Decrease in accumulation of macrolide antibiotics as a mechanism of resistance in Staphylococcus aureus

A meta-analysis on the prevalence of resistance of Staphylococcus aureus to different antibiotics in Nigeria

BACKGROUND

Rapid emergence of multidrug resistant Staphylococcus aureus has resulted to difficulty in treatment of infections caused by such strains. The aim of this meta-analysis study was to determine the pooled prevalence of resistance of S. aureus to different antibiotics in Nigeria.

METHODS

Literature search for studies was done using Google scholar, PubMed, Science direct, and African Journal Online. The prevalence of S. aureus resistance to different antibiotics was evaluated using the meta-analysis proportion command in MedCalc software version 20.0 adopting a rand effect model. I² statistic and Egger test in MedCalc was used to evaluate the heterogeneity and the presence of publication bias among studies respectively.

RESULTS

A total of 40, 682 studies were retrieved through the database search of which 98 studies met the study inclusion criteria. Prevalence of resistance of S. aureus to different antibiotics ranges from 13 to 82%. Results showed a very high degree of resistance to penicillin G (82% [95% confidence interval (CI) 61%, 0.96%]), cloxacillin (77% [95% CI 64%, 88%]), amoxacillin (74% [95% CI 66%, 81%]), cefuroxime (69% [95% CI 51%, 85%]), ampicillin (68% [95% CI 53%, 81%]). Moderately resistance to erythromycin (47% [95% CI 40%, 53%]), chloramphenicol (47% [95% CI 37%, 56%]), methicillin (46% [95% CI 37%, 56%]), ofloxacin (24% [95% CI 18%, 31%]) and rifampicin 24% [95% CI 6%, 48%]). Low resistance was observed in vancomycin 13% (95% CI 7%, 21%). For each individual meta-analysis, high heterogeneity was observed with I² range (79.36-98.60%) at p-values ≤ 0.01). Egger's tests for regression intercept in funnel plots indicated no evidence of publication bias.

CONCLUSION

This meta-analysis study established that S. aureus in Nigeria has developed resistance to commonly used antibiotics such as the beta-lactam class antibiotics, sulphonamides, tetracyclines, chloramphenicol, and vancomycin. Hence it is imperative to develop programs to promote rational use of antimicrobial agents, infection prevention and control to reduce the incidence of antimicrobial resistance.

Resistance of Staphylococcus aureus to antimicrobial agents in Ethiopia: a meta-analysis

Background

Emergence of antimicrobial resistance by Staphylococcus aureus has limited treatment options against its infections. The purpose of this study was to determine the pooled prevalence of resistance to different antimicrobial agents by S. aureus in Ethiopia.

Methods

Web-based search was conducted in the databases of PubMed, Google Scholar, Hinari, Scopus and the Directory of Open Access Journals (DOAJ) to identify potentially eligible published studies. Required data were extracted and entered into Excel spread sheet. Statistical analyses were performed using Stata version 13.0. The metaprop Stata command was used to pool prevalence values. Twenty-one separate meta-analysis were done to estimate the pooled prevalence of the resistance of S. aureus to twenty-one different antimicrobial agents. Heterogeneity among the studies was assessed using the I² statistic and chi-square test. Publication bias was assessed using Egger’s test. Because of significant heterogeneity amongst the studies, the random effects model was used to pool prevalence values.

Results

The electronic database search yielded 1317 studies among which 45 studies met our inclusion criteria. Our analyses demonstrated very high level of resistance to amoxicillin (77% [95% confidence interval (CI): 68%, 0.85%]), penicillin (76% [95% CI: 67%, 84%]), ampicillin (75% [95% CI: 65%, 85%]), tetracycline (62% [95% CI: 55%, 68%]), methicillin (47% [95% CI: 33%, 61%]), cotrimoxaziole (47% [95% CI: 40%, 55%]), doxycycline (43% [95% CI: 26%, 60%]), and erythromycin (41% [95% CI: 29%, 54%]). Relatively low prevalence of resistance was observed with kanamycin (14% [95% CI: 5%, 25%]) and ciprofloxacin (19% [95% CI: 13%, 26%]). The resistance level to vancomycin is 11% 995% CI: (4%, 20%). High heterogeneity was observed for each of the meta-analysis performed (I² ranging from 79.36% to 95.93%; all p-values ≤0.01). Eggers’ test did not show a significant publication bias for all antimicrobial agents except for erythromycin and ampicillin.

