Diversity of Staphylococcus aureus associated with mastitis from dairy cows in Rwanda

OBJECTIVES

The objective of the present study was to examine the diversity of Staphylococcus aureus from mastitis milk samples of cows in Rwanda.

METHODS

A total of 1080 quarter milk samples from 279 dairy cows were collected in 80 different farms from all five provinces of Rwanda. In total, 135 S. aureus isolates were obtained and subjected to genotyping (spa typing, DNA microarray, whole-genome sequencing (WGS)), antimicrobial susceptibility testing (AST) and phenotypic profiling by Fourier Transform Infrared (FTIR) spectroscopy (including capsular serotyping).

RESULTS

Resistance to penicillin and/or tetracycline was most frequently observed. Ten sequence types (STs) (ST1, ST151, ST152, ST5477, ST700, ST7110, ST7983, ST7984, ST8320, ST97) belonging to seven clonal complexes (CCs) (CC1, CC130, CC152, CC3591, CC3666, CC705, CC97) were detected. The Panton-Valentine leukocidin (PVL) genes (lukF-PV/lukS-PV), the bovine leukocidin genes (lukM/lukF-P83) and the human and bovine toxic shock syndrome toxin gene tst-1 variants were detected. FTIR-based capsular serotyping showed CC-specific differences. Most CC97 (cap5 allele) isolates were primarily nonencapsulated (82%), whereas isolates of CC3591 and CC3666 (cap8 allele) were mostly encapsulated (86.4% and 57.8%, respectively). Our results underline the widespread global distribution of cattle-adapted CC97.

CONCLUSION

The presence of CC3591 and CC3666 in bovine mastitis suggests an important role in cattle health and dairy production in Rwanda. The results of the present study support the need for a rigorous One-Health Surveillance program of the bovine-human interface.

Diversity of Staphylococcus aureus isolated from nares of ruminants

AIMS

To examine the diversity of Staphylococcus aureus isolated from nasal swabs of ruminants in Rwanda.

METHODS AND RESULTS

A total of 454 nasal swabs from 203 cows, 170 goats, and 81 sheep were examined for the presence of S. aureus, and 30 S. aureus isolates were detected and characterized pheno- and genotypically. Resistance to penicillin and/or tetracycline was observed. The isolates were assigned to eight different spa types (t21057 (novel), t10103, t18853, t20842, t318, t355, t458, and t9432) belonging to six clonal complexes (CCs) (CC152, CC30, CC3591, CC3666, CC522, and CC97). Panton-Valentine leukocidin (PVL) genes (lukF-PV/lukS-PV), the bovine leukocidin genes (lukM/lukF-P83), and the human and bovine variants of the toxic shock syndrome toxin gene tst-1 variants were detected.

CONCLUSION

These findings demonstrate that the nares of ruminants in Rwanda are colonized with mastitis-associated S. aureus, including lineages that are also carried by humans, underscoring the zoonotic risk, especially for livestock keepers. These results highlight the crucial importance of hygiene measures when handling livestock.

Mycoplasma bradburyae sp. nov. isolated from the trachea of sea birds

In the search for mollicutes in wild birds, six Mycoplasma strains were isolated from tracheal swabs taken from four different species of seabirds. Four strains originated from three Yellow-legged gulls (Larus michahellis) and a Cory's shearwater (Calonectris borealis) from Spain, one from a South African Kelp gull (Larus dominicanus), and one from an Italian Black-headed gull (Chroicocephalus ridibundus). These Mycoplasma strains presented 99 % 16S rRNA gene sequence similarity values with Mycoplasma (M.) gallisepticum. Phylogenetic analyses of marker genes (16S rRNA gene and rpoB) confirmed the close relationship of the strains to M. gallisepticum and M. tullyi. The seabirds' strains grew well in modified Hayflick medium, and colonies showed typical fried egg morphology. They produced acid from glucose and mannose but did not hydrolyze arginine or urea. Transmission electron microscopy revealed a cell morphology characteristic of mycoplasmas, presenting spherical to flask-shaped cells with an attachment organelle. Gliding motility was also observed. Furthermore, serological tests, MALDI-ToF mass spectrometry and genomic studies demonstrated that the strains were different to any known Mycoplasma species, for which the name Mycoplasma bradburyae sp. nov. is proposed; the type strain is T158T (DSM 110708 = NCTC 14398).

The expression of GapA and CrmA correlates with the Mycoplasma gallisepticum in vitro infection process in chicken TOCs

Mycoplasma (M.) gallisepticum is the most pathogenic mycoplasma species in poultry. Infections cause mild to severe clinical symptoms associated with respiratory epithelial lesion development. Adherence, biofilm formation, and cell invasion of M. gallisepticum contribute to successful infection, immune evasion, and survival within the host. The important M. gallisepticum membrane-bound proteins, GapA and CrmA, are key factors for host cell interaction and the bacterial life-cycle, including its gliding motility, although their precise role in the individual infection step is not yet fully understood. In this study, we investigated the correlation between the host-pathogen interaction and the GapA/CrmA expression in an environment that represents the natural host's multicellular compartment. We used an in vitro tracheal organ culture (TOC) model, allowing the investigation of the M. gallisepticum variants, Rlow, RCL1, RCL2, and Rhigh, under standardised conditions. In this regard, we examined the bacterial adherence, motility and colonisation pattern, host lesion development and alterations of mucociliary clearance. Compared to low virulent RCL2 and Rhigh, the high virulent Rlow and RCL1 were more efficient in adhering to TOCs and epithelium colonisation, including faster movement from the cilia tips to the apical membrane and subsequent cell invasion. RCL2 and Rhigh showed a more localised invasion pattern, accompanied by significantly fewer lesions than Rlow and RCL1. Unrelated to virulence, comparable mucus production was observed in all M. gallisepticum infected TOCs. Overall, the present study demonstrates the role of GapA/CrmA in virulence factors from adherence to colonisation, as well as the onset and severity of lesion development in the tracheal epithelium.

