Molecular characterization of acquired enrofloxacin resistance in Mycoplasma synoviae field isolates.

The in vitro activity of enrofloxacin against 73 Mycoplasma synoviae field strains isolated in Israel and Europe was determined by broth microdilution. Decreased susceptibility to enrofloxacin was identified in 59% of strains, with the MICs ranging from 1 to >16 µg/ml. The estimated MIC50 and MIC90 values for enrofloxacin were 2 and 8 µg/ml, respectively. Moreover, this study showed that 92% of recent Israeli field isolates (2009 to 2011) of M. synoviae have MICs of ≥ 2 µg/ml to enrofloxacin. Comparison of the quinolone resistance-determining regions (QRDRs) in M. synoviae isolates revealed a clear correlation between the presence of one of the amino acid substitutions Asp79-Asn, Thr80-Ala/Ile, Ser81-Pro, and Asp84-Asn/Tyr/His of the ParC QRDR and decreased susceptibility to enrofloxacin (MIC, ≥ 1 µg/ml). Amino acid substitutions at positions GyrA 87, GyrB 401/402, and ParE 420/454 were also identified, but there was no clear-cut correlation with susceptibility to enrofloxacin. Comparison of vlhA molecular profiles revealed the presence of 9 different genotypes in the Israeli M. synoviae field isolates and 10 genotypes in the European isolates; only one vlhA genotype (type 4) was identified in both cohorts. Based on results of vlhA molecular typing, several mechanisms for emergence and dissemination of Israeli enrofloxacin-resistant M. synoviae isolates are suggested.

Discrepancy between minimal inhibitory concentration to enrofloxacin and mutations present in the quinolone-resistance determining regions of Mycoplasma gallisepticum field strains.

Molecular characterization of the quinolone-resistance determining regions (QRDRs) of DNA gyrase and topoisomerase IV in 93 Mycoplasma gallisepticum field strains isolated in different geographic regions revealed discrepancies between minimal inhibitory concentration values and presence of amino acid substitutions within the QRDRs of GyrA and ParC in 9/93 (10%) strains. This may delimitate applicability of a gene-based assay to detect fluoroquinolone resistance in this avian pathogen.

Rapid detection of a point mutation in the parC gene associated with decreased susceptibility to fluoroquinolones in Mycoplasma bovis.

Comparison of the quinolone resistance-determining regions (QRDRs) in 42 Mycoplasma bovis clinical isolates revealed amino acid substitutions at both GyrA (position 83) and ParC (position 84) in 10/11 enrofloxacin-resistant strains. The mutation present in the parC QRDR was discriminative for enrofloxacin resistance by parC PCR-restriction fragment length polymorphism. Comparison of molecular profiles by insertion sequence typing suggests that the currently prevalent enrofloxacin-resistant M. bovis strain evolved by selection under field conditions from one of the susceptible strains.

Molecular characterization and typing of enrofloxacin-resistant clinical isolates of Mycoplasma gallisepticum.

Emergence of resistance to fluoroquinolones is mainly due to chromosomal mutations in genes encoding the subunits of the drug's target enzymes, DNA gyrase and topoisomerase IV, which are essential for DNA replication. The quinolone resistance-determining regions (QRDRs) of these genes were characterized in 25 Mycoplasma gallisepticum strains isolated from commercial poultry flocks during 1997-2007, which exhibited different levels of susceptibility to fluoroquinolones. All enrofloxacin-resistant isolates harbored amino acid substitutions in the QRDRs of each of three proteins (GyrA, GyrB, and ParC). Molecular typing of those strains by random amplification of polymorphic DNA and gene-targeted sequencing supports ongoing, stepwise selection of resistant strains from the existing reservoir of susceptible M. gallisepticum strains.

Molecular variability of the adhesin-encoding gene pvpA among Mycoplasma gallisepticum strains and its application in diagnosis.

