Identification, characterization, and application of a recombinant antigen for the serological investigation of feline hemotropic Mycoplasma infections

A case of mistaken identity: a systematic review, meta-analysis, and reinvestigation of hemotropic Mycoplasma spp. infection in Ctenocephalides felis (cat flea)

BACKGROUND

Feline-associated hemotropic Mycoplasma (hemoplasmas) are believed to be transmitted by two primary mechanisms: (1) direct transmission via fighting and (2) vector-borne transmission by the cat flea (Ctenocephalides felis). While the efficiency of transmission by C. felis appears low, most manuscripts focus on the prevalence of hemoplasmas in wild-caught fleas and report either a very low (< 3%) or a high (> 26%) prevalence. Therefore, we aimed to assess the influence of sample processing and PCR methods on C. felis hemoplasma infection prevalence.

METHODS

A systemic review of PubMed articles identified 13 manuscripts (1,531 fleas/flea pools) that met the inclusion criteria (performed PCR for >1 hemoplasma on C. felis collected from cats). Risk of bias was assessed utilizing the ROBINS-E tool. Meta-analysis performed in R of these manuscripts found that not washing samples and a common set of 16S rRNA primers first published in Jensen et al. 2001 were associated with increased hemoplasma prevalence. To evaluate the influence of washing on newly collected fleas, we assessed the hemoplasma status of 20 pools of 5 C. felis each, half of which were washed and half not washed.

RESULTS

Flea washing did not influence the detection of hemoplasma but instead amplified Spiroplasma. To assess non-specific amplification with the Jensen et al. 2001 primers, 67 C. felis samples (34% previously reported hemoplasma infected) were subject to PCR and sequencing. By this method, hemoplasma was detected in only 3% of samples. In the remaining "hemoplasma infected" fleas, PCR amplified Spiroplasma or other bacteria.

CONCLUSIONS

Therefore, we concluded that hemoplasma infection in C. felis is rare, and future flea prevalence studies should sequence all positive amplicons to validate PCR specificity. Further investigation of alternative methods of feline-associated hemoplasma transmission and the ability of C. felis to maintain hemoplasma infection is necessary.

Worldwide occurrence of haemoplasmas in wildlife: Insights into the patterns of infection, transmission, pathology and zoonotic potential

Haemotropic mycoplasmas (haemoplasmas) have increasingly attracted the attention of wildlife disease researchers due to a combination of wide host range, high prevalence and genetic diversity. A systematic review identified 75 articles that investigated haemoplasma infection in wildlife by molecular methods (chiefly targeting partial 16S rRNA gene sequences), which included 131 host genera across six orders. Studies were less common in the Eastern Hemisphere (especially Africa and Asia) and more frequent in the Artiodactyla and Carnivora. Meta-analysis showed that infection prevalence did not vary by geographic region nor host order, but wild hosts showed significantly higher prevalence than captive hosts. Using a taxonomically flexible machine learning algorithm, we also found vampire bats and cervids to have greater prevalence, whereas mink, a subclade of vesper bats, and true foxes all had lower prevalence compared to the remaining sampled mammal phylogeny. Haemoplasma genotype and nucleotide diversity varied little among wild mammals but were marginally lower in primates and bats. Coinfection with more than one haemoplasma species or genotype was always confirmed when assessed. Risk factors of infection identified were sociality, age, males and high trophic levels, and both prevalence and diversity were often higher in undisturbed environments. Haemoplasmas likely use different and concurrent transmission routes and typically display enzootic dynamics when wild populations are studied longitudinally. Haemoplasma pathology is poorly known in wildlife but appears subclinical. Candidatus Mycoplasma haematohominis, which causes disease in humans, probably has it natural host in bats. Haemoplasmas can serve as a model system in ecological and evolutionary studies, and future research on these pathogens in wildlife must focus on increasing the geographic range and taxa of studies and elucidating pathology, transmission and zoonotic potential. To facilitate such work, we recommend using universal PCR primers or NGS protocols to detect novel haemoplasmas and other genetic markers to differentiate among species and infer cross-species transmission.

