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J Antimicrob Chemother. 2017 Nov 1;72(11):3043-3046. doi: 10.1093/jac/dkx258.

Cryptic silver resistance is prevalent and readily activated in certain Gram-negative pathogens.

Author information

1
Antimicrobial Research Centre and School of Molecular and Cellular Biology, University of Leeds, Leeds LS29JT, UK.
2
Department of Microbiology, Northampton General Hospital NHS Trust, Cliftonville, Northampton NN15BD, UK.

Abstract

Objectives:

To assess the prevalence of cryptic silver (Ag+) resistance amongst clinical isolates of Gram-negative bacteria, and to examine how overt Ag+ resistance becomes activated in such strains.

Methods:

Established methods were used to determine the susceptibility of 444 recent clinical isolates to Ag+, and to evaluate the potential for overt Ag+ resistance to emerge in susceptible isolates by spontaneous mutation. The genetic basis for Ag+ resistance was investigated using PCR amplification and DNA sequencing.

Results:

None of the isolates tested displayed overt Ag+ resistance. However, upon silver challenge, high-level Ag+ resistance (silver nitrate MIC >128 mg/L) was selected at high frequency (10-7 to 10-8) in 76% of isolates of Enterobacter spp., ∼58% of isolates of Klebsiella spp. and ∼0.7% of isolates of Escherichia coli. All strains in which Ag+ resistance could be selected harboured the sil operon, with resistance apparently resulting from activation of this system as a consequence of single missense mutations in silS. By contrast, Ag+ resistance was not selected in isolates lacking sil, which included all tested representatives of Pseudomonas aeruginosa, Acinetobacter spp., Citrobacter spp. and Proteus spp.

Conclusions:

Whilst overt Ag+ resistance in Gram-negative pathogens is uncommon, cryptic Ag+ resistance pertaining to the sil operon is prevalent and readily activated in particular genera (Enterobacter and Klebsiella).

PMID:
28981647
DOI:
10.1093/jac/dkx258
[Indexed for MEDLINE]
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