scholarly journals Risk Factors for Detection, Survival, and Growth of Antibiotic-Resistant and PathogenicEscherichia coliin Household Soils in Rural Bangladesh

2018 ◽  
Vol 84 (24) ◽  
Author(s):  
Maria Camila Montealegre ◽  
Subarna Roy ◽  
Franziska Böni ◽  
Muhammed Iqbal Hossain ◽  
Tala Navab-Daneshmand ◽  
...  
Keyword(s):  
Risk Factors ◽  
Physicochemical Characteristics ◽  
Antibiotic Resistant ◽  
Content Type ◽  
Growth And Survival ◽  
Household Level ◽  
E Coli ◽  
Rural Bangladesh ◽  
Sanitation And Hygiene ◽  
Soil Physicochemical Characteristics

ABSTRACTSoils in household environments in low- and middle-income countries may play an important role in the persistence, proliferation, and transmission ofEscherichia coli. Our goal was to investigate the risk factors for detection, survival, and growth ofE. coliin soils collected from household plots.E. coliwas enumerated in soil and fecal samples from humans, chickens, and cattle from 52 households in rural Bangladesh. Associations betweenE. coliconcentrations in soil, household-level risk factors, and soil physicochemical characteristics were investigated. Susceptibility to 16 antibiotics and the presence of intestinal pathotypes were evaluated for 175E. coliisolates. The growth and survival ofE. coliin microcosms using soil collected from the households were also assessed.E. coliwas isolated from 44.2% of the soil samples, with an average of 1.95 log10CFU/g dry soil. Soil moisture and clay content were associated withE. coliconcentrations in soil, whereas no household-level risk factor was significantly correlated. Antibiotic resistance and pathogenicity were common amongE. coliisolates, with 42.3% resistant to at least one antibiotic, 12.6% multidrug resistant (≥3 classes), and 10% potentially pathogenic. Soil microcosms demonstrate growth and/or survival ofE. coli, including an enteropathogenic extended-spectrum beta-lactamase (ESBL)-producing isolate, in some, but not all, of the household soils tested. In rural Bangladesh, defined soil physicochemical characteristics appear more influential forE. colidetection in soils than household-level risk factors. Soils may act as reservoirs in the transmission of antibiotic-resistant and potentially pathogenicE. coliand therefore may impact the effectiveness of water, sanitation, and hygiene interventions.IMPORTANCESoil may represent a direct source or act as an intermediary for the transmission of antibiotic-resistant and pathogenicEscherichia colistrains, particularly in low-income and rural settings. Thus, determining risk factors associated with detection, growth, and long-term survival ofE. coliin soil environments is important for public health. Here, we demonstrate that household soils in rural Bangladesh are reservoirs for antibiotic-resistant and potentially pathogenicE. colistrains and can supportE. coligrowth and survival, and defined soil physicochemical characteristics are drivers ofE. colisurvival in this environment. In contrast, we found no evidence that household-level factors, including water, sanitation, and hygiene indicators, were associated withE. colicontamination of household soils.

scholarly journals High Genomic Diversity and Heterogenous Origins of Pathogenic and Antibiotic-Resistant Escherichia coli in Household Settings Represent a Challenge to Reducing Transmission in Low-Income Settings

mSphere ◽  
2020 ◽  
Vol 5 (1) ◽  
Author(s):  
Maria Camila Montealegre ◽  
Alba Talavera Rodríguez ◽  
Subarna Roy ◽  
Muhammed Iqbal Hossain ◽  
Mohammad Aminul Islam ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Low Income ◽  
Pathogen Transmission ◽  
Whole Genome ◽  
Antibiotic Resistant ◽  
Content Type ◽  
E Coli ◽  
Rural Bangladesh ◽  
High Level ◽  
High Diversity

