Gary M. Aron

Bacteriophage Ecology in Escherichia coli and Pseudomonas aeruginosa Mixed-Biofilm Communities

ABSTRACT Phage therapy is being reexamined as a strategy for bacterial control in medical and other environments. As microorganisms often live in mixed populations, we examined the effect of Escherichia coli bacteriophage λW60 and Pseudomonas aeruginosa bacteriophage PB-1 infection on the viability of monoculture and mixed-species biofilm and planktonic cultures. In mixed-species biofilm communities, E. coli and P. aeruginosa maintained stable cell populations in the presence of one or both phages. In contrast, E. coli planktonic populations were severely depleted in coculture in the presence of λW60. Both E. coli and P. aeruginosa developed phage resistance in planktonic culture; however, reduced resistance was observed in biofilm communities. Increased phage titers and reduced resistance in biofilms suggest that phage can replicate on susceptible cells in biofilms. Infectious phage could be released from mixed-culture biofilms upon treatment with Tween 20 but not upon treatment with chloroform. Tween 20 and chloroform treatments had no effect on phage associated with planktonic cells, suggesting that planktonic phage were not cell or matrix associated. Transmission electron microscopy showed bacteriophage particles to be enmeshed in the extracellular polymeric substance component of biofilms and that this substance could be removed by Tween 20 treatment. Overall, this study demonstrates how mixed-culture biofilms can maintain a reservoir of viable phage and bacterial populations in the environment.

Effect of Bacteriophage Infection in Combination with Tobramycin on the Emergence of Resistance in Escherichia coli and Pseudomonas aeruginosa Biofilms

Bacteriophage infection and antibiotics used individually to reduce biofilm mass often result in the emergence of significant levels of phage and antibiotic resistant cells. In contrast, combination therapy in Escherichia coli biofilms employing T4 phage and tobramycin resulted in greater than 99% and 39% reduction in antibiotic and phage resistant cells, respectively. In P. aeruginosa biofilms, combination therapy resulted in a 60% and 99% reduction in antibiotic and PB-1 phage resistant cells, respectively. Although the combined treatment resulted in greater reduction of E. coli CFUs compared to the use of antibiotic alone, infection of P. aeruginosa biofilms with PB-1 in the presence of tobramycin was only as effective in the reduction of CFUs as the use of antibiotic alone. The study demonstrated phage infection in combination with tobramycin can significantly reduce the emergence of antibiotic and phage resistant cells in both E. coli and P. aeruginosa biofilms, however, a reduction in biomass was dependent on the phage-host system.

Carbon and clay nanoparticles induce minimal stress responses in gram negative bacteria and eukaryotic fish cells.

We investigated in vitro the potential mutagenic and toxic effects of two clay‐based nanoparticles, Cloisite® Na+ (Cloisite) and halloysite; and multi‐walled carbon nanotubes (MWCNT), commonly used in the polymer composite industry. Using the Ames test, the three nanoparticles did not have a true mutagenic effect, although growth of Salmonella enterica var. Typhimurium (S.typhimurium) was diminished at higher nanoparticle concentrations. We investigated the impact of nanoparticles on Escherichia coli and S. typhimurium including oxyR and rpoS mutants, which are susceptible to oxidative stress. The oxyR mutants were inhibited in the presence of nanoparticles, when grown aerobically with light. Toxicity was not observed in the absence of light or during anaerobic growth. E. coli rpoS mutants exhibited some toxicity when cultured with Cloisite and MWCNT only when grown aerobically with light. There was no effect with other nanoparticles, or with S. typhimurium rpoS mutants. MWCNT exhibited a slight toxic effect against Epithelioma papulosum cyprini (EPC) cells only at the highest concentration tested. There was no discernable toxicity to EPC cells caused by the clay nanoparticles. We conclude that clay‐based nanoparticles and MWCNT do not exert a mutagenic effect and do not have a general toxic effect across all bacterial species or between prokaryotic and eukaryotic cells. Modest toxicity was only observed in eukaryotic EPC cells against MWCNT at the highest concentration tested. Limited species‐specific toxicity to clay based and MWCNT nanoparticles was seen in bacterial strains primarily due to culture conditions and mutations that exacerbate oxidative stress.

