Association between antimicrobial resistance and virulence in Escherichia coli blood and faeces isolates from humans in Denmark

Abstract number: p1376

Bagger-Skjøt  L., Sandvang  D., Lester  C.H., Porsbo  L.J., Monnet  D.L., Frimodt-Møller  N., Hammerum  A.M.

Objectives: 

The aim of this study was to investigate possible associations between resistance phenotype and virulence genes in Escherichia coli isolates obtained from the blood of bacteraemic patients and from the faeces of non-hospitalised humans.

Methods: 

Between January and September 2003, 123 consecutive E. coli blood isolates were collected at the Clinical Microbiology Laboratory, Statens Serum Institut. During the same period, 85 E. coli faeces isolates from non-hospitalised human volunteers were obtained as part of the Danish Integrated Antimicrobial Resistance Monitoring and Research Programme (DANMAP). Susceptibility to 17 antimicrobial agents was determined by micro-broth dilution using the Sensititre system (Trek Diagnostics Systems Ltd., East Grinstead, United Kingdom). The presence of the following 9 virulence genes was assessed by PCR: iutA, fyuA and iroN (siderophores); hlyA and cnf1 (toxins); sfaS and focG (adhesins); traT, associated with serum resistance; and malX, a marker for a pathogenicity-associated island.

Results: 

The associations between antimicrobial resistance phenotype and virulence gene that were significant are presented in the Table. Table. Significant associations (P < 0.006, Bonferroni correction) among antimicrobial resistance phenotypes (S, susceptible; R, resistant) and presence of virulence factor genes (VF+)

Conclusion: 

Clear associations were found between certain common resistance phenotypes and two virulence genes, i.e. iutA and traT, both in E. coli isolated from the blood of patients with bacteraemia and from the faeces of non-hospitalised humans. It is difficult to explain these associations and further studies are needed. However, such links between resistance and virulence are disturbing since the use of antimicrobial agents may result not only in the selection of resistant isolates, but also of more virulent ones.