ArcAB system promotes biofilm formation through direct repression of hapR transcription in Vibrio cholerae

Vibrio cholerae, the causative agent of cholera, can efficiently adapt its metabolic processes, including biofilm formation, in response to varying respiratory conditions- such as aerobic, microaerobic, and anaerobic- through the ArcAB system. In this study, we elucidate the activation mechanism of V. cholerae ArcB and ArcA and identify ArcB residues H292, D577, and H722, along with ArcA residue D54 as key phosphorylation sites. Furthermore, we demonstrate that the ArcAB system plays a crucial role in regulating biofilm formation under both aerobic and anaerobic conditions. Our findings reveal that the positive regulation of biofilm formation by the ArcAB systems involves the high cell density (HCD) quorum sensing (QS) regulator HapR. Specifically, phosphorylated ArcA represses hapR transcription, thereby promoting biofilm formation under anaerobic condition. This study also highlights an epistatic relationship between ArcA and HapR in biofilm regulation. Overall, our results underscore the critical role of the ArcAB system in the biofilm formation of pathogenic V. cholerae under oxygen-limiting conditions.

Comprehensive genomic and evolutionary analysis of biofilm matrix clusters and proteins in the Vibrio genus

Vibrio cholerae pathogens cause cholera, an acute diarrheal disease resulting in significant morbidity and mortality worldwide. Biofilms in vibrios enhance their survival in natural ecosystems and facilitate transmission during cholera outbreaks. Critical components of the biofilm matrix include the Vibrio polysaccharides produced by the vps-1 and vps-2 gene clusters and the biofilm matrix proteins encoded in the rbm gene cluster, together comprising the biofilm matrix cluster. However, the biofilm matrix clusters and their evolutionary patterns in other Vibrio species remain underexplored. In this study, we systematically investigated the distribution, diversity, and evolution of biofilm matrix clusters and proteins across the Vibrio genus. Our findings reveal that these gene clusters are sporadically distributed throughout the genus, even appearing in species phylogenetically distant from Vibrio cholerae. Evolutionary analysis of the major biofilm matrix proteins RbmC and Bap1 shows that they are structurally and sequentially related, having undergone structural domain and modular alterations. Additionally, a novel loop-less Bap1 variant was identified, predominantly represented in two phylogenetically distant V. cholerae subspecies clades that share specific gene groups associated with the presence or absence of the protein. Furthermore, our analysis revealed that rbmB, a gene involved in biofilm dispersal, shares a recent common ancestor with Vibriophage tail proteins, suggesting that phages may mimic host functions to evade biofilm-associated defenses. Our study offers a foundational understanding of the diversity and evolution of biofilm matrix clusters in vibrios, laying the groundwork for future biofilm engineering through genetic modification.

IMPORTANCE

Biofilms help vibrios survive in nature and spread cholera. However, the genes that control biofilm formation in vibrios other than Vibrio cholerae are not well understood. In this study, we analyzed the biofilm matrix gene clusters and proteins across diverse Vibrio species to explore their patterns and evolution. We discovered that these genes are spread across different Vibrio species, including those not closely related to V. cholerae. We also found various forms of key biofilm proteins with different structures. Additionally, we identified genes involved in biofilm dispersal that are related to vibriophage genes, highlighting the role of phages in biofilm development. This study not only provides a foundational understanding of biofilm diversity and evolution in vibrios but also leads to new strategies for engineering biofilms through genetic modification, which is crucial for managing cholera outbreaks and improving the environmental resilience of these bacteria.

Vibrio cholerae virulence and its suppression through the quorum-sensing system

Vibrio cholerae is a cholera-causing pathogen known to instigate severe contagious diarrhea that affects millions globally. Survival of vibrios depend on a combination of multicellular responses and adapt to changes that prevail in the environment. This process is achieved through a strong communication at the cellular level, the process has been recognized as quorum sensing (QS). The severity of infection is highly dependent on the QS of vibrios in the gut milieu. The quorum may exist in a low/high cell density (LCD/HCD) state to exert a positive or negative response to control the regulatory pathogenic networks. The impact of this regulation reflects on the transition of pathogenic V. cholerae from the environment to infect humans and cause outbreaks or epidemics of cholera. In this context, the review portrays various regulatory processes and associated virulent pathways, which maneuver and control LCD and HCD states for their survival in the host. Although several treatment options are existing, promotion of therapeutics by exploiting the virulence network may potentiate ineffective antibiotics to manage cholera. In addition, this approach is also useful in resource-limited settings, where the accessibility to antibiotics or conventional therapeutic options is limited.

