Antimicrobial susceptibility of Mycoplasma bovis isolates from veal calves and dairy cattle in the Netherlands

Toward a Method for Harmonized Susceptibility Testing of Mycoplasma bovis by Broth Microdilution

Mycoplasma bovis is a fastidious pathogen of cattle causing massive economic losses in the calf and dairy industries worldwide. Since there is no approved standard method for antimicrobial susceptibility testing (AST) of M. bovis, the Clinical and Laboratory Standards Institute has requested the development of a suitable method. Therefore, this study aimed at developing a method for harmonized broth microdilution AST of M. bovis. For this, 131 M. bovis field isolates and M. bovis strain DSM 22781T were collected and macrorestriction analysis was performed to select 15 epidemiologically unrelated M. bovis strains for method validation steps. To select a suitable broth for AST of M. bovis, growth determinations were performed using five media and growth curves were compiled. Then, susceptibility testing was performed considering the exact (precondition of five identical MICs) and essential (MIC mode, accepting a deviation of ±1 dilution step) MIC agreements to evaluate the reproducibility of MIC values using a panel of 16 antimicrobial agents. Subsequently, the remaining field isolates were tested and the suitability of quality control (QC) strains was assessed. Growth experiments showed that SP4 broth was the only one of the five media that yielded sufficient growth of M. bovis. Therefore, it was selected as the test medium for AST and homogeneous MIC values were obtained (exact and essential agreements of 36 to 100% and 92 to 100%, respectively). For all other isolates tested, easy-to-read MIC endpoints were determined with this medium. High overall MIC50 and/or MIC90 values were observed for aminoglycosides and macrolides, and some isolates showed elevated MICs of fluoroquinolones, gentamicin, and/or tiamulin. Since the MICs of four commonly used QC strains were partially not within their ranges, a 20-fold MIC testing of M. bovis DSM 22781T was performed and met the criteria for a new QC strain. For harmonized AST of M. bovis, SP4 broth seems to be suitable with an incubation time of 72 ± 2 h and further validation of M. bovis DSM 22781T as a future QC strain is recommended.

Antimicrobial Use and Resistance in Surplus Dairy Calf Production Systems

Surplus calves, which consist predominately of male calves born on dairy farms, are an underrecognized source of antimicrobial-resistant (AMR) pathogens. Current production systems for surplus calves have important risk factors for the dissemination of pathogens, including the high degree of commingling during auction and transportation and sometimes inadequate care early in life. These circumstances contribute to an increased risk of respiratory and other infectious diseases, resulting in higher antimicrobial use (AMU) and the development of AMR. Several studies have shown that surplus calves harbor AMR genes and pathogens that are resistant to critically important antimicrobials. This is a potential concern as the resistant pathogens and genes can be shared between animal, human and environmental microbiomes. Although knowledge of AMU and AMR has grown substantially in dairy and beef cattle systems, comparable studies in surplus calves have been mostly neglected in North America. Therefore, the overall goal of this narrative review is to summarize the existing literature regarding AMU and AMR in surplus dairy calf production, highlight the management practices contributing to the increased AMU and the resulting AMR, and discuss potential strategies and barriers for improved antimicrobial stewardship in surplus calf production systems.

Genome-Wide Association Study of Nucleotide Variants Associated with Resistance to Nine Antimicrobials in Mycoplasma bovis

Antimicrobial resistance (AMR) studies of Mycoplasma bovis have generally focused on specific loci versus using a genome-wide association study (GWAS) approach. A GWAS approach, using two different models, was applied to 194 Mycoplasma bovis genomes. Both a fixed effects linear model (FEM) and a linear mixed model (LMM) identified associations between nucleotide variants (NVs) and antimicrobial susceptibility testing (AST) phenotypes. The AMR phenotypes represented fluoroquinolones, tetracyclines, phenicols, and macrolides. Both models identified known and novel NVs associated (Bonferroni adjusted p < 0.05) with AMR. Fluoroquinolone resistance was associated with multiple NVs, including previously identified mutations in gyrA and parC. NVs in the 30S ribosomal protein 16S were associated with tetracycline resistance, whereas NVs in 5S rRNA, 23S rRNA, and 50S ribosomal proteins were associated with phenicol and macrolide resistance. For all antimicrobial classes, resistance was associated with NVs in genes coding for ABC transporters and other membrane proteins, tRNA-ligases, peptidases, and transposases, suggesting a NV-based multifactorial model of AMR in M. bovis. This study was the largest collection of North American M. bovis isolates used with a GWAS for the sole purpose of identifying novel and non-antimicrobial-target NVs associated with AMR.

