Characterization of In Vivo Acquired Resistance of Mycoplasma hyopneumoniae to Macrolides and Lincosamides

Drug Susceptibility Test and Analysis of Quinolone Resistance Genes in Mycoplasma hyopneumoniae Vaccine Strains and Field Isolates from China

Background

Enrofloxacin is a commonly used animal-specific drug in veterinary clinics. However, this drug has no epidemiological cutoff values (ECVs/ECOFFs) for Mycoplasma hyopneumoniae in CLSI and EUCAST. Defining the epidemiological cutoff values (ECOFFs) of enrofloxacine to Mycoplasma hyopneumoniae (M. hyo) can inform an early detection of bacterial resistance to better manage the resistance prevention and also help in establishing drug resistance breakpoints;.

Methods

We determined the susceptibility breakpoint of M. hyo to enrofloxacin by the American Clinical and Laboratory Standards Institute (CLSI) standard method based on the PCR of vaccine strains and wild strains drug resistance genes;.

Results

Eighty strains of M.hyo isolated in Tibet were moderately sensitive (S) to tetracycline, florfenicol, spiramycin, erythromycin thiocyanate, tilmicosin, tiamulin, lincomycin, clindamycin, ofloxacin, enrofloxacin, gentamicin, amikacin, with MICs below 0.5 μg/mL. For vaccine 168L, RM48, and J strains, the susceptibility to the same antibacterial drugs was lower compared to the Tibetan isolates. The resistance of J strain to erythromycin thiocyanate was confirmed. Gene point mutation was confirmed in Quinolone Resistance Determining Regions (QRDR) of HNSH strain Topoisomerase IV subunit A, this finding is compared with the sequencing results of 168L strain reference sequence (Accession number: CP003131). Arg-Lys amino acid mutation (G921A and G1179A) was confirmed for the increase of MIC value involved in M.hyo to enrofloxacine;.

Conclusion

The cut-off value of M.hyo to enrofloxacin was set as 1 μg/mLby ECOFFinder XL 2010 V2.1.

Antimicrobial susceptibilities and mechanisms of resistance of commensal and invasive Mycoplasma salivarium isolates

Mycoplasma salivarium, an oral commensal organism, can cause severe invasive infections in immunocompromised individuals. Currently there is no treatment guidance for such infections. We performed antimicrobial susceptibility tests on 39 commensal and invasive M. salivarium isolates and investigated the mechanisms of antimicrobial resistance. Clindamycin was the most active agent [minimum inhibition concentration (MIC) range: 0.004–128 mg/L, MIC₅₀ = 0.031 mg/L, MIC₉₀ = 0.125 mg/ml], followed by tetracycline and levofloxacin. All isolates were resistant to erythromycin (MIC ≥4 mg/L) due to the presence of 2057A (Escherichia coli numbering) in 23S rRNA. Three isolates with elevated clindamycin MICs (≥8 mg/L) harbored A2058T/G mutations in 23S rRNA gene; four sequential isolates from one patient developed C2611T and A2059G mutations accompanying the increase of clindamycin MICs. Five isolates with elevated tetracycline MICs (≥4 mg/L) had mutations in 16S rRNA gene (A965G/T, G966T, or A967C/T) and one of them harbored TetM. Nine isolates with elevated levofloxacin MICs (≥4 mg/L) had one or more mutations in gyrA, gyrB, parC, or parE. Susceptibility breakpoints for clindamycin, tetracycline and levofloxacin were suggested to be ≤0.125, ≤2, and ≤2 mg/L, respectively. Antimicrobial resistance to any of the three agents (clindamycin, tetracycline, or levofloxacin) was documented in 12 (34.3%) non-duplicate isolates, of which 10 were invasive. Levofloxacin resistance was most frequent (25.7%). Multi-drug resistance was also observed (14.3%). This study demonstrates the frequent occurrence of antimicrobial resistance in M. salivarium, emphasizing the need for culture and susceptibility testing to guide antimicrobial therapy.

