Robinsoniella peoriensis: An emerging pathogen and rare cause of wound infection in children.

BACKGROUND: Robinsoniella peoriensis is an anaerobic gram-positive bacilli first isolated from swine manure in 2003 but has since been associated with human infections. METHODS: We describe a pediatric case of R. peoriensis infection following a below-knee amputation for a limb injury and its treatment. Methods of identifying R. peoriensis and reported in vitro antimicrobial minimum inhibitory concentrations from the literature are reviewed. RESULTS: R. peoriensis is readily identifiable via 16S rRNA gene sequencing and Matrix-Assisted Laser Desorption Ionization-Time of Flight. There is variability in the antibiotic susceptibility profiles reported in the literature, but antibiotics with low in vitro minimum inhibitor concentrations against R. peoriensis include beta-lactam/beta-lactamase inhibitors, carbapenems, vancomycin, and metronidazole. CONCLUSION: This is the first reported case of R. peoriensis infection following a traumatic injury in Canada to our knowledge and highlights the importance of recognizing this organism and other anaerobes in settings where wounds are grossly contaminated with soil.

HISTORIQUE: Le Robinsoniella peoriensis est un bacille anaérobie à Gram positif d'abord isolé en 2003 dans le lisier de porc, mais qui a été associé à des infections humaines depuis. MÉTHODOLOGIE: Les auteurs décrivent un cas pédiatrique d'infection à R. peoriensis après une amputation au-dessous du genou à cause de la lésion d'un membre et de son traitement. Les chercheurs ont examiné les méthodes pour identifier le R. peoriensis et les concentrations minimales inhibitrices antimicrobiennes in vitro tirées des publications. RÉSULTATS: Le R. peoriensis est facile à identifier au moyen du séquençage du gène d'ARNr 16S et du spectromètre de masse à temps de vol pour la désorption-ionisation laser assistée par matrice. La description des profils de susceptibilité des antibiotiques est variable selon les publications, mais les antibiotiques aux concentrations minimales inhibitrices contre le R. peoriensis sont les bêta-lactamines et les inhibiteurs de bêta-lactamase, les carbapénems, la vancomycine et le métronidazole. CONCLUSION: À la connaissance des auteurs, il s'agit du premier cas déclaré d'infection à R. peoriensis après une lésion traumatique au Canada, ce qui fait ressortir l'importance de tenir compte de cet organisme et d'autres anaérobies lorsque les plaies sont grandement contaminées par de la terre.

Point of care molecular and antigen detection tests for COVID-19: current status and future prospects.

INTRODUCTION: Detection of severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) has been critical to support and management of the COVID-19 pandemic. Point of care testing (POCT) for SARS-CoV-2 has been a widely used tool for detection of SARS-CoV-2. AREAS COVERED: POCT nucleic acid amplification tests (NAATs) and rapid antigen tests (RATs) have been the most readily used POCT for SARS-CoV-2. Here, current knowledge on the utility of POCT NAATs and RATs for SARS-CoV-2 are reviewed and discussed alongside aspects of quality assurance factors that must be considered for successful and safe implementation of POCT. EXPERT OPINION: Use cases for implementation of POCT must be evidence based, regardless of the test used. A quality assurance framework must be in place to ensure accuracy and safety of POCT.

Effect of delayed entry of blood culture bottles in BACTEC automated blood culture system in the context of laboratory consolidation.

Delayed entry of blood culture bottles is frequent in consolidated laboratories. A retrospective study evaluated time from insertion to detection and total detection time as a function of preincubation time, and we prospectively looked for false negative results. 69,604 blood culture bottles were reviewed for preincubation time, incubation time and total detection time. Positive cultures for specific bacterial subtypes were reviewed to assess the effect of preincubation time on likelihood of detection. 492 negative blood cultures were prospectively tested by 16S RNA PCR and Staphylococcus-specific PCR for the presence of bacterial DNA. Mean preincubation time for samples collected within the city-limits was 3.94 h versus 9.49-18.89 h for other client sites. Higher preincubation times were partially mitigated by a lower incubation time, with an overall increase in total detection time. A lower odds ratio of recovery of Staphylococcus spp was identified, but not confirmed by terminal subcultures and molecular assays. Prolonged preincubation of blood cultures affects total detection time despite a reduction in incubation time. Successful centralization of microbiological services may depend upon optimization of courier routes for inoculated blood culture bottles. Our data supports consideration for an increase in suggested maximum preincubation times.