Quantitative analysis of Mycoplasma wenyonii and 'Candidatus Mycoplasma haemobos" infections in cattle using novel gapN-based realtime PCR assays

Hemotrophic mycoplasmas (HMs) are associated with anemia and other disease complexes in a wide range of livestock and wild animals. Two bovine HM species have been identified to date, i.e. Mycoplasma wenyonii and 'Candidatus Mycoplasma haemobos'. The study aim was to develop quantitative real-time PCR assays (qPCRs) to detect and quantify M. wenyonii and 'C. M. haemobos' and to apply these assays to DNA samples extracted from bovine blood collected in Germany (n = 220) from 22 herds. The qPCR assays specific for M. wenyonii and 'C. M. haemobos' were designed using the gapN of the respective hemoplasma species as gene target which encodes the NADP-dependent glyceraldehyde 3-phosphate dehydrogenases (GAPN). The sensitivity of both assays was 10 genome equivalents per reaction, corresponding to 2500 genome equivalents per ml blood. No cross-reactivity with non-target bovine HMs. and other bovine pathogens was observed. Bovine HM DNA was detected in 137 samples (62.27%) with 118 samples (53.64%) being positive for 'C.M. haemobos' and 19 samples (8.64%) being positive for M. wenyonii. Thereof, 11 animals (5.00%) were co-infected with both bovine HM species. The found herd prevalence for `C. M. haemobos` was 100.00%, and for M. wenyonii 36.36% with mean bacterial loads of 3.7 × 10⁷ `C. M. haemobos`/mL blood and of 4.29 × 10⁵M. wenyonii/mL blood respectively. Clinical and economic relevance of bovine HM species should be goal of future studies for which the novel gapN qPCR assays can serve as a valuable diagnostic tool.

Consecutive antibiotic treatment with doxycycline and marbofloxacin clears bacteremia in Mycoplasma haemofelis-infected cats

Mycoplasma haemofelis is the most pathogenic feline hemoplasma species and a causative agent of infectious hemolytic anemia in cats. Current treatment protocols are effective in reducing M. haemofelis blood loads and clinical signs but consistent bacteremia clearance is rarely achieved. The aim of this study was to develop an antibiotic treatment protocol capable of clearing M. haemofelis bacteremia. Doxycycline and marbofloxacin treatment protocols were evaluated in chronically M. haemofelis infected cats in two pre-experiments and a controlled treatment study (main experiment) using five treated and four untreated cats. The blood bacterial loads in the main experiment were monitored weekly by real-time PCR for 203 days. Cats were treated with doxycycline (5 mg/kg bid orally) for 28 days. Cats that remained M. haemofelis PCR-positive or became positive again (all 5 cats in the main experiment) were switched to marbofloxacin treatment (2 mg/kg sid orally) for 14 days; then, all cats were PCR-negative. Immunosuppression after the antibiotic treatment did not lead to reactivation of bacteremia. Fine needle aspirates of different organs and bone marrow collected before and after immunosuppression were PCR-negative. Overall, 5 cats cleared bacteremia with doxycycline alone (showing lower bacterial loads at the treatment start), while 10 cats needed to be switched to marbofloxacin. Based on our results, we recommend doxycycline treatment (10 mg/kg up to 28 days) for clearance of M. haemofelis infection and monitoring bacterial loads by real-time PCR. Only if bacteremia persists or reoccurs, antibiotic treatment should be switched to marbofloxacin (2 mg/kg sid for 14 days).

The surface-displayed chaperones GroEL and DnaK of Mycoplasma pneumoniae interact with human plasminogen and components of the extracellular matrix

Mycoplasma pneumoniae is a common cause of community-acquired infections of the human respiratory tract. The strongly reduced genome of the cell wall-less bacteria results in limited metabolic pathways and a small number of known virulence factors. In addition to the well-characterized adhesion apparatus and the expression of tissue-damaging substances, surface-exposed proteins with a primary function in cytosol-located processes such as glycolysis have been attracting attention in recent years. Due to interactions with host factors, it has been suggested that these bacterial proteins contribute to pathogenesis. Here, we investigated the chaperones GroEL and DnaK of M. pneumoniae as candidates for such moonlighting proteins. After successful expression in Escherichia coli and production of polyclonal antisera, the localization of both chaperones on the surface of bacteria was confirmed. Binding of recombinant GroEL and DnaK to human A549 cells, to plasminogen as well as to vitronectin, fibronectin, fibrinogen, lactoferrin and laminin was demonstrated. In the presence of both recombinant proteins and host activators, plasminogen can be activated to the protease plasmin, which is able to degrade vitronectin and fibrinogen. The results of the study extend the spectrum of surface-exposed proteins in M. pneumoniae and indicate an additional role of both chaperones in infection processes.

