Bovine respiratory disease is the leading user of antibiotics (AB) in calf production. Mycoplasma (M.) bovis could lead to greater use of AB as it is a persistent and AB resistant causative agent for ...respiratory diseases. Two cross-sectional studies were set up to assess the effects of lot size and feeding system on M. bovis infection and the effects of M. bovis seroconversion, lot size and feeding system on AB use in calves’ feedlots. Twenty-six lots in 22 fattening farms were monitored for 41–81 days, from all-in entry of calves until three consecutive weeks without using any collective antibiotics. M. bovis spread was estimated by measuring seroconversion at entry and at the end of study period in 10–15 calves randomly sampled in each lot. All AB treatments used in the meanwhile were recorded. The lots were selected according to feeding system, i.e. individual bucket (n = 7) vs. automated milk feeder (AMF, n = 19), and lot size (30–519 calves), less than 50 calves (n = 9) vs. more than 50 calves (n = 17). Statistical analysis was performed using multivariable generalised linear models with fattening farms as random effect. M. bovis spread increased with lot size (odds ratio (OR) 2.91.4; 5.8 per two-fold increase in lot size). This proportion of seroconverted calves was lower in bucket-fed lots compared to lots fed with the AMF using a shared nipple (OR = 0.030.003; 0.41). The main risk factor for AB use was the lot size, with an increase of 1.50.94; 1.98 treatments per two-fold increase in lot size. For same size lots, the use of bucket can decrease AB consumption by up to 1.03−2.18; 0.14 treatments per calf compared to AMF. Analysis of the association between seroconversion to M. bovis and AB use was inconclusive. We found that bucket feeding in small-size lots, i.e. up to a maximum of 50 calves in the same space, limits seroconversion to M. bovis and enables lower use of AB in veal calf production.
Mycoplasmas are minimal, wall-less bacteria but have retained the ability to secrete complex carbohydrate polymers that constitute a glycocalyx. In members of the Mycoplasma mycoides cluster, which ...are important ruminant pathogens, the glycocalyx includes both cell-attached and cell-free polysaccharides. This report explores the potential secretion of polysaccharides by M. agalactiae, another ruminant pathogen that belongs to a distant phylogenetic group. Comparative genomic analyses showed that M. agalactiae possesses all the genes required for polysaccharide secretion. Notably, a putative synthase gene (gsmA) was identified, by in silico reconstruction of the biosynthetic pathway, that could be involved in both polymerization and export of the carbohydrate polymers. M. agalactiae polysaccharides were then purified in vitro and found to be mainly cell attached, with a linear β-(1→6)-glucopyranose structure β-(1→6)-glucan. Secretion of β-(1→6)-glucan was further shown to rely on the presence of a functional gsmA gene, whose expression is subjected to high-frequency phase variation. This event is governed by the spontaneous intraclonal variation in length of a poly(G) tract located in the gsmA coding sequence and was shown to occur in most of the M. agalactiae clinical isolates tested in this study. M. agalactiae susceptibility to serum-killing activity appeared to be dictated by ON/OFF switching of β-(1→6)-glucan secretion, suggesting a role of this phenomenon in survival of the pathogen when it invades the host bloodstream. Finally, β-(1→6)-glucan secretion was not restricted to M. agalactiae but was detected also in M. mycoides subsp. capri PG3(T), another pathogen of small ruminants.
Many if not all bacteria are able to secrete polysaccharides, either attached to the cell surface or exported unbound into the extracellular environment. Both types of polysaccharides can play a role in bacterium-host interactions. Mycoplasmas are no exception despite their poor overall metabolic capacity. We showed here that M. agalactiae secretes a capsular β-(1→6)-glucopyranose thanks to a specific glycosyltransferase with synthase activity. This secretion is governed by high-frequency ON/OFF phase variation that might be crucial in mycoplasma host dissemination, as cell-attached β-(1→6)-glucopyranose increases serum-killing susceptibility. Our results provide functional genetic data about mycoplasmal glycosyltransferases with dual functions, i.e., assembly and export of the sugar polymers across the cell membrane. Furthermore, we demonstrated that nonprotein epitopes can be subjected to surface antigenic variation in mycoplasmas. Finally, the present report contributes to unravel the role of secreted polysaccharides in the virulence and pathogenicity of these peculiar bacteria.