Bovine Respiratory Disease: Conventional to Culture-Independent Approaches to Studying Antimicrobial Resistance in North America

Numerous antimicrobial resistance (AMR) surveillance studies have been conducted in North American feedlot cattle to investigate the major bacterial pathogens of the bovine respiratory disease (BRD) complex, specifically: Mannheimia haemolytica, Pasteurella multocida, Histophilus somni, and Mycoplasma bovis. While most bacterial isolates recovered from healthy cattle are susceptible to a repertoire of antimicrobials, multidrug resistance is common in isolates recovered from cattle suffering from BRD. Integrative and conjugative elements (ICE) have gained increasing notoriety in BRD-Pasteurellaceae as they appear to play a key role in the concentration and dissemination of antimicrobial resistant genes. Likewise, low macrolide susceptibility has been described in feedlot isolates of M. bovis. Horizontal gene transfer has also been implicated in the spread of AMR within mycoplasmas, and in-vitro experiments have shown that exposure to antimicrobials can generate high levels of resistance in mycoplasmas via a single conjugative event. Consequently, antimicrobial use (AMU) could be accelerating AMR horizontal transfer within all members of the bacterial BRD complex. While metagenomics has been applied to the study of AMR in the microbiota of the respiratory tract, the potential role of the respiratory tract microbiome as an AMR reservoir remains uncertain. Current and prospective molecular tools to survey and characterize AMR need to be adapted as point-of-care technologies to enhance prudent AMU in the beef industry.

Integrating the Human and Animal Sides of Mycoplasmas Resistance to Antimicrobials

Mycoplasma infections are frequent in humans, as well as in a broad range of animals. However, antimicrobial treatment options are limited, partly due to the lack of a cell wall in these peculiar bacteria. Both veterinary and human medicines are facing increasing resistance prevalence for the most commonly used drugs, despite different usage practices. To date, very few reviews have integrated knowledge on resistance to antimicrobials in humans and animals, the latest dating back to 2014. To fill this gap, we examined, in parallel, antimicrobial usage, resistance mechanisms and either phenotype or genotype-based methods for antimicrobial susceptibility testing, as well as epidemiology of resistance of the most clinically relevant human and animal mycoplasma species. This review unveiled common features and differences that need to be taken into consideration in a "One Health" perspective. Lastly, two examples of critical cases of multiple drug resistance are highlighted, namely, the human M. genitalium and the animal M. bovis species, both of which can lead to the threat of untreatable infections.

Suitability of Nasal and Deep Nasopharyngeal Swab Sampling of Calves in the Mycoplasma bovis Control Program

Mycoplasma bovis is an important cattle pathogen affecting animal health, welfare, and productivity. The main disease syndromes are mastitis, pneumonia, and otitis media in young stock, as well as arthritis. Response to antibiotic treatment is poor and no effective vaccine is available. Asymptomatic carriers are common and usually harbor the organism in the airways or mammary glands. Purchase of carrier animals is a major risk for the introduction of infection into naive herds. Following the detection of M. bovis in Finland in 2012, a voluntary control program was established. It aims to prevent the spread of the infection and to help farms attain certification of a low M. bovis risk. Among the diagnostic tools in the program, nasal swabs (NS) from young calves have been tested for M. bovis to indicate the infection status of the herd. In this study, we assessed the suitability of this test method. We analyzed the effectiveness of NS and deep nasopharyngeal swabs (NP) to detect M. bovis in pneumonic and healthy calves in dairy herds recently infected with M. bovis. In pneumonic calves, NP sampling followed by culture and real-time PCR demonstrated a proportion of positive agreement (PPA) of 0.91 compared with bronchoalveolar lavage (BAL), whereas NS showed only 0.5 PPA compared with BAL. Among healthy dairy calves, overall M. bovis prevalence in NS was 29.6%. The highest rate of shedding (43%) occurred in calves 31–60 days old. At the calf level, M. bovis prevalence in NP samples was 47% compared with 33% in NS samples among the 284 studied calves. However, at the herd level, NS sampling classified 51 out of 54 herds with a positive infection status as infected, whereas in NP sampling, the respective figure was 43 out of 54 herds (p = 0.061). In conclusion, NS sampling from calves under 6 months of age and analyzed by real-time PCR is a cost-efficient method for a control program to detect M. bovis in dairy herds, even if no M. bovis mastitis has been detected in the herd. For pneumonic calves, we recommend only NP or BAL sampling.

Advances in antimicrobial activity analysis of fluoroquinolone, macrolide, sulfonamide, and tetracycline antibiotics for environmental applications through improved bacteria selection

The widespread use of antibiotics has led to their ubiquitous presence in water and wastewater and raised concerns about antimicrobial resistance. Clinical antibiotic susceptibility assays have been repurposed to measure removal of antimicrobial activity during water and wastewater treatment processes. The corresponding protocols have mainly employed growth inhibition of Escherichia coli. The present work focused on optimizing bacteria selection to improve the sensitivity of residual antimicrobial activity measurements by broth microdilution assays. Thirteen antibiotics from four classes (i.e., fluoroquinolones, macrolides, sulfonamides, tetracyclines) were investigated against three gram-negative organisms, namely E. coli, Mycoplasma microti, and Pseudomonas fluorescens. The minimum inhibitory concentration (MIC) and half-maximal inhibitory concentration (IC₅₀) were calculated for each antibiotic-bacteria pair. P. fluorescens produces a fluorescent siderophore, pyoverdine, that was used to assess sublethal effects and further enhance the sensitivity of antimicrobial activity measurements. The optimal antibiotic-bacteria pairs were as follows: fluoroquinolone-E. coli (growth inhibition); macrolide- and sulfonamide-M. microti (growth inhibition); and, tetracycline-P. fluorescens (pyoverdine inhibition). Compared to E. coli growth inhibition, the sensitivity of antimicrobial activity analysis was improved by up to 728, 19, and 2.7 times for macrolides (tylosin), sulfonamides (sulfamethoxazole), and tetracyclines (chlortetracycline), facilitating application of these bioassays at environmentally-relevant conditions.

