Phages of Lactobacillus casei/paracasei: response to environmental factors and interaction with collection and commercial strains

Genomic and biological characterization of bacteriophages against Enterobacter cloacae, a high-priority pathogen

Enterobacter cloacae is a clinically significant pathogen due to its multi-resistance to antibiotics, presenting a challenge in the treatment of infections. As concerns over antibiotic resistance escalate, novel therapeutic approaches have been explored. Bacteriophages, characterized by their remarkable specificity and ability to self-replicate within target bacteria, are emerging as a promising alternative therapy. In this study, we isolated and partially characterized nine lytic bacteriophages targeting E. cloacae, with two selected for comprehensive genomic analysis based on their host range and bacteriolytic activity. All identified phages exhibited a narrow host range, demonstrated stability within a temperature range of 30-60 °C, displayed pH tolerance from 3 to 10, and showed an excellent bacteriolytic capacity for up to 18 h. Notably, the fully characterized phage genomes revealed an absence of lysogenic, virulence, or antibiotic-resistance genes, positioning them as promising candidates for therapeutic intervention against E. cloacae-related diseases. Nonetheless, translating this knowledge into practical therapeutic applications mandates a deeper understanding of bacteriophage interactions within complex biological environments.

Isolation, characterization, and application of lytic bacteriophages for controlling Enterobacter cloacae complex (ECC) in pasteurized milk and yogurt

Reducing bacterial pathogen contamination not only improves overall global public health but also diminishes food waste and loss. The use of lytic bacteriophages (phages) that infect and kill bacteria could be a beneficial tool for suppressing bacterial growth during dairy products storage time. Four Enterobacter cloacae (E. cloacae) complex isolates which were previously isolated from contaminated dairy products were used to identify lytic phages in wastewater. Phages specific to multi-drug resistant (MDR) E. cloacae complex 6AS1 were isolated from local sewage. Two novel phages vB_EclM-EP1 and vB_EclM-EP2 were identified as myoviral particles and have double-stranded DNA genome. Their host range and lytic capabilities were detected using spot test and efficiency of plating (EOP) against several bacterial isolates. The phages had a latent period of 30 min, and a large burst size of about 100 and 142 PFU/cell for vB_EclM-EP1 and vB_EclM-EP2, respectively. Both phages were viable at pH ranging 5-9 and stable at 70 °C for 60 min. The individual phages and their cocktail preparations (vB_EclM-EP1 and vB_EclM-EP2) reduced and inhibited the growth of E. cloacae complex 6AS1 during challenge test in milk and yogurt samples. These results indicate that the E. cloacae complex-specific phages (vB_EclM-EP1 and vB_EclM-EP2) have a potential application as microbicidal agents in packaged milk and milk derivatives during storage time. In addition, our environment is a rich sources of lytic phages which have potential use in eliminating multidrug-resistant isolates in food industry as well as in biocontrol.

A novel lytic phage exhibiting a remarkable in vivo therapeutic potential and higher antibiofilm activity against Pseudomonas aeruginosa

BACKGROUND

Pseudomonas aeruginosa is a nosocomial bacterium responsible for variety of infections. Inappropriate use of antibiotics could lead to emergence of multidrug-resistant (MDR) P. aeruginosa strains. Herein, a virulent phage; vB_PaeM_PS3 was isolated and tested for its application as alternative to antibiotics for controlling P. aeruginosa infections.

METHODS

Phage morphology was observed using transmission electron microscopy (TEM). The phage host range and efficiency of plating (EOP) in addition to phage stability were analyzed. One-step growth curve was performed to detect phage growth kinetics. The impact of isolated phage on planktonic cells and biofilms was assessed. The phage genome was sequenced. Finally, the therapeutic potential of vB_PaeM_PS3 was determined in vivo.

RESULTS

Isolated phage has an icosahedral head and a contractile tail and was assigned to the family Myoviridae. The phage vB_PaeM_PS3 displayed a broad host range, strong bacteriolytic ability, and higher environmental stability. Isolated phage showed a short latent period and large burst size. Importantly, the phage vB_PaeM_PS3 effectively eradicated bacterial biofilms. The genome of vB_PaeM_PS3 consists of 93,922 bp of dsDNA with 49.39% G + C content. It contains 171 predicted open reading frames (ORFs) and 14 genes as tRNA. Interestingly, the phage vB_PaeM_PS3 significantly attenuated P. aeruginosa virulence in host where the survival of bacteria-infected mice was markedly enhanced following phage treatment. Moreover, the colonizing capability of P. aeruginosa was markedly impaired in phage-treated mice as compared to untreated infected mice.

CONCLUSION

Based on these findings, isolated phage vB_PaeM_PS3 could be potentially considered for treating of P. aeruginosa infections.

Isolation and characterization of a novel mycobacteriophage Kashi-VT1 infecting Mycobacterium species

Mycobacteriophages are viruses that infect members of genus Mycobacterium. Because of the rise in antibiotic resistance in mycobacterial diseases such as tuberculosis, mycobacteriophages have received renewed attention as alternative therapeutic agents. Mycobacteriophages are highly diverse, and, on the basis of their genome sequences, they are grouped into 30 clusters and 10 singletons. In this article, we have described the isolation and characterization of a novel mycobacteriophage Kashi-VT1 (KVT1) infecting Mycobacterium >smegmatis mc2 155 (M. smegmatis) and Mycobacterium fortuitum isolated from Varanasi, India. KVT1 is a cluster K1 temperate phage that belongs to Siphoviridae family as visualized in transmission electron microscopy. The phage genome is 61,010 base pairs with 66.5% Guanine/Cytosine (GC) content, encoding 101 putative open reading frames. The KVT1 genome encodes an immunity repressor, a tyrosine integrase, and an excise protein, which are the characteristics of temperate phages. It also contains genes encoding holin, lysin A, and lysin B involved in host cell lysis. The one-step growth curve demonstrated that KVT1 has a latency time of 90 min and an average burst size of 101 phage particles per infected cell. It can withstand a temperature of up to 45°C and has a maximum viability between pH 8 and 9. Some mycobacteriophages from cluster K are known to infect the pathogenic Mycobacterium tuberculosis (M. tuberculosis); hence, KVT1 holds potential for the phage therapy against tuberculosis, and it can also be engineered to convert into an exclusively lytic phage.

Characteristics and Whole-Genome Analysis of Limosilactobacillus fermentum Phage LFP02

Limosilactobacillus fermentum is a bacterium widely used in food production, medicine, and industrial fermentation. However, fermentation could fail due to phage contamination. L. fermentum bacteriophage LFP02 can be induced from L. fermentum IMAU 32579 using mitomycin C. To better understand the characteristics of this phage, its physiological and genomic characteristics were evaluated. The results showed that its optimal multiplicity of infection was 0.01, and the burst size was 148.03 ± 2.65 pfu/infective center. Compared to temperature, pH had a more obvious influence on phage viability, although its adsorption capacity was not affected by the divalent cations (Ca²⁺ and Mg²⁺) or chloramphenicol. Its genome size was 43,789 bp and the GC content was 46.06%, including 53 functional proteins. Compared to other L. fermentum phages, phage LFP02 had chromosome deletion, insertion, and inversion, which demonstrated that it was a novel phage. This study could expand the knowledge of the biological characteristics of L. fermentum bacteriophages and provide some theoretical basis for bacteriophage prevention during fermentation.

