Vibrio cholerae O1 and Escherichia coli O157:H7 from drinking water and wastewater in Addis Ababa, Ethiopia.

BACKGROUND: In Addis Ababa, Ethiopia, open ditches along innner roads in residential areas serve to convey domestic wastewater and rainwater away from residences. Contamination of drinking water by wastewater through faulty distribution lines could expose households to waterborne illnesses. This prompted the study to assess the microbiological safety of wastewater and drinking water in Addis Ababa, identify the pathogens therein, and determine their antibiotic resistance patterns. RESULTS VIBRIO CHOLERAE: O1, mainly Hikojima serotype, was isolated from 23 wastewater and 16 drinking water samples. Similarly, 19 wastewater and 10 drinking water samples yielded Escherichia coli O157:H7. V. cholerae O1 were 100% resistant to the penicillins (Amoxacillin and Ampicillin), and 51-82% were resistant to the cephalosporins. About 44% of the V. cholerae O1 isolates in this study were Extended Spectrum Beta-Lactamase (ESBL) producers. Moreover, 26% were resistant to Meropenem. Peperacillin/Tazobactam was the only effective ß-lactam antibiotic against V. cholerae O1. V. cholerae O1 isolates showed 37 different patterns of multiple resistance ranging from a minimum of three to a maximum of ten antimicrobials. Of the E. coli O157:H7 isolates, 71% were ESBL producers. About 96% were resistant to Ampicillin. Amikacin and Gentamicin were very effective against E. coli O157:H7 isolates. The isolates from wastewater and drinking water showed multiple antibiotic resistance against three to eight antibiotic drugs. CONCLUSIONS: Open ditches for wastewater conveyance along innner roads in residence areas and underground faulty municipal water distribution lines could be possible sources for V. cholerae O1 and E. coli O157:H7 infections to surrounding households and for dissemination of multiple drug resistance in humans and, potentially, the environment.

Elevated concentrations of polymyxin B elicit a biofilm-specific resistance mechanism in Vibrio cholerae.

Vibrio cholerae can form biofilms in the aquatic environment and in the human intestine, facilitating the release of hyper-infectious aggregates. Due to the increasing antibiotic resistance, alternatives need to be found. One of these alternatives is antimicrobial peptides, including polymyxin B (PmB). In this study, we first investigated the resistance of V. cholerae O1 El Tor strain A1552 to various antimicrobials under aerobic and anaerobic conditions. An increased resistance to PmB is observed in anaerobiosis, with a 3-fold increase in the dose required for 50 % growth inhibition. We then studied the impact of the PmB on the formation and the degradation of V. cholerae biofilms to PmB. Our results show that PmB affects more efficiently biofilm formation under anaerobic conditions. On the other hand, preformed biofilms are susceptible to degradation by PmB at concentrations close to the minimal inhibitory concentration. At higher concentrations, we observe an opacification of the biofilm structures within 20 min post-treatment, suggesting a densification of the structure. This densification does not seem to result from the overexpression of matrix genes but rather from DNA release through massive cell lysis, likely forming a protective shield that limits the penetration of the PmB into the biofilm.

Clinical and socio-environmental determinants of multidrug-resistant vibrio cholerae 01 in older children and adults in Bangladesh.

OBJECTIVES: Few studies have evaluated determinants of multidrug-resistant (MDR) Vibrio cholerae O1 in older children and adults. This study aimed to characterize the prevalence of MDR V. cholerae O1 and associated risk factors among patients over five years of age in Bangladesh. METHODS: Stool culture and antimicrobial susceptibility testing were performed as a part of a larger study at Dhaka Hospital in Bangladesh from March 2019-March 2020. Univariate statistics and multiple logistic regression were used to assess the association between a range of variables and MDR V. cholerae O1. RESULTS: MDR was found in 175 of 623 (28.1%) V. cholerae O1 isolates. High levels of resistance were found to erythromycin (99.2%), trimethoprim-sulfamethoxazole (99.7%), and ampicillin (88.9%), while susceptibility was high to tetracyclines (99.7%), azithromycin (99.2%), ciprofloxacin (99.8%), and cephalosporins (98.6%). MDR was associated with prior antibiotic use, longer transport time to hospital, higher income, non-flush toilet use, greater stool frequency, lower blood pressure, lower mid-upper arm circumference, and lower percent dehydration. CONCLUSIONS: MDR V. cholerae O1 was common among patients over five in an urban hospital in Bangladesh. Significant factors associated with MDR may be actionable in identifying patients with a high likelihood of MDR.

