metallo-β-lactamase genes in Elizabethkingia genus

Elizabethkingia genus is an opportunistic life-threatening pathogen with an intrinsic multidrug-resistant phenotype. It is the only known microorganism with multi-chromosome-borne metallo-β-lactamase (MBL) genes. To determine the diversity and distribution of MBLs Bla_BlaB and Bla_GOB in this genus, comprehensive bioinformatic screening was applied in 109 available Elizabethkingia genomes. A total of 23 and 32 novel Bla_BlaB and Bla_GOB variants were found in Elizabethkingia spp., respectively; 12 and 15 clusters were assigned in these Bla_BlaB and Bla_GOB based on the amino acid identities and phylogenetic studies. Clustering of some variants did not conform to species-specific clades, which indicated potential inter-species dissemination of MBL genes among Elizabethkingia species. Cloning of representative bla_BlaB and bla_GOB into E. coli DH5α resulted in increased and diverse minimum inhibitory concentrations (MICs) to most β-lactams, including cephalosporins, carbapenems, and β-lactams-inhibitors. This study extends the database of class B carbapenemases, emphasizing the diversity of different MBL genes in the genus Elizabethkingia, which may represent potential reservoirs of acquired MBLs.

Elizabethkingia bruuniana Infections in Humans, Taiwan, 2005-2017

Using 16S rRNA and rpoB gene sequencing, we identified 6 patients infected with Elizabethkingia bruuniana treated at E-Da Hospital (Kaohsiung, Taiwan) during 2005–2017. We describe patient characteristics and the molecular characteristics of the E. bruuniana isolates, including their MICs. Larger-scale studies are needed for more robust characterization of this pathogen.

Elizabethkingia in Children: A Comprehensive Review of Symptomatic Cases Reported From 1944 to 2017

Elizabethkingia species often exhibit extensive antibiotic resistance and result in high morbidity and mortality, yet no systematic reviews exist that thoroughly characterize and quantify concerns for infected infants and children. We performed a review of literature and identified an initial 902 articles; 96 articles reporting 283 pediatric cases met our inclusion criteria and were subsequently reviewed. Case reports spanned 28 countries and ranged from 1944 to 2017. Neonatal meningitis remains the most common presentation of this organism in children, along with a range of other clinical manifestations. The majority of reported cases occurred as isolated cases, rather than within outbreaks. Mortality was high but has decreased in recent years, although neurologic sequelae among survivors remains concerning. Child outcomes can be improved through effective prevention measures and early identification and treatment of infected patients.

Sulfated steroids of Halichondriidae family sponges - Natural inhibitors of polysaccharide-degrading enzymes of bacterium Formosa algae, inhabiting brown alga Fucus evanescens

Inhibiting effects of sulfated steroids from marine sponges of Halichondriidae family: halistanol sulfate, topsentiasterol sulfate D and chlorotopsentiasterol sulfate D were investigated on three different types of enzymes degrading polysaccharides of brown algae: endo-1,3-β-d-glucanase GFA, fucoidan hydrolase FFA2 and bifunctional alginate lyase ALFA3 from marine bacterium Formosa algae KMM 3553T, inhabiting thalli of brown alga Fucus evanescens. This is the first research, devoted to influence of a marine natural compound on three functionally related enzymes that make up the complex of enzymes, necessary to degrade unique carbohydrate components of brown algae. Alginic acid, 1,3-β-D-glucan (laminaran) and fucoidan jointly constitute practically all carbohydrate biomass of brown algae, so enzymes, able to degrade such polysaccharides, are crucial for digesting brown algae biomass as well as for organisms surviving and proliferating on brown algae thalli. Halistanol sulfate irreversibly inhibited native endo-1,3-β-D-glucanases of marine mollusks, but reversibly competitively inhibited recombinant endo-1,3-β-d-glucanase GFA. This fact indicates that there are significant structural differences between the enzymes of practically the same specificity. For alginate lyase and fucoidan hydrolase halistanol sulfate was irreversible inhibitor. Topsentiasterol sulfate D was less active inhibitor whereas chlorotopsentiasterol sulfate D was the strongest inhibitor of enzymes under the study. Chlorotopsentiasterol sulfate D caused 98% irreversible inhibition of GFA. Chlorotopsentiasterol sulfate D also caused reversible and 100% inhibition of ALFA3, which is unusual for reversible inhibitors. Inhibition of FFA2 was complete and irreversible in all cases.

