Antimicrobial resistance and plasmid profile of Gram-positive and Gram-negative bacterial strains isolated from the urbanized Eltsovka-1 River (Russia) were investigated. Sequencing of the 16S rRNA of of G+ strains showed 99-100% identity to that of Bacillus aerophilus, Bacillus altitudinis, Bacillus amyloliquefaciens, Bacillus anthrancis, Bacillus barbaricus, Bacillus cereus, Bacillus flexus, Bacillus indriensis, Bacillus stratosphericus, Bacillus subtilis subsp. subtilis, Bacillus thuringiensis, Streptomyces albidoflavus, Streptomyces albus, Streptomyces exfoliatus, Streptomyces odorifer, and Streptomyces sampsonii. Sequencing of the 16S rRNA of G-strains was similar in 99-100% to that of Aeromonas bestiarum, Aeromonas encheleia, Aeromonas hydrophila, A. hydrophila subsp. anaerogenes, A. hydrophila subsp. dhakensis, Aeromonas media, Aeromonas molluscorum, Aeromonas popoffii, Aeromonas salmonicida subsp. masoucida, A. salmonicida subsp. pectinolytica, A. salmonicida subsp. salmonicida, Aeromonas punctata, Aeromonas sobria, and Shewanella putrefaciens. The highest percentage (88.4%) of strains was resistant to polymyxin B followed by 69% to lincomycin, 61.5% to benzilpenicillin, 57.7% to ampicillin, and 50% to carbenicillin. A low level of resistance (4%) was found to kanamycin (8%), to streptomycin (11.5%), to neomycin and tetracycline, and (15%) to erythromycin. No resistance was found to gentamycin, monomycin, and chloroamphenicol. The majority (80.7%) of strains was multidrug-resistant. Ninety-two percent of all strains carried plasmid DNA of various sizes.

Resistance to Ampicillin and Kanamycin displayed by heterotrophic bacteria isolated in Summer and in Spring from the littoral and the central parts of Lake Shira (a therapeutic lake in the Khakasia Republic, Russia) has been investigated. It has been found that in Summer, human and animal microflora featuring multiple antibiotic resistance (to Ampicillin and Kanamycin) predominates in all the studied stations of the littoral zone of the lake. In Spring, concentrations of bacteria featuring multiple antibiotic resistance decrease significantly and bacteria sensitive to antibiotics predominate in the lake. Emergence of multiple antibiotic resistance in bacteria of Lake Shira is caused by the input of allochthonous bacteria into the lake; this feature of heterotrophic bacteria of Lake Shira can be used to monitor the impact on the ecosystem made by health resorts.

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The study addresses the effect of abiotic (medium salinity and copper ions) and biotic (interactions between populations) factors on the formation of structured communities by binary associations consisting of halotolerant bacteria (Alcaligenes sp. 1-1 or Acinetobacter sp. 1-19) and a wild-type B. subtilis 2335 strain or a transgenic strain. The results showed that 250 mg l(-1) of copper ions inhibit formation of biofilms by monocultures of the tested strains. Binary associations of the strains were more resistant to high concentrations (250 mg l(-1)) of copper ions. At the lowest NaCl concentration (0.05% and 2.5%) and in the presence of copper ions, bacilli seemed to help halotolerant bacteria survive. Under increased salinity and in the presence of copper ions, structured communities developed due to halotolerant bacteria. Coexistence under stressful conditions was beneficial for the both groups of bacteria.

Studies were conducted to investigate the antibiotic resistance of freshwater, halophile and moderate halotolerant bacteria isolated from the nearshore part of Shira lake, which is affected by the activity of a health resort, and from the central part of the lake in the summer (June to August) of 1999. It has been shown that the allochthonous microflora, which is brought into the lake with the resort effluent in mid-summer, is the anthropogenic factor contributing to an increase in the number of freshwater bacteria that feature multiple antibiotic resistance in the central part of the lake. It has been found that resistance to ampicillin of freshwater and halophile heterotrophic bacteria is related to the increase in the biomass of blue-green and green algae in the central part of Shira lake between mid-July and the end of August. A mathematical model has been constructed to describe the dynamics of the antibiotic resistance of heterotrophic bacteria in the close-to-resort and the central parts of Shira lake under natural and anthropogenic impacts.KEY WORDS: Heterotrophic bacteria · Halotolerance · Antibiotic resistance · Anthropogenic load · Brackish lake · Mathematical modeling Resale or republication not permitted without written consent of the publisherAquat Microb Ecol 30: [11][12][13][14][15][16][17][18] 2002 upstream (Parnachev 1997). The result of all these processes may be a disturbance of the natural biodiversity of Shira lake.There are various ways to estimate the anthropogenic load on an ecosystem, including chemical analysis, bioindication, bioassays, etc. (Doust et al. 1994, Ostroumov 2000, Lindstron-Seppa et al. 2001, Samecka-Cymerman & Kempers 2001. Bacteria are often used to monitor the state of the environment (Jacobs et al. 1995, Schwedt et al. 1997, Backhaus & Grimme 1999, as their evolution rate is very high, and under the effect of environmental factors they can acquire various specific features, and thus, serve as good indicators for the presence of pollutants. One of the properties of bacteria used to assess the anthropogenic load is their antibiotic resistance (Hagedorn et al. 1999, Goni-Urriza et al. 2000, Mary et al. 2000, McArthur & Tuckfield 2000.Antibiotic resistance in bacteria can be determined both by chromosome genes and by extrachromosome genetic elements (R-plasmids) (Gomes-Lus 1998, Ho et al. 1998. The acquisition of antibiotic resistance is realized as an active process only under the conditions selective for such genes (Chandrasekaran et al. 1998, Guardabassi et al. 1998, Goni-Urriza et al. 2000. Thus, if antibiotic resistance is recorded in a great number of heterotrophic bacteria, a drastic change in the environmental conditions due to direct or indirect impact of non-natural factors may be assumed.The aim of this work is to investigate the dynamics of antibiotic resistance of heterotrophic bacteria varying in halotolerance in the central and the close-to-resort parts of Shira lake. In addition, we determine the relationship between antibiotic resistance of ...