Virstatin-Conjugated Gold Nanoparticle with Enhanced Antimicrobial Activity against the Vibrio cholerae El Tor Biotype.

Because of the emergence of multidrug-resistant pathogenic bacteria, there is a growing interest for the development of an efficient alternative to antibiotics. Gold nanoparticles (AuNPs) are promising candidates due to their inherent non-toxicity and can be used as effective carriers of drugs. Cholera caused by Gram-negative Vibrio cholerae is still a potential threat in many developing countries. Virstatin, a small molecule, has been reported to inhibit virulence regulation in V. cholerae. Herein, we report an efficient synthesis of virstatin-conjugated gold nanoparticles (VL-AuNPs) and their antibacterial efficacy against the El Tor biotype of V. cholerae (VcN16961). The spherical-shaped NPs have an average diameter of ∼17 nm. The uniqueness of VL-AuNPs relies in the enhanced antibacterial efficacy compared to virstatin, as evidenced from the inhibitory concentration obtained from growth kinetics, and attributed to the inhibition of ATPase activity and DNA damage. More importantly, the expression of cholera toxin, the most important virulence factor of V. cholera, is reduced to a far greater extent than by any of the component molecules. The effect of VL-AuNPs on VcN16961 was monitored using various assays such as confocal microscopy, FACS, fluorescence spectroscopy, and so on. Overall, VL-AuNPs could be a potential candidate for the use as an effective agent for combating diarrheal diseases caused by V. cholera.

Dissemination of Polymyxin B Sensitivity in El Tor Vibrio cholerae O1 Strains in Odisha, India.

The Vibrio species undergo cryptic changes in their genetic material for better adaptability, which accounts for antibiotic resistance. In the present study, we investigated the emergence and spread of sensitivity to polymyxin B (PB) by El Tor V. cholerae O1 strains from 1995 to 2019 in Odisha, India. The results showed that out of 1200 V. cholerae O1 strains, 89.4% were resistant and the remaining 10.6% strains were sensitive to PB. The sensitivity to PB of V. cholerae O1 strains emerged from 2005 to 2019, except in 2015, clearly signifying the presence of classical biotype characteristics in the El Tor variant of V. cholerae O1 strains. The Etest assay revealed some interesting traits of PB susceptibility in the ctxB1 and ctxB7 genotypes of V. cholerae O1 strains. The minimum inhibitory concentration (MIC) of ctxB7 genotypes showed reduced MIC values of ≤ 4 µg/mL, whereas ctxB1 genotypes exhibited higher MIC values of 24 and 32 µg/mL.

Geographical distribution and antibiotics susceptibility patterns of toxigenic Vibrio cholerae isolates from Kisumu County, Kenya.