Ottowia testudinis sp. nov., isolated from the cloaca of a giant Asian pond turtle (Heosemys grandis)

A bacterial strain designated 27CT isolated from the cloaca of a giant Asian pond turtle was subjected to polyphasic taxonomic characterization. The strain was Gram-stain negative and oxidase- and catalase-positive. It had highest 16S rRNA gene sequence similarity to Ottowia beijingensis GCS-AN-3T (97.6 %) and Ottowia flava GY511T 96.0% and less than 96.0 % to other established species including Ramlibacter rhizophilus YS3.2.7T, Ottowia konkukae SK3863T, Acidovorax caeni E-24608T and Ottowia thiooxydans DSM 14619T. Phylogenetically, strain 27CT formed a branch with O. beijingensis GCS-AN-3T within the Ottowia clade. The genome size was 4.32 Mbp and the G+C content was 65.7 mol%. Strain 27CT shared highest ANIb values with O. beijingensis GCS-AN-3T (82.71/82.73 %) followed by O. oryzae KADR8-3T (78.9/79.0 %) and O. caeni BD-1T (73.3/75.2 %). The diagnostic diamino acid of the peptidoglycan was meso-diaminopimelic acid and the quinone system was ubiquinone Q-8. Predominant compounds in the polar lipid profile were diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine and phosphatidylmonomethylethanolamine. Major polyamines were 2-hydroxyputrescine and putrescine. In the fatty acid profile, summed feature 3 (C16 : 1  ω7c and/or C16 : 1  ω6c), C16 : 0, summed feature 8 (C18 : 1  ω7c and/or C18 : 1  ω6c), C14 : 0, C10 : 0 3-OH and C16 : 0 2-OH were detected. All these data identify strain 27CT as representing a novel species of the genus Ottowia and hence we propose the name Ottowia testudinis sp. nov. The type strain is 27CT (=CCM 9138T=LMG 32213T).

Dogs as carriers of virulent and resistant genotypes of Clostridioides difficile

While previous research on zoonotic transmission of community-acquired Clostridioides difficile infection (CA-CDI) focused on food-producing animals, the present study aimed to investigate whether dogs are carriers of resistant and/or virulent C. difficile strains. Rectal swabs were collected from 323 dogs and 38 C. difficile isolates (11.8%) were obtained. Isolates were characterized by antimicrobial susceptibility testing, whole-genome sequencing (WGS) and a DNA hybridization assay. Multilocus sequence typing (MLST), core genome MLST (cgMLST) and screening for virulence and antimicrobial resistance genes were performed based on WGS. Minimum inhibitory concentrations for erythromycin, clindamycin, tetracycline, vancomycin and metronidazole were determined by E-test. Out of 38 C. difficile isolates, 28 (73.7%) carried genes for toxins. The majority of isolates belonged to MLST sequence types (STs) of clade I and one to clade V. Several isolates belonged to STs previously associated with human CA-CDI. However, cgMLST showed low genetic relatedness between the isolates of this study and C. difficile strains isolated from humans in Austria for which genome sequences were publicly available. Four isolates (10.5%) displayed resistance to three of the tested antimicrobial agents. Isolates exhibited resistance to erythromycin, clindamycin, tetracycline and metronidazole. These phenotypic resistances were supported by the presence of the resistance genes erm(B), cfr(C) and tet(M). All isolates were susceptible to vancomycin. Our results indicate that dogs may carry virulent and antimicrobial-resistant C. difficile strains.

Outbreak of Cronobacter turicensis in European brown hares (Lepus europaeus)

This is the first report of acute deaths in five European brown hares (Lepus europaeus) attributed to mucoid and necrotizing typhlocolitis caused by genetically different Cronobacter (C.) turicensis strains in northeastern Austria. As this opportunistic pathogen is mainly known for causing disease in immunocompromised humans and neonates, this previously unrecognized potential for a spillover from a wildlife reservoir to humans warrants further attention.

Mycoplasma tauri sp. nov. isolated from the bovine genital tract

Since 2006, a Mycoplasma species unidentifiable to the species level has been regularly isolated from the semen and prepuce of apparently healthy bulls, and occasionally from cattle displaying inflammatory disease of the genital tract. Seven of these Mycoplasma isolates were subjected to a comprehensive taxonomic study. The strains investigated grew well in modified Hayflick's medium and colonies on agar exhibited typical fried egg morphology and produced 'film and spots'. Transmission electron microscopy revealed a cell morphology characteristic of mycoplasmas with spherically shaped cells bounded by a bi-layered cell membrane. The strains studied neither produced acid from sugar carbon sources nor did hydrolyse arginine or urea, and genome annotation indicated that organic acids (pyruvate, lactate) are used as energy sources. Phylogenetic analyses of 16S rRNA gene sequences, the 16S-23S intergenic spacer region, and partial rpoB gene and protein sequences placed the strains within the Mycoplasma (M.) bovis cluster of the Hominis group with M. primatum, M. agalactiae, and M. bovis being their closest relatives. Genomic information including whole-genome similarity metrics (ANIb, ANIm, TETRA, dDDH, AAI) and phylogenomics, proteomic features revealed by matrix-assisted laser desorption ionization time of flight (MALDI-ToF) mass spectrometry as well as serological reactions and polar lipid profiling strongly indicated that the strains examined were representatives of a hitherto unclassified species of genus Mycoplasma, for which the name Mycoplasma tauri sp. nov. with type strain Zaradi2^T (=ATCC BAA-1891^T = DSM 22451^T) is proposed.

The First Bacterial Endocarditis Due to Achromobacter xylosoxidans in a Dog

Infectious endocarditis (IE) in dogs is often associated with a high mortality rate as diagnostic work-up as well as antibiotic treatment might be challenging. The present case describes bacteremia in a dog caused by Achromobacter xylosoxidans, leading to an infectious endocarditis. Achromobacter xylosoxidans (A. xylosoxidans) is an aerobic Gram-negative rod-shaped bacterium, which has been associated with multiple nosocomial opportunistic diseases in human medicine. One such manifestation of A. xylosoxidans infection is endocarditis. A. xylosoxidans infections are challenging to treat due to the reduced effectiveness of a wide range of antimicrobial agents. To date, only a few case reports of infections with A. xylosoxidans in animals have been described. This is the first case report of A. xylosoxidans endocarditis in a dog. Whole-genome sequencing was performed to determine the sequencing type and to gain more information about this bacterium regarding its intrinsic resistance genes. With this case report, we seek to increase awareness of A. xylosoxidans as an opportunistic nosocomial pathogen in dogs and to provide a short summary regarding the current state of general knowledge and known resistance patterns.

New Insights into the Host-Pathogen Interaction of Mycoplasma gallisepticum and Avian Metapneumovirus in Tracheal Organ Cultures of Chicken

Respiratory pathogens are a health threat for poultry. Co-infections lead to the exacerbation of clinical symptoms and lesions. Mycoplasma gallisepticum (M. gallispeticum) and Avian Metapneumovirus (AMPV) are two avian respiratory pathogens that co-circulate worldwide. The knowledge about the host-pathogen interaction of M. gallispeticum and AMPV in the chicken respiratory tract is limited. We aimed to investigate how co-infections affect the pathogenesis of the respiratory disease and whether the order of invading pathogens leads to changes in host-pathogen interaction. We used chicken tracheal organ cultures (TOC) to investigate pathogen invasion and replication, lesion development, and selected innate immune responses, such as interferon (IFN) α, inducible nitric oxide synthase (iNOS) and IFNλ mRNA expression levels. We performed mono-inoculations (AMPV or M. gallispeticum) or dual-inoculations in two orders with a 24-h interval between the first and second pathogen. Dual-inoculations compared to mono-inoculations resulted in more severe host reactions. Pre-infection with AMPV followed by M. gallispeticum resulted in prolonged viral replication, more significant innate immune responses, and lesions (p < 0.05). AMPV as the secondary pathogen impaired the bacterial attachment process. Consequently, the M. gallispeticum replication was delayed, the innate immune response was less pronounced, and lesions appeared later. Our results suggest a competing process in co-infections and offer new insights in disease processes.

