Many bacterial species have been found to exist in a viable but non-culturable (VBNC) state since its discovery in 1982. VBNC cells are characterized by a loss of culturability on routine agar, which impairs their detection by conventional plate count techniques. This leads to an underestimation of total viable cells in environmental or clinical samples, and thus poses a risk to public health. In this review, we present recent findings on the VBNC state of human bacterial pathogens. The characteristics of VBNC cells, including the similarities and differences to viable, culturable cells and dead cells, and different detection methods are discussed. Exposure to various stresses can induce the VBNC state, and VBNC cells may be resuscitated back to culturable cells under suitable stimuli. The conditions that trigger the induction of the VBNC state and resuscitation from it are summarized and the mechanisms underlying these two processes are discussed. Last but not least, the significance of VBNC cells and their potential influence on human health are also reviewed.

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The importance of the viable but non-culturable state in human bacterial pathogens.

The ability of probiotic bacteria to adhere to the intestinal epithelium play an important role in colonization of the gastrointestinal tract, preventing their elimination by peristalsis and providing a competitive advantage in this ecosystem. To identify bacterial traits related to adhesion the probiotic strain L. acidophilus M92 was examined for autoaggregation ability and cell surface hydrophobicity L. acidophilus M92 exhibits a strong autoaggregation phenotype and also coaggregation with some pathogen microorganisms that may form a barrier that prevents their colonization. The examined probiotic strain manifests a good degree of hydrophobicity determined by microbial adhesion to hydrocarbons. Aggregation and hydrophobicity were abolished upon exposure of the cells to pronase, which suggests the possible role of cell surface layer (S-layer) proteins, approximated at 45 kDa, in a L. acidophilus M92. The relationship between autoaggregation and adhesion ability to intestinal tissue was investigated by observing the adhesivity of L. acidophilus M92 to porcine ileal epithelial cells. Removal of the S-layer proteins by extraction with 5 M LiCl reduced autaggregation and in vitro adhesion of this strain.

Adhesion and aggregation ability of probiotic strain Lactobacillus acidophilus M92

https://jcp.bmj.com/content/jclinpath/33/9/907.1.full.pdf

Principles and Practice of Infectious Diseases

Prosthetic Joint Infections

Like for all microbes, the goal of every pathogen is to survive and replicate. However, to overcome the formidable defenses of their hosts, pathogens are also endowed with traits commonly associated with virulence, such as surface attachment, cell or tissue invasion, and transmission. Numerous pathogens couple their specific virulence pathways with more general adaptations, like stress resistance, by integrating dedicated regulators with global signaling networks. In particular, many of nature's most dreaded bacteria rely on nucleotide alarmones to cue metabolic disturbances and coordinate survival and virulence programs. Here we discuss how components of the stringent response contribute to the virulence of a wide variety of pathogenic bacteria.

ppGpp Conjures Bacterial Virulence

Stress response and pathogenic potential of Campylobacter jejuni cells exposed to starvation

Listeria monocytogenes has been recognized as a significant pathogen, occurring worldwide, capable of causing animal and human infections. In its most severe form, listeriosis is an invasive disease that affects immunocompromised patients. Additionally, pregnant women represent a high-risk group for L. monocytogenes infection. Abortion, stillbirth or severe neonatal infection can be the serious outcome of such an infection. In an experimental murine model of pregnancy-associated listeriosis we studied the impact of L. monocytogenes on the maternal immune response and pregnancy outcome. In comparison to virgin animals, pregnant mice mounted lower levels of protective cytokines and were inable to eliminate the pathogen. The impaired maternal immune response that has been found both on the systemic and local level, faciliated bacterial multiplication in the liver, placenta and ultimately in the fetal tissues. This resulted in severe necrotizing hemorrhagic hepatitis and Listeria-induced placental necrosis, increasing the incidence of postimplantation loss and poor pregnancy outcome.

Murine model of pregnancy-associated Listeria monocytogenes infection

Background: Exposure to microorganisms elicts the production of cytokines. These soluble factors enhance several innate immune functions and regulate the ensuing specific immune response aimed at limiting the spread of infection. Aim: This study was undertaken to quantify the plasma levels of pro-inflammatory cytokines during the course of primary Listeria monocytogenes and Campylobacter jejuni infection. Using an in vivo infection the relationship between endogenous cytokines and the bacterial number in the liver of infected animals was examined. Methods: C57BL/6 mice were infected by the intraperitoneal route. At different time points we determined the number of colony-forming units of bacteria in the liver of infected animals and paralled these with the plasma levels of interferon-gamma (IFN-g ), tumor necrosis factor-alpha (TNF-a ) and interleukin6 (IL-6) measured by enzyme immunoassays. Results: L. monocytogenes infection lasted 10‐11 days. IFN-g production occurred in the early phase but was more pronounced after day 4, following the appearance of specific immunity. The duration of experimental campylobacteriosis was 15 days. Early IFN-g production was not significant but a progressive rise of this cytokine in plasma was seen during the second week post infection. Mice produced measurable amounts of plasma TNF-a immediately after being given viable L. monocytogenes, peaking on day 2‐3 when the greatest number of bacteria was present in the examined organs. During C. jejuni infection plasma TNF-a was produced in a similar manner, but the highest concentrations were found a few days later than in listeriosis, in correlation with the different course of campylobacteriosis. The quantity of IL-6 increased and decreased in concordance with clearance of L. monocytogenes and the clinical status of the animals. C. jejuni did not promote the induction of this cytokine. This is to some extent an unusual finding. With respect to the role of IL-6 in Th2 responses and antibody production, the appearance of this cytokine in campylobacteriosis was more expected. Discussion: During systemic bacterial infection, a network of pro-inflammatory cytokines is activated and blood levels of these cytokines are elevated, albeit inconsistently, with large individual variations and depending on microbial characteristics and structure.

/pdf/plasma-cytokine-response-in-mice-with-bacterial-infection-59a2qq157o.pdf

Plasma cytokine response in mice with bacterial infection.

PrimaryCampylobacter jejuniinfection in different mice strains

The impact of L. monocytogenes infection on maternal immune responses as well as on the outcome of pregnancy was studied in a murine model of pregnancy-associated listeriosis. Mice infected i.v. with L. monocytogenes at day 15 of pregnancy showed a significantly impaired bacterial elimination, which resulted in a severe necrotizing hemorrhagic hepatitis. The aggravated course of the infection could be attributed to a suppressed transcription and production of anti-listerial, pro-inflammatory cytokines and chemokines, namely interferon-gamma, tumor necrosis factor, interleukin-12p40, inducible nitric oxide synthase, murine monokine induced by interferon-gamma, and interferon-gamma-inducible protein-10. In addition, listeriosis significantly increased the abortion rate. Infection of the placenta and fetuses was characterized by placental and fetal necrosis with unrestricted bacterial multiplication. A weak transcription of anti-listerial cytokines in the placenta in the absence of a cellular immune response could not prevent the fatal outcome of pregnancy-associated listeriosis.

Effects of pregnancy-associated Listeria monocytogenes infection: necrotizing hepatitis due to impaired maternal immune response and significantly increased abortion rate

Darinka Vučković

Papers

Stress response and pathogenic potential of Campylobacter jejuni cells exposed to starvation

Murine model of pregnancy-associated Listeria monocytogenes infection

Plasma cytokine response in mice with bacterial infection.

PrimaryCampylobacter jejuniinfection in different mice strains

Effects of pregnancy-associated Listeria monocytogenes infection: necrotizing hepatitis due to impaired maternal immune response and significantly increased abortion rate