Cepacia Complex Strains Research Articles

Examining the activity of cefepime-taniborbactam against Burkholderia cepacia complex and Burkholderia gladioli isolated from cystic fibrosis patients in the United States.

The novel clinical-stage β-lactam-β-lactamase inhibitor combination, cefepime-taniborbactam, demonstrates promising activity toward many Gram-negative bacteria producing class A, B, C, and/or D β-lactamases. We tested this combination against a panel of 150 Burkholderia cepacia complex (Bcc) and Burkholderia gladioli strains. The addition of taniborbactam to cefepime shifted cefepime minimum inhibitory concentrations toward the provisionally susceptible range in 59% of the isolates tested. Therefore, cefepime-taniborbactam possessed similar activity as first-line agents, ceftazidime and trimethoprim-sulfamethoxazole, supporting further development.

Enfeksiyon Etkeni Nonfermenter Gram Negatif İzolatlar ve Antibiyotik Dirençleri: Üç Yıllık Veri

Objective: This study aimed to investigate clinical non-fermenting gram-negative isolates and antibiotic resistance profiles for three years in a tertiary hospital.Materials and Methods: A total of 3817 non-fermenting gram-negative strains isolated from various cultures between January 2017 and December 2019 in Balıkesir Atatürk City Hospital were investigated retrospectively. Identification and antibiotic susceptibilities were performed using conventional methods and PhoenixTM 100 system (Becton Dickinson, MA, USA).Results: A total of 2201 (57.7%) P. aeruginosa, 1283 (33.6%) A. baumannii-calcoaceticus complex, 202 (5.3%) S. maltophilia and 131 (3.4%) B. cepacia complex strains were identified. The majority of strains were isolated from intensive care units (54.5%), followed by internal medicine (33.4%) and surgical services (12.1%). All A. baumannii-calcoaceticus complex species showed over 70% resistance to most antibiotics. In addition to β-lactam antibiotic resistance (generally over 30%), resistance to fluoroquinolones (30.4%) seemed to have particular importance. Co-trimoxazole showed below 10% resistance in S. maltophilia isolates. In B. cepacia complex, ceftazidime resistance increased in years (2018, 22.2%; 2019, 67.0%). Conclusion: The issue of antibiotic resistance cannot be won by just developing novel antimicrobials, but also by increasing the efficiency of current ones. The first step is to “diagnose” the current condition, like local surveillance studies.

Biosynthesis of Ditropolonyl Sulfide, an Antibacterial Compound Produced by Burkholderia cepacia Complex Strain R-12632.

Burkholderia cepacia complex strain R-12632 produces ditropolonyl sulfide, an unusual sulfur-containing tropone, via a yet-unknown biosynthetic pathway. Ditropolonyl sulfide purified from a culture of strain R-12632 inhibits the growth of various Gram-positive and Gram-negative resistant bacteria, with MIC values as low as 16 μg/ml. In the present study, we used a transposon mutagenesis approach combined with metabolite analyses to identify the genetic basis for antibacterial activity of strain R-12632 against Gram-negative bacterial pathogens. Fifteen of the 8304 transposon mutants investigated completely lost antibacterial activity against Klebsiella pneumoniae LMG 2095. In these loss-of-activity mutants, nine genes were interrupted. Four of those genes were involved in assimilatory sulfate reduction, two were involved in phenylacetic acid (PAA) catabolism, and one was involved in glutathione metabolism. Via semipreparative fractionation and metabolite identification, it was confirmed that inactivation of the PAA degradation pathway or glutathione metabolism led to loss of ditropolonyl sulfide production. Based on earlier studies on the biosynthesis of tropolone compounds, the requirement for a functional PAA catabolic pathway for antibacterial activity in strain R-12632 indicated that this pathway likely provides the tropolone backbone for ditropolonyl sulfide. Loss of activity observed in mutants defective in assimilatory sulfate reduction and glutathione biosynthesis suggested that cysteine and glutathione are potential sources of the sulfur atom linking the two tropolone moieties. The demonstrated antibacterial activity of the unusual antibacterial compound ditropolonyl sulfide warrants further studies into its biosynthesis and biological role. IMPORTANCEBurkholderia bacteria are historically known for their biocontrol properties and have been proposed as a promising and underexplored source of bioactive specialized metabolites. Burkholderia cepacia complex strain R-12632 inhibits various Gram-positive and Gram-negative resistant pathogens and produces numerous specialized metabolites, among which is ditropolonyl sulfide. This unusual antimicrobial has been poorly studied and its biosynthetic pathway remains unknown. In the present study, we performed transposon mutagenesis of strain R-12632 and performed genome and metabolite analyses of loss-of-activity mutants to study the genetic basis for antibacterial activity. Our results indicate that phenylacetic acid catabolism, assimilatory sulfate reduction, and glutathione metabolism are necessary for ditropolonyl sulfide production. These findings contribute to understanding of the biosynthesis and biological role of this unusual antimicrobial.

