Development of an amplicon-based sequencing approach in response to the global emergence of mpox

The 2022 multicountry mpox outbreak concurrent with the ongoing Coronavirus Disease 2019 (COVID-19) pandemic further highlighted the need for genomic surveillance and rapid pathogen whole-genome sequencing. While metagenomic sequencing approaches have been used to sequence many of the early mpox infections, these methods are resource intensive and require samples with high viral DNA concentrations. Given the atypical clinical presentation of cases associated with the outbreak and uncertainty regarding viral load across both the course of infection and anatomical body sites, there was an urgent need for a more sensitive and broadly applicable sequencing approach. Highly multiplexed amplicon-based sequencing (PrimalSeq) was initially developed for sequencing of Zika virus, and later adapted as the main sequencing approach for Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2). Here, we used PrimalScheme to develop a primer scheme for human monkeypox virus that can be used with many sequencing and bioinformatics pipelines implemented in public health laboratories during the COVID-19 pandemic. We sequenced clinical specimens that tested presumptively positive for human monkeypox virus with amplicon-based and metagenomic sequencing approaches. We found notably higher genome coverage across the virus genome, with minimal amplicon drop-outs, in using the amplicon-based sequencing approach, particularly in higher PCR cycle threshold (Ct) (lower DNA titer) samples. Further testing demonstrated that Ct value correlated with the number of sequencing reads and influenced the percent genome coverage. To maximize genome coverage when resources are limited, we recommend selecting samples with a PCR Ct below 31 Ct and generating 1 million sequencing reads per sample. To support national and international public health genomic surveillance efforts, we sent out primer pool aliquots to 10 laboratories across the United States, United Kingdom, Brazil, and Portugal. These public health laboratories successfully implemented the human monkeypox virus primer scheme in various amplicon sequencing workflows and with different sample types across a range of Ct values. Thus, we show that amplicon-based sequencing can provide a rapidly deployable, cost-effective, and flexible approach to pathogen whole-genome sequencing in response to newly emerging pathogens. Importantly, through the implementation of our primer scheme into existing SARS-CoV-2 workflows and across a range of sample types and sequencing platforms, we further demonstrate the potential of this approach for rapid outbreak response.

Development of an amplicon-based sequencing approach in response to the global emergence of human monkeypox virus

The 2022 multi-country monkeypox (mpox) outbreak concurrent with the ongoing COVID-19 pandemic has further highlighted the need for genomic surveillance and rapid pathogen whole genome sequencing. While metagenomic sequencing approaches have been used to sequence many of the early mpox infections, these methods are resource intensive and require samples with high viral DNA concentrations. Given the atypical clinical presentation of cases associated with the outbreak and uncertainty regarding viral load across both the course of infection and anatomical body sites, there was an urgent need for a more sensitive and broadly applicable sequencing approach. Highly multiplexed amplicon-based sequencing (PrimalSeq) was initially developed for sequencing of Zika virus, and later adapted as the main sequencing approach for SARS-CoV-2. Here, we used PrimalScheme to develop a primer scheme for human monkeypox virus that can be used with many sequencing and bioinformatics pipelines implemented in public health laboratories during the COVID-19 pandemic. We sequenced clinical samples that tested presumptive positive for human monkeypox virus with amplicon-based and metagenomic sequencing approaches. We found notably higher genome coverage across the virus genome, with minimal amplicon drop-outs, in using the amplicon-based sequencing approach, particularly in higher PCR cycle threshold (lower DNA titer) samples. Further testing demonstrated that Ct value correlated with the number of sequencing reads and influenced the percent genome coverage. To maximize genome coverage when resources are limited, we recommend selecting samples with a PCR cycle threshold below 31 Ct and generating 1 million sequencing reads per sample. To support national and international public health genomic surveillance efforts, we sent out primer pool aliquots to 10 laboratories across the United States, United Kingdom, Brazil, and Portugal. These public health laboratories successfully implemented the human monkeypox virus primer scheme in various amplicon sequencing workflows and with different sample types across a range of Ct values. Thus, we show that amplicon based sequencing can provide a rapidly deployable, cost-effective, and flexible approach to pathogen whole genome sequencing in response to newly emerging pathogens. Importantly, through the implementation of our primer scheme into existing SARS-CoV-2 workflows and across a range of sample types and sequencing platforms, we further demonstrate the potential of this approach for rapid outbreak response.