A mathematical model has been developed to predict the thermal behaviour of heat pipes with thermal storage during a cooling cycle. A heat transfer model based upon the various mechanisms of ...conduction, convection as well as heat of fusion of the melted ice is presented. The thermal behaviour of heat pipes has also been studied experimentally and analyzed under different conditions. Comparisons were made against the experimental data for validation of the predictive model. The model fairly predicted experimental data obtained at various inlet conditions.
Aims
Mycoplasma agalactiae is responsible for Contagious Agalactia, a severe syndrome affecting small ruminants worldwide and resulting in significant economic losses in countries with an important ...dairy industry. The aim of this study was to examine the antimicrobial susceptibility patterns of M. agalactiae isolates in France, their evolution over the last 25 years and their relationships with the genetic diversity of isolates and their origin (geographical and animal host).
Methods and Results
Susceptibility patterns were determined by measuring minimal inhibitory concentrations (MICs) of several antimicrobials used against mycoplasmas. Caprine M. agalactiae strains showed increased MICs over time for most of the antimicrobials tested, except fluoroquinolones. This susceptibility loss was homogeneous despite the considerable genetic and geographical heterogeneity of the isolates. In contrast, all the ovine isolates originating from a single clone and the same region showed increased MICs only to some macrolides.
Conclusions
MICs have evolved differently depending on the origin of the isolates but the overall loss in susceptibility has remained far more moderate than that of Mycoplasma bovis, a cattle pathogen closely related to M. agalactiae.
Significance and Impact of the Study
Several hypotheses are proposed to explain the differences in susceptibility patterns, such as local, specific, nonmycoplasma‐targeting antibiotic treatments and the genetic background of isolates in connection with their animal host.
•No statistically-significant increase in tetracyclines MICs in recent years for Contagious Agalactia agents.•Same MICs distributions in France and Spain despite differences in tetracyclines use.•The ...subspecies most often isolated are more prone to have increased MICs.•Mutations in 16S rRNA genes cannot account for all observed increases in MICs.
Contagious agalactia is a mycoplasmosis that affects small ruminants, is associated with loss of milk production and high morbidity rates, and is highly deleterious to dairy industries. The etiological agents are four mycoplasma (sub)species, of which the relative importance depends on the countries and the animal host. Tetracyclines are non-expensive, broad-spectrum antimicrobials and are often used to control mastitis in dairy herds. However, the in vitro efficiency of tetracyclines against each of the etiological agents of contagious agalactia has been poorly assessed.
The aims of this study were i) to compare the tetracycline susceptibilities of various field isolates, belonging to different mycoplasma (sub)species and subtypes, collected over the years from different clinical contexts in France or Spain, and ii) to investigate the molecular mechanisms behind the decreased susceptibility of some isolates to tetracyclines.
The Minimum Inhibitory Concentrations (MICs) of tetracyclines were determined in vitro on a set of 120 isolates. Statistical analyses were run to define the significance of any observed differences in MICs distribution. As mutations in the genes encoding the tetracycline targets (rrs loci) are most often associated with increased tetracycline MICs in animal mycoplasmas, these genes were sequenced.
The loss of susceptibility to tetracyclines after year 2010 is not significant and recent MICs are higher in M. agalactiae, especially isolates from mastitis cases, than in other etiological agents of contagious agalactia. The observed increases in MICs were not always associated with mutations in the rrs alleles which suggests the existence of other resistance mechanisms yet to be deciphered.