Emergence and Mechanism of Resistance of Tulathromycin Against Mycoplasma hyopneumoniae in a PK/PD Model and the Fitness Costs of 23S rRNA Mutants

Macrolides are widely used in diseases caused by Mycoplasma spp. The new semi-synthetic macrolide antibiotic tulathromycin is currently in wide use for the treatment of respiratory diseases of livestock. The objective of this study was to evaluate the antibacterial effect of tulathromycin against Mycoplasma hyopneumoniae using an in vitro pharmacokinetic/pharmacodynamic (PK/PD) model to reveal mechanisms of antibiotic resistance and to evaluate the fitness of drug-resistant strains. In this study, high performance liquid chromatography-tandem mass spectrometry was used to determine drug concentrations for the in vitro model after dosing. The peak concentrations were in the range 0.3125–20 μg/mL (1 × MIC-64 × MIC). The ratio of the area under the concentration-time curve (AUC) over 72 h divided by the MIC (AUC_72h/MIC) had the highest correlation with the antibacterial effect of tulathromycin against M. hyopneumoniae. Tulathromycin also showed concentration-dependent antimicrobial effects and promoted the emergence of drug-resistant bacteria after being cultured for 168 h and most were mutations in 23S rRNA at site A2058G (E.coli numbering) and only a single isolate was an A2058T (E.coli numbering) mutant. In the presence of reserpine, we determined the MIC of tulathromycin, tilmicosin, tiamulin and tylosin against these drug-resistant bacteria and the strains with efflux pump mechanisms were found among the strains resistant to tilmicosin. Gene expression analysis indicated that the ABC and MATE transporter efflux pump genes RS01935, RS02670, RS01115, RS01970, RS02395 and RS03540 (MATE family efflux transporter) were up-regulated in the three strains (P < 0.05 or P < 0.01). These investigations provide guidance for clinical administration of tulathromycin and elucidate the mechanism and fitness cost of drug resistance in M. hyopneumoniae.

Antimicrobial susceptibility monitoring of Mycoplasma hyopneumoniae isolated from seven European countries during 2015-2016

Mycoplasma hyopneumoniae is the causative agent of porcine enzootic pneumonia, a chronic respiratory disease, causing significant economic losses. Results from the 2015-2016 MycoPath pan-European antimicrobial susceptibility monitoring survey of M. hyopneumoniae are presented. In total, 147 M. hyopneumoniae porcine isolates from Belgium, France, Germany, Great Britain, Hungary, Italy, and Spain were tested. One isolate per farm was retained from pigs that had not been recently treated with antimicrobial agents. The minimal inhibitory concentration (MIC) of 13 antimicrobial agents was determined in a central laboratory using a broth microdilution method, with Friis Medium, incubated at 35 ± 1 °C for 5-12 days. M. hyopneumoniae NCTC 10110 was used as Quality Control. MIC₅₀/MIC₉₀ (mg/L) values were: enrofloxacin 0.06/1; marbofloxacin 0.06/2; spiramycin 0.06/0.25; tulathromycin ≤0.001/0.004; gamithromycin 0.06/0.5; tylosin 0.016/0.06; tilmicosin 0.06/0.5; florfenicol 0.5/1; doxycycline 0.25/1; oxytetracycline 0.25/2; lincomycin 0.06/0.25; tiamulin 0.016/0.06 and valnemulin ≤0.001/0.004. Compared with the data from 2010 to 2012 MycoPath study (50 isolates), MIC_50/90 results were similar and the majority were within ± two dilution steps, except for the MIC₅₀ of oxytetracycline which is more than two dilution steps higher in the present study. Between-country comparisons show some differences in the MIC values for the fluoroquinolones, tulathromycin and tylosin, but the limited sample size per country precludes performing meaningful country comparisons for several countries. Standardized laboratory methods and interpretive criteria for MIC testing of veterinary mycoplasmas are clearly needed; there are currently no clinical breakpoints available to facilitate data interpretation and correlation of MICs with in vivo efficacy.

Antimicrobial drug resistance mechanisms among Mollicutes

Representatives of the Mollicutes class are the smallest, wall-less bacteria capable of independent reproduction. They are widespread in nature, most are commensals, and some are pathogens of humans, animals and plants. They are also the main contaminants of cell cultures and vaccine preparations. Despite limited biosynthetic capabilities, they are highly adaptable and capable of surviving under various stress and extreme conditions, including antimicrobial selective pressure. This review describes current understanding of antibiotic resistance (ABR) mechanisms in Mollicutes. Protective mechanisms in these bacteria include point mutations, which may include non-target genes, and unique gene exchange mechanisms, contributing to transfer of ABR genes. Better understanding of the mechanisms of emergence and dissemination of ABR in Mollicutes is crucial to control these hypermutable bacteria and prevent the occurrence of highly ABR strains.