Tetracycline induces wsp operon expression to promote biofilm formation in Pseudomonas putida

The overuse and wanton discharge of antibiotics produces a threat to bacteria in the environment, which, in turn, stimulates the more rapid emergence of antibiotic-resistant bacteria. Pseudomonas putida actively forms biofilms to protect the population under tetracycline stress, but the molecular mechanism remains unclear. This study found that tetracycline at sub-minimal inhibitory concentrations increased cyclic diguanylate (c-di-GMP), a second messenger that positively regulates biofilm formation. Four c-di-GMP-metabolizing proteins were found to be involved in the tetracycline-mediated biofilm promotion, including DibA, WspR, PP_3242, and PP_3319. Among them, the diguanylate cyclase WspR displayed the most significant effect on c-di-GMP level and biofilm formation. WspR belongs to the wsp operon comprising seven genes (wspA-wspF and wspR). The wsp operon contained six promoters, including one major start promoter (PwspA) and five internal promoters (PwspB, PwspC, PwspD, PwspF, and PwspR), and tetracycline promoted the activity of PwspA. The stress-response sigma factor RpoS directly bound to PwspA and positively regulated its activity under tetracycline stress. Moreover, RpoS was required for tetracycline to induce PwspA activity and promote biofilm formation. Our results enrich the transcriptional regulation of the wsp operon and reveal the mechanism by which tetracycline promotes biofilm formation in P. putida.IMPORTANCEThe overuse and wanton discharge of antibiotics produces a threat to bacteria in the environment, which, in turn, stimulates the more rapid emergence of antibiotic-resistant bacteria. The Pseudomonas putida actively forms biofilm against antibiotic threats, but the mechanism remains unclear. Here, our results showed that tetracycline treatment at sub-minimal inhibitory concentrations could induce the expression of the Wsp system via the sigma factor RpoS in P. putida, resulting in elevated c-di-GMP levels, which leads to increased biofilm formation. The wsp operon contains one major promoter and five internal promoters, and RpoS directly binds to the major promoter to promote its activity.

Wastewater-based surveillance of Vibrio cholerae: Molecular insights on biofilm regulatory diguanylate cyclases, virulence factors and antibiotic resistance patterns

Vibrio cholerae is an inherent inhabitant of aquatic ecosystems. The Indian state of West Bengal, especially the Gangetic delta region is the highest cholera affected region and is considered as the hub of Asiatic cholera. V. cholerae were isolated from publicly accessible wastewater of Midnapore, West Bengal, India. Serotyping determined all isolates to be of non-O1/non-O139 serogroups. Moderate biofilm-forming abilities were noticed in most of the isolates (74.7 %) while, high biofilm formation was recorded for only 6.3 % isolates and 19 % of isolates exhibited low/non-biofilm-forming abilities. PCR-based screening of crucial diguanylate cyclases (DGCs) involved in cyclic-di-GMP-mediated biofilm signaling was performed. cdgH and cdgM were the most abundant DGCs among 93.7 % and 91.5 % of isolates, respectively. Other important DGCs, i.e., cdgK, cdgA, cdgL, and vpvC were present in 84 %, 75.5 %, 72 % and 68 % of isolates, respectively. Besides, the non-O1/non-O139 isolates were screened for the occurrence of virulence factor encoding genes. Moreover, among these non-O1/non-O139 isolates, two strains (3.17 %) harbored both ctxA and ctxB genes, which encode the cholera toxin associated with epidemic cholera. ompU was the most prevalent virulence factor, present in 24.8 % of isolates. Other virulence factors like, zot and st were found in 4.7 % and 9.5 % of isolates. Genes encoding tcp and ace were found to be PCR-negative for the isolates. Additionally, crucial virulence factor regulators, toxT, toxR and hapR were found to be PCR-positive in all the isolates. Antibiotic resistance patterns displayed further vulnerabilities with decreased sensitivity towards commonly used antibiotics with multiple antibiotic resistance index ranging between 0.37 and 0.62. The presence of cholera toxin-encoding multi-drug resistant (MDR) V. cholerae strains in environmental settings is alarming. High occurrence of DGCs are considered to encourage further investigations to use them as alternative therapeutic targets against MDR cholera pathogen due to their unique presence in bacterial systems.

