Jonathan H. Cove

Inducible erythromycin resistance in staphlyococci is encoded by a member of the ATP‐binding transport super‐gene family

A Staphylococcus epidermidis plasmid conferring inducible resistance to 14‐membered ring macrolides and type B streptogramins has been analysed and the DNA sequence of the gene responsible for resistance determined. A single open reading frame of 1.464kbp, preceded by a complex control region containing a promoter and two ribosomal binding sites, was identified. The deduced sequence of the 488‐amino‐acid protein (MsrA) revealed the presence of two ATP‐binding motifs homologous to those of a family of transport‐related proteins from Gram‐negative bacteria and eukaryotic cells, including the P‐glycoprotein responsible for multidrug resistance. In MsrA, but not these other proteins, the two potential ATP‐binding domains are separated by a Q‐linker of exceptional length. Q‐linkers comprise a class of flexible inter‐domain fusion junctions that are typically rich in glutamine and other hydrophilic amino acids and have a characteristic spacing of hydrophobic amino acids, as found in the MsrA sequence. Unlike the other transport‐related proteins, which act in concert with one or more hydrophobic membrane proteins, MsrA appears to function independently when cloned in a heterologous host (Staphylococcus aureus RN4220). MsrA might, therefore, interact with and confer antibiotic specificity upon other transmembrane efflux complexes of staphylococcal cells. The active efflux of [14C]‐erythromycin from cells of S. aureus RN4220 containing msrA has been demonstrated.

Antibiotic-resistant acne: lessons from Europe.

Summary Background Propionibacterium acnes and P. granulosum are widely regarded as the aetiological agents of inflammatory acne. Their proliferation and metabolism are controlled using lengthy courses of oral and/or topical antibiotics. Despite numerous reports of skin colonization by antibiotic‐resistant propionibacteria among acne patients, accurate prevalence data are available only for the U.K.

Erythromycin resistant propionibacteria in antibiotic treated acne patients: association with therapeutic failure

Erythromycin resistant (EmR propionibacteria were isolated from the skin surface of 51% of patients treated with oral erythromycin and 42% of patients treated with topical clindamycin compared with 3% of untreated control subject (P < 0.001). Amongst the topical clindamycin‐treated patients, there was a higher incidence of EmR propionibacterial carriage in those patients who had previously been treated with oral erythromycin (64%) than in patients with no known previous exposure to erythromycin (20%; 0.01 > P > 0.001). Patients responding to oral erythromycin treatment carried EmR propionibacteria less frequently (24%) than patients who were not responding or who had relapsed (70%; P < 0.001). These observations suggest that the use of oral erythromycin and/or topical clindamycin encourages the development of resistant propionibacteria and that the emergence of resistant strains is associated with therapeutic failure in erythromycin‐treated patients. In total 63 resistant isolates were obtained from 52 subjects. There were 42 strains of Propionibacterium acnes, 16 strains of Propionibacterium granulosum and five strains of Propionibacterium avidum. The majority of isolates were inducibly or constitutively resistant to macrolide (e.g. erythromycin), lincosamide (e.g. clindamycin) and streptogramin B type antibiotics. Therefore, the isolates are phenotypically indistinguishable from the majority of EmR bacteria in which resistance is due to methylation of 23S ribosomal RNA.

Prevalence of antibiotic‐resistant propionibacteria on the skin of acne patients: 10‐year surveillance data and snapshot distribution study

Summary Background Cutaneous propionibacteria are implicated in acne pathogenesis, although their exact role in the genesis of inflammation is still poorly understood. Agents, including antibiotics, that reduce the numbers of propionibacteria on skin are therapeutic. Resistance in the target organism is a well‐recognized consequence of antibiotic therapy for acne but formal prevalence and distribution data are lacking.

