Macrolide Resistance Mechanisms Research Articles

Crystal structure of ErmE - 23S rRNA methyltransferase in macrolide resistance

Pathogens often receive antibiotic resistance genes through horizontal gene transfer from bacteria that produce natural antibiotics. ErmE is a methyltransferase (MTase) from Saccharopolyspora erythraea that dimethylates A2058 in 23S rRNA using S-adenosyl methionine (SAM) as methyl donor, protecting the ribosomes from macrolide binding. To gain insights into the mechanism of macrolide resistance, the crystal structure of ErmE was determined to 1.75 Å resolution. ErmE consists of an N-terminal Rossmann-like α/ß catalytic domain and a C-terminal helical domain. Comparison with ErmC’ that despite only 24% sequence identity has the same function, reveals highly similar catalytic domains. Accordingly, superposition with the catalytic domain of ErmC’ in complex with SAM suggests that the cofactor binding site is conserved. The two structures mainly differ in the C-terminal domain, which in ErmE contains a longer loop harboring an additional 310 helix that interacts with the catalytic domain to stabilize the tertiary structure. Notably, ErmE also differs from ErmC’ by having long disordered extensions at its N- and C-termini. A C-terminal disordered region rich in arginine and glycine is also a present in two other MTases, PikR1 and PikR2, which share about 30% sequence identity with ErmE and methylate the same nucleotide in 23S rRNA.

LB11. Rapid Rise in Decreased Susceptibility to Azithromycin among Shigella Isolates in the United States: A Look at National Surveillance Data, 2011–2017

Background Shigella spp. cause ~500,000 illnesses in the United States annually. Antibiotics are recommended for immunocompromised patients and shorten the duration of illness, thus limiting spread. First-line treatments include ciprofloxacin (CIP) and azithromycin (AZM). CIP resistance is a growing problem in the United States; decreased susceptibility to AZM (DSA) has been reported globally, particularly among men who have sex with men (MSM). We reviewed National Antimicrobial Resistance Monitoring System (NARMS) data to determine DSA trends among Shigella isolates in the United States.MethodsHealth departments nationwide forward every 20th Shigella isolate to CDC NARMS for antimicrobial susceptibility testing using broth microdilution. We defined CIP resistance using CLSI clinical breakpoints and DSA using epidemiological cutoff values where available. We performed whole genome sequencing on isolates from 2016 and screened the sequences for resistance determinants using ResFinder 3.0.ResultsTo date, we have tested 3,044 Shigella isolates collected during 2011–2017. Overall, 264 isolates (9%) had DSA, increasing from 3% in 2011 to 23% in 2017; 41 (16%) were also CIP resistant. The odds of DSA increased by 1.5 (95% confidence interval [CI] 1.4–1.6) annually. DSA was more common among adult males (OR 21.2, CI 14.9–30.3), in isolates from the West census region (OR 2.4, CI 1.8–3.2), and in S. flexneri (OR 8.2, CI 6.3–10.7). Of 543 sequenced isolates, 52 (10%) had DSA; of these, 31 (60%) contained both mph(A) and erm(B) genes, 17 (33%) contained mph(A) only, and 4 (8%) had no identified macrolide-resistance mechanism.ConclusionsIn 2017, nearly 1 in 4 Shigella isolates tested had DSA, a 7-fold increase since 2011. This rapid rise in DSA parallels that seen in other countries, where resistance to other clinically relevant drugs is high and macrolides are no longer useful as empiric treatment. The increased risk of DSA in adult males is consistent with previous reports of DSA Shigella in MSM. The resistance genes observed are typically plasmid-mediated and can be transferred to other bacteria. Public health strategies to mitigate the spread of resistant Shigella should include antibiotic stewardship and novel approaches for sexually transmitted infection prevention in MSM. Disclosures All authors: No reported disclosures.

A study of community-acquired Mycoplasma pneumoniae in Yantai, China.