BACKGROUND: Multiple drug resistance has become a major threat to the treatment of cholera. Recent studies in Kenya have described the epidemiology, especially the risk factors, of cholera; however, there is little information on the phenotypic and drug susceptibility patterns of Vibrio cholerae (V. cholerae) in outbreaks that in the recent past have occurred in western Kenya. AIM: To characterise and determine the antibiotics' susceptibility profiling of toxigenic V. cholerae isolates from Kisumu County. SETTING: The project was conducted in Kisumu County, Kenya. METHODS: A total of 119 V. cholerae O1, biotype El Tor, isolates collected during 2017 cholera outbreak in Kisumu County were used for this study. The samples were cultured on thiosulphate-citrate-bile salts sucrose (TCBS) agar and biochemical tests were carried out using standard procedures. Susceptibility tests were conducted by using various conventional antibiotics against standard procedures. RESULTS: Of the 119 isolates, 101 were confirmed to be V. cholerae belonging to serotypes Inaba and Ogawa, with Inaba being the predominant serotype (73.95%). The isolates were susceptible to ciprofloxacin (100%), ofloxacin (100%), gentamycin (100%), doxycycline (99%), ceftriaxone (99%) and streptomycin (96.04%) antimicrobials, and resistant to erythromycin (53.47%), amoxicillin (64.4%), nalidixic acid (83.2%) and ampicillin (89.11%), with high resistance to cotrimoxazole (99%) and tetracycline (97%). CONCLUSION: Vibrio cholerae was resistant to multiple antibiotics, including those commonly used in the management of cholera. Taken together, there is a need to carry out regular surveillance on antimicrobial drug resistance during outbreaks.

Characterization of the Vibriocidal Activity of Chitosan Microparticles: A Potential Therapeutic Agent for Emerging Multidrug-Resistant Cholera Infections.

Due to increasing reports of multidrug-resistant (MDR) Vibrio cholerae O1, the goal of this study was to characterize the in vitro antimicrobial activity of chitosan microparticles (CMs) to evaluate their potential as a novel therapeutic agent for cholera. We examined the antimicrobial activity of CMs against toxigenic V. cholerae O1 using direct enumeration, microscopy, and fluorescence microplate assays. Bacterial viability kinetics were measured with different concentrations of CMs, solution pH, and salt content using a live/dead staining technique. Growth inhibition of CM-exposed V. cholerae strains was conducted using a redox-sensitive stain and compared between wild-type and isogenic outer membrane (OM) mutants. CM concentrations above 0.1 wt % were sufficient to kill V. cholerae O1 suspensions with approximately 108 CFU/mL within 3 h. The nonviable cells demonstrated increased OM permeability that corresponded to gross morphological changes observed through scanning electron microscopy. CMs exhibited dose-dependent bactericidal activity that increased predictably at lower pH and decreased with salt addition. V. cholerae O1 strains lacking O-antigen were twice as susceptible to growth inhibition by CMs, whereas those with glycine modification to lipid A were ten times more resistant. We propose that CMs exert vibriocidal activity via electrostatic surface interactions between their positively charged amine groups and the negatively charged Gram-negative bacterial OM, resulting in disruption, increased permeability, decreased redox metabolism, and subsequent loss of cellular viability. Further research should be conducted in vivo to evaluate the efficacy of CMs as luminal agents to treat infections caused by MDR, toxigenic V. cholerae and other diarrheal pathogens.

Adaptive laboratory evolution of Vibrio cholerae to doxycycline associated with spontaneous mutation.

Cholera, caused by the Gram-negative bacterium Vibrio cholerae, remains a serious threat in underdeveloped countries. Although rehydration therapy has been the mainstay of disease management, antibiotics are also being used as an adjunct treatment, resulting in an increase in the circulation of antimicrobial-resistant V. cholerae strains. In the present study, adaptive laboratory evolution, whole-genome sequencing and molecular docking studies were performed to identify putative mutations related to doxycycline resistance in V. cholerae isolates. The V57L mutation in the RpsJ protein was identified to be important in conferring doxycycline resistance. As revealed by molecular docking studies, the mutation was identified to alter the ribosome structure near the doxycycline binding site. Doxycycline stress also induced co-resistance to colistin, a last-resort antibiotic to treat extensively drug-resistant bacteria. This study illustrates for the first time a possible mechanism of doxycycline-selected resistance in V. cholerae as well as doxycycline-selected co-resistance, warranting strict restrictions on the indiscriminate use of antibiotics.

A Point Mutation in carR Is Involved in the Emergence of Polymyxin B-Sensitive Vibrio cholerae O1 El Tor Biotype by Influencing Gene Transcription.