A protracted cholera outbreak in Nairobi City County accentuated by mass gathering events, Kenya, 2017

Cholera continues to cause many outbreaks in low and middle-income countries due to inadequate water, sanitation, and hygiene services. We describe a protracted cholera outbreak in Nairobi City County, Kenya in 2017. We reviewed the cholera outbreak line lists from Nairobi City County in 2017 to determine its extent and factors associated with death. A suspected case of cholera was any person aged >2 years old who had acute watery diarrhea, nausea, or vomiting, whereas a confirmed case was where Vibrio cholerae was isolated from the stool specimen. We summarized cases using means for continuous variables and proportions for categorical variables. Associations between admission status, sex, age, residence, time to care seeking, and outbreak settings; and cholera associated deaths were assessed using odds ratio (OR) with 95% confidence interval (CI). Of the 2,737 cholera cases reported, we analyzed 2,347 (85.7%) cases including 1,364 (58.1%) outpatients, 1,724 (73.5%) not associated with mass gathering events, 1,356 (57.8%) male and 2,202 (93.8%) aged ≥5 years, and 35 deaths (case fatality rate: 1.5%). Cases were reported from all the Sub Counties of Nairobi City County with an overall county attack rate of 50 per 100,000 people. Vibrio cholerae Ogawa serotype was isolated from 78 (34.8%) of the 224 specimens tested and all isolates were sensitive to tetracycline and levofloxacin but resistant to amikacin. The odds of cholera-related deaths was lower among outpatient cases (aOR: 0.35; [95% CI: 0.17-0.72]), age ≥5 years old (aOR: 0.21 [95% CI: 0.09-0.55]), and mass gathering events (aOR: 0.26 [95% CI: 0.07-0.91]) while threefold higher odds among male (aOR: 3.04 [95% CI: 1.30-7.13]). Nairobi City County experienced a protracted and widespread cholera outbreak with a high case fatality rate in 2017.

Goethite adaptation prompts alterations in antibiotic susceptibility and suppresses development of antibiotic resistance in bacteria

Understanding the impact of environmental factors on antibiotic sensitivity and the emergence of antibiotic resistance in microorganism is crucial for antibiotics management and environmental risk assessment. Natural materials, like mineral particles, are prevalent in aquatic and terrestrial ecosystems. However, it remains unclear how microorganism adapt to the physical stress of mineral particles and whether this adaptation influences antibiotic sensitivity and the evolution of antibiotic resistance. In this study, the model bacterium Escherichia coli (E. coli) was exposed to the mineral particle goethite for 30 generations. Adaptive morphogenesis, including an increase in the fraction of spherical bacteria, variations in bacterial mobility, a slightly increased cell membrane thickness, and genome-wide changes in the transcriptomic profile, were observed in adapted E. coli samples to counteract the stress. Moreover, the goethite adapted E. coli showed increased susceptibility to antibiotics including amoxicillin and tetracycline, and decreased susceptibility to kanamycin compared to its ancestral counterparts. These alterations in antibiotic susceptibility in the adapted E. coli were not heritable, as evidenced by the gradual recovery of antibiotic tolerance in cells with the cessation of goethite exposure. Transcriptomic data and a series of experiments suggested that these changes may be associated with variations in cell membrane property and iron metabolism. In addition, the evolution of antibiotic resistance in adapted cells occurred at a slower rate compared to their ancestral counterparts. For instance, E. coli adapted to goethite at a concentration of 1 mg/mL did not acquire antibiotic resistance even after 13 generations, probably due to its poor biofilm-formation capacity. Our findings underscore the occurrence of microbial adaptation to goethite, which influenced antibiotic sensitivity and decelerated the development of resistance in microorganisms. This insight contributes to our comprehension of the natural dynamics surrounding the evolution of antibiotic resistance and opens new perspectives for addressing this issue through nanotechnology-based approaches.

Pharmacological Management of Cholera: A Century of Expert Opinions in Cecil Textbook of Medicine

BACKGROUND

Cholera is a potentially lethal diarrheal disease produced by Vibrio cholerae serotypes O1 El Tor and O139. Known since antiquity, the condition causes epidemics in many areas, particularly in Asia, Africa, and South America. Left untreated, the mortality may reach 50%. The crucial therapeutic intervention is intravenous or oral rehydration and correction of acidosis, dyselectrolytemia, and renal impairment. Antibiotic use represents the main pharmacological intervention.

STUDY QUESTION

What are the milestones of the antibiotics use recommended by experts for the pharmacological management of cholera in the past century?

STUDY DESIGN

To determine the changes in the experts' approach to the management of cholera and particularly the use of antibiotics as presented in a widely used textbook in the United States.

DATA SOURCES

The chapters describing the management of cholera in the 26 editions of Cecil Textbook of Medicine published from 1927 through 2020.

RESULTS

Sulfonamides were recommended in 1947, followed by the introduction of tetracyclines, chloramphenicol, and furazolidone in 1955. The options were restricted in 2000 to doxycycline. In the past decade, patients infected with strains known to have a degree a resistance to tetracyclines were treated with azithromycin or ciprofloxacin. Antibiotic use decreases the volume of stool and the duration of diarrhea but has not been considered lifesaving. Drugs with antimotility, antiemetic, or antisecretory properties are not useful.

