Commensal Escherichia coli of healthy humans: a reservoir for antibiotic-resistance determinants

Abstract

This study examined in detail the population structure of Escherichia coli from healthy adults with respect to the prevalence of antibiotic resistance and specific resistance determinants. E. coli isolated from the faeces of 20 healthy adults not recently exposed to antibiotics was tested for resistance to ten antibiotics and for carriage of integrons and resistance determinants using PCR. Strain diversity was assessed using biochemical and molecular criteria. E. coli was present in 19 subjects at levels ranging from 2.0¾10 4 to 1.7¾10 8 c.f.u. (g faeces). Strains resistant to one to six antibiotics were found at high levels (.30 %) in only ten individuals, but at significant levels (.0.5 %) in 14. Resistant isolates with the same phenotype from the same individual were indistinguishable, but more than one susceptible strain was sometimes found. Overall, individuals harboured one to four E. coli strains, although in 17 samples one strain was dominant (.70 % of isolates). Eighteen strains resistant to ampicillin, sulfamethoxazole, tetracycline and trimethoprim in 15 different combinations were observed. One resistant strain was carried by two unrelated individuals and a susceptible strain was shared by two cohabiting subjects. Two minority strains were derivatives of a more abundant resistant strain in the same sample, showing that continuous evolution is occurring in vivo. The trimethoprim-resistance genes dfrA1, dfrA5, dfrA7, dfrA12 or dfrA17 were in cassettes in a class 1 or class 2 integron. Ampicillin resistance was conferred by the bla TEM gene, sulfamethoxazole resistance by sul1, sul2 or sul3 and tetracycline resistance by tetA(A) or tetA(B). Chloramphenicol resistance (cmlA1 gene) was detected only once. Phylogenetic groups A and B2 were more common than B1 and D. Commensal E. coli of healthy humans represent an important reservoir for numerous antibiotic-resistance genes in many combinations. However, measuring the true extent of resistance carriage in commensal E. coli requires in-depth analysis.

Occurrence and characterization of class 1 integrons in Escherichia coli from healthy individuals and those with urinary infection

“…UPEC is classified primarily into the pathogenic phylogenetic group B2 and to a lesser extent group D [38]. Although our study revealed the dominance of group A in commensal isolates, group B2, which carries more virulence factors than strains belonging to phylogroups A, B1 and D [39,40], was also found in high proportion (43 %); this was also observed by Bailey et al [41]. A similar frequency was found for commensal E. coli strains from healthy American women and Swedish infants [40,42], although other studies showed that strains from phylogenetic groups A and B1 are the most common [43,44].…”

Resistance genes to sulphonamide in commensal Escherichia coli isolated from stool of patients in Mansoura University Children Hospital

“…This antibiotic resistance profile was previously detected in healthy individuals by Bartoloni et al (1998) in Bolivia, van de Mortel et al (1998) in Venezuela and Okeke et al (2000) in Ile-ife, Nigeria. These data are also consistent with the finding of further studies that showed a great antibiotic resistance pattern recorded by the commensal E. coli from lowresource settings (Bailey et al, 2010).…”

Phenotypic Identification and Phylogenetic Characterization of Uropathogenic Escherichia coli in Symptomatic Pregnant Women With Urinary Tract Infections in South-Western Nigeria

“…Non-detection of group B2 strains in this study may be due to differences in geographical locations and temporal variation as well as specific features of the population. Moreover, it could also be attributed to the enormous diverse pool of E. coli species (Bailey et al, 2010), or the bacterial characteristics in different topographical arena under the influence of antibiotics usage or the host genetic factor (Duriez et al, 2001). …”