Mycoplasma gallisepticum is an important pathogen of chickens and turkeys that causes considerable economic losses to the poultry industry worldwide. The reemergence of M. gallisepticum outbreaks among poultry, the increased use of live M. gallisepticum vaccines, and the detection of M. gallisepticum in game and free-flying song birds has strengthened the need for molecular diagnostic and strain differentiation tests. Molecular techniques, including restriction fragment length polymorphism of genomic DNA (RFLP) and PCR-based random amplification of polymorphic DNA (RAPD), have already been utilized as powerful tools to detect intraspecies variation. However, certain intrinsic drawbacks constrain the application of these methods. The main goal of this study was to determine the feasibility of using an M. gallisepticum-specific gene encoding a phase-variable putative adhesin protein (PvpA) as the target for molecular typing. This was accomplished using a pvpA PCR-RFLP assay. Size variations among PCR products and nucleotide divergence of the C-terminus-encoding region of the pvpA gene were the basis for strain differentiation. This method can be used for rapid differentiation of vaccine strains from field isolates by amplification directly from clinical samples without the need for isolation by culture. Moreover, molecular epidemiology of M. gallisepticum outbreaks can be performed using RFLP and/or sequence analysis of the pvpA gene.

Use of arbitrarily primed polymerase chain reaction to investigate Mycoplasma bovis outbreaks.

Colony lineages from three Mycoplasma bovis outbreaks representing different husbandry conditions in the United States were characterized with arbitrarily primed polymerase chain reaction (AP-PCR). Cases studied included a closed beef herd, a dairy calf ranch, and a feedlot. The DNA was obtained from colony lineages and used for AP-PCR with primers REP1R-I and REP2-I. Case A and C lineages were uniform by AP-PCR analysis. Lineages from case B showed heterogeneity with AP-PCR. Outbreaks A and C were therefore both infected by one source, while the ranch (case B) was infected by multiple calf shipments. The AP-PCR typing method provides genotypic epidemiological information to successfully characterize M. bovis from sequential sampling of outbreaks and different husbandry conditions.

A chromosomal region of Mycoplasma agalactiae containing vsp-related genes undergoes in vivo rearrangement in naturally infected animals.

A Mycoplasma agalactiae genomic fragment carrying four vsp-related genes (designated avg: agalactiae variable genes) was cloned, sequenced and compared to the vspA gene of Mycoplasma bovis. The following features were revealed: (i) the presence of a highly conserved vsp 5' upstream region; (ii) a highly homologous vsp N-terminal end encoding a putative lipoprotein signal sequence; (iii) sequence divergence of the rest of the mature proteins. By using avg specific probes in Southern blot analysis of genomic DNAs of M. agalactiae strains as well as of isolates from infected animals, marked DNA polymorphism of avg fragments was demonstrated. In addition, the avg genomic fingerprints were monitored for a period of 7 months, in isolates of M. agalactiae from an individual chronically infected animal. The results provided evidence that a chromosomal region of M. agalactiae, carrying vsp-related genes, undergoes rearrangements in vivo in the natural animal host during the course of infection.

Avian mycoplasmosis (Mycoplasma gallisepticum).

Mycoplasma gallisepticum is the most economically significant mycoplasma pathogen of poultry, and has a world-wide distribution. In common with other mycoplasmas, M. gallisepticum is minute in size with minimal genetic information and with a total lack of a bacterial cell wall. These properties are reflected in a high degree of interdependence between M. gallisepticum and the host animal, and in the fastidious nature of the organism in vitro. Strains of M. gallisepticum differ markedly with respect to important biological properties such as pathogenicity, infectivity, tissue tropism and transmissibility. In addition, phenotypic variation of major surface antigens occurs at high frequency, which is a probable explanation for chronic infection by M. gallisepticum despite a strong immune response. Infection with M. gallisepticum has a wide variety of clinical manifestations, but even in the absence of overt clinical signs, the economic impact may be significant. The most dramatic disease presentation of M. gallisepticum is chronic respiratory disease in meat-type birds, often as one of several aetiological agents in a multi-factorial disease complex. Transmission of M. gallisepticum in ovo from infected breeder birds to progeny is the major route of dissemination of the infection, and is the prime consideration for international trade. In most countries, control programmes for M. gallisepticum are based on maintaining commercial breeding stock free of infection. In instances where control of M. gallisepticum infection is not feasible, vaccination, especially with newly developed live M. gallisepticum vaccines, is being evaluated as an option. Major advances in diagnostic methods have been made in recent years. Control programmes have been based on serological methods, with screening for infection usually accomplished by the slide plate agglutination (SPA) test or by enzyme-linked immunosorbent assay. Further serological testing and/or demonstration of the presence of the organism must be used to confirm SPA suspected positive tests. In principle, detection of the presence of the M. gallisepticum organism can be by isolation of the organism or detection of the deoxyribonucleic acid by molecular methods. Polymerase chain reaction represents a rapid and sensitive alternative to traditional culture methods, which require time-consuming specialised techniques. The development of molecular typing methods affords new opportunities for epidemiological studies and identification of reservoirs of infection.