CONCLUSIONS

The utility of antibiotic use in cholera has been endorsed by experts, but only as an adjunct to rapid and complete fluid and electrolyte replacement.

Sub-lethal concentration of a colloidal nanosilver formulation (Silversol®) triggers dysregulation of iron homeostasis and nitrogen metabolism in multidrug resistant Pseudomonas aeruginosa

BACKGROUND

Pseudomonas aeruginosa is a notorious pathogen. Its multidrug resistant strains are listed among priority pathogens against whom discovery of novel antibacterial agents and, elucidation of new anti-pathogenicity mechanisms are urgently warranted. This study describes multiple antibacterial effects of a colloidal nano-silver formulation- Silversol® against a multi-drug resistant strain of P. aeruginosa.

RESULTS

Minimum inhibitory concentration (MIC) of Silversol® against P. aeruginosa was found to be 1.5 ppm; and at sub-MIC of 1 ppm, it was able to alter quorum-sensing regulated pigmentation (pyocanin 82%↓; pyoverdine 48%↑), exopolysaccharide synthesis (76%↑) and biofilm formation, susceptibility to antibiotics (streptomycin and augmentin), protein synthesis and export (65%↑), nitrogen metabolism (37%↑ nitrite accumulation), and siderophore production in this pathogen. Network analysis of the differentially expressed genes in the transcriptome of the silversol-treated bacterium identified ten genes as the potential molecular targets: norB, norD, nirS, nirF, nirM, nirQ, nosZ, nosY, narK1, and norE (all associated with nitrogen metabolism or denitrification). Three of them (norB, narK1, and norE) were also validated through RT-PCR.

CONCLUSIONS

Generation of nitrosative stress and disturbance of iron homeostasis were found to be the major mechanisms associated with anti-Pseudomonas activity of Silversol®.

Microplastics exhibit accumulation and horizontal transfer of antibiotic resistance genes

Although the fates of microplastics (0.1-5 mm) in marine environments and freshwater are increasingly studied, little is known about their vector effect in wastewater treatment plants (WWTPs). Previous studies have evaluated the accumulation of antibiotic resistance genes (ARGs) on microplastics, but there is no direct evidence for the selection and horizontal transfer of ARGs on different microplastics in WWTPs. Here, we show biofilm formation as well as bacterial community and ARGs in these biofilms grown on four kinds of microplastics via incubation in the aerobic and anaerobic tanks of a WWTP. Microplastics showed differential capacities for bacteria and ARGs enrichment, differing from those of the culture environment. Furthermore, ARGs in microplastic biofilms were horizontally transferred at frequencies higher than those in water samples in both tanks. Therefore, microplastics in WWTPs can act as substrates for horizontal transfer of ARGs, potentially causing a great harm to the ecological environment and adversely affecting human health.

Vibrio cholerae Invasion Dynamics of the Chironomid Host Are Strongly Influenced by Aquatic Cell Density and Can Vary by Strain

Cholera has been a human scourge since the early 1800s and remains a global public health challenge, caused by the toxigenic strains of the bacterium Vibrio cholerae. In its aquatic reservoirs, V. cholerae has been shown to live in association with various arthropod hosts, including the chironomids, a diverse insect family commonly found in wet and semiwet habitats. The association between V. cholerae and chironomids may shield the bacterium from environmental stressors and amplify its dissemination. However, the interaction dynamics between V. cholerae and chironomids remain largely unknown.  In this study, we developed freshwater microcosms with chironomid larvae to test the effects of cell density and strain on V. cholerae-chironomid interactions. Our results show that chironomid larvae can be exposed to V. cholerae up to a high inoculation dose (109 cells/mL) without observable detrimental effects. Meanwhile, interstrain variability in host invasion, including prevalence, bacterial load, and effects on host survival, was highly cell density-dependent. Microbiome analysis of the chironomid samples by 16S rRNA gene amplicon sequencing revealed a general effect of V. cholerae exposure on microbiome species evenness. Taken together, our results provide novel insights into V. cholerae invasion dynamics of the chironomid larvae with respect to various doses and strains. The findings suggest that aquatic cell density is a crucial driver of V. cholerae invasion success in chironomid larvae and pave the way for future work examining the effects of a broader dose range and environmental variables (e.g., temperature) on V. cholerae-chironomid interactions. IMPORTANCE Vibrio cholerae is the causative agent of cholera, a significant diarrheal disease affecting millions of people worldwide. Increasing evidence suggests that the environmental facets of the V. cholerae life cycle involve symbiotic associations with aquatic arthropods, which may facilitate its environmental persistence and dissemination. However, the dynamics of interactions between V. cholerae and aquatic arthropods remain unexplored. This study capitalized on using freshwater microcosms with chironomid larvae to investigate the effects of bacterial cell density and strain on V. cholerae-chironomid interactions. Our results suggest that aquatic cell density is the primary determinant of V. cholerae invasion success in chironomid larvae, while interstrain variability in invasion outcomes can be observed under specific cell density conditions. We also determined that V. cholerae exposure generally reduces species evenness of the chironomid-associated microbiome. Collectively, these findings provide novel insights into V. cholerae-arthropod interactions using a newly developed experimental host system.

