Antibiotic resistance in Acinetobacter spp. isolated from sewers receiving waste effluent from a hospital and a pharmaceutical plant

Antibiotic resistance of E. coli in sewage and sludge

The aim of the study is the evaluation of resistance patterns of E. coli in wastewater treatment plants without an evaluation of basic antibiotic resistance mechanisms. Investigations have been done in sewage, sludge and receiving waters from three different sewage treatment plants in southern Austria. A total of 767 E. coli isolates were tested regarding their resistance to 24 different antibiotics. The highest resistance rates were found in E. coli strains of a sewage treatment plant which treats not only municipal sewage but also sewage from a hospital. Among the antimicrobial agents tested, the highest resistance rates in the penicillin group were found for Ampicillin (AM) (up to 18%) and Piperacillin (PIP) (up to 12%); in the cephalosporin group for Cefalothin (CF) (up to 35%) and Cefuroxime-Axetil (CXMAX) (up to 11%); in the group of quinolones for Nalidixic acid (NA) (up to 15%); and for Trimethoprime/Sulfamethoxazole (SXT) (up to 13%) and for Tetracycline (TE) (57%). Median values for E. coli in the inflow (crude sewage) of the plants were between 2.0 x 10(4) and 6.1 x 10(4)CFU/ml (Coli ID-agar, BioMerieux 42017) but showed a 200-fold reduction in all three plants in the effluent. Nevertheless, more than 10(2)CFU E. coli/ml reached the receiving water and thus sewage treatment processes contribute to the dissemination of resistant bacteria in the environment.

Impact of integrated fish farming on antimicrobial resistance in a pond environment

Integrated fish farming combines livestock production with fish farming. Animal manure is shed directly into a fish pond as fertilizer and supports the growth of photosynthetic organisms. The livestock, mainly chickens and pigs, is often fed feed containing growth promoters. In this study we investigated the impact of integrated fish farming on the levels of antimicrobial-resistant bacteria in a pond environment. One integrated broiler chicken-fish farm was studied for 2 months immediately after the start of a new fish production cycle. A significant increase over time in the resistance to six different antimicrobials was found for the indicator organism Acinetobacter spp. isolated from composite water-sediment samples. The initial resistance levels prior to the new production cycle were 1 to 5%. After 2 months the levels of resistance to oxytetracycline and sulfamethoxazole reached 100%, and the levels of resistance to ciprofloxacin were more than 80%. The long-term effects of resistance on integrated farming were studied on seven additional farms. The resistance levels were particularly high among Enterococcus spp. and were also high among Acinetobacter spp. isolated from water-sediment samples compared to the resistance levels at four control farms. In conclusion, integrated fish farming seems to favor antimicrobial-resistant bacteria in the pond environment. This could be attributed to the selective pressure of antimicrobials in the pond environment and/or to the introduction of antimicrobial-resistant bacteria from animal manure. Potential risks to human health were not addressed in this study and remain to be elucidated.

Antibiotic resistance in soil and water environments

Seven locations were screened for antibiotic-resistant bacteria using a modified agar dilution technique. Isolates resistant to high levels of antibiotics were screened for r plasmids. Low-level resistance (25 micro g x ml(-1)) was widespread for ampicillin, penicillin, tetracycline, vancomycin and streptomycin but not for kanamycin. Resistant populations dropped sharply at high antibiotic levels, suggesting that intrinsic non-emergent mechanisms were responsible for the multiple drug resistance exhibited at low doses. Dairy farm manure contained significantly (P < 0.01) more (%) resistant bacteria than the other sites. Bacteria isolated from a dairy water canal, a lake by a hospital and a residential garden (fertilized by farm manure) displayed resistance frequencies of 77, 75 and 70%, respectively. Incidence of tetracycline resistance was most prevalent at 47-89% of total bacteria. Out of 200 representative isolates analyzed, Pseudomonas, Enterococcus-like bacteria, Enterobacter and Burkholderia species constituted the dominant reservoirs of resistance at high drug levels (50-170 micro g x ml(-1)). Plasmids were detected in only 29% (58) of these bacteria with tetracycline resistance accounting for 65% of the plasmid pool. Overall, resistance trends correlated to the abundance and type of bacterial species present in the habitat. Environmental reservoirs of resistance include opportunistic pathogens and constitute some public health concern.