New benzo(a)pyrene-degrading strains of the Burkholderia cepacia complex prospected from activated sludge in a petrochemical wastewater treatment plant.

The prospection of bacteria that are resistant to polyaromatic hydrocarbons (PAH) of activated sludge from a Petrochemical Wastewater Treatment Plant (WWTP) allows investigating potential biodegraders of PAH. For this purpose, sludge samples were cultured with benzo(a)pyrene and/or naphthalene as carbon sources. The recovered isolates were characterized by biochemical methods and identified based on the analysis of the sequence of three genes: 16S, recA and gyrB. The isolated strains were shown to be capable of producing surfactants, which are important for compound degradation. The ability to reduce benzo(a)pyrene in vitro was tested by gas chromatography. After 20 days of experiment, the consortium that was enriched with 1 mg/L of benzo(a)pyrene was able to reduce 30% of the compound when compared to a control without bacteria. The four isolated strains that significantly reduced benzo(a)pyrene belong to the Burkholderia cepacia complex and were identified within the consortium as the species B. cenocepacia IIIa, B. vietnamiensis, B. cepacia, and B. multivorans. This finding demonstrates the biotechnological potential of the B. cepacia complex strains for use in wastewater treatment and bioremediation. Previous studies on hydrocarbon-degrading strains focused mainly on contaminated soil or marine areas. In this work, the strains were prospected from activated sludge in a WWTP and showed the potential of indigenous samples to be used in both improving treatment systems and bioremediation of areas contaminated with petrochemical waste.

In Vitro Susceptibility of Burkholderia cepacia Complex Isolated from Cystic Fibrosis Patients to Ceftazidime-Avibactam and Ceftolozane-Tazobactam.

We tested the in vitro susceptibility of ceftazidime-avibactam and ceftolozane-tazobactam and 13 other antibiotics against 91 Burkholderia cepacia complex (BCC) strains isolated from cystic fibrosis patients since 2012. The highest susceptibility (82%) was found for trimethoprim-sulfamethoxazole. Eighty-one and 63% of all BCC strains were susceptible to ceftazidime-avibactam and ceftolozane-tazobactam, respectively. For temocillin, ceftazidime, piperacillin-tazobactam, and meropenem, at least 50% of the strains were susceptible. B. stabilis seems to be more resistant than other BCC species.

Elucidation of the mechanism behind the potentiating activity of baicalin against Burkholderia cenocepacia biofilms.