Implementation of the Abbott ID Now COVID-19 assay at a tertiary care center: a prospective pragmatic implementation study during the third wave of SARS-CoV-2 in Ontario.

The Abbott ID Now COVID-19 assay is a point-of-care molecular diagnostic tool for the detection of SARS-CoV-2. We prospectively monitored implementation of the assay in a tertiary care hospital emergency department (ED) for the diagnosis of early symptomatic patients. A total of 269 paired nasopharyngeal swabs were tested in parallel with the ID Now and laboratory-based molecular methodologies, 191 of which met selection criteria for testing based on symptoms description and duration. Forty-six and 48 samples were positive for SARS-CoV-2 with the ID Now and reference molecular assays respectively. Percent positive and negative agreement were high (93.8% and 99.6% respectively), as were the sensitivity and specificity (93.8% and 99.5%). ID Now results were available 17.47 hours earlier than qRT-PCR. In symptomatic patients seen in ED within 7 to 10 days of symptoms onset, the ID Now COVID-19 assay allows for rapid and accurate detection of infection.

Therapeutic Drug Monitoring of Vancomycin in Adult Patients with Methicillin-Resistant Staphylococcus aureus Bacteremia or Pneumonia.

BACKGROUND: Vancomycin remains widely used for methicillin-resistant Staphylococcus aureus (MRSA) infections; however, treatment failure rates up to 50% have been reported. At the authors' institution, monitoring of trough concentration is the standard of care for therapeutic drug monitoring of vancomycin. New guidelines support use of the ratio of 24-hour area under the concentration-time curve to minimum inhibitory concentration (AUC24/MIC) as the pharmacodynamic index most likely to predict outcomes in patients with MRSA-associated infections. OBJECTIVES: To determine the discordance rate between trough levels and AUC24/MIC values and how treatment failure and nephrotoxicity outcomes compare between those achieving and not achieving their pharmacodynamic targets. METHODS: This retrospective cohort study involved patients with MRSA bacteremia or pneumonia admitted to the study hospital between March 1, 2014, and December 31, 2018, and treated with vancomycin. Data for trough concentrations were collected, and minimum concentrations (C min) were extrapolated. The AUC24/MIC values were determined using validated population pharmacokinetic models. The C min and AUC24/MIC values were characterized as below, within, or above pharmacodynamic targets (15-20 mg/L and 400-600, respectively). Discordance was defined as any instance where a patient's paired C min and AUC24/MIC values fell in different ranges (i.e., below, within, or above) relative to the target ranges. Predictors of treatment failure and nephrotoxicity were determined using logistic regression. RESULTS: A total of 128 patients were included in the analyses. Of these, 73 (57%) received an initial vancomycin dose less than 15 mg/kg. The discordance rate between C min and AUC24/MIC values was 21% (27/128). Rates of treatment failure and nephrotoxicity were 34% (43/128) and 18% (23/128), respectively. No clinical variables were found to predict discordance. Logistic regression identified initiation of vancomycin after a positive culture result (odds ratio [OR] 4.41, 95% confidence interval [CI] 1.36-14.3) and achievement of target AUC24/MIC after 4 days (OR 3.48, 95% CI 1.39-8.70) as modifiable predictors of treatment failure. CONCLUSIONS: The relationship between vancomycin monitoring and outcome is likely confounded by inadequate empiric or initial dosing. Before any modification of practice with respect to vancomycin monitoring, empiric vancomycin dosing should be optimized.

