Many bacteria, including a variety of important human pathogens, are known to respond to various environmental stresses by entry into a novel physiological state, where the cells remain viable, but are no longer culturable on standard laboratory media. On resuscitation from this ‘viable but nonculturable’ (VBNC) state, the cells regain culturability and the renewed ability to cause infection. It is likely that the VBNC state is a survival strategy, although several interesting alternative explanations have been suggested. This review describes the VBNC state, the various chemical and physical factors known to induce cells into this state, the cellular traits and gene expression exhibited by VBNC cells, their antibiotic resistance, retention of virulence and ability to attach and persist in the environment, and factors that have been found to allow resuscitation of VBNC cells. Along with simple reversal of the inducing stresses, a variety of interesting chemical and biological factors have been shown to allow resuscitation, including extracellular resuscitation-promoting proteins, a novel quorum-sensing system (AI-3) and interactions with amoeba. Finally, the central role of catalase in the VBNC response of some bacteria, including its genetic regulation, is described.

Recent findings on the viable but nonculturable state in pathogenic bacteria.

In the last decades, attention to cholera epidemiology increased, as cholera epidemics became a worldwide health problem. Detailed investigation of V. cholerae interactions with its host and with other organisms in the environment suggests that cholera dynamics is much more complex than previously thought. Here, I formulate a mathematical model of cholera epidemiology that incorporates an environmental reservoir of V. cholerae. The objective is to explore the role of the aquatic reservoir on the persistence of endemic cholera as well as to define minimum conditions for the development of epidemic and endemic cholera.

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Endemic and epidemic dynamics of cholera: the role of the aquatic reservoir

The facultative human pathogen Vibrio cholerae can be isolated from estuarine and aquatic environments. V. cholerae is well recognized and extensively studied as the causative agent of the human intestinal disease cholera. In former centuries cholera was a permanent threat even to the highly developed populations of Europe, North America, and the northern part of Asia. Today, cholera still remains a burden mainly for underdeveloped countries, which cannot afford to establish or to maintain necessary hygienic and medical facilities. Especially in these environments, cholera is responsible for significant mortality and economic damage. During the last three decades, intensive research has been undertaken to unravel the virulence properties and to study the epidemiology of this significant human pathogen. More recently, researchers have been elucidating the environmental lifestyle of V. cholerae. This review provides an overview of the current knowledge of both the host- and environment-specific physiological attributes of V. cholerae.

Vibrio cholerae and cholera: Out of the water and into the host

It has long been realized that plate counts can dramatically underestimate the total number of bacteria (typically determined by direct microscopic examination) present in samples taken from natural environments. In the late 1970s, several easily performed noncultural methods (Zimmerman et al., 1978; Kogure et al., 1979) for determining cell viability allowed confirmation of earlier microautoradiographic studies (e.g., Hoppe, 1976) which demonstrated that many of these nonculturable cells are indeed viable and able to actively metabolize. Such studies led to the further realization that some bacteria, in response to certain environmental stresses, may lose the ability to grow on media on which they are routinely cultured, while remaining viable. This state is of considerable interest to our understanding of microbial ecology. It is of special concern when considering release into the environment of genetically engineered microorganisms, and for those indicator bacteria (e.g., coliforms) and human pathogens which enter this nonculturable state and are thus not detectable through routine bacteriological procedures.

Formation of Viable but Nonculturable Cells

1. Semantics and Strategies 2. Morphological Changes Leading to the Nonculturable State 3. Size Matters: Dwarf Cells in Soil and Subsurface Terrestrial Environments 4. Membrane Bioenergetics in Reference to Marine Bacterial Culturability 5. Diversity of Uncultured Microorganisms in the Environment 6. Molecular Genetic Methods for Detection of Viable but Nonculturable Organisms 7. Environmental Parameters Associated with the Viable but Nonculturable State 8. Starved and Nonculturable Microorganisms in Biofilms 9. Phenotyic Plasticity in Bacterial Biofilms as it Affects Issues of Viability and Culturability 10. Survival, Dormancy and Nonculturable Cells in Extreme Deep-Sea Environments 11. Bacterial Viruses and Hosts: Influence of Culturable State 12. The Importance of Viable but Nonculturable Bacteria in Biogeochemistry 13. Viable but Nonculturable Cells in Plant-Associated Bacterial Populations 14. Implications of the Viable but Nonculturable State in Risk Assessment Based on Field Testing for Genetically Engineered Microorganisms 15. Chemical Disinfection and Injury of Bacteria in Water 16. The Public Health Significance of Viable but Nonculturable Bacteria 17. Epidemiological Significance of Viable but Nonculturable Microorganisms 18. Bacterial Death Revisited