Introduction: Community-acquired pneumonia (CAP) is a global disease responsible for a large number of deaths, with significant economic impact. As diagnostic tools have increased in sensitivity, understanding of the etiology of CAP has begun to change. Mycoplasma pneumoniae is one of the major pathogens causing CAP. Macrolides and related antibiotics are first-line treatments for M. pneumoniae. Macrolide resistance has been spreading for 15 years and now occurs in worldwide. We undertook the first study on macrolide resistance of M. pneumoniae in Yantai. This may be helpful to determine the appropriate therapy for CAP in this population.Objective: To investigate the rate and mechanism of macrolide resistance in Yantai.Methods: Pharyngeal swab samples were collected from adult CAP patients. Samples were assayed by polymerase chain reaction (PCR) and cultivated to test for M. pneumoniae. Nested PCR was used to specifically amplify M. pneumoniae 23S rRNA gene fragments containing mutations, and amplicons were analyzed by CE-SSCP for macrolide resistance mutations. Results were confirmed by sequencing. Twenty-seven strains of M. pneumoniae were isolated and the activities of nine antibiotics against M. pneumoniae were tested in vitro.Results: Out of 128 samples tested, 27 were positive for M. pneumoniae. Mycoplasma 100% macrolides resistance to Mycoplasma pneumoniae. The mechanism of macrolides resistance was A2063G point mutation in the sequence directly binding to macrolides in the 23S rRNA V domain in vitro. The mean pyretolytic time for the fluoroquinolone group was 4.7 ±2.9 d, which was significantly shorter than 8.2 ±4.1 d for the azithromycin group.Conclusions: Macrolides are not the first-line treatment for M. pneumoniae respiratory tract infections in Yantai.

Preliminary Study on Drug Susceptibility Profile and Resistance Mechanisms to Macrolides of Clinical Isolates of Non-tuberculous Mycobacteria from China

ObjectiveMacrolide susceptibility and drug resistance mechanisms of clinical non-tuberculous mycobacteria (NTM) isolates were preliminarily investigated for more accurate diagnosis and treatment of the infection in China. MethodsFour macrolides, including clarithromycin (CLAR), azithromycin (AZM), roxithromycin (ROX), and erythromycin (ERY), were used to test the drug susceptibility of 310 clinical NTM isolates from six provinces of China with the broth microdilution method. Two resistance mechanisms, 23S rRNA and erm, were analyzed with nucleotide sequence analysis. ResultsVaried effectiveness of macrolides and species-specific resistance patterns were observed. Most Mycobacterium abscessus subsp. massiliense were susceptible and all M. fortuitum were highly resistant to macrolides. All the drugs, except for erythromycin, exhibited excellent activities against slow-growing mycobacteria, and drug resistance rates were below 22.2%. Only four highly resistant strains harbored 2,058/2,059 substitutions on rrl and none of other mutations were related to macrolide resistance. G2191A and T2221C on rrl were specific for the M. abscessus complex (MABC). Seven sites, G2140A, G2210C, C2217G, T2238C, T2322C, T2404C, and A2406G, were specifically carried by M. avium and M. intracellulare. Three sites, A2192G, T2358G, and A2636G, were observed only in M. fortuitum and one site G2152A was specific for M. gordonae. The genes erm(39) and erm(41) were detected in M. fortuitum and M. abscessus and inducible resistance was observed in relevant sequevar. ConclusionThe susceptibility profile of macrolides against NTM was demonstrated. The well-known macrolide resistance mechanisms, 23S rRNA and erm, failed to account for all resistant NTM isolates, and further studies are warranted to investigate macrolide resistance mechanisms in various NTM species.

Resistance to quinolones, cephalosporins and macrolides in Escherichia coli causing bacteraemia in Peruvian children.

To characterise the β-lactam, quinolone and macrolide resistance levels and mechanisms in 62 Escherichia coli isolates causing bacteraemia in Peruvian children. Minimum inhibitory concentrations (MICs) of ciprofloxacin, nalidixic acid (NAL) and azithromycin were determined in the presence and absence of Phe-Arg-β-naphthylamide. Susceptibility to other 14 antimicrobial agents was also established. Extended-spectrum β-lactamases (ESBLs) were identified, and mutations in gyrA and parC as well as the presence of transferable mechanisms of quinolone resistance (TMQR) and macrolide resistance (TMMR) were determined. Fifty isolates (80.6%) were multidrug-resistant. High proportions of resistance to ampicillin (93.5%), NAL (66.1%) and trimethoprim/sulfamethoxazole (66.1%) were observed. No isolate showed resistance to carbapenems and only two isolates were resistant to nitrofurantoin. Twenty-seven isolates carried ESBL-encoding genes: 2 blaSHV-12; 13 blaCTX-M-15; 4 blaCTX-M-2; 6 blaCTX-M-65; and 2 non-identified ESBLs. Additionally, 27 blaTEM-1 and 9 blaOXA-1-like genes were detected. All quinolone-resistant isolates showed target mutations, whilst TMQR were present in four isolates. Efflux pumps played a role in constitutive NAL resistance. The association between quinolone resistance and ESBL production was significant (P=0.0011). The mph(A) gene was the most frequent TMMR (16 isolates); msr(A) and erm(B) genes were also detected. Only one TMMR-carrying isolate [presenting mph(A) and erm(B) concomitantly] remained resistant to azithromycin when efflux pumps were inhibited. A variety of ESBL-encoding genes and widespread of blaCTX-M-15 in Lima has been shown. The role of efflux pumps in azithromycin resistance needs to be further evaluated, as well as effective control of the use of antimicrobial agents.