Reduced antimicrobial susceptibility due to resistance and tolerance has become a serious threat to human health. An approach to overcome this reduced susceptibility is the use of antibiotic adjuvants, also known as potentiators. These are compounds that have little or no antibacterial effect on their own but increase the susceptibility of bacterial cells towards antimicrobial agents. Baicalin hydrate, previously described as a quorum sensing inhibitor, is such a potentiator that increases the susceptibility of Burkholderia cenocepacia J2315 biofilms towards tobramycin. The goal of the present study is to elucidate the molecular mechanisms behind the potentiating activity of baicalin hydrate and related flavonoids. We first determined the effect of multiple flavonoids on susceptibility of B. cenocepacia J2315 towards tobramycin. Increased antibiotic susceptibility was most pronounced in combination with apigenin 7-O-glucoside and baicalin hydrate. For baicalin hydrate, also other B. cepacia complex strains and other antibiotics were tested. The potentiating effect was only observed for aminoglycosides and was both strain- and aminoglycoside-dependent. Subsequently, gene expression was compared between baicalin hydrate treated and untreated cells, in the presence and absence of tobramycin. This revealed that baicalin hydrate affected cellular respiration, resulting in increased reactive oxygen species production in the presence of tobramycin. We subsequently showed that baicalin hydrate has an impact on oxidative stress via several pathways including oxidative phosphorylation, glucarate metabolism and by modulating biosynthesis of putrescine. Furthermore, our data strongly suggest that the influence of baicalin hydrate on oxidative stress is unrelated to quorum sensing. Our data indicate that the potentiating effect of baicalin hydrate is due to modulating the oxidative stress response, which in turn leads to increased tobramycin-mediated killing.

Reclassification of the Specialized Metabolite Producer Pseudomonas mesoacidophila ATCC 31433 as a Member of the Burkholderia cepacia Complex

ABSTRACTPseudomonas mesoacidophila ATCC 31433 is a Gram-negative bacterium, first isolated from Japanese soil samples, that produces the monobactam isosulfazecin and the β-lactam-potentiating bulgecins. To characterize the biosynthetic potential of P. mesoacidophila ATCC 31433, its complete genome was determined using single-molecule real-time DNA sequence analysis. The 7.8-Mb genome comprised four replicons, three chromosomal (each encoding rRNA) and one plasmid. Phylogenetic analysis demonstrated that P. mesoacidophila ATCC 31433 was misclassified at the time of its deposition and is a member of the Burkholderia cepacia complex, most closely related to Burkholderia ubonensis. The sequenced genome shows considerable additional biosynthetic potential; known gene clusters for malleilactone, ornibactin, isosulfazecin, alkylhydroxyquinoline, and pyrrolnitrin biosynthesis and several uncharacterized biosynthetic gene clusters for polyketides, nonribosomal peptides, and other metabolites were identified. Furthermore, P. mesoacidophila ATCC 31433 harbors many genes associated with environmental resilience and antibiotic resistance and was resistant to a range of antibiotics and metal ions. In summary, this bioactive strain should be designated B. cepacia complex strain ATCC 31433, pending further detailed taxonomic characterization.IMPORTANCE This work reports the complete genome sequence of Pseudomonas mesoacidophila ATCC 31433, a known producer of bioactive compounds. Large numbers of both known and novel biosynthetic gene clusters were identified, indicating that P. mesoacidophila ATCC 31433 is an untapped resource for discovery of novel bioactive compounds. Phylogenetic analysis demonstrated that P. mesoacidophila ATCC 31433 is in fact a member of the Burkholderia cepacia complex, most closely related to the species Burkholderia ubonensis. Further investigation of the classification and biosynthetic potential of P. mesoacidophila ATCC 31433 is warranted.

Preliminary data on antibacterial activity of Echinacea purpurea-associated bacterial communities against Burkholderia cepacia complex strains, opportunistic pathogens of Cystic Fibrosis patients

Burkholderia cepacia complex bacteria (Bcc) represent a serious threat for immune-compromised patient affected by Cystic Fibrosis (CF) since they are resistant to many substances and to most antibiotics. For this reason, the research of new natural compounds able to inhibit the growth of Bcc strains has raised new interest during the last years. A source of such natural compounds is represented by medicinal plants and, in particular, by bacterial communities associated with these plants able to produce molecules with antimicrobial activity. In this work, a panel of 151 (endophytic) bacteria isolated from three different compartments (rhizospheric soil, roots, and stem/leaves) of the medicinal plant Echinacea purpurea were tested (using the cross-streak method) for their ability to inhibit the growth of 10 Bcc strains. Data obtained revealed that bacteria isolated from the roots of E. purpurea are the most active in the inhibition of Bcc strains, followed by bacteria isolated from the rhizospheric soil, and endophytes from stem/leaf compartment. At the same time, Bcc strains of environmental origin showed a higher resistance toward inhibition than the Bcc strains with clinical (i.e. CF patients) origin. Differences in the inhibition activity of E. purpurea-associated bacteria are mainly linked to the environment −the plant compartment- rather than to their taxonomical position.

