Resistance of bacterial pathogens to four aminoglycosides and six other antibacterials and prevalence of aminoglycoside modifying enzymes, in 20 UK centres.

A total of 5116 non-fastidious bacterial strains isolated from either blood or urine culture were collected from 20 geographically distributed centres within the UK. Upon receipt the strains were identified and the minimum inhibitory concentrations of ten antimicrobial agents in hospital usage were determined for each of the strains. All laboratories submitted a similar range of bacterial species and in species normally considered as sensitive the overall rates of resistance to the different antibiotics tested were: amikacin 2.4%, gentamicin 3.7%, netilmicin 2.6%, tobramycin 3.4%, ampicillin 41.7%, cefadroxil 11.6%, cefotaxime 1.4% [corrected], cefuroxime 4.3%, ciprofloxacin 0.6% and trimethoprim 13.0%. For those strains resistant to one or more aminoglycosides the mechanisms of resistance responsible were determined from the aminoglycoside-resistance patterns of the strains to 16 different aminoglycoside antibiotics. The predominant mechanisms of resistance found were APH(2") + AAC(6') production in staphylococci. AAC(2') production in Providencia spp., and AAC(3) production in the other Gram-negative genera.

Cloning and characterization of an AAC(6') gene from Serratia marcescens.

A gene encoding AAC(6') mediated resistance to netilmicin and amikacin was cloned from the chromosome of a nosocomial strain of Serratia marcescens into the BamHI site of pACYC184. The resistance determinant was localized to a sequence of approximately 1 kb. A 490 base pair BamHI-PvuII restriction fragment from the cloned DNA was used as a probe in Southern hybridization studies. Homology with a 920 base pair fragment of PvuII digested S. marcescens DNA from AAC(6')-producing strains was observed. No homology was detected with aminoglycoside sensitive S. marcescens or Escherichia coli.