Molecular characterization of the Mycoplasma gallisepticum pvpA gene which encodes a putative variable cytadhesin protein.

A putative cytadhesin-related protein (PvpA) undergoing variation in its expression was identified in the avian pathogen Mycoplasma gallisepticum. The pvpA gene was cloned, expressed in Escherichia coli, and sequenced. It exhibits 54 and 52% homology with the P30 and P32 cytadhesin proteins of the human pathogens Mycoplasma pneumoniae and Mycoplasma genitalium, respectively. In addition, 50% homology was found with the MGC2 cytadhesin of M. gallisepticum and 49% homology was found with a stretch of 205 amino acids of the cytadherence accessory protein HMW3 of M. pneumoniae. The PvpA molecule possesses a proline-rich carboxy-terminal region (28%) containing two identical directly repeated sequences of 52 amino acids and a tetrapeptide motif (Pro-Arg-Pro-X) which is repeated 14 times. Genetic analysis of several clonal isolates representing different expression states of the PvpA product ruled out chromosomal rearrangement as the mechanism for PvpA phase variation. The molecular basis of PvpA variation was revealed in a short tract of repeated GAA codons, encoding five successive glutamate resides, located in the N-terminal region and subject to frequent mutation generating an in-frame UAA stop codon. Size variation of the PvpA protein was observed among M. gallisepticum strains, ranging from 48 to 55 kDa and caused by several types of deletions occurring at the PvpA C-terminal end and within the two directly repeated sequences. By immunoelectron microscopy, the PvpA protein was localized on the mycoplasma cell surface, in particular on the terminal tip structure. Collectively, these findings suggest that PvpA is a newly identified variable surface cytadhesin protein of M. gallisepticum.

The vsp locus of Mycoplasma bovis: gene organization and structural features.

Major lipoprotein antigens, known as variable membrane surface lipoproteins (Vsps), on the surface of the bovine pathogen Mycoplasma bovis were shown to spontaneously undergo noncoordinate phase variation between ON and OFF expression states. The high rate of Vsp phenotypic switching was also shown to be linked with DNA rearrangements that occur at high frequency in the M. bovis chromosome (I. Lysnyansky, R. Rosengarten, and D. Yogev, J. Bacteriol. 178:5395-5401, 1996). In the present study, 13 single-copy vsp genes organized in a chromosomal cluster were identified and characterized. All vsp genes encode highly conserved N-terminal domains for membrane insertion and lipoprotein processing but divergent mature Vsp proteins. About 80% of each vsp coding region is composed of reiterated coding sequences that create a periodic polypeptide structure. Eighteen distinct repetitive domains of different lengths and amino acid sequences are distributed within the products of the various vsp genes that are subject to size variation due to spontaneous insertions or deletions of these periodic units. Some of these repeats were found to be present in only one Vsp family member, whereas other repeats recurred at variable locations in several Vsps. Each vsp gene is also 5' linked to a highly homologous upstream region composed of two internal cassettes. The findings that rearrangement events are associated with Vsp phenotypic switching and that multiple regions of high sequence similarity are present upstream of the vsp genes and within the vsp coding regions suggest that modulation of the Vsp antigenic repertoire is determined by recombination processes that occur at a high frequency within the vsp locus of M. bovis.

Mycoplasma sturni from blue jays and northern mockingbirds with conjunctivitis in Florida.

Northern mockingbirds (Mimus polyglottos) and blue jays (Cyanocitta cristata) in a Florida (USA) wildlife care facility developed clinical signs and gross lesions suggestive of the ongoing outbreak of Mycoplasma gallisepticum (MG) conjunctivitis in house finches (Carpodacus mexicanus) and American goldfinches (Carduelis tristis). Mycoplasmal organisms were cultured from conjunctival/corneal swabs of birds with sinusitis, conjunctivitis, and/or epiphora. All of the isolates tested were identified as Mycoplasma sturni by indirect immunofluorescence. Mycoplasma sturni as well as MG should be considered in the differential diagnosis of songbirds with conjunctivitis.