CONTEXTE: La vancomycine reste largement utilisée contre les infections dues au Staphylococcus aureus méthicillinorésistant (SAMR); cependant, on rapporte des taux d'échec de traitement allant jusqu'à 50 %. Dans l'institution où travaillent les auteurs, la surveillance de la concentration minimale constitue la norme de soins du suivi thérapeutique pharmacologique de la vancomycine. De nouvelles lignes directrices soutiennent l'utilisation du ratio de 24 h de l'aire sous la courbe de concentration-temps à concentration minimale inhibitrice (AUC24/MIC) en tant qu'indice pharmacodynamique, vraisemblablement pour prédire certains résultats concernant les patients présentant des infections associées au SAMR. OBJECTIFS: Déterminer le taux de discordance entre la concentration minimale et les valeurs de l'AUC24/MIC et la manière dont les échecs de traitement et les résultats de néphrotoxicité se comparent entre les personnes atteignant leurs cibles pharmacodynamiques et celles qui ne l'atteignent pas. MÉTHODES: Cette étude de cohorte rétrospective impliquait des patients atteints d'une bactériémie au SAMR ou d'une pneumonie au SAMR, admis à l'hôpital où se déroulait l'étude entre le 1er mars 2014 et le 31 décembre 2018 et traités à l'aide de vancomycine. Les données relatives aux concentrations minimales ont été recueillies, et les concentrations minimales (C min) extrapolées. Les valeurs de l'AUC24/MIC ont été déterminées à l'aide de modèles de population pharmacocinétiques validés. La caractérisation des valeurs de la C min et des valeurs de l'AUC24/MIC se décrit comme suit: « en dessous ¼, « à l'intérieur ¼ ou « au-dessus ¼ des cibles pharmacodynamiques (respectivement 15­20 mg/L et 400­600). La discordance était définie comme une situation où les valeurs associées de la C min et de l'AUC24/MIC tombaient dans des plages différentes (c.-à-d., en dessous, à l'intérieur ou au-dessus) par rapport aux plages cibles. Une régression logistique a permis de déterminer les prédicteurs d'échecs de traitement et de néphrotoxicité. RÉSULTATS: Au total, 128 patients ont été inclus dans les analyses. De ceux-ci, 73 (57 %) ont reçu une dose initiale de vancomycine de moins de 15 mg/kg. Le taux de discordance entre les valeurs de la C min et de l'AUC24/MIC était de 21 % (27/128). Les taux d'échec de traitement et de néphrotoxicité se montaient respectivement à 34 % (43/128) et 18 % (23/128). Aucune variable clinique n'a pu prédire la discordance. La régression logistique a permis de déterminer le début de l'administration de la vancomycine après un résultat de culture positif (rapport de cotes [RC] 4,41, 95 % intervalle de confiance [IC] 1,36­14,3) et l'atteinte de la cible de l'AUC24/MIC après quatre jours (RC 3,48, 95 % IC 1,39­8,70) en tant que prédicteurs modifiables de l'échec du traitement. CONCLUSIONS: Il existe probablement une confusion relative à la relation entre la surveillance de la vancomycine et le résultat à cause d'un dosage empirique ou initial inadéquat. Avant de modifier la pratique relative à la surveillance de la vancomycine, le pharmacien doit optimiser son dosage empirique.

Evaluation of the Abbott PanbioTM COVID-19 Ag rapid antigen test for the detection of SARS-CoV-2 in asymptomatic Canadians.

Several rapid testing methodologies have been approved for testing of symptomatic individuals but have not been validated for asymptomatic screening. We evaluated performance of the Abbott PanbioTM COVID-19 rapid antigen assay in the asymptomatic setting. We conducted a prospective study in an urban assessment center and in the context of long-term care staff screening. A total of 3014 individuals submitted paired nasopharyngeal samples, which were tested in parallel with the rapid antigen and laboratory-based, RT-PCR assays SARS-CoV-2 detection. There was 54.5% concordance in positive results between the rapid antigen assay and RT-PCR. All positive rapid antigen assay results were confirmed by RT-PCR. The negative predictive value of the rapid antigen assay minimally improved on the negative pre-test probability of SARS-CoV-2 infection. The Abbott PanbioTM COVID-19 rapid antigen test allowed for faster identification of infected individuals but cannot be used to rule-out SARS-CoV-2 infection.

Ignatzschineria indica bacteremia in a patient with a maggot-infested heel ulcer: a case report and literature review.

An elderly patient was admitted with sepsis to a community hospital. The individual was found to have a foot wound infested with maggots, and clinical evidence of cellulitis. A blood culture was positive on day 2 with Ignatzschineria indica . The patient was treated successfully with a combination of antibiotics and manual removal of the maggots. Poor living conditions were central to his presentation.

Incidental post-partum isolation of Brucella melitensis in an asymptomatic woman.

A 25-year-old Somali-born female was admitted to the hospital in active labour. Following post-partum hemorrhage, Brucella melitensis grew from a blood culture and the placenta. Identification and relatedness were determined through reverse transcriptase polymerase chain reaction (RT-PCR), single nucleotide polymorphism (SNP), and whole genome sequencing. The patient and her child were completely asymptomatic at their initial assessment.

