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Adherence and intracellular survival within human macrophages of Enterococcus faecalis isolates from coastal marine
Raffaella Sabatino1, Andrea Di Cesare2, Sonia Pasquaroli3
1Department of Biomolecular Sciences, Section of Biochemistry and Molecular Biology, Università degli Studi "Carlo Bo", via A. Saffi 2, 61029, Urbino, Italy; Istituto Auxologico Italiano, Neurobiology Laboratory, Strada Cadorna 90, 28824, Piancavallo di Oggebbio, Italy.
Abstract:
Enterococcus faecalis is part of the human intestinal microbiota and an important nosocomial pathogen. It can be found in the marine environment, where it is also employed as a fecal indicator. To assess the pathogenic potential of marine E. faecalis, four strains isolated from marine sediment were analyzed for their ability to survive in human macrophages. Escherichia coli DH5α was used as a negative control. The number of adherent and intracellular bacteria was determined 2.5 h after the infection (T0) and after further 24h (T24) by CFU and qPCR counts. At T24 adherent and intracellular enterococcal CFU counts were increased for all strains, the increment in intracellular bacteria being particularly marked. No CFU of E. coli DH5α were detected. In contrast, qPCR counts of intracellular enterococcal and E. coli bacteria were similar at both time points. These findings suggest that whereas E. coli was killed within macrophages (no CFU, positive qPCR), the E. faecalis isolates not only escaped killing, but actually multiplied, as demonstrated by the increase in the viable cell population. These findings support earlier data by our group, further documenting that marine sediment can be a reservoir of pathogenic enterococci.
Insights
Marine Enterococcus faecalis strains survived and multiplied within human macrophages, unlike E. coli. Marine sediment may harbor pathogenic enterococci, posing a potential health risk.
Area of Science:
- Microbiology
- Environmental Science
- Immunology
Background:
- Enterococcus faecalis is a human gut microbe and a significant nosocomial pathogen.
- Marine environments harbor E. faecalis, where it serves as a fecal indicator organism.
- The pathogenic potential of marine-derived E. faecalis requires further investigation.
Purpose of the Study:
- To evaluate the pathogenic capacity of marine Enterococcus faecalis strains.
- To determine the survival and proliferation of marine E. faecalis within human macrophages.
- To compare the intracellular survival of marine E. faecalis with a control bacterium, Escherichia coli.
Main Methods:
- Four strains of marine E. faecalis isolated from sediment were used.
- Human macrophages were infected with E. faecalis and Escherichia coli DH5α (control).
- Bacterial survival was quantified using Colony Forming Units (CFU) and quantitative Polymerase Chain Reaction (qPCR) at 2.5h (T0) and 24h (T24).
Main Results:
- Marine E. faecalis strains demonstrated increased adherent and intracellular CFU counts at T24.
- Intracellular viable cell populations of E. faecalis significantly increased from T0 to T24.
- Escherichia coli DH5α showed no detectable CFU at T24, indicating cell death, despite similar qPCR counts.
- qPCR indicated similar intracellular bacterial loads for both E. faecalis and E. coli at both time points.
Conclusions:
- Marine E. faecalis isolates are capable of surviving and multiplying within human macrophages.
- E. faecalis exhibits distinct intracellular survival mechanisms compared to E. coli within macrophages.
- Marine sediment represents a potential reservoir for pathogenic enterococci with implications for public health.
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