Distribution of macrolide resistance mechanisms in Bulgarian clinical isolates of Streptococcus pyogenes during the years of 2013-2016.

Objectives of the present study was to determine and evaluate the distribution of genetic mechanisms associated with certain phenotypes of macrolide resistance in Bulgarian GAS isolated during the years of 2013-2016. All GAS strains were screened for the macrolide resistance genes erm(A), erm(B) and mef(A), using multiplex polymerase chain reaction (PCR). The minimal inhibitory concentrations (MICs) of erythromycin, azithromycin, clarithromycin, clindamycin were determined by E-tests. Almost 23% of GAS isolates obtained in 2013-2014 and near 40% of them in 2015-2016 contained various elements of resistance. The predominant gene was mef(A), which encodes an efflux pump (M-phenotype), identified in 57.84% of the macrolide-resistant strains. The next frequently prevalent mechanism was a combination of mef(A) and erm(B) in 22.55%, which determined high-level inducible or constitutive resistance to macrolides, lincosamides and streptogramins (iMLSB or cMLSB). The highest MIC value (>256mg/L) was detected in association with erm(B) (p<0.05). The MIC range was observed to be much higher in the isolates with combinations of resistance genes vs. those with mef genes alone (p<0.05). The data about the distribution and prevalence of macrolide resistance mechanisms obtained in this study can help in the treatment of persistent and recurrent GAS infections and in the correct choice of empiric therapy.

A Population-Based Assessment of the Impact of 7- and 13-Valent Pneumococcal Conjugate Vaccines on Macrolide-Resistant Invasive Pneumococcal Disease: Emergence and Decline of Streptococcus pneumoniae Serotype 19A (CC320) With Dual Macrolide Resistance Mechanisms.

Macrolide efflux encoded by mef(E)/mel and ribosomal methylation encoded by erm(B) confer most macrolide resistance in Streptococcus pneumoniae. Introduction of the heptavalent pneumococcal conjugate vaccine (PCV7) in 2000 reduced macrolide-resistant invasive pneumococcal disease (MR-IPD) due to PCV7 serotypes (6B, 9V, 14, 19F, and 23F). In this study, the impact of PCV7 and PCV13 on MR-IPD was prospectively assessed. A 20-year study of IPD performed in metropolitan Atlanta, Georgia, using active, population-based surveillance formed the basis for this study. Genetic determinants of macrolide resistance were evaluated using established techniques. During the decade of PCV7 use (2000-2009), MR-IPD decreased rapidly until 2002 and subsequently stabilized until the introduction of PCV13 in 2010 when MR-IPD incidence decreased further from 3.71 to 2.45/100000 population. In 2003, serotype 19A CC320 isolates containing both mef(E)/mel and erm(B) were observed and rapidly expanded in 2005-2009, peaking in 2010 (incidence 1.38/100000 population), accounting for 36.1% of MR-IPD and 11.7% of all IPD isolates. Following PCV13 introduction, dual macrolide-resistant IPD decreased 74.1% (incidence 0.32/100000 in 2013). However, other macrolide-resistant serotypes (eg, 15A and 35B) not currently represented in PCV formulations increased modestly. The selective pressures of widespread macrolide use and PCV7 and PCV13 introductions on S. pneumoniae were associated with changes in macrolide resistance and the molecular basis over time in our population. Durable surveillance and programs that emphasize the judicious use of antibiotics need to continue to be a focus of public health strategies directed at S. pneumoniae.