Intrinsic Resistance of Burkholderia cepacia Complex to Benzalkonium Chloride.

ABSTRACTPharmaceutical products that are contaminated with Burkholderia cepacia complex (BCC) bacteria may pose serious consequences to vulnerable patients. Benzyldimethylalkylammonium chloride (BZK) cationic surfactants are extensively used in medical applications and have been implicated in the coselection of antimicrobial resistance. The ability of BCC to degrade BZK, tetradecyldimethylbenzylammonium chloride (C14BDMA-Cl), dodecyldimethylbenzylammonium chloride (C12BDMA-Cl), decyldimethylbenzylammonium chloride (C10BDMA-Cl), hexyldimethylbenzylammonium chloride, and benzyltrimethylammonium chloride was determined by incubation in 1/10-diluted tryptic soy broth (TSB) to determine if BCC bacteria have the ability to survive and inactivate these disinfectants. With BZK, C14BDMA-Cl, and C12BDMA-Cl, inhibition of the growth of 20 BCC strains was observed in disinfectant solutions that ranged from 64 to 256 µg/ml. The efflux pump inhibitor carbonyl cyanide m-chlorophenylhydrazone increased the sensitivity of bacteria to 64 µg/ml BZK. The 20 BCC strains grew well in 1/10-diluted TSB medium with BZK, C12BDMA-Cl, and C10BDMA-Cl; they absorbed and degraded the compounds in 7 days. Formation of benzyldimethylamine and benzylmethylamine as the initial metabolites suggested that the cleavage of the C alkyl-N bond occurred as the first step of BZK degradation by BCC bacteria. Proteomic data confirmed the observed efflux activity and metabolic inactivation via biodegradation in terms of BZK resistance of BCC bacteria, which suggests that the two main resistance mechanisms are intrinsic and widespread.

S101 Pathogen associated molecular patterns in cystic fibrosis pathogens: Analysis of peptidoglycan structure

BackgroundPathogen associated molecular patterns (PAMPS) are key virulence determinants in triggering immune mediated damage in cystic fibrosis. The lipopolysaccharide (LPS) in Pseudomonas aeruginosa strains isolated from CF-lungs has “CF specific”...

Genomic analysis of three sponge-associated Arthrobacter Antarctic strains, inhibiting the growth of Burkholderia cepacia complex bacteria by synthesizing volatile organic compounds

In this work we analyzed the ability of three Arthrobacter strains (namely TB23, TB26 and CAL618), which were isolated from the Antarctic sponges Haliclonissa verrucosa and Lyssodendrix nobilis, to specifically inhibit the growth of a panel of 40 Burkholderia cepacia complex strains, representing a major cause of infections in patients that are affected by Cystic Fibrosis. The inhibitory activity was due to the synthesis of antimicrobial compounds, very likely volatile organic compounds (VOCs), and was partially dependent on the growth media that were used for Antarctic strains growth. The phylogenetic analysis revealed that two of them (i.e. CAL 618 and TB23) were very close and very likely belonged to the same Arthrobacter species, whereas the strain TB26 was placed in a distant branch. The genome of the strains TB26 and CAL618 was also sequenced and compared with that of the strain TB23. The analysis revealed that TB23 and CAL618 shared more genomic properties (GC content, genome size, number of genes) than with TB26. Since the three strains exhibited very similar inhibition pattern vs Bcc strains, it is quite possible that genes involved in the biosynthesis of antimicrobial compounds very likely belong to the core genome.

