Roland Leclercq

Plasmid-Mediated Resistance to Vancomycin and Teicoplanin in Enterococcus Faecium

THE glycopeptide antibiotic agents vancomycin and teicoplanin are useful in the treatment of severe infections due to gram-positive bacteria.1 2 3 Staphylococci, streptococci, and enterococci are a...

Mechanisms of Resistance to Macrolides and Lincosamides: Nature of the Resistance Elements and Their Clinical Implications

Resistance to macrolides and lincosamides is increasingly reported in clinical isolates of gram-positive bacteria. The multiplicity of mechanisms of resistance, which include ribosomal modification, efflux of the antibiotic, and drug inactivation, results in a variety of phenotypes of resistance. There is controversy concerning the clinical relevance of in vitro macrolide resistance. Recent data, however, have shown that eradication of bacteria correlates with clinical outcome of acute otitis media in children and that macrolide therapy results in delayed eradication of macrolide-resistant pneumococci. These results support the need for in vitro detection of macrolide resistance and correct interpretation of susceptibility tests to guide therapy.

Modes and Modulations of Antibiotic Resistance Gene Expression

SUMMARY Since antibiotic resistance usually affords a gain of function, there is an associated biological cost resulting in a loss of fitness of the bacterial host. Considering that antibiotic resistance is most often only transiently advantageous to bacteria, an efficient and elegant way for them to escape the lethal action of drugs is the alteration of resistance gene expression. It appears that expression of bacterial resistance to antibiotics is frequently regulated, which indicates that modulation of gene expression probably reflects a good compromise between energy saving and adjustment to a rapidly evolving environment. Modulation of gene expression can occur at the transcriptional or translational level following mutations or the movement of mobile genetic elements and may involve induction by the antibiotic. In the latter case, the antibiotic can have a triple activity: as an antibacterial agent, as an inducer of resistance to itself, and as an inducer of the dissemination of resistance determinants. We will review certain mechanisms, all reversible, that bacteria have elaborated to achieve antibiotic resistance by the fine-tuning of the expression of genetic information.

Resistance to Macrolides and Related Antibiotics in Streptococcus pneumoniae

Resistance to erythromycin in Streptococcus pneumoniae was first detected in 1967 in the United States and subsequently worldwide (11, 20). The corresponding mechanism was rapidly identified as ribosomal methylation, which had been primarily reported as being responsible for erythromycin resistance in staphylococci (44). Further spread of resistance was then noted in a few countries, such as France, where hospitals observed a sharp increase in the proportion of resistant pneumococci, which reached approximately 20% in 1984 (16). This trend was observed several years before the emergence and spread of penicillin resistance in pneumococci in France. Recently, an increasing number of countries have noted changes in the evolution of macrolide resistance. In some of them, such as the United States, increased incidence has been correlated with the emergence of a new mechanism of erythromycin resistance—efflux (39). This review is devoted to the mechanisms responsible for resistance to macrolides and related antibiotics in pneumococci.

Diversity of Ribosomal Mutations Conferring Resistance to Macrolides, Clindamycin, Streptogramin, and Telithromycin in Streptococcus pneumoniae

ABSTRACT Mechanisms of resistance were studied in 22 macrolide-resistant mutants selected in vitro from 5 parental strains of macrolide-susceptible Streptococcus pneumoniae by serial passage in various macrolides (T. A. Davies, B. E. Dewasse, M. R. Jacobs, and P. C. Appelbaum, Antimicrob. Agents Chemother., 44:414–417, 2000). Portions of genes encoding ribosomal proteins L22 and L4 and 23S rRNA (domains II and V) were amplified by PCR and analyzed by single-strand conformational polymorphism analysis to screen for mutations. The DNA sequences of amplicons from mutants that differed from those of parental strains by their electrophoretic migration profiles were determined. In six mutants, point mutations were detected in the L22 gene (G95D, P99Q, A93E, P91S, and G83E). The only mutant selected by telithromycin (for which the MIC increased from 0.008 to 0.25 μg/ml) contained a combination of three mutations in the L22 gene (A93E, P91S, and G83E). L22 mutations were combined with an L4 mutation (G71R) in one strain and with a 23S rRNA mutation (C2611A) in another strain. Nine other strains selected by various macrolides had A2058G (n = 1), A2058U (n = 2), A2059G (n = 1), C2610U (n = 1), and C2611U (n = 4) mutations (Escherichia coli numbering) in domain V of 23S rRNA. One mutant selected by clarithromycin and resistant to all macrolides tested (MIC, >32 μg/ml) and telithromycin (MIC, 4 μg/ml) had a single base deletion (A752) in domain II. In six remaining mutants, no mutations in L22, L4, or 23S rRNA could be detected.

