Reaction of roxithromycin and clarithromycin with macrolide-inactivating enzymes from highly erythromycin-resistant Escherichia coli

Immunomodulatory Effects of Macrolides Considering Evidence from Human and Veterinary Medicine

Macrolide antimicrobial agents have been in clinical use for more than 60 years in both human and veterinary medicine. The discovery of the non-antimicrobial properties of macrolides and the effect of immunomodulation of the inflammatory response has benefited patients with chronic airway diseases and impacted morbidity and mortality. This review examines the evidence of antimicrobial and non-antimicrobial properties of macrolides in human and veterinary medicine with a focus toward veterinary macrolides but including important and relevant evidence from the human literature. The complete story for these complex and important molecules is continuing to be written.

Impact of roxithromycin on waste activated sludge anaerobic digestion: Methane production, carbon transformation and antibiotic resistance genes

The macrolide antibiotic roxithromycin is widely detected in varying aquatic environments, especially in the wastewater systems, as an emerging contaminant and leads to significant impacts on the microorganisms involved. In this study, the impact of a shock load of roxithromycin on waste activated sludge (WAS) anaerobic digestion was comprehensively investigated. The biochemical methane potential tests showed that the methane production from WAS anaerobic digestion was significantly inhibited by roxithromycin. With the dosage of roxithromycin increasing from 0 to 1000 μg/L, the maximum cumulative methane production decreased from 163.5 ± 2.6 mL/g VS to 150.9 ± 4.5 mL/g VS. In particular, roxithromycin inhibited the acidogenesis and methanogenesis in WAS anaerobic digestion, leading to the decreased methane production. The methanogenic archaea in the studied system mainly belonged to the genera of Methanoseata, Candidatus Methanofastidiosum and Methanolinea and their relative abundances also decreased with roxithromycin addition. The analysis of antibiotic resistance genes (ARGs) in the digested sludge indicated that the abundances of most ARGs detected in this study were increased with roxithromycin exposure, suggesting the potential of growing antibiotic resistance, which was probably caused by enhancing the effect of esterases, methylases and phosphorylases. This work reveals how roxithromycin affects the WAS anaerobic digestion and the change of ARGs in the anaerobic digestion with roxithromycin exposure, and provides useful information for practical operation.

Resistance to Macrolide Antibiotics in Public Health Pathogens

Macrolide resistance mechanisms can be target-based with a change in a 23S ribosomal RNA (rRNA) residue or a mutation in ribosomal protein L4 or L22 affecting the ribosome's interaction with the antibiotic. Alternatively, mono- or dimethylation of A2058 in domain V of the 23S rRNA by an acquired rRNA methyltransferase, the product of an erm (erythromycin ribosome methylation) gene, can interfere with antibiotic binding. Acquired genes encoding efflux pumps, most predominantly mef(A) + msr(D) in pneumococci/streptococci and msr(A/B) in staphylococci, also mediate resistance. Drug-inactivating mechanisms include phosphorylation of the 2'-hydroxyl of the amino sugar found at position C5 by phosphotransferases and hydrolysis of the macrocyclic lactone by esterases. These acquired genes are regulated by either translation or transcription attenuation, largely because cells are less fit when these genes, especially the rRNA methyltransferases, are highly induced or constitutively expressed. The induction of gene expression is cleverly tied to the mechanism of action of macrolides, relying on antibiotic-bound ribosomes stalled at specific sequences of nascent polypeptides to promote transcription or translation of downstream sequences.

Mechanism and diversity of the erythromycin esterase family of enzymes

Macrolide antibiotics such as azithromycin and erythromycin are mainstays of modern antibacterial chemotherapy, and like all antibiotics, they are vulnerable to resistance. One mechanism of macrolide resistance is via drug inactivation: enzymatic hydrolysis of the macrolactone ring catalyzed by erythromycin esterases, EreA and EreB. A genomic enzymology approach was taken to gain insight into the catalytic mechanisms and origins of Ere enzymes. Our analysis reveals that erythromycin esterases comprise a separate group in the hydrolase superfamily, which includes homologues of uncharacterized function found on the chromosome of Bacillus cereus, Bcr135 and Bcr136, whose three-dimensional structures have been determined. Biochemical characterization of Bcr136 confirms that it is an esterase that is, however, unable to inactivate macrolides. Using steady-state kinetics, homology-based structure modeling, site-directed mutagenesis, solvent isotope effect studies, pH, and inhibitor profiling performed in various combinations for EreA, EreB, and Bcr136 enzymes, we identified the active site and gained insight into some catalytic features of this novel enzyme superfamily. We rule out the possibility of a Ser/Thr nucleophile and show that one histidine, H46 (EreB numbering), is essential for catalytic function. This residue is proposed to serve as a general base in activation of a water molecule as the reaction nucleophile. Furthermore, we show that EreA, EreB, and Bcr136 are distinct, with only EreA inhibited by chelating agents and hypothesized to contain a noncatalytic metal. Detailed characterization of these esterases allows for a direct comparison of the resistance determinants, EreA and EreB, with their prototype, Bcr136, and for the discussion of their potential connections.