Characterization and Genome Study of a Newly Isolated Temperate Phage Belonging to a New Genus Targeting Alicyclobacillus acidoterrestris

The spoilage of juices by Alicyclobacillus spp. remains a serious problem in industry and leads to economic losses. Compounds such as guaiacol and halophenols, which are produced by Alicyclobacillus, create undesirable flavors and odors and, thus, decrease the quality of juices. The inactivation of Alicyclobacillus spp. constitutes a challenge because it is resistant to environmental factors, such as high temperatures, and active acidity. However, the use of bacteriophages seems to be a promising approach. In this study, we aimed to isolate and comprehensively characterize a novel bacteriophage targeting Alicyclobacillus spp. The Alicyclobacillus phage strain KKP 3916 was isolated from orchard soil against the Alicyclobacillus acidoterrestris strain KKP 3133. The bacterial host's range and the effect of phage addition at different rates of multiplicity of infections (MOIs) on the host's growth kinetics were determined using a Bioscreen C Pro growth analyzer. The Alicyclobacillus phage strain KKP 3916, retained its activity in a wide range of temperatures (from 4 °C to 30 °C) and active acidity values (pH from 3 to 11). At 70 °C, the activity of the phage decreased by 99.9%. In turn, at 80 °C, no activity against the bacterial host was observed. Thirty minutes of exposure to UV reduced the activity of the phages by almost 99.99%. Based on transmission-electron microscopy (TEM) and whole-genome sequencing (WGS) analyses, the Alicyclobacillus phage strain KKP 3916 was classified as a tailed bacteriophage. The genomic sequencing revealed that the newly isolated phage had linear double-stranded DNA (dsDNA) with sizes of 120 bp and 131 bp and 40.3% G+C content. Of the 204 predicted proteins, 134 were of unknown function, while the remainder were annotated as structural, replication, and lysis proteins. No genes associated with antibiotic resistance were found in the genome of the newly isolated phage. However, several regions, including four associated with integration into the bacterial host genome and excisionase, were identified, which indicates the temperate (lysogenic) life cycle of the bacteriophage. Due to the risk of its potential involvement in horizontal gene transfer, this phage is not an appropriate candidate for further research on its use in food biocontrol. To the best of our knowledge, this is the first article on the isolation and whole-genome analysis of the Alicyclobacillus-specific phage.

Isolation and Characterization of Lytic Pseudomonas aeruginosa Bacteriophages Isolated from Sewage Samples from Tunisia

Bacteriophages could be a useful adjunct to antibiotics for the treatment of multidrug-resistant Pseudomonas aeruginosa infections. In this study, lytic P. aeruginosa myoviruses PsCh, PsIn, Ps25, and Ps12on-D were isolated from Tunisian sewage samples. Phage Ps12on-D displayed an adsorption time of ~10 min, a short latency period (~10 min), and a large burst size (~115 PFU per infected cell) under standard growth conditions. All phages were active at broad temperature (4 °C to 50 °C) and pH (3.0 to 11.0) ranges and were able to lyse a wide variety of P. aeruginosa strains isolated from clinical and environmental samples worldwide. Illumina sequencing revealed double-stranded DNA genomes ranging from 87,887 and 92,710 bp with high sequence identity to Pseudomonas phage PAK_P1. All four phages based on sequence analysis were assigned to the Pakpunavirus genus. The presented characterization and preclinical assessment are part of an effort to establish phage therapy treatment as an alternative strategy for the management of multidrug-resistant P. aeruginosa infections in Tunisia.

Efficacy of diversely isolated lytic phages against multi-drug resistant Enterobacter cloacae isolates in Kenya

Background

Enterobacter cloacae causes nosocomial infections in 15% of patients in low- and middle-income countries with emergence of carbapenem resistance. The utilisation of bacteriophages for therapeutic purposes is crucial for eradicating these resistant bacterial strains.

Objective

This study evaluated the efficacy of lytic phages on bacterial isolates of E. cloacae and determined their stability in various physicochemical conditions.

Methods

Twenty-nine lytic phages were isolated from the waste water of six informal settlements in Nairobi County, Kenya, from July 2019 to December 2020 and cross-reacted with 30 anonymised clinical isolates of E. cloacae. Six phages were then selected for physicochemical property studies. Phages were described as potent upon lysing any bacterial strain in the panel.

Results

Selected phages were stable at 4 °C – 50 °C with a 5.1% decrease in titre in four of six phages and a 1.8% increase in titre in two of six phages at 50 °C. The phages were efficient following two weeks incubation at 4 °C with optimal activity at human body temperature (37 °C) and an optimal pH of 7.5. Phages were active at 0.002 M and 0.015 M concentrations of Ca²⁺ ions. The efficiency of all phages decreased with increased exposure to ultraviolet light. All phages (n = 29) showed cross-reactivity against anonymised clinical isolates of E. cloacae strains (n = 30). The most potent phage lysed 67.0% of bacterial strains; the least potent phage lysed 27.0%.

Conclusion

This study reveals the existence of therapeutic phages in Kenya that are potent enough for treatment of multi-drug resistant E. cloacae.

Microencapsulation of Bacteriophages for the Delivery to and Modulation of the Human Gut Microbiota through Milk and Cereal Products

There is a bidirectional interaction between the gut microbiota and human health status. Disturbance of the microbiota increases the risk of pathogen infections and other diseases. The use of bacteriophages as antibacterial therapy or prophylaxis is intended to counteract intestinal disorders. To deliver bacteriophages unharmed into the gut, they must be protected from acidic conditions in the stomach. Therefore, an encapsulation method based on in situ complexation of alginate (2%), calcium ions (0.5%), and milk proteins (1%) by spray drying was investigated. Powdered capsules with particle sizes of ~10 µm and bacteriophage K5 titers of ~108 plaque forming units (pfu) g−1 were obtained. They protected the bacteriophages from acid (pH 2.5) in the stomach for 2 h and released them within 30 min under intestinal conditions (in vitro). There was no loss of viability during storage over two months (4 °C). Instead of consuming bacteriophage capsules in pure form (i.e., as powder/tablets), they could be inserted into food matrices, as exemplary shown in this study using cereal cookies as a semi-solid food matrix. By consuming bacteriophages in combination with probiotic organisms (e.g., via yoghurt with cereal cookies), probiotics could directly repopulate the niches generated by bacteriophages and, thus, contribute to a healthier life.

Phenotypic characterization and genome analysis of a novel Salmonella Typhimurium phage having unique tail fiber genes

Salmonella enterica serovar Typhimurium is a foodborne pathogen causing occasional outbreaks of enteric infections in humans. Salmonella has one of the largest pools of temperate phages in its genome that possess evolutionary significance for pathogen. In this study, we characterized a novel temperate phage Salmonella phage BIS20 (BIS20) with unique tail fiber genes. It belongs to the subfamily Peduovirinae genus Eganvirus and infects Salmonella Typhimurium strain (SE-BS17; Acc. NO MZ503545) of poultry origin. Phage BIS20 was viable only at biological pH and temperature ranges (pH7 and 37 °C). Despite being temperate BIS20 significantly slowed down the growth of host strain for 24 h as compared to control (P < 0.009). Phage BIS20 features 29,477-base pair (bp) linear DNA genome with 53% GC content and encodes for 37 putative ORFs. These ORFs have mosaic arrangement as indicated by its ORF similarity to various phages and prophages in NCBI. Genome analysis indicates its similarity to Salmonella enterica serovar Senftenberg prophage (SEStP) sequence (Nucleotide similarity 87.7%) and Escherichia virus 186 (~ 82.4% nucleotide similarity). Capsid genes were conserved however those associated with tail fiber formation and assembly were unique to all members of genus Eganvirus. We found strong evidence of recombination hotspot in tail fiber gene. Our study identifies BIS20 as a new species of genus Eganvirus temperate phages as its maximum nucleotide similarity is 82.4% with any phage in NCBI. Our findings may contribute to understanding of origin of new temperate phages.