ABSTRACT Escherichia coli is present in multiple hosts and environmental compartments as a normal inhabitant, temporary or persistent colonizer, and as a pathogen. Transmission of E. coli between hosts and with the environment is considered to occur more often in areas with poor sanitation. We performed whole-genome comparative analyses on 60 E. coli isolates from soils and fecal sources (cattle, chickens, and humans) in households in rural Bangladesh. Isolates from household soils were in multiple branches of the reconstructed phylogeny, intermixed with isolates from fecal sources. Pairwise differences between all strain pairs were large (minimum, 189 single nucleotide polymorphisms [SNPs]), suggesting high diversity and heterogeneous origins of the isolates. The presence of multiple virulence and antibiotic resistance genes is indicative of the risk that E. coli from soil and feces represent for the transmission of variants that pose potential harm to people. Analysis of the accessory genomes of the Bangladeshi E. coli relative to E. coli genomes available in NCBI identified a common pool of accessory genes shared among E. coli isolates in this geographic area. Together, these findings indicate that in rural Bangladesh, a high level of E. coli in soil is likely driven by contributions from multiple and diverse E. coli sources (human and animal) that share an accessory gene pool relatively unique to previously published E. coli genomes. Thus, interventions to reduce environmental pathogen or antimicrobial resistance transmission should adopt integrated One Health approaches that consider heterogeneous origins and high diversity to improve effectiveness and reduce prevalence and transmission. IMPORTANCE Escherichia coli is reported in high levels in household soil in low-income settings. When E. coli reaches a soil environment, different mechanisms, including survival, clonal expansion, and genetic exchange, have the potential to either maintain or generate E. coli variants with capabilities of causing harm to people. In this study, we used whole-genome sequencing to identify that E. coli isolates collected from rural Bangladeshi household soils, including pathogenic and antibiotic-resistant variants, are diverse and likely originated from multiple diverse sources. In addition, we observed specialization of the accessory genome of this Bangladeshi E. coli compared to E. coli genomes available in current sequence databases. Thus, to address the high level of pathogenic and antibiotic-resistant E. coli transmission in low-income settings, interventions should focus on addressing the heterogeneous origins and high diversity.

scholarly journals Impact of Extended-Spectrum β-Lactamase Production on Treatment Outcomes of Acute Pyelonephritis Caused by Escherichia coli in Patients without Health Care-Associated Risk Factors

2015 ◽  
Vol 59 (4) ◽  
pp. 1962-1968 ◽  
Author(s):  
Sun Hee Park ◽  
Su-Mi Choi ◽  
Dong-Gun Lee ◽  
Sung-Yeon Cho ◽  
Hyo-Jin Lee ◽  
...  
Keyword(s):  
Risk Factors ◽  
Escherichia Coli ◽  
Health Care ◽  
Treatment Outcomes ◽  
Acute Pyelonephritis ◽  
Esbl Production ◽  
Content Type ◽  
E Coli ◽  
Extended Spectrum ◽  
The Impact

ABSTRACTExtended-spectrum β-lactamase-producingEscherichia coli(ESBL-EC) is increasingly identified as a cause of acute pyelonephritis (APN) among patients without recent health care contact, i.e., community-associated APN. This case-control study compared 75 cases of community-associated ESBL-EC APN (CA-ESBL) to 225 controls of community-associated non-ESBL-EC APN (CA-non-ESBL) to identify the risk factors for ESBL-EC acquisition and investigate the impact of ESBL on the treatment outcomes of community-associated APN (CA-APN) caused byE. coliat a Korean hospital during 2007 to 2013. The baseline characteristics were similar between the cases and controls; the risk factors for ESBL-EC were age (>55 years), antibiotic use within the previous year, and diabetes with recurrent APN. The severity of illness did not differ between CA-ESBL and CA-non-ESBL (Acute Physiology and Chronic Health Evaluation [APACHE] II scores [mean ± standard deviation], 7.7 ± 5.9 versus 6.4 ± 5.3;P= 0.071). The proportions of clinical (odds ratio [OR], 1.76; 95% confidence interval [CI], 0.57 to 5.38;P= 0.323) and microbiological (OR, 1.16; 95% CI, 0.51 to 2.65;P= 0.730) cures were similar, although the CA-ESBL APN patients were less likely to receive appropriate antibiotics within 48 h. A multivariable Cox proportional hazards analysis of the prognostic factors for CA-APN caused byE. colishowed that ESBL production was not a significant factor for clinical (hazard ratio [HR], 0.39; 95% CI, 0.12 to 1.30;P= 0.126) or microbiological (HR, 0.49; 95% CI, 0.21 to 1.12;P= 0.091) failure. The estimates did not change after incorporating weights calculated using propensity scores for acquiring ESBL-EC. Therefore, ESBL production did not negatively affect treatment outcomes among patients with community-associatedE. coliAPN.