Antimicrobial peptides play an important role in host defense against Vibrio cholerae Generally, the V. cholerae O1 classical biotype is polymyxin B (PB) sensitive and El Tor is relatively resistant. Detection of classical biotype traits like the production of classical cholera toxin and PB sensitivity in El Tor strains has been reported in recent years, including in the devastating Yemen cholera outbreak during 2016-2018. To investigate the factor(s) responsible for the shift in the trend of sensitivity to PB, we studied the two-component system encoded by carRS, regulating the lipid A modification of El Tor vibrios, and found that only carR contains a single nucleotide polymorphism (SNP) in recently emerged PB-sensitive strains. We designated the two alleles present in PB-resistant and -sensitive strains carRr and carRs alleles, respectively, and replaced the carRs allele of a sensitive strain with the carRr allele, using an allelic-exchange approach. The sensitive strain then became resistant. The PB-resistant strain N16961 was made susceptible to PB in a similar fashion. Our in silico CarR protein models suggested that the D89N substitution in the more stable CarRs protein brings the two structural domains of CarR closer, constricting the DNA binding cleft. This probably reduces the expression of the carR-regulated almEFG operon, inducing PB susceptibility. Expression of almEFG in PB-sensitive strains was found to be downregulated under natural culturing conditions. In addition, the expression of carR and almEG decreased in all strains with increased concentrations of extracellular Ca2+ but increased with a rise in pH. The downregulation of almEFG in CarRs strains confirmed that the G265A mutation is responsible for the emergence of PB-sensitive El Tor strains.

Genome Dynamics of Vibrio cholerae Isolates Linked to Seasonal Outbreaks of Cholera in Dhaka, Bangladesh.

The temporal switching of serotypes from serotype Ogawa to Inaba and back to Ogawa was identified in Vibrio cholerae O1, which was responsible for seasonal outbreaks of cholera in Dhaka during the period 2015 to 2018. In order to delineate the factors responsible for this serotype transition, we performed whole-genome sequencing (WGS) of V. cholerae O1 multidrug-resistant strains belonging to both the serotypes that were isolated during this interval where the emergence and subsequent reduction of the Inaba serotype occurred. The whole-genome-based phylogenetic analysis revealed clonal expansion of the Inaba isolates mainly responsible for the peaks of infection during 2016 to 2017 and that they might have evolved from the prevailing Ogawa strains in 2015 which coclustered with them. Furthermore, the wbeT gene in these Inaba serotype isolates was inactivated due to insertion of a transposable element at the same position signifying the clonal expansion. Also, V. cholerae isolates in the Inaba serotype dominant clade mainly contained classical ctxB allele and revealed differences in the genetic composition of Vibrioseventh pandemic island II (VSP-II) and the SXT integrative and conjugative element (SXT-ICE) compared to those of Ogawa serotype strains which remerged in 2018. The variable presence of phage-inducible chromosomal island-like element 1 (PLE1) was also noted in the isolates of the Inaba serotype dominant clade. The detailed genomic characterization of the sequenced isolates has shed light on the forces which could be responsible for the periodic changes in serotypes of V. cholerae and has also highlighted the need to analyze the mobilome in greater detail to obtain insights into the mechanisms behind serotype switching.IMPORTANCE The switching of serotype from Ogawa to Inaba and back to Ogawa has been observed temporally in Vibrio cholerae O1, which is responsible for endemic cholera in Bangladesh. The serospecificity is key for effective intervention and for preventing cholera, a deadly disease that continues to cause significant morbidity and mortality worldwide. In the present study, WGS of V. cholerae allowed us to better understand the factors associated with the serotype switching events observed during 2015 to 2018. Genomic data analysis of strains isolated during this interval highlighted variations in the genes ctxB, tcpA, and rtxA and also identified significant differences in the genetic content of the mobilome, which included key elements such as SXT ICE, VSP-II, and PLE. Our results indicate that selective forces such as antibiotic resistance and phage resistance might contribute to the clonal expansion and predominance of a particular V. cholerae serotype responsible for an outbreak.

Alterations in glucose metabolism in Vibrio cholerae serogroup O1 El Tor biotype strains.

