Histologic and bacteriologic findings in valvular endocarditis of slaughter-age pigs

Bacterial and host factors involved in zoonotic Streptococcal meningitis

Zoonotic streptococci cause several invasive diseases with high mortality rates, especially meningitis. Numerous studies elucidated the meningitis pathogenesis of zoonotic streptococci, some specific to certain bacterial species. In contrast, others are shared among different bacterial species, involving colonization and invasion of mucosal barriers, survival in the bloodstream, breaching the blood-brain and/or blood-cerebrospinal fluid barrier to access the central nervous system, and triggering inflammation of the meninges. This review focuses on the recent advancements in comprehending the molecular and cellular events of five major zoonotic streptococci responsible for causing meningitis in humans or animals, including Streptococcus agalactiae, Streptococcus equi subspecies zooepidemicus, Streptococcus suis, Streptococcus dysgalactiae, and Streptococcus iniae. The underlying mechanism was summarized into four themes, including 1) bacterial survival in blood, 2) brain microvascular endothelial cell adhesion and invasion, 3) penetration of the blood-brain barrier, and 4) activation of the immune system and inflammatory reaction within the brain. This review may contribute to developing therapeutics to prevent or mitigate injury of streptococcal meningitis and improve risk stratification.

Pathomolecular epidemiology, antimicrobial resistance, and virulence genes of Streptococcus dysgalactiae subsp. equisimilis isolates from slaughtered pigs in India

AIMS

We aimed to investigate the prevalence, pathology, and characterization of Streptococcus dysgalactiae subsp. equisimilis (SDSE) in slaughtered pigs of India.

METHODS AND RESULTS

We collected 1254 morbid tissues (lungs-627 and spleen-627) and 627 heart-blood from 627 slaughtered pigs. The bacterial isolation, antibiogram, virulence gene profiling, and mouse pathogenicity testing were performed for the detection and characterization of SDSE. A total of 177 isolates (heart-blood-160 and tissues-17) were recovered from 627 slaughtered pigs with higher isolation rate in heart-blood (25.51%). The prevalence of SDSE was 11% in morbid tissues by polymerase chain reaction. Majority of isolates showed higher detection of streptolysin O, followed by streptokinase and extracellular phospholipase A virulence genes with higher degree of resistance to azithromycin, clindamycin, erythromycin, and penicillin antibiotics. Mouse pathogenicity testing confirmed virulence based on histopathological lesions and re-isolation of SDSE.

CONCLUSIONS

Our findings highlight the high prevalence of SDSE in slaughtered pigs. The presence of virulence genes and mouse pathogenicity testing confirm their pathogenic potential.

Understanding Bartonella-Associated Infective Endocarditis: Examining Heart Valve and Vegetation Appearance and the Role of Neutrophilic Leukocytes

BACKGROUND

The endocardium and cardiac valves undergo severe impact during infective endocarditis (IE), and the formation of vegetation places IE patients at a heightened risk of embolic complications and mortality. The relevant literature indicates that 50% of IE cases exhibit structurally normal cardiac valves, with no preceding history of heart valve disease. Gram-positive cocci emerge as the predominant causative microorganisms in IE, while Gram-negative Bartonella spp., persisting in the endothelium, follow pathogenic pathways distinct from those of typical IE-causing agents. Employing clinical as well as advanced microbiological and molecular assays facilitated the identification of causative pathogens, and various morphological methods were applied to evaluate heart valve damage, shedding light on the role of neutrophilic leukocytes in host defense. In this research, the immunohistochemical analysis of neutrophilic leukocyte activation markers such as myeloperoxidase, neutrophil elastase, calprotectin, and histone H3, was performed. A distinct difference in the expression patterns of these markers was observed when comparing Bartonella spp.-caused and non-Bartonella spp.-caused IE. The markers exhibited significantly higher expression in non-Bartonella spp.-caused IE compared to Bartonella spp.-caused IE, and they were more prevalent in vegetation than in the valvular leaflets. Notably, the expression of these markers in all IE cases significantly differed from that in control samples. Furthermore, we advocated the use of 16S rRNA Next-Generation Sequencing on excised heart valves as an effective diagnostic tool for IE, particularly in cases where blood cultures yielded negative results. The compelling results achieved in this study regarding the enigmatic nature of Bartonella spp. IE's pathophysiology contribute significantly to our understanding of the peculiarities of inflammation and immune responses.