Neutralizing antibodies against the SARS-CoV-2 Delta and Omicron variants following heterologous CoronaVac plus BNT162b2 booster vaccination

The recent emergence of the SARS-CoV-2 Omicron variant is raising concerns because of its increased transmissibility and its numerous spike mutations, which have the potential to evade neutralizing antibodies elicited by COVID-19 vaccines. Here we evaluated the effects of a heterologous BNT162b2 mRNA vaccine booster on the humoral immunity of participants who had received a two-dose regimen of CoronaVac, an inactivated vaccine used globally. We found that a heterologous CoronaVac prime vaccination of two doses followed by a BNT162b2 booster induces elevated virus-specific antibody levels and potent neutralization activity against the ancestral virus and the Delta variant, resembling the titers obtained after two doses of mRNA vaccines. Although neutralization of Omicron was undetectable in participants who had received a two-dose regimen of CoronaVac, the BNT162b2 booster resulted in a 1.4-fold increase in neutralization activity against Omicron compared with the two-dose mRNA vaccine. Despite this increase, neutralizing antibody titers were reduced by 7.1-fold and 3.6-fold for Omicron compared with the ancestral strain and the Delta variant, respectively. These findings have immediate implications for multiple countries that previously used a CoronaVac regimen and reinforce the idea that the Omicron variant is associated with immune escape from vaccines or infection-induced immunity, highlighting the global need for vaccine boosters to combat the impact of emerging variants.

Agritourism and Kidding Season: A Large Outbreak of Human Shiga Toxin-Producing Escherichia coli O157 (STEC O157) Infections Linked to a Goat Dairy Farm-Connecticut, 2016

The objective of this study was to determine sources of Shiga toxin-producing Escherichia coli O157 (STEC O157) infection among visitors to Farm X and develop public health recommendations. A case-control study was conducted. Case-patients were defined as the first ill child (aged <18 years) in the household with laboratory-confirmed STEC O157, or physician-diagnosed hemolytic uremic syndrome with laboratory confirmation by serology, who visited Farm X in the 10 days prior to illness. Controls were selected from Farm X visitors aged <18 years, without symptoms during the same time period as case-patients. Environment and animal fecal samples collected from Farm X were cultured; isolates from Farm X were compared with patient isolates using whole genome sequencing (WGS). Case-patients were more likely than controls to have sat on hay bales at the doe barn (adjusted odds ratio: 4.55; 95% confidence interval: 1.41–16.13). No handwashing stations were available; limited hand sanitizer was provided. Overall, 37% (29 of 78) of animal and environmental samples collected were positive for STEC; of these, 62% (18 of 29) yielded STEC O157 highly related by WGS to patient isolates. STEC O157 environmental contamination and fecal shedding by goats at Farm X was extensive. Farms should provide handwashing stations with soap, running water, and disposable towels. Access to animal areas, including animal pens and enclosures, should be limited for young children who are at risk for severe outcomes from STEC O157 infection. National recommendations should be adopted to reduce disease transmission.

Combining genomic and epidemiological data to compare the transmissibility of SARS-CoV-2 lineages

Emerging SARS-CoV-2 variants have shaped the second year of the COVID-19 pandemic and the public health discourse around effective control measures. Evaluating the public health threat posed by a new variant is essential for appropriately adapting response efforts when community transmission is detected. However, this assessment requires that a true comparison can be made between the new variant and its predecessors because factors other than the virus genotype may influence spread and transmission. In this study, we develop a framework that integrates genomic surveillance data to estimate the relative effective reproduction number (R t ) of co-circulating lineages. We use Connecticut, a state in the northeastern United States in which the SARS-CoV-2 variants B.1.1.7 and B.1.526 co-circulated in early 2021, as a case study for implementing this framework. We find that the R t of B.1.1.7 was 6-10% larger than that of B.1.526 in Connecticut in the midst of a COVID-19 vaccination campaign. To assess the generalizability of this framework, we apply it to genomic surveillance data from New York City and observe the same trend. Finally, we use discrete phylogeography to demonstrate that while both variants were introduced into Connecticut at comparable frequencies, clades that resulted from introductions of B.1.1.7 were larger than those resulting from B.1.526 introductions. Our framework, which uses open-source methods requiring minimal computational resources, may be used to monitor near real-time variant dynamics in a myriad of settings.