The 2 biotypes of Vibrio cholerae O1 serogroup strains-classical and El Tor-use glucose in distinct ways. Classical biotype strains perform organic acid-producing fermentation and eventually lose viability due to the self-induced creation of an acidic environment, whereas El Tor biotype strains use an alternative neutral fermentation pathway, which confers them with survival advantages. However, we report that the neutral fermentation pathway has only been recruited in prototype Wave 1 El Tor biotype strains, which have not been isolated since the mid-1990s. Current Wave 2 and Wave 3 atypical El Tor strains contain a single-base deletion in a gene that directs bacteria toward neutral fermentation, resulting in the loss of neutral fermentation and an appearance that is similar to classical biotype strains. Moreover, when sufficient glucose was supplied, Wave 1 El Tor strains maintained their use of acid-producing fermentation, in parallel with neutral fermentation, and thus lost viability in the late stationary phase. The global replacement of Wave 1 El Tor strains by Wave 2 and 3 atypical El Tor strains implies that the acidic fermentation pathway may not be disadvantageous to V. cholerae. The characteristics that we have reported might improve oral rehydration in the treatment of cholera.

Emergence of Haitian variant genotype and altered drug susceptibility in Vibrio cholerae O1 El Tor-associated cholera outbreaks in Solapur, India.

It is evident from previous cholera epidemics/outbreaks in India, Africa and America that isolates of the seventh pandemic Vibrio cholerae El Tor (7PET) with Haitian cholera toxin (HCT) genotype were associated with increased mortality. The present study highlights the emergence of 7PET-HCT isolates causing two cholera outbreaks in Walsang and Wagdari (Solapur, India) in 2016. Molecular analyses revealed that 7PET strains from earlier outbreaks (2010 and 2012) were progenitors of the current 7PET-HCT isolates. Isolates from the 2016 outbreaks carried qnrVC and floR genes and showed reduced susceptibility to tetracycline, ciprofloxacin and azithromycin, drugs recommended by the World Health Organization (WHO) for the treatment of cholera. Remarkably, protein profiling and mass spectrometry revealed disappearance of the outer membrane protein U (OmpU) porin in 7PET-HCT isolates from the second outbreak in 2016. Downregulation of ompU gene expression was also confirmed at the transcriptional level. Strains with downregulated OmpU showed reduced minimum inhibitory concentrations (MICs) for polymyxin B, which is a pore-forming antimicrobial agent. A multipronged approach is of utmost importance to prevent further spread of circulating 7PET-HCT strains. There is a pressing need for the formulation and implementation of international policies to closely monitor the effective use of antibiotics in order to prevent the further rise and spread of antimicrobial resistance.

Changing epidemiology and antimicrobial resistance in Vibrio cholerae: AMR surveillance findings (2006-2016) from Nepal.

BACKGROUND: In Nepal, cases of Cholera occur annually either as sporadic or as outbreaks claiming the lives of many in rural areas. The present study is a laboratory based surveillance which aims to analyze the changing epidemiology and antimicrobial susceptibility trend of V. cholerae strains isolated or referred to National Public Health Laboratory (NPHL) over a period of 11 years (2006-2016). METHODS: Specimens of fresh stool /rectal swab either received at sentinel sites or NPHL were processed following standard microbiological techniques. Suspected colonies on selective medium were identified using routine biochemical tests and confirmed by serotyping. Antimicrobial susceptibility testing was performed following Kirby Baeur disc diffusion method. RESULTS: Of the 836 confirmed isolates, 87% (728/836) were V.cholerae O1 Ogawa,12% (103/836) were V.cholerae O1 Inaba and only 6 isolates were V.cholerae O1 Hikojima. In 2006 all the Vibrio isolates were of Inaba serotype, followed by all 3 serotypes during 2007.During 2008-2014 only Ogawa serotype was isolated while few cases of Inaba again surfaced in 2015. Resistance to ampicillin decreased from 93% in 2006 to 18% by 2010 and again raised to 100% by 2016.Cotrimoxazole resistance remained at constant range (77-100%).Nalidixic acid resistance was 100% since 2006.Ciprofloxacin and tetracycline resistance emerged in 2007, reached a peak during 2010-2012 and declined to 0 by 2016.Susceptibility to Furazolidone has re-emerged.63.6% of the isolates were Multi drug resistant. CONCLUSION: With changing epidemiology and antibiogram of V.cholerae in Nepal, the present study reflects the importance of continuous monitoring, which could be used by policy makers and health professionals for better management of outbreaks. Decline in tetracycline and ciprofloxacin resistance along with emerging sensitivity to furazolidone shows that these drugs could make an effective comeback in future.

