The Streptomycin-Sulfadiazine-Tetracycline Antimicrobial Resistance Element of Calf-Adapted
            <i>Escherichia coli</i>
            Is Widely Distributed among Isolates from Washington State Cattle

Khachatryan, Artashes R.; Besser, Thomas E.; Call, Douglas R.

doi:10.1128/aem.01534-07

Cited by 26 publications

(32 citation statements)

References 20 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…We failed to find any evidence of plasmids, based on plasmid analysis followed by purification with polyethylene glycol. A previous study also failed to find phenotypic evidence of colicins or plasmids in the E. coli 25 strain (15).…”

Section: Discussionmentioning

confidence: 93%

See 1 more Smart Citation

Proximity-Dependent Inhibition in Escherichia coli Isolates from Cattle

Sawant

Casavant

Call

et al. 2011

Appl Environ Microbiol

Self Cite

View full text Add to dashboard Cite

We describe a novel proximity-dependent inhibition phenotype of Escherichia coli that is expressed when strains are cocultured in defined minimal media. When cocultures of "inhibitor" and "target" strains approached a transition between logarithmic and stationary growth, target strain populations rapidly declined >4 log CFU per ml over a 2-h period. Inhibited strains were not affected by exposure to conditioned media from inhibitor and target strain cocultures or when the inhibitor and target strains were incubated in shared media but physically separated by a 0.4-m-pore-size membrane. There was no evidence of lytic phage or extracellular bacteriocin involvement, unless the latter was only present at effective concentrations within immediate proximity of the inhibited cells. The inhibitory activity observed in this study was effective against a diversity of E. coli strains, including enterohemorrhagic E. coli serotype O157:H7, enterotoxigenic E. coli expressing F5 (K99) and F4 (K88) fimbriae, multidrug-resistant E. coli, and commensal E. coli. The decline in counts of target strains in coculture averaged 4.8 log CFU/ml (95% confidence interval, 4.0 to 5.5) compared to their monoculture counts. Coculture of two inhibitor strains showed mutual immunity to inhibition. These results suggest that proximity-dependent inhibition can be used by bacteria to gain a numerical advantage when populations are entering stationary phase, thus setting the stage for a competitive advantage when growth conditions improve.With the discovery of quorum sensing in the 1960s and 1970s, in comparison to the discovery of colicins in the 1920s, it became evident that populations of individual cells are capable of coordinating functions by using signaling molecules for communication. These communications can enhance fitness in a multispecies community, help exploit nutrients more efficiently, increase cooperation with neighboring cells, or harm competing bacteria. Some of the cell-to-cell communications have been well characterized. Streptococcus oralis 34 secretes an autoinducer that signals Actinomyces naeslundii T14V to congregate with S. oralis 34 and form a mutualistic biofilm in saliva (21). Vibrio cholerae uses autoinducers to shut down expression of virulence factors and biofilm formation at high cell densities (13). As an SOS response, certain bacteria can produce toxins, called bacteriocins, which can kill a narrow spectrum of competing cells that express suitable cell surface receptors (8)(9)(10)14). Bacteria can also produce inhibitory phage particles and iron-sequestering aerobactin to gain an advantage over competing bacteria (6,23).Many of these mechanisms enhance the fitness of bacterial strains in a given environment. Khachatryan et al. in 2004 observed a fitness trait allowing certain multidrug-resistant Escherichia coli in Holstein calves to dominate the enteric E. coli population (16). Neither antimicrobial drug use nor the presence of antimicrobial resistance genes was associated with the fitness trait observed in the ...

show abstract

Section: Discussionmentioning

confidence: 93%

“…E. coli 25 (SSuT r ) was used as a positive-control competitor for in vitro growth experiments with other commensal E. coli strains and is representative of the persistent SSuT r E. coli strains observed in dairy calves (15). Wild-type E. coli 25 and E. coli O157:H7 strain 1 were used for detailed competition experiments.…”

Section: Resultsmentioning

confidence: 99%

Proximity-Dependent Inhibition in Escherichia coli Isolates from Cattle

Sawant

Casavant

Call

et al. 2011

Appl Environ Microbiol

Self Cite

View full text Add to dashboard Cite

show abstract

“…For example, multidrug resistance genes may be linked on a common element, in which case selection for one resistance trait would lead to the propagation of all of the linked resistance traits (1,9,25,28). In addition, there is evidence that linkage to fitness traits unrelated to antimicrobial resistance may also be a mechanism by which resistance genes are maintained in bacterial populations in the absence of a resistance advantage (29)(30)(31)(32)52). If this is correct, we can predict that bacterial populations growing in the absence of antibiotic selection pressure will accumulate and retain more deleterious mutations in resistance genes than bacterial populations under intense antimicrobial selection pressure.…”

mentioning

confidence: 99%

Genotypic-Phenotypic Discrepancies between Antibiotic Resistance Characteristics of Escherichia coli Isolates from Calves in Management Settings with High and Low Antibiotic Use

Davis

Besser

Orfe

et al. 2011

Appl Environ Microbiol

Self Cite

View full text Add to dashboard Cite

We hypothesized that bacterial populations growing in the absence of antibiotics will accumulate more resistance gene mutations than bacterial populations growing in the presence of antibiotics. If this is so, the prevalence of dysfunctional resistance genes (resistance pseudogenes) could provide a measure of the level of antibiotic exposure present in a given environment. As a proof-of-concept test, we assayed field strains of Escherichia coli for their resistance genotypes using a resistance gene microarray and further characterized isolates that had resistance phenotype-genotype discrepancies. We found a small but significant association between the prevalence of isolates with resistance pseudogenes and the lower antibiotic use environment of a beef cow-calf operation versus a higher antibiotic use dairy calf ranch (Fisher's exact test, P ‫؍‬ 0.044). Other significant findings include a very strong association between the dairy calf ranch isolates and phenotypes unexplained by well-known resistance genes (Fisher's exact test, P < 0.0001). Two novel resistance genes were discovered in E. coli isolates from the dairy calf ranch, one associated with resistance to aminoglycosides and one associated with resistance to trimethoprim. In addition, isolates resistant to expanded-spectrum cephalosporins but negative for bla CMY-2 had mutations in the promoter regions of the chromosomal E. coli ampC gene consistent with reported overexpression of native AmpC beta-lactamase. Similar mutations in hospital E. coli isolates have been reported worldwide. Prevalence or rates of E. coli ampC promoter mutations may be used as a marker for high expanded-spectrum cephalosporin use environments.

show abstract

“…1) revealed similarity to a SSuT resistance element in a commensal E. coli strain, although the order of the genes is slightly different (13). This sequence was derived from an isolate representing bovine fecal commensal E. coli strains that have a similar and widespread AMR-SSuT (13). Occurrence of the AMR gene cluster in STEC O157 PTs 23, 45, and 67.…”

mentioning

confidence: 99%

“…1), hypothetical proteins, and ORFs for truncated genes (pseudogenes) that included an adhesin, GTPase, and partial trans- (Fig. 1) revealed similarity to a SSuT resistance element in a commensal E. coli strain, although the order of the genes is slightly different (13). This sequence was derived from an isolate representing bovine fecal commensal E. coli strains that have a similar and widespread AMR-SSuT (13).…”

mentioning

confidence: 99%