Macrolide antibiotics in food-animal health

Several 14- and 16-membered-ring macrolide antibiotics have acquired important roles in the modern production of food animals. Macrolide antibiotics exhibit many similar antimicrobial properties whether used in veterinary or human medicine. In addition to their direct inhibitory action on micro-organisms, macrolides exert a variety of subinhibitory concentration (sub-MIC) effects that are being increasingly recognised as important factors in the explanation of therapeutic results. Macrolides achieve wide tissue distribution and high intracellular concentrations that contribute prominently to their efficacy. Another important factor governing efficacy is the complex interaction between macrolides, micro-organisms, and phagocytes that may enable the host defence system to enhance the antibiotic's inhibitory action. A potential role for macrolides in modulating inflammatory processes has also been recognised. In both sub-MIC effects and interactions with the host immune system, different macrolides exert different responses that may reinforce or oppose each other. This complexity of responses requires additional studies in appropriate disease states and animal species in order to elucidate a more comprehensive understanding and explanation of in vivo outcomes.

Purification and characterization of an erythromycin esterase from an erythromycin-resistant Pseudomonas sp

An erythromycin esterase (molecular mass 51200 Da) was purified from Pseudomonas sp. GD100, which was isolated from a salmon hatchery sediment sample from Washington State. The pI of the protein was 4.5-4.8. The enzyme was inhibited by 1 mM mercuric acid, and had the substrate specificity for structurally related 14-membered macrolides, which decreased in the order of oleandomycin, erythromycin A and erythromycin A enol ether. The activity for erythromycin A varied with temperature, but the effect of pH was minimal at pH 6.0-9.0. The half-life of the enzyme was estimated to be 8.9 h at 35 degrees C and 0.23 h at 55 degrees C, and the activation energy of the catalytic reaction of erythromycin A was estimated at 16.2 kJ mol(-1).

Identification of functional amino acids in the macrolide 2'-phosphotransferase II

Macrolide 2'-phosphotransferase [MPH(2')] transfers the gamma phosphate of ATP to the 2'-OH group of macrolide antibiotics. The role of aspartic acids in the putative ATP-binding site of MPH(2')II was investigated through the substitution of alanine for aspartate by site-directed mutagenesis. D200A, D209A, D219A, and D231A mutant strains were unable to inactivate the substrate oleandomycin, while a D227A mutant retained 7% of the activity of the original enzyme.

Identification of Escherichia coli clinical isolates producing macrolide 2'-phosphotransferase by a highly sensitive detection method

Macrolide is inactivated with ATP plus crude extract of Escherichia coli producing macrolide 2'-phosphotransferase (MPH(2')), but not by living cells. Therefore, a convenient method for detection of MPH(2') using intact cells is needed. In this report, we determine that the modified lysozyme-DNase-RNase (LDR) method (named ELDR method) is at least one hundred times more sensitive for the detection of MPH(2') activity than the LDR method and, in addition, highly sensitive for the detection of aminoglycoside-modifying enzymes. Therefore, three new MPH(2')-producing strains were found in clinically isolated E. coli in Japan in 1997 by this method. It suggests that MPH(2')-producing E. coli have been spread in Japanese clinical fields.

Novel metallo beta-lactamase mediated by a Shigella flexneri plasmid

Novel carbapenem-hydrolyzing beta-lactamase (newly named MET-1) encoded on a transferable plasmid pMS390 from Shigella flexneri JS19622 was purified. The molecular weight was 28,000 by SDS-PAGE and the isoelectric point was higher than 9.3. This beta-lactamase favorably hydrolyzed classical cephalosporins and oxyimino-cephalosporins rather than penicillins and carbapenems, but did not hydrolyze monobactams. The enzymatic activity was inhibited by EDTA, and the enzyme was found to contain two moles of zinc per mole of enzyme protein by means of atomic absorption spectrophotometry. These results indicated that the enzyme is a zinc beta-lactamase which differs from known metallo beta-lactamases, especially in its cephalosporinase-type substrate profile.

Expression of the mphB gene for macrolide 2'-phosphotransferase II from Escherichia coli in Staphylococcus aureus

The genes mphA and mphB encode macrolide 2'-phosphotransferases I and II, respectively, and they confer resistance to macrolide antibiotics in Escherichia coli. To study the expression of these genes in Gram-positive bacteria, we constructed recombinant plasmids that consisted of an mph gene and the pUB110 vector in Bacillus subtilis. When these plasmids were introduced into Staphylococcus aureus, the mphB gene was active and macrolide 2'-phosphotransferase II was produced. The gene endowed S. aureus with high-level resistance to spiramycin, a macrolide antibiotic with a 16-membered ring. Moreover, transcription of the mphB gene in S. aureus began at the promoter that was active in E. coli.

Detection of erythromycin-resistant determinants by PCR

Erythromycin resistance determinants include Erm methylases, efflux pumps, and inactivating enzymes. To distinguish the different mechanisms of resistance in clinical isolates, PCR primers were designed so that amplification of the partial gene products could be detected in multiplex PCRs. This methodology enables the direct sequencing of amplified PCR products that can be used to compare resistance determinants in clinical strains. Further, this methodology could be useful in surveillance studies of erythromycin-resistant determinants.