Nonculturable Microorganisms in the Environment

Epidemiological studies of shigellosis in Bangladesh have demonstrated that surface-water sources can act as foci of infection. Studies of laboratory microcosms have shown that shigellae become nonculturable but remain viable when exposed to environmental samples of water. The present study was carried out to detect viable but nonculturable Shigella dysenteriae 1 from laboratory microcosms by the polymerase chain reaction and the fluorescent-antibody techniques. S. dysenteriae 1 was inoculated into laboratory microcosms consisting of water samples collected from ponds, lakes, rivers, and drains in Bangladesh. The survival of S. dysenteriae in microcosms was assessed by viable counting on MacConkey agar. After 2 to 3 weeks, S. dysenteriae 1 became nonculturable but remained viable. After 6 weeks, this nonculturable but viable S. dysenteriae 1 was detected by both the polymerase chain reaction and the fluorescent-antibody methods. The viable but nonculturable state of S. dysenteriae 1 demonstrated in this study may be important for understanding the epidemiology of shigellosis.

https://aem.asm.org/content/aem/59/2/536.full.pdf

Use of the polymerase chain reaction and fluorescent-antibody methods for detecting viable but nonculturable Shigella dysenteriae type 1 in laboratory microcosms

Detection of non-culturable Vibrio cholerae O1 associated with a cyanobacterium from an aquatic environment in Bangladesh.

The protection against emerging SARS-CoV-2 variants by pre-existing antibodies elicited due to the current vaccination or natural infection is a global concern. We aimed to investigate the rate of SARS-CoV-2 infection and its clinical features among infection-naïve, infected, vaccinated, and post-infection-vaccinated individuals. A cohort was designed among icddr,b staff registered for COVID-19 testing by real-time reverse transcriptase-polymerase chain reaction (rRT-PCR). Reinfection cases were confirmed by whole-genome sequencing. From 19 March 2020 to 31 March 2021, 1644 (mean age, 38.4 years and 57% male) participants were enrolled; where 1080 (65.7%) were tested negative and added to the negative cohort. The positive cohort included 750 positive patients (564 from baseline and 186 from negative cohort follow-up), of whom 27.6% were hospitalized and 2.5% died. Among hospitalized patients, 45.9% had severe to critical disease and 42.5% required oxygen support. Hypertension and diabetes mellitus were found significantly higher among the hospitalised patients compared to out-patients; risk ratio 1.3 and 1.6 respectively. The risk of infection among positive cohort was 80.2% lower than negative cohort (95% CI 72.6-85.7%; p < 0.001). Genome sequences showed that genetically distinct SARS-CoV-2 strains were responsible for reinfections. Naturally infected populations were less likely to be reinfected by SARS-CoV-2 than the infection-naïve and vaccinated individuals. Although, reinfected individuals did not suffer severe disease, a remarkable proportion of naturally infected or vaccinated individuals were (re)-infected by the emerging variants. 

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COVID-19 reinfections among naturally infected and vaccinated individuals

Currently, Bangladesh is experiencing an epidemic of acute watery diarrhea caused by Vibrio cholerae O139 Surface waters were collected and cultured for vibrious following enrichment Twelve percent (11 of 92) of samples yielded V cholerae O139, and all of them were positive for cholera toxin The data suggest that V cholerae O139 is easily culturable from surface water samples Images

Mojnu Miah

Papers

Use of the polymerase chain reaction and fluorescent-antibody methods for detecting viable but nonculturable Shigella dysenteriae type 1 in laboratory microcosms

Detection of non-culturable Vibrio cholerae O1 associated with a cyanobacterium from an aquatic environment in Bangladesh.

COVID-19 reinfections among naturally infected and vaccinated individuals

Isolation of Vibrio cholerae O139 synonym Bengal from the aquatic environment in Bangladesh: implications for disease transmission.

Isolation of Vibrio cholerae 0139 Bengal from water In Bangladesh