Multiplex qPCR discriminates variants of concern to enhance global surveillance of SARS-CoV-2

With the emergence of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) variants that may increase transmissibility and/or cause escape from immune responses, there is an urgent need for the targeted surveillance of circulating lineages. It was found that the B.1.1.7 (also 501Y.V1) variant, first detected in the United Kingdom, could be serendipitously detected by the Thermo Fisher TaqPath COVID-19 PCR assay because a key deletion in these viruses, spike Δ69-70, would cause a "spike gene target failure" (SGTF) result. However, a SGTF result is not definitive for B.1.1.7, and this assay cannot detect other variants of concern (VOC) that lack spike Δ69-70, such as B.1.351 (also 501Y.V2), detected in South Africa, and P.1 (also 501Y.V3), recently detected in Brazil. We identified a deletion in the ORF1a gene (ORF1a Δ3675-3677) in all 3 variants, which has not yet been widely detected in other SARS-CoV-2 lineages. Using ORF1a Δ3675-3677 as the primary target and spike Δ69-70 to differentiate, we designed and validated an open-source PCR assay to detect SARS-CoV-2 VOC. Our assay can be rapidly deployed in laboratories around the world to enhance surveillance for the local emergence and spread of B.1.1.7, B.1.351, and P.1.

Early introductions and transmission of SARS-CoV-2 variant B.1.1.7 in the United States

The emergence and spread of SARS-CoV-2 lineage B.1.1.7, first detected in the United Kingdom, has become a global public health concern because of its increased transmissibility. Over 2,500 COVID-19 cases associated with this variant have been detected in the United States (US) since December 2020, but the extent of establishment is relatively unknown. Using travel, genomic, and diagnostic data, we highlight that the primary ports of entry for B.1.1.7 in the US were in New York, California, and Florida. Furthermore, we found evidence for many independent B.1.1.7 establishments starting in early December 2020, followed by interstate spread by the end of the month. Finally, we project that B.1.1.7 will be the dominant lineage in many states by mid- to late March. Thus, genomic surveillance for B.1.1.7 and other variants urgently needs to be enhanced to better inform the public health response.

PCR assay to enhance global surveillance for SARS-CoV-2 variants of concern

With the emergence of SARS-CoV-2 variants that may increase transmissibility and/or cause escape from immune responses 1-3 , there is an urgent need for the targeted surveillance of circulating lineages. It was found that the B.1.1.7 (also 501Y.V1) variant first detected in the UK 4,5 could be serendipitously detected by the ThermoFisher TaqPath COVID-19 PCR assay because a key deletion in these viruses, spike Δ69-70, would cause a "spike gene target failure" (SGTF) result. However, a SGTF result is not definitive for B.1.1.7, and this assay cannot detect other variants of concern that lack spike Δ69-70, such as B.1.351 (also 501Y.V2) detected in South Africa 6 and P.1 (also 501Y.V3) recently detected in Brazil 7 . We identified a deletion in the ORF1a gene (ORF1a Δ3675-3677) in all three variants, which has not yet been widely detected in other SARS-CoV-2 lineages. Using ORF1a Δ3675-3677 as the primary target and spike Δ69-70 to differentiate, we designed and validated an open source PCR assay to detect SARS-CoV-2 variants of concern 8 . Our assay can be rapidly deployed in laboratories around the world to enhance surveillance for the local emergence spread of B.1.1.7, B.1.351, and P.1.

