Genetic basis of resistance in Propionibacterium acnes strains isolated from diverse types of infection in different European countries

Abstract

The purpose of the study was to characterize the resistance mechanism of 36 clindamycin (CL) and erythromycin (EM) resistant Propionibacterium acnes strains and 27 tetracycline (TET) resistant P. acnes isolates, collected from nine European countries, both from acne patients and from patients with different infections. PCR and sequencing of the genes encoding domain V of 23S rRNA for CL and EM resistant strains and 16S rRNA for TET resistant strains were performed. Pulsed-field gel electrophoresis was used as a typing method to establish the relationship between resistance genotypes and pulsed-field types.

Several unique resistant genotypes were found to be distributed throughout Europe. P. acnes CL and EM resistant strains carrying one of the mutations within the 23S rRNA were predominantly isolated from Swedish acne patients (64%) compared to other infections (43%), OR=2.33 [CI=1.16–4.69]. Of 36 P. acnes isolates tested, none was found to carry the erm(X) resistance gene. Forty-four percent of TET resistant strains were found to carry a G–C transition in the 16S rRNA of the small ribosomal subunit and all these strains were isolated from Swedish acne patients. MIC of TET among all strains carrying this G–C mutation ($n=12$) was 32 mg/L and the MIC range for the strains where no mutation was detected ranged from 2 to 8 mg/L. The MIC values of TET were unaffected by the presence of reserpine, a well-known inhibitor of efflux pumps. Those TET resistant strains harbouring the mutation at 16S rRNA were clustered in one pulsotype. For TET resistant strains where no mutation was found, greater variability was noticed. No correlation was noticed between different resistance genotypes of CL and EM resistant strains and pulsed-field types.

Introduction

Propionibacterium acnes, a resident commensal bacterium that colonizes the lipid-rich environment of the pilosebaceous unit of the skin, produces chemotactic factors and proinflammatory molecules responsible for the inflammatory phase of acne [1]. This microorganism has also been implicated in severe infections, especially in compromised patients and newborn infants [2], [3].

Erythromycin (EM), clindamycin (CL) and tetracycline (TET) are antibiotics commonly used for acne treatment, with therapy courses lasting from weeks to months. This will result in a high pressure of resistance development among P. acnes strains [4], [5]. It has recently been shown that antimicrobial resistance against EM, CL and TET among P. acnes strains isolated from systemic infections has emerged [3].

Ross et al. [6] have shown the genetic base of resistance against EM and CL in cutaneous propionibacteria. The most prevalent mechanism was due to three different point mutations in genes encoding domain V, the peptidyltransferase loop of the 23S rRNA, and the authors found that each of these mutations is associated with a specific cross-resistance phenotype. An A–G transition at base 2058 determined strains highly resistant to EM and variable resistance to other macrolides and CL (phenotype I). A G–A transition at base 2057 is associated with low level resistance to EM (phenotype III) and an A–G transition at base 2059 is associated with high level resistance to all macrolides and elevated but variable resistance to CL (phenotype IV) [6].

The corynebacterial transposon Tn 5432 carrying erm(X) resistance gene has been detected in P. acnes strains highly resistant to the MLS antibiotics and corresponds to phenotypic resistance group II [7].

Generally, resistance to TET has previously been shown to be linked to resistance to EM and CL [3], [4], [8]. It was found that a single G–C transition in the 16S rRNA of the small ribosomal subunit at Escherichia coli equivalent base 1058 was responsible for clinical TET resistance in P. acnes [9].

The purpose of the present study was to characterize the resistance mechanisms of 36 CL and EM resistant P. acnes strains and 27 TET resistant P. acnes strains collected from different European countries, and originating from acne patients and from patients with systemic infections.