Trimethoprim Resistance In Urinary Pathogens Research Articles

Antimicrobial resistance in urinary pathogens and culture-independent detection of trimethoprim resistance in urine from patients with urinary tract infection

BackgroundAlthough urinary tract infections (UTIs) are extremely common, isolation of causative uropathogens is not always routinely performed, with antibiotics frequently prescribed empirically. This study determined the susceptibility of urinary isolates from two Health and Social Care Trusts (HSCTs) in Northern Ireland to a range of antibiotics commonly used in the treatment of UTIs. Furthermore, we determined if detection of trimethoprim resistance genes (dfrA) could be used as a potential biomarker for rapid detection of phenotypic trimethoprim resistance in urinary pathogens and from urine without culture.MethodsSusceptibility of E. coli and Klebsiella spp. isolates (n = 124) to trimethoprim, amoxicillin, ceftazidime, ciprofloxacin, co-amoxiclav and nitrofurantoin in addition to susceptibility of Proteus mirabilis (n = 61) and Staphylococcus saprophyticus (n = 17) to trimethoprim was determined by ETEST® and interpreted according to EUCAST breakpoints. PCR was used to detect dfrA genes in bacterial isolates (n = 202) and urine samples(n = 94).ResultsResistance to trimethoprim was observed in 37/124 (29.8%) E. coli and Klebsiella spp. isolates with an MIC90 > 32 mg/L. DfrA genes were detected in 29/37 (78.4%) trimethoprim-resistant isolates. Detection of dfrA was highly sensitive (93.6%) and specific (91.4%) in predicting phenotypic trimethoprim resistance among E. coli and Klebsiella spp. isolates. The dfrA genes analysed were detected using a culture-independent PCR method in 16/94 (17%) urine samples. Phenotypic trimethoprim resistance was apparent in isolates cultured from 15/16 (94%) dfrA-positive urine samples. There was a significant association (P < 0.0001) between the presence of dfrA and trimethoprim resistance in urine samples containing Gram-negative bacteria (Sensitivity = 75%; Specificity = 96.9%; PPV = 93.8%; NPV = 86.1%).ConclusionsThis study demonstrates that molecular detection of dfrA genes is a good indicator of trimethoprim resistance without the need for culture and susceptibility testing.

Trimethoprim resistance in urinary pathogens in northern Scotland: epidemic spread of a resistance plasmid encoding the type Ib trimethoprim-resistant dihydrofolate reductase

The prevalence of trimethoprim resistance in enterobacterial urinary pathogens from hospitalised patients in the Angus district of northern Scotland (22.8%) was twice that found in similar isolates from patients attending general practitioners (11.2%). Thirty-three of the 143 trimethoprim-resistant strains were shown to harbour transferable plasmids conferring high-level trimethoprim resistance. In total, 17 different plasmid types were distinguished. Two plasmids, pUK1184 and pUK1185, accounted for 36% of the trimethoprim resistance plasmids and were shown by restriction endonuclease digestion fingerprints to be closely related to plasmid pUK28, previously demonstrated to be endemic in urinary pathogens in the Edinburgh area. Only 21% of the plasmids were shown to encode the type Ia trimethoprim-resistant dihydrofolate reductase, whereas 70% of the trimethoprim resistance plasmids were found to encode the type Ib dihydrofolate reductase. Hybridisation of the trimethoprim resistance plasmids identified in this study with gene probes specific for the integrase genes of transposons Tn7 and Tn21 indicates that the dhfrIa is rarely present within Tn7 or related transposons in these plasmids and may be more prevalent within Tn21-like transposons. In contrast, with the exception of the two endemic plasmids that harboured the dhfrIb gene within a Tn7-like transposon, the majority of dhfrIb genes were not found to be associated with either Tn7- or Tn21-like structures.

Distribution and transferability of plasmids encoding trimethoprim resistance in urinary pathogens from Greece

Of 505 strains of Enterobacteriaceae responsible for significant bacteriuria and isolated from hospital patients in two Greek cities in 1989, 151 strains (30%) were resistant to trimethoprim (MIC greater than or equal to 4 mg/L) and 220 (44%) were resistant to sulphamethoxazole (MIC greater than or equal to 64 mg/L); 127 (84%) of the trimethoprim-resistant strains exhibited high-level resistance (MIC greater than 1024 mg/L) and 121 (80%) were additionally resistant to four or more other antibiotics. Plasmids were detected in 141 (93%) of the trimethoprim-resistant strains. Trimethoprim resistance was encoded on self-transmissible plasmids in 79 (52%) of the resistant strains, and in a further seven strains (5%), plasmids coding for trimethoprim resistance could be mobilised by X+ factor. Co-transfer of various other antimicrobial resistances with trimethoprim resistance was observed, tetracycline resistance being the most common. The low degree of linkage observed between trimethoprim resistance and resistance to streptomycin and spectinomycin suggests that Tn7 is relatively uncommon in Greece. Classification of trimethoprim-resistance plasmids on the basis of their antimicrobial-resistance patterns and molecular mass revealed 39 different profiles. Overall, these findings differ from those from other European countries where the prevalence of transferable high-level trimethoprim resistance is low and where chromosomal Tn7-encoded trimethoprim resistance is common.