Early introductions and community transmission of SARS-CoV-2 variant B.1.1.7 in the United States

The emergence and spread of SARS-CoV-2 lineage B.1.1.7, first detected in the United Kingdom, has become a global public health concern because of its increased transmissibility. Over 2500 COVID-19 cases associated with this variant have been detected in the US since December 2020, but the extent of establishment is relatively unknown. Using travel, genomic, and diagnostic data, we highlight the primary ports of entry for B.1.1.7 in the US and locations of possible underreporting of B.1.1.7 cases. Furthermore, we found evidence for many independent B.1.1.7 establishments starting in early December 2020, followed by interstate spread by the end of the month. Finally, we project that B.1.1.7 will be the dominant lineage in many states by mid to late March. Thus, genomic surveillance for B.1.1.7 and other variants urgently needs to be enhanced to better inform the public health response.

Coast-to-Coast Spread of SARS-CoV-2 during the Early Epidemic in the United States

The novel coronavirus SARS-CoV-2 was first detected in the Pacific Northwest region of the United States in January 2020, with subsequent COVID-19 outbreaks detected in all 50 states by early March. To uncover the sources of SARS-CoV-2 introductions and patterns of spread within the United States, we sequenced nine viral genomes from early reported COVID-19 patients in Connecticut. Our phylogenetic analysis places the majority of these genomes with viruses sequenced from Washington state. By coupling our genomic data with domestic and international travel patterns, we show that early SARS-CoV-2 transmission in Connecticut was likely driven by domestic introductions. Moreover, the risk of domestic importation to Connecticut exceeded that of international importation by mid-March regardless of our estimated effects of federal travel restrictions. This study provides evidence of widespread sustained transmission of SARS-CoV-2 within the United States and highlights the critical need for local surveillance.

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Connecticut’s COVID-19 outbreak resulted from multiple domestic virus introductions

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SARS-CoV-2 genomic data indicate that coast-to-coast spread occurred in the United States

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Risk of introduction by domestic air travel exceeded international travel in March

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Restrictions on international travel did not significantly alter risk estimates

Coast-to-coast spread of SARS-CoV-2 in the United States revealed by genomic epidemiology

Since its emergence and detection in Wuhan, China in late 2019, the novel coronavirus SARS-CoV-2 has spread to nearly every country around the world, resulting in hundreds of thousands of infections to date. The virus was first detected in the Pacific Northwest region of the United States in January, 2020, with subsequent COVID-19 outbreaks detected in all 50 states by early March. To uncover the sources of SARS-CoV-2 introductions and patterns of spread within the U.S., we sequenced nine viral genomes from early reported COVID-19 patients in Connecticut. Our phylogenetic analysis places the majority of these genomes with viruses sequenced from Washington state. By coupling our genomic data with domestic and international travel patterns, we show that early SARS-CoV-2 transmission in Connecticut was likely driven by domestic introductions. Moreover, the risk of domestic importation to Connecticut exceeded that of international importation by mid-March regardless of our estimated impacts of federal travel restrictions. This study provides evidence for widespread, sustained transmission of SARS-CoV-2 within the U.S. and highlights the critical need for local surveillance.

548. Carbapenem-Resistant Acinetobacter baumannii Antibiotic Susceptibility Testing and Antibiogram Formation, Connecticut 2017–2019

Background

Carbapenem-resistant Acinetobacter baumanii (CRAB) is an infectious disease threat with limited treatment options. Statewide CRAB reporting and isolate submission has been mandated in Connecticut (CT) since 2017, which allowed the creation of a statewide CRAB antibiogram to assist with empiric treatment options for CRAB.

Methods

Clinical CRAB isolates from 2017 through the first quarter of 2019 underwent carbapenemase and expanded susceptibility testing at the CT State Public Health Laboratory or the Antibiotic Resistance Laboratory Network regional lab for carbapenemase and expanded susceptibility testing. Susceptibility testing was done by broth microdilution and disk diffusion, and interpreted using Clinical and Laboratory Standards Institute breakpoints. Carbapenemase producers were detected by the modified carbapenem inactivation method. Polymerase chain reaction testing identified carbapenemase genes.