Assessing public health risk factors for internally displaced households in North Darfur, Sudan

2020 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Elfadil Mohammed Mahmoud ◽  
Indraijt Pal ◽  
Mokbul Morshed Ahmad
Keyword(s):  
Public Health ◽  
Risk Factors ◽  
Health Risk ◽  
Vulnerable Groups ◽  
Health Risk Factors ◽  
Public Health Risk ◽  
Content Type ◽  
Internally Displaced ◽  
Household Level ◽  
The Public

PurposeThe purpose of this paper is to assess the public health risk factors of internally displaced households and suggest appropriate measures and strategies for health risk reduction in the context of IDPs.Design/methodology/approachThe composite Index (CI) method was used to compare the public health risk factors at the household level in three IDP camps. A set of 22 indicators were studied in 326 households. Households were selected by using a two-stage cluster sampling technique.FindingsThe findings indicate that the Shangil Tobaya camp is at the highest risk for communicable diseases (63.6%) followed by Zamzam (52.4%) and Abu Shouk (42.7%) at the household level. Eight indicators appeared to have made differential impacts between Abu Shouk and Shangil Tobaya, these include: level of education, walking time to health facilities, water source, latrines type, safe disposal of child feces, frequency of visit by pregnant women to antenatal care services, place of delivery and women delivering their children with the help of skilled birth attendants.Research limitations/implicationsSince the selection criteria of the camps were predefined; there are variations in the number of samples between the camps. Therefore, the generalizability may be compromised.Social implicationsIncreased access to healthcare services particularly reproductive health services to the most vulnerable groups (women). Community involvement in services management to promote ownership.Originality/valueThe methods used in this study is original and flexible and can be replicated for other emergency areas and risks.

scholarly journals Predicting Antibiotic Resistance in Gram-Negative Bacilli from Resistance Genes

2019 ◽  
Vol 63 (4) ◽  
Author(s):  
G. Terrance Walker ◽  
Julia Quan ◽  
Stephen G. Higgins ◽  
Nikhil Toraskar ◽  
Weizhong Chang ◽  
...  
Keyword(s):  
Antibiotic Resistance ◽  
Resistance Genes ◽  
Antibiotic Resistance Genes ◽  
Unknown Origin ◽  
Bacterial Isolates ◽  
Antibiotic Resistant ◽  
Predictive Values ◽  
Content Type ◽  
Phenotypic Resistance ◽  
E Coli

ABSTRACT We developed a rapid high-throughput PCR test and evaluated highly antibiotic-resistant clinical isolates of Escherichia coli (n = 2,919), Klebsiella pneumoniae (n = 1,974), Proteus mirabilis (n = 1,150), and Pseudomonas aeruginosa (n = 1,484) for several antibiotic resistance genes for comparison with phenotypic resistance across penicillins, cephalosporins, carbapenems, aminoglycosides, trimethoprim-sulfamethoxazole, fluoroquinolones, and macrolides. The isolates originated from hospitals in North America (34%), Europe (23%), Asia (13%), South America (12%), Africa (7%), or Oceania (1%) or were of unknown origin (9%). We developed statistical methods to predict phenotypic resistance from resistance genes for 49 antibiotic-organism combinations, including gentamicin, tobramycin, ciprofloxacin, levofloxacin, trimethoprim-sulfamethoxazole, ertapenem, imipenem, cefazolin, cefepime, cefotaxime, ceftazidime, ceftriaxone, ampicillin, and aztreonam. Average positive predictive values for genotypic prediction of phenotypic resistance were 91% for E. coli, 93% for K. pneumoniae, 87% for P. mirabilis, and 92% for P. aeruginosa across the various antibiotics for this highly resistant cohort of bacterial isolates.

scholarly journals Extraintestinal Pathogenic and Antimicrobial-Resistant Escherichia coli, Including Sequence Type 131 (ST131), from Retail Chicken Breasts in the United States in 2013

2017 ◽  
Vol 83 (6) ◽  
Author(s):  
James R. Johnson ◽  
Stephen B. Porter ◽  
Brian Johnston ◽  
Paul Thuras ◽  
Sarah Clock ◽  
...  
Keyword(s):  
United States ◽  
Escherichia Coli ◽  
Virulence Genes ◽  
Meat Products ◽  
The United States ◽  
Sequence Type ◽  
The Other ◽  
Antibiotic Resistant ◽  
Content Type ◽  
E Coli