Generally overlooked fundamentals of bacterial genetics and ecology

Several important aspects of the antimicrobial resistance problem have not been treated extensively in previous monographs on this subject. This section very briefly updates information on these topics and suggests how this information is of value in assessing the contributions of human and agricultural use of antimicrobial agents on the problem of increasing antimicrobial resistance. The overall themes are (1) that propagation of resistance is an ecological problem, and thus (2) that ameliorating this problem requires recognition of long-established information on the commensal microbiota of mammals, as well as that of recent molecular understanding of the genetic agents involved in the movement of resistance genes.

The effects of tertiary wastewater treatment on the prevalence of antimicrobial resistant bacteria

The effects of tertiary wastewater treatment on the prevalence of antimicrobial resistant bacteria were investigated in two large-scale municipal treatment plants during a period of six months. Total and relative numbers of resistant bacteria were determined in raw sewage, treated sewage and anaerobically digested sludge by bacteriological counts on media selective for coliforms (MacConkey agar) and Acinetobacter spp. (Baumann agar). In addition, the level of antimicrobial susceptibility was determined by the disc-diffusion method in 442 Acinetobacter isolates identified by colony hybridisation with a genus-specific DNA probe. Independent of the different antibiotics and media used, the total numbers of resistant bacteria in treated sewage were 10-1000 times lower than in raw sewage. Based on linear regression analysis of data on bacteriological counts, the prevalences of antimicrobial-resistant presumptive coliforms and Acinetobacter spp. in treated sewage and digested sludge were not significantly higher compared with raw sewage. On the contrary at one plant, statistically significant decreases were observed in the prevalence of ampicillin-resistant presumptive Acinetobacter spp. (p = 0.0188) following sewage treatment, and in the prevalence of either ampicillin-resistant presumptive Acinetobacter spp. (p = 0.0013) or ampicillin- and gentamicin-resistant presumptive coliforms (p = 0.0273 and p = 0.0186) following sludge treatment. The results obtained by bacteriological counts were confirmed by antimicrobial susceptibility testing of Acinetobacter isolates. Based on logistic regression analysis, isolates from treated sewage and digested sludge were generally not significantly more resistant compared with isolates from raw sewage. Based on these evidences, it was concluded that tertiary wastewater treatment did not result in a selection of antimicrobial resistant bacteria.

Analysis of oxytetracycline, tetracycline, and chlortetracycline in water using solid-phase extraction and liquid chromatography-tandem mass spectrometry

A method using liquid chromatography-tandem mass spectrometry has been developed for determination of trace levels of tetracycline antibiotics in ground water and confined animal feeding operation waste water. Oxytetracycline (OTC), tetracycline (TC), and chlortetracycline (CTC) were extracted from water samples using both polymeric and C18 extraction cartridges. The addition of a buffer containing potassium phosphate and citric acid improved tetracycline recoveries in lagoon water. Method detection limits determined in reagent water fortified with 1 microg l(-1) OTC, TC, and CTC were 0.21, 0.20, and 0.28 microg l(-1). Method detection limits in lagoon water samples fortified at 20 microg l(-1) for OTC, TC, and CTC were 3.6, 3.1, and 3.8 microg l(-1). Variability in recovery from laboratory fortified blanks ranged from 86 to 110% during routine analysis.

Comparison of the antimicrobial tolerance of oxytetracycline-resistant heterotrophic bacteria isolated from hospital sewage and freshwater fishfarm water in Belgium

The aim of this study was to investigate the relationship between antimicrobial tolerance and taxonomic diversity among the culturable oxytetracycline-resistant (Ot(r)) heterotrophic bacterial population in two Belgian aquatic sites receiving wastewater either from human medicine or from aquaculture. The study of Ot(r) heterotrophs and mesophilic Aeromonas spp. allowed comparison of tolerance data at the intergenus as well as at the intragenus level. In total, 354 independently obtained Ot(r) isolates were subjected to antimicrobial tolerance testing and identified by GLC analysis of their cellular fatty acid methyl esters (FAMEs), by API 20E profiling and/or by Fluorescent Amplified Fragment Length Polymorphism (FAFLP) DNA fingerprinting. In general, Ot(r) hospital heterotrophs displayed a higher frequency (84%) of ampicillin (Amp) tolerance compared to the Ot(r) heterotrophs from the freshwater fishfarm site (22%). FAME results indicated that this effect was linked to the predominance of intrinsically ampicillin-resistant Ot(r) Aeromonas strains over representatives of Acinetobacter and Escherichia coli within the hospital strain set. Among the Ot(r) mesophilic Aeromonas strain set, the global tolerance profiles of the two sites only differed in a higher number of kanamycin (Kan) -tolerant strains (43%) for hospital aeromonads in comparison with the fishfarm aeromonads (8%). To some extent, this finding was correlated with the specific presence of Aeromonas caviae DNA hybridisation group (HG) 4. Collectively, these results suggest that the profiles for Amp and Kan tolerance observed in both sites arose from taxonomic differences in the culturable Ot(r) bacterial population at the generic or subgeneric level. In addition, our identification data also revealed that Enterobacter sp., Stenotrophomonas maltophilia, and A. veronii biovar sobria HG8 may be considered potential indicator organisms to assess microbial tolerance in various compartments of the aquatic environment.