Antimicrobial Resistant Streptococcus pneumoniae: Prevalence, Mechanisms, and Clinical Implications.

Streptococcus pneumoniae is a major cause of pneumonia, meningitis, sepsis, bacteremia, and otitis media. S. pneumoniae has developed increased resistance to multiple classes of antibiotics. Systematic literature review of prevalence, mechanisms, and clinical implications in S. pneumoniae resistance. Since S. pneumoniae resistance to penicillin was first reported with subsequent development of resistance to other classes of drugs, selection of appropriate antibiotic treatment is challenging. We searched PubMed (English language) for citations to antibiotic resistance in S. pneumoniae published before March 1, 2016. We present a review of S. pneumoniae resistance to beta-lactams, macrolides, lincosamides, fluoroquinolones, tetracyclines, and trimethoprim-sulfamethoxazole (TMP-SMX). There has been a steady decline in susceptibility of S. pneumoniae to commonly used beta-lactams. Phenotypic expression of penicillin resistance occurs as a result of a genetic structural modification in penicillin-binding proteins. Between 20% and 40% of S. pneumoniae isolates are resistant to macrolides. Macrolide resistance mechanisms include ribosomal target site alteration, alteration in antibiotic transport, and modification of the antibiotic. Approximately 22% of S. pneumoniae isolates are resistant to clindamycin. Similar to macrolide resistance, clindamycin involves a target site alteration. The prevalence of fluoroquinolone resistance is low, although increasing. S. pneumoniae resistance to fluoroquinolones occurs by accumulated mutations within the bacterial genome, increased efflux, or acquisition of plasmid-encoded genes. S. pneumoniae resistance has also increased for the tetracyclines. The primary mechanism is mediated by 2 genes that confer ribosomal protection. The prevalence of TMP-SMX resistance is around 35%. As with fluoroquinolones, resistance to TMP-SMX is secondary to mutations in the bacterial genome. Effective treatment of resistant S. pneumoniae is a growing concern. New classes of drugs, newer formulations of older drugs, combination antibiotic therapy, nonantibiotic modalities, better oversight of antibiotic usage, and enhanced preventive measures hold promise.

Solithromycin: A novel ketolide antibiotic.

The pharmacology, pharmacokinetics, pharmacodynamics, antimicrobial activity, clinical safety, and current regulatory status of solithromycin are reviewed. Solithromycin is a novel ketolide antibiotic developed for the treatment of community-acquired bacterial pneumonia (CABP). Its pharmacologic, pharmacokinetic, and pharmacodynamic properties provide activity against a broad range of intracellular organisms, including retained activity against pathogens displaying various mechanisms of macrolide resistance. Phase III clinical trials of solithromycin demonstrated noninferiority of both oral and i.v.-to-oral regimens of 5-7 days' duration compared with moxifloxacin for patients with moderately severe CABP. Nearly one third of patients receiving i.v. solithromycin experienced infusion-site reactions. Although no liver-related adverse events were reported in patients receiving oral solithromycin, more patients receiving i.v.-to-oral solithromycin experienced asymptomatic, transient transaminitis, with alanine transaminase levels of >3 to >5 times the upper limit, compared with those treated with moxifloxacin. These results led the Food and Drug Administration to conclude that the solithromycin new drug application was not approvable as filed, adding that the risk of hepatotoxicity had not yet been adequately characterized. The agency further recommended a comparative study of patients with CABP to include approximately 9,000 patients exposed to solithromycin in order to exclude drug-induced liver injury events occurring at a rate of 1 in 3,000 with 95% probability. Solithromycin is a novel ketolide antibiotic with activity against a broad spectrum of intracellular organisms, including those displaying macrolide resistance. While demonstrating noninferiority to a current first-line agent in the treatment of CABP, concerns for drug-induced liver injury and infusion-site reactions have placed its regulatory future in doubt.

Virulence and Antimicrobial Resistance in Campylobacter spp. from a Peruvian Pediatric Cohort.