Conclusions

S. aureus in Ethiopia has gotten notoriously resistant to almost to all of antimicrobial agents in use including, penicillin, cephalosporins, tetracyclines, chloramphenicol, methicillin, vancomycin and sulphonamides. The resistance level to vancomycin is bothersome and requires a due attention. Continued and multidimensional efforts of antimicrobial stewardship program promoting rational use of antibiotics, infection prevention and containment of AMR are urgently needed.

Electronic supplementary material

The online version of this article (doi:10.1186/s13756-017-0243-7) contains supplementary material, which is available to authorized users.

Mechanisms of bacterial resistance to macrolide antibiotics

Macrolides have been used in the treatment of infectious diseases since the late 1950s. Since that time, a finding of antagonistic action between erythromycin and spiramycin in clinical isolates1 led to evidence of the biochemical mechanism and to the current understanding of inducible or constitutive resistance to macrolides mediated by erm genes containing, respectively, the functional regulation mechanism or constitutively mutated regulatory region. These resistant mechanisms to macrolides are recognized in clinically isolated bacteria. (1) A methylase encoded by the erm gene can transform an adenine residue at 2058 (Escherichia coli equivalent) position of 23S rRNA into an 6N, 6N-dimethyladenine. Position 2058 is known to reside either in peptidyltransferase or in the vicinity of the enzyme region of domain V. Dimethylation renders the ribosome resistant to macrolides (MLS). Moreover, another finding adduced as evidence is that a mutation in the domain plays an important role in MLS resistance: one of several mutations (transition and transversion) such as A2058G, A2058C or U, and A2059G, is usually associated with MLS resistance in a few genera of bacteria. (2) M (macrolide antibiotics)- and MS (macrolide and streptogramin type B antibiotics)- or PMS (partial macrolide and streptogramin type B antibiotics)-phenotype resistant bacteria cause decreased accumulation of macrolides, occasionally including streptogramin type B antibiotics. The decreased accumulation, probably via enhanced efflux, is usually inferred from two findings: (i) the extent of the accumulated drug in a resistant cell increases as much as that in a susceptible cell in the presence of an uncoupling agent such as carbonylcyanide-m-chlorophenylhydrazone (CCCP), 2,4-dinitrophenol (DNP), and arsenate; (ii) transporter proteins, in M-type resistants, have mutual similarity to the 12-transmembrane domain present in efflux protein driven by proton-motive force, and in MS- or PMS-type resistants, transporter proteins have mutual homology to one or two ATP-binding segments in efflux protein driven by ATP. (3) Two major macrolide mechanisms based on antibiotic inactivation are dealt with here: degradation due to hydrolysis of the macrolide lactone ring by an esterase encoded by the ere gene; and modification due to macrolide phosphorylation and lincosamide nucleotidylation mediated by the mph and lin genes, respectively. But enzymatic mechanisms that hydrolyze or modify macrolide and lincosamide antibiotics appear to be relatively rare in clinically isolated bacteria at present. (4) Important developments in macrolide antibiotics are briefly featured. On the basis of information obtained from extensive references and studies of resistance mechanisms to macrolide antibiotics, the mode of action of the drugs, as effectors, and a hypothetical explanation of the regulation of the mechanism with regard to induction of macrolide resistance are discussed.

Localization of a determinant mediating partial macrolide resistance in Staphylococcus aureus

Four out of more than 8,200 Staphylococcus aureus strains isolated in Japan between 1961 and 1980 were constitutively resistant to a variety of macrolide antibiotics except tylosin and rokitamycin, but susceptible to lincosamide and streptogramin type B antibiotics (PM). The data obtained by agarose gel electrophoresis, CsCl-ethidium bromide density gradient analysis, diagnosis with ATP-dependent deoxyribonuclease, and a test transducing into a rec- mutant with phage 80L2 propagated on PM-resistant S. aureus all suggested that the determinant for the PM-resistance is located in chromosome.

Inducible erythromycin resistance in staphylococci 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 1.464 kbp, 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 interdomain 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.

Binding of novel macrolide structures to macrolides-lincosamides-streptogramin B-resistant ribosomes inhibits protein synthesis and bacterial growth