Discovery of Novel Resistance Mechanisms of Vibrio parahaemolyticus Biofilm against Aminoglycoside Antibiotics

Inappropriate use of antibiotics eventually leads to the emergence of antibiotic-resistant strains and invalidates the treatment of infectious diseases. Aminoglycoside antibiotics (AGAs) are a class of broad-spectrum cationic antibiotics widely used for the treatment of Gram-negative bacterial infections. Understanding the AGA resistance mechanism of bacteria would increase the efficacy of treating these infections. This study demonstrates a significant correlation between AGA resistance and the adaptation of biofilms by Vibrio parahaemolyticus (VP). These adaptations were the result of challenges against the aminoglycosides (amikacin and gentamicin). Confocal laser scanning microscope (CLSM) analysis revealed an enclosure type mechanism where the biological volume (BV) and average thickness (AT) of V. parahaemolyticus biofilm were significantly positively correlated with amikacin resistance (BIC) (p < 0.01). A neutralization type mechanism was mediated by anionic extracellular polymeric substances (EPSs). The biofilm minimum inhibitory concentrations of amikacin and gentamicin were reduced from 32 µg/mL to 16 µg/mL and from 16 µg/mL to 4 µg/mL, respectively, after anionic EPS treatment with DNase I and proteinase K. Here, anionic EPSs bind cationic AGAs to develop antibiotic resistance. Transcriptomic sequencing revealed a regulatory type mechanism, where antibiotic resistance associated genes were significantly upregulated in biofilm producing V. parahaemolyticus when compared with planktonic cells. The three mechanistic strategies of developing resistance demonstrate that selective and judicious use of new antibiotics are needed to win the battle against infectious disease.

New Insights into Vibrio cholerae Biofilms from Molecular Biophysics to Microbial Ecology

With the discovery that 48% of cholera infections in rural Bangladesh villages could be prevented by simple filtration of unpurified waters and the detection of Vibrio cholerae aggregates in stools from cholera patients it was realized V. cholerae biofilms had a central function in cholera pathogenesis. We are currently in the seventh cholera pandemic, caused by O1 serotypes of the El Tor biotypes strains, which initiated in 1961. It is estimated that V. cholerae annually causes millions of infections and over 100,000 deaths. Given the continued emergence of cholera in areas that lack access to clean water, such as Haiti after the 2010 earthquake or the ongoing Yemen civil war, increasing our understanding of cholera disease remains a worldwide public health priority. The surveillance and treatment of cholera is also affected as the world is impacted by the COVID-19 pandemic, raising significant concerns in Africa. In addition to the importance of biofilm formation in its life cycle, V. cholerae has become a key model system for understanding bacterial signal transduction networks that regulate biofilm formation and discovering fundamental principles about bacterial surface attachment and biofilm maturation. This chapter will highlight recent insights into V. cholerae biofilms including their structure, ecological role in environmental survival and infection, regulatory systems that control them, and biomechanical insights into the nature of V. cholerae biofilms.

Synergistic antibacterial and anti-biofilm activities of resveratrol and polymyxin B against multidrug-resistant Pseudomonas aeruginosa

Bacterial infection caused by multidrug-resistant Pseudomonas aeruginosa has become a challenge in clinical practice. Polymyxins are used as the last resort agent for otherwise untreatable Gram-negative bacteria, including multidrug-resistant P.aeruginosa. However, pharmacodynamic (PD) and pharmacokinetic (PK) data on polymyxins suggest that polymyxin monotherapy is unlikely to generate reliably efficacious plasma concentrations. Also, polymyxin resistance has been frequently reported, especially among multidrug-resistant P.aeruginosa, which further limits its clinical use. A strategy for improving the antibacterial activity of polymyxins and preventing the development of polymyxin resistance is to use polymyxins in combination with other agents. In this study, we have demonstrated that resveratrol, a well tolerated compound, has synergistic effects when tested in vitro with polymyxin B on antibacterial and anti-biofilm activities. However, its' systemic use is limited as the required high plasma levels of resveratrol are not achievable. This suggests that it could be a partner for the combination therapy of polymyxin B in the treatment of topical bacterial infection caused by MDR P.aeruginosa.