Systemic Streptococcus agalactiae infection with meningo-ventriculitis in a Linnaeus's two-toed sloth (Choloepus didactylus)

A captive male Linnaeus's two-toed sloth died without any obvious clinical signs. At necropsy, multifocal ulceration at the lumbar and perianal skin, mitral valve vegetation, and multifocal hemorrhage in the leptomeninges were observed. Histopathologically, suppurative meningo-ventriculitis, dermatitis, and endocarditis characterized by severe neutrophilic infiltration were observed. Gram-positive cocci arranged in pairs or chains were present in these inflammatory lesions. Streptococcus agalactiae gene was detected in the skin, heart, and brain tissues by PCR and sequence analysis. These findings may indicate that S. agalactiae primarily infected the skin and then caused septicemia resulting in endocarditis and meningo-ventriculitis. The present case suggests that S. agalactiae infection can cause severe meningo-ventriculitis in two-toed sloth without any specific clinical signs.

Dos and don'ts in large animal models of aortic insufficiency

Aortic insufficiency caused by paravalvular leakage (PVL) is one of the most feared complications following transcatheter aortic valve replacement (TAVI) in patients. Domestic pigs (Sus scrofa domestica) are a popular large animal model to study such conditions and develop novel diagnostic and therapeutic techniques. However, the models based on prosthetic valve implantation are time intensive, costly, and often hamper further hemodynamic measurements such as PV loop and 4D MRI flow by causing implantation-related wall motion abnormalities and degradation of MR image quality. This study describes in detail, the establishment of a minimally invasive porcine model suitable to study the effects of mild-to-moderate “paravalvular“ aortic regurgitation on left ventricular (LV) performance and blood flow patterns, particularly under the influence of altered afterload, preload, inotropic state, and heart rate. Six domestic pigs (Swiss large white, female, 60–70 kg of body weight) were used to establish this model. The defects on the hinge point of aortic leaflets and annulus were created percutaneously by the pierce-and-dilate technique either in the right coronary cusp (RCC) or in the non-coronary cusp (NCC). The hemodynamic changes as well as LV performance were recorded by PV loop measurements, while blood flow patterns were assessed by 4D MRI. LV performance was additionally challenged by pharmaceutically altering cardiac inotropy, chronotropy, and afterload. The presented work aims to elaborate the dos and don'ts in porcine models of aortic insufficiency and intends to steepen the learning curve for researchers planning to use this or similar models by giving valuable insights ranging from animal selection to vascular access choices, placement of PV Loop catheter, improvement of PV loop data acquisition and post-processing and finally the induction of paravalvular regurgitation of the aortic valve by a standardized and reproducible balloon induced defect in a precisely targeted region of the aortic valve.

Residual Bioprosthetic Valve Immunogenicity: Forgotten, Not Lost

Despite early realization of the need to control inherent immunogenicity of bioprosthetic replacement heart valves and thereby mitigate the ensuing host response and its associated pathology, including dystrophic calcification, the problem remains unresolved to this day. Concerns over mechanical stiffness associated with prerequisite high cross-link density to effect abrogation of this response, together with the insinuated role of leaching glutaraldehyde monomer in subsequent dystrophic mineralization, have understandably introduced compromises. These have become so entrenched as a benchmark standard that residual immunogenicity of the extracellular matrix has seemingly been relegated to a very subordinate role. Instead, focus has shifted toward the removal of cellular compartment antigens renowned for their implication in the failure of vascularized organ xenotransplants. While decellularization certainly offers advantages, this review aims to refocus attention on the unresolved matter of the host response to the extracellular matrix. Furthermore, by implicating remnant immune and inflammatory processes to bioprosthetic valve pathology, including pannus overgrowth and mineralization, the validity of a preeminent focus on decellularization, in the context of inefficient antigen and possible residual microbial remnant removal, is questioned.