Effect of metaphylactic administration of tildipirosin on the incidence of pneumonia and otitis and on the upper respiratory tract and fecal microbiome of preweaning Holstein calves

The objectives of this study were to evaluate the effect of the metaphylactic use of a semi-synthetic long-acting macrolide (tildipirosin) on the prevention of pneumonia and otitis in preweaning Holstein calves, as well as its effects on the microbiome of their upper respiratory tract (URT) and feces. Newborn healthy Holstein heifers, collectively housed, were randomly allocated to 1 of 2 treatment groups: treatment (TRT; n = 932) or control (CTR; n = 927). Calves in the TRT group received a single subcutaneous injection of 4 mg/kg tildipirosin (Zuprevo, Merck Animal Health) at 7 ± 7 d of life. Calves in the CTR group received no drug injection. All enrolled calves were evaluated from 1 to 63 ± 3 d of life (weaning age) and monitored daily for any adverse health events during this period. Daily physical examination was performed to diagnose pneumonia and otitis, and body weight was measured weekly in all animals. From a randomly selected subset of 217 calves, blood samples for biochemical variables analysis and swabs were collected weekly from the URT and rectum for analysis of the nasal and fecal microbiome, respectively, via next-generation sequencing of the 16S rRNA gene. Total bacterial load was evaluated using quantitative PCR. In addition, another subset of 26 calves was randomly selected and fecal swabs were collected in a more intensive sampling to investigate the short-term effect of tildipirosin administration on the fecal microbiome. We performed general mixed linear models and logistic regression to analyze continuous and binary outcomes, respectively. Tildipirosin metaphylaxis reduced the incidence of otitis (CTR = 47.03%; TRT = 37.55%) and tended to reduce the incidence of pneumonia (CTR = 20.71%; TRT = 17.38%) and the overall mortality risk (CTR = 6.69%; TRT = 4.94%). We observed no significant differences between groups for mortality due to pneumonia (CTR = 0.86%; TRT = 0.97%) or mortality due to otitis (CTR = 2.05%; TRT = 1.39%). Calves in the TRT group had a higher average daily gain than calves in the CTR group. Furthermore, metaphylaxis had no significant effects on the total bacterial load, genus, or phylum analysis of the fecal microbiome from the 2 subset groups. However, for the URT microbiota, we observed a significant decrease in total bacterial load for the TRT group compared to the CTR group 1 week after metaphylactic injection. Tildipirosin metaphylaxis decreased the mean relative abundance of the genera Mannheimia, Moraxella, and Pasteurella but significantly increased the mean relative abundance of Mycoplasma. Although tildipirosin had no positive effect on Mycoplasma, it reduced the mean relative abundance of important pathogenic bacteria in the URT and had positive effects for the control of otitis. The metaphylactic use of tildipirosin can be a suitable strategy for the control of otitis on farms with a high prevalence of this disease.

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 Susceptibility of Mycoplasma bovis Isolates from Veal, Dairy and Beef Herds

Mycoplasma bovis is an important pathogen causing mostly pneumonia in calves and mastitis in dairy cattle. In the absence of an effective vaccine, antimicrobial therapy remains the main control measure. Antimicrobial use in veal calves is substantially higher than in conventional herds, but whether veal calves also harbor more resistant M. bovis strains is currently unknown. Therefore, we compared antimicrobial susceptibility test results of M. bovis isolates from different cattle sectors and genomic clusters. The minimum inhibitory concentration of nine antimicrobials was determined for 141 Belgian M. bovis isolates (29 dairy, 69 beef, 12 mixed, 31 veal farms), and was used to estimate the epidemiological cut-off. Acquired resistance was frequently observed for the macrolides, while no acquired resistance to oxytetracycline and doxycycline, minimal acquired resistance to florfenicol and tiamulin, and a limited acquired resistance to enrofloxacin was seen. M. bovis isolates from beef cattle or genomic cluster III had higher odds of being gamithromycin-resistant than those from dairy cattle or genomic clusters IV and V. In this study, no cattle industry could be identified as source of resistant M. bovis strains. A single guideline for antimicrobial use for M. bovis infections, with a small remark for gamithromycin, is likely sufficient.

