Tetracycline Resistance in Escherichia coli and Persistence in the Infantile Colonic Microbiota

Abstract

The ecological impact of antibiotic resistance in the absence of selective pressure has been poorly studied. We assessed the carriage of tetracycline resistance genes, persistence in the microbiota, fecal population counts and virulence factor genes in 309 commensal, intestinal Escherichia coli strains obtained from 128 Swedish infants followed during the first year of life with regular quantitative fecal cultures. No infant was given tetracycline, but 25% received other antibiotics. Tetracycline resistance was identified in 12% of strains, all of which carried either tet(A) (49%) or tet(B) (51%) genes. Resistance to other antibiotics occurred in 50% of tet(A)-positive strains, 42% of tet(B)-positive strains and 13% of tetracycline-sensitive strains. However, colonization with tetracycline-resistant strains was unrelated to treatment with antibiotics. Strains that were tet(B)-or tet(A)-positive carried the genes for P fimbriae and aerobactin, respectively, more often than susceptible strains. Tetracycline-resistant and -susceptible strains were equally likely to persist among the intestinal microbiota for >3 weeks and had similar population numbers. However, when a resistant strain and a susceptible strain colonized a child simultaneously, the resistant variety showed lower counts (P ‫؍‬ 0.03). In cases of long-term colonization by initially tetracycline-resistant E. coli strains, loss of tet genes occurred in 3 of 13 cases with variable effects on population counts. The results indicate that there is limited pressure against the carriage of tet genes in the infantile gut microbiota even in the absence of antibiotics. Resistant strains may possess colonization factors that balance the cost of producing resistance elements.

Patterns of Efflux Pump Genes Among Tetracycline Resistance Uropathogenic Escherichia coli Isolates Obtained From Human Urinary Infections

“…In 2006, Karami et al studied the prevalence of tetracycline resistance genes in intestinal E. coli strains and identified tetB and tetA as the most common tetracycline resistance genes in human E. coli (10). Our findings about the frequency of tetracycline resistance genes in urinary E. coli are in agreement with their results.…”

“…Tetracycline susceptibility profiles of isolated uropathogenic E. coli were determined via the disc diffusion method (10). A 15 mm Muller-Hinton medium plate was swabbed with nutrient broth inoculated with E. coli and incubated to a turbidity of 0/5 McFarland standard.…”

Antibiotic resistant bacteria in terrestrial and aquatic environments: A review

“…The mechanisms of MARB spreading from animals to humans remain somewhat controversial; colonization of the human intestinal tract with resistant bacteria from chickens was clearly demonstrated [47]. At slaughterhouses and poultry farms, both pathogenic and nonpathogenic strains from domestic animals can spread to humans by eating contaminated egg, meat and dairy products of the infected animals [16,22,36,47,55,56,57].…”

“…At slaughterhouses and poultry farms, both pathogenic and nonpathogenic strains from domestic animals can spread to humans by eating contaminated egg, meat and dairy products of the infected animals [16,22,36,47,55,56,57].…”

“…Antibiotic resistant Gram-negative bacilli from fecal specimens, especially Enterobacteriaceae, have been of particular interest because of the increasing risk of gastroenteritis caused by strains carrying R-plasmids. E. coli is the most common facultative bacterium in the intestinal microbiota of humans and many animals [47] has been reported to be a significant reservoir for genes encoding antimicrobial drug resistance [48]. The widespread use of various antibiotics as growth promoters and as treatments for chicken infections has selected antibiotic-resistant strains and has made chickens an important potential source of multiple antibioticresistant bacteria [7].…”