Minimization and management of wastes from biomedical research

Several committees were established by the National Association of Physicians for the Environment to investigate and report on various topics at the National Leadership Conference on Biomedical Research and the Environment held at the 1--2 November 1999 at the National Institutes of Health in Bethesda, Maryland. This is the report of the Committee on Minimization and Management of Wastes from Biomedical Research. Biomedical research facilities contribute a small fraction of the total amount of wastes generated in the United States, and the rate of generation appears to be decreasing. Significant reductions in generation of hazardous, radioactive, and mixed wastes have recently been reported, even at facilities with rapidly expanding research programs. Changes in the focus of research, improvements in laboratory techniques, and greater emphasis on waste minimization (volume and toxicity reduction) explain the declining trend in generation. The potential for uncontrolled releases of wastes from biomedical research facilities and adverse impacts on the general environment from these wastes appears to be low. Wastes are subject to numerous regulatory requirements and are contained and managed in a manner protective of the environment. Most biohazardous agents, chemicals, and radionuclides that find significant use in research are not likely to be persistent, bioaccumulative, or toxic if they are released. Today, the primary motivations for the ongoing efforts by facilities to improve minimization and management of wastes are regulatory compliance and avoidance of the high disposal costs and liabilities associated with generation of regulated wastes. The committee concluded that there was no evidence suggesting that the anticipated increases in biomedical research will significantly increase generation of hazardous wastes or have adverse impacts on the general environment. This conclusion assumes the positive, countervailing trends of enhanced pollution prevention efforts by facilities and reductions in waste generation resulting from improvements in research methods will continue.

Characterization of oxytetracycline-resistant heterotrophic bacteria originating from hospital and freshwater fishfarm environments in England and Ireland

This ecotaxonomic study compared the antibiotic tolerance among culturable oxytetracyline-resistant (Ot(r)) heterotrophic strains isolated from two aquatic environments representing human activities in health care and aquaculture, namely hospital effluents and freshwater fishfarms. Using a standardized methodology, samples taken in England and Ireland were analyzed to determine the antibiotic tolerance profiles of two groups of culturable Ot(r) bacterial isolates at the intergeneric and intrageneric level comprising heterotrophs (189 strains) and mesophilic Aeromonas spp. (153 strains), respectively. Antibiogram data of heterotrophic isolates revealed that Irish hospital strains comprised higher frequencies of multi-tolerance than those originating from fishfarm environments whereas a reverse correlation was found among the English heterotrophs. Polyphasic identification of the isolates using fatty acid analysis and API 20E profiling showed that this difference arose from the unique taxonomic diversity within each heterotrophic strain set. Acinetobacter (27%) and Brevundimonas (22%) were predominant among the Irish Ot(r) fishfarm isolates, whereas isolates originating from the English aquaculture site almost entirely consisted of Stenotrophomonas maltophilia (86%) exhibiting high frequencies of tolerance to ampicillin and streptomycin. Within both the English and the Irish Ot(r) Aeromonas strain sets, on the other hand, the hospital strain sets displayed higher numbers of multi-tolerant isolates than to fishfarm isolates although country-specific differences were observed for individual antimicrobial agents. The typical occurrence of kanamycin-tolerant aeromonads in the Irish hospital site could to some extent be linked to the typical presence of A. hydrophila DNA hybridization group (HG) 3 strains as determined by fatty acid analysis and fluorescent amplified fragment length polymorphism (FAFLP) fingerprinting. Essentially, these data indicate that tolerance profiles in a specific environment of one country do not necessarily reflect the corresponding tolerance profiles of the same type of environment in another country, and this mainly as a result of the unique taxonomic composition of each site. Ot(r) representatives of Acinetobacter, S. maltophilia, and A. veronii biovar sobria HG8 were common to most if not all of the four sites under study, indicating that these three taxa may serve as potential indicator organisms for monitoring antibiotic tolerance among indigenous bacterial populations in various aquatic environments.