Flagella-dependent inhibition of biofilm formation by sub-inhibitory concentration of polymyxin B in Vibrio cholerae.

Biofilm formation is a common strategy used by bacteria in order to survive and persist in the environment. In Vibrio cholerae (V. cholerae), a Gram-negative pathogen responsible for the cholera disease, biofilm-like aggregates are important for the pathogenesis and disease transmission. Biofilm formation is initiated by the attachment of the bacteria to a surface, followed by maturation stages involving the formation of a biofilm matrix. In V. cholerae, flagella are essential for the initial step of biofilm formation, allowing the bacteria to swim and to detect a surface. In this study, we explored the effect of polymyxin B (PmB), a cationic bacterial antimicrobial peptide, on biofilm formation in pathogenic V. cholerae strains belonging to the O1 and O139 serotypes. We found that sub-inhibitory concentration of PmB induces a reduction of the biofilm formation by V. cholerae O1 and O139. Experiment on preformed biofilm demonstrated that the biofilm formation inhibition occurs at the initial step of biofilm formation, where the flagella are essential. We further characterize the effect of PmB on V. cholerae flagellation. Our results demonstrate that the flagellin expression is not reduced in presence of sub-inhibitory concentration of PmB. However, a decrease of the abundance of flagellin associated with the bacterial cells together with an increase in the secretome was observed. Electron microscopy observations also suggest that the abundance of aflagellated bacteria increases upon PmB supplementation. Finally, in agreement with the effect on the flagellation, a reduction of the bacterial motility is observed. Altogether, our results suggest that the PmB affect V. cholerae flagella resulting in a decrease of the motility and a compromised ability to form biofilm.

Characterization of Vibrio cholerae O1 isolates responsible for cholera outbreaks in Kenya between 1975 and 2017.

Kenya is endemic for cholera with different waves of outbreaks having been documented since 1971. In recent years, new variants of Vibrio cholerae O1 have emerged and have replaced most of the traditional El Tor biotype globally. These strains also appear to have increased virulence, and it is important to describe and document their phenotypic and genotypic traits. This study characterized 146 V. cholerae O1 isolates from cholera outbreaks that occurred in Kenya between 1975 and 2017. Our study reports that the 1975-1984 strains had typical classical or El Tor biotype characters. New variants of V. cholerae O1 having traits of both classical and El Tor biotypes were observed from 2007 with all strains isolated between 2015 and 2017 being sensitive to polymyxin B and carrying both classical and El Tor type ctxB. All strains were resistant to Phage IV and harbored rstR, rtxC, hlyA, rtxA and tcpA genes specific for El Tor biotype indicating that the strains had an El Tor backbone. Pulsed field gel electrophoresis (PFGE) genotyping differentiated the isolates into 14 pulsotypes. The clustering also corresponded with the year of isolation signifying that the cholera outbreaks occurred as separate waves of different genetic fingerprints exhibiting different genotypic and phenotypic characteristics. The emergence and prevalence of V. cholerae O1 strains carrying El Tor type and classical type ctxB in Kenya are reported. These strains have replaced the typical El Tor biotype in Kenya and are potentially more virulent and easily transmitted within the population.

A systematic review and meta-analysis on the epidemiology of antibiotic resistance of Vibrio cholerae in Iran.