ABSTRACT Chicken meat products are hypothesized to be vehicles for transmitting antimicrobial-resistant and extraintestinal pathogenic Escherichia coli (ExPEC) to consumers. To reassess this hypothesis in the current era of heightened concerns about antimicrobial use in food animals, we analyzed 175 chicken-source E. coli isolates from a 2013 Consumer Reports national survey. Isolates were screened by PCR for ExPEC-defining virulence genes. The 25 ExPEC isolates (12% of 175) and a 2:1 randomly selected set of 50 non-ExPEC isolates were assessed for their phylogenetic/clonal backgrounds and virulence genotypes for comparison with their resistance profiles and the claims on the retail packaging label (“organic,” “no antibiotics,” and “natural”). Compared with the findings for non-ExPEC isolates, the group of ExPEC isolates had a higher prevalence of phylogroup B2 isolates (44% versus 4%; P < 0.001) and a lower prevalence of phylogroup A isolates (4% versus 30%; P = 0.001), a higher prevalence of multiple individual virulence genes, higher virulence scores (median, 11 [range, 4 to 16] versus 8 [range, 1 to 14]; P = 0.001), and higher resistance scores (median, 4 [range, 0 to 8] versus 3 [range, 0 to 10]; P < 0.001). All five isolates of sequence type 131 (ST131) were ExPEC (P = 0.003), were as extensively resistant as the other isolates tested, and had higher virulence scores than the other isolates tested (median, 12 [range, 11 to 13] versus 8 [range, 1 to 16]; P = 0.005). Organic labeling predicted lower resistance scores (median, 2 [range, 0 to 3] versus 4 [range, 0 to 10]; P = 0.008) but no difference in ExPEC status or virulence scores. These findings document a persisting reservoir of extensively antimicrobial-resistant ExPEC isolates, including isolates from ST131, in retail chicken products in the United States, suggesting a potential public health threat. IMPORTANCE We found that among Escherichia coli isolates from retail chicken meat products purchased across the United States in 2013 (many of these isolates being extensively antibiotic resistant), a minority had genetic profiles suggesting an ability to cause extraintestinal infections in humans, such as urinary tract infection, implying a risk of foodborne disease. Although isolates from products labeled “organic” were less extensively antibiotic resistant than other isolates, they did not appear to be less virulent. These findings suggest that retail chicken products in the United States, even if they are labeled “organic,” pose a potential health threat to consumers because they are contaminated with extensively antibiotic-resistant and, presumably, virulent E. coli isolates.

scholarly journals Carbapenem Therapy for Bacteremia Due to Extended-Spectrum-β-Lactamase-Producing Escherichia coli or Klebsiella pneumoniae: Implications of Ertapenem Susceptibility

2012 ◽  
Vol 56 (6) ◽  
pp. 2888-2893 ◽  
Author(s):  
Nan-Yao Lee ◽  
Ching-Chi Lee ◽  
Wei-Han Huang ◽  
Ko-Chung Tsui ◽  
Po-Ren Hsueh ◽  
...  
Keyword(s):  
Risk Factors ◽  
Escherichia Coli ◽  
Klebsiella Pneumoniae ◽  
Content Type ◽  
Extended Spectrum Beta Lactamase ◽  
E Coli ◽  
Medical Centers ◽  
Extended Spectrum ◽  
Appropriate Therapy ◽  
Related Mortality

ABSTRACTA retrospective study was conducted at two medical centers in Taiwan to evaluate the clinical characteristics, outcomes, and risk factors for mortality among patients treated with a carbapenem for bacteremia caused by extended-spectrum-beta-lactamase (ESBL)-producing organisms. A total of 251 patients with bacteremia caused by ESBL-producingEscherichia coliandKlebsiella pneumoniaeisolates treated by a carbapenem were identified. Among these ESBL-producing isolates, rates of susceptibility to ertapenem (MICs ≤ 0.25 μg/ml) were 83.8% and 76.4%, respectively; those to meropenem were 100% and 99.3%, respectively; and those to imipenem were 100% and 97.9%, respectively. There were no significant differences in the critical illness rate (P= 0.1) or sepsis-related mortality rate (P= 0.2) for patients with bacteremia caused by ESBL-producingK. pneumoniae(140 isolates, 55.8%) andE. coli(111 isolates, 44.2%). Multivariate analysis of variables related to sepsis-related mortality revealed that the presence of severe sepsis (odds ratio [OR], 15.9; 95% confidence interval [CI], 5.84 to 43.34;P< 0.001), hospital-onset bacteremia (OR, 4.65; 95% CI, 1.42 to 15.24;P= 0.01), and ertapenem-nonsusceptible isolates (OR, 5.12; 95% CI, 2.04 to 12.88;P= 0.001) were independent risk factors. The patients receiving inappropriate therapy had a higher sepsis-related mortality than those with appropriate therapy (P= 0.002), irrespective of ertapenem, imipenem, or meropenem therapy. Infections due to the ertapenem-susceptible isolates (MICs ≤ 0.25 μg/ml) were associated with a more favorable outcome than those due to ertapenem-nonsusceptible isolates (MICs > 0.25 μg/ml), if treated by a carbapenem. However, the mortality for patients with bacteremic episodes due to isolates with MICs of ≤0.5 μg/ml was similar to the mortality for those whose isolates had MICs of >0.5 μg/ml (P= 0.8). Such a finding supports the rationale of the current CLSI 2011 criteria for carbapenems forEnterobacteriaceae.