Mycoplasma bovis in Nordic European Countries: Emergence and Dominance of a New Clone

Mycoplasma (M.) bovis is an important pathogen of cattle implicated in a broad range of clinical manifestations that adversely impacts livestock production worldwide. In the absence of a safe, effective commercial vaccine in Europe, the reported reduced susceptibility to antimicrobials for this organism has contributed to difficulties in controlling infection. Despite global presence, some countries have only recently experienced outbreaks of this pathogen. In the present study, M. bovis isolates collected in Denmark between 1981 and 2016 were characterized to determine (i) genetic diversity and phylogenetic relationships using whole genome sequencing and various sequence-based typing methods and (ii) patterns of antimicrobial resistance compared to other European isolates. The M. bovis population in Denmark was found to be highly homogeneous genomically and with respect to the antimicrobial resistance profile. Previously dominated by an old genotype shared by many other countries (ST17 in the PubMLST legacy scheme), a new predominant type represented by ST94-adh1 has emerged. The same clone is also found in Sweden and Finland, where M. bovis introduction is more recent. Although retrieved from the Netherlands, it appears absent from France, two countries with a long history of M. bovis infection where the M. bovis population is more diverse.

Efficacy of Two Antibiotic-Extender Combinations on Mycoplasma bovis in Bovine Semen Production

Mycoplasma bovis is an important bovine pathogen. Artificial insemination (AI) using contaminated semen can introduce the agent into a naïve herd. Antibiotics, most often gentamycin, tylosin, lincomycin, spectinomycin (GTLS) combination are added to semen extender to prevent transmission of pathogenic bacteria and mycoplasmas. In a commercial AI straw production system with industrial scale procedures, we analyzed the mycoplasmacidal efficacy of GTLS and ofloxacin on M. bovis ATCC and wild type strain isolated from commercial AI straws. The strains were spiked at two concentrations (10⁶ and 10³ CFU/mL) into semen. Viable M. bovis in frozen semen straws was detected by enrichment culture and real-time PCR. We also compared different protocols to extract M. bovis DNA from spiked semen. None of the antibiotic protocols had any effect on the viability of either of the M. bovis strains at high spiking concentration. At low concentration, the wild type was inhibited by all other protocols, except low GTLS, whereas the ATCC strain was inhibited only by high GTLS. The InstaGene™ matrix was the most effective method to extract M. bovis DNA from semen. When there is a low M. bovis contamination level in semen, GTLS used at high concentrations, in accordance with Certified Semen Services requirements, is more efficient than GTLS used at concentrations stated in the OIE Terrestrial Code.

Molecular characteristics and antibiotic susceptibility profiles of Mycoplasma bovis associated with mastitis on dairy farms in China

Mycoplasma bovis (M. bovis) is regarded as the most prevalent mycoplasma species causing bovine mastitis worldwide. This study was conducted with the objectives to: (1) estimate M. bovis prevalence in samples from clinical mastitis and bulk tank milk; (2) assess genetic diversity and population structure of isolates; and (3) determine antibiotic susceptibility of isolates to nine antimicrobials. Milk samples (n = 476), including 450 clinical mastitis and 26 bulk tank milk samples from 23 farms (each with >1000 lactating cows) in 10 provinces of China were collected between May 2018 and September 2019. M. bovis cultured from milk samples were analyzed by multi-locus sequence typing. Minimum inhibitory concentrations of all isolates to nine antimicrobials were determined. Differences in minimum inhibitory concentration values were assessed by Kruskal-Wallis test with Bonferroni correction. The positive proportions of M. bovis in clinical mastitis samples and bulk tank milk samples were 39/450 (8.7%) and 11/26 (42.3%), respectively. Based on multi-locus sequence typing, the 50 isolates were identified as three sequence types, including sequence type 10 and two novel sequence types (newly registered as sequence type 172 and sequence type 173). The most prevalent type, sequence type 172 (31/50, 62.0%), had allelic profile 4, 3, 2, 3, 5, 7, 4. In addition, sequence type 10 with allelic profile 4, 3, 2, 3, 5, 3, 4 had a mid-range prevalence (11/50, 22.0%), whereas sequence type 173 with allelic profile 10, 3, 6, 13, 21, 6, 10 was the least prevalent (8/50, 16.0%). Both sequence type 10 and sequence type 172 were clustered in Clonal Complex 3, with isolates from the USA. M. bovis isolates in this study uniformly had low level minimum inhibitory concentrations to enrofloxacin and tiamulin. Overall variances among isolates were significant (Kruskal-Wallis test) for clindamycin (P = 0.006), erythromycin (P = 0.012) and tylosin (P =0.004). Relative to the sequence type 10 group, there were higher minimum inhibitory concentrations levels for the sequence type 173 group (H = -19.795, P = 0.003, for clindamycin; H = -19.574, P = 0.003, for erythromycin; and H = -18.881, P = 0.003, for tylosin) by post-hoc comparisons using pairwise comparisons of mean ranks following Kruskal-Wallis test with Bonferroni correction. Hence, increasing antimicrobial resistance may have contributed to emergence of novel sequence types. These data provided a baseline for elucidating genetic diversity and antibiotic susceptibility profiles of M. bovis in the main dairy-farming provinces in China.