Passive immunization does not provide protection against experimental infection with Mycoplasma haemofelis

Mycoplasma haemofelis (Mhf) is the most pathogenic feline hemotropic mycoplasma. Cats infected with Mhf that clear bacteremia are protected from Mhf reinfection, but the mechanisms of protective immunity are unresolved. In the present study we investigated whether the passive transfer of antibodies from Mhf-recovered cats to naïve recipient cats provided protection against bacteremia and clinical disease following homologous challenge with Mhf; moreover, we characterized the immune response in the recipient cats. Ten specified pathogen-free (SPF) cats were transfused with pooled plasma from cats that had cleared Mhf bacteremia; five control cats received plasma from naïve SPF cats. After homologous challenge with Mhf, cats were monitored for 100 days using quantitative PCR, hematology, blood biochemistry, Coombs testing, flow cytometry, DnaK ELISA, and red blood cell (RBC) osmotic fragility (OF) measurement. Passively immunized cats were not protected against Mhf infection but, compared to control cats, showed significantly higher RBC OF and B lymphocyte (CD45R/B220⁺) counts and occasionally higher lymphocyte, monocyte and activated CD4⁺ T lymphocyte (CD4⁺CD25⁺) counts; they also showed higher bilirubin, total protein and globulin levels compared to those of control cats. At times of peak bacteremia, a decrease in eosinophils and lymphocytes, as well as subsets thereof (B lymphocytes and CD5⁺, CD4⁺ and CD8⁺ T lymphocytes), and an increase in monocytes were particularly significant in the passively immunized cats. In conclusion, passive immunization does not prevent bacteremia and clinical disease following homologous challenge with Mhf, but enhances RBC osmotic fragility and induces a pronounced immune response.

Lack of cross-protection against Mycoplasma haemofelis infection and signs of enhancement in "Candidatus Mycoplasma turicensis"-recovered cats

“Mycoplasma haemofelis” and “Candidatus Mycoplasma turicensis” are feline hemoplasmas that induce hemolytic anemia. Protection from homologous re-challenge was recently demonstrated in cats recovered from primary infection. Here, we determined if cats recovered from “Cand. M. turicensis” infection were protected against infections with the more pathogenic M. haemofelis. Ten specified pathogen-free cats were exposed to M. haemofelis. Five of the ten cats had recovered from “Cand. M. turicensis” bacteremia (group A), and five cats were naïve controls (group B). No cross-protection was observed. By contrast, the “Cand. M. turicensis”-recovered cats displayed faster M. haemofelis infection onset (earlier PCR-positive and anemic) than the controls. No “Cand. M. turicensis” was detected in any cat. M. haemofelis shedding was observed in saliva, feces and urine. In both groups, evidence of a Th1 response was observed (high IFN-γ, low IL-4), but IL-10 levels were also high. In group A, total, CD4+ and CD8+ T cells increased within days after M. haemofelis exposure. At times of maximal bacteremia, macrocytic hypochromic anemia, neutropenia, monocytosis and a decrease in leukocyte, eosinophil, and lymphocyte counts and subsets thereof (B- and T-cells, CD4+, CD8+ and CD4+CD25+ cells) were particularly significant in group A. Moreover, an increase in protein concentrations, hypoalbuminemia and a polyclonal hypergammaglobulinemia were observed. Five of ten M. haemofelis-infected cats subsequently cleared bacteremia without antibiotic treatment. In conclusion, the study suggests that a previous hemoplasma infection, even when the cat has ostensibly recovered, may influence subsequent infections, lead to an enhancement phenomenon and other differences in infection kinetics.