Antibiofilm and anticancer activities of unripe and ripe Azadirachta indica (neem) seed extracts

BACKGROUND

Antibiotic resistances of pathogens and breast cancer warrant the search for new alternative strategies. Phytoextracts can eradicate microbe-borne diseases as well as cancer with lower side effects compared to conventional antibiotics.

AIM

Unripe and ripe Azadirachta indica (neem) seed extracts were explored as potential antibiofilm and anticancer agents in combating multidrug-resistant infectious bacteria as well as anticancer agents against the MDR breast cancer cell lines.

METHODS

Shed-dried neem seeds (both unripe and ripe) were pulverized and extracted using methanol. The chemical components were identified with FTIR and gas chromatography - mass spectrometry. Antibiofilm activity of neem seed extracts were assessed in terms of minimum biofilm inhibitory concentration (MBIC), minimum biofilm eradication concentration (MBEC), and fluorescence microscopic studies on Staphylococcus aureus and Vibrio cholerae. Bacterial cells were studied by fluorescence microscopy using acridine orange/ethidium bromide as the staining agents. Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values were evaluated to observe the antibacterial activities. Cytotoxicity of the extracts against human blood lymphocytes and the anticancer activity against drug-resistant breast cancer cell lines were assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and fluorescence-activated cell sorting (FACS) studies.

RESULTS

4-Ethyl-2-hydroxy-2-cyclopentene-1-one, phthalic acid, and 2-hexyl-tetrahydro thiophane were the major compounds in unripe neem seed, whereas 3,5-dihydroxy-6-methyl-2,3-dihydro-4-H-pyran-4-one and 4-ethylbenzamide were predominant in ripe neem seed. Triazine derivatives were also common for both the extracts. MBIC values of unripe and ripe neem seed extracts for S. aureus are 75 and 100 µg/mL, respectively, and for V. cholerae, they are 100 and 300 µg/mL, respectively. MBEC values of unripe and ripe seed extracts are 500 and 300 µg/mL, respectively for S. aureus and for V. cholerae the values are 700 and 500 µg/mL, respectively. Fluorescence microscopic studies at 16 and 24 h, after bacterial culture, demonstrate enhanced antibiofilm activity for the ripe seed extract than that of the unripe seeds for both the bacteria. MTT assay reveals lower cytotoxicity of both the extracts towards normal blood lymphocytes, and anticancer activity against breast cancer cell line (MDA-MB-231) with superior activity of ripe seed extract. FACS studies further supported higher anticancer activity for ripe seed extract.

CONCLUSIONS

Methanolic extract of neem seeds could substantially inhibit and eradicate biofilm along with their potent antibacterial and anticancer activities. Both the extracts showed higher antibiofilm and antibacterial activity against S. aureus (gram-positive) than V. cholerae (gram-negative). Moreover, ripe seed extract showed higher antibiofilm and anticancer activity than unripe extracts.

A 'time bomb' in the human intestine-the multiple emergence and spread of antibiotic-resistant bacteria

Antibiotics have a strong killing effect on bacteria and are the first choice for the prevention and treatment of bacterial infectious diseases. Therefore, they have been widely used in the medical field, animal husbandry and planting industry. However, with the massive use of antibiotics, more and more antibiotic-resistant bacteria (ARB) have emerged. Because human intestines are rich in nutrients, have suitable temperature, and are high in bacterial abundance, they can easily become a hotbed for the spread of ARB and antibiotic-resistant genes (ARGs). When opportunistic pathogenic bacteria in the intestine acquire ARGs, the infectious diseases caused by such opportunistic pathogens will become more difficult to treat, or even impossible to cure. Therefore, ARB in the human intestine are like a 'time bomb'. In this review, we discuss the sources of intestinal ARB and the transmission routes of ARGs in the human intestine from the perspective of One Health. Further, we describe various methods to prevent the emergence of ARB and inhibit the spread of ARGs in the human intestine. Finally, we may be able to overcome ARB in the human intestine using an interdisciplinary 'One Health' approach.