Expression profiling of microRNAs in the Mycoplasma bovis infected mammary gland tissue in Holstein Friesian cattle

The immune response associated with mastitis caused by Mycoplasma bovis is a very complicated biological process in several type of cells, including immune cells, mammary epithelial cells, and endothelial cells. Thus, revealing of the microRNAs in the Mycoplasma bovis infected mammary gland tissues is particularly important for the immune response mechanism to Mycoplasma bovis. Firstly, 20 mammary gland tissue samples were collected from Holstein Friesian cattle that was located in Erzurum province at 2018 and screened for Mycoplasma bovis. Then, total RNA was isolated from Mycoplasma bovis infected tissues and high-throughput sequencing was performed. After bioinformatics analysis, GO and KEGG analysis of target genes of identified microRNAs were conducted. In this study, a total of 616 microRNAs were found. Our results revealed that 24 of the known microRNAs were expressed differently and 13 of the novel microRNAs were expressed differently in Mycoplasma bovis positive tissues. The target genes of these microRNAs were found to be associated with especially inflammation pathways, including B cell and T cell receptor signaling, Fc gamma R-mediated, phagocytosis/chemokine signaling, and MAPK signaling. In conclusion, this study demonstrated that identified miRNAs may be involved in the signaling pathways during mastitis caused by Mycoplasma bovis.

Investigation of Macrolide Resistance Genotypes in Mycoplasma bovis Isolates from Canadian Feedlot Cattle

Mycoplasma bovis is associated with bovine respiratory disease (BRD) and chronic pneumonia and polyarthritis syndrome (CPPS) in feedlot cattle. No efficacious vaccines for M. bovis exist; hence, macrolides are commonly used to control mycoplasmosis. Whole genome sequences of 126 M. bovis isolates, derived from 96 feedlot cattle over 12 production years, were determined. Antimicrobial susceptibility testing (AST) of five macrolides (gamithromycin, tildipirosin, tilmicosin, tulathromycin, tylosin) was conducted using a microbroth dilution method. The AST phenotypes were compared to the genotypes generated for 23S rRNA and the L4 and L22 ribosomal proteins. Mutations in domains II (nucleotide 748; E. coli numbering) and V (nucleotide 2059 and 2060) of the 23S rRNA (rrl) gene alleles were associated with resistance. All isolates with a single mutation at Δ748 were susceptible to tulathromycin, but resistant to tilmicosin and tildipirosin. Isolates with mutations in both domain II and V (Δ748Δ2059 or Δ748Δ2060) were resistant to all five macrolides. However, >99% of isolates were resistant to tildipirosin and tilmicosin, regardless of the number and positions of the mutations. Isolates with a Δ748 mutation in the 23S rRNA gene and mutations in L4 and L22 were resistant to all macrolides except for tulathromycin.

Monitoring Mycoplasma bovis Diversity and Antimicrobial Susceptibility in Calf Feedlots Undergoing a Respiratory Disease Outbreak

Bovine respiratory diseases (BRD) are widespread in veal calf feedlots. Several pathogens are implicated, both viruses and bacteria, one of which, Mycoplasma bovis, is under-researched. This worldwide-distributed bacterium has been shown to be highly resistant in vitro to the main antimicrobials used to treat BRD. Our objective was to monitor the relative prevalence of M. bovis during BRD episodes, its diversity, and its resistance phenotype in relation to antimicrobial use. For this purpose, a two-year longitudinal follow-up of 25 feedlots was organized and 537 nasal swabs were collected on 358 veal calves at their arrival in the lot, at the BRD peak and 4 weeks after collective antimicrobial treatments. The presence of M. bovis was assessed by real-time PCR and culture. The clones isolated were then subtyped (polC subtyping and PFGE analysis), and their susceptibility to five antimicrobials was determined. The course of the disease and the antimicrobials used had no influence on the genetic diversity of the M. bovis strains: The subtype distribution was the same throughout the BRD episode and similar to that already described in France, with a major narrowly-variable subtype circulating, st2. The same conclusion holds for antimicrobial resistance (AMR) phenotypes: All the clones were already multiresistant to the main antimicrobials used (except for fluoroquinolones) prior to any treatments. By contrast, changes of AMR phenotypes could be suspected for Pasteurellaceae in two cases in relation to the treatments registered.

Mycoplasma bovis in Spanish Cattle Herds: Two Groups of Multiresistant Isolates Predominate, with One Remaining Susceptible to Fluoroquinolones

Mycoplasma bovis is an important bovine pathogen causing pneumonia, mastitis, and arthritis and is responsible for major economic losses worldwide. In the absence of an efficient vaccine, control of M. bovis infections mainly relies on antimicrobial treatments, but resistance is reported in an increasing number of countries. To address the situation in Spain, M. bovis was searched in 436 samples collected from beef and dairy cattle (2016–2019) and 28% were positive. Single-locus typing using polC sequences further revealed that two subtypes ST2 and ST3, circulate in Spain both in beef and dairy cattle, regardless of the regions or the clinical signs. Monitoring of ST2 and ST3 isolates minimum inhibitory concentration (MIC) to a panel of antimicrobials revealed one major difference when using fluoroquinolones (FQL): ST2 is more susceptible than ST3. Accordingly, whole-genome sequencing (WGS) further identified mutations in the gyrA and parC regions, encoding quinolone resistance-determining regions (QRDR) only in ST3 isolates. This situation shows the capacity of ST3 to accumulate mutations in QRDR and might reflect the selective pressure imposed by the extensive use of these antimicrobials. MIC values and detection of mutations by WGS also showed that most Spanish isolates are resistant to macrolides, lincosamides, and tetracyclines. Valnemulin was the only one effective, at least in vitro, against both STs.