The presence of virulence factors (VFs) and mechanisms of quinolones and macrolide resistance was analyzed in Campylobacter spp. from a pediatric cohort study in Lima. In 149 isolates (39 Campylobacter jejuni and 24 Campylobacter coli from diarrheic cases; 57 C. jejuni and 29 C. coli from controls), the presence of the cdtABC and cadF genes and iam marker was established. Nalidixic acid, ciprofloxacin, erythromycin, and azithromycin susceptibilities were established in 115 isolates and tetracycline-susceptibility was established in 100 isolates. The presence of mutations in the gyrA, parC, and 23S rRNA genes was determined. The cadF gene and all genes from the cdtABC operon were significantly more frequent among C. jejuni (P < 0.0001); the iam marker was more frequent in C. coli (P < 0.0001). No differences were observed in VFs between cases and controls. Almost all isolates were tetracycline-resistant; nalidixic acid and ciprofloxacin resistance reached levels of 90.4% and 88.7%, respectively. Resistance to macrolides was 13% (C. jejuni 4.3%; C. coli 26.1%). Resistance to ciprofloxacin was related to GyrA Thr86 substitutions, while 13 of 15 macrolide-resistant isolates possessed a 23S rRNA mutation (A2075G). Differences in the presence of VFs and alarming levels of resistance to tested antimicrobial agents were observed among C. jejuni and C. coli.

SEROTYPES AND ANTIMICROBIAL SUSCEPTIBILITY OF NASOPHARYNGEAL PNEUMOCOCCI ISOLATED FROM CHILDREN IN 2010–2016: A RETROSPECTIVE COHORT STUDY

Background. Pneumococci (Streptococcus pneumoniae) represent major pathogens that cause acute infections in children. Objective. Our aim was to analyze dynamics of the distribution of nasopharyngeal pneumococcal serotypes and their antimicrobial susceptibility in children. Methods. A retrospective cohort study was conducted. We examined nasopharyngeal pneumococci isolated from children getting care at the National Medical Research Center of Children’s Health (Moscow) in 2010–2016. Serotyping was performed using specific antisera and/or by molecular typing employing PCR. Susceptibility to oxacillin (OXA), erythromycin (ERY), clindamycin (CLI), trimethoprim/sulfamethoxazol, chloramphenicol and tetracycline was tested by the disk diffusion method. In 2013–2016, penicillin (PEN), amoxicillin (AMX), ERY and CLI minimal inhibitory concentrations (MIC) were measured. Results. A total of 1,111 pneumococcal isolates were examined; the sample was obtained from children with a median age of 4 years (P25–P75, 2.4–6.5 years). We identified 48 pneumococcal serotypes; six leading serotypes were serotypes 3, 6А, 6В, 14, 19F and 23F aggregating a proportion of 63.2% in the overall distribution. From 2010 to 2016, the distribution of serotypes has not changed. Wherein, 13-valent pneumococcal conjugate vaccine covered 74% of serotypes in children under 5 years. The five leading serotypes (6А, 6В, 14, 19F, 23F and serotype 19A) had the highest resistance rate. Within 2010–2016, the proportion of OXA- and ERY-resistant pneumococci grew from 21.3% to 35.9% and from 24.5% to 36.9%, respectively. The majority (81.3%) of ERY-resistant isolates possessed an MLSB-phenotype, i. e. were resistant to macrolides, lincosamides, and streptogramin B. In 2013–2016, the rate of PEN- and AMX-resistant pneumococci was 34.6% and 3.5%, respectively. Conclusion. Within the seven year study period, no major shifts in the nasopharyngeal pneumococcal serotype distribution were observed. The pneumococci remained highly susceptible to AMX, but activity of macrolides was significantly reduced. Considering the leading mechanism of macrolide resistance, the use of any macrolides or lincosamides for empiric treatment of pneumococcal infections in children is questionable.

Determination of Characteristics of Erythromycin Resistant Streptococcus pneumoniae with Preferred PCV Usage in Iran.