Entomomonas asaccharolytica sp. nov., isolated from Acheta domesticus

Strain F2A^T, isolated from the cricket Acheta domesticus, was subjected to a polyphasic taxonomic characterization. Cells of the strain were rod-shaped, Gram-stain-negative and catalase- and oxidase-positive. It did not assimilate any carbohydrates. The strain's 16S rRNA gene sequence showed highest similarity to Entomomonas moraniae QZS01^T (96.4 %). The next highest similarity values were found to representatives of related genera (<93 %). The genome size of strain F2A^T was 3.2 Mbp and the G+C content was 36.4 mol%. Average nucleotide identity values based on blast and MUMmer and average amino acid identity values between strain F2A^T and E. moraniae QZS01^T were 74.29/74.43, 83.88 and 74.70 %, respectively. The quinone system predominantly contained ubiquinone Q-8. In the polar lipid profile, diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol and an unidentified phospholipid were detected. The polyamine pattern consisted of the major compounds putrescine and spermidine. Major fatty acids were C_18 : 1 ω7c and C_16 : 0 and the hydroxyl acids were C_12 : 0 3-OH, C_14 : 0 2-OH and C_14 : 0 3-OH. The diagnostic diamino acid of the peptidoglycan was meso-diaminopimelic acid. Due to its association with the only species of the genus Entomomonas but its distinctness from E. moraniae we here propose the novel species Entomomonas asaccharolytica sp. nov. F2A^T (=CCM 9136^T=LMG 32211^T).

Presence of β-Lactamase-producing Enterobacterales and Salmonella Isolates in Marine Mammals

Marine mammals have been described as sentinels of the health of marine ecosystems. Therefore, the aim of this study was to investigate (i) the presence of extended-spectrum β-lactamase (ESBL)- and AmpC-producing Enterobacterales, which comprise several bacterial families important to the healthcare sector, as well as (ii) the presence of Salmonella in these coastal animals. The antimicrobial resistance pheno- and genotypes, as well as biocide susceptibility of Enterobacterales isolated from stranded marine mammals, were determined prior to their rehabilitation. All E. coli isolates (n = 27) were screened for virulence genes via DNA-based microarray, and twelve selected E. coli isolates were analyzed by whole-genome sequencing. Seventy-one percent of the Enterobacterales isolates exhibited a multidrug-resistant (MDR) pheno- and genotype. The gene bla_CMY (n = 51) was the predominant β-lactamase gene. In addition, bla_TEM-1 (n = 38), bla_SHV-33 (n = 8), bla_CTX-M-15 (n = 7), bla_OXA-1 (n = 7), bla_SHV-11 (n = 3), and bla_DHA-1 (n = 2) were detected. The most prevalent non-β-lactamase genes were sul2 (n = 38), strA (n = 34), strB (n = 34), and tet(A) (n = 34). Escherichia coli isolates belonging to the pandemic sequence types (STs) ST38, ST167, and ST648 were identified. Among Salmonella isolates (n = 18), S. Havana was the most prevalent serotype. The present study revealed a high prevalence of MDR bacteria and the presence of pandemic high-risk clones, both of which are indicators of anthropogenic antimicrobial pollution, in marine mammals.

Diversity of methicillin-resistant coagulase-negative Staphylococcus spp. and methicillin-resistant Mammaliicoccus spp. isolated from ruminants and New World camelids

Information about livestock carrying methicillin-resistant coagulase-negative staphylococci and mammaliicocci (MRCoNS/MRM) is scarce. The study was designed to gain knowledge of the prevalence, the phenotypic and genotypic antimicrobial resistance and the genetic diversity of MRCoNS/MRM originating from ruminants and New World camelids. In addition, a multi-locus sequence typing scheme for the characterization of Mammaliicoccus (formerly Staphylococcus) sciuri was developed. The study was conducted from April 2014 to January 2017 at the University Clinic for Ruminants and the Institute of Microbiology at the University of Veterinary Medicine Vienna. Seven hundred twenty-three nasal swabs originating from ruminants and New World camelids with and without clinical signs were examined. After isolation, MRCoNS/MRM were identified by MALDI-TOF, rpoB sequencing and typed by DNA microarray-based analysis and PCR. Antimicrobial susceptibility testing was conducted by agar disk diffusion. From all 723 nasal swabs, 189 MRCoNS/MRM were obtained. Members of the Mammaliicoccus (M.) sciuri group were predominant (M. sciuri (n = 130), followed by M. lentus (n = 43), M. fleurettii (n = 11)). In total, 158 out of 189 isolates showed phenotypically a multi-resistance profile. A seven-loci multi-locus sequence typing scheme for M. sciuri was developed. The scheme includes the analysis of internal segments of the house-keeping genes ack, aroE, ftsZ, glpK, gmk, pta1 and tpiA. In total, 28 different sequence types (STs) were identified among 92 selected M. sciuri isolates. ST1 was the most prevalent ST (n = 35), followed by ST 2 (n = 15), ST3 and ST5 (each n = 5), ST4 (n = 3), ST6, ST7, ST8, ST9, ST10 and ST11 (each n = 2).

Urban brown rats (Rattus norvegicus) as possible source of multidrug-resistant Enterobacteriaceae and meticillin-resistant Staphylococcus spp., Vienna, Austria, 2016 and 2017

Background

Brown rats (Rattus norvegicus) are an important wildlife species in cities, where they live in close proximity to humans. However, few studies have investigated their role as reservoir of antimicrobial-resistant bacteria.

Aim

We intended to determine whether urban rats at two highly frequented sites in Vienna, Austria, carry extended-spectrum β-lactamase-producing Enterobacteriaceae, fluoroquinolone-resistant Enterobacteriaceae and meticillin-resistant (MR) Staphylococcus spp. (MRS).

Methods

We surveyed the presence of antimicrobial resistance in 62 urban brown rats captured in 2016 and 2017 in Vienna, Austria. Intestinal and nasopharyngeal samples were cultured on selective media. We characterised the isolates and their antimicrobial properties using microbiological and genetic methods including disk diffusion, microarray analysis, sequencing, and detection and characterisation of plasmids.