The Addition of Lactobacillus spp., Enrofloxacin or Doxycycline Negatively Affects the Viability of Mycoplasma bovis in Diluted Bovine Semen

Simple Summary

Mycoplasma bovis is an important infectious agent in cattle. The pathogen may cause a wide range of clinical signs, including mastitis, arthritis, pneumonia and reproductive disorders. Artificial insemination with contaminated semen may be a source of infection in infection-free areas or herds. Hence, the antimicrobials used in the preparation of seminal doses should be re-evaluated, or alternative measures to antimicrobials should be tested. This in vitro study aims to evaluate novel strategies to reduce the risk of the transmission of the pathogen through contaminated semen during artificial insemination. Hence, we assess the effect of the addition of (1) the antimicrobial enrofloxacin, (2) the antimicrobial doxycycline, or (3) a probiotic of human origin that contains acid lactic bacteria of the genus Lactobacillus, on the viability of Mycoplasma bovis in diluted bull semen in a Tris-citrate-fructose medium. The data show that the pathogen is negatively affected by the addition of 0.125 μg/mL of enrofloxacin, 0.0625 μg/mL of doxycycline, or the probiotic at a concentration of 3.24 × 10⁶ or 3.24 × 10⁸ colony-forming units/mL in diluted semen. Our results are promising in the field, as they may support new strategies to reduce the risk of the transmission of Mycoplasma bovis through artificial insemination.

Abstract

Mycoplasma bovis is an important etiologic agent of bovine mycoplasmosis in cattle. Different transmission routes have been described, including those related to reproduction. The presence of mycoplasma in semen has led to its appearance in infection-free areas through artificial insemination (AI). Semen was recently reported to be the initial source of two M. bovis mastitis outbreaks in two closed dairy herds in Finland. This questions the effectiveness of the antimicrobials currently used in semen extenders to control the pathogens in contaminated semen. They should be re-evaluated, or alternative measures to antimicrobials should be tested to obtain M. bovis-free semen. This in vitro study aimed to assess different strategies to reduce the risk of transmission of M. bovis through AI technologies. The viability of M. bovis (PG45, NCTC 10131) in bull semen diluted (DS) in a Tris-citrate-fructose solution was tested, after the addition of enrofloxacin, doxycycline or a Lactobacillus spp.-based probiotic. The data show the susceptibility of the pathogen to the addition of 0.125 μg/mL of enrofloxacin or 0.0625 μg/mL of doxycycline and to the addition of the probiotic at a concentration of 3.24 × 10⁶ colony forming units (CFU)/mL or 3.24 × 10⁸ CFU/mL in DS. The Tris-citrate-fructose medium negatively affected the viability of M. bovis, although this effect was lower than that observed after the addition of the probiotic and antimicrobials (p < 0.05). Our results may support new strategies for reducing the risk of M. bovis transmission through AI.

Antimicrobial Sensitivity Testing of Mycoplasma bovis Isolates Derived from Western Canadian Feedlot Cattle

Mycoplasma bovis is particularly adept at evading the immune system, resulting in chronic infections of the lungs and joints of feedlot cattle. The chronicity of the lesions results in prolonged antimicrobial therapy, possibly exacerbating antimicrobial resistance. This cross-sectional study generated in vitro antimicrobial susceptibility testing (AST) data on 211 M. bovis isolates recovered from 159 healthy, diseased, and dead cattle, spanning the period of 2006-2018. Nine antimicrobials commonly administered to western Canadian feedlot cattle were assessed. The data were analyzed with non-parametric statistical tests with a level of significance of p < 0.05 (two-tailed). Minimum inhibitory concentration (MIC) values tended to increase between the isolates from healthy versus dead cattle and over time (2006-2018). Isolates from dead versus healthy cattle were more likely to be resistant to tulathromycin, gamithromycin, tylosin and enrofloxacin. There was no difference in the distributions of the MICs generated from the isolates recovered from the lungs and joints (p ≥ 0.124) and the lungs and deep nasal passages (p ≥ 0.157) of the same animals.