Une femme d'origine somalienne de 25 ans a été hospitalisée en travail actif. Après une hémorragie postpartum, le Brucella melitensis s'est développé dans une hémoculture et dans le placenta. La réaction de transcriptase inverse et d'amplification en chaîne de la polymérase (RT-PCR), le polymorphisme du nucléotide simple (SNP) et le séquençage du génome entier ont permis d'identifier la bactérie et d'établir sa parenté génétique. La patiente et son enfant étaient complètement asymptomatiques à l'évaluation initiale.

Biofilm formation by virulent and non-virulent strains of Haemophilus parasuis.

Haemophilus parasuis is a commensal bacterium of the upper respiratory tract of healthy pigs. It is also the etiological agent of Glässer's disease, a systemic disease characterized by polyarthritis, fibrinous polyserositis and meningitis, which causes high morbidity and mortality in piglets. The aim of this study was to evaluate biofilm formation by well-characterized virulent and non-virulent strains of H. parasuis. We observed that non-virulent strains isolated from the nasal cavities of healthy pigs formed significantly (p < 0.05) more biofilms than virulent strains isolated from lesions of pigs with Glässer's disease. These differences were observed when biofilms were formed in microtiter plates under static conditions or formed in the presence of shear force in a drip-flow apparatus or a microfluidic system. Confocal laser scanning microscopy using different fluorescent probes on a representative subset of strains indicated that the biofilm matrix contains poly-N-acetylglucosamine, proteins and eDNA. The biofilm matrix was highly sensitive to degradation by proteinase K. Comparison of transcriptional profiles of biofilm and planktonic cells of the non-virulent H. parasuis F9 strain revealed a significant number of up-regulated membrane-related genes in biofilms, and genes previously identified in Actinobacillus pleuropneumoniae biofilms. Our data indicate that non-virulent strains of H. parasuis have the ability to form robust biofilms in contrast to virulent, systemic strains. Biofilm formation might therefore allow the non-virulent strains to colonize and persist in the upper respiratory tract of pigs. Conversely, the planktonic state of the virulent strains might allow them to disseminate within the host.

Actinobacillus pleuropneumoniae genes expression in biofilms cultured under static conditions and in a drip-flow apparatus.

BACKGROUND: Actinobacillus pleuropneumoniae is the Gram-negative bacterium responsible for porcine pleuropneumonia. This respiratory infection is highly contagious and characterized by high morbidity and mortality. The objectives of our study were to study the transcriptome of A. pleuropneumoniae biofilms at different stages and to develop a protocol to grow an A. pleuropneumoniae biofilm in a drip-flow apparatus. This biofilm reactor is a system with an air-liquid interface modeling lung-like environment. Bacteria attached to a surface (biofilm) and free floating bacteria (plankton) were harvested for RNA isolation. Labelled cDNA was hybridized to a microarray to compare the expression profiles of planktonic cells and biofilm cells. RESULTS: It was observed that 47 genes were differentially expressed (22 up, 25 down) in a 4 h-static growing/maturing biofilm and 117 genes were differentially expressed (49 up, 68 down) in a 6h-static dispersing biofilm. The transcriptomes of a 4 h biofilm and a 6 h biofilm were also compared and 456 genes (235 up, 221 down) were identified as differently expressed. Among the genes identified in the 4 h vs 6h biofilm experiment, several regulators of stress response were down-regulated and energy metabolism associated genes were up-regulated. Biofilm bacteria cultured using the drip-flow apparatus differentially expressed 161 genes (68 up, 93 down) compared to the effluent bacteria. Cross-referencing of differentially transcribed genes in the different assays revealed that drip-flow biofilms shared few differentially expressed genes with static biofilms (4 h or 6 h) but shared several differentially expressed genes with natural or experimental infections in pigs. CONCLUSION: The formation of a static biofilm by A. pleuropneumoniae strain S4074 is a rapid process and transcriptional analysis indicated that dispersal observed at 6 h is driven by nutritional stresses. Furthermore, A. pleuropneumoniae can form a biofilm under low-shear force in a drip-flow apparatus and analyses indicated that the formation of a biofilm under low-shear force requires a different sub-set of genes than a biofilm grown under static conditions. The drip-flow apparatus may represent the better in vitro model to investigate biofilm formation of A. pleuropneumoniae.

Transcriptional profiling of Actinobacillus pleuropneumoniae during the acute phase of a natural infection in pigs.