scholarly journals Risk Factors for Infection or Colonization with CTX-M Extended-Spectrum-β-Lactamase-Positive Escherichia coli

2012 ◽  
Vol 56 (11) ◽  
pp. 5575-5580 ◽  
Author(s):  
Jennifer H. Han ◽  
Kei Kasahara ◽  
Paul H. Edelstein ◽  
Warren B. Bilker ◽  
Ebbing Lautenbach
Keyword(s):  
Risk Factors ◽  
Escherichia Coli ◽  
Control Strategies ◽  
Content Type ◽  
E Coli ◽  
Extended Spectrum ◽  
Increased Risk ◽  
Urinary Culture ◽  
Multivariable Analyses ◽  
And Control

ABSTRACTThere has been a significant increase in the prevalence ofEnterobacteriaceaethat produce CTX-M-type extended-spectrum β-lactamases. The objective of this study was to evaluate risk factors for infection or colonization with CTX-M-positiveEscherichia coli. A case-control study was conducted within a university system from 1 January 2007 to 31 December 2008. All patients with clinical cultures withE. colidemonstrating resistance to extended-spectrum cephalosporins were included. Case patients were designated as those with cultures positive for CTX-M-positiveE. coli, and control patients were designated as those with non-CTX-M-producingE. coli. Multivariable logistic regression analyses were performed to evaluate risk factors for CTX-M-positive isolates. A total of 83 (56.8%) of a total of 146 patients had cultures with CTX-M-positiveE. coli. On multivariable analyses, there was a significant association between infection or colonization with CTX-M-type β-lactamase-positiveE. coliand receipt of piperacillin-tazobactam in the 30 days prior to the culture date (odds ratio [OR], 7.36; 95% confidence interval [CI], 1.61 to 33.8;P= 0.01) and a urinary culture source (OR, 0.36; 95% CI, 0.17 to 0.77;P= 0.008). The rates of resistance to fluoroquinolones were significantly higher in isolates from case patients than in isolates from control patients (90.4 and 50.8%, respectively;P< 0.001). We found that nonurinary sources of clinical cultures and the recent use of piperacillin-tazobactam conferred an increased risk of colonization or infection with CTX-M-positiveE. coli. Future studies will need to focus on outcomes associated with infections due to CTX-M-positiveE. coli, as well as infection control strategies to limit the spread of these increasingly common organisms.

scholarly journals Antimicrobial Resistance in Fecal Escherichia coli Isolates from Healthy Urban Children of Two Age Groups in Relation to Their Antibiotic Therapy

2011 ◽  
Vol 55 (6) ◽  
pp. 3005-3007 ◽  
Author(s):  
Ivan Literak ◽  
Radim Petro ◽  
Monika Dolejska ◽  
Erika Gruberova ◽  
Hana Dobiasova ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Czech Republic ◽  
Antimicrobial Resistance ◽  
Age Groups ◽  
Antibiotic Resistant ◽  
The Czech Republic ◽  
Content Type ◽  
E Coli ◽  
Significant Difference ◽  
Two Age Groups

ABSTRACTThe study was performed in the Czech Republic during 2007 to 2009. OfEscherichia coliisolates from 275 children aged 6 weeks, 36% (n= 177) were resistant to 1 to 7 antibiotics. Of isolates from 253 children aged 6 to 17 years, 24% (n= 205) were resistant to 1 to 5 antibiotics. There was no significant difference in the prevalences of antibiotic-resistantE. coliisolates between these groups of children, even though the consumptions of antibiotics were quite different.