Streptococcus gallolyticus and Bacterial Endocarditis in Swine, United States, 2015-2020

To evaluate trends in bacterial causes of valvular endocarditis in swine, we retrospectively analyzed 321 cases diagnosed at Iowa State University Veterinary Diagnostic Laboratory (Ames, IA, USA) during May 2015--April 2020. Streptococcus gallolyticus was the causative agent for 7.59% of cases. This emerging infection in swine could aid study of endocarditis in humans.

The preliminary evaluation of differential characteristics and factor evaluation of the microbial structure of rural household toilet excrement in China

Recent studies on the microbial community composition of human excrement after rural household toilet treatment are unclear regarding the effects and risks of using recycled products as fertilizers in agriculture. In this study, we used Illumina high-throughput sequencing to investigate the microbial community structure of the excrement from 50 Chinese rural household toilets on a spatial scale, and we evaluated the impact of select geochemical factors on the bacterial and fungal communities in the human excrement. Multivariate analysis showed that there was a significant spatial differentiation of the human excrement in microbial communities after all toilet treatments. Twenty dry toilet samples and thirty septic tank samples had similar bacterial (Firmicutes, Proteobacteria, Actinobacteria, and Bacteroidetes) and fungal phyla (Ascomycota and Basidiomycota), differing only in the proportions of the microorganisms. For both dry toilet samples and septic tank samples, the pH and ammonium nitrogen were found to be the major driving forces affecting the changes in bacterial community structures (p<0.05), while there was no correlation found for the fungal community with environmental factors in China (p>0.05), except in the northern regions, where the total phosphorus was found to be significantly correlated with the fungal community (p<0.05). Network analysis confirmed that NH4+-N had the most significant impact on the content of pathogens. Certain pathogens were still detected after toilet treatment, such as Streptococcus, Bacteroides, Aspergillus, and Chrysosporium, and the proportion of potential pathogenic bacteria in dry toilets was higher than that in septic tanks, suggesting that septic tanks were better than dry toilets in treating human excrement. These results provide an ecological perspective for understanding the large-scale geographic distribution of household excrement microbial communities in rural areas and for improving human excrement treatment technologies and avoiding the risks of agricultural applications.

Association of Novel Streptococcus sanguinis Virulence Factors With Pathogenesis in a Native Valve Infective Endocarditis Model

Streptococcus sanguinis (S. sanguinis) is an abundant oral commensal which can cause disseminated human infection if it gains access to the bloodstream. The most important among these diseases is infective endocarditis (IE). While virulence phenotypes of S. sanguinis have been correlated to disease severity, genetic factors mediating these phenotypes, and contributing to pathogenesis are largely uncharacterized. In this report, we investigate the roles of 128 genes in virulence-related phenotypes of S. sanguinis and characterize the pathogenic potential of two selected mutants in a left-sided, native valve IE rabbit model. Assays determining the ability of our mutant strains to produce a biofilm, bind to and aggregate platelets, and adhere to or invade endothelial cells identified sixteen genes with novel association to these phenotypes. These results suggest the presence of many uncharacterized genes involved in IE pathogenesis which may be relevant for disease progression. Two mutants identified by the above screening process – SSA_1099, encoding an RTX-like protein, and mur2, encoding a peptidoglycan hydrolase – were subsequently evaluated in vivo. Wild type (WT) S. sanguinis reliably induced cardiac vegetations, while the SSA_1099 and mur2 mutants produced either no vegetation or vegetations of small size. Splenomegaly was reduced in both mutant strains compared to WT, while pathology of other distal organs was indistinguishable. Histopathology analyses suggest the cardiac lesions and vegetations in this model resemble those observed in humans. These data indicate that SSA_1099 and mur2 encode virulence factors in S. sanguinis which are integral to pathogenesis of IE.