Results

Of the 64 CRAB isolates submitted, 40 remained after confirmation of carbapenem resistance, i.e., resistance to at least one carbapenem, and deduplication of patients. Of these, 19 were carbapenemase producers (CP), and 21 were non-carpabenemase producers (Non-CP). All isolates were non-susceptible to cefepime, ceftazidime, levofloxacin and all carbapenems. Colistin susceptibilities were available for 33 isolates, 32 (97%) of which were susceptible. Tobramycin susceptibilities were available for 31 isolates, only 10 (32%) of which were susceptible. Of the CP, all 15 were susceptible to colistin, but only 2 (14%) were susceptible to tobramycin. Of the Non-CP, 16 (89%) were susceptible to colistin, and 8 (47%) were susceptible to tobramycin. Most CRABs had a tigecycline minimum inhibitory concentration (MIC) of ≤2 μg/mL, with a higher proportion of Non-CP with lower MIC values than CP.

Conclusion

CRAB shows resistance to all carbapenems, and most non-carbapenem antibiotics except colistin and in rare circumstances tobramycin. Most CRAB isolates had tigecycline MICs of ≤2 μg/mL. The statewide antibiogram illustrates the lack of approved antibiotics for the treatment of CRAB, underscoring the importance of further antibiotic development for CRAB treatment.

Disclosures

All authors: No reported disclosures.

536. Challenges in Using MALDI-TOF Technology to Assess for KPC Resistance in Klebsiella pneumoniae isolates in America

Background

The emergence of Klebsiella pneumoniae Carbapenemase-producing Enterobacteriaceae (KPC-E) has created a major public health concern. In clinical practice, rapid identification of KPC-KP has important implications for clinical management and infection control. In some settings matrix-assisted laser desorption ionization time of flight (MALDI-TOF) software has been used for rapid detection of KPC producing K. pneumoniae with high sensitivity and specificity. Genomic sequencing has determined that the 11.09 m/z peak is related to protein expression from the P109 gene found mostly in Tna4401a isoform among KPC-E. In our study, we evaluated the use of MALDI-TOF automated detection software to evaluate for KPC detection among a diverse group of KPC-E isolates.

Methods

We tested 52 KPC-E isolates from various hospitals in Connecticut and the Centers for Disease Control and Prevention (CDC) Antibiotic Resistance (AR) Bank. All specimens were verified as KPC-producing strains by detection of the bla_KPCgene through polymerase chain reaction. Protein extraction using the standard extraction method was performed on sub-cultured isolates. Each isolate was tested three times on MALDI-TOF MS with the incorporated bio-subtype KPC module. An organism confidence or log score value of 2 or higher was considered valid.

Results

Among 52 tested KPC-K. pneumoniae isolates, 44 (85%) were from various hospitals in Connecticut, eight (15%) came from the AR Bank. Only 15 (25.1%) of the isolates were detected as KPC-producing using the MALDI-TOF KPC module. Further investigation by peak analysis confirmed all 15 isolates detected positive demonstrated a peak at 11.09 m/z. The 11.09 m/z peak was not found in the 37 specimens that were not detected.

Conclusion

The results from our study suggest low sensitivity using this software and contradicts results seen in previous European studies. The Tna4401a isoform is often seen in KPC-2 strains, which may be less prevalent in our sample of isolates, explaining the poor sensitivity of MALDI-TOF. Further study is needed to explore this finding and potential opportunities for MALDI-TOF for rapid identification of KPC-KP.

Disclosures

All authors: No reported disclosures.

2396. Fosfomycin Resistance Among Carbapenem-Resistant Enterobacteriaceae Clinical Isolates in Connecticut, 2017

Background

Fosfomycin is among the limited treatment options for carbapenem-resistant Enterobacteriaceae (CRE) infections. Despite its use, prevalence of fosfomycin resistance among CRE in the United States is largely unknown. In 2017, submission of Enterobacteriaceae isolates resistant to ≥1 carbapenem became mandated in Connecticut (CT), allowing further characterization at the state public health laboratory (SPHL). We analyzed fosfomycin resistance among CRE isolates in CT during 2017, and explored demographic and molecular factors potentially associated with resistance.

Methods

After confirming carbapenem resistance, SPHL tests fosfomycin susceptibility using disk diffusion. For each CRE patient, the isolate most resistant to fosfomycin was included in this analysis. We used the Clinical and Laboratory Standards Institute (CLSI) fosfomycin breakpoint for Escherichia coli (nonsusceptible <16 mm) to evaluate associations among fosfomycin resistance and demographic factors, carbapenemase activity (modified carbapenem inactivation method, mCIM) and carbapenemase genes tested at SPHL. We report fosfomycin resistance rate by European Committee on Antimicrobial Susceptibility Testing (EUCAST, resistance <24 mm for E. coli) criteria for comparison.