The two-component system TarR-TarS is regulated by c-di-GMP/FleQ and FliA and modulates antibiotic susceptibility in Pseudomonas putida

Two-component systems (TCSs) are predominant means by which bacteria sense and respond to environment signals. Genome of Pseudomonas putida contains dozens of putative TCS-encoding genes, but phenotypical-genotypical correlation and transcriptional regulation of these genes are largely unknown. Herein, we characterized function and transcriptional regulation of a conserved P. putida TCS, named TarR-TarS. TarS (PP_0769) encodes a potential histidine kinase, and tarR (PP_0768) encodes a potential response regulator. Protein-protein interaction assay and phosphorylation assay confirmed that TarR-TarS was a functional TCS. Growth assay under antibiotics revealed that TarR-TarS positively regulated bacterial resistance to multiple antibiotics. Pull-down assay revealed that TarR directly interacted with PP_0800 (a hypothetical protein) and GroEL (the chaperonin). GroEL played a positive role in antibiotic resistance, while PP_0800 seemed to have no effect on antibiotic resistance. The regulator FleQ indirectly activated tarR-tarS transcription. However, the second messenger c-di-GMP antagonized FleQ activation to inhibit tarR-tarS transcription. The sigma factor FliA directly activated tarR-tarS transcription via a consensus motif. These findings reveal function and transcriptional regulation of TarR-TarS, and enrich knowledge regarding the relationship between c-di-GMP and antibiotic susceptibility in P. putida.

TonB-Dependent Receptors Affect the Spontaneous Oxytetracycline Resistance Evolution in Aeromonas hydrophila

It is well known that most microbial populations develop their intrinsic antibiotics resistance at low concentrations in antibiotics environments, but the factors influencing spontaneous resistance are still largely unknown. In this study, Aeromonas hydrophila strains with different resistance levels to oxytetracycline (OXY) were induced by sublethal antibiotic selection pressure, and differential expression of proteins was compared among them using iTRAQ-based quantitative proteomics. Our following bioinformatic analysis showed that energy metabolism-related proteins were downregulated, while several iron-related proteins were upregulated in high OXY-resistant strains. To further investigate the role of spontaneous OXY resistance evolution, four TonB-dependent receptor-coded genes were deleted, and their OXY susceptibility capabilities and antibiotic evolutionary assays were performed, respectively. Our results showed that the deletion of these genes did not affect the susceptibility to OXY, but showed different evolution rates in the spontaneous OXY evolution compared with wild-type strain, especially for AHA_0971 and AHA_4251. Therefore, this study indicates the important role of TonB-dependent receptor proteins during the bacterial antibiotics resistance evolution and may provide a new prophylactic strategy against the development of antibiotic resistance.

Effects of Cefazolin and Meropenem in Eradication Biofilms of Clinical and Environmental Isolates of Proteus mirabilis

Proteus mirabilis is an opportunistic Gram-negative bacterium belonging to the family Enterobacteriaceae and is known for its ability to cause urinary tract infections. The aim of this study was to determine the value of the minimum concentration of cefazolin and meropenem on biofilm eradication, as well as the resistance profiles and genetic diversity of clinical and environmental isolates of P. mirabilis. We compared the isolates collected from a hospital environment and from an urban stream impacted in Recife-Pernambuco, Brazil. Biochemical tests were performed to determine the profiles of susceptibility, hydrophobicity, biofilm formation and eradication. The genetic diversity was verified using the ERIC-PCR method. The results revealed that two clinical isolates (ICP4 and ICP5) were multi-drug resistant, whereas the environmental isolates showed resistance only to tetracycline, except for CP₅25S, which was resistant also to ampicillin. Of the isolates investigated, three were moderately hydrophobic, while the remaining were hydrophilic. Genetic diversity analysis verified the presence of clones indicating that the stream is harboring and disseminating bacteria of hospital origin. All isolates formed a biofilm, however, high concentrations of cefazolin and meropenem were required to eradicate the already formed biofilm. Our study analyzed the survival strategies of these bacteria in the environments investigated and corresponds to first report the use of these antibiotics to eliminate P. mirabilis biofilms.

The Impact of Protozoan Predation on the Pathogenicity of Vibrio cholerae

In the aquatic environment, Vibrio spp. interact with many living organisms that can serve as a replication niche, including heterotrophic protists, or protozoa. Protozoa engulf bacteria and package them into phagosomes where the cells are exposed to low pH, antimicrobial peptides, reactive oxygen/nitrogen species, proteolytic enzymes, and low concentrations of essential metal ions such as iron. However, some bacteria can resist these digestive processes. For example, Vibrio cholerae and Vibrio harveyi can resist intracellular digestion. In order to survive intracellularly, bacteria have acquired and/or developed specific factors that help them to resist the unfavorable conditions encountered inside of the phagosomes. Many of these intra-phagosomal factors used to kill and digest bacteria are highly conserved between eukaryotic cells and thus are also expressed by the innate immune system in the gastrointestinal tract as the first line of defense against bacterial pathogens. Since pathogenic bacteria have been shown to be hypervirulent after they have passed through protozoa, the resistance to digestion by protist hosts in their natural environment plays a key role in enhancing the infectious potential of pathogenic Vibrio spp. This review will investigate the current knowledge in interactions of bacteria with protozoa and human host to better understand the mechanisms used by both protozoa and human hosts to kill bacteria and the bacterial response to them.