BACKGROUND: Actinobacillus pleuropneumoniae is the etiological agent of porcine pleuropneumonia, a respiratory disease which causes great economic losses worldwide. Many virulence factors are involved in the pathogenesis, namely capsular polysaccharides, RTX toxins, LPS and many iron acquisition systems. In order to identify genes that are expressed in vivo during a natural infection, we undertook transcript profiling experiments with an A. pleuropneumoniae DNA microarray, after recovery of bacterial mRNAs from serotype 5b-infected porcine lungs. AppChip2 contains 2033 PCR amplicons based on the genomic sequence of App serotype 5b strain L20, representing more than 95% of ORFs greater than 160 bp in length. RESULTS: Transcriptional profiling of A. pleuropneumoniae recovered from the lung of a pig suffering from a natural infection or following growth of the bacterial isolate in BHI medium was performed. An RNA extraction protocol combining beadbeating and hot-acid-phenol was developed in order to maximize bacterial mRNA yields and quality following total RNA extraction from lung lesions. Nearly all A. pleuropneumoniae transcripts could be detected on our microarrays, and 150 genes were deemed differentially expressed in vivo during the acute phase of the infection. Our results indicate that, for example, gene apxIVA from an operon coding for RTX toxin ApxIV is highly up-regulated in vivo, and that two genes from the operon coding for type IV fimbriae (APL_0878 and APL_0879) were also up-regulated. These transcriptional profiling data, combined with previous comparative genomic hybridizations performed by our group, revealed that 66 out of the 72 up-regulated genes are conserved amongst all serotypes and that 3 of them code for products that are predicted outer membrane proteins (genes irp and APL_0959, predicted to code for a TonB-dependent receptor and a filamentous hemagglutinin/adhesin respectively) or lipoproteins (gene APL_0920). Only 4 of 72 up-regulated genes had previously been identified in controled experimental infections. CONCLUSIONS: These genes that we have identified as up-regulated in vivo, conserved across serotypes and coding for potential outer membrane proteins represent potential candidates for the development of a cross-protective vaccine against porcine pleuropneumonia.

Effects of growth conditions on biofilm formation by Actinobacillus pleuropneumoniae.

Biofilm formation is an important virulence trait of many bacterial pathogens. It has been reported in the literature that only two of the reference strains of the swine pathogen Actinobacillus pleuropneumoniae, representing serotypes 5b and 11, were able to form biofilm in vitro. In this study, we compared biofilm formation by the serotype 1 reference strain S4074 of A. pleuropneumoniae grown in five different culture media. We observed that strain S4074 of A. pleuropneumoniae is able to form biofilms after growth in one of the culture conditions tested brain heart infusion (BHI medium, supplier B). Confocal laser scanning microscopy using a fluorescent probe specific to the poly-N-acetylglucosamine (PGA) polysaccharide further confirmed biofilm formation. In accordance, biofilm formation was susceptible to dispersin B, a PGA hydrolase. Transcriptional profiles of A. pleuropneumoniae S4074 following growth in BHI-B, which allowed a robust biofilm formation, and in BHI-A, in which only a slight biofilm formation was observed, were compared. Genes such as tadC, tadD, genes with homology to autotransporter adhesins as well as genes pgaABC involved in PGA biosynthesis and genes involved in zinc transport were up-regulated after growth in BHI-B. Interestingly, biofilm formation was inhibited by zinc, which was found to be more present in BHI-A (no or slight biofilm) than in BHI-B. We also observed biofilm formation in reference strains representing serotypes 3, 4, 5a, 12 and 14 as well as in 20 of the 37 fresh field isolates tested. Our data indicate that A. pleuropneumoniae has the ability to form biofilms under appropriate growth conditions and transition from a biofilm-positive to a biofilm-negative phenotype was reversible.

malT knockout mutation invokes a stringent type gene-expression profile in Actinobacillus pleuropneumoniae in bronchoalveolar fluid.