Genomic Variability and Post-translational Protein Processing Enhance the Immune Evasion of Mycoplasma hyopneumoniae and Its Interaction With the Porcine Immune System

Mycoplasma hyopneumoniae (M. hyopneumoniae, Mhp) is a geographically widespread and economically devastating pathogen that colonizes ciliated epithelium; the infection of Mhp can damnify the mucociliary functions as well as leading to Mycoplasma pneumonia of swine (MPS). MPS is a chronic respiratory infectious disease with high infectivity, and the mortality can be increased by secondary infections as the host immunity gets down-regulated during Mhp infection. The host immune responses are regarded as the main driving force for the disease development, while MPS is prone to attack repeatedly in farms even with vaccination or other treatments. As one of the smallest microorganisms with limited genome scale and metabolic pathways, Mhp can use several mechanisms to achieve immune evasion effect and derive enough nutrients from its host, indicating that there is a strong interaction between Mhp and porcine organism. In this review, we summarized the immune evasion mechanisms from genomic variability and post-translational protein processing. Besides, Mhp can induce the immune cells apoptosis by reactive oxygen species production, excessive nitric oxide (NO) release and caspase activation, and stimulate the release of cytokines to regulate inflammation. This article seeks to provide some new points to reveal the complicated interaction between the pathogen and host immune system with Mhp as a typical example, further providing some new strategies for the vaccine development against Mhp infection.

The PK/PD Integration and Resistance of Tilmicosin against Mycoplasma hyopneumoniae

Mycoplasma hyopneumoniae is the major pathogen causing enzootic pneumonia in pigs. M. hyopneumoniae infection can lead to considerable economic losses in the pig-breeding industry. Here, this study established a first-order absorption, one-compartment model to study the relationship between the pharmacokinetics/pharmacodynamics (PK/PD) index of tilmicosin against M. hyopneumoniae in vitro. We simulated different drug concentrations of timicosin in the fluid lining the lung epithelia of pigs. The minimum inhibitory concentration (MIC) of tilmicosin against M. hyopneumoniae with an inoculum of 10⁶ CFU/mL was 1.6 μg/mL using the microdilution method. Static time-kill curves showed that if the drug concentration >1 MIC, the antibacterial effect showed different degrees of inhibition. At 32 MIC, the amount of bacteria decreased by 3.16 log₁₀ CFU/mL, thereby achieving a mycoplasmacidal effect. The M. hyopneumoniae count was reduced from 3.61 to 5.11 log₁₀ CFU/mL upon incubation for 96 h in a dynamic model with a dose of 40-200 mg, thereby achieving mycoplasmacidal activity. The area under the concentration-time curve over 96 h divided by the MIC (AUC_{0-96 h}/MIC) was the best-fit PK/PD parameters for predicting the antibacterial activity of tilmicosin against M. hyopneumoniae (R² = 0.99), suggesting that tilmicosin had concentration-dependent activity. The estimated value for AUC_{0-96 h}/MIC for 2log₁₀ (CFU/mL) reduction and 3log₁₀ (CFU/mL) reduction from baseline was 70.55 h and 96.72 h. Four M. hyopneumoniae strains (M1-M4) with reduced sensitivity to tilmicosin were isolated from the four dose groups. The susceptibility of these strains to tylosin, erythromycin and lincomycin was also reduced significantly. For sequencing analyses of 23S rRNA, an acquired A2058G transition in region V was found only in resistant M. hyopneumoniae strains (M3, M4). In conclusion, in an in vitro model, the effect of tilmicosin against M. hyopneumoniae was concentration-dependent and had a therapeutic effect. These results will help to design the optimal dosing regimen for tilmicosin in M. hyopneumoniae infection, and minimize the emergence of resistant bacteria.

Analysis of the mutant selection window and killing of Mycoplasma hyopneumoniae for doxycycline, tylosin, danofloxacin, tiamulin, and valnemulin