Microbiology of Elizabethkingia spp. isolates in hospitalized patients

An increasing number of infections due to Elisabethkingia spp. have been observed and reported in recent years. Here we report the microbiological aspects of 13 cases with positive cultures for Elizabethkingia spp. from 1998 to 2017. Elizabethkingia isolates were identified using the Vitek 2 Compact 60 (AES software) Gram-Negative Identification test (GNI) card (bioMerieux. Marcy-l'Etoile, France). The MICs were determined using Vitek 2 and interpreted according to CLSI guidelines based on the interpretive MIC breakpoints for Acinetobacter spp. Vitek 2 susceptibility results were confirmed using the manual E-test and the colistin result was confirmed using the broth dilution method. Twelve cases were observed between 2010 and 2017 with four cases in 2017. Of the 2017 samples, three out of four isolates were obtained outside the intensive care units compared to one out of eight samples between 2010 and 2016. There was variable susceptibility to trimethoprim/sulfamethoxazole (58.3%), ciprofloxacin (41.7%), piperacillin/tazobactam and gentamicin (16.6% each), and all were resistant to colistin. There is a high rate of drug resistance and further studies to identify the source of the infection are needed to build up a profile of Elizabethkingia spp. to inform public health policy in this context.

Myroides odoratimimus urinary tract infection in an immunocompromised patient: an emerging multidrug-resistant micro-organism

Background

Myroides spp. are common environmental organisms and they can be isolated predominantly in water, soil, food and in sewage treatment plants. In the last two decades, an increasing number of infections such as urinary tract infections and skin and soft tissue infections, caused by these microorganisms has been reported. Selection of appropriate antibiotic therapy to treat the infections caused by Myroides spp. is difficult due to the production of a biofilm and the organism's intrinsic resistance to many antibiotic classes.

Case presentation

We report the case of a 69-year-old immunocompromised patient who presented with repeated episodes of macroscopic haematuria, from Northern Italy.A midstream urine sample cultured a Gram negative rod in significant amounts (> 105 colony-forming units (cfu)/mL), which was identified as Myroides odoratimimus. The patient was successfully treated with trimethoprim/sulfamethoxazole after antibiotic susceptibility testing confirmed its activity.

Conclusion

This case underlines the emergence of multidrug resistant Myroides spp. which are ubiquitous in the environment and it demands that clinicians should be more mindful about the role played by atypical pathogens, which may harbour or express multidrug resistant characteristics, in immunocompromised patients or where there is a failure of empiric antimicrobial therapy.

Determination of Elizabethkingia Diversity by MALDI-TOF Mass Spectrometry and Whole-Genome Sequencing

In a hospital-acquired infection with multidrug-resistant Elizabethkingia, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and 16S rRNA gene analysis identified the pathogen as Elizabethkingia miricola. Whole-genome sequencing, genus-level core genome analysis, and in silico DNA-DNA hybridization of 35 Elizabethkingia strains indicated that the species taxonomy should be further explored.

First reported isolation of an emerging opportunistic pathogen (Elizabethkingia anophelis) from hospital water systems in Greece

After the Elizabethkingia anophelis outbreak in Wisconsin, USA, an active search for the detection of the microorganism in hospital water systems from Central and Northern Greece was performed from June to December 2016. In total, 457 water samples from 11 hospitals were analyzed. Elizabethkingia spp. was detected in three samples collected from two hospitals, both of which are located in Northern Greece. Two of the three isolated strains were identified as Elizabethkingia anophelis. No cases of Elizabethkingia infection were reported in either hospital during 2016. This is the first reported isolation of the pathogen in water supply systems in Greece.