New antimicrobial susceptibility data from monitoring of Mycoplasma bovis isolated in Europe

Mycoplasma bovis is an important respiratory pathogen of cattle across Europe and is included in the MycoPath pan-European antimicrobial susceptibility monitoring programme. M. bovis strains (232) were isolated from cattle, not recently treated with antimicrobials, at diverse geographical locations in France, Great Britain, Hungary, Italy and Spain during 2014 to 2016. Only one isolate per farm and per outbreak was retained. For each isolate, the MICs of ten antimicrobials were determined in a central laboratory using a broth microdilution method with modified Eaton's medium and incubation at 35 °C ± 1 °C for 24 ± 6 h. MIC₅₀/MIC₉₀ (mg/L) values for the 232 strains were: danofloxacin 0.25/1; enrofloxacin 0.5/8; marbofloxacin 1/4; gamithromycin >64/>64; spiramycin 8/16; tilmicosin >64/>64; tulathromycin >64/>64; tylosin 64/>64; florfenicol 4/8; oxytetracycline 8/32. Minor between-country differences in the MIC₉₀ values were observed for the fluoroquinolones, spiramycin and oxytetracycline, whilst the MIC values for the other compounds were similar. Spain and Italy had the higher MIC₉₀ values for the fluoroquinolones. Compared with the 2010-2012 study (156 isolates) results are similar, with an overall MIC₅₀ increase of at most one doubling dilution for enrofloxacin, spiramycin, tylosin, florfenicol and oxytetracycline. In contrast, the MIC₉₀ value for oxytetracycline decreased from >64 to 32 mg/L. 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.

Pharmacokinetics of enrofloxacin and danofloxacin in premature calves

The aim of this study was to determine the pharmacokinetics/pharmacodynamics of enrofloxacin (ENR) and danofloxacin (DNX) following intravenous (IV) and intramuscular (IM) administrations in premature calves. The study was performed on twenty-four calves that were determined to be premature by anamnesis and general clinical examination. Premature calves were randomly divided into four groups (six premature calves/group) according to a parallel pharmacokinetic (PK) design as follows: ENR-IV (10 mg/kg, IV), ENR-IM (10 mg/kg, IM), DNX-IV (8 mg/kg, IV), and DNX-IM (8 mg/kg, IM). Plasma samples were collected for the determination of tested drugs by high-pressure liquid chromatography with UV detector and analyzed by noncompartmental methods. Mean PK parameters of ENR and DNX following IV administration were as follows: elimination half-life (t_1/2λz ) 11.16 and 17.47 hr, area under the plasma concentration-time curve (AUC_0-48 ) 139.75 and 38.90 hr*µg/ml, and volume of distribution at steady-state 1.06 and 4.45 L/kg, respectively. Total body clearance of ENR and DNX was 0.07 and 0.18 L hr^-1  kg^-1 , respectively. The PK parameters of ENR and DNX following IM injection were t_1/2λz 21.10 and 28.41 hr, AUC_0-48 164.34 and 48.32 hr*µg/ml, respectively. The bioavailability (F) of ENR and DNX was determined to be 118% and 124%, respectively. The mean AUC_0-48CPR /AUC_0-48ENR ratio was 0.20 and 0.16 after IV and IM administration, respectively, in premature calves. The results showed that ENR (10 mg/kg) and DNX (8 mg/kg) following IV and IM administration produced sufficient plasma concentration for AUC_0-24 /minimum inhibitory concentration (MIC) and maximum concentration (C_max )/MIC ratios for susceptible bacteria, with the MIC₉₀ of 0.5 and 0.03 μg/ml, respectively. These findings may be helpful in planning the dosage regimen for ENR and DNX, but there is a need for further study in naturally infected premature calves.

Characterisation of the course of Mycoplasma bovis infection in naturally infected dairy herds

Mycoplasma bovis causes bovine respiratory disease, mastitis, arthritis and otitis. The importance of M. bovis has escalated because of recent outbreaks and introductions into countries previously free of M. bovis. We characterized the course of M. bovis infection on 19 recently infected dairy farms over 24 months. Our objective was to identify diagnostic tools to assess the efficacy of control measures to assess low risk infection status on M. bovis infected farms. PCR assays and culture were used to detect M. bovis, and in-house and BioX ELISAs were used to follow antibody responses. Cows and young stock were sampled on four separate occasions, and clinical cases were sampled when they arose. On 17 farms, a few cases of clinical mastitis were detected, mostly within the first eight weeks after the index case. Antibodies detected by in-house ELISA persisted in the serum of cows at least for 1.5 years on all farms, regardless of the M. bovis infection status or signs of clinical disease or subclinical mastitis on the farm. Six out of 19 farms became low risk as the infection was resolved. Our results suggest that, for biosecurity purposes, regular monitoring should be conducted on herds by screening for M. bovis in samples from cows with clinical mastitis and calves with pneumonia, in conjunction with testing young stock by screening longitudinally collected nasal swabs for M. bovis and sequential serum samples for antibody against recombinant antigen.

Mycoplasma bovis arthritis and pneumonia in calves in Jordan: An emerging disease

Aim:

Clinical, microbiological, molecular, and pathological assays were undertaken to characterize an outbreak of increasingly reported signs of unresponsive arthritis and pneumonia of Mycoplasma bovis infection in young calves in Jordan.

Materials and Methods:

Clinical history of the affected bovine herd was investigated for the presence of respiratory and/or joint problems. Two calves with such history were clinically examined and necropsied. Representative tissues were sent for microbiological, molecular, and pathological examinations for M. bovis infection.