Mycoplasma hyopneumoniae is the major pathogenic microorganism causing enzootic pneumonia in pigs. With increasing resistance of M. hyopneumoniae to conventional antibiotics, treatment is becoming complicated. Herein, we investigated the mutant selection window (MSW) of doxycycline, tylosin, danofloxacin, tiamulin, and valnemulin for treating the M. hyopneumoniae type strain (ATCC 25934) to determine the likelihood of promoting resistance with continued use of these antibiotics. Minimum inhibitory concentration (MIC) values against M. hyopneumoniae were determined for each antimicrobial agent based on microdilution broth and agar dilution methods (bacterial numbers ranged from 10⁵ colony-forming units (CFU)/mL to 10⁹ CFU/mL). The minimal concentration inhibiting colony formation by 99% (MIC₉₉) and the mutant prevention concentration (MPC) were determined by the agar dilution method with three inoculum sizes. Antimicrobial killing was determined based on MIC₉₉ and MPC values for all five agents. MIC values ranged from 0.001 to 0.25 μg/mL based on the microdilution broth method, and from 0.008 to 1.0 μg/mL based on the agar dilution method. MPC values ranged from 0.0016 to 10.24 μg/mL. MPC/MIC₉₉ values were ordered tylosin > doxycycline > danofloxacin > tiamulin > valnemulin. MPC achieved better bactericidal action than MIC₉₉. Based on pharmacodynamic analyses, danofloxacin, tylosin, and doxycycline are more likely to select resistant mutants than tiamulin and valnemulin.

Antimicrobial treatment of Mycoplasma hyopneumoniae infections

Mycoplasma hyopneumoniae (M. hyopneumoniae) is the primary agent of enzootic pneumonia, a chronic and economically important respiratory disease of pigs. Control and prevention of M. hyopneumoniae infections can be accomplished by optimization of management and housing conditions, and by vaccination. The present paper summarizes the current knowledge on the main characteristics and efficacy of antimicrobials used for the treatment of clinical M. hyopneumoniae infections, the in vitro and in vivo activities of these antimicrobials and the reported resistance mechanisms against some. Potentially active antimicrobials against M. hyopneumoniae include tetracyclines, macrolides, lincosamides, pleuromutilins, amphenicols, aminoglycosides, aminocyclitols and fluoroquinolones. Antimicrobial treatment can be administered either orally or parenterally. Based on the overall results of efficacy studies performed under experimental and/or field conditions, the majority of agents belonging to these antimicrobial classes improved clinical parameters (clinical signs, lung lesions) and reduced performance losses due to M. hyopneumoniae infection. Antimicrobials may, however, not be able to prevent infection or to eradicate the bacterium from the respiratory tract. The decision to medicate should, therefore, be considered carefully. M. hyopneumoniae shows an intrinsic resistance against β-lactam antibiotics, sulfonamides and trimethoprim. A few reports have shown acquired antimicrobial resistance against some antibiotics, along with associated resistance mechanisms. The results of antimicrobial susceptibility testing are difficult to interpret in terms of treatment outcome, as no clinical breakpoints have been defined for M. hyopneumoniae.

Pharmacokinetic-pharmacodynamic integration and resistance of tiamulin against Mycoplasma hyopneumoniae in an in vitro dynamic model

Mycoplasma hyopneumoniae is the major pathogen of enzootic pneumonia in pigs. We established an in vitro dynamic model to investigate the relationship between the pharmacokinetic and pharmacodynamic (PK-PD) parameters of tiamulin against M. hyopneumoniae. Static time-killing curves showed that mycoplasmacidal activity (reduced 3.0 log₁₀ (CFU/mL)) was achieved during 48 h when the drug concentration was 8 MIC, and with a maximum kill rate of 0.072/h. In dynamic time-killing studies, only the dose-fractionated regimen achieved mycoplasmacidal activity when drug concentration was 1.44 and 1.92 mg/L. The duration of post antibiotic effect (PAE) at 1 × MIC was 6.27 ± 0.11 h, and prolonged as the concentration of tiamulin increased. The cumulative percentage of time over a 48-h period that the drug concentration exceeds the MIC (%T > MIC) was the best PK-PD parameter to predict the antimicrobial activity of tiamulin against M. hyopneumoniae (R² = 0.98). Tiamulin showed time-dependent and prolonged PAE activity. Two strains of M. hyopneumoniae (M1, M2) had acquired resistance to tiamulin as well as to valnemulin, tylosin and amikacin. The genome of strain ATCC 25934 was used as a reference for gene-mutation analysis. For strains M1 and M2, a A2058C mutation occurred in domain V of 23S rRNA. These data showed that tiamulin had excellent efficacy and concentration-dependent characteristics against M. hyopneumoniae in vitro. The lower dose was not safe because it could lead to enrichment of resistant bacteria.