Results

Eight multidrug-resistant Escherichia coli and two extensively drug-resistant New Delhi metallo-β-lactamases-1 (NDM-1)-producing Enterobacter xiangfangensis ST114 (En. cloacae complex) were isolated from nine of 62 rats. Nine Enterobacteriaceae isolates harboured the bla_CTX-M gene and one carried a plasmid-encoded ampC gene (bla_CMY-2). Forty-four MRS were isolated from 37 rats; they belonged to seven different staphylococcal species: S. fleurettii, S. sciuri, S. aureus, S. pseudintermedius, S. epidermidis, S. haemolyticus (all mecA-positive) and mecC-positive S. xylosus.

Conclusion

Our findings suggest that brown rats in cities are a potential source of multidrug-resistant bacteria, including carbapenem-resistant En. xiangfangensis ST114. Considering the increasing worldwide urbanisation, rodent control remains an important priority for health in modern cities.

Broad-Spectrum Cephalosporin-Resistant and/or Fluoroquinolone-Resistant Enterobacterales Associated with Canine and Feline Urogenital Infections

The aim of the present study was to characterize Enterobacterales resistant to 3rd and 4th generation cephalosporins, carbapenems and/or fluoroquinolones, isolated from dogs and cats with urogenital infections. In total, 36 strains (Escherichia coli (n = 28), Klebsiella pneumoniae (n = 3), Serratia marcescens, Raoultella ornithinolytica, Proteus mirabilis, Citrobacter portucalensis and Enterobacter cloacae (each n = 1)) were included in the present study, 28 from Austria and 8 from Serbia. Isolates were characterized by a polyphasic approach including susceptibility pheno- and genotyping and microarray-based assays. Escherichia (E.) coli isolates were additionally characterized by two-locus (fumC and fimH) sequence phylotyping and multi-locus sequence typing (MLST) of selected isolates. MLST of carbapenem-resistant Enterobacter cloacae isolates was also performed. Among E. coli, the most dominant phylogenetic group was B1 (27.8%), followed by C, (16.6%), A and Clade II (5.5% each), B2 and F (2.77% each). The most predominant β-lactam resistance genes were blaTEM (70%) and blaCTX-M (38.8%), blaCMY (25%). blaNDM was detected in one carbapenem-resistant Enterobacter cloacae ST114. The most common ST among selected E. coli was 744 (10.7% isolates). The pandemic clones ST131 and ST648 carrying CTX-M-15 were also detected. Remaining STs belonged to 469, 1287, 1463 and 1642. E. coli clonotyping revealed 20 CH types. Based on the presence of certain virulence genes, three isolates were categorized as ExPEC/UPEC. The most prevalent virulence factors were fimH detected in 61%, iucD and iss both in 55%, iroN in 27.8%, papC in 13.8% and sat in 8.3% isolates.

Increased genetic diversity of methicillin-resistant Staphylococcus aureus (MRSA) isolated from companion animals

The aim of the present study was to investigate the diversity of methicillin-resistant Staphylococcus aureus (MRSA) that originated from Austrian companion animals during the last five-year period. A total of 90 non-repetitive MRSA isolates were obtained during diagnostic activities from autumn 2013 to autumn 2018. They originated from horses (n = 62), cats (n = 13), dogs (n = 10), rabbits (n = 2), a domestic canary, a zoo-kept hammer-headed bat (Hypsignathus monstrosus) and a semi-captive northern bald ibis (Geronticus eremita). Antimicrobial susceptibility testing was performed. All isolates were mecA-positive and mecC-negative. The isolates were genotyped by SCCmec, spa and dru typing, Multiple-Locus Variable number of tandem repeat Analyses (MLVA), S. aureus DNA microarray, and whole-genome sequencing (WGS). Eight sequence types (STs - ST398, ST5275 (new ST), ST225, ST8, ST22, ST152, ST1, and ST45), three SCCmec types (II, IV, and V), sixteen spa types (t003, t008, t011, t015, t032, t034, t1381, t1928, t1985, t223, t334, t355, t430, t6447, t6867, and t7105), fourteen dru types (dt10a, dt10az, dt10q, dt10r, dt11a, dt5e, dt6j, dt9a, dt9ak, dt9g, and four new types dt8as, dt7ak, dt4j, dt14n), and thirty-five MLVA types were detected. WGS-based core genome MLST (cgMLST) displayed five main clusters. Compared to the time period 2004-2013, the results of the present study show not only a higher diversity among the MRSA isolates within the population of Austrian companion animals, but also the introduction of new clones. Although ST398 isolates remained predominant, mainly due to high presence of this lineage among horses, increasing isolation rates of human-associated MRSA clones were observed in cats and dogs.

First description of two moderately halophilic and psychrotolerant Mycoplasma species isolated from cephalopods and proposal of Mycoplasma marinum sp. nov. and Mycoplasma todarodis sp. nov

Two moderately halophilic and psychrotolerant new Mycoplasma species were isolated from common cephalopods. Three strains were isolated in pure culture from two individual European flying squid (Todarodes sagittatus), and two individual octopuses (Octopus vulgaris). The strains showed optimal growth at 25 °C and a salinity of 3% (w/v) NaCl. Molecular analyses revealed that the isolates belonged to two new, but phylogenetically related species, divergent from all previously described Mollicutes, representing the first marine isolates of the class, and also the first Mycoplasma strains for which NaCl requirement has been demonstrated. A genome search against all available marine metagenomes and 16S rRNA gene databases indicated that these two species represent a novel non-free-living marine lineage of Mollicutes, specifically associated with marine animals. Morphology and physiology were compatible with other members of this group, and genomic and phenotypic analyses demonstrated that these organisms represent two novel species of the genus Mycoplasma, for which the names Mycoplasma marinum sp. nov. and Mycoplasma todarodis sp. nov. are proposed; the type strains are PE^T (DSM 105487^T, CIP 111404^T) and 5H^T (DSM 105,488^T, CIP 111405^T), respectively.

Characterization of mecC gene-carrying coagulase-negative Staphylococcus spp. isolated from various animals

The presence of the methicillin resistance gene mecC in coagulase-negative Staphylococcus spp. (CoNS) is scarce. The aim of this study was to characterize mecC-positive CoNS isolated from various wild and domestic animals. The presence of the mecC gene was screened in 4299 samples from wild animals and domestic animals. Fifteen coagulase-negative staphylococci, that displayed a cefoxitin-resistant phenotype, were tested mecC-positive by PCR. Antimicrobial susceptibility testing was performed for all isolates. The 15 isolates were genotyped by sequencing of the entire class E mec gene complex (blaZ-mecC-mecR1-mecI), the ccrA and ccrB recombinase genes and other determinants within the type XI SCCmec element. DNA microarray analysis was performed and five selected isolates were additionally whole genome sequenced and analyzed. S. stepanovicii (n = 3), S. caprae (n = 1), S. warneri (n = 1), S. xylosus (n = 1) and S. sciuri (n = 9) were detected. All but the S. sciuri isolates were found to be susceptible to all non-beta lactams. The entire class E mec gene complex was detected in all isolates but ccrA and ccrB genes were not identified in S. stepanovicii and S. xylosus. The genes erm(B) and fexA (n = 4, each) were the most predominant non-beta lactam resistance genes detected in the S. sciuri isolates. Even though the presence of the mecC gene among CoNS is a rare observation, this study further expands our knowledge by showing that the mecC gene, including its allotypes, are present in more staphylococcal species from different animal species than has been previously described.