Genome Analysis and Therapeutic Evaluation of a Novel Lytic Bacteriophage of Salmonella Typhimurium: Suggestive of a New Genus in the Subfamily Vequintavirinae

Salmonella Typhimurium, a foodborne pathogen, is a major concern for food safety. Its MDR serovars of animal origin pose a serious threat to the human population. Phage therapy can be an alternative for the treatment of such MDR Salmonella serovars. In this study, we report on detailed genome analyses of a novel Salmonella phage (Salmonella-Phage-SSBI34) and evaluate its therapeutic potential. The phage was evaluated for latent time, burst size, host range, and bacterial growth reduction in liquid cultures. The phage stability was examined at various pH levels and temperatures. The genome analysis (141.095 Kb) indicated that its nucleotide sequence is novel, as it exhibited only 1-7% DNA coverage. The phage genome features 44% GC content, and 234 putative open reading frames were predicted. The genome was predicted to encode for 28 structural proteins and 40 enzymes related to nucleotide metabolism, DNA modification, and protein synthesis. Further, the genome features 11 tRNA genes for 10 different amino acids, indicating alternate codon usage, and hosts a unique hydrolase for bacterial lysis. This study provides new insights into the subfamily Vequintavirinae, of which SSBI34 may represent a new genus.

The characteristic and potential therapeutic effect of isolated multidrug-resistant Acinetobacter baumannii lytic phage

BACKGROUND

Widespread misuse of antibiotics caused bacterial resistance increasingly become a serious threat. Bacteriophage therapy promises alternative treatment strategies for combatting drug-resistant bacterial infections. In this study, we isolated and characterized a novel, potent lytic bacteriophage against multi-drug resistant (MDR) Acinetobacter baumannii and described the lytic capability and endolysin activity of the phage to evaluate the potential in phage therapy.

METHODS

A novel phage, pIsf-AB02, was isolated from hospital sewage. The morphological analysis, its host range, growth characteristics, stability under various conditions, genomic restriction pattern were systematically investigated. The protein pattern of the phage was analyzed, and the endolysin activity of the phage was determined under the non-denaturing condition on SDS-PAGE. The optimal lytic titer of phage was assessed by co-culture of the phage with clinical MDR A. baumannii isolates. Finally, HeLa cells were used to examine the safety of the phage.

RESULTS

The morphological analysis revealed that the pIsf-AB02 phage displays morphology resembling the Myoviridae family. It can quickly destroy 56.3% (27/48) of clinical MDR A. baumannii isolates. This virulent phage could decrease the bacterial host cells (from 10⁸ CFU/ml to 10³ CFU/ml) in 30 min. The optimum stability of the phage was observed at 37 °C. pH 7 is the most suitable condition to maintain phage stability. The 15 kDa protein encoded by pIsf-AB02 was detected to have endolysin activity. pIsf-AB02 did not show cytotoxicity to HeLa cells, and it can save HeLa cells from A. baumannii infection.

CONCLUSION

In this study, we isolated a novel lytic MDR A. baumannii bacteriophage, pIsf-AB02. This phage showed suitable stability at different temperatures and pHs, and demonstrated potent in vitro endolysin activity. pIsf-AB02 may be a good candidate as a therapeutic agent to control nosocomial infections caused by MDR A. baumannii.

Characterization of a Coliphage AS1 isolated from sewage effluent in Pakistan

The emergence of multi-drug resistant (MDR) bacterial strains, which are posing a global health threat has developed the interest of scientists to use bacteriophages instead of conventional antibiotics therapy. In light of an increased interest in the use of phage as a bacterial control agent, the study aimed to isolate and characterize lytic phages from sewage effluent. During the current study, bacteriophage AS1 was isolated from sewage effluent against E.coli S2. The lytic activity of phageAS1 was limited to E.coli S2 strain showing monovalent behavior. The calculated phage titer was 3.5×109 pfu/ml. PhageAS1 was stable at a wide range of pH and temperature. The maximum stability was recorded at 37ºC and pH 7.0, while showing its normal lytic activity at temperature 60ºC and from pH 5.0 to11.0 respectively. At temperature 70ºC, phage activity was somewhat reduced whereas, further increase in temperature and decrease or increase in pH completely inactivated the phage. From the current study, it was concluded that waste water is a best source for finding bacteriophages against multi-drug resistant bacterial strains and can be used as bacterial control agent.

The Effect of Oxygen Availability on Bacteriophage Infection: A Review

Bacteriophages offer a viable solution to addressing the global issue of bacterial resistance to antimicrobials. Although knowledge of bacteriophages has increased greatly since their discovery in 1915, a significant amount of what is currently known is based on studies conducted in model conditions and aerobic environments. There are a variety of environments in which bacteriophages could be applied to successfully replace or supplement antimicrobials in agriculture, food production, and human medicine where the amount of oxygen is limited. There is a need to use phages in oxygen-limited environments, but few studies have examined the impact oxygen-limited environments have on the ability of phages to kill their hosts. The work that has been done is, however, insightful and will likely stimulate this area that is growing in importance as our need to use phages grows. This review summarizes the studies to date that have reported the characteristics of phages in both oxygen-rich and oxygen-limited environments. We also discuss the importance of considering the ultimate environment a phage will be applied to when designing experiments to isolate and characterize phages for use in phage-based antimicrobial products.

Patterns of virus growth across the diversity of life

Although viruses in their natural habitats add up to less than 10% of the biomass, they contribute more than 90% of the genome sequences [1]. These viral sequences or 'viromes' encode viruses that populate the Earth's oceans [2, 3] and terrestrial environments [4, 5], where their infections impact life across diverse ecological niches and scales [6, 7], including humans [8-10]. Most viruses have yet to be isolated and cultured [11-13], and surprisingly few efforts have explored what analysis of available data might reveal about their nature. Here, we compiled and analyzed seven decades of one-step growth and other data for viruses from six major families, including their infections of archaeal, bacterial and eukaryotic hosts [14-191]. We found that the use of host cell biomass for virus production was highest for archaea at 10%, followed by bacteria at 1% and eukarya at 0.01%, highlighting the degree to which viruses of archaea and bacteria exploit their host cells. For individual host cells, the yield of virus progeny spanned a relatively narrow range (10-1000 infectious particles per cell) compared with the million-fold difference in size between the smallest and largest cells. Furthermore, healthy and infected host cells were remarkably similar in the time they needed to multiply themselves or their virus progeny. Specifically, the doubling time of healthy cells and the delay time for virus release from infected cells were not only correlated (r = 0.71, p < 10-10, n = 101); they also spanned the same range from tens of minutes to about a week. These results have implications for better understanding the growth, spread and persistence of viruses in complex natural habitats that abound with diverse hosts, including humans and their associated microbes.