Protective immunity against infection with Mycoplasma haemofelis

Hemoplasmas are potentially zoonotic mycoplasmal pathogens, which are not consistently cleared by antibiotic therapy. Mycoplasma haemofelis is the most pathogenic feline hemoplasma species. The aim of this study was to determine how cats previously infected with M. haemofelis that had recovered reacted when rechallenged with M. haemofelis and to characterize the immune response following de novoM. haemofelis infection and rechallenge. Five specific-pathogen-free (SPF)-derived naive cats (group A) and five cats that had recovered from M. haemofelis infection (group B) were inoculated subcutaneously with M. haemofelis. Blood M. haemofelis loads were measured by quantitative PCR (qPCR), antibody response to heat shock protein 70 (DnaK) by enzyme-linked immunosorbent assay (ELISA), blood lymphocyte cell subtypes by flow cytometry, and cytokine mRNA levels by quantitative reverse transcriptase PCR. Group A cats all became infected with high bacterial loads and seroconverted, while group B cats were protected from reinfection, thus providing the unique opportunity to study the immunological parameters associated with this protective immune response against M. haemofelis. First, a strong humoral response to DnaK was only observed in group A, demonstrating that an antibody response to DnaK is not important for protective immunity. Second, proinflammatory cytokine interleukin-6 (IL-6) mRNA levels appeared to increase rapidly postinoculation in group B, indicating a possible role in protective immunity. Third, an increase in IL-12p35 and -p40 mRNA and decrease in the Th2/Th1 ratio observed in group A suggest that a Th1-type response is important in primary infection. This is the first study to demonstrate protective immunity against M. haemofelis reinfection, and it provides important information for potential future hemoplasma vaccine design.

Tissue sequestration of 'Candidatus Mycoplasma turicensis'

'Candidatus Mycoplasma turicensis' ('Candidatus M. turicensis') is a hemoplasma species that infects felids. It differs from other feline hemoplasma species due to its particular infection kinetics and phylogenetic similarity to rodent hemoplasma species. The lower and shorter bacteremia produced by 'Candidatus M. turicensis' suggests a possible tissue sequestration of the organism. The aim of this study was to explore this possibility. Five specified-pathogen free cats were subcutaneously inoculated with 'Candidatus M. turicensis' and sacrificed 86 days after inoculation. Thirty-one selected organs were collected upon necropsy, and samples were analyzed by real-time Taqman(®) PCR. The humoral immune response was monitored by DnaK ELISA. All five cats had detectable 'Candidatus M. turicensis' loads in the majority (52-100%) of the tested tissues. High 'Candidatus M. turicensis' tissue loads (average 3.46×10(4) copies/10 mg) were detected in the samples. The presence of the organisms in the tissues could not be explained by the blood burdens because the blood of four out of five cats tested PCR-negative at the time of necropsy. This is the first study to describe the distribution of 'Candidatus M. turicensis' in various organs; it also demonstrates that, in contrast to other feline hemoplasma species, significant sequestration of 'Candidatus M. turicensis' occurs in many tissues. These results represent an important step toward the understanding of the pathogenesis of 'Candidatus M. turicensis'.

Haemoplasmas: lessons learnt from cats

The haemotropic mycoplasmas (haemoplasmas) are a group of bacteria that can induce anaemia in a wide variety of mammals, including domestic cats and wild felids. Different feline haemoplasma species of varying pathogenicity exist, with the more pathogenic Mycoplasma haemofelis (Mhf) capable of inducing severe haemolytic anaemia, whilst 'Candidatus Mycoplasma haemominutum' (CMhm) and 'Candidatus Mycoplasma turicensis' (CMt) are infrequently associated with clinical disease. Chronic haemoplasma infections are common and cats are frequently infected by two or more haemoplasmas, complicating the clinical picture. The natural route of transmission of haemoplasma infection between cats has not yet been determined; however, experimental transmission has been demonstrated via both oral and parenteral administration of infected blood. To date the haemoplasmas have been unable to be cultured in vitro, and accurate diagnosis is currently reliant on detection of bacterial DNA using PCR assays. Treatment of clinical haemoplasmosis is focussed on supportive care in combination with empirical treatment with antimicrobials (tetracyclines or fluoroquinolones). A significant number of asymptomatic cats are positive for haemoplasma infection. These cats may play a role in the maintenance of haemoplasma infection within a population, and need to be considered when choosing potential blood donors. Use of PCR assays has provided an accurate method of diagnosing haemoplasma infection and quantifying response to therapy, including in non-feline host animals, as presumed zoonotic haemoplasma infections are now being documented. Recent advances in genome sequencing techniques have allowed the whole genome sequences of the feline haemoplasmas Mhf and CMhm to be derived, as well as a number of non-feline haemoplasma species. These data have aided the identification of antigens for use in the development of serological tests, allowed the proteomic study of haemoplasmas and provided clues as to how the haemoplasmas can persist within the host. Future areas of study include investigation of their zoonotic potential, mechanisms of immune system evasion and transmission of these emerging pathogens.