Bacteriophages Isolated from Chicken Meat and the Horizontal Transfer of Antimicrobial Resistance Genes

Antimicrobial resistance in microbes poses a global and increasing threat to public health. The horizontal transfer of antimicrobial resistance genes was thought to be due largely to conjugative plasmids or transposons, with only a minor part being played by transduction through bacteriophages. However, whole-genome sequencing has recently shown that the latter mechanism could be highly important in the exchange of antimicrobial resistance genes between microorganisms and environments. The transfer of antimicrobial resistance genes by phages could underlie the origin of resistant bacteria found in food. We show that chicken meat carries a number of phages capable of transferring antimicrobial resistance. Of 243 phages randomly isolated from chicken meat, about a quarter (24.7%) were able to transduce resistance to one or more of the five antimicrobials tested into Escherichia coli ATCC 13706 (DSM 12242). Resistance to kanamycin was transduced the most often, followed by that to chloramphenicol, with four phages transducing tetracycline resistance and three transducing ampicillin resistance. Phages able to transduce antimicrobial resistance were isolated from 44% of the samples of chicken meat that we tested. The statistically significant (P = 0.01) relationship between the presence of phages transducing kanamycin resistance and E. coli isolates resistant to this antibiotic suggests that transduction may be an important mechanism for transferring kanamycin resistance to E. coli. It appears that the transduction of resistance to certain antimicrobials, e.g., kanamycin, not only is widely distributed in E. coli isolates found on meat but also could represent a major mechanism for resistance transfer. The result is of high importance for animal and human health.

First identification of proteins involved in motility of Mycoplasma gallisepticum

Mycoplasma gallisepticum, the most pathogenic mycoplasma in poultry, is able to glide over solid surfaces. Although this gliding motility was first observed in 1968, no specific protein has yet been shown to be involved in gliding. We examined M. gallisepticum strains and clonal variants for motility and found that the cytadherence proteins GapA and CrmA were required for gliding. Loss of GapA or CrmA resulted in the loss of motility and hemadsorption and led to drastic changes in the characteristic flask-shape of the cells. To identify further genes involved in motility, a transposon mutant library of M. gallisepticum was generated and screened for motility-deficient mutants, using a screening assay based on colony morphology. Motility-deficient mutants had transposon insertions in gapA and the neighbouring downstream gene crmA. In addition, insertions were seen in gene mgc2, immediately upstream of gapA, in two motility-deficient mutants. In contrast to the GapA/CrmA mutants, the mgc2 motility mutants still possessed the ability to hemadsorb. Complementation of these mutants with a mgc2-hexahistidine fusion gene restored the motile phenotype. This is the first report assigning specific M. gallisepticum proteins to involvement in gliding motility.

Development of a site-directed integration plasmid for heterologous gene expression in Mycoplasma gallisepticum

Deciphering the molecular basis of the interactions between the parasite Mycoplasma gallisepticum and its avian hosts suffers from the lack of genetic tools available for the pathogen. In the absence of well established methods for targeted disruption of relevant M. gallisepticum genes, we started to develop suicide vectors and equipped them with a short fragment of M. gallisepticum origin or replication (oriC MG). We failed to create a disruption vector, although by adding a further short fragment of the M. gallisepticum tufB upstream region we created a "Trojan horse" plasmid. This is fully integrated into the genomic DNA of M. gallisepticum, always at the same site, oriC MG, and is able to carry and express any gene of interest in the genetic background of M. gallisepticum. Successful expression of a heterologous gene was shown with the lacZ gene of E. coli. When used for gene complementation or expression of hybrid genes in M. gallisepticum, a site-specific combined integration/expression vector constitutes an improvement on randomly integrating transposons, which might have unexpected effects on the expression of chromosomal genes.

Comparative immunogenicity of the hepatitis B virus core 149 antigen displayed on the inner and outer membrane of bacterial ghosts

Two membrane compartments of Escherichia coli ghosts, representing empty bacterial cell envelopes, were investigated as carriers of foreign antigens. By subcutaneous immunisation of mice the immunogenicity of bacterial ghosts carrying the Hepatitis B virus core 149 protein (HBcAg-149) as model antigen anchored either in the inner or the outer membrane of E. coli was compared. Both systems induced significant immune responses against the foreign target antigen, the HBcAg-149, in mice. Results indicate that bacterial ghosts provide an excellent carrier system for antigen delivery.

Modulation of gene expression by promoter mutants of the lambdacI857/pRM/pR system

Gene expression driven by the p(R) promoter of the lambdacI857/p(RM)/p(R) system results from inactivation of the temperature-sensitive CI857 repressor. The CI857 repressor, whose gene is transcribed by the divergently orientated p(RM) promoter, is destabilised at temperatures above 30 degrees C. In this study, the lambdacI857/p(RM)/p(R) system was modified by the introduction of a single (A-32G) and a double mutation (A-32G and T-41C). The mutated lambdap(R) expression modules, 32G and 32G/41C, tightly repressed the highly lethal phage PhiX174 lysis gene E at temperatures up to 37 and 39 degrees C, respectively. Expression of protein E and subsequent lysis of Escherichia coli was still induced by a temperature up-shift to 42 degrees C. The impact of the mutations on gene expression levels driven by the lambdap(R) and p(RM) promoters was evaluated at various temperatures using the lacZ reporter gene. Results indicate that the A-32G mutation confers a lambdap(R) promoter-down phenotype. The additional increase in the temperature stability of the 32G/41C expression system is due to the T-41C mutation leading to a higher p(RM) activity. The described lambdap(R) expression modules can be used to obtain a defined expression level at a given temperature and to tightly repress in particular highly lethal genes at different bacterial growth temperatures.

Escherichia coli ghost production by expression of lysis gene E and Staphylococcal nuclease

The production of bacterial ghosts from Escherichia coli is accomplished by the controlled expression of phage phiX174 lysis gene E and, in contrast to other gram-negative bacterial species, is accompanied by the rare detection of nonlysed, reproductive cells within the ghost preparation. To overcome this problem, the expression of a secondary killing gene was suggested to give rise to the complete genetic inactivation of the bacterial samples. The expression of staphylococcal nuclease A in E. coli resulted in intracellular accumulation of the protein and degradation of the host DNA into fragments shorter than 100 bp. Two expression systems for the nuclease are presented and were combined with the protein E-mediated lysis system. Under optimized conditions for the coexpression of gene E and the staphylococcal nuclease, the concentration of viable cells fell below the lower limit of detection, whereas the rates of ghost formation were not affected. With regard to the absence of reproductive cells from the ghost fractions, the reduction of viability could be determined as being at least 7 to 8 orders of magnitude. The lysis process was characterized by electrophoretic analysis and absolute quantification of the genetic material within the cells and the culture supernatant via real-time PCR. The ongoing degradation of the bacterial nucleic acids resulted in a continuous quantitative clearance of the genetic material associated with the lysing cells until the concentrations fell below the detection limits of either assay. No functional, released genetic units (genes) were detected within the supernatant during the lysis process, including nuclease expression.

