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First-time characterization of viable but non-culturable Proteus mirabilis: Induction and resuscitation
Reham Wasfi1, Ghada Refaat Abdellatif2, Hisham Mohamed Elshishtawy3
1Department of Microbiology and Immunology, Faculty of Pharmacy, October University for Modern Sciences and Arts (MSA), Giza, Egypt.
Abstract:
Pathogenic bacteria can enter into a viable but non-culturable (VBNC) state under unfavourable conditions. Proteus mirabilis is responsible for dire clinical consequences including septicaemia, urinary tract infections and pneumonia, but is not a species previously known to enter VBNC state. We suggested that stress-induced P. mirabilis can enter a VBNC state in which it retains virulence. P. mirabilis isolates were incubated in extreme osmotic pressure, starvation, low temperature and low pH to induce a VBNC state. Resuscitation was induced by temperature upshift and inoculation in tryptone soy broth with Tween 20 and brain heart infusion broth. Cellular ultrastructure and gene expression were examined using transmission electron microscopy (TEM) and quantitative real-time polymerase chain reaction (qPCR), respectively. High osmotic pressure and low acidity caused rapid entry into VBNC state. Temperature upshift caused the highest percentage of resuscitation (93%) under different induction conditions. In the VBNC state, cells showed aberrant and dwarf morphology, virulence genes and stress response genes (envZ and rpoS) were expressed (levels varied depending on strain and inducing factors). This is the first-time characterization of VBNC P. mirabilis. The ability of P. mirabilis pathogenic strains to enter a stress-induced VBNC state can be a serious public health threat.
Insights
Proteus mirabilis can enter a viable but non-culturable (VBNC) state under stress, retaining virulence. This discovery highlights a potential public health threat from this opportunistic pathogen.
Area of Science:
- Microbiology
- Pathogen Research
- Bacterial Physiology
Background:
- Pathogenic bacteria can enter a viable but non-culturable (VBNC) state when exposed to unfavorable environmental conditions.
- Proteus mirabilis is a significant human pathogen causing severe infections, but its ability to enter the VBNC state was previously unknown.
Purpose of the Study:
- To investigate if stress conditions can induce a VBNC state in Proteus mirabilis.
- To characterize the virulence and gene expression of P. mirabilis in the VBNC state.
- To determine the resuscitation efficiency of VBNC P. mirabilis.
Main Methods:
- Induction of VBNC state in P. mirabilis using extreme osmotic pressure, starvation, low temperature, and low pH.
- Resuscitation experiments using temperature upshift and specific broth media.
- Analysis of cellular ultrastructure via transmission electron microscopy (TEM).
- Examination of gene expression using quantitative real-time polymerase chain reaction (qPCR).
Main Results:
- High osmotic pressure and low pH effectively induced the VBNC state in P. mirabilis.
- Temperature upshift was the most effective resuscitation method, achieving 93% recovery.
- VBNC P. mirabilis cells exhibited aberrant morphology and maintained expression of virulence and stress response genes (envZ, rpoS).
Conclusions:
- Proteus mirabilis can enter a stress-induced VBNC state, maintaining its virulence factors.
- This VBNC capability poses a potential public health risk due to the pathogen's clinical significance.
- This study provides the first characterization of VBNC P. mirabilis.