Surveillance and control of Mycoplasma spp. responsible for contagious agalactia (CA) in caprine herds are important challenges in countries with a large small-ruminant dairy industry. In the absence ...of any clinical signs, being able to determine the potential circulation of mycoplasmas within a herd could help to prevent biosecurity issues during animal exchanges between farms and improve health management practices. The objective of this study was to determine whether regular sampling of bulk tank milk was suitable for such surveillance. Twenty farms were sampled once a month for 2 yr and CA-responsible mycoplasmas were detected by real-time PCR on DNA extracted from milk, using 3 different DNA extraction methods. The pattern of mycoplasma excretion in bulk tank milk was assessed over time and several herd characteristics were recorded together with any event occurring within the herds. In general, the results obtained with the different detection methods were comparable and mainly agreed with the culture results. Several patterns of excretion were observed but were not related to herd characteristics (size, breed, and so on). Recurrence of the same (sub)species and same pulsed-field gel electrophoresis subtype during the 2-yr period is indicative of the considerable persistence of mycoplasmas. This persistence was associated with intermittent excretion. In conclusion, bulk tank milk sampling could be valuable for controlling CA in caprine herds provided it is repeated several times, yet to be defined, per year and analyzed using an appropriate methodology and the right cut-off for interpretation.
Most severe goat mycoplasmosis outbreaks in France are caused by
Mycoplasma mycoides subsp.
mycoides biotype LC (
MmmLC). However,
MmmLC can also be recovered from ear canals of healthy goats or from ...bulk milk collected in herds showing no clinical signs of mycoplasmosis. To improve our understanding of how
MmmLC strains are balanced between pathogenic ones and asymptomatically carried ones, descriptive epidemiological data were analysed, together with the genomic fingerprints of isolates generated using pulsed-field gel electrophoresis (PFGE). PGFE analyses were performed with isolates collected from the ear canals of goats or bulk milk in healthy herds, from individual clinical cases in different diseased herds at different times, and within a single herd during a severe outbreak, from various body sites including the ear canals at autopsy. Results showed that each isolate collected in healthy herds yielded a unique and characteristic PFGE profile. Isolates from diseased herds had profiles that were distinct for each outbreak and the group of 41 isolates from a single severe outbreak had 2 predominant PFGE profiles that persisted throughout the outbreak. These data suggest that while several distinct isolates are carried by healthy animals, only a few are responsible for the clinical signs observed within one herd during an outbreak. Whether this reflects differences in virulence between different field strains of
MmmLC remains to be demonstrated.
Strains of
Mycoplasma mycoides subspecies
capri (
Mmc) are frequently isolated from goats with contagious agalactia, but they can also be recovered from herds that have shown no clinical signs of ...mycoplasmosis for several years. The present study was conducted in order to explore the potential genetic and antigenic differences existing between an
Mmc strain isolated from an outbreak (septicaemic) and a strain isolated from the ear canal of a goat belonging to a herd with no recent episode of mycoplasmosis (carriage strain). The genomes of the two strains, compared by suppression subtractive hybridization, were shown to be poorly divergent. The two strains were inoculated into goats to produce specific antisera, but both induced fatal mycoplasmosis. These results indicate that septicaemic and carriage strains cannot be distinguished by their genetic background or by their pathogenic capacity under experimental conditions.
'Type III secretion' allows extracellular adherent bacteria to inject bacterial effector proteins into the cytosol of their animal or plant host cells. In the archetypal Yersinia system the secreted ...proteins are called Yops. Some of them are intracellular effectors, while YopB and YopD have been shown by genetic analyses to be dedicated to the translocation of these effectors. Here, the secretion of Yops by Y.enterocolitica was induced in the presence of liposomes, and some Yops, including YopB and YopD, were found to be inserted into liposomes. The proteoliposomes were fused to a planar lipid membrane to characterize the putative pore-forming properties of the lipid-bound Yops. Electrophysiological experiments revealed the presence of channels with a 105 pS conductance and no ionic selectivity. Channels with those properties were generated by mutants devoid of the effectors and by lcrG mutants, as well as by wild-type bacteria. In contrast, mutants devoid of YopB did not generate channels and mutants devoid of YopD led to current fluctuations that were different from those observed with wild-type bacteria. The observed channel could be responsible for the translocation of Yop effectors.
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