Characterization of genotypes for Burkholderia cepacia complex strains isolated from patients in hospitals of the Russian federation

Eighty-eight cultures of microorganisms classed as part of the Burkholderia cepacia complex (Bcc) during initial identification were analyzed by multilocus sequencing (multilocus sequence typing, MLST). Thirteen genotypes (sequence type, ST) were detected; nine of them (708, 709, 710, 711, 712, 714, 727, 728, 729) were identified for the first time. Two new alleles for the gene trpB (357, 358) and one of the genes atpD (306) and gltB 9352 were detected and registered. It was found that strains of two genotypes (711, 712) belong to the species B. multivorans, one (ST102) to B. contaminans, one (ST51) to B. stabilis, and one (ST729) to B. vietnamiensis. Most strains of the sample representing eight genotypes (208, 241, 728, 727, 708, 709, 710, 714) belong to the species B. cenocepacia. The identified genotypes differ in global extent: four genotypes (51, 102, 208, 241) have intercontinental distribution, and one (712) has intracontinental distribution. It is shown that strains causing nosocomial infections in most cases refer to genotypes 728 and 708. Genotype 709 detected in strains isolated from patients in seven federal districts (FDs) of Russia should be recognized as epidemiologically significant for patients with cystic fibrosis. The Bcc strains of genotypes 241 (B. cenocepacia) and 729 (B. vietnamiensis) were isolated from the patients of the Far Eastern FD. They are not typical for the other FDs of Russia. The possibility of concomitant infection in cystic fibrosis patient with two genotypes (709, 708), that is, are epidemiologically significant and nosocomial was indicated. The longterm persistence of a single genotype strain in the organism of patients with cystic fibrosis was shown both for Bcc species B. cenocepacia (ST 709) and for B. multivorans (ST712). The possibility of transfection of the Bcc strain typical for a nosocomial environment to patients with cystic fibrosis during surgery was observed.

Photodynamic Antimicrobial Chemotherapy (PACT) in combination with antibiotics for treatment of Burkholderia cepacia complex infection

This study aimed to determine if Photodynamic Antimicrobial Chemotherapy (PACT) was effective in the treatment of Burkholderia cepacia complex infection and whether a synergistic effect was evident if PACT was used in combination with antibiotics. The susceptibility of both planktonic and biofilm cultures of B. cepacia complex strains to methylene blue (MB) and meso-tetra(n-methyl-4-pyridyl)porphine tetra-tosylate (TMP)–mediated PACT was determined alone and in combination with antibiotics used in the treatment of Cystic Fibrosis pulmonary infection caused by these bacteria. When B. cepacia complex strains were grown planktonically, high levels of kill of were achieved with both TMP and MB-mediated PACT with strain and photosensitizer specific differences apparent. When strains were grown in biofilm, antibiotic treatment alone was bactericidal in 17/36 (47%) strain/antibiotic combinations tested. When antibiotic treatment was combined with PACT, bactericidal activity was apparent for 33/36 (92%) strain/antibiotic combinations. No antagonism was detected between PACT and antibiotic treatment with the combination synergistic for 6/36 (17%) and indifferent for 30/36 (83%) strain/antibiotic combinations. PACT could be a viable treatment option, either alone or in combination with antibiotics for treatment of B. cepacia complex pulmonary infection.

Study of class I integron in a Burkholderia cepacia complex strain isolated from blood colture

The Burkholderia cepacia complex (Bcc) consists of several species that cause lung infections in patients with cystic fibrosis but are also capable to colonize immunocompromised patients. Once established, the infection is usually difficult to eradicate, as Bcc is intrinsically resistant to many antibiotics. Besides, the acquisition of additional resistance determinants by horizontal gene transfer makes very difficult the therapeutic approach to these infections. Among horizontally acquired DNAs, integrons have been frequently reported in many Gramnegative bacteria that affect human health, but they have not been found frequently in Burkholderia isolates until now. In the present work we report on a Bcc isolate, recovered from the blood of an immunocompromised patient, that carries a 2.3 kb class I integron already described in a Salmonella enterica isolate eight years ago, coding for aacA4, aadA1 and catB2 in its cassette array.