Potential pathogenicity and antibiotic resistance of aquatic Vibrio isolates from freshwater in Slovakia

This study aimed to evaluate the potential pathogenicity and antibiotic resistance of 31 environmental Vibrio isolates obtained from surface water in southern and eastern Slovakia. Isolates were identified as Vibrio cholerae non-O1/non-O139 and Vibrio metschnikovii by biochemical tests, MALDI biotyping, and 16S RNA gene sequencing. Analysis of the susceptibility to 13 antibacterial agents showed susceptibility of all isolates to ciprofloxacin, trimethoprim/sulfamethoxazole, chloramphenicol, gentamicin, imipenem, tetracyclin, and doxycycline. We recorded high rates of resistance to β-lactams and streptomycin. Investigation of antibiotic resistance showed five different antibiotic profiles with resistance to antibacterials from three classes, but no multidrug resistance was observed. The investigation of the pathogenic potential of V. cholerae isolates showed that neither the cholera toxin coding gene ctxA nor the genes zot (zonula occludens toxin), ace (accessory cholera toxin), and tcpA (toxin-coregulated pilus) were present in any of 31 isolated samples. Gene ompU (outer membrane protein) was confirmed in 80% and central regulatory protein-coding gene toxR in 71% of V. cholerae isolates, respectively. A high prevalence of the hemolysin coding gene hlyA in all V. cholerae was observed. The data point toward the importance of systematic monitoring and comparative studies of potentially pathogenic vibrios in European countries.

Inhibition of protein synthesis eradicates persister cells of V. cholerae

In the present work, we studied the antibiotic-induced persister formation in Vibrio cholerae. Persisters vary with the bacterial growth phase with minimum persisters in log phase and maximum in stationary phase. Only 10% of the stationary phase cells of V. cholerae were tolerant of ampicillin and ciprofloxacin. In comparison, more than 90% of the stationary phase cells of E. coli were tolerant of ampicillin and ciprofloxacin. Frequency of ciprofloxacin-induced persisters of V. cholerae would vary with the bacteriological media used for the growth of the cells. In tryptone soy broth (TSB) and in buffered peptone water (BPW), V. cholerae could form more than 10% persisters, whereas in Luria-Bertani broth (LB) and alkaline peptone water (APW) persister fraction was less than 1%. When exposed to protein synthesis inhibitors (kanamycin, chloramphenicol, tetracycline, erythromycin and gentamicin), V. cholerae did not form persisters. Persister recovery assay, LIVE/DEAD analysis and QRDR sequence analysis showed that persister population neither included resistant mutants nor VBNC population. Starvation, anaerobic conditions and inhibition of ATP synthesis also induced persisters, but not when protein synthesis is inhibited. These observations suggest that the protein synthesis is critical for persister formation, persister maintenance, and also for dormancy maintenance in V. cholerae. Contrary to these observations, E. coli can form persisters when protein synthesis is inhibited, suggesting fundamental mechanistic differences between the two species.

Generation and In Vivo Characterization of Tn5-Induced Biofilm Mutants of Vibrio cholerae O139

The Gram-negative bacterium Vibrio cholerae is a unique pathogen with an ability to colonize human intestine as well as outside environments. The biofilm, an organized polymeric structure produced by this bacterium known to be a significant factor for the survival and persistence in hostile conditions. However, the direct role of biofilm formation by this bacterium in environmental persistence, in vivo colonization, and pathogenesis remains unexplored. In this study, we have generated biofilm-altered Tn5 mutants of V. cholerae O139 and evaluated their in vivo colonization ability on mouse model. These Tn5 mutants were found to harbor an independent, single Tn5 insertion in their genome. The DNA sequence analysis revealed that genomic region wherein Tn5 insertion occurred is identified to be involved in functions like LPS biosynthesis, efflux transporters, motility, purine metabolism, stringent response, VPS synthesis, and a hypothetical protein of unknown function. In single-strain infection with the planktonic culture, the biofilm-altered as well as the biofilm intermediate mutants were found to be more or less similar in their intestinal colonization ability, however infection with their biofilm form, a marked difference was observed between the biofilm deficient and other biofilm forming strains. Further, in the competition experiments, biofilm deficient and proficient mutants were found reduced in their colonization ability and outcompeted by their parent strain. In conclusion, biofilm formation in V. cholerae O139 is a genetically complex process and the controlled and regulated production of biofilm appeared to be necessary for its efficient colonization of mouse intestine.