Microbiological characteristics of a novel species most closely related to 'Bergeyella cardium' as a pathogen of infectious endocarditis

Infectious endocarditis (IE) can be caused by various pathogens, from dominating agents such as viridans group streptococci and staphylococci to rare species that are less virulent and not typically considered to be pathogens. In this study, we have isolated a novel species from a patient with problem of IE which was genetically most closely related to 'Bergeyella cardium', a causative pathogen of IE first reported in Korea in 2015 as a new species of the genus Bergeyella, with a similarity of 98.8% in 16S rRNA sequences. Microbiological characteristics, including morphology, biochemical identification and antimicrobial susceptibility profiling, of this novel species were determined. This fastidious Gram-negative bacillus could only be identified successfully by molecular sequencing analysis at present, and it exhibited low minimum inhibitory concentrations to the antibiotics tested except for aminoglycosides. Phylogeny analysis revealed this novel species clustered well with 'B. cardium' and other close species of genus Bergeyella.

Waterborne Elizabethkingia meningoseptica in Adult Critical Care

This outbreak might reflect improved diagnostic testing, indicating that E. meningoseptica is a pseudo-emerging pathogen.

Elizabethkingia meningoseptica is an infrequent colonizer of the respiratory tract; its pathogenicity is uncertain. In the context of a 22-month outbreak of E. meningoseptica acquisition affecting 30 patients in a London, UK, critical care unit (3% attack rate) we derived a measure of attributable morbidity and determined whether E. meningoseptica is an emerging nosocomial pathogen. We found monomicrobial E. meningoseptica acquisition (n = 13) to have an attributable morbidity rate of 54% (systemic inflammatory response syndrome >2, rising C-reactive protein, new radiographic changes), suggesting that E. meningoseptica is a pathogen. Epidemiologic and molecular evidence showed acquisition was water-source–associated in critical care but identified numerous other E. meningoseptica strains, indicating more widespread distribution than previously considered. Analysis of changes in gram-negative speciation rates across a wider London hospital network suggests this outbreak, and possibly other recently reported outbreaks, might reflect improved diagnostics and that E. meningoseptica thus is a pseudo-emerging pathogen.

Evidence for Elizabethkingia anophelis transmission from mother to infant, Hong Kong

Genome sequencing can provide rapid insights on transmission and pathogenesis of emerging pathogens.

Elizabethkingia anophelis, recently discovered from mosquito gut, is an emerging bacterium associated with neonatal meningitis and nosocomial outbreaks. However, its transmission route remains unknown. We use rapid genome sequencing to investigate 3 cases of E. anophelis sepsis involving 2 neonates who had meningitis and 1 neonate’s mother who had chorioamnionitis. Comparative genomics revealed evidence for perinatal vertical transmission from a mother to her neonate; the 2 isolates from these patients, HKU37 and HKU38, shared essentially identical genome sequences. In contrast, the strain from another neonate (HKU36) was genetically divergent, showing only 78.6% genome sequence identity to HKU37 and HKU38, thus excluding a clonal outbreak. Comparison to genomes from mosquito strains revealed potential metabolic adaptations in E. anophelis under different environments. Maternal infection, not mosquitoes, is most likely the source of neonatal E. anophelis infections. Our findings highlight the power of genome sequencing in gaining rapid insights on transmission and pathogenesis of emerging pathogens.

Biosurfactant activity, heavy metal tolerance and characterization of Joostella strain A8 from the Mediterranean polychaete Megalomma claparedei (Gravier, 1906)

The effect of heavy metals on the activity of biosurfactants produced by Joostella strain A8 from the polychaete Megalomma claparedei was investigated. Biosurfactant activity was first improved by evaluating the influence of abiotic parameters. Higher E(24) indices were achieved at 25 °C in mineral salt medium supplemented with 2 % glucose, 3 % sodium chloride (w/v) and 0.1 % ammonium chloride (w/v). Considerable surface tension reduction was never recorded. Heavy metal tolerance was preliminarily assayed by plate diffusion method resulting in the order of toxicity Cd > Cu > Zn. The activity of biosurfactants was then evaluated in the presence of heavy metals at different concentrations in liquid cultures that were incubated under optimal conditions for biosurfactant activity. The production of stable emulsions resulted generally higher in the presence of metals. These findings suggest that biosurfactant production could represent a bacterial adaptive strategy to defend cells from a stress condition derived from heavy metals in the bulk environment.