Porcine Models of Biofilm Infections with Focus on Pathomorphology

Bacterial biofilm formation is one of the main reasons for a negative treatment outcome and a high recurrence rate for many chronic infections in humans. The optimal way to study both the biofilm forming bacteria and the host response simultaneously is by using discriminative, reliable, and reproducible animal models of the infections. In this review, the advantages of in vivo studies are compared to in vitro studies of biofilm formation in infectious diseases. The pig is the animal of choice when developing and applying large animal models of infectious diseases due to its similarity of anatomy, physiology, and immune system to humans. Furthermore, conventional pigs spontaneously develop many of the same chronic bacterial infections as seen in humans. Therefore, in this review porcine models of five different infectious diseases all associated with biofilm formation and chronicity in humans are described. The infectious diseases are: chronic wounds, endocarditis, pyelonephritis, hematogenous osteomyelitis, and implant-associated osteomyelitis (IAO).

Streptococcus suis serotype 9 endocarditis and subsequent severe meningitis in a growing pig despite specific bactericidal humoral immunity

INTRODUCTION

. Meningitis and endocarditis are common pathologies of Streptococcussuis infections in pigs and humans. S. suis serotype 9 strains contribute substantially to health problems in European pig production, and immune prophylaxis against this serotype is very difficult.

CASE PRESENTATION

. We report the clinical course and histopathological picture of a 10-week-old growing pig following experimental intravenous infection with S. suis serotype 9. The piglet showed rapid onset of severe clinical signs of meningitis 11 days post-intravenous challenge following prime-booster vaccination. Histopathological findings revealed a diffuse fibrinosuppurative leptomeningitis. Additionally, a polyphasic endocarditis valvularis thromboticans with numerous bacterial colonies was diagnosed. Bacteriological culture of the brain and the mitral valve confirmed association with the challenge strain. However, virulent serotype 2 and 9 strains were killed in the blood of this piglet ex vivo prior experimental infection.

CONCLUSION

. Endocarditis induced by S. suis infection might develop and persist despite the presence of high specific bactericidal activity in the blood. Severe leptomeningitis is a putative sequela of such an endocarditis.

Auxotrophic Actinobacillus pleurpneumoniae grows in multispecies biofilms without the need for nicotinamide-adenine dinucleotide (NAD) supplementation

Background

Actinobacillus pleuropneumoniae is the etiologic agent of porcine contagious pleuropneumonia, which causes important worldwide economic losses in the swine industry. Several respiratory tract infections are associated with biofilm formation, and A. pleuropneumoniae has the ability to form biofilms in vitro. Biofilms are structured communities of bacterial cells enclosed in a self-produced polymer matrix that are attached to an abiotic or biotic surface. Virtually all bacteria can grow as a biofilm, and multi-species biofilms are the most common form of microbial growth in nature. The goal of this study was to determine the ability of A. pleuropneumoniae to form multi-species biofilms with other bacteria frequently founded in pig farms, in the absence of pyridine compounds (nicotinamide mononucleotide [NMN], nicotinamide riboside [NR] or nicotinamide adenine dinucleotide [NAD]) that are essential for the growth of A. pleuropneumoniae.

Results

For the biofilm assay, strain 719, a field isolate of A. pleuropneumoniae serovar 1, was mixed with swine isolates of Streptococcus suis, Bordetella bronchiseptica, Pasteurella multocida, Staphylococcus aureus or Escherichia coli, and deposited in 96-well microtiter plates. Based on the CFU results, A. pleuropneumoniae was able to grow with every species tested in the absence of pyridine compounds in the culture media. Interestingly, A. pleuropneumoniae was also able to form strong biofilms when mixed with S. suis, B. bronchiseptica or S. aureus. In the presence of E. coli, A. pleuropneumoniae only formed a weak biofilm. The live and dead populations, and the matrix composition of multi-species biofilms were also characterized using fluorescent markers and enzyme treatments. The results indicated that poly-N-acetyl-glucosamine remains the primary component responsible for the biofilm structure.