Amongst 100 Streptococcus pneumoniae isolated from clinical cases and nasopharynx of healthy individuals, 60 erythromycin resistant strains were isolated and characterized using MLST, PFGE, transposon analysis and Quellung reaction. Most of the S. pneumoniae erythromycin resistant (80%) were found to be attributable to the ermB-edncoded ribosome methylase activity which differs from the dominant mechanism of macrolide resistance seen in North America.The most predominant transposons were; Tn1545/6003 (27%), Tn6002 (22%), Tn2009 (20%), Tn2010 (17%). Number of the clinical isolates carrying Tn2010 was more significant than the normal flora. The serotypes found were; 14 (33%), 3 (22%), 23F (15%), 19F (15%), 19A (7%), 6A (3%), 9V (3%) and 6B (2%). The most prevalent serotypes among the clinical (n = 28) and normal flora (n = 32) isolates were serotypes 14 (46%) and 3 (31%), respectively. The most prevalent vaccine serotypes amongst the clinical isolates and the healthy individuals were pneumococcal conjugate vaccines (PCV) 13 and PCV10, respectively. PFGE revealed 34 pulsotypes with 9 common and 25 single types. Significant number of the normal isolates belonged to CT5 and CT6. On the other hand, significant number of clinical isolates belonged to CT8 as compared to the normal flora isolates. MLST showed 2 dominant sequence types. ST3130 (23%) and ST180 (22%) were the most predominant sequence types in the clinical and normal isolates, respectively. There was no significant difference in other sequence types between clinical and normal flora isolates. Three polyclonal complexes including Sweden15A -25, Spain23F-1 and Spain9V-3 constituted 58% of the isolates. Our results suggest that the genetic diversity and transposon distribution were high among S. pneumoniae, particularly in the isolates containing erm(B) and double antibiotic resistant genes (erm/mef). The results presented here could influence the change in the current vaccination practices in Iran which currently calls for vaccination with PCV7 or PCV10.

Solithromycin: A Novel Fluoroketolide for the Treatment of Community-Acquired Bacterial Pneumonia.

Solithromycin is a novel fluoroketolide developed in both oral and intravenous formulations to address increasing macrolide resistance in pathogens causing community-acquired bacterial pneumonia (CABP). When compared with its macrolide and ketolide predecessors, solithromycin has several structural modifications which increase its ribosomal binding and reduce its propensity to known macrolide resistance mechanisms. Solithromycin, like telithromycin, affects 50S ribosomal subunit formation and function, as well as causing frame-shift errors during translation. However, unlike telithromycin, which binds to two sites on the ribosome, solithromycin has three distinct ribosomal binding sites. Its desosamine sugar interacts at the A2058/A2059 cleft in domain V (as all macrolides do), an extended alkyl-aryl side chain interacts with base pair A752-U2609 in domain II (similar to telithromycin), and a fluorine at C-2 of solithromycin provides additional binding to the ribosome. Studies describing solithromycin activity against Streptococcus pneumoniae have reported that it does not induce erm-mediated resistance because it lacks a cladinose moiety, and that it is less susceptible than other macrolides to mef-mediated efflux due to its increased ribosomal binding and greater intrinsic activity. Solithromycin has demonstrated potent in vitro activity against the most common CABP pathogens, including macrolide-, penicillin-, and fluoroquinolone-resistant isolates of S. pneumoniae, as well as Haemophilus influenzae and atypical bacterial pathogens. Solithromycin displays multi-compartment pharmacokinetics, a large volume of distribution (>500L), approximately 67% bioavailability when given orally, and serum protein binding of 81%. Its major metabolic pathway appears to follow cytochrome P450 (CYP) 3A4, with metabolites of solithromycin undergoing biliary excretion. Its serum half-life is approximately 6-9h, which is sufficient for once-daily administration. Pharmacodynamic activity is best described as fAUC0-24/MIC (the ratio of the area under the free drug concentration-time curve from 0 to 24h to the minimum inhibitory concentration of the isolate). Solithromycin has completed one phase II and two phase III clinical trials in patients with CABP. In the phase II trial, oral solithromycin was compared with oral levofloxacin and demonstrated similar clinical success rates in the intention-to-treat (ITT) population (84.6 vs 86.6%). Clinical success in the clinically evaluable patients group was 83.6% of patients receiving solithromycin compared with 93.1% for patients receiving levofloxacin. In SOLITAIRE-ORAL, a phase III trial which assessed patients receiving oral solithromycin or oral moxifloxacin for CABP, an equivalent (non-inferior) early clinical response in the ITT population was demonstrated for patients receiving either solithromycin (78.2%) or moxifloxacin (77.9%). In a separate phase III trial, SOLITAIRE-IV, patients receiving intravenous-to-oral solithromycin (79.3%) demonstrated non-inferiority as the primary outcome of early clinical response in the ITT population compared with patients receiving intravenous-to-oral moxifloxacin (79.7%). Overall, solithromycin has been well tolerated in clinical trials, with gastrointestinal adverse events being most common, occurring in approximately 10% of patients. Transaminase elevation occurred in 5-10% of patients and generally resolved following cessation of therapy. None of the rare serious adverse events that occurred with telithromycin (i.e., hepatotoxicity) have been noted with solithromycin, possibly due to the fact that solithromycin (unlike telithromycin) does not possess a pyridine moiety in its chemical structure, which has been implicated in inhibiting nicotinic acetylcholine receptors. Because solithromycin is a possible substrate and inhibitor of both CYP3A4 and P-glycoprotein (P-gp), it may display drug interactions similar to macrolides such as clarithromycin. Overall, the in vitro activity, clinical efficacy, tolerability, and safety profile of solithromycin demonstrated to date suggest that it continues to be a promising treatment for CABP.