[Elizabethkingia meningosepticum bacteremia in a patient with Bardet-Biedl syndrome and chronic renal failure]

Elizabethkingia meningosepticum, a gram-negative opportunistic pathogen may cause life-threatening nosocomial infections especially in newborns and immunosuppressive patients. This bacterium has a peculiar antibiotic resistance profile. It is resistant to most of the antibiotics against gram-negative bacteria and susceptible to antibiotics that are used to treat gram-positive bacteria, such as vancomycin and trimethoprim-sulphamethoxazole (SXT). For this reason appropriate treatment of E.meningosepticum infections are based on the proper identification of bacteria. In this report, a case of catheter-related E.meningosepticum bacteremia in a patient with chronic renal failure due to Bardet-Biedl syndrome, a genetic disorder characterized by multiorgan dysfunction, was presented. A 25-year-old male patient with Bardet-Biedl syndrome was admitted to the emergency room with the complaints of high fever with shivers that started the day before. The patient had a femoral dialysis catheter. Venous blood samples drawn at the time of administration were cultured immediately. Two days later, blood cultures which yielded positive signals were passaged onto blood and MacConkey agar plates and after incubation at 37°C for 16 hours, wet-raised colonies with clear margin, gray colour and large size similar to gram-negative bacterial colonies were detected on blood agar medium. No growth was observed on MacConkey agar plate at the end of five days. The isolate was found positive for KOH, oxidase, catalase, urease, esculine and MOI (Motility Indole Ornithine) tests, whereas it was citrate negative. Gram staining revealed faintly stained thin gram-negative bacilli. The isolate was identified as E.meningosepticum by Vitek® 2 system (bioMérieux, USA), and confirmed by sequence analysis of 16S RNA gene region amplified with PCR method. The antibiotic susceptibility profile of the strain was detected by the Vitek 2 system, while vancomycin susceptibility was investigated by Kirby-Bauer disc diffusion method. The isolate was found resistant to ampicillin/sulbactam, piperacillin/tazobactam, ceftazidime, cefepime, meropenem, imipenem, amikacin, gentamicin, netilmicin, levofloxacin, tetracycline, colistin and rifampicin; intermediate to tigecyclin and tetracyclin; susceptible to cefoperazone/sulbactam, ciprofloxacin, levofloxacin, SXT and vancomycin. One gram vancomycin once every four days was administered to the patient, however on the ninth day of the treatment he developed fever again. Blood cultures obtained again yielded E.meningosepticum. After changing his dialysis catheter and extending the vancomycin treatment to 15 days, the patient was discharged with cure. In conclusion, clinicians should consider E.meningosepticum as a possible causative agent of bacteremia non-responsive to the empirical antibiotic regimens and when gram-negative bacteria are isolated from the blood cultures of such patients with underlying diseases. Accurate and prompt identification of E.meningosepticum will allow immediate administration of the specific antibiotic treatment, thereby decreasing the mortality and morbidity rates.

[Effect of autoinducer 2 on Riemerell antatipestifer adherence and invasion to Vero cells]

OBJECTIVE

Autoinducer 2 (AI-2), used to communicate among bacterial species, regulates numerous physiological functions of bacteria. In this study, we studied the effect of AI-2 on adherence and invasion of Riemerella antatipestifer (RA) strain CH3 to Vero cells and transcriptional levels of virulence-related and metabolism-related genes were investigated.

METHODS

To verify whether the adherence and invasion of CH3 was affected by AI-2, we added different concentrations of AI-2 to the cocultures of Vero cells and CH3 and then calculated adherence percentages and invasion percentages of tested groups. We further added AI-2 (184.0 micromol/L) to the tryptone soya broth culture of CH3 and then detected the effect of transcriptional levels of related genes of CH3 using real-time PCR.

RESULTS

The adherence of CH3 to Vero cells was decreased most to 62% with 18.4 micromol/L AI-2 and the invasion of CH3 to Vero cells was increased most to 194% with 184.0 micromol/L AI-2. The result of real-time PCR shows that AI-2 increased transcriptional levels of some virulence-related genes and decreased transcriptional levels of some metabolism-related genes.

CONCLUSION

These results suggest that AI-2 affected adherence and invasion of CH3 to Vero cells. Moreover, AI-2 could regulate some genes of CH3 to modulate particular physiological behaviors.