Prevalence of Antibiotic-Resistant Fecal Escherichia coli Isolates from Penned Broiler and Scavenging Local Chickens in Arusha, Tanzania

2016 ◽  
Vol 79 (8) ◽  
pp. 1424-1429 ◽  
Author(s):  
BERNADETHER T. RUGUMISA ◽  
DOUGLAS R. CALL ◽  
GASPARY O. MWANYIKA ◽  
REHEMA I. MRUTU ◽  
CATHERINE M. LUANDA ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Broiler Chickens ◽  
Antibiotic Resistant ◽  
Household Level ◽  
E Coli ◽  
Free Range ◽  
Mixed Breed ◽  
Commercial Source ◽  
Prophylactic Use ◽  
Local Chickens

ABSTRACT We compared the prevalence of antibiotic-resistant Escherichia coli isolates from household-level producers of broiler (commercial source breeds) and local chickens in the Arusha District of Tanzania. Households were composed of a single dwelling or residence with independent, penned broiler flocks. Free-range, scavenging chickens were mixed breed and loosely associated with individual households. A total of 1,800 E. coli isolates (1,200 from broiler and 600 from scavenging local chickens) from 75 chickens were tested for their susceptibility against 11 antibiotics by using breakpoint assays. Isolates from broiler chickens harbored a higher prevalence of antibiotic-resistant E. coli relative to scavenging local chickens, including sulfamethoxazole (80.3 versus 34%), followed by trimethoprim (69.3 versus 27.7%), tetracycline (56.8 versus 20%), streptomycin (52.7 versus 24.7%), amoxicillin (49.6 versus 17%), ampicillin (49.1 versus 16.8%), ciprofloxacin (21.9 versus 1.7%), and chloramphenicol (1.5 versus 1.2%). Except for resistance to chloramphenicol, scavenging local chickens harbored fewer resistant E. coli isolates (P &lt; 0.05). Broiler chickens harbored more isolates that were resistant to ≥7 antibiotics (P &lt; 0.05). The higher prevalence of antibiotic-resistant E. coli from broiler chickens correlated with the reported therapeutic and prophylactic use of antibiotics in this poultry population. We suggest that improved biosecurity measures and increased vaccination efforts would reduce reliance on antibiotics by these households.

scholarly journals β-Lactams and Florfenicol Antibiotics Remain Bioactive in Soils while Ciprofloxacin, Neomycin, and Tetracycline Are Neutralized

2011 ◽  
Vol 77 (20) ◽  
pp. 7255-7260 ◽  
Author(s):  
Murugan Subbiah ◽  
Shannon M. Mitchell ◽  
Jeffrey L. Ullman ◽  
Douglas R. Call
Keyword(s):  
High Performance ◽  
Selective Pressure ◽  
Luria Bertani ◽  
Resistant Bacteria ◽  
Antibiotic Resistant ◽  
Content Type ◽  
Adsorption Mechanisms ◽  
E Coli ◽  
Luria Bertani Broth ◽  
Contamination Levels

ABSTRACTIt is generally assumed that antibiotic residues in soils select for antibiotic-resistant bacteria. This assumption was tested by separately adding 10 different antibiotics (≥200 ppm) to three soil-water slurries (silt-loam, sand-loam, and sand; 20% soil [wt/vol]) and incubating mixtures for 24 h at room temperature. The antibiotic activity of the resultant supernatant was assessed by culturing a sensitiveEscherichia colistrain in the filter-sterilized supernatant augmented with Luria-Bertani broth. We found striking differences in the abilities of supernatants to suppress growth of the indicatorE. coli. Ampicillin, cephalothin, cefoxitin, ceftiofur, and florfenicol supernatants completely inhibited growth while bacterial growth was uninhibited in the presence of neomycin, tetracycline, and ciprofloxacin supernatants. High-performance liquid chromatography (HPLC) analysis demonstrated that cefoxitin and florfenicol were almost completely retained in the supernatants, whereas tetracycline and ciprofloxacin were mostly removed. Antibiotic dissipation in soil, presumably dominated by adsorption mechanisms, was sufficient to neutralize 200 ppm of tetracycline; this concentration is considerably higher than reported contamination levels. Soil pellets from the tetracycline slurries were resuspended in a minimal volume of medium to maximize the interaction between bacteria and soil particles, but sensitive bacteria were still unaffected by tetracycline (P= 0.6). Thus, residual antibiotics in soil do not necessarily exert a selective pressure, and the degree to which the pharmaceutical remains bioactive depends on the antibiotic. Efforts to control antibiotic contamination would be better directed toward compounds that retain biological activity in soils (e.g., cephalosporins and florfenicol) because these are the antibiotics that could exert a selective pressure in the environment.

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