Pasteurella multocida- and Pasteurella haemolytica-ghosts: new vaccine candidates

Pasteurella multocida is an important animal pathogen. Bacterial ghosts produced by the expression of phage PhiX174 lysis gene E are empty cells devoid of cytoplasmic and genomic material. Lysis of P. multocida 7A and P. haemolytica A1 carrying Pasteurella-specific lysis vectors (pSR2 and pSON2) occurred 140 min after induction of gene E expression induced by temperature upshift. The E-mediated cell lysis and killing activity was the same in both Pasteurella species and no viable cells could be detected after lysis of P. multocida and P. haemolytica. Pasteurella ghosts were used for immunization of rabbits and mice. Rabbits immunized subcutaneously with either P. multocida- or P. haemolytica-ghosts developed antibodies reacting with the immunizating strain, as well as with other Pasteurella strains. The number of proteins in whole cell protein extracts recognized by the sera constantly increased during the observation period of 51 days. In addition, dose-dependent protection against homologous challenge was observed in mice immunized with P. multocida-ghosts. Animals which received 1.15 x 10(8) ghosts and a challenge dose of up to 60 cfu (LD90), showed 100% protection. According to these results, we suggest ghosts of P. multocida and P. haemolytica as new vaccine candidates.

Protective immunity against pasteurellosis in cattle, induced by Pasteurella haemolytica ghosts

Pasteurella haemolytica is a cattle pathogen of significant economic impact. An effective vaccine against bovine pneumonic pasteurellosis is therefore of high importance. Apart from economic concerns, pasteurellosis caused by P. haemolytica is a serious disease leading to death in cattle if it remains untreated. In this study P. haemolytica-ghosts are presented as a promising vaccine candidate in cattle. To obtain sufficient vaccination material a fermentation protocol for P. haemolytica-ghost production was established. With the obtained experimental P. haemolytica-ghost vaccine, cattle immunization studies were performed based on a Pasteurella cattle challenge model developed specifically for vaccine validation. It was shown that protective immunization of cattle against homologous challenge was induced by adjuvanted P. haemolytica-ghosts. The level of protection was similar to a commercially available vaccine.

Online monitoring of Escherichia coli ghost production

Controlled expression of cloned phi X174 gene E in gram-negative bacteria results in lysis of the bacteria by the formation of a transmembrane tunnel structure built through the cell envelope complex. Production of bacterial ghosts is routinely monitored by classical microbiological procedures. These include determination of the turbidity of the culture and the total number of cells and the number of reproductive cells present during the time course of growth and lysis. Although conceptually simple, these methods are labor intensive and time consuming, providing a complete set of results after the determination of viable cell counts. To avoid culturing methods for bacterial growth, an alternative flow cytometric procedure is presented for the quantification of ghosts and polarized, as well as depolarized, nonlysed cells within a culture. For this method, which is based on the discriminatory power of the membrane potential-sensitive dye bis-(1,3-dibutylbarbituric acid) trimethine oxonol, a staining protocol was developed and optimized for the maximum discrepancy in fluorescence between bacterial ghosts and viable cells. The total quantitative analysis procedure takes less than 2 min. The results derived from classical or cytometric analyses correlate with respect to the total cell numbers and the viability of the culture.

Green fluorescent protein (GFP)-dependent separation of bacterial ghosts from intact cells by FACS

BACKGROUND

E. coli and Salmonella ghost preparations, produced by applying the PhiX174 protein E-mediated lysis system, contain nonlysed bacteria at a very low percentage. To use the ghosts as vaccines, additional methods have to be identified to remove any viable cell, to end up in totally inactivated ghost fractions. Materials and Methods To increase the purity of ghost fractions, we established a green fluorescent protein (GFP)-dependent "in vivo staining" method to be combined with the E-mediated lysis system. Several gfp expression vectors were constructed, and the corresponding cellular fluorescence was analyzed. Bacterial fluorescence, exclusively preserved in nonlysed cells, was utilized to separate these cells from ghost preparations via flow cytometric sorting.

RESULTS

High-level production of GFP prior to induction of the lysis system did not affect bacterial growth rates and caused no inhibitory effects on the subsequent protein E-mediated lysis of the cells. The population of reproductive or inactivated but nonlysed cells was highly fluorescent at mean intensities 215-fold higher than ghosts, which exhibited fluorescence at background level. Fluorescent cells could effectively be separated from ghost preparations via flow cytometric sorting. Cell sorting subsequent to protein E-mediated lysis reduced the number of viable cells within ghost preparations by a factor of 3 x 10(5).

CONCLUSIONS

The presented procedure is compatible with the protein E-mediated lysis system, is highly effective in separation of nonlysed fluorescent cells, and may serve as a prototype for ghost-purification in applications where only a minimum number of viable cells within ghost preparations can be tolerated.

Bacterial ghosts as drug carrier and targeting vehicles

A novel system for the packaging of drugs as well as vaccines is presented. Bacterial ghosts are intact, non-denatured bacterial envelopes that are created by lysis of bacteria through the expression of cloned phage PhiX174 gene E. Inhibition of induced E-mediated lysis by MgSO(4), harvesting of cells by centrifugation, and resuspension in low-ionic-strength buffers leads to rapid, violent lysis and results in empty bacterial envelopes with large (approximately 1 microm in diameter) openings. The construction of plasmid pAV1, which encodes a streptavidin fusion protein with an N-terminal membrane anchor sequence, allows the loading of the inner side of the cytoplasmic membrane with streptavidin. The functionality and efficacy of binding of even large biotinylated compounds in such streptavidin ghosts (SA-ghosts) was assessed using the enzyme alkaline phosphatase. The successful binding of biotinylated fluorescent dextran, as well as fluorescent DNA complexed with biotinylated polylysine, was demonstrated microscopically. The display by bacterial ghosts of morphological and antigenic surface structures of their living counterparts permits their attachment to target tissues such as the mucosal surfaces of the gastrointestinal and respiratory tract, and their uptake by phagocytes and M cells. In consequence, SA-ghosts are proposed as drug carriers for site-specific drug delivery.