BACKGROUND: Cholera, an acute diarrheal disease caused by Vibrio cholerae (V. cholerae), is an endemic disease and a major public health problem in Iran. Antibiotic therapy can decrease duration of the disease, transmission of infection and contamination of the environment. Considering different pattern of V. cholerae antibiotic resistance around the world, the aim of the current systematic review and meta-analysis was to evaluate the prevalence of antibiotic resistance of V. cholerae in Iran. METHODS: A systematic review of the literature was performed using related keywords in the electronic national and international databases including SID, Irandoc, Iran Medex and Magiran as well as PubMed, Scopus, Google Scholar and ISI web of knowledge. Up to July 31, 2018, 27 eligible papers were included in our meta-analysis based on the defined inclusion criteria. RESULTS: V. cholerae O1 was the most prevalent strain isolated in Iran and exhibited a high resistance rate against numerous antibiotics including chloramphenicol (33.6%), oxytetracycline (40.2%), trimethoprim/sulphamethoxazole (86%), tetracycline (34.5%), furazolidone (69.8%), streptomycin (93.8%), polymyxin (80.7%), ampicillin (32.1%), nalidixic acid (88.9%), kanamycin (29%) and amoxicillin (30.5%). CONCLUSIONS: According to the meta-analysis results, antibiotic therapy with ciprofloxacin, doxycycline, erythromycin, gentamicin, azithromycin, cefixime and cefepime could be effective for the treatment of severe cases of cholera in Iran.

Cholera Toxin Encapsulated within Several Vibrio cholerae O1 Serotype Inaba Outer Membrane Vesicles Lacks a Functional B-Subunit.

Cholera toxin (CT), the major virulence factor of Vibrio cholerae, is an AB5 toxin secreted through the type II secretion system (T2SS). Upon secretion, the toxin initiates endocytosis through the interaction of the B pentamer with the GM1 ganglioside receptor on small intestinal cells. In addition to the release of CT in the free form, the bacteria secrete CT in association with outer membrane vesicles (OMVs). Previously, we demonstrated that strain 569B releases OMVs that encapsulate CT and which interact with host cells in a GM1-independent mechanism. Here, we have demonstrated that OMV-encapsulated CT, while biologically active, does not exist in an AB5 form; rather, the OMVs encapsulate two enzymatic A-subunit (CTA) polypeptides. We further investigated the assembly and secretion of the periplasmic CT and found that a major fraction of periplasmic CTA does not participate in the CT assembly process and instead is continuously encapsulated within the OMVs. Additionally, we found that the encapsulation of CTA fragments in OMVs is conserved among several Inaba O1 strains. We further found that under conditions in which the amount of extracellularly secreted CT increases, the concentration of OMV-encapsulated likewise CTA increases. These results point to a secondary mechanism for the secretion of biologically active CT that does not depend on the CTB-GM1 interaction for endocytosis.

Investigating the virulence genes and antibiotic susceptibility patterns of Vibrio cholerae O1 in environmental and clinical isolates in Accra, Ghana.

BACKGROUND: Cholera has been endemic in Ghana since its detection in 1970. It has been shown that long-term survival of the bacteria may be attained in aquatic environments. Consequently, cholera outbreaks may be triggered predominantly in densely populated urban areas. We investigated clinical and environmental isolates of Vibrio cholerae O1 in Accra to determine their virulence genes, antibiotic susceptibility patterns and environmental factors maintaining their persistence in the environment. METHODS: Water samples from various sources were analyzed for the presence of V. cholerae O1 using culture methods. Forty clinical isolates from a previous cholera outbreak were included in the study for comparison. Antibiotic susceptibility patterns of the bacteria were determined by disc diffusion. Virulence genes were identified by analyzing genes for ctx, tcpA (tcpAEl Tor tcpACl), zot, ompW, rbfO1 and attRS using PCR. Physicochemical characteristics of water were investigated using standard methods. One-way ANOVA and student t - test were employed to analyze the relationship between physicochemical factors and the occurrence of V. cholerae O1. RESULTS: Eleven V. cholerae O1 strains were successfully isolated from streams, storage tanks and wells during the study period. All isolates were resistant to one or more of the eight antibiotics used. Multidrug resistance was observed in over 97% of the isolates. All isolates had genes for at least one virulence factor. Vibrio cholerae toxin gene was detected in 82.4% of the isolates. Approximately 81.8% of the isolates were positive for tcpAEl Tor gene, but also harbored the tcpAcl gene. Isolates were grouped into thirteen genotypes based on the genes analyzed. High temperature, salinity, total dissolved solids and conductivity was found to significantly correlate positively with isolation of V. cholerae O1. V. cholerae serotype Ogawa biotype El tor is the main biotype circulating in Ghana with the emergence of a hybrid strain. CONCLUSIONS: Multidrug resistant V. cholerae O1 with different genotypes and pathogenicity are present in water sources and co-exist with non O1/O139 in the study area.