Successful cessation of transmitting healthcare-associated inpections due to Burkholderia cepacia complex in a neonatal intensive care unit in a japanese children's hospital

BackgroundBurkholderia cepacia strains have been known to possess the capability to cause serious infections especially in neonatal intensive care units (NICUs), and their multi-drug resistances become a severe threat in hospital settings. The aim of this investigation was to evaluate the B. cepacia complex infections in the NICU in Nagano Children's Hospital, Azumino 399-8288, Japan, and to report the intervention leading to the successful cessation of the outbreak.MethodologyThe incidence of isolation and antimicrobial susceptibilities of nosocomial Burkholderia cepacia complex strains during a four-year period were retrospectively examined by clinical microbiological records, and by pulsed-field gel electrophoresis analyses along with the bacteriological verification of disinfectant device itself and procedures for its maintenance routinely used in the NICU.ResultsDuring the period surveyed between 2007 and 2009, only an isolate per respective year of B. cepacia complex was recovered from each neonate in the NICU. However, in 2010, the successive 6 B. cepacia complex isolates were recovered from different hospitalized neonates. Among them, an isolate was originated from peripheral blood of a neonate, apparently giving rise to systemic infection. In addition, the hospitalized neonate with bacteremia due to B. cepacia complex also exhibited positive cultures from repeated catheterized urine samples together with tracheal aspirate secretions. However other 5 isolates were considered as the transients or contaminants having little to do with infections. Moreover, the 5 isolates between July and October in 2010 revealed completely the same electrophoresis patterns by means of pulsed-field gel electrophoresis analyses, strongly indicating that they were infected through the same medical practices, or by transmission of the same contaminant.ConclusionsA small outbreak due to B. cepacia complex was brought about in the NICU in 2010, which appeared to be associated with the same genomovar of B. cepacia complex. The source or the rout of infection was unknown in spite of the repeated epidemiological investigation. It is noteworthy that no outbreak due to B. cepacia complex was noted in the NICU after extensive surveillance intervention.

In vitro activity of ceftazidime+NXL104 against Pseudomonas aeruginosa and other non-fermenters

NXL104 potentiates ceftazidime and ceftaroline against Enterobacteriaceae with extended-spectrum, AmpC, KPC and OXA β-lactamases. We examined whether similar potentiation was obtained against non-fermenters, which are less permeable than Enterobacteriaceae and have more potent efflux. MICs of ceftazidime+NXL104 (with NXL104 at 4 mg/L) and comparators were determined by CLSI agar dilution for: (i) Pseudomonas aeruginosa AmpC mutants and extended-spectrum β-lactamase (ESBL)-producing transconjugants; (ii) clinical P. aeruginosa isolates with AmpC enzymes, ESBLs or up-regulated efflux; (iii) P. aeruginosa and Burkholderia cepacia complex isolates from cystic fibrosis patients; and (iv) Acinetobacter baumannii with OXA carbapenemases, which also compromise ceftazidime. NXL104 reversed AmpC-mediated ceftazidime resistance in P. aeruginosa, reducing MICs for fully derepressed mutants and isolates to ≤ 8 mg/L. NXL104 also reversed ceftazidime resistance caused by the ESBL PER-1, but not that due to OXA ESBLs or VEB-1 enzyme. Efflux-mediated resistance was unaffected. Resistance to ceftazidime in isolates of P. aeruginosa and the B. cepacia complex from patients with cystic fibrosis was variably overcome, generally to greater effect for B. cepacia. NXL104 had little effect on MICs of ceftazidime for A. baumannii isolates with OXA carbapenemases. The potentiation of ceftazidime against many β-lactamase-producing P. aeruginosa and B. cepacia complex strains confirms that NXL104 penetrates these organisms. The utility of the combination against these pathogens will depend on the local prevalence of strains with β-lactamase- versus efflux-mediated resistance. The lack of potentiation against A. baumannii may reflect failure of NXL104 to penetrate these bacteria to inhibit relevant (OXA-23, -40, -51 and -58) carbapenemases.

