High-Level Pacidamycin Resistance in Pseudomonas aeruginosa Is Mediated by an Opp Oligopeptide Permease Encoded by theopp-fabIOperon

Abstract

ABSTRACTPacidamycins (or uridyl peptide antibiotics) possess selectivein vivoactivity againstPseudomonas aeruginosa. An important limitation for the therapeutic use of pacidamycins withP. aeruginosais the high frequency (10−6to 10−7) at which resistant mutants emerge. To elucidate the mechanism(s) of this resistance, pacidamycin-resistantP. aeruginosamutants were isolated. Two types of mutants were obtained. Type 1, or high-level resistance mutants with a pacidamycin MIC of 512 μg/ml, were more abundant, with a frequency of ∼2 × 10−6, and did not show cross-resistance with other antibiotics. Type 2, low-level resistance mutants, were isolated with a frequency of ∼10−8and had a pacidamycin MIC of 64 μg/ml (the MIC for the wild-type strain was 4 to 16 μg/ml). These mutants were cross-resistant to levofloxacin, tetracycline, and erythromycin and were shown to overexpress either the MexAB-OprM or MexCD-OprJ multidrug resistance efflux pumps. High-level resistant mutants were isolated by transposon mutagenesis and one insertion was localized tooppB, one of two periplasmic binding protein components of an oligopeptide transport system which is encoded by theopp-fabIoperon. The Opp system is required for uptake of pacidamycin across the inner membrane, since variousopp, but notfabI, mutants were resistant to high levels of pacidamycin. Both of the two putative Opp periplasmic binding proteins, OppA and OppB, were required for pacidamycin uptake. Although both impaired uptake into and efflux from the cell can cause pacidamycin resistance inP. aeruginosa, our data suggest that impaired uptake is the primary reason for the high-frequency and high-level pacidamycin resistance.