A comparison of the antifouling/foul-release characteristics of non-biocidal xerogel and commercial coatings toward micro- and macrofouling organisms

Five non-biocidal xerogel coatings were compared to two commercial non-biocidal coatings and a silicone standard with respect to antifouling (AF)/fouling-release (FR) characteristics. The formation and release of biofilm of the marine bacterium Cellulophaga lytica, the attachment and release of the microalga Navicula incerta, and the fraction removal and critical removal stress of reattached adult barnacles of Amphibalanus amphitrite were evaluated in laboratory assays. Correlations of AF/FR performance with surface characteristics such as wettability, surface energy, elastic modulus, and surface roughness were examined. Several of the xerogel coating compositions performed well against both microfouling organisms while the commercial coatings performed less well toward the removal of microalgae. Reattached barnacle adhesion as measured by critical removal stress was significantly lower on the commercial coatings when compared to the xerogel coatings. However, two xerogel compositions showed release of 89-100% of reattached barnacles. These two formulations were also tested in the field and showed similar results.

Combinatorial materials research applied to the development of new surface coatings IX: an investigation of novel antifouling/fouling-release coatings containing quaternary ammonium salt groups

Polysiloxane coatings containing chemically-bound ("tethered") quaternary ammonium salt (QAS) moieties were investigated for potential application as environmental-friendly coatings to control marine biofouling. A combinatorial/high-throughput approach was applied to the investigation to enable multiple variables to be probed simultaneously and efficiently. The variables investigated for the moisture-curable coatings included QAS composition, ie alkyl chain length, and concentration as well as silanol-terminated polysiloxane molecular weight. A total of 75 compositionally unique coatings were prepared and characterized using surface characterization techniques and biological assays. Biological assays were based on two different marine microorganisms, a bacterium, Cellulophaga lytica and a diatom, Navicula incerta, as well as a macrofouling alga, Ulva. The results of the study showed that all three variables influenced coating surface properties as well as antifouling (AF) and fouling-release (FR) characteristics. The incorporation of QAS moieties into a polysiloxane matrix generally resulted in an increase in coating surface hydrophobicity. Characterization of coating surface morphology revealed a heterogeneous, two-phase morphology for many of the coatings investigated. A correlation was found between water contact angle and coating surface roughness, with the contact angle increasing with increasing surface roughness. Coatings based on the QAS moiety containing the longest alkyl chain (18 carbons) displayed the highest micro-roughness and, thus, the most hydrophobic surfaces. With regard to AF and FR properties, coatings based on the 18 carbon QAS moieties were very effective at inhibiting C. lytica biofilm formation and enabling easy removal of Ulva sporelings (young plants) while coatings based on the 14 carbon QAS moities were very effective at inhibiting biofilm growth of N. incerta.

Chimaereicella boritolerans sp. nov., a boron-tolerant and alkaliphilic bacterium of the family Flavobacteriaceae isolated from soil

A non-motile, Gram-negative, boron-tolerant and alkaliphilic bacterium was isolated from soil of the Hisarcik area in the Kutahya Province of Turkey that was naturally high in boron minerals. The novel isolate, designated T-22T, formed rod-shaped cells, was catalase- and oxidase-positive and tolerated up to 300 mM boron. The strain also survived on agar medium containing up to 3 % (w/v) NaCl. The pH range for growth of this strain was 6.5–10.0 (optimum pH 8.0–9.0) and the temperature range was 16–37 °C (optimum 28–30 °C). Phylogenetic analysis based on 16S rRNA gene sequences revealed a clear affiliation with the genusChimaereicella, with 97.4 % sequence similarity toChimaereicella alkaliphilaAC-74T, which was the highest similarity among cultivated bacteria. The DNA–DNA relatedness withC. alkaliphilaAC-74Twas 28.3 %. The major respiratory quinone system was MK-7 and the predominant cellular fatty acids were iso-C15 : 0, iso-C17 : 1ω9c, iso-C17 : 03-OH and summed feature 3 (iso-C15 : 02-OH and/or iso-C16 : 1ω7c). The DNA G+C content was 42.5 mol%. Based on the phylogenetic analysis and physiological, chemotaxonomic and genetic data, we concluded that strain T-22Tshould be classified in the genusChimaereicella, and we propose the nameChimaereicella boritoleranssp. nov. for this novel species. The type strain is strain T-22T(=DSM 17298T=NBRC 101277T=ATCC BAA-1189T).