Cholera Outbreak in Dadaab Refugee Camp, Kenya - November 2015-June 2016.

Dadaab Refugee camp in Garissa County, Kenya, hosts nearly 340,000 refugees in five subcamps (Dagahaley, Hagadera, Ifo, Ifo2, and Kambioos) (1). On November 18 and 19, 2015, during an ongoing national cholera outbreak (2), two camp residents were evaluated for acute watery diarrhea (three or more stools in ≤24 hours); Vibrio cholerae serogroup O1 serotype Ogawa was isolated from stool specimens collected from both patients. Within 1 week of the report of index cases, an additional 45 cases of acute watery diarrhea were reported. The United Nations High Commissioner for Refugees and their health-sector partners coordinated the cholera response, community outreach and water, sanitation, and hygiene (WASH) activities; Médecins Sans Frontiéres and the International Rescue Committee were involved in management of cholera treatment centers; CDC performed laboratory confirmation of cases and undertook GIS mapping and postoutbreak response assessment; and the Garissa County Government and the Kenya Ministry of Health conducted a case-control study. To prevent future cholera outbreaks, improvements to WASH and enhanced disease surveillance systems in Dadaab camp and the surrounding area are needed.

Comparative genomics of Vibrio cholerae O1 isolated from cholera patients in Bangladesh.

Whole genome sequencing was utilized to investigate the genomic profile of Vibrio cholerae O1 strains, isolated from symptomatic patients in a low-income urban area of Dhaka, Bangladesh. Comparative genomics using bioinformatics tools were applied to identify major virulence factors, biotype and antimicrobial resistance genes in three V. cholerae O1 strains (VC-1, 2 and 3) isolated from two case patients. A phylogenetic SNP (single nucleotide polymorphism)-based analysis was conducted to infer the relatedness to V. cholerae O1 strains isolated elsewhere. The V. cholerae strains were the El Tor variant carrying ctxB1 (standard classical genotype). SNP-based global phylogeny revealed that the three isolates were strictly clonal and the closest neighbouring genomes were epidemic clones of V. cholerae O1 isolated in 2010 from cholera patients in Pakistan. All strains harboured the integrase gene of the SXT element (intSXT ), antimicrobial resistance genes for aminoglycosides, phenicol, sulphonamide and trimethoprim except VC-1 that lacked sulphonamide resistance genes. The multilocus sequence typing (MLST) revealed that the strains belonged to sequence type, ST69. The study provides knowledge on current genetic traits of clinical V. cholerae O1 circulating in urban household clusters of Bangladesh which may help in predicting emergence of new pandemic strains in Bangladesh. SIGNIFICANCE AND IMPACT OF THE STUDY: Vibrio cholerae has frequently experienced genetic changes with rapid evolution of pandemic clones in the Ganges Delta region. Whole genome sequencing can reveal genetic information of current pathogenic V. cholerae in Bangladesh which includes cefotaxime genotypes, virulence factors, altered antimicrobial resistance pattern as well as mobile genetic element compared to global pandemic strains. This study data could be used in planning future surveillance strategies in Ganges Delta region by informing new epidemiology of current outbreak strains.