16S rRNA Mutation Associated with Tetracycline Resistance in a Gram-Positive Bacterium

ABSTRACT A genetic basis for tetracycline resistance in cutaneous propionibacteria was suggested by comparing the nucleotide sequences of the 16S rRNA genes from 16 susceptible and 21 resistant clinical isolates and 6 laboratory-selected tetracycline-resistant mutants of a susceptible strain. Fifteen clinical isolates resistant to tetracycline were found to have cytosine instead of guanine at a position cognate with Escherichia coli 16S rRNA base 1058 in a region important for peptide chain termination and translational accuracy known as helix 34. Cytosine at base 1058 was not detected in the laboratory mutants or the tetracycline-susceptible strains. The apparent mutation was recreated by site-directed mutagenesis in the cloned E. coli ribosomal operon, rrnB, encoded by pKK3535. E. coli strains carrying the mutant plasmid were more resistant to tetracycline than those carrying the wild-type plasmid both in MIC determinations and when grown in tetracycline-containing liquid medium. These data are consistent with a role for the single 16S rRNA base mutation in clinical tetracycline resistance in cutaneous propionibacteria.

Phenotypic and genotypic characterization of antibiotic-resistant Propionibacterium acnes isolated from acne patients attending dermatology clinics in Europe, the U.S.A., Japan and Australia

Background Propionibacterium acnes is the target of antimicrobial treatments for acne vulgaris. Acquired resistance to erythromycin, clindamycin and tetracyclines has been reported in strains from diverse geographical loci, but the molecular basis of resistance, via mutations in genes encoding 23S and 16S rRNA, respectively, has so far only been elucidated for isolates from the U.K.

EFFECTS OF BENZOYL PEROXIDE AND ERYTHROMYCIN ALONE AND IN COMBINATION AGAINST ANTIBIOTIC-SENSITIVE AND -RESISTANT SKIN BACTERIA FROM ACNE PATIENTS

Topical formulations of erythromycin and benzoyl peroxide are popular and effective treatments for mild to moderate acne vulgaris. Use of the former is associated with resistance gain in both skin propionibacteria and coagulase‐negative staphylococci, whereas use of the latter is not. We evaluated the efficacy of a combination of erythromycin and benzoyl peroxide against a total of 40 erythromycin‐sensitive and ‐resistant strains of Staphylococcus epidermidis and skin propioni‐ bacteria in vitro. Using the checkerboard technique, five erythromycin resistant strains of Propionibacterium acnes were inhibited synergistically or additively by the combination. Complete mutual indifference was exhibited between the drugs against the remaining 35 strains. However, erythromycin resistant staphylococci and propionibacteria were inhibited by the same concentration of benzoyl peroxide as erythromycin‐sensitive strains. These results suggest that, although the combination of erythromycin and benzoyl peroxide is not synergistic against the majority of erythromycin‐resistant staphylococci and propionibacteria, the concomitant therapeutic use of both drugs should counteract the selection of erythromycin‐resistant variants and reduce the number of pre‐existing resistant organisms on the skin of acne patients.

An Expanded Multilocus Sequence Typing Scheme for Propionibacterium acnes: Investigation of ‘Pathogenic’, ‘Commensal’ and Antibiotic Resistant Strains

The Gram-positive bacterium Propionibacterium acnes is a member of the normal human skin microbiota and is associated with various infections and clinical conditions. There is tentative evidence to suggest that certain lineages may be associated with disease and others with health. We recently described a multilocus sequence typing scheme (MLST) for P. acnes based on seven housekeeping genes (http://pubmlst.org/pacnes). We now describe an expanded eight gene version based on six housekeeping genes and two ‘putative virulence’ genes (eMLST) that provides improved high resolution typing (91eSTs from 285 isolates), and generates phylogenies congruent with those based on whole genome analysis. When compared with the nine gene MLST scheme developed at the University of Bath, UK, and utilised by researchers at Aarhus University, Denmark, the eMLST method offers greater resolution. Using the scheme, we examined 208 isolates from disparate clinical sources, and 77 isolates from healthy skin. Acne was predominately associated with type IA1 clonal complexes CC1, CC3 and CC4; with eST1 and eST3 lineages being highly represented. In contrast, type IA2 strains were recovered at a rate similar to type IB and II organisms. Ophthalmic infections were predominately associated with type IA1 and IA2 strains, while type IB and II were more frequently recovered from soft tissue and retrieved medical devices. Strains with rRNA mutations conferring resistance to antibiotics used in acne treatment were dominated by eST3, with some evidence for intercontinental spread. In contrast, despite its high association with acne, only a small number of resistant CC1 eSTs were identified. A number of eSTs were only recovered from healthy skin, particularly eSTs representing CC72 (type II) and CC77 (type III). Collectively our data lends support to the view that pathogenic versus truly commensal lineages of P. acnes may exist. This is likely to have important therapeutic and diagnostic implications.