Development of molecular biological tools for the rapid determination of antibiotic susceptibility of Mycoplasma hyopneumoniae isolates

Mycoplasma hyopneumoniae is the etiologic agent of porcine enzootic pneumonia, a contagious respiratory disease, causing significant economic losses worldwide. Antibiotic treatment is commonly utilised in the pig industry to control M. hyopneumoniae infection. Since the conventional antibiotic susceptibility test is time-consuming, taking up to weeks' period, antibiotics are usually empirically chosen. Certain single nucleotide polymorphisms in the parC (C239A/T, G250A) and gyrA (G242C, C247 T, A260 G) genes show correlation with decreased fluoroquinolone susceptibility by the change of the target site. Furthermore, the nucleotide alteration A2059 G in the 23S rRNA sequence correlates with significantly decreased macrolide and lincosamide susceptibility of M. hyopneumoniae. Mismatch amplification mutation assays (MAMA) and high resolution melt (HRM) analysis, capable to detect the mentioned resistance markers, were developed in the present study, in order to provide susceptibility data in a considerably shorter time than the conventional methods. The results of the MAMA and HRM assays were congruent with the results of the conventional antibiotic susceptibility method of the tested M. hyopneumoniae field isolates. The sensitivity of the MAMAs was 10³-10⁴ copy numbers, while that of the HRM assay was 10⁵-10⁶ copy numbers. To the best of our knowledge this was the first time that MAMA and HRM assays were developed for the rapid detection of decreased fluoroquinolone, macrolide or lincosamide susceptibility in M. hyopneumoniae strains.

Mycoplasma hyopneumoniae variability: Current trends and proposed terminology for genomic classification

Mycoplasma hyopneumoniae (M. hyopneumoniae) is the aetiologic agent of enzootic pneumonia in swine, a prevalent chronic respiratory disease worldwide. Mycoplasma hyopneumoniae is a small, self-replicating microorganism that possesses several characteristics allowing for limited biosynthetic abilities, resulting in the fastidious, host-specific growth and unique pathogenic properties of this microorganism. Variation across several isolates of M. hyopneumoniae has been described at antigenic, proteomic, transcriptomic, pathogenic and genomic levels. The microorganism possesses a minimal number of genes that regulate the transcription process. Post-translational modifications (PTM) occur frequently in a wide range of functional proteins. The PTM by which M. hyopneumoniae regulates its surface topography could play key roles in cell adhesion, evasion and/or modulation of the host immune system. The clinical outcome of M. hyopneumoniae infections is determined by different factors, such as housing conditions, management practices, co-infections and also by virulence differences among M. hyopneumoniae isolates. Factors contributing to adherence and colonization as well as the capacity to modulate inflammatory and immune responses might be crucial. Different components of the cell membrane (i.e. proteins, glycoproteins and lipoproteins) may serve as adhesins and/or be toxic for the respiratory tract cells. Mechanisms leading to virulence are complex and more research is needed to identify markers for virulence. The utilization of typing methods and complete or partial-gene sequencing for M. hyopneumoniae characterization has increased in diagnostic laboratories as control and elimination strategies for this microorganism are attempted worldwide. A commonly employed molecular typing method for M. hyopneumoniae is Multiple-Locus Variable number tandem repeat Analysis (MLVA). The agreement of a shared terminology and classification for the various techniques, specifically MLVA, has not been described, which makes inferences across the literature unsuitable. Therefore, molecular trends for M. hyopneumoniae have been outlined and a common terminology and classification based on Variable Number Tandem Repeats (VNTR) types has been proposed.

Antimicrobial Resistance in Mycoplasma spp

Mycoplasmas are intrinsically resistant to antimicrobials targeting the cell wall (fosfomycin, glycopeptides, or β-lactam antibiotics) and to sulfonamides, first-generation quinolones, trimethoprim, polymixins, and rifampicin. The antibiotics most frequently used to control mycoplasmal infections in animals are macrolides and tetracyclines. Lincosamides, fluoroquinolones, pleuromutilins, phenicols, and aminoglycosides can also be active. Standardization of methods used for determination of susceptibility levels is difficult since no quality control strains are available and because of species-specific growth requirements. Reduced susceptibility levels or resistances to several families of antimicrobials have been reported in field isolates of pathogenic Mycoplasma species of major veterinary interest: M. gallisepticum and M. synoviae in poultry; M. hyopneumoniae, M. hyorhinis, and M. hyosynoviae in swine; M. bovis in cattle; and M. agalactiae in small ruminants. The highest resistances are observed for macrolides, followed by tetracyclines. Most strains remain susceptible to fluoroquinolones. Pleuromutilins are the most effective antibiotics in vitro. Resistance frequencies vary according to the Mycoplasma species but also according to the countries or groups of animals from which the samples were taken. Point mutations in the target genes of different antimicrobials have been identified in resistant field isolates, in vitro-selected mutants, or strains reisolated after an experimental infection followed by one or several treatments: DNA-gyrase and topoisomerase IV for fluoroquinolones; 23S rRNA for macrolides, lincosamides, pleuromutilins, and amphenicols; 16S rRNAs for tetracyclines and aminoglycosides. Further work should be carried out to determine and harmonize specific breakpoints for animal mycoplasmas so that in vitro information can be used to provide advice on selection of in vivo treatments.

