Regional dissemination of a trimethoprim-resistance gene cassette via a successful transposable element.

BACKGROUND: Antimicrobial resistance is a growing international problem. We observed a 50% increase in the prevalence of trimethoprim resistance among fecal Escherichia coli from healthy Nigerian students between 1998 and 2005, a trend to increase that continued in 2009. METHODS AND FINDINGS: A PCR-based screen revealed that 131 (43.1%) of isolates obtained in Nigeria in 2005 and 2009 carried integron-borne dfrA cassettes. In the case of 67 (51.1%) of these isolates, the cassette was a class 1-integron-borne dfrA7 gene, which has been reported at high prevalence from E. coli isolates from other parts of Africa. Complete sequencing of a 27 Kb dfrA7-bearing plasmid from one isolate located the dfrA7 gene within a Tn21-type transposon. The transposon also contained an IS26-derived bla/sul/str element, encoding resistance to ß-lactams, sulphonamides and streptomycin, and mercury resistance genes. Although the plasmid backbone was only found in 12 (5.8%) of trimethoprim-resistant isolates, dfrA7 and other transposon-borne genes were detected in 14 (16.3%) and 32 (26.3%) of trimethoprim resistant isolates collected in Nigeria in 2005 and 2009, respectively. Additionally, 37 (19.3%) of trimethoprim-resistant E. coli isolates collected between 2006 and 2008 from Ghana were positive for the dfrA7 and a transposon marker, but only 4 (2.1%) harbored the plasmid backbone. CONCLUSIONS: Our data point to transposition as a principal mechanism for disseminating dfrA7 among E. coli from Nigeria and Ghana. On-going intensive use of the affordable broad-spectrum antibacterials is likely to promote selective success of a highly prevalent transposable element in West Africa.

Carriage of diarrhoeagenic Escherichia coli by older children and adults in Accra, Ghana.

Diarrhoeagenic Escherichia coli (DEC) were sought in stool specimens from 72 adults and children aged over 3 years, who presented with diarrhoea at a hospital in Accra, Ghana, and 72 matched controls. Only diffusely-adherent E. coli were significantly associated with disease in these older individuals (P=0.029). We additionally tested 53 specimens from infants among whom DEC were collectively associated with disease (P=0.012). Enteropathogenic, enterotoxigenic and enteroaggregative E. coli, the most commonly isolated pathotypes from infants with diarrhoea, were frequently recovered from healthy adults. Asymptomatic carriage of DEC by older individuals in Accra may place young children at risk for diarrhoea.