Use of next generation sequence to investigate potential novel macrolide resistance mechanisms in a population of Moraxella catarrhalis isolates.

Although previous studies have confirmed that 23S rRNA gene mutation could be responsible for most of macrolide resistance in M. catarrhalis, a recent study suggested otherwise. Next generation sequence based comparative genomics has revolutionized the mining of potential novel drug resistant mechanisms. In this study, two pairs of resistant and susceptible M. catarrhalis isolates with different multilocus sequence types, were investigated for potential differential genes or informative single nucleotide polymorphisms (SNPs). The identified genes and SNPs were evaluated in 188 clinical isolates. From initially 12 selected differential genes and 12 informative SNPs, 10 differential genes (mboIA, mcbC, mcbI, mboIB, MCR_1794, MCR_1795, lgt2B/C, dpnI, mcbB, and mcbA) and 6 SNPs (C619T of rumA, T140C of rplF, G643A of MCR_0020, T270G of MCR_1465, C1348A of copB, and G238A of rrmA) were identified as possibly linked to macrolide resistance in M. catarrhalis. Most of the identified differential genes and SNPs are related to methylation of ribosomal RNA (rRNA) or DNA, especially MCR_0020 and rrmA. Further studies are needed to determine the function and/or evolution process, of the identified genes or SNPs, to establish whether some novel or combined mechanisms are truly involved in M. catarrhalis macrolide resistance mechanism.

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.

Macrolones Are a Novel Class of Macrolide Antibiotics Active against Key Resistant Respiratory Pathogens In Vitro and In Vivo.

As we face an alarming increase in bacterial resistance to current antibacterial chemotherapeutics, expanding the available therapeutic arsenal in the fight against resistant bacterial pathogens causing respiratory tract infections is of high importance. The antibacterial potency of macrolones, a novel class of macrolide antibiotics, against key respiratory pathogens was evaluated in vitro and in vivo MIC values against Streptococcus pneumoniae, Streptococcus pyogenes, Staphylococcus aureus, and Haemophilus influenzae strains sensitive to macrolide antibiotics and with defined macrolide resistance mechanisms were determined. The propensity of macrolones to induce the expression of inducible erm genes was tested by the triple-disk method and incubation in the presence of subinhibitory concentrations of compounds. In vivo efficacy was assessed in a murine model of S. pneumoniae-induced pneumonia, and pharmacokinetic (PK) profiles in mice were determined. The in vitro antibacterial profiles of macrolones were superior to those of marketed macrolide antibiotics, including the ketolide telithromycin, and the compounds did not induce the expression of inducible erm genes. They acted as typical protein synthesis inhibitors in an Escherichia coli transcription/translation assay. Macrolones were characterized by low to moderate systemic clearance, a large volume of distribution, a long half-life, and low oral bioavailability. They were highly efficacious in a murine model of pneumonia after intraperitoneal application even against an S. pneumoniae strain with constitutive resistance to macrolide-lincosamide-streptogramin B antibiotics. Macrolones are the class of macrolide antibiotics with an outstanding antibacterial profile and reasonable PK parameters resulting in good in vivo efficacy.