Unusual Distribution of Burkholderia cepacia Complex Species in Danish Cystic Fibrosis Clinics May Stem from Restricted Transmission between Patients

Forty-four of 48 Burkholderia cepacia complex strains cultured from Danish cystic fibrosis patients were Burkholderia multivorans, a distribution of species that has not been reported before. Although cases of cross infections were demonstrated, no major epidemic clone was found. The species distribution may represent the sporadic acquisition of bacteria from the environment.

Burkholderia cepacia keratitis with endophthalmitis

Keratitis with endophthalmitis of the right eye occurred in a 78-year-female following a complicated cataract surgery. Prompt intravitreal vancomycin and ceftazidime with topical fortified tobramycin and cefazolin treatments were started. The corneal, aqueous and vitreous cultures grew a Burkholderia cepacia complex (Bcc) strain on the fourth day. Restriction fragment length polymorphism analysis of the recA amplicon revealed B. cepacia genomovar I. The organism was found to be susceptible to ceftazidime, ciprofloxacin and ofloxacin. Topical ciprofloxacin was given immediately. At day 10, the pain relieved and the clinical condition of the patient improved with resolution of the purulent discharge, severe circumcorneal congestion and chemosis. The size of the corneal abscess and anterior chamber exudation decreased. The Bcc should be included among the bacterial species that may cause keratitis following intraocular surgeries.

In vitro activity of ceftazidime, ciprofloxacin, meropenem, minocycline, tobramycin and trimethoprim/sulfamethoxazole against planktonic and sessile Burkholderia cepacia complex bacteria

The goal of the present study was to obtain a comprehensive overview of the bacteriostatic and bactericidal effects of six commonly used antibiotics on planktonic as well as on sessile Burkholderia cepacia complex cells. The bacteriostatic and bactericidal activities of ceftazidime, ciprofloxacin, meropenem, minocycline, tobramycin and trimethoprim/sulfamethoxazole were determined against 38 B. cepacia complex strains. MICs and minimal biofilm inhibitory concentrations (MBICs) were determined using a traditional broth microdilution method and a novel resazurin-based viability staining, respectively. The bactericidal effects of the investigated antibiotics (using antibiotic concentrations corresponding to 10 x MIC; except for tobramycin, for which a final concentration of 4 x MIC was tested) on stationary phase planktonic cultures and on 24-h-old biofilms were evaluated using conventional plate count methods. Our results confirm the innate resistance of B. cepacia complex organisms to six first-line antibiotics used to treat infected cystic fibrosis patients. All antibiotics showed similar bacteriostatic activities against exponentially growing B. cepacia complex planktonic cells and freshly adhered sessile cells (4 h). In addition, most of the antibiotics showed similar bactericidal effects on stationary phase planktonic cultures and on young and older biofilms. Despite the general assumption that sessile cells show a decreased susceptibility to antibiotics, our data indicate similar bacteriostatic and bactericidal activity of six selected antibiotics against planktonic and sessile B. cepacia complex bacteria.

A rapid and efficient method for directed screening of lipase-producing Burkholderia cepacia complex strains with organic solvent tolerance from rhizosphere

Lipase from Burkholderia cepacia strain is one of the most versatile biocatalysts and is used widely in many biotechnological application fields including detergent additives, the resolution of racemic compounds, etc. Based on the known whole genomic information of B. cepacia strain, both ampicillin and kanamycin were added to the TB-T medium to screen B. cepacia complex stains from rhizosphere soil samples. The selected colonies from the modified TB-T medium were then qualitatively determined the ability to produce extracellular lipase on the rhodamine B-olive oil agar plates. A total of 35 lipolytic pseudo-B. cepacia complex strains were isolated and the positive rate of lipolytic bacteria was 65%. Among them, 15 pseudo-B. cepacia complex strains showed tolerance to benzene, n-hexane and n-heptane at concentration of 10% (V/V) and were identified by the recA gene sequence. All of the 14 lipolytic bacteria were identified as B. cepacia complex strains except that the recA gene sequence of one lipolytic bacterium, strain ZMB009, was not obtained.