BACKGROUND: Actinobacillus pleuropneumoniae causes contagious pleuropneumonia, an economically important disease of commercially reared pigs throughout the world. To cause this disease, A. pleuropneumoniae must rapidly overcome porcine pulmonary innate immune defenses. Since bronchoalveolar fluid (BALF) contains many of the innate immune and other components found in the lungs, we examined the gene expression of a virulent serovar 1 strain of A. pleuropneumoniae after exposure to concentrated BALF for 30 min. RESULTS: In reverse transcription PCR differential display (RT-PCR DD) experiments, A. pleuropneumoniae CM5 exposed to BALF up-regulated, among other genes, a gene predicted to encode LamB, an outer-membrane transport protein of the maltose regulon. To determine the role of the lamB and other genes of the maltose regulon in the pathogenesis of A. pleuropneumoniae, knockout mutations were created in the lamB and malT genes, the latter being the positive transcriptional regulator of the maltose regulon. Relative to the lamB mutant and the wild type, the malT mutant had a significant (P < 0.05) decrease in growth rate and an increased sensitivity to fresh porcine serum and high concentrations (more than 0.5 M) of sodium chloride. In DNA microarray experiments, the BALF-exposed malT mutant exhibited a gene-expression profile resembling that of a stringent type gene-expression profile seen in bacteria facing amino acid or carbon starvation. Genes encoding proteins for protein synthesis, energy metabolism, and DNA replication were down-regulated, while genes involved in stringent response (e.g., relA), amino acid and nucleotide biosynthesis, biofilm formation, DNA transformation, and stress response were up-regulated. CONCLUSION: These results suggest that MalT may be involved in protection against some stressors and in the transport of one or more essential nutrients in BALF. Moreover, if MalT is directly or indirectly linked to the stringent response, an important global mechanism of bacterial persistence and virulence in many bacterial pathogens, it might play a role in A. pleuropneumoniae pathogenesis.

Modulation of gene expression in Actinobacillus pleuropneumoniae exposed to bronchoalveolar fluid.

BACKGROUND: Actinobacillus pleuropneumoniae, the causative agent of porcine contagious pleuropneumonia, is an important pathogen of swine throughout the world. It must rapidly overcome the innate pulmonary immune defenses of the pig to cause disease. To better understand this process, the objective of this study was to identify genes that are differentially expressed in a medium that mimics the lung environment early in the infection process. METHODS AND PRINCIPAL FINDINGS: Since bronchoalveolar lavage fluid (BALF) contains innate immune and other components found in the lungs, we examined gene expression of a virulent serovar 1 strain of A. pleuropneumoniae after a 30 min exposure to BALF, using DNA microarrays and real-time PCR. The functional classes of genes found to be up-regulated most often in BALF were those encoding proteins involved in energy metabolism, especially anaerobic metabolism, and in cell envelope, DNA, and protein biosynthesis. Transcription of a number of known virulence genes including apxIVA and the gene for SapF, a protein which is involved in resistance to antimicrobial peptides, was also up-regulated in BALF. Seventy-nine percent of the genes that were up-regulated in BALF encoded a known protein product, and of these, 44% had been reported to be either expressed in vivo and/or involved in virulence. CONCLUSIONS: The results of this study suggest that in early stages of infection, A. pleuropneumoniae may modulate expression of genes involved in anaerobic energy generation and in the synthesis of proteins involved in cell wall biogenesis, as well as established virulence factors. Given that many of these genes are thought to be expressed in vivo or involved in virulence, incubation in BALF appears, at least partially, to simulate in vivo conditions and may provide a useful medium for the discovery of novel vaccine or therapeutic targets.

Microarray-based comparative genomic profiling of reference strains and selected Canadian field isolates of Actinobacillus pleuropneumoniae.

BACKGROUND: Actinobacillus pleuropneumoniae, the causative agent of porcine pleuropneumonia, is a highly contagious respiratory pathogen that causes severe losses to the swine industry worldwide. Current commercially-available vaccines are of limited value because they do not induce cross-serovar immunity and do not prevent development of the carrier state. Microarray-based comparative genomic hybridizations (M-CGH) were used to estimate whole genomic diversity of representative Actinobacillus pleuropneumoniae strains. Our goal was to identify conserved genes, especially those predicted to encode outer membrane proteins and lipoproteins because of their potential for the development of more effective vaccines. RESULTS: Using hierarchical clustering, our M-CGH results showed that the majority of the genes in the genome of the serovar 5 A. pleuropneumoniae L20 strain were conserved in the reference strains of all 15 serovars and in representative field isolates. Fifty-eight conserved genes predicted to encode for outer membrane proteins or lipoproteins were identified. As well, there were several clusters of diverged or absent genes including those associated with capsule biosynthesis, toxin production as well as genes typically associated with mobile elements. CONCLUSION: Although A. pleuropneumoniae strains are essentially clonal, M-CGH analysis of the reference strains of the fifteen serovars and representative field isolates revealed several classes of genes that were divergent or absent. Not surprisingly, these included genes associated with capsule biosynthesis as the capsule is associated with sero-specificity. Several of the conserved genes were identified as candidates for vaccine development, and we conclude that M-CGH is a valuable tool for reverse vaccinology.