Isolation and characterization of bacteriophage to control multidrug-resistant Pseudomonas aeruginosa planktonic cells and biofilm

Pseudomonas aeruginosa is Gram-negative bacterium, one of the leading cause of drug-resistant nosocomial infections in developing countries. This bacterium possesses chromosomally encoded efflux pumps, poor permeability of outer-membrane and high tendency for biofilm formation which are tools to confer resistance. Bacteriophages are regarded as feasible treatment option for control of resistant P. aeruginosa. The aim of the current study was isolate and characterized a bacteriophage against P. aeruginosa with MDR and biofilm ability. A bacteriophage MA-1 with moderate host range was isolated from waste water. The phage was considerable heat and pH stable. Electron microscopy revealed that phage MA-1 belongs to Myoviridae family. Its genome was dsDNA (≈50 kb), coding for eighteen different proteins (ranging from 12 to 250 KDa). P. aeruginosa-2949 log growth phase was significantly reduced by phage MA-1 (2.5 × 10³ CFU/ml) as compared to control (without phage). Phage MA-1 also showed significant reductions of 2.0, 2.5 and 3.2 folds in 24, 48, and 74 h old biofilms after 6 h treatment with phage respectively as compared to control. It was concluded from this study that phage MA-1 has capability of killing P. aeruginosa planktonic cells and biofilm, but for complete eradication cocktail will more effective to avoid resistance.

Virulence of Leuconostoc phages: Influence of stress conditions associated to dairy processes on their host-phage interactions

In this work, we assessed the impact of technological cell stress conditions, commonly present in industrial dairy processes, on the host strain-phage interactions in Leuconostoc. Adsorption and burst size of LDG (Leuconostoc pseudomesenteroides) and Ln-9 (Leuconostoc mesenteroides) phages were evaluated under the following conditions: i) MRS broth, 30 °C; ii) MRS broth at pH 5.5, 30 °C (acidic stress); iii) MRS broth added of NaCl at 4% w/v, 30 °C (osmotic stress) and iv) MRS broth, 10 °C (cold stress). Experiences were performed with the host strains growing both in MRS broth (30 °C) and under stress conditions. On the other hand, the effect of diverse levels of NaCl, KCl, saccharose and glucose on the adsorption for LDG phage was evaluated. Acidic and cold conditions did not significantly affect the adsorption rates for any phage. However, adsorption rate of phage LDG was highly reduced under osmotic stress (NaCl), except when the host strain previously grew in presence of the salt. LDG phage adsorption was not modified by addition of saccharides, but it drastically decreased in presence of salts. Acidic conditions did not affect the burst size for LDG phage, but Ln-9 phage diminished this parameter (61 phage particles/infected cell). Latency time showed a lengthening of 10 min for both phages, while the burst time remained unaltered for LDG and it was delayed 10 min for Ln-9. LDG phage did not propagate under osmotic conditions, but Ln-9 phage released phage particles with an important increase of its latent period and burst time. No phage particles were released within 90 min after the adsorption step under cold stress. This is the first report about this subject. Under certain conditions of technological stress (osmotic and cold) associated to dairy processes, phage infections on the two systems studied in this work could be delayed/inhibited.

Characterization and adsorption of a Lactobacillus plantarum virulent phage

Bacteriophage infection of lactic acid bacteria is considered one of the biggest worldwide problems in the food industry. Bacteriophages may cause negative effects on the fermentation of various dairy-based products. A virulent bacteriophage was isolated from an abnormal fermentation liquid of Lactobacillus plantarum IMAU10120. The characterization and influence of temperature, pH, divalent cations, and chloramphenicol on the adsorption ability of this phage were evaluated. The results showed that this phage belonged to the Siphoviridae family. It exhibited a burst time of 135 min and a burst size of approximately 215 counts expressed per milliliter per infective center. No significant effect was shown to influence its viability and adsorption at 10 to 37°C. More than 90% of phages exhibited infectivity from pH 5 to 9. Divalent ions and chloramphenicol did not have a significant influence on the adsorption of this phage. The information obtained in this study will enrich the database of lactobacilli virulent phages and provide a basis of information for the control of phages in the food fermentation industry.

Isolation, characterization and efficacy of phage MJ2 against biofilm forming multi-drug resistant Enterobacter cloacae

Biofilm is involved in a variety of infections, playing a critical role in the chronicity of infections. Enterobacter cloacae is a biofilm-forming and multi-drug-resistant (MDR) nosocomial pathogen leading to significant morbidity and mortality. This study aimed at isolation of a bacteriophage against MDR clinical strain of E. cloacae and its efficacy against bacterial planktonic cells and biofilm. A bacteriophage MJ2 was successfully isolated from wastewater and was characterized. The phage exhibited a wide range of thermal and pH stability and demonstrated considerable adsorption to host bacteria in the presence of CaCl₂ or MgCl₂. Transmission electron microscopy (TEM) showed MJ2 head as approximately 62 and 54 nm width and length, respectively. It had a short non-contractile tail and was characterized as a member of the family Podoviridae [order Caudovirales]. The phage MJ2 was found to possess 11 structural proteins (12-150 kDa) and a double-stranded DNA genome with an approximate size of 40 kb. The log-phase growth of E. cloacae both in biofilm and suspension was significantly reduced by the phage. The E. cloacae biofilm was formed under different conditions to evaluate the efficacy of MJ2 phage. Variable reduction pattern of E. cloacae biofilm was observed while treating it for 4 h with MJ2, i.e., biofilm under static conditions. The renewed media with intervals of 24, 72, and 120 h showed biomass decline of 2.8-, 3-, and 3.5-log, respectively. Whereas, the bacterial biofilm formed with dynamic conditions with refreshing media after 24, 72, and 120 h demonstrated decline in growth at 2.5-, 2.6-, and 3.3-log, respectively. It was, therefore, concluded that phage MJ2 possessed considerable inhibitory effects on MDR E. cloacae both in planktonic and biofilm forms.

Characterization of Bacteriophages Infecting Clinical Isolates of Clostridium difficile

Clostridium difficile is recognized as a problematic pathogen, causing severe enteric diseases including antibiotic-associated diarrhea and pseudomembranous colitis. The emergence of antibiotic resistant C. difficile has driven a search for alternative anti-infection modalities. A promising strategy for controlling bacterial infection includes the use of bacteriophages and their gene products. Currently, knowledge of phages active against C. difficile is still relatively limited by the fact that the isolation of phages for this organism is a technically demanding method since bacterial host themselves are difficult to culture. To isolate and characterize phages specific to C. difficile, a genotoxic agent, mitomycin C, was used to induce temperate phages from 12 clinical isolates of C. difficile. Five temperate phages consisting of ΦHR24, ΦHN10, ΦHN16-1, ΦHN16-2, and ΦHN50 were successfully induced and isolated. Spotting assays were performed against a panel of 92 C. difficile isolates to screen for susceptible bacterial hosts. The results revealed that all the C. difficile phages obtained in this work displayed a relatively narrow host range of 0-6.5% of the tested isolates. Electron microscopic characterization revealed that all isolated phages contained an icosahedral head connected to a long contractile tail, suggesting that they belonged to the Myoviridae family. Restriction enzyme analysis indicated that these phages possess unique double-stranded DNA genome. Further electron microscopic characterization revealed that the ΦHN10 absorbed to the bacterial surface via attachment to cell wall, potentially interacting with S-layer protein. Bacteriophages isolated from this study could lead to development of novel therapeutic agents and detection strategies for C. difficile.