Results

Among 138 CRE isolates, 39 (28.3%) were fosfomycin nonsusceptible by CLSI criteria. Most nonsusceptible isolates were Enterobacter cloacae (18; 46.2%) or Klebsiella pneumoniae (17; 43.6%). Isolates from patients aged ≥65 years were more likely to be fosfomycin nonsusceptible than isolates from patients aged <65 years (χ² = 3.8; P = 0.050). No other demographic characteristics were statistically significant. Of fosfomycin nonsusceptible isolates, 12 (30.8%) produced a carbapenemase (mCIM-positive), and 9 (23.1%) had the bla_KPC gene. By EUCAST criteria, 96 (69.6%) CRE isolates were fosfomycin resistant.

Conclusion

A substantial proportion of CRE in CT during 2017 were fosfomycin nonsusceptible, and nonsusceptibility was associated with older patient age. Fosfomycin resistance risk factors and molecular mechanisms need further exploration. The substantial proportion of isolates with results falling between CLSI and EUCAST breakpoints warrants evaluation.

Disclosures

All authors: No reported disclosures.

Evaluation of a real-time polymerase chain reaction assay for the diagnosis of malaria in patients from Thailand

We compared the diagnosis of malaria in 297 patients from Thailand by a real-time polymerase chain reaction (PCR) assay using the LightCycler with conventional microscopy using Giemsa-stained thick and thin blood films. The PCR assay can be completed in one hour and has the potential to detect and identify four species of Plasmodium in a single reaction by use of melting temperature curve analysis (however, we did not detect Plasmodium ovale in this study). Blood was collected, stored, and transported on IsoCode STIX, which provide a stable matrix for the archiving and rapid simple extraction of DNA. A genus-specific primer set corresponding to the 18S ribosomal RNA was used to amplify the target sequence. Fluorescence resonance energy technology hybridization probes were designed for P. falciparum over a region containing basepair mismatches, which allowed differentiation of the other Plasmodium species. The PCR results correlated with the microscopic results in 282 (95%) of 297 patient specimens. Most of these were single-species infections caused by P. vivax (150) and P. falciparum (120), along with 5 P. malariae, 2 mixed infections (P. falciparum and P. vivax), and 5 negative specimens. No negative microscopy specimens were positive by PCR (100% specificity for detection of any Plasmodium). The 15 discrepant results could not be resolved, but given the subjective nature of microscopy and the analytical objectivity of the PCR, the PCR results may be correct. The ability of the PCR method to detect mixed infections or to detect P. ovale could not be determined in this study. Within the limitations of initial equipment costs, this real-time PCR assay is a rapid, accurate, and efficient method for the specific diagnosis of malaria. It may have application in clinical laboratories, as well as in epidemiologic studies and antimalarial efficacy trials.

Recombinant Leishmania major secreting biologically active granulocyte-macrophage colony-stimulating factor survives poorly in macrophages in vitro and delays disease development in mice

Leishmania is an intracellular pathogen that replicates inside macrophages. Activated macrophages produce a specific subset of cytokines that play an important role in the control of Leishmania infections. As part of our interest in developing suicide parasites that produce abortive infections for the purposes of vaccination, we engineered recombinant Leishmania major strains producing biologically active granulocyte-macrophage colony-stimulating factor (GM-CSF). We showed that GM-CSF is being produced in the phagosomes of infected macrophages and that it can be detected in the culture supernatants of both infected macrophages and extracellular parasites. Our data support the notion that GM-CSF secreted by both developmental forms of recombinant L. major can activate macrophages to produce high levels of proinflammatory cytokines such as interleukin-1beta (IL-1beta), IL-6, and IL-18 and various chemokines including RANTES/CCL5, MIP-1alpha/CCL3, MIP-1beta/CCL4, MIP-2/CXCL2, and MCP-1/CCL2, which enhance parasite killing. Indeed, GM-CSF-expressing parasites survive poorly in macrophages in vitro and produce delayed lesion development in susceptible BALB/c mice in vivo. Selective killing of intracellular Leishmania expressing cytokine genes capable of activating cellular responses may constitute a promising strategy to control and/or prevent parasitic infections.