Pigs aerogenously immunized with genetically inactivated (ghosts) or irradiated Actinobacillus pleuropneumoniae are protected against a homologous aerosol challenge despite differing in pulmonary cellular and antibody responses

Aerosol immunization is a safe way to induce complete protection against pleuropneumonia in pigs caused by the lung pathogenic bacterium Actinobacillus pleuropneumoniae. In order to determine the local immune responses of vaccinees in concomitant with protection, lung lining fluid before and 3 weeks after immunization from pigs immunized three times with aerosols of either genetically inactivated ghosts which represent whole cell envelope preparations, or irradiated bacteria were examined following an homologous aerosol challenge. Specific antibody isotypes in the bronchoalveolar lavage were assayed by whole cell ELISAs. Total and relative numbers of cells including lymphocyte subsets were determined. In both vaccinated groups a net influx of plasma cells and lymphocytes, as well as a significant increase of specific IgG occurred. Concurrently, the CD4+/CD8+ ratio was found to increase after aerosol immunization. The lymphocyte subsets of IgG+ and IgA+ cells were found significantly higher in the group immunized with irradiated bacteria when compared to pigs immunized with bacterial ghosts. The latter group showed a significant increase of IgA, IgM, and a net influx of lymphoid blasts and granulocytes in the bronchoalveolar lining fluid. Although differences between the local immune responses of both immunized groups occurred, a significant increase of specific IgG and a net influx of plasma cells and lymphocytes were found to be associated with complete protection against a homologous aerosol challenge infection.

Extended recombinant bacterial ghost system

Controlled expression of cloned PhiX174 gene E in Gram-negative bacteria results in lysis of the bacteria by formation of an E-specific transmembrane tunnel structure built through the cell envelope complex. Bacterial ghosts from a variety of bacteria are used as non-living candidate vaccines. In the recombinant ghost system, foreign proteins are attached on the inside of the inner membrane as fusions with specific anchor sequences. Ghosts have a sealed periplasmic space and the export of proteins into this space vastly extends the capacity of ghosts or recombinant ghosts to function as carriers of foreign antigens. In addition, S-layer proteins forming shell-like self assembly structures can be expressed in candidate vaccine strains prior to E-mediated lysis. Such recombinant S-layer proteins carrying foreign epitopes further extend the possibilities of ghosts as carriers of foreign epitopes. As ghosts have inherent adjuvant properties, they can be used as adjuvants in combination with subunit vaccines. Subunits or other ligands can also be coupled to matrixes like dextran which are used to fill the internal lumen of ghosts. Oral, aerogenic or parenteral immunization of experimental animals with recombinant ghosts induced specific humoral and cellular immune responses against bacterial and target components including protective mucosal immunity. The most relevant advantage of recombinant bacterial ghosts as immunogens is that no inactivation procedures that denature relevant immunogenic determinants are employed in this production. This fact explains the superior quality of ghosts when compared to other inactivated vaccines. The endotoxic component of the outer membrane does not limit the use of ghosts as vaccine candidates but triggers the release of several potent immunoregulatory cytokines. As carriers, there is no limitation in the size of foreign antigens that can be inserted in the membrane and the capacity of all spaces including the membranes, peri-plasma and internal lumen of the ghosts can be fully utilized. This extended recombinant ghost system represents a new strategy for adjuvant free combination vaccines.

Altered temperature induction sensitivity of the lambda pR/cI857 system for controlled gene E expression in Escherichia coli

Cell lysis of Gram-negative bacteria can be efficiently achieved by expression of the cloned lysis gene E of bacteriophage PhiX174. Gene E expression is tightly controlled by the rightward lambda pR promoter and the temperature-sensitive repressor cI857 on lysis plasmid pAW12. The resulting empty bacterial cell envelopes, called bacterial ghosts, are currently under investigation as candidate vaccines. Expression of gene E is stringently repressed at temperatures up to 30 degrees C, whereas gene E expression, and thus cell lysis, is induced at temperatures higher than 30 degrees C due to thermal inactivation of the cI857 repressor. As a consequence, the production of ghosts requires that bacteria have to be grown at 28 degrees C before the lysis process is induced. In order to reflect the growth temperature of pathogenic bacteria in vivo, it seemed favorable to extend the heat stability of the lambda pR promoter/cI857 repressor system, allowing pathogens to grow at 37 degrees C before induction of lysis. In this study we describe a mutation in the lambda pR promoter, which allows stringent repression of gene E expression at temperatures up to 36 degrees C, but still permits induction of cell lysis at 42 degrees C.

New strategies for combination vaccines based on the extended recombinant bacterial ghost system

Controlled expression of cloned PhiX174 gene E in Gram-negative bacteria results in lysis of the bacteria by formation of an E-specific transmembrane tunnel structure built through the cell envelope complex. Bacterial ghosts have been produced from a great variety of bacteria and are used as non-living candidate vaccines. In the recombinant ghost system, foreign proteins are attached on the inside of the inner membrane as fusions with specific anchor sequences. Ghosts have a sealed periplasmic space and the export of proteins into this space vastly extents the capacity of ghosts or recombinant ghosts to function as carriers of foreign antigens, immunomodulators or other substances. In addition, S-layer proteins forming shell-like self assembly structures can be expressed in bacterial candidate vaccine strains prior to E-mediated lysis. Such recombinant S-layer proteins carrying inserts of foreign epitopes of up to 600 amino acids within the flexible surface loop areas of the S-layer further extend the possibilities of ghosts as carriers of foreign epitopes. As ghosts do not need the addition of adjuvants to induce immunity in experimental animals they can also be used as carriers or targeting vehicles or as adjuvants in combination with subunit vaccines. Matrixes like dextran which can be used to fill the internal lumen of ghosts can be substituted with various ligands to bind the subunit or other materials of interest. Oral, aerogenic or parenteral immunization of experimental animals with recombinant ghosts induced specific humoral and cellular immune responses against bacterial and target components including protective mucosal immunity. The most relevant advantage of ghosts and recombinant bacterial ghosts as immunogens is that no inactivation procedures that denature relevant immunogenic determinants are employed in the production of ghosts. This fact explains the superior quality of ghosts when compared to other inactivated vaccines. As carriers of foreign antigens there is no limitation in the size of foreign antigens to be inserted and the capacity of all spaces including the membranes, periplasma and internal lumen of the ghosts can be fully utilized. Using the different building blocks and combining them into the recombinant ghost system represents a new strategy for adjuvant free combination vaccines.