Dimethylation of adenine 2058 in 23S rRNA renders bacteria resistant to macrolides, lincosamides, and streptogramin B (MLS resistance), because the antibiotic binding site on the altered 50S ribosomal subunit is no longer accessible. We now report that certain 6-O-methyl-11,12-cyclic carbamate derivatives of erythromycin are able to bind to dimethylated MLS-resistant 50S ribosomal subunits, thus inhibiting protein synthesis and cell growth. One of these novel structures, an 11-deoxy-11-(carboxyamino)-6-O-methylerythromycin A 11,12-(cyclic ester) derivative, structure 1a, was studied in detail. It inhibited in vitro protein synthesis in extracts prepared from both susceptible and MLS-resistant Bacillus subtilis with 50% inhibitory concentrations of 0.4 and 20 microM, respectively. The derivative bound specifically to a single site on the 50S subunit of MLS-resistant ribosomes prepared from B. subtilis and Staphylococcus aureus, and no binding to 30S subunits was observed. The association rate constant of derivative 1a with sensitive and resistant ribosomes was 100- and 500-fold slower, respectively, than that of the parent compound, erythromycin, with sensitive ribosomes. The dissociation rate constant of 1a from sensitive and resistant ribosomes was 50- to 100-fold slower than the rate of erythromycin dissociation from sensitive ribosomes. Furthermore, 1a binding to sensitive 50S subunits led to induction of ermC and ermD, while binding to resistant 50S subunits did not, showing that perturbation of sensitive and resistant 50S subunit function by 1a differs. These data demonstrated that 1a is unique in its interaction with MLS-resistant ribosomes and that this interaction causes a novel allosteric perturbation of ribosome function.

Mechanisms of macrolide resistance in Ureaplasma urealyticum: a study on collection and clinical strains

Ureaplasma urealyticum is considered as a species which is intrinsically sensitive to macrolides (MIC less than 1 microgram/ml). Nevertheless, some of the strains recently isolated in our laboratories showed moderate to high levels of resistance (MICs ranging from 2 micrograms/ml to 100 micrograms/ml). In particular, a strain (CT28) isolated from a patient with nongonococcal urethritis long treated with erythromycin revealed a MIC greater than 100 micrograms/ml for this antibiotic. In order to investigate the mechanisms of resistance, strain CT28 and ten clinical and laboratory U. urealyticum strains were compared for the sensitivity to six antibiotics including three macrolides. Moreover the amount of macrolide uptake and the specific antibiotic binding to ribosomes were studied. Strain CT28 was resistant to josamycin, erythromycin, roxithromycin, lincomycin and clindamycin but sensitive to minocycline. When compared to a sensitive strain, strain CT28 showed a six-fold reduction in intracellular macrolide influx and accumulation and a reduction in antibiotic binding to ribosomes. The mechanisms implicated in these differences may be important for macrolide resistance in U. urealyticum.

Novel mechanism for plasmid-mediated erythromycin resistance by pNE24 from Staphylococcus epidermidis

We describe an unusual type of erythromycin resistance (Emr) mediated by a plasmid designated pNE24 from Staphylococcus epidermidis. This 26.5-kilobase plasmid encodes resistance strictly to 14-membered macrolide antibiotics, erythromycin, and oleandomycin. Resistance to other macrolide-lincosamide-streptogramin B (MLS) antibiotics was not observed even after a prior induction stimulus with various MLS antibiotics. Plasmid pNE24 was found to express resistance constitutively and manifested a low to intermediate MIC (62.5 micrograms/ml) for erythromycin. The resistance gene, designated erpA, appears to mediate resistance by altering the permeability of the host cell for erythromycin, because the measured uptake of 14C-labeled erythromycin by strain 958-2 (containing pNE24) was lower than for the erythromycin-susceptible, isogenic strain 958-1. No inactivation of erythromycin in overnight broth culture supernatants could be detected. In addition, no significant loss in binding affinity between [14C]erythromycin and ribosome could be detected for ribosomes isolated from strain 958-2 relative to 958-1, indicating that pNE24 probably does not produce a modification of the bacterial ribosome. No other selectable marker was found associated with pNE24; however, a 60,000-dalton protein was present only in the membrane fractions of cells (958-2) containing pNE24 and may play a role in mediating resistance to erythromycin.

Macrolide resistance in Staphylococcus aureus: induction of macrolide-resistant protein synthesis

Induction of resistance to macrolide-, lincosamide-, and streptogramin B-type antibiotics in Staphylococcus aureus was studied by monitoring the appearance of erythromycin A (EM)-resistant [(14)C]leucine incorporation. Examination of the induction process revealed saturation kinetics and a time course much like that reported for penicillinase in gram-positive bacteria. Induction kinetics in exponentially growing cells were sigmoidal and appeared to reach a maximum and constant rate when growth reached stationary phase. Since the induction of EM-resistant colony-forming ability was complete within 60 min, ribosome modification cannot be limited to a fraction of the population and must occur in essentially every cell. However, EM-resistant growth was expressed in cells where less than half the [(14)C]leucine-incorporating activity was resistant to EM. This suggests that resistance requires that only a threshold level of ribosome modification be exceeded and that, once exceeded, resistance is dominant to sensitivity.