Isolation and characterization of a novel IgD-binding protein from Moraxella catarrhalis

A novel surface protein of the bacterial species Moraxella catarrhalis that displays a high affinity for IgD (MID) was solubilized in Empigen and isolated by ion exchange chromatography and gel filtration. The apparent molecular mass of monomeric MID was estimated to approximately 200 kDa by SDS-PAGE. The mid gene was cloned and expressed in Escherichia coli. The complete mid nucleotide gene sequence was determined, and the deduced amino acid sequence consists of 2123 residues. The sequence of MID has no similarity to other Ig-binding proteins and differs from all previously described outer membrane proteins of M. catarrhalis. MID was found to exhibit unique Ig-binding properties. Thus, in ELISA, dot blots, and Western blots, MID bound two purified IgD myeloma proteins, four IgD myeloma sera, and finally one IgD standard serum. No binding of MID was detected to IgG, IgM, IgA, or IgE myeloma proteins. MID also bound to the surface-expressed B cell receptor IgD, but not to other membrane molecules on human PBLs. This novel Ig-binding reagent promises to be of theoretical and practical interest in immunological research.

Cloning and expression of a gene encoding the lytic functions of Bacillus amyloliquefaciens phage: Evidence of an auxiliary lysis system

A bacteriophage specific to Bacillus amyloliquefaciens, a gram-positive bacterium, was isolated from a local sewage treatment center. Using a lysis assay, a gene, lys1521, was isolated and its nucleotide sequence revealed one open reading frame of 375 bp. Homology studies showed amino acid alignment similarity with gene 5A of Bacillus subtilis phages PZA and phi29. Overexpression of the cloned gene yielded a 13 kDa protein corresponding to the predicted gene product. Despite the fact that no significant homology with known cell wall lytic enzymes was apparent, the lytic profile obtained in an in vivo expression assay showed that lys1521 had cell wall hydrolysis activity. This is a significant revelation since the function of the homologous gene 5A product of phage phi29 has been suggested to be required for the in vivo elongation of phage DNA replication. The lys1521 gene could be evidence of the presence in gram-positive bacteriophages of a third lysis gene in addition to the well characterized two-step lysis system.

Protection against Leishmania major challenge infection in mice vaccinated with live recombinant parasites expressing a cytotoxic gene

A "suicide" system based on thymidine kinase-ganciclovir combination was developed and tested in a Leishmania major experimental model. Susceptible BALB/c mice were infected with L. major expressing the thymidine kinase gene of herpes simplex virus type 1 and treated for 2 consecutive weeks with 7.5 mg/kg/day ganciclovir at different times from the initial infection. Ganciclovir treatment at varying times after infection had different effects on the outcome of disease. A complete inhibition of intracellular parasites was obtained in mice treated 1 or 4 days after infection, whereas ganciclovir administration 2 weeks later resulted in the control of infection only when the drug was provided. Variable levels of protection, from partial to total, against challenge infection with virulent L. major were observed, depending on the timing of ganciclovir treatment. The thymidine kinase-ganciclovir approach represents an excellent experimental model to control Leishmania infection and to evaluate the immunologic response of the host.

Selective killing of Leishmania amastigotes expressing a thymidine kinase suicide gene

The thymidine kinase gene of Herpes simplex type-1 virus was transfected into several Leishmania species to create drug-sensitive mutants. Expression of the thymidine kinase gene is not by itself harmful to Leishmania cells but it is capable of phosphorylating ganciclovir, a nucleoside analog, into a highly toxic product. In addition to the generation of Leishmania promastigotes highly sensitive to ganciclovir, the thymidine kinase gene was expressed similarly by amastigotes engulfed either by murine or by human macrophages. Leishmania major amastigotes expressing thymidine kinase were eliminated by 85% when treated with ganciclovir. Selective killing of parasites expressing suicide genes at their infective stage could suggest novel strategies for controlling parasitic infections.