Genetic variation among Mycoplasma agalactiae isolates detected by the variant surface lipoprotein gene (vspA) of Mycoplasma bovis.

Multiple restriction fragments, homologous to the previously described Mycoplasma bovis vspA gene, were identified in the chromosome of Mycoplasma agalactiae. The vspA, a representative variable surface lipoprotein gene of the vsp gene family, and four synthetic oligonucleotides, representing sequences complementary to selected regions of the vsp genes, were used as probes against digested chromosomal DNAs of several M. agalactiae clinical isolates. The resulting Southern blot analysis demonstrated a marked DNA polymorphism of multiple vspA-related fragments among the isolates. An oligonucleotide representing a conserved 5'-region common to all known vsp genes, was found to hybridize to multiple M. agalactiae genomic fragments while the other three oligonucleotides, representing distinct repetitive structures within the coding region of three known vsp genes (vspA, vspE, and vspF), failed to react. These results argue for the possible existence of a gene family in M. agalactiae analogous to the vsp system of M. bovis but comprised of diverse genes.

Molecular epidemiologic investigations of Mycoplasma gallisepticum conjunctivitis in songbirds by random amplified polymorphic DNA analyses.

An ongoing outbreak of conjunctivitis in free-ranging house finches (Carpodacus mexicanus) began in 1994 in the eastern United States. Bacterial organisms identified as Mycoplasma gallisepticum (MG) were isolated from lesions of infected birds. MG was also isolated from a blue jay (Cyanocitta cristata) that contracted conjunctivitis after being housed in a cage previously occupied by house finches with conjunctivitis, and from free-ranging American goldfinches (Carduelis tristis) in North Carolina in 1996. To investigate the molecular epidemiology of this outbreak, we produced DNA fingerprints of MG isolates by random amplification of polymorphic DNA (RAPD). We compared MG isolates from songbirds examined from 1994 through 1996 in 11 states, representing three host species, with vaccine and reference strains and with contemporary MG isolates from commercial poultry. All MG isolates from songbirds had RAPD banding patterns identical to each other but different from other strains and isolates tested. These results indicate that the outbreak of MG in songbirds is caused by the same strain, which suggests a single source; the outbreak is not caused by the vaccine or reference strains analyzed; and MG infection has not been shared between songbirds and commercial poultry.

Adherence of Mycoplasma gallisepticum involves variable surface membrane proteins.

Adherence of Mycoplasma gallisepticum to erythrocytes was examined by colony immunoblotting, detergent phase fractionation, trypsin treatment, comparison of protein profiles, and comparison of erythrocyte-bound mycoplasma protein fractions of hemadsorption-positive and -negative mutants. The binding of M. gallisepticum to chicken or human erythrocytes was found to be mediated via surface-exposed membrane proteins undergoing high-frequency phase variation.

Detection of Mycoplasma meleagridis and M. iozvae from dead-in-shell turkey embryos by polymerase chain reaction and culture.

This work reports the development of a 16S rRNA-based polymerase chain reaction (PCR) test for the detection of Mycoplasma meleagridis, and the application, together with a previously described multi-species PCR, for the diagnosis of M. meleagridis and M. iowae in dead-in-shell turkey embryos. Forty-six allantoic fluid samples from dead-in-shell turkey embryos from hatcheries in Israel and the United States were tested by PCR and cultured for the detection of M. meleagridis and M. iowae. Three methods of DNA extraction for PCR assay were compared in allantoic fluid samples from turkey embryos experimentally infected with M. iowae. The two PCR assays provided more rapid detection than culture and were more effective in detecting the components of a mixed infection. Furthermore, PCR has the ability to recognize all M. iowae strains irrespective of antigenic variation.

Use of species-specific oligonucleotide probes to detect Mycoplasma gallisepticum, M. synoviae, and M. iowae PCR amplification products.

