Comparative survival of antibiotic-resistant and -sensitive fecal indicator bacteria in estuarine water

107

Differential decreases over time of two bacterial species, Escherichia coli and Enterococcus faecalis, in a freshwater and a marine ecosystem were observed and explained by a differential rate of digestion of these bacteria by phagotrophic flagellates and ciliates. For this purpose, fluorescence-labeled bacteria (FLB) were used and prepared from the two species cited above. The number of FLB was observed for 5 days in fresh and marine waters in the presence or absence (0.2-,unm-pore-size-filtered water) of natural microbiota. These experiments showed a longer persistence of Enterococcusfaecalis FLB as opposed to Escherichia coli FLB in the presence of natural microbiota. Removal of FLB was due to protozoan grazing because no decrease of FLB number was observed in the absence of natural microbiota. In short-term (about 40 min) ingestion experiments, we found similar clearance rates of Escherichia coli and Enterococcus faecalis FLB by assemblages of flagelates from the freshwater and the marine ecosystem and by cultured assemblages of ciliates from the marine ecosystem. Clearance rates of Enterococcus faecalis FLB were greater than those of Escherichia coli FLB for assemblages of ciliates from the freshwater ecosystem. Comparison of rates of ingestion and digestion of FLB by protozoa showed that Escherichia coli FLB were digested and ingested at similar rates. However, Enterococcusfaecalis FLB were digested slower than they were ingested. These results suggest that a longer persistence of Enterococcus faecalis as opposed to Escherichia coli can be explained by a differential digestion by flagellates and ciliates in aquatic ecosystems. Moreover, rates of ingestion and digestion were strongly correlated for both FLB types.

Section: Discussionmentioning

confidence: 99%

Differential Rates of Digestion of Bacteria by Freshwater and Marine Phagotrophic Protozoa

González

Iriberri

Egea

et al. 1990

107

“…Rif' E. coli K-12 demonstrated membrane protein changes and a decreased ability to colonize germfree mice when in competition with isogenic strains (13). Pettibone et al found that antibiotic-resistant derivatives of fecal indicator organisms displayed altered recovery from wild-type strains in studies of survival in estuarine waters (16). Some antibiotic-resistant mutants of Rhizobium spp.…”

Section: Discussionmentioning

confidence: 99%

“…Spontaneous antibiotic resistance has provided a potentially simple and effective method to genetically mark bacterial strains for monitoring after introduction into complex ecosystems. Such mutants are being used to study root nodulation and competition among symbiotic nitrogen-fixing strains of rhizobia (2,15), the survival of fecal indicator bacteria in waters (16) and soil (22), and the persistence of organisms of potential use in genetic engineering (10).…”

mentioning

confidence: 99%

Survival of rifampin-resistant mutants of Pseudomonas fluorescens and Pseudomonas putida in soil systems

Compeau

Al-Achi

Platsouka

et al. 1988

240

The fate of spontaneous chromosomal rifampin-resistant (Rifr) mutants of Pseudomonas putida and Pseudomonasfluorescens in sterile and live organic soil from which they were isolated was studied. In sterile native-soil assays, a Rifr mutant of P. putida showed no decrease in competitive fitness when compared with the wild-type parent. However, mutants of P. fluorescens were of two general categories. Group 1 showed no difference from the wild type in terms of growth rate, competitive fitness, and membrane protein composition. Group 2 showed a slower growth rate in both minimal and enriched media and an altered membrane protein profile. These mutants also demonstrated decreased competitive fitness compared with the wild-type strain. In live soil, the Rif' P. putida strain persisted throughout the 38-day test period with a decay rate of 0.7 log10 CFU/g of soil per 10 days. A group 1 Rifr p. fluorescens mutant maintained its inoculated titer for 7 to 10 days and then decayed at a rate of 0.2 to 0.4 loglo CFU/g of soil per 10 days. A group 2 Rifr P. fluorescens mutant remained at its titer for 1 to 5 days before decaying at a twoto threefold-faster rate. These findings indicate that rifampin resistance may not be an innocuous mutation in some pseudomonads and that marked strains should be compared with wild-type parents before being used as monitors of parental strain survival. Colonization of sterile soil with either the wild-type or mutant strain precluded normal colonization of the second added strain. These results suggest that there are limited sites for colonization of Pseudomonas species in these soils, a finding which may relate to the eventual fate of the introduced organisms.

“…These microorganisms have developed a complex physiological adaptation strategy that allows them to remain viable over long periods of nutrient deprivation (23,25). Enteric bacteria, introduced into this environment in wastewater effluents, can survive the high salt concentrations and nutrient deprivation for long periods but may not be able to multiply (2,13,28,31,33). The degree of survival depends on the strains of enteric bacteria involved (24,34).…”

mentioning

confidence: 99%

Conjugative Plasmid Transfer between Bacteria under Simulated Marine Oligotrophic Conditions

Goodman

Hild

Marshall

et al. 1993

Marine Vibrio S14 strains and an Escherichia coli strain were starved in artificial seawater (NSS) with no added carbon, nitrogen, or phosphorus. The broad-host-range plasmid RP1 was transferred between the starving S14 strains and also from the E. coli donor to the S14 recipient under oligotrophic conditions, in which mixtures of donor and recipient cells were held on Nuclepore filters either floated on NSS or held such that NSS flowed through the filter. Transconjugants were obtained from S14 donors and recipients starved for at least 15 days before being mixed together for conjugation, whereas transconjugants were recovered from the E. coli donor and S14 recipient for up to 3 days of prestarvation, but not after 5 days. Transconjugants were obtained when there were as few as about 105 and 104 cells of starving S14 donors and recipients, respectively, per ml held on the filters. Starved donor and recipient mixtures incubated at 4 or 26°C, as well as those allowed to mate for 2, 5, or 24 h, all yielded numbers of transconjugants which were not significantly (P > 0.05) different.