Chemical modifications of Pokeweed antiviral protein: effects upon ribosome inactivation, antiviral activity and cytotoxicity

Pokeweed antiviral protein (PAP) is a protein known to inactivate eukaryotic ribosomes by an unknown enzymatic action and inhibit the production of mammalian viruses in tissue culture. This protein was subjected to a variety of chemical modifications to determine their effects upon ribosomal inactivation, antiviral action, and cytotoxicity. It was found that modifications of a number of different amino acid residues had similar effects upon all 3 activities. Also the inactivation of PAP with diethylpyrocarbonate was not due to its reaction with a histidine residue but to a modification of an unidentified amino acid residue.

Phenotype characterization of genetically defined microorganisms and growth of bacteriophage in biofilms.

Phenotypic characterization will be a pivotal aspect of future research in understanding the biofilm mode of growth. We hope that the concepts and techniques presented in this chapter will benefit other investigators in this field. Although initial studies will necessarily involve monocultures, eventually mixed culture work will have to be performed to understand biofilm growth in the natural environment. As the study of biofilm-phage interactions is new, there is considerable fundamental work that needs to be addressed. Here, we anticipate that some phage are better adapted to growth in biofilms, some are adept in growing in mixed culture biofilms, and others are better adapted to infecting planktonic organisms. Whereas biofilms are now widely accepted as a fundamental aspect of microbial growth in nature, the field of phage ecology is quite new and an exciting challenge for the future.

Potential for Largemouth Bass Virus to Associate with and Gain Protection from Bacterial Biofilms

Quantitative PCR (qPCR) was used to investigate whether largemouth bass virus (LMBV) can exist within biofilms. Suspended LMBV was partitioned into either laboratory-grown Pseudomonas fluorescens biofilms or pond-grown, mixed-population biofilms. Biofilm-entrapped LMBV retained infectivity when tested on epithelioma papillosum cyprini tissue culture cells. The LMBV associated with P. fluorescens biofilms were resistant to disinfection by sodium hypochlorite and an iodine-based compound (betadine) but were susceptible to ethanol. Largemouth bass virus was not detected in biofilms or water from ponds that had previously contained LMBV-positive fish, suggesting either that the viral concentrations were below the detection limit of qPCR or that the fish represented the main LMBV reservoir. This study illustrates the potential for LMBV to associate with bacterial biofilms and thereby gain protection from some chemical disinfectants.

Investigation of the Toxicity and Cellular Uptake of Na4[B20H17SH] in EMT6 Cells

The development of boron-containing compounds for application in the boron neutron capture therapy (BNCT) of cancer is not only dependent on the synthesis of appropriate compounds, but also the biological evaluation of tumor uptake and retention, toxicity, and pharmacokinetics. Unilamellar liposomes of a specific size and composition have been shown to deliver polyhedral borane compounds having little or no inherent tumor specificity to the tumor mass. Compounds with suitable reactivity are retained by the tumor in therapeutic amounts and other compounds, which lack suitable reactivity, are rapidly cleared from all tissues.1,2 Based on the proposed mechanisms of retention, the thiol derivative, Na4[B20H17SH], was prepared for investigation.3 This compound possesses two characteristics known to enhance tumor retention: the thiol substituent, analogous to the known Na2B12H11SH (BSH), and the potential to oxidize to a more reactive species, Na2[B20H17SH]. Although the gross distribution of boron was elucidated from the murine biodistribution4 of the encapsulated compound, the cellular toxicity and pharmacokinetics of the encapsulated polyhedral borane was unknown.

Production of infectious particles at the nonpermissive temperature by a temperature-sensitive mutant of bacteriophage SH-133 specific forPseudomonas facilis

The preliminary characterization of a unique temperature-sensitive (ts) mutant of bacteriophage SH-133, designatedts18, is reported. The mutant showed a substantial reduction in the ability to form plaques at the nonpermissive temperature (32°C) when compared with its plaqueforming ability at the permissive temperature (27°C). However, the supernatant fromts18-infected cells grown at 32°C exhibited significant infectivity when assayed at 27°C, which indicates that the reduced titer ofts18 at 32°C is not due to its inability to form phage particles at that temperature. Phage particles produced at 32°C, but not at 27°C, were thermolabile when tested at 32°C. The thermolability of phage yields from cells mixedly infected at 32°C with increasing wild-type/ts18 input ratios was independent of the quantity of wild-type gene product per cell. Thermostable phage particles were yielded byts18-infected cells that received short pulses of permissive temperature during the latter part of the latent period. These data indicate that the defect of the mutant is due to the production of a nonstructural assembly protein that misfunctions when viral maturation proceeds at the nonpermissive temperature.