High rate of macrolide resistance in Staphylococcus aureus strains from patients with cystic fibrosis reveals high proportions of hypermutable strains.

Incidence of resistance to erythromycin at our institution reached 53% in 122 Staphylococcus aureus isolates obtained from patients with cystic fibrosis (CF) from 1997 to 1999. Macrolide-resistance genes were sought for in 20 erythromycin-resistant isolates from 9 patients with CF by use of polymerase chain reaction; 13 strains did not contain any known macrolide-resistance genes. Sequence of ribosomal genes rrl (23S rRNA), rplD (L4 protein), and rplV (L22 protein) revealed the presence of mutations in the target site of macrolides in 15 of the 20 isolates. A higher proportion of hypermutator strains was observed in a group of 89 CF staphylococcal isolates, compared with that in the 74 non-CF control isolates (13/89 vs. 1/74 with resistance to rifampin [P=.0045]; 9/89 vs. 1/74 with resistance to streptomycin [P=.04]). Various mutations or deletions of the mutator mutS gene were found not only in 5 of 11 hypermutable strains but also in 3 nonhypermutable strains harboring a large number of ribosomal mutations. The presence of a high proportion of hypermutable strains might explain the adaptation of certain strains in the patients, as well as the emergence of macrolide resistance as a result of antibiotic selective pressure in CF.

Phenotypic and genotypic heterogeneity of glycopeptide resistance determinants in gram-positive bacteria.

Gram-positive glycopeptide-resistant bacteria isolated in various hospitals in Europe and in the United States between 1986 and 1988 were collected. Three resistance phenotypes could be distinguished. Thirty-one enterococci were highly resistant to vancomycin and teicoplanin. Resistance was transferable to other enterococci by conjugation for 16 of the 22 isolates that were tested. Homology was detected by hybridization between a probe specific for the vanA gene, which encodes an inducible high-level glycopeptide resistance protein in Enterococcus faecium BM4147, and DNA of the 31 clinical isolates and the 16 corresponding transconjugants. This indicates that a single class of resistance determinants accounts for high-level glycopeptide resistance in enterococci. The strains differed in their biotypes and resistance phenotypes and harbored resistance plasmids of various sizes, suggesting that spread of this resistance phenotype is due to dissemination of a gene rather than of a bacterial clone or of a single plasmid. Four enterococcal isolates were resistant to low levels of vancomycin and susceptible to teicoplanin. Twenty-three coagulase-negative staphylococcal isolates were resistant to teicoplanin and susceptible to vancomycin. These two groups of strains did not hybridize with the vanA probe and did not transfer resistance at a detectable frequency. The vanA gene was not detected in the glycopeptide-producing strains of Amycolatopsis orientalis (vancomycin) and Actinoplanes teichomyceticus (teicoplanin) or in various gram-positive bacteria intrinsically resistant to glycopeptides.

Twenty-five years of shared life with vancomycin-resistant enterococci: is it time to divorce?