Protection from reinfection in "Candidatus Mycoplasma turicensis"-infected cats and characterization of the immune response

“Candidatus Mycoplasma turicensis” (CMt) is a hemoplasma species of felids. Recent evidence has shown that cats that overcome bacteremia may be protected from reinfection. The purposes of this study were to (1) re-inoculate ostensibly recovered cats, (2) evaluate the immune response and (3) assess CMt tissue loads. Fifteen specified pathogen-free cats were subcutaneously inoculated with CMt: 10 cats (group A) had previously undergone bacteremia and recovered, and 5 naïve cats (group B) served as controls. CMt infections were monitored by real-time PCR using blood and tissue, and the humoral immune response was assessed using DnaK ELISA. Cytokine mRNA expression levels were measured by real-time PCR, and lymphocyte subsets were detected by flow cytometry. The cats in group A were protected from reinfection (no detectable bacteremia) and showed a transient decrease in antibodies. Eosinophilia was noted in cats from group A. The cats from group B became PCR-positive and seroconverted. All of the tissues analyzed from the cats in group B but none of the tissues analyzed from the cats in group A were CMt PCR-positive. Significant changes were observed in the expression of tumor necrosis factor-α, interferon-γ, interleukin-4 and the Th2/Th1 ratio in both groups. The cats from group A occasionally showed higher numbers of CD4⁺, CD8⁺, CD4⁺CD25⁺ and CD5⁺MHCII⁺ T lymphocytes than the control cats. In conclusion, this study describes, for the first time, the occurrence of immunological protection within the same hemoplasma species. Furthermore, the immune response during CMt infections appeared to be skewed toward the Th2 type.

Quantification of the humoral immune response and hemoplasma blood and tissue loads in cats coinfected with 'Candidatus Mycoplasma haemominutum' and feline leukemia virus

'Candidatus Mycoplasma haemominutum' (CMhm) is a hemotropic mycoplasma (aka hemoplasma) of domestic cats and wild felids. In a transmission study, we exposed eight specified pathogen-free cats to blood from Iberian lynxes (Lynx pardinus) infected with CMhm. The cats were coinfected with feline leukemia virus (FeLV) from an Iberian lynx or with a prototype FeLV. The goal of the present study was to quantify the humoral immune response to CMhm and to identify potential target tissues and sequestration sites. Antibodies were measured by a recombinant antigen-based enzyme-linked immunosorbent assay, and blood and tissue loads were quantified using real-time PCR. Seven out of eight cats became CMhm-infected; all of these cats seroconverted between 3 and 13 weeks after inoculation. Antibody levels correlated with the CMhm blood loads. The peak CMhm blood loads were inversely correlated with the incubation period. PCR-positive results were found in all 24 tissues tested but not for all samples. Although all tissues were PCR-positive in one cat euthanized ten weeks after infection, many tissues tested negative in six cats euthanized at week 20 after infection. In several cats, the spleen, lung, liver, heart and aorta contained more copies than expected given the tissue's blood supply, but most tissues contained fewer copies than expected. In conclusion, this is the first study to quantify the humoral immune response and tissue loads in CMhm-FeLV-coinfected cats. The tissue loads appeared to correlate with the duration of infection and with the blood loads, but no evidence of significant CMhm tissue sequestration was found.