Three digoxigenin-labeled oligonucleotide probes, complementary to the variable region of the 16S ribosomal RNA (rRNA) gene of Mycoplasma gallisepticum, M. synoviae, and M. iowae were designed. The oligonucleotides were used in a dot blot hybridization assay. The target DNA is a 780-bp fragment of the 16S rRNA gene of avian mycoplasmas amplified by a single set of primers (multispecies polymerase chain reaction [PCR]). The oligonucleotide probes were specific for their corresponding PCR products at hybridization conditions of 56 C and 50% formamide. The detection limit of the dot blot hybridization assay was approximately 70, 50, and 30 colony-forming units for M. gallisepticum, M. synoviae, and M. iowae, respectively, per 4 microliters of PCR. In general, the oligonucleotide probe dot blotting assay was a more sensitive and effective method of detecting PCR products than detection by gel electrophoresis.

In vivo variation of Mycoplasma gallisepticum antigen expression in experimentally infected chickens.

The antigen expression profiles of Mycoplasma gallisepticum isolates obtained from tracheal swabs of chickens after aerosol-inoculation with M. gallisepticum strain R or clonal variant R/E were examined in western immunoblots. A reference anti-M. gallisepticum chicken antiserum and antisera from individual infected chickens as well as monoclonal antibodies (mAbs) specific for surface proteins were used to monitor in vivo antigenic variation. mAbs 1E5 and 12D8, recognizing PvpA and p67a, recently shown to undergo high-frequency in vitro phase variation, were used for consecutive staining of colony and western immunoblots in order to distinguish between the resultant phenotypes with respect to the corresponding epitopes. Marked differences in the expression of major immunogenic proteins, including p67a, were observed between the two inocula as well as among reisolates recovered at different times of infection. Comparative western immunoblot analysis of the rapidly changing chicken serum antibody response and reisolates recovered during the course of an experimental infection with M. gallisepticum R or clonal variant R/E suggest that immune modulation may have a key role in generating surface diversity. In addition, comparison of colony immunoblots of strain R inoculum and of reisolated colonies from tracheas of birds 8 days post infection indicated an in vivo selection of the PvpA+p67a- phenotype. This study established that surface antigens of M. gallisepticum are subjected in vivo to rapid alteration in their expression. This variability may function as a crucial adaptive mechanism, enabling the organism to escape from the host immune defense and to adapt to the changing host environment at different stages of a natural infection.

Detection of Mycoplasma gallisepticum, M. synoviae, and M. iowae by multi-species polymerase chain reaction and restriction fragment length polymorphism.

A single set of oligonucleotide primers was designed from known 16S ribosomal RNA (rRNA) sequences of Mycoplasma gallisepticum (MG), M. synoviae (MS), and M. iowae (MI). This set of primers selectively amplifies a 780-base-pair DNA fragment within the 16S rRNA gene of MG, MS, and MI but does not amplify other avian mycoplasmas or other bacteria. The detection limit of the multi-species polymerase chain reaction (PCR) was approximately 100 mycoplasma (MG, MS, MI) colony-forming units per PCR reaction. The PCR product was differentiated by restriction fragment length polymorphism with the restriction enzymes HpaI, HpaII, and MboI. Preliminary results from field samples suggest that this technique could be a useful and rapid diagnostic test for the detection of these three pathogenic poultry mycoplasmas.

Species identification of avian mycoplasmas by polymerase chain reaction and restriction fragment length polymorphism analysis.

Polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP) analysis were used to detect and differentiate four pathogenic species (Mycoplasma gallisepticum, M. iowae, M. meleagridis, and M. synoviae) and ten nonpathogenic species of avian mycoplasma. A sequence of 1026 base pairs within the gene for 16S ribosomal RNA (16S rRNA) from avian mycoplasmas was successfully amplified by PCR with oligonucleotide primers (M16SPCR5' and M16SPCR3') common to all avian mycoplasmas tested. Restriction endonucleases (REs) with unique restriction sites, selected by computer-assisted analysis of known sequences of the amplified segment of avian mycoplasma, were then used to digest the PCR products. After electrophoresis of the resulting RE fragments, the RFLP patterns were compared. Combinations of up to six REs (HpaI, HhaI, HaeIII, HphI, FokI, and NlaIV) produced unique RFLP patterns by which the 14 species of avian mycoplasmas could be differentiated. The newly classified avian species M. imitans was also investigated by this method; M. imitans and M. gallisepticum gave identical RFLP patterns with the REs used in this study. The results obtained by the PCR and RFLP analysis were in agreement with current methods for species identification of avian mycoplasmas.