Twenty-five years ago, isolation of vancomycin-resistant Enterococcus faecium (VREm) was reported both in the UK and in France. Since then, VREm has spread worldwide in hospitals. Hospital outbreaks appeared to be related to the evolution since the end of 1980s of a subpopulation of E. faecium highly resistant to ampicillin and fluoroquinolones (the so-called clonal complex CC17) that later acquired resistance to vancomycin. CC17 isolates are presumably better adapted than other E. faecium isolates to the constraints of the hospital environment and most contain mobile genetic elements, phage genes, genes encoding membrane proteins, regulatory genes, a putative pathogenicity island and megaplasmids. Colonization and persistence are major features of VREm. Inherent characteristics of E. faecium including a remarkable genome plasticity, in part due to acquisition of IS elements, in particular IS16, have facilitated niche adaptation of this distinct E. faecium subpopulation that is multiply resistant to antibiotics. Quinupristin/dalfopristin and linezolid are licensed for the treatment of VREm infections, with linezolid often used as a first-line treatment. However, the emergence of plasmid-mediated resistance to linezolid by production of a Cfr methyltransferase in Enterococcus faecalis is worrying. Daptomycin has not been extensively evaluated for the treatment of VREm infections and resistant mutants have been selected under daptomycin therapy. Although control of VRE is challenging, a laissez-faire policy would result in an increased number of infections and would create an irreversible situation. Although so far unsuccessful, dissemination of glycopeptide-resistant Staphylococcus aureus with van genes acquired from resistant enterococci cannot be ruled out.

Epidemiology and Risk Factors for Gram- Positive Coccal Infections in Neutropenia: Toward a More Targeted Antibiotic Strategy

The objective of this study was to evaluate the risk of acquiring gram-positive coccal infections in febrile neutropenic patients and to develop risk indexes for gram-positive and streptococcal infections. This prospective, multicenter study included 513 patients. The prevalence of gram-positive coccal infections was 21% (14% were staphylococcal infections and 7.8% were streptococcal infections). The mortality rate during the month after study enrollment was 5%. On multivariate analysis, the occurrence of gram-positive coccal infections was significantly associated with receipt of high-dose cytarabine therapy, proton pump inhibitors, and gut decontamination with colimycin without glycopeptides and presence of chills. Staphylococcal infection was significantly associated with use of nonabsorbable colimycin, and streptococcal infection was associated with diarrhea, use of nonabsorbable antifungals, receipt of high-dose cytarabine, and gut decontamination with colimycin. The relative risks for streptococcal infection were 2.9, 13.2, and 20.7 in the presence of 1, 2, and > or =3 parameters, respectively. Risk factors for staphylococcal and streptococcal infections differ among neutropenic patients. A simple scoring system for predicting streptococcal infection is proposed.

Genome Sequence of Streptococcus gallolyticus: Insights into Its Adaptation to the Bovine Rumen and Its Ability To Cause Endocarditis

Streptococcus gallolyticus (formerly known as Streptococcus bovis biotype I) is an increasing cause of endocarditis among streptococci and frequently associated with colon cancer. S. gallolyticus is part of the rumen flora but also a cause of disease in ruminants as well as in birds. Here we report the complete nucleotide sequence of strain UCN34, responsible for endocarditis in a patient also suffering from colon cancer. Analysis of the 2,239 proteins encoded by its 2,350-kb-long genome revealed unique features among streptococci, probably related to its adaptation to the rumen environment and its capacity to cause endocarditis. S. gallolyticus has the capacity to use a broad range of carbohydrates of plant origin, in particular to degrade polysaccharides derived from the plant cell wall. Its genome encodes a large repertoire of transporters and catalytic activities, like tannase, phenolic compounds decarboxylase, and bile salt hydrolase, that should contribute to the detoxification of the gut environment. Furthermore, S. gallolyticus synthesizes all 20 amino acids and more vitamins than any other sequenced Streptococcus species. Many of the genes encoding these specific functions were likely acquired by lateral gene transfer from other bacterial species present in the rumen. The surface properties of strain UCN34 may also contribute to its virulence. A polysaccharide capsule might be implicated in resistance to innate immunity defenses, and glucan mucopolysaccharides, three types of pili, and collagen binding proteins may play a role in adhesion to tissues in the course of endocarditis.