Optimization of Antimicrobial Treatment to Minimize Resistance Selection

Optimization of antimicrobial treatment is a cornerstone in the fight against antimicrobial resistance. Various national and international authorities and professional veterinary and farming associations have released generic guidelines on prudent antimicrobial use in animals. However, these generic guidelines need to be translated into a set of animal species- and disease-specific practice recommendations. This article focuses on prevention of antimicrobial resistance and its complex relationship with treatment efficacy, highlighting key situations where the current antimicrobial drug products, treatment recommendations, and practices may be insufficient to minimize antimicrobial selection. The authors address this topic using a multidisciplinary approach involving microbiology, pharmacology, clinical medicine, and animal husbandry. In the first part of the article, we define four key targets for implementing the concept of optimal antimicrobial treatment in veterinary practice: (i) reduction of overall antimicrobial consumption, (ii) improved use of diagnostic testing, (iii) prudent use of second-line, critically important antimicrobials, and (iv) optimization of dosage regimens. In the second part, we provided practice recommendations for achieving these four targets, with reference to specific conditions that account for most antimicrobial use in pigs (intestinal and respiratory disease), cattle (respiratory disease and mastitis), dogs and cats (skin, intestinal, genitourinary, and respiratory disease), and horses (upper respiratory disease, neonatal foal care, and surgical infections). Lastly, we present perspectives on the education and research needs for improving antimicrobial use in the future.

Antibiotic susceptibility testing of Mycoplasma hyopneumoniae field isolates from Central Europe for fifteen antibiotics by microbroth dilution method

Mycoplasma hyopneumoniae infections are responsible for significant economic losses in the swine industry. Commercially available vaccines are not able to inhibit the colonisation of the respiratory tract by M. hyopneumoniae absolutely, therefore vaccination can be completed with antibiotic treatment to moderate clinical signs and improve performances of the animals. Antibiotic susceptibility testing of M. hyopneumoniae is time-consuming and complicated; therefore, it is not accomplished routinely. The aim of this study was to determine the in vitro susceptibility to 15 different antibiotics of M. hyopneumoniae isolates originating from Hungarian slaughterhouses and to examine single-nucleotide polymorphisms (SNPs) in genes affecting susceptibility to antimicrobials. Minimum inhibitory concentration (MIC) values of the examined antibiotics against 44 M. hyopneumoniae strains were determined by microbroth dilution method. While all of the tested antibiotics were effective against the majority of the studied strains, high MIC values of fluoroquinolones (enrofloxacin 2.5 μg/ml; marbofloxacin 5 μg/ml) were observed against one strain (MycSu17) and extremely high MIC values of macrolides and lincomycin (tilmicosin, tulathromycin and lincomycin >64 μg/ml; gamithromycin 64 μg/ml; tylosin 32 μg/ml and tylvalosin 2 μg/ml) were determined against another, outlier strain (MycSu18). Amino acid changes in the genes gyrA (Gly81Ala; Ala83Val; Glu87Gly, according to Escherichia coli numbering) and parC (Ser80Phe/Tyr; Asp84Asn) correlated with decreased antibiotic susceptibility to fluoroquinolones and a SNP in the nucleotide sequence of the 23S rRNA (A2059G) was found to be associated with increased MIC values of macrolides. The correlation was more remarkable when final MIC values were evaluated. This study presented the antibiotic susceptibility profiles of M. hyopneumoniae strains circulating in the Central European region, demonstrating the high in vitro efficacy of the tested agents. The observed high MIC values correlated with the SNPs in the examined regions and support the relevance of susceptibility testing and directed antibiotic therapy.