Identification, bioinformatics analyses, and expression of immunoreactive antigens of Mycoplasma haemofelis

Mycoplasma haemofelis infection frequently causes anemia in cats. Despite an intense immune response and/or antibiotic treatment, cats often remain asymptomatic carriers following infection. Our hypothesis is that detection of antibodies to M. haemofelis is a sensitive approach for identifying infected cats, particularly carriers. To date, no immunoassay has been developed. This is due largely to the inability to culture M. haemofelis in vitro; hence, a source of antigen is not readily available. The objective of this study was to identify, express, and purify immunogenic proteins of M. haemofelis. To accomplish this, two whole-genomic expression libraries were created in the Lambda ZapII vector and immunoscreened with preimmune plasma, plasma from specific-pathogen-free cats, and pooled acute- and convalescent-phase plasma from experimentally infected cats. The inserts from 21 immunoreactive clones were sequenced, resulting in the identification of 60 genes coding for putative proteins necessary for diverse cellular functions, along with several novel genes of M. haemofelis. Fragments of selected genes based on bioinformatic analyses were PCR amplified, cloned into a high-level protein expression system, and subsequently expressed in Escherichia coli as a His(6)-fusion protein. The recombinant fusion proteins of M. haemofelis were purified and evaluated as an antigen in a Western blot to verify the findings of previous immunoscreening. Together with bioinformatics analyses of individual genes, this approach provided several putative candidate antigens. Five antigens of M. haemofelis were reactive by Western blotting against the immune plasma and negative against nonimmune plasma; these antigens might be useful serologic or even vaccine targets.

Chronic "Candidatus Mycoplasma turicensis" infection

"Candidatus Mycoplasma turicensis" infects felids. The pathogenesis of "Candidatus M. turicensis" chronic infection is poorly understood. The goals of the present study were to (1) induce reactivation of the infection in chronic carrier cats by attempted immunosuppression, (2) identify potential tissue sequestration using real-time TaqMan® PCR and (3) monitor the humoral immune response by DnaK enzyme-linked immunosorbent assay (ELISA). Ten specified pathogen-free cats that had ostensibly recovered from experimental "Candidatus M. turicensis" infection were used: five cats (group 1) received high dose methylprednisolone (attempted immunosuppression), while five cats served as untreated controls (group 2). Besides weekly blood samples, tissue samples were collected from bone marrow, kidney, liver and salivary glands at selected time points. The cats in group 1 had significantly lower lymphocyte counts and higher blood glucose levels after methylprednisolone administration than the controls. After methylprednisolone administration one blood and three tissue samples from cats in group 1 tested PCR-positive; before the administration, only one sample was positive. All other samples tested PCR-negative. All cats stayed seropositive; the antibody levels of the cats in group 1 showed a significant transient decrease after methylprednisolone administration. This is the first study to report the presence of "Candidatus M. turicensis" in tissues of chronically infected cats and the persistence of anti-feline hemoplasma antibodies in the absence of detectable bacteremia. Methylprednisolone administration did not lead to a significant reactivation of the infection. Our results enhance the knowledge of "Candidatus M. turicensis" infection pathogenesis and are clinically relevant to the prognosis of hemoplasma-infected cats.

First morphological characterization of 'Candidatus Mycoplasma turicensis' using electron microscopy

At least three haemotropic mycoplasmas have been recognized in cats: Mycoplasma haemofelis (Mhf), ‘Candidatus Mycoplasma haemominutum’ (CMhm) and ‘Candidatus M. turicensis’ (CMt). The latter was originally identified in a Swiss pet cat with haemolytic anaemia and shown to be prevalent in domestic cats and wild felids worldwide using molecular methods. So far, there has been no confirmatory morphological evidence of the existence of CMt presumably due to low blood loads during infection while CMhm has only been characterized by light microscopy with discrepant results. This study aimed to provide for the first time electron microscopic characteristics of CMt and CMhm and to compare them to Mhf. Blood samples from cats experimentally infected with CMt, CMhm and Mhf were used to determine copy numbers in blood by real-time PCR and for transmission and scanning electron microscopy. High resolution scanning electron microscopy revealed CMt and CMhm to be discoid-shaped organisms of 0.3 μm in diameter attached to red blood cells (RBCs). In transmission electron microscopy of CMt, an oval organism of about 0.25 μm with several intracellular electron dense structures was identified close to the surface of a RBC. CMhm and CMt exhibited similar morphology to Mhf but had a smaller diameter. This is the first study to provide morphological evidence of CMt thereby confirming its status as a distinct haemoplasma species, and to present electron microscopic features of CMhm.