Potential use of soilborne lytic Podoviridae phage as a biocontrol agent against Ralstonia solanacearum

A new podovirus RsPod1EGY Ralstonia phage (GenBank accession no MG711516) with a specific action against R. solanacearum phylotype IIa, sequevar I (race 3, biovar 2) was isolated from Egyptian soil. The potential efficacy of the isolated phage to be used as biocontrol agent was evaluated in vitro and under greenhouse conditions. The podovirus phage produced a plaque size of 3.0-4.0 mm in diameter and completed its infection cycle in 180 min after infection with a burst size of ∼27 virions per infected cell. On the basis of restriction endonuclease analysis, the genome size of the phage was about 41 kb of double-stranded DNA. In vitro studies showed that RsPod1EGY is stable at higher temperatures (up to 60 °C), and at a wide pH range (5-9). SDS-PAGE analysis indicated the major structural protein to be approximately 32 kDa. Bacteriolytic activity of RsPod1EGY against R. solanacearum was detected at different multiplicity of infection (MOI). RsPod1EGY proved to be effective in reduction and prevention of formation of surface polysaccharides of R. solanacearum, during the exponential growth phase of the latter. Interestingly, RsPod1EGY was effective in suppression of R. solanacearum under greenhouse conditions. All Phage-treated tomato plants showed no wilt symptoms or any latent infection during the experimental period, whereas all untreated plants have wilted by 10 days post-infection. The lytic stability of RsPod1EGY phage at higher temperature as well as its effective suppression of wilting symptoms under greenhouse conditions would contribute to biocontrol the bacterial wilt disease in Egypt under field conditions.

Isolation and Characterization of a Phage to Control Vancomycin Resistant Enterococcus Faecium

Enterococcus faecium, is an important nosocomial pathogen with increased incidence of multidrug resistance (MDR) - specifically Vancomycin resistance. E. faecium constitutes the normal microbiota of the human intestine as well as exists in the hospitals and sewage, thus making the microorganism difficult to eliminate. Phage therapy has gained attention for controlling bacterial MDR infections and contaminations. We have successfully isolated from waste water and characterized a lytic bacteriophage STH1 capable of targeting Vancomycin resistant Enterococcus faecium (VREF) with high specificity. The phage was isolated from sewage water of a hospital at district Dera Ismail Khan, Pakistan. Initial characterization showed that magnesium and calcium ions significantly increased phage adsorption to the host. One step growth experiment showed a latent period of 18 min with burst size of 334 virions per cell. Optimal temperature and pH of the phage was 37°C and 7.0, respectively. Phage application to host strain grown in milk and water (treated and untreated) showed that the phage efficiently controlled bacterial growth. The study suggests that the phage STH1 can serve as potential control agent for E. faecium infections in medical facilities and in other environmental contaminations.

Isolation and characterization of a bacteriophage and its utilization against multi-drug resistant Pseudomonas aeruginosa-2995

AIMS

To identify, isolate, and characterize a lytic bacteriophage against the multiple-drug resistant clinical strain of Pseudomonas aeruginosa-2995 and to determine the phage efficacy against the bacterial planktonic cells and the biofilm.

MAIN METHODS

Wastewater was used to isolate a bacteriophage. The phage was characterized with Transmission electron microscopy (TEM). Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS PAGE) was used to identify the expressed proteins. Bacteria were cultured in both suspension and biofilm to check and compare their susceptibility to phage lytic action. The activity of the phage (determined as AZ1) was determined against P. aeruginosa-2995 in both planktonic cells and the biofilm.

KEY FINDINGS

A bacteriophage, designated as AZ1, was isolated from waste water showing a narrow host range. AZ1 was characterized by TEM and could be identified as an isolate in the family Siphoviridae [order Caudovirals]. Seventeen structural proteins ranging from about 12 to 110kDa were found through SDS-PAGE analysis. Its genome was confirmed as dsDNA with a length of approx. 50kb. The log-phase growth of P. aeruginosa-2995 was significantly reduced after treatment with AZ1 (4.50×10⁸ to 2.1×10³CFU/ml) as compared to control. Furthermore, phage AZ1 significantly reduced 48h old biofilm biomass about 3-fold as compared to control.

SIGNIFICANCE

Pseudomonas aeruginosa is a ubiquitous free-living opportunistic human pathogen characterized by high antibiotic tolerance and tendency for biofilm formation. The phage, identified in this study, AZ1, showed promising activity in the destruction of both planktonic cells and biofilm of P. aeruginosa-2995. However, complete eradication may require a combination of phages.

Effectiveness of a Lytic Phage SRG1 against Vancomycin-Resistant Enterococcus faecalis in Compost and Soil

Nosocomial infections caused by vancomycin-resistant Enterococcus have become a major problem. Bacteriophage therapy is proposed as a potential alternative therapy. Bacteriophages are viruses that infect bacteria and are ubiquitous in nature. Lytic bacteriophage was isolated from sewage water that infects VREF, the causative agent of endocarditis, bacteraemia, and urinary tract infections (UTIs). The phage produced clear plaques with unique clear morphology and well-defined boundaries. TEM results of phage revealed it to be 108 ± 0.2 nm long and 90 ± 0.5 nm wide. The characterization of bacteriophage revealed that infection process of phage was calcium and magnesium dependent and phage titers were highest under optimum conditions for VREF, with an optimal temperature range of 37–50°C. The maximum growth was observed at 37°C, hence having 100% viability. The latent period for phage was small with a burst size of 512 viral particles per bacterial cell. The phage was tested against various clinical strains and results proved it to be host specific. It can be used as a potential therapeutic agent for VREF infections. The phage efficiently eradicated VREF inoculated in cattle compost, poultry compost, and a soil sample which makes it a potential agent for clearing compost and soil sample.

Changes in Environmental Conditions Modify Infection Kinetics of Dairy Phages

Latent period, burst time, and burst size, kinetic parameters of phage infection characteristic of a given phage/host system, have been measured for a wide variety of lactic acid bacteria. However, most studies to date were conducted in optimal growth conditions of host bacteria and did not consider variations due to changes in external factors. In this work, we determined the effect of temperature, pH, and starvation on kinetic parameters of phages infecting Lactobacillus paracasei, Lactobacillus plantarum, and Leuconostoc mesenteroides. For kinetics assessment, one-step growth curves were carried out in MRS broth at optimal conditions (control), lower temperature, pH 6.0 and 5.0 (MRS₆ and MRS₅, respectively), or in medium lacking carbon (MRS_N) or nitrogen (MRS_C) sources. Phage infection was progressively impaired as environmental conditions were modified from optimal. At lower temperature or pH, infection was delayed, as perceived by longer latent and burst times. Burst size, however, was lower, equal or higher than for controls, but this effect was highly dependent on the particular phage-host system studied. Phage infection was strongly inhibited in MRS_C, but only mildly impaired in MRS_N. Nevertheless, growth of all the bacterial strains tested was severely compromised by starvation, without significant differences between MRS_C and MRS_N, indicating that nitrogen compounds are specifically required for a successful phage infection, beyond their influence on bacterial growth.