Update on Mycoplasma hyopneumoniae infections in pigs: Knowledge gaps for improved disease control

Mycoplasma hyopneumoniae (M. hyopneumoniae) is the primary pathogen of enzootic pneumonia, a chronic respiratory disease in pigs. Infections occur worldwide and cause major economic losses to the pig industry. The present paper reviews the current knowledge on M. hyopneumoniae infections, with emphasis on identification and analysis of knowledge gaps for optimizing control of the disease. Close contact between infected and susceptible pigs is the main route of M. hyopneumoniae transmission. Management and housing conditions predisposing for infection or disease are known, but further research is needed to better understand M. hyopneumoniae transmission patterns in modern pig production systems, and to assess the importance of the breeding population for downstream disease control. The organism is primarily found on the mucosal surface of the trachea, bronchi and bronchioles. Different adhesins and lipoproteins are involved in the adherence process. However, a clear picture of the virulence and pathogenicity of M. hyopneumoniae is still missing. The role of glycerol metabolism, myoinositol metabolism and the Mycoplasma Ig binding protein-Mycoplasma Ig protease system should be further investigated for their contribution to virulence. The destruction of the mucociliary apparatus, together with modulating the immune response, enhances the susceptibility of infected pigs to secondary pathogens. Clinical signs and severity of lesions depend on different factors, such as management, environmental conditions and likely also M. hyopneumoniae strain. The potential impact of strain variability on disease severity is not well defined. Diagnostics could be improved by developing tests that may detect virulent strains, by improving sampling in live animals and by designing ELISAs allowing discrimination between infected and vaccinated pigs. The currently available vaccines are often cost-efficient, but the ongoing research on developing new vaccines that confer protective immunity and reduce transmission should be continued, as well as optimization of protocols to eliminate M. hyopneumoniae from pig herds.

In vitro activity of tylvalosin against Spanish field strains of Mycoplasma hyopneumoniae

Mycoplasma hyopneumoniae is involved in the porcine enzootic pneumonia and respiratory disease complex; therefore, the search for new treatment options that contribute to the control of this organism is relevant. The minimal inhibitory concentrations (MICs) and minimal bactericidal concentrations of tylvalosin and 19 other antimicrobial agents against 20 Spanish field isolates of M. hyopneumoniae were determined using the broth microdilution method, with the type strain (J) as a control strain. Tylvalosin had MIC50 and MIC90 values of 0.016 and 0.06 µg/ml, respectively, and was the second-most effective of the assayed antibiotics, after valnemulin. Tiamulin, tylosin and lincomycin were also among the antibiotics with the lowest MIC50 and MIC90 values against the 20 field isolates (0.06-0.25 µg/ml). However, resistance to tylosin and spiramycin, which like tylvalosin, are 16-membered macrolides, was observed. The MIC50 and MIC90 values for ciprofloxacin and enrofloxacin ranged from 0.125 to 1 µg/ml; the corresponding values ranged from 2 to 4 µg/ml for oxytetracyline, which was the most active tetracycline. Furthermore, tylvalosin and valnemulin exhibited the highest bactericidal activities. In conclusion, the macrolide tylvalosin and the pleuromutilin valnemulin exhibited the highest in vitro antimicrobial activities against M. hyopneumoniae field isolates in comparison with the other tested antibiotics.

Macrolides and lincosamides in cattle and pigs: use and development of antimicrobial resistance

Macrolides and lincosamides are important antibacterials for the treatment of many common infections in cattle and pigs. Products for in-feed medication with these compounds in combination with other antimicrobials are commonly used in Europe. Most recently approved injectable macrolides have very long elimination half-lives in both pigs and cattle, which allows once-only dosing regimens. Both in-feed medication and use of long-acting injections result in low concentrations of the active substance for prolonged periods, which causes concerns related to development of antimicrobial resistance. Acquired resistance to macrolides and lincosamides among food animal pathogens, including some zoonotic bacteria, has now emerged. A comparison of studies on the prevalence of resistance is difficult, since for many micro-organisms no agreed standards for susceptibility testing are available. With animal pathogens, the most dramatic increase in resistance has been seen in the genus Brachyspira. Resistance towards macrolides and lincosamides has also been detected in staphylococci isolated from pigs and streptococci from cattle. This article reviews the use of macrolides and lincosamides in cattle and pigs, as well as the development of resistance in target and some zoonotic pathogens. The focus of the review is on European conditions.

In vitro susceptibility of Mycoplasma hyopneumoniae field isolates and occurrence of fluoroquinolone, macrolides and lincomycin resistance

A total of 159 Thai isolates of Mycoplasma hyopneumoniae isolated from pneumonic lungs of pigs during 2006-2011 were investigated for their in vitro susceptibility to 12 antimicrobial agents. Low activity of chlortetracycline was indicated by the MIC range from 3.12-100 μg/ml and MIC90 of 50 μg/ml. Seventy-six isolates showed resistance to enrofloxacin, whereas 2 isolates showed resistance to macrolides and lincomycin. In addition, a point mutation at A2058G was revealed by sequence analysis of 23S ribosomal RNA in both isolates. The present results confirmed the rapid increase of resistant M. hyopneumoniae isolates against chlortetracycline, enrofloxacin, macrolides and lincomycin in Thailand. Selection of drugs to control swine diseases in Thailand must be done more prudently in consideration of reducing the antimicrobial resistance.