Impact of an urban effluent on antibiotic resistance of riverine Enterobacteriaceae and Aeromonas spp

In order to evaluate the impact of an urban effluent on antibiotic resistance of freshwater bacterial populations, water samples were collected from the Arga river (Spain), upstream and downstream from the wastewater discharge of the city of Pamplona. Strains of Enterobacteriaceae (representative of the human and animal commensal flora) (110 isolates) and Aeromonas (typically waterborne bacteria) (118 isolates) were selected for antibiotic susceptibility testing. Most of the Aeromonas strains (72%) and many of the Enterobacteriaceae (20%) were resistant to nalidixic acid. Singly nalidixic acid-resistant strains were frequent regardless of the sampling site for Aeromonas, whereas they were more common upstream from the discharge for enterobacteria. The most common resistances to antibiotics other than quinolones were to tetracycline (24.3%) and beta-lactams (20.5%) for Enterobacteriaceae and to tetracycline (27.5%) and co-trimoxazole (26.6%) for Aeromonas. The rates of these antibiotic resistances increased downstream from the discharge at similar degrees for the two bacterial groups; it remained at high levels for enterobacteria but decreased along the 30-km study zone for Aeromonas. Genetic analysis of representative strains demonstrated that these resistances were mostly (enterobacteria) or exclusively (Aeromonas) chromosomally mediated. Moreover, a reference strain of Aeromonas caviae (CIP 7616) could not be transformed with conjugative R plasmids of enterobacteria. Thus, the urban effluent resulted in an increase of the rates of resistance to antibiotics other than quinolones in the riverine bacterial populations, despite limited genetic exchanges between enterobacteria and Aeromonas. Quinolone resistance probably was selected by heavy antibiotic discharges of unknown origin upstream from the urban effluent.

Class I integrons containing a dhfrI trimethoprim resistance gene cassette in aquatic Acinetobacter spp

The presence of antibiotic resistance gene cassettes in class I integrons was investigated in 24 sulfamethoxazole-resistant and -sensitive Acinetobacter isolates derived from two Danish freshwater trout farms. Integrons were detected in five isolates from one of the fish farms, and their inserts were characterised by DNA sequencing. Each isolate contained a dhfrI gene cassette encoding resistance to trimethoprim and an open reading frame orfC of unknown function identical to the content of an integron previously found in a clinical enterobacterial isolate. Among the five isolates, at least two different strains were differentiated based on phenotypic tests and randomly amplified polymorphic DNA analysis. To our knowledge, this is the first report and characterisation of an integron in environmental bacteria.

Phenotypic characterization and antibiotic resistance of Acinetobacter spp. isolated from aquatic sources

A total of 99 Acinetobacter isolates from sewage, freshwater aquaculture habitats, trout intestinal contents and frozen shrimps was characterized phenotypically and antibiotic susceptibility patterns determined. One group of genomic species, including Ac. johnsonii, Ac. lwoffi and spp. 15TU, was detected in all sample types and represented the majority of the isolates (n = 54). Isolates belonging to the Acb complex (Ac. calcoaceticus, Ac. baumannii and genomic species 3) were detected in sewage (n = 6) and frozen shrimps (n = 1), Ac. haemolyticus in frozen shrimps (n = 6) and trout intestinal contents (n = 2) and genomic species 11 in freshwater aquaculture habitats (n = 6) and trout intestinal contents (n = 1). Acinetobacter junii (n = 5), genomic species 10 (n = 2), 14BJ (n = 8) and 16BJ (n = 4) were only isolated from sewage. Acinetobacter isolates from sewage were generally more biochemically reactive and resistant to antimicrobial agents compared with isolates from other sample types. Different strains, often belonging to different genomic species, were isolated from sites situated upstream and downstream of the discharge point of a pharmaceutical plant. This finding supported the hypothesis that the waste effluent from the pharmaceutical plant was likely to cause a change in the distribution of Acinetobacter spp. by selecting and/or introducing antibiotic-resistant strains into the recipient sewers.