Isolation and Genome Sequencing of a Novel Pseudoalteromonas Phage PH1

The family Pseudoalteromonas is highly adaptable to dissimilar ecological habitats and plays an important ecological role in the marine environment. In this study, a new Pseudoalteromonas phage PH1 was isolated from the Yellow Sea. To better understand the bacteriophage, its biological properties, including morphology, host range, growth phenotype, thermal and pH stability, and nucleic acid composition, were investigated in detail. The result showed that the phage PH1 is a Podoviridae-phage with an icosahedral head (60 nm of diameter) and a short tail (26 nm in length). The phage PH1 genome consists of 42,685 bp length double-stranded DNA with a G+C content of 42.24% and is predicted to have 55 open reading frames (ORFs) with an average length of 740 bp nucleotides each. The phage PH1 genome adds a new Podoviridae-phage genome to marine bacteriophage dataset, which will provide useful basic information for further molecular research on interaction mechanisms between bacteriophages and their hosts.

Characterization and adsorption of Lactobacillus virulent phage P1

Bacteriophage infection of lactic acid bacteria is considered an important problem worldwide in the food fermentation industry, as it may produce low quality or unsafe foods, cause fermentation failure, and result in economic losses. To increase current knowledge on the properties of Lactobacillus virulent phages, we evaluated the effect of divalent cations, temperature, pH, and chloramphenicol on the adsorption ability of Lactobacillus virulent phage P1. Phage P1 was isolated from the abnormal fermentation liquid of Lactobacillus plantarum IMAU10120. The results showed that this phage belonged to the Siphoviridae family. The latent period of this phage was 45min, and the burst time was 90min. Burst size was 132.88±2.37 phage counts expressed per milliliter per infective center. This phage showed good tolerance at different temperatures, but incubation at 50°C only affected its adsorption. Adsorption rate reached a maximum value between 30 and 42°C. A high adsorption value of phage infectivity was obtained from pH 6 to 8. Moreover, calcium ions promoted and increased the adsorption capacity of phage P1, but magnesium ions had negative effects. Chloramphenicol had no effect on phage adsorption. This study increased current knowledge on the characterization and biological aspects of Lactobacillus virulent phages, and may provide some basic information that can be used to design successful antiphage strategies in the food industry.

A virulent phage JHP against Pseudomonas aeruginosa showed infectivity against multiple genera

The resistance to antibiotics in clinically important bacteria is one of the major global health concerns. Phage therapy could be one reliable alternative therapeutic strategy to combat these superbugs. In this study, we assessed host range of a novel bacteriophage, JHP, and characterized for its potential use in phage therapy. The bacteriophage demonstrated infectivity over a broad range of genera including multidrug resistant clinical isolates of Pseudomonas aeruginosa, members of family Enterobacteracae, and other important human pathogens. The antibacterial activity was highest at pH 7, and at temperature of 37 °C. The phage lytic activity gradually decreased till 60 °C and showed no activity when temperature was further raised. The bacteriophage could safely be stored at 4 °C or -20 °C. The latent period of the bacteriophage was 25 min and showed a burst size of 433 virions per cell. The size of JHP genome was approximately 30 kb. Family, Siphoviridae was assigned to JHP based on its icosahedral head with non-contractile tail. The diameter of JHP head and tail length was found 115 and 152 nm, respectively. To sum up, the broad spectrum Siphoviridae phage JHP is an ingenious candidate for phage therapy.

Isolation and Characterization of a Novel Virulent Phage of Lactobacillus casei ATCC 393

A new virulent phage (Lcb) of Lactobacillus casei ATCC 393 was isolated from Chinese sauerkraut. It was specific to L. casei ATCC 393. Electron micrograph revealed that it had an icosahedral head (60.2 ± 0.8 nm in diameter) and a long tail (251 ± 2.6 nm). It belonged to the Siphoviridae family. The genome of phage Lcb was estimated to be approximately 40 kb and did not contain cohesive ends. One-step growth kinetics of its lytic development revealed latent and burst periods of 75 and 45 min, respectively, with a burst size of 16 PFU per infected cell. The phage was able to survive in a pH range between 4 and 11. However, a treatment of 70 °C for 30 min and 75% ethanol or isopropanol for 20 min was observed to inactivate phage Lcb thoroughly. The presence of both Ca(2+) and Mg(2+) showed a little influence on phage adsorption, but they were indispensable to gain complete lysis and improve plaque formation. The adsorption kinetics were similar on viable or nonviable cells, and high adsorption rates maintained between 10 and 37 °C. The highest adsorption rate was at 30 °C. This study increased the knowledge on phages of L. casei. The characterization of phage Lcb is helpful to establish a basis for adopting effective strategies to control phage attack in industry.

Isolation and Characterization of a Myoviridae MJ1 Bacteriophage Against Multi-Drug Resistant Escherichia coli 3

Background:

Antibiotic resistance in Escherichia coli, a member of the Enterobacteriaceae, is of particular concern because it is the most common (Gram-negative) pathogen causing nosocomial and community infections. Researchers are now considering the use of phages for the control of various antibiotic-resistant bacterial infections.

Objectives:

The purpose of this study was to isolate and characterize a novel pathogenic/lytic phage that targets multi-drug resistant (MDR) E. coli 3, and to investigate its effectiveness at lysing this bacterium.

Materials and Methods:

A clinical strain of E. coli 3 was identified based on its 16S rRNA sequencing and its antibiotic resistance profile was determined by the disc diffusion method. A bacteriophage was isolated from wastewater and its various characteristics, such as host range, heat tolerance, pH stability, one step growth, total protein content, and genome size, were determined. The antibacterial property of the phage was determined against log-phase bacterial planktonic cells at 37°C.

Results:

The bacteriophage, designated MJ1, was isolated by testing against a clinical MDR E. coli 3 strain. The MJ1 phage showed a wide range of heat and pH stability. The phage morphology, determined by transmission electron microscopy, revealed a structure comprised of a head (108 ± 0.2 nm long by 128 ± 0.5 nm wide) and a contractile tail (123 ± 0.5 nm long by 15 - 26 nm wide). These features placed the MJ1 phage in the family Myoviridae and the order Caudovirales. Eleven structural proteins (17 to 200 kDa) for this phage were detected by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). A double stranded DNA, approximately 32 kb, in size was detected for this phage on agarose gels. The phage efficacy against E. coli 3 planktonic cells was also investigated. The MJ1 phage demonstrated a very good capability to reduce the numbers of E. coli 3 planktonic cells, as determined by a change in the bacterial growth (an optical density decrease at 600 nm from 0.40 to 0.12).

Conclusions:

MJ1 phage has much potential for use in phage therapy and other applications.

Characterization of Siphoviridae phage Z and studying its efficacy against multidrug-resistant Klebsiella pneumoniae planktonic cells and biofilm

Biofilm has many serious consequences for public health and is a major virulence factor contributing to the chronicity of infections. The aim of the current study was to isolate and characterize a bacteriophage that inhibits multidrug-resistant Klebsiella pneumonia (M) in planktonic form as well as biofilm. This phage, designated bacteriophage Z, was isolated from wastewater. Its adsorption rate to its host bacterium was significantly enhanced by MgCl2 and CaCl2. It has a wide range of pH and heat stability. From its one-step growth, latent time and burst size were determined to be 24 min and about 320 virions per cell, respectively. As analysed by transmission electron microscopy, phage Z had an icosahedral head of width 76±10 nm, length 92±14 nm and icosahedron side 38 nm, and a non-contractile tail 200±15 nm long and 14-29 nm wide. It belongs to the family Siphoviridae in the order Caudovirales. Six structural proteins ranging from 18 to 65 kDa in size were revealed by SDS-PAGE. The genome was found to comprise double-stranded DNA with an approximate size of 36 kb. Bacteria were grown in suspension and as biofilms to compare the susceptibility of both phenotypes to the phage lytic action. Phage Z was effective in reducing biofilm biomass after 24 and 48 h, showing more than twofold and threefold reduction, respectively. Biofilm cells and stationary-phase planktonic bacteria were killed at a lower rate than exponential-phase planktonic bacteria.