Cold-sensitive E-lysis systems

The release of recombinant bacteria into the environment is undesirable because of possible risks associated with the genetically modified organisms. The aim of this study was to establish a cold-sensitive killing system with a lethal gene, activated when bacteria encounter lower environmental temperatures. To obtain cold-sensitive lysis vectors, the lambdacI857 repressor/pR promoter expression system was combined with either the lacI/lacZpo or the phage 434 cI/pR system that control the expression of the lysis gene E of bacteriophage phiX174. Escherichia coli strains harbouring such suicide vectors are able to grow at 37 degrees C, but cell lysis takes place at temperatures below 30 degrees C. By replacing gene E with a beta-galactosidase reporter gene we also showed that the onset of beta-galactosidase activity corresponds with the onset of lysis at 28 degrees C. Results indicate that these newly combined promoter/repressor systems can also be used to confer cold-sensitive expression to any gene of interest.

Endotoxicity does not limit the use of bacterial ghosts as candidate vaccines

Gram-negative bacterial ghosts produced by controlled expression of the plasmid-encoded lysis gene E offers a promising approach in non-living vaccine technology. Bacterial cell wall complex and hence the antigenic determinants of the living cells are not affected by denaturation due to cell killing. However, the endotoxin content of the Gram-negative cell wall has been discussed as a potential problem for this kind of whole cell or envelope vaccines. Here we show that bacterial ghosts prepared from Escherichia coli O26:B6 and Salmonella typhimurium C5 induce dose-dependent antibody responses against bacterial cells or their corresponding lipopolysaccharides (LPS) in doses 25 ng kg-1 when administered intravenously to rabbits in a standard immunization protocol. No differences between the immune responses of the rabbits were observed when comparing equivalent doses of bacterial ghosts and antibiotic-treated whole cells. The results indicate that the bacterial ghosts exhibit all the antigenic properties of the living cells. No significant fever responses in rabbits have been recorded in doses of < 250 ng kg-1 E. coli O26:B6 ghosts and up to doses of 250 ng kg-1 S. typhimurium C5 ghosts when applying test methods recommended by the US pharmacopoeia. These findings correlate with cell culture experiments where doses 100 ng ml-1 of bacterial ghosts were needed for the release of tumour necrosis factor alpha (TNF alpha) and prostaglandin E2 (PGE2) from RAW mouse macrophage cultures. Free LPS of Salmonella abortus equi commonly used as a LPS-standard, however, stimulated TNF alpha and PGE2 synthesis of RAW cells in doses of 1 ng ml-1. The endotoxic activity of our bacterial preparations analysed by a standard limulus amoebocyte lysate and 2-keto-3-deoxyoctonate assay correlated with the capacity to stimulate the release of PGE2 and TNF alpha in RAW mouse macrophage cultures and the endotoxic responses in rabbits. It can be concluded that these in vitro systems can be used as easy predictive test systems for preparations of bacterial vaccines, particularly for bacterial ghosts.

Bacterial ghosts as multifunctional vaccine particles

Expression of cloned PhiX174 gene E in Gram-negative bacteria results in lysis of the bacteria by formation of an E-specific transmembrane tunnel structure built through the cell envelope complex. Bacterial ghosts have been produced from a variety of bacteria including Escherichia coli. Salmonella typhimurium, Salmonella enteritidis, Vibrio cholerae, Klebsiella pneumoniae, Actinobacillus pleuropneumoniae, Haemophilus influenzae, Pasteurella haemolytica, Pasteurella multocida, and Helicobacter pylori. Such ghosts are used as non-living candidate vaccines and represent an alternative to heat or chemically inactivated bacteria. In recombinant ghosts, foreign proteins can be inserted into the inner membrane prior to E-mediated lysis via specific N-, or C-, or N- and C-terminal anchor sequences. The export of proteins into the periplasmic space or the expression of recombinant S-layer proteins vastly extents the capacity of ghosts or recombinant ghosts as carriers of foreign epitopes or proteins. Oral, aerogenic or parenteral applications of (recombinant) ghosts in experimental animals induced specific humoral and cellular immune responses against bacterial and target components including protective mucosal immunity. The most relevant advantage of ghosts and recombinant bacterial ghosts as immunogens is that no inactivation procedures that denature relevant immunogenic determinants are employed in the production of ghosts used as vaccines or as carriers of relevant antigens. The inserted target antigens into the inner membrane or into S-layer proteins are not limited in size.

Bacterial ghosts: non-living candidate vaccines

Expression of cloned PhiX174 gene E in bacteria results in lysis of bacteria. It is unique among phage lysis systems as it introduces a transmembrane tunnel structure through the cell envelope complex of Gram-negative bacteria. The resulting bacterial ghosts have intact envelope structures devoid of cytoplasmic contents. E-mediated lysis has been achieved in a variety of Gram-negative bacteria including Escherichia coli, Salmonella typhimurium, Vibrio cholerae, Klebsiella pneumoniae, and Actinobacillus pleuropneumoniae. Such ghosts, derived from human or animal pathogens, have been proposed as non-living candidate vaccines and represent an alternative to heat or chemically inactivated bacteria. In 'recombinant ghosts', foreign proteins (e.g., viral proteins) are inserted into the inner membrane via specific N-, or C-, or N- and C-terminal anchor sequences prior to lysis. Relevant advantages of (recombinant) bacterial ghosts as immunogens include: (i) inactivation procedures that denature relevant immunogenic determinants are not employed in the production of ghosts used as vaccines or as carriers of relevant antigens; (ii) the recombinant proteins are inserted into a highly immune stimulatory environment; (iii) there is no size limitation of the foreign protein moieties: multiple antigenic determinants can be presented simultaneously; (iv) bacterial ghosts can be produced inexpensively in large quantities; (v) (recombinant) ghosts are stable for long periods of time and do not require the cold chain storage system. Intraperitoneal, subcutaneous or intramuscular applications of recombinant ghosts in experimental animals induced specific humoral and cellular immune responses against bacterial and viral components. Initial aerosol vaccinations of swine with ghosts from Actinobacillus pleuropneumoniae showed that protective immunity can be established by this route of application and that the well-preserved surface structures of ghosts obtained by E-mediated lysis are able to target the mucosal immune system.

Production of Vibrio cholerae ghosts (VCG) by expression of a cloned phage lysis gene: potential for vaccine development

The protein E-specific lysis mechanism of the Escherichia coli-specific bacteriophage PhiX174 was employed to produce Vibrio cholerae ghosts (VCG). VCG consist of both rounded and collapsed cells that have lost their cytoplasmic contents through an E-specific hole in the cell envelope. These ghosts are proposed as non-living material for immunization against cholera. A specific membrane anchor sequence was used to insert the human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT) fusion protein into the cell envelope of V. cholerae. The identity of the expression products was confirmed by Western blot analysis employing an RT-specific monoclonal antibody. HIV-1 RT was chosen as a model for the purpose of evaluating heterologous gene expression in V. cholerae and the carrier potential of VCG. Intraperitoneal immunization of mice was used to evaluate the immunogenic potential of VCG. Preliminary results showed significant seroconversions to intact whole-cell vibrio antigens in mice immunized with VCG or a heat-killed whole-cell vibrio preparation.