The effects of acne treatment with a combination of benzoyl peroxide and erythromycin on skin carriage of erythromycin resistant propionibacteria

Summary Concomitant application of 5% w/w benzoyl peroxide and 3% w/w erythromycin has previously been shown to prevent the overgrowth, on the skin of acne patients, of crythromycin‐resistant coagulase‐negative staphylococci, which occurs when the antibiotic is used alone. Two in vivo studies were carried out to assess the ability of the same therapeutic combination to inhibit the growth of pre‐existing erythromycin‐resistant propionibacteria and to prevent the selection of resistant strains during treatment. A double‐blind clinical trial in 37 patients with mild to moderate acne vulgaris showed that the combination brought about a > 3 log10 c.f.u. reduction in total propionibacterial numbers/cm2 after 6 weeks therapy (P < 0.001, Wilcoxons matched pairs) and also significantly reduced the number of erythromycin‐resistant propionibacteria (P < 0.05). In contrast, erythromycin alone reduced the total propionibacterial count by < 1.5 log10 c.f.u./cm2 after 6 weeks (P < 0.05) and did not affect the number of erythromycin‐resistant strains. The combined formulation was significantly more effective at reducing total propionibacterial numbers at 6 (P < 0.01, Mann‐Whitney) and 12 weeks (P < 0.05) than erythromycin alone, although, after 12 weeks, the anti‐propionibacterial efficacy of both preparations was less marked. Five patients on combination therapy, and five treated with erythromycin alone, acquired erythromycin‐resistant strains de novo at week 6 or week 12. In an open study in 21 acne patients, who each carried > 103 c.f.u. erythromycin‐resistant propionibacteria/cm2 skin pretreatment, the combination of erythromycin and benzoyl peroxide reduced the total propionibacterial count by > 2.5 log10 and the number of erythromycin‐resistant strains by a similar amount (P < 0.001, Wilcoxon). This was accompanied by highly significant reductions in acne grade and lesion counts (P < 0.001). These data suggest that the combination of 5% w/w benzoyl peroxide and 3% w/w erythromycin has greater in vivo antipropionibacterial activity than 3% w/w erythromycin alone, and brings about significant clinical improvement in acne patients with high numbers of erythromycin‐resistant propionibacterial strains pretreatment.

Is antibiotic resistance in cutaneous propionibacteria clinically relevant? : implications of resistance for acne patients and prescribers.

AbstractIt is well recognized that some patients with acne do not respond adequately to antibiotic therapy. It is important to distinguish antibiotic recalcitrant acne which we would suggest represents acne that shows a diminished response to treatment irrespective of the cause as opposed to ‘antibiotic-resistant acne’ which is acne that is less responsive to treatment as a direct consequence of skin colonization with resistant propionibacteria. Here we show that antibiotic-resistant acne is not just a theoretical possibility but a real phenomenon that could have important consequences for patients and prescribers. The relationship between skin colonization by antibiotic-resistant propionibacteria and treatment outcomes is a complex one that is explained at the follicular level by physiological differences affecting local drug concentrations. A systematic review of the literature on antibiotic-resistant propionibacteria revealed methodological shortcomings in studies of their prevalence and a paucity of evidence on their clinical significance. Despite the elucidation of resistance mechanisms in cutaneous propionibacteria, our continuing inability to distinguish between strains of Propionibacterium acnes means that we still do not fully understand how resistance spreads, although person-to-person transfer is most likely. Finally, we present a decision tree for acne management in an era of prudent antimicrobial prescribing that provides an alternative to existing treatment algorithms by placing topical retinoids and not antibiotics at the cornerstone of acne management.