Characterization of Two Temperate Lactobacillus paracasei Bacteriophages: Morphology, Kinetics and Adsorption

Background/Aims: Adsorption and kinetic parameters, latent period, burst size and burst time, are characteristics of phage/host systems and can be affected by several environmental factors. As only few studies have focused on temperate dairy phages, we characterized these parameters on temperate Lactobacillus paracasei phages Φ iLp84 and Φ iLp1308, infective for probiotic strains. Methods: Phages were characterized by transmission electron microscopy and genomic DNA restriction. Adsorption under different environmental conditions, phage kinetics and efficiency of plating (EOP) were determined using the double-layer titration method. Results: Phages Φ iLp84 and Φ iLp1308 belong to the Siphoviridae family and have genome sizes of 38 and 34 kbp, respectively. Adsorption was affected by calcium concentration, pH, temperature and host viability, and reached a limit at very high multiplicity of infection. Latency, burst time and burst size were of 85 min, 131 min and 46 for Φ iLp84, and 51 min, 92 min and 28 for Φ iLp1308, respectively, at 37°C. A clear influence of temperature on phage kinetics was observed. Regarding EOP, Φ iLp84 produced plaques on only 1 out of 8 strains tested. Conclusion: Noticeable differences in adsorption, kinetics and EOP were found for two morphologically identical temperate L. paracasei phages of similar origin.

Characterization of new Myoviridae bacteriophage WZ1 against multi-drug resistant (MDR) Shigella dysenteriae

Shigella dysenteriae is a normal inhabitant of the human gastrointestinal tract, but sometimes it causes severe infection known as shigellosis (bacillary dysentery). Bacteriophages are considered very safe and effective agents for controlling bacterial infections and contaminations. In this study, we describe the isolation and characterization of bacteriophage WZ1, isolated from waste water which inhibits the growth of S. dysenteriae. Phage WZ1 showed maximum stability at 37 °C and was stable up to 65 °C but was totally inactive at 70 °C. The pH stability increased from low to high and was totally inactive at pH 3 while maximum stability was observed at optimal pH 7. Phage WZ1 adsorption rate to the host bacterium was significantly enhanced by the addition of CaCl2 . It has a latent time and burst time of 24 min and about 430 virions/cell, respectively. Transmission electron microscopy of phage WZ1 revealed a head width of 10 ± 0.5 nm and length of 10 ± 0.2 nm with a contractile tail of 128 ± 25 nm long and 21 ± 0.5 nm wide and belongs to family Myoviridae of order Caudovirales. Twelve structural proteins ranging from 22 to 150 kDa were detected by Sodium Dodecyl Sulfate Polyacrylamide Gel Electrophoresis (SDS-PAGE). The genome was found to be double stranded DNA with an approximate size of 38 kb. It has a very good reduction potential for S. dysenteriae by lowering abruptly the optical density of the planktonic S. dysenteriae culture. Phage WZ1 is a very promising candidate for phage therapy and other applications such as phage typing.

Transposon mutagenesis of probiotic Lactobacillus casei identifies asnH, an asparagine synthetase gene involved in its immune-activating capacity

Lactobacillus casei ATCC 27139 enhances host innate immunity, and the J1 phage-resistant mutants of this strain lose the activity. A transposon insertion mutant library of L. casei ATCC 27139 was constructed, and nine J1 phage-resistant mutants out of them were obtained. Cloning and sequencing analyses identified three independent genes that were disrupted by insertion of the transposon element: asnH, encoding asparagine synthetase, and dnaJ and dnaK, encoding the molecular chaperones DnaJ and DnaK, respectively. Using an in vivo mouse model of Listeria infection, only asnH mutant showed deficiency in their ability to enhance host innate immunity, and complementation of the mutation by introduction of the wild-type asnH in the mutant strain recovered the immuno-augmenting activity. AsnH protein exhibited asparagine synthetase activity when the lysozyme-treated cell wall extracts of L. casei ATCC 27139 was added as substrate. The asnH mutants lost the thick and rigid peptidoglycan features that are characteristic to the wild-type cells, indicating that AsnH of L. casei is involved in peptidoglycan biosynthesis. These results indicate that asnH is required for the construction of the peptidoglycan composition involved in the immune-activating capacity of L. casei ATCC 27139.

Complete Genome Sequences of Lactobacillus Phages J-1 and PL-1

Lactobacillus phages J-1 and PL-1 were isolated during the 1960s from abnormal fermentations of Yakult. The genomes are almost identical, but PL-1 has a deletion in the genetic switch region and also differs in a gene coding for a putative tail protein.

Characterization of a virulent bacteriophage LK1 specific for Citrobacter freundii isolated from sewage water

Citrobacter freundii is a worldwide emerging nosocomial pathogen with escalating incidence of multidrug resistance. Citrobacter freundii exists in natural environment, especially in health care settings and is difficult to eradicate. Phage therapy is considered as an alternative way of controlling bacterial infections and contaminations. In this study, we have described isolation and characterization of a virulent bacteriophage LK1 capable of specifically infecting Citrobacter freundii. A virulent bacteriophage LK1, specific for Citrobacter freundii was isolated from sewage water sample. TEM showed that phage Lk1 has an icosahedral head 70 nm in diameter and short tail of 17 nm, and can be classified as a member of the Podoviridae family. Restriction analysis indicated that phage LK1 was a dsDNA virus with an approximate genome size of 20-23 kb. Proteomic pattern generated by SDS PAGE using purified LK1 phage particles, revealed three major and six minor protein bands with molecular weight ranging from 25 to 80 kDa. Adsorption rate of LK1 relative to the host bacterium was also determined which showed significant improvement in adsorption with the addition of CaCl2 . In a single step growth experiment, LK1 exhibited a latent period of 24 min and burst size of 801 particle/cell. Moreover, pH and thermal stability of phage LK1 demonstrated a pH range of 5.0-6.0 and phage viability decreased to 0% at 65 °C. When LK1 was used to infect six other clinically isolated pathogenic strains, it showed relatively narrow host range. LK1 was capable of eliciting efficient lysis of Citrobacter freundii, revealing its potential as a non-toxic sanitizer for controlling Citrobacter freundii infection and contamination in both hospital and other public environments.

Characterization of two virulent phages of Lactobacillus plantarum

We characterized two Lactobacillus plantarum virulent siphophages, ATCC 8014-B1 (B1) and ATCC 8014-B2 (B2), previously isolated from corn silage and anaerobic sewage sludge, respectively. Phage B2 infected two of the eight L. plantarum strains tested, while phage B1 infected three. Phage adsorption was highly variable depending on the strain used. Phage defense systems were found in at least two L. plantarum strains, LMG9211 and WCSF1. The linear double-stranded DNA genome of the pac-type phage B1 had 38,002 bp, a G+C content of 47.6%, and 60 open reading frames (ORFs). Surprisingly, the phage B1 genome has 97% identity with that of Pediococcus damnosus phage clP1 and 77% identity with that of L. plantarum phage JL-1; these phages were isolated from sewage and cucumber fermentation, respectively. The double-stranded DNA (dsDNA) genome of the cos-type phage B2 had 80,618 bp, a G+C content of 36.9%, and 127 ORFs with similarities to those of Bacillus and Lactobacillus strains as well as phages. Some phage B2 genes were similar to ORFs from L. plantarum phage LP65 of the Myoviridae family. Additionally, 6 tRNAs were found in the phage B2 genome. Protein analysis revealed 13 (phage B1) and 9 (phage B2) structural proteins. To our knowledge, this is the first report describing such high identity between phage genomes infecting different genera of lactic acid bacteria.