Purification and characterization of an extracellular, uracil specific ribonuclease from a Bizionia species isolated from the marine environment of the Sundarbans

The first ribonuclease (RNase) from the Cytophaga-Flavobacterium-Bacteroides phylum, dominant in the marine environment, and also from the first Bizionia species isolated from the tropics was purified and characterized. Extracellular RNase production occurred when the culture medium contained 5-7% (w/v) NaCl. The 53.0 kDa enzyme was purified 29 folds with a recovery of 4% and specific activity of 630unit/mg protein. The pH and temperature optima are 6.5 and 35 degrees C, respectively and the enzyme retains more than half of its activity (relative to optimal assay conditions) after 1h pre-incubation separately with 5% (w/v) NaCl or from pH 5.0 to 8.5 or at 50 degrees C. Dithiothreitol and beta-mercaptoethanol do not inhibit whereas human placental RNase inhibitor protein halves the RNase activity. While Mg(2+), Ba(2+) and Ca(2+) enhanced the enzyme activity, Fe(2+), Cu(2+) and Hg(2+) inactivated it. This RNase degrades uracil containing nucleic acids only. Our isolate could be a novel renewable source of deoxyribonuclease (DNase)--free RNase enzyme.

Enumeration and characterization of culturable arsenate resistant bacteria in a large estuary

Arsenic is a toxic element that exists in two major inorganic forms, arsenate and arsenite. A number of bacteria have been shown to resist arsenic exposure, and even more bacteria appear to possess the genes for arsenic resistance. In this study, the numbers of culturable arsenate-resistant bacteria present in water at three coastal sites in the Lake Pontchartrain estuary, Louisiana, was determined. Despite insignificant (less than 1.33 microM) levels of arsenic in this system, 20-50% of the viable count of bacteria showed appreciable arsenate resistance, suggesting that arsenic-resistant bacteria are common and widespread. A diverse array of arsenate-resistant isolates was obtained, with 16S rRNA sequence analysis indicating 37 different bacterial strains, representing six major bacterial groups. Many of these isolates were affiliated with groups of bacteria that have been poorly characterized in terms of arsenic resistance, such as the Betaproteobacteria or Flavobacteria. Some isolates were capable of tolerating very high (> 100 mM) levels of arsenate, although arsenite resistance was generally much lower. The results suggest that arsenic-resistant bacteria are common, even in environments with insignificant arsenic contamination, and that many different groups of aquatic bacteria show appreciable arsenic resistance.

Recommendation of an appropriate medium for in vitro drug susceptibility testing of the fish pathogen Tenacibaculum maritimum

In the present study, Anacker and Ordal agar, marine agar (MA), and Flexibacter maritimus medium (FMM) were compared with the dilute versions of Mueller-Hinton agar (DMHA) medium recommended by the National Committee for Clinical Laboratory Standards (NCCLS) for their use in disk diffusion tests with Tenacibaculum maritimum strains and to calculate the MICs of five drugs by the Etest method. Preliminary growth tests performed with 32 strains of this pathogen on each medium revealed that all strains failed to grow on DMHA, while the remaining media supported good growth of all isolates. In the susceptibility tests, which were carried out with the other three media, all strains were resistant to oxolinic acid and were highly susceptible to amoxicillin and trimethoprim-sulfamethoxazole, showing a good correspondence with the Etest values, which ranged from 0.064 to 0.75 and 0.006 to 1.5 mug/ml, respectively. Enrofloxacin and oxytetracycline produced significantly smaller inhibition zones and MICs on MA than on the other media assayed. However, fast, clear, and well-defined zones of inhibition were displayed for all strains at 24 h of incubation only on FMM by both the disk diffusion assay and Etest. In addition, FMM prepared with commercial sea salts instead of seawater was also suitable for bacterial isolation as well as for susceptibility testing. On the basis of these results, the use of FMM to determine the in vitro susceptibility of T. maritimum and its inclusion in a future revision of the NCCLS M42 report are recommended.