Abstract
Persistence phenotype and small colony variants (SCVs) can be part of a bacterial bet-hedging strategy for survival under environmental stresses, such as antimicrobial exposure. These phenotypes are of particular concern in persistent and relapsing infections, since cells resume to normal growth after cessation of the stressful condition. In this context, we found persisters and unstable SCVs as phenotypic variants of Salmonella enterica that were able to survive ciprofloxacin exposure. A high heterogeneity in persister levels was observed among S. enterica isolates grown under planktonic and biofilm conditions and exposed to ciprofloxacin or ceftazidime, which may indicate persistence as a non-multidrug-tolerant phenotype. Nevertheless, a comparable variability was not found in the formation of SCVs among the isolates. Indeed, similar proportions of SCV in relation to normal colony phenotype (NCP) were maintained even after three successive cycles of ciprofloxacin exposure testing colonies from both origins (SCV or NCP). Additionally, we found filamentous and dividing cells in the same scanning electron microscopy images from both SCV and NCP. These findings lead us to hypothesize that besides variability among isolates, a single isolate may generate distinct populations of persisters, where cells growing under distinct conditions may adopt different and perhaps complementary survival strategies.
Highlights
Salmonella enterica comprises pathogens adapted to infect and survive inside human and animal epithelial and phagocytic cells[1,2], including some non-host adapted serovars that are among the most important zoonotic pathogens worldwide
S. enterica isolates were characterized as weak biofilm producers after growth in polystyrene microplates for 48 h, and cell densities ranged from 6.1 × to 3.9 × CFU (Supplementary Tables S1 and S2)
Persister cells were detected in all S. enterica isolates after 72-h exposure to high concentrations of ciprofloxacin or ceftazidime in both planktonic and biofilm cultures
Summary
Biofilm intensity and minimum inhibitory concentration to ciprofloxacin and ceftazidime. Persister cells were detected in all S. enterica isolates after 72-h exposure to high concentrations of ciprofloxacin or ceftazidime in both planktonic and biofilm cultures. A high heterogeneity in persister levels was found among S. enterica isolates when cultured under the same conditions and exposed to a same antimicrobial, especially planktonically grown cells exposed to ciprofloxacin (Fig. 3A,C and Supplementary Tables S1 and S2). Taking together the persister fractions from all isolates, it was possible to notice higher levels of persisters in biofilms compared to planktonic cultures, and in both of those exposed to ciprofloxacin (p < 0.001) or ceftazidime (p < 0.05) (Fig. 4). When analysing the persister levels during 72-h ciprofloxacin exposure in each cycle for both isolates, we detected similar fractions from cells growing as SCVs or NCPs, regardless of their source (Fig. 5 and Table 2). An extracellular substance was noticed circumventing SCVs cells obtained from planktonic culture (Fig. 6C,D), and filamentous cells were observed in SCVs and NCPs from both planktonic and biofilm cultures
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
