Intramacrophage survival of uropathogenic Escherichia coli: differences between diverse clinical isolates and between
Nilesh J Bokil1, Makrina Totsika, Alison J Carey
1The University of Queensland, Institute for Molecular Bioscience, Qld 4072, Australia.
Abstract:
Uropathogenic E. coli (UPEC) are the primary cause of urinary tract infections. Recent studies have demonstrated that UPEC can invade and replicate within epithelial cells, suggesting that this bacterial pathogen may occupy an intracellular niche within the host. Given that many intracellular pathogens target macrophages, we assessed the interactions between UPEC and macrophages. Colonization of the mouse bladder by UPEC strain CFT073 resulted in increased expression of myeloid-restricted genes, consistent with the recruitment of inflammatory macrophages to the site of infection. In in vitro assays, CFT073 was able to survive within primary mouse bone marrow-derived macrophages (BMM) up to 24h post-infection. Three additional well-characterized clinical UPEC isolates associated with distinct UTI symptomatologies displayed variable long-term survival within BMM. UPEC strains UTI89 and VR50, originally isolated from patients with cystitis and asymptomatic bacteriuria respectively, showed elevated bacterial loads in BMM at 24h post-infection as compared to CFT073 and the asymptomatic bacteriuria strain 83972. These differences did not correlate with differential effects on macrophage survival or initial uptake of bacteria. E. coli UTI89 localized to a Lamp1(+) vesicular compartment within BMM. In contrast to survival within mouse BMM, intracellular bacterial loads of VR50 were low in both human monocyte-derived macrophages (HMDM) and in human T24 bladder epithelial cells. Collectively, these data suggest that some UPEC isolates may subvert macrophage anti-microbial pathways, and that host species differences may impact on intracellular UPEC survival.
Insights
Uropathogenic E. coli (UPEC) can survive inside macrophages, suggesting a potential intracellular niche. Different UPEC strains exhibit variable survival within macrophages, indicating possible subversion of host defenses.
Area of Science:
- Microbiology
- Immunology
- Pathogen-host interactions
Background:
- Uropathogenic E. coli (UPEC) are a leading cause of urinary tract infections (UTIs).
- UPEC's ability to invade and replicate within host epithelial cells suggests an intracellular lifestyle.
- Intracellular pathogens often target macrophages, prompting investigation into UPEC-macrophage interactions.
Purpose of the Study:
- To investigate the interactions between UPEC and macrophages.
- To determine if UPEC can survive within macrophages and if this varies between strains.
- To explore potential mechanisms of UPEC intracellular survival and host species differences.
Main Methods:
- In vitro infection assays using primary mouse bone marrow-derived macrophages (BMM) and human monocyte-derived macrophages (HMDM).
- Infection assays using human T24 bladder epithelial cells.
- Assessment of bacterial loads within host cells at various time points post-infection.
- Analysis of UPEC strain localization within host cells (e.g., Lamp1+ vesicles).
- Monitoring of host cell survival and bacterial uptake.
Main Results:
- UPEC strain CFT073 survived within mouse BMM up to 24 hours post-infection.
- Clinical UPEC isolates showed variable long-term survival within BMM.
- UPEC strains UTI89 and VR50 demonstrated higher bacterial loads in BMM compared to CFT073 and 83972 at 24 hours.
- Differences in survival did not correlate with host cell death or initial bacterial uptake.
- UPEC UTI89 localized to a Lamp1+ compartment within BMM.
- Intracellular VR50 loads were low in human macrophages and bladder epithelial cells.
Conclusions:
- Some UPEC strains may evade or subvert macrophage antimicrobial mechanisms.
- Host species (mouse vs. human) significantly influences intracellular UPEC survival.
- UPEC's intracellular survival in macrophages represents a potential virulence factor in UTIs.