Characterization of in vivo-acquired resistance to macrolides of Mycoplasma gallisepticum strains isolated from poultry

The macrolide class of antibiotics, including tylosin and tilmicosin, is widely used in the veterinary field for prophylaxis and treatment of mycoplasmosis. In vitro susceptibility testing of 50 strains of M. gallisepticum isolated in Israel during the period 1997-2010 revealed that acquired resistance to tylosin as well as to tilmicosin was present in 50% of them. Moreover, 72% (13/18) of the strains isolated from clinical samples since 2006 showed acquired resistance to enrofloxacin, tylosin and tilmicosin. Molecular typing of the field isolates, performed by gene-target sequencing (GTS), detected 13 molecular types (I-XIII). Type II was the predominant type prior to 2006 whereas type X, first detected in 2008, is currently prevalent. All ten type X strains were resistant to both fluoroquinolones and macrolides, suggesting selective pressure leading to clonal dissemination of resistance. However, this was not a unique event since resistant strains with other GTS molecular types were also found. Concurrently, the molecular basis for macrolide resistance in M. gallisepticum was identified. Our results revealed a clear-cut correlation between single point mutations A2058G or A2059G in domain V of the gene encoding 23S rRNA (rrnA, MGA_01) and acquired macrolide resistance in M. gallisepticum. Indeed, all isolates with MIC ≥ 0.63 μg/mL to tylosin and with MIC ≥ 1.25 μg/mL to tilmicosin possess one of these mutations, suggesting an essential role in decreased susceptibility of M. gallisepticum to 16-membered macrolides.

Application of flow cytometry for the determination of minimal inhibitory concentration of several antibacterial agents on Mycoplasma hyopneumoniae

AIM

In this study, flow cytometry was evaluated for the determination of the minimal inhibitory concentrations (MICs) of nine antibacterial agents (enrofloxacin, ciprofloxacin, oxytetracycline, chloramphenicol, tylosin, lincomycin, gentamycin, spectinomycin and streptomycin) against M. hyopneumoniae.

METHODS AND RESULTS

Flow cytometry was able to detect Mycoplasma hyopneumoniae inhibition at 12 h postincubation, whereas the results obtained by the traditional method were only obtained at 48 h, when a visible change in the medium had occurred. At 48 h, both methods gave the same result for eight antibacterial agents, whereas flow cytometry gave slightly higher MIC values for one antibacterial agent (tylosin). This was attributed to the fact that the M. hyopneumoniae growth that had occurred in those tubes was not enough to visibly change the colour of the medium. A good relationship was found between the flow cytometry and the traditional method.

CONCLUSION

Flow cytometry was found to be a good method for the determination of antimicrobial MICs in M. hyopneumoniae.

SIGNIFICANCE AND IMPACT OF THE STUDY

The flow cytometric method allows the determination of the response of M. hyopneumoniae to each of the antibacterial agents in near real time, and has potential for the identification and study of resistant subpopulations.

In vitro susceptibilities of Mycoplasma putrefaciens field isolates

MICs were determined for 15 antimicrobial agents against 37 Mycoplasma putrefaciens isolates. The most effective antimicrobial drug classes were the fluoroquinolones, the tetracyclines, the lincosamide lincomycin, and the macrolides. The susceptibility profile of the isolates correlated with the geographic origin. This is the first report of decreased susceptibility to the macrolides, lincomycin, and the tetracyclines in M. putrefaciens strains.

Flow cytometric determination of the effects of antibacterial agents on Mycoplasma agalactiae, Mycoplasma putrefaciens, Mycoplasma capricolum subsp. capricolum, and Mycoplasma mycoides subsp. mycoides large colony type

Flow cytometry together with SYBR green I and propidium iodide was used to study the effects of enrofloxacin, ciprofloxacin, gentamicin, chloramphenicol, oxytetracycline, and tylosin on four mycoplasma species. Inhibition of mycoplasma growth could be detected by as early as 3 h after the start of treatment. The strongest effect was observed with enrofloxacin- and ciprofloxacin-treated cells.