Results:

The outbreak started in a herd of 220 nursing calves, 2 months before the receiving of two calves for postmortem examination. Clinically, respiratory signs and infection of one or more joints dominated in the affected calves. The morbidity and case fatality rates were 27.27% and 61.7%, respectively. The left carpal joint was markedly swollen in both calves and exhibited necrofibrinous to granulomatous arthritis in varying degrees of severity. The anteroventral lung lobes in both calves were consistently affected and revealed multifocal to coalescing severe necrogranulomatous and fibrinopurulent bronchopneumonia. Microbiological and molecular findings confirmed the pathological examination. Furthermore, bovine viral diarrhea (BVD) was diagnosed in one calf by histopathology and polymerase chain reaction.

Conclusion:

This investigation reports the first outbreak of M. bovis infection in calves located in Jordan that could occur concurrently with BVD.

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.

Antimicrobial activity of bovine NK-lysin-derived peptides on Mycoplasma bovis

Antimicrobial peptides (AMPs) are a diverse group of molecules which play an important role in the innate immune response. Bovine NK-lysins, a type of AMP, have been predominantly found in the granules of cytotoxic T-lymphocytes and NK-cells. Bovine NK-lysin-derived peptides demonstrate antimicrobial activity against various bacterial pathogens, including several involved in bovine respiratory disease complex (BRDC) in cattle; however, such studies are yet to be performed with one important contributor to the BRDC, Mycoplasma bovis. Therefore, the goal of this study was to assess the antimicrobial activity of bovine NK-lysin-derived peptides on M. bovis. Thirty-mer synthetic peptides corresponding to the functional region helices 2 and 3 of bovine NK-lysins NK1, NK2A, NK2B, and NK2C were evaluated for killing activity on M. bovis isolates. Among four peptides, NK2A and NK2C showed the highest antimicrobial activity against the M. bovis isolates tested. All four NK-lysin peptides induced rapid plasma membrane depolarization in M. bovis at two concentrations tested. However, based on propidium iodide uptake, only NK2A and NK2C appeared capable of causing structural damage to M. bovis plasma membrane. Confocal microscopy, flow cytometry, and transmission electron microscopy further suggested NK-lysin-induced damage to the plasma membrane. Taken together, the findings in this study suggest that plasma membrane depolarization alone was insufficient to induce lethality, but disruption/permeabilization of the M. bovis plasma membrane was the cause of lethality.

Semen as a source of Mycoplasma bovis mastitis in dairy herds

Mycoplasma bovis infections are responsible for substantial economic losses in the cattle industry, have significant welfare effects and increase antibiotic use. The pathogen is often introduced into naive herds through healthy carrier animals. In countries with a low prevalence of M. bovis, transmission from less common sources can be better explored as the pathogen has limited circulation compared to high prevalence populations. In this study, we describe how M. bovis was introduced into two closed and adequately biosecure dairy herds through the use of contaminated semen during artificial insemination (AI), leading to mastitis outbreak in both herds. Epidemiological analysis did not reveal an infection source other than semen. In both farms the primary clinical cases were M. bovis mastitis in cows inseminated with the semen of the same bull four weeks before the onset of the disease. One semen straw derived from the semen tank on the farm and other semen lots of this bull were positive for M. bovis. In contrast, semen samples were negative from other bulls that had been used for insemination in previous or later oestrus to those cows with M. bovis mastitis. Furthermore, cgMLST of M. bovis isolates supported the epidemiological results. To our knowledge this is the first study describing the introduction of M. bovis infection into a naive dairy herd via processed semen. The antibiotics used in semen extenders should be re-evaluated in order to provide farms with M. bovis-free semen or tested M. bovis-free semen should be available.

Mutations Associated with Decreased Susceptibility to Seven Antimicrobial Families in Field and Laboratory-Derived Mycoplasma bovis Strains

The molecular mechanisms of resistance to fluoroquinolones, tetracyclines, an aminocyclitol, macrolides, a lincosamide, a phenicol, and pleuromutilins were investigated in Mycoplasma bovis For the identification of mutations responsible for the high MICs of certain antibiotics, whole-genome sequencing of 35 M. bovis field isolates and 36 laboratory-derived antibiotic-resistant mutants was performed. In vitro resistant mutants were selected by serial passages of M. bovis in broth medium containing subinhibitory concentrations of the antibiotics. Mutations associated with high fluoroquinolones MICs were found at positions 244 to 260 and at positions 232 to 250 (according to Escherichia coli numbering) of the quinolone resistance-determining regions of the gyrA and parC genes, respectively. Alterations related to elevated tetracycline MICs were described at positions 962 to 967, 1058, 1195, 1196, and 1199 of genes encoding the 16S rRNA and forming the primary tetracycline binding site. Single transversion at position 1192 of the rrs1 gene resulted in a spectinomycin MIC of 256 μg/ml. Mutations responsible for high macrolide, lincomycin, florfenicol, and pleuromutilin antibiotic MICs were identified in genes encoding 23S rRNA. Understanding antibiotic resistance mechanisms is an important tool for future developments of genetic-based diagnostic assays for the rapid detection of resistant M. bovis strains.