A novel bacteriophage KSL-1 of 2-Keto-gluconic acid producer Pseudomonas fluorescens K1005: isolation, characterization and its remedial action

Background

Bacteriophages have the destructive damage on the industrial bioprocess. 2-Keto-gluconic acid (2KGA) producing bacteria had also been attacked and lysed by bacteriophages which lowered the glucose consumption and 2KGA yield and even stopped the fermentation process. In this study, we presented the characteristics of a novel virulent bacteriophage specifically infecting Pseudomonas fluorescens K1005 and proposed an efficient remedial action for this phage infection to reduce the production loss.

Results

The phage KSL-1 of Pseudomonas fluorescens K1005 was isolated from abnormal 2KGA fermentation broth. It belonged to the Siphoviridae family with a hexagonal head diameter of about 99 nm and a non-contractile tail of about 103 nm × 39 nm. The genome size of phage KSL-1 was estimated to be approximately 53 kbp. Its optimal MOI to infect P. fluorescens K1005 was about 0.001. One-step growth curve gave its latent and burst periods of 90 min and 75 min with a burst size of 52 phage particles per infected cell. This phage was stable with a pH range of 7.0–10.0, and sensitive to thermal treatment. Finally, a simple remedial action was proposed by feeding fresh seed culture. Compared with the infected 2KGA fermentation, the remedial experiments restored 2KGA fermentation performance by increasing the produced 2KGA concentration to 159.89 g/L and shortening the total fermentation time of 80 h with the productivity and yield of 2.0 g/L.h and 0.89 g/g. The obtained data proved that this method was effective to combat the phage infections problems during the 2KGA fermentation.

Conclusion

The phage KSL-1 was a novel bacteriophage specifically infecting Pseudomonas fluorescens K1005. The remedial action of feeding fresh seed culture to the infected broth was an easily-operating and effective method to maintain a high 2KGA yield and avoid the draft of infected broth.

Isolation and partial characterization of ΦSP-1, a Salmonella specific lytic phage from intestinal content of broiler chicken

Salmonella enterica subsp. enterica serovar Enteritidis is a major causative agent of gastroenteritis with contaminated eggs and chicken meat being the major source of infection. Phages are seriously being considered as a safe and cheaper alternative to antibiotics. The intestinal content of chicken was used as source for isolating phages. Phage designated as ΦSP-1 was selected for the study. Transmission electron microscopy (TEM) of phage ΦSP-1 revealed that it belonged to family Podoviridae. The optimal multiplicity of infection (MOI) was 5 phages/cell. Latent and rise period were calculated to be 30 and 55 minutes respectively, while burst size was 44 phages/bacterial cell. The genome size of ΦSP-1 was estimated to be 86 kb from pulsed-field gel electrophoresis analysis (PFGE). The effect of different physical and chemical parameters like temperature, pH, salinity and CaCl₂ were analyzed to optimize the conditions for large scale production of phages and to check the viability of ΦSP-1 under different physiochemical conditions. A temperature of 40 °C, pH 8 and 0.25 M NaCl were found to be optimum for phage adsorption and it was able to survive up to a temperature of 50 °C for 3 min. Capability to survive under hostile environmental conditions, absence of virulence genes in genome and genus specificity suggest suitability of ΦSP-1 to be used as a biocontrol agent.

Isolation and partial characterization of a virulent bacteriophage IHQ1 specific for Aeromonas punctata from stream water

Aeromonas punctata is the causative agent of septicemia, diarrhea, wound infections, meningitis, peritonitis, and infections of the joints, bones and eyes. Bacteriophages are often considered alternative agents for controlling bacterial infection and contamination. In this study, we described the isolation and preliminary characterization of bacteriophage IHQ1 (family Myoviridae) active against the Gram-negative bacterial strain A. punctata. This virulent bacteriophage was isolated from stream water sample. Genome analysis indicated that phage IHQ1 was a double-stranded DNA virus with an approximate genome size of 25-28 kb. The initial characterization of this newly isolated phage showed that it has a narrow host range and infects only A. punctata as it failed to infect seven other clinically isolated pathogenic strains, i.e., methicillin-resistant Staphylococcus aureus 6403, MRSA 17644, Acinetobacter 33408, Acinetobacter 1172, Pseudomonas aeruginosa 22250, P. aeruginosa 11219, and Escherichia coli. Proteomic pattern of phage IHQ1, generated by SDS-PAGE using purified phage particles, showed three major and three minor protein bands with molecular weights ranging from 25 to 70 kDa. The adsorption rate of phage IHQ1 to the host bacterium was also determined, which was significantly enhanced by the addition of 10 mM CaCl(2). From the single-step growth experiment, it was inferred that the latent time period of phage IHQ1 was 24 min and a burst size of 626 phages per cell. Moreover, the pH and thermal stability of phage IHQ1 were also investigated. The maximum stability of the phage was observed at optimal pH 7.0, and it was totally unstable at extreme acidic pH 3; however, it was comparatively stable at alkaline pH 11.0. At 37°C the phage showed maximum number of plaques, and the viability was almost 100%. The existence of Aeromonas bacteriophage is very promising for the eradication of this opportunistic pathogen and also for future applications such as the design of new detection and phage typing (diagnosis) methods. The specificity of the bacteriophage for A. punctata makes it an attractive candidate for phage therapy of A. punctata infections.

Efficacy of bacteriophage therapy in experimental sepsis and meningitis caused by a clone O25b:H4-ST131 Escherichia coli strain producing CTX-M-15

We evaluated phage therapy in experimental infections due to S242, a fatal neonatal meningitis Escherichia coli strain belonging to the worldwide-distributed O25b:H4-ST131 clone that produces extended-spectrum beta-lactamase CTX-M-15. A lytic phage, EC200(PP), active against S242, was isolated from environmental water. After determining in vitro and ex vivo stabilities and pharmacokinetic properties of EC200(PP) in rat pups, we assessed the therapeutic efficacy of a single dose of 10(8) PFU using models of sepsis and meningitis in which fatality was 100%. EC200(PP) was partially neutralized by human serum. In contrast to the high concentration of phage in the spleen and the kidney, low titers in urine and the central nervous system were observed. Nevertheless, in the sepsis model, EC200(PP) administered 7 h or 24 h postinfection resulted in 100% and 50% pup survival, respectively. In the meningitis model, EC200(PP) administered 1 h or 7 h postinfection rescued 100% of the animals. The most delayed treatments were associated with the selection of phage-resistant S242 mutants. However, a representative mutant was highly sensitive to killing serum activity and avirulent in an animal model. EC200(PP) is a potential therapeutic agent for sepsis and meningitis caused by the widespread E. coli O25:H4-ST131 multidrug-resistant clone.