Phenotypic and molecular characterization of resistance to macrolides, lincosamides and type B streptogramin of clinical isolates of Staphylococcus spp. of a university hospital in Recife, Pernambuco, Brazil

IntroductionThere is a mechanism of macrolide resistance in Staphylococcus spp. which also affects the lincosamides and type B streptogramins characterizing the so-called MLSB resistance, whose expression can be constitutive (cMLSB) or inducible (iMLSB) and is encoded mainly by ermA and ermC genes. The cMLSB resistance is easily detected by susceptibility testing used in the laboratory routine, but iMLSB resistance is not. Therapy with clindamycin in cases of infection with isolated iMLSB resistance may fail. ObjectiveTo characterize the phenotypic (occurrence of cMLSB and iMLSB phenotypes) and molecular (occurrence of ermA and ermC genes) profiles of MLSB resistance of clinical isolates of susceptible and methicillin-resistant Staphylococcus aureus and CNS (coagulase-negative Staphylococcus) from patients of a university hospital, in Pernambuco. MethodsThe antimicrobial susceptibility of 103 isolates was determined by the disk diffusion technique in Mueller–Hinton agar followed by oxacillin screening. The iMLSB phenotype was detected by D test. Isolates with cMLSB and iMLSB phenotypes were subjected to polymerase chain reaction (PCR) for the detection of ermA and ermC genes. ResultsThe cMLSB and iMLSB phenotypes were respectively identified in 39 (37.9%) and five (4.9%) isolates. The iMLSB phenotype was found only in four (10.8%) methicillin-susceptible S. aureus and one (4.5%) methicillin-resistant S. aureus. In the 44 isolates subjected to PCR, four (9.1%) only ermA gene was detected, a lower frequency when compared to only ermC 17 (38.6%) gene and to one (2.3%) isolate presenting both genes. ConclusionIn the Staphylococcus spp. analyzed, the ermC gene was found more often than the ermA, although the iMLSB phenotype had been less frequent than the cMLSB. It was important to perform the D test for its detection to guide therapeutic approaches.

Whole Genome Sequence Analysis of Pig Respiratory Bacterial Pathogens with Elevated Minimum Inhibitory Concentrations for Macrolides.

Macrolides are often used to treat and control bacterial pathogens causing respiratory disease in pigs. This study analyzed the whole genome sequences of one clinical isolate of Actinobacillus pleuropneumoniae, Haemophilus parasuis, Pasteurella multocida, and Bordetella bronchiseptica, all isolated from Australian pigs to identify the mechanism underlying the elevated minimum inhibitory concentrations (MICs) for erythromycin, tilmicosin, or tulathromycin. The H. parasuis assembled genome had a nucleotide transition at position 2059 (A to G) in the six copies of the 23S rRNA gene. This mutation has previously been associated with macrolide resistance but this is the first reported mechanism associated with elevated macrolide MICs in H. parasuis. There was no known macrolide resistance mechanism identified in the other three bacterial genomes. However, strA and sul2, aminoglycoside and sulfonamide resistance genes, respectively, were detected in one contiguous sequence (contig 1) of A. pleuropneumoniae assembled genome. This contig was identical to plasmids previously identified in Pasteurellaceae. This study has provided one possible explanation of elevated MICs to macrolides in H. parasuis. Further studies are necessary to clarify the mechanism causing the unexplained macrolide resistance in other Australian pig respiratory pathogens including the role of efflux systems, which were detected in all analyzed genomes.

Macrolide resistance mechanisms and virulence factors in erythromycin-resistant Campylobacter species isolated from chicken and swine feces and carcasses.

Resistance to antimicrobials was measured in 73 isolates of Campylobacter jejuni (C. jejuni) and 121 isolates of Campylobacter coli (C. coli) from chicken and swine feces and carcasses in Korea. Both bacterial species showed the highest resistance to (fluoro) quinolones (ciprofloxacin and nalidixic acid) out of the nine antimicrobials tested. Erythromycin resistance was much higher in C. coli (19.0%, 23/121) than in C. jejuni (6.8%, 5/73). The mutation in the 23S rRNA gene was primarily responsible for macrolide resistance in Campylobacter isolates. Several amino acid substitutions in the L4 and L22 ribosomal proteins may play a role in the mechanism of resistance, but the role requires further evaluation. A total of eight virulence genes were detected in 28 erythromycin-resistant Campylobacter isolates. All C. jejuni isolates carried more than four such genes, while C. coli isolates carried fewer than three such genes. The high rate of resistance highlights the need to employ more prudent use of critically important antimicrobials, such as fluoroquinolones and macrolides, in swine and poultry production, and to more carefully monitor antimicrobial resistance in Campylobacter isolates in food animals.

Macrolide resistance mechanisms in Streptococcus pneumoniae: Opening Pandora’s box

Macrolide resistance mechanisms in Streptococcus pneumoniae: Opening Pandora’s box