Conclusions

In conclusion, A. pleuropneumoniae apparently is able to satisfy the requirement of pyridine compounds through of other swine pathogens by cross-feeding, which enables A. pleuropneumoniae to grow and form multi-species biofilms.

Electronic supplementary material

The online version of this article (doi:10.1186/s12866-016-0742-3) contains supplementary material, which is available to authorized users.

Systemic Streptococcus dysgalactiae subspecies equisimilis infection in a Yorkshire pig with severe disseminated suppurative meningoencephalomyelitis

An 18-week-old female breeding Yorkshire pig displayed symptoms of astasia and subsequently died. Histologically, severe disseminated suppurative meningoencephalomyelitis was detected, as were numerous myocardial microabscesses. Gram-positive cocci were detected in these suppurative lesions, and these cocci reacted with an antibody against Streptococcus C group species. Gram-positive cocci were isolated from the liver, spleen, kidney, heart, lungs, pleural abscess and articular fluid of the right tarsal joint. The isolates were β-hemolytic, categorized into Lancefield group C and were identified as Streptococcus dysgalactiae subspecies equisimilis by analysis of the 16S ribosomal DNA sequence. This is the first report of systemic S. equisimilis infection in a pig with severe disseminated suppurative meningoencephalomyelitis.

Antimicrobial resistance and prudent drug use forStreptococcus suis

This paper reviews information on antimicrobial resistance patterns and prudent use of antimicrobials to reduce the impact and spread of resistantStreptococcus suisstrains.S. suisis an important pathogen in swine, which can cause significant economic loss. Prudent use of antimicrobials forS. suisis essential to preserve the therapeutic efficacy of broad-spectrum antimicrobials and to minimize selection of resistantS. suisstrains. Resistance ofS. suisto antimicrobials commonly used in swine, including lincosamides, macrolides, sulphonamides, and tetracycline, has been documented worldwide, with resistance in up to 85% of strains. Among antimicrobials examined, resistance ofS. suishas been demonstrated to be relatively low for penicillin (0–27%), ampicillin (0.6–23%), and ceftiofur (0–23%). For penicillin, this result may be due in part to the unique mechanism by which resistance is acquired through modifications in the structure of penicillin-binding proteins. Recommendations to controlS. suisinfection include focused and careful choice and appropriate use of antimicrobials, together with preventive measures intended to improve swine management.

Identification of pathogens in mastitis milk samples with fluorescent in situ hybridization

Traditionally, the bacteriological examination of mastitis milk samples is performed by culture followed by biochemical tests on the cultured bacteria to allow identification of the causative pathogen. Depending on the species involved, this classic identification is time-consuming compared to other techniques such as fluorescent in situ hybridization (FISH), a culture-independent method that utilizes oligonucleotides (labeled with a fluorophore) that are specific to a string of target DNA/RNA. In the current study, the applicability of FISH was evaluated for the detection of mastitis pathogens directly in milk samples. To remove interfering lipids and proteins from mastitis milk samples prior to FISH, a previously published enzymatic treatment with savinase was evaluated. FISH was performed using oligonucleotides specific for Staphylococcus aureus, Streptococcus agalactiae, Streptococcus uberis, Enterococcus faecalis, Enterococcus faecium, Escherichia coli, and Trueperella (Arcanobacterium) pyogenes. The enzymatic pretreatment and the sensitivity of FISH were evaluated using spiked whole milk samples and mastitis milk samples with bacterial loads of less than 10(3) up to 10(8) colony-forming units (CFU)/ml. Bacteria were reliably detected in milk samples with bacterial numbers of 10(6) CFU/ml or higher. However, bacteria present in numbers below 10(6) CFU/ml were not detectable in all cases. The ability of FISH to identify mastitis-causing pathogens directly in milk samples, and therefore earlier than classical culture methods, can supplement the classic diagnostic procedures for mastitis milk samples.

Endocarditis-associated brain lesions in slaughter pigs

Left-sided valvular endocarditis (LSVE) is a common finding in slaughter pigs. The lesion is often associated with renal thromboembolism, but information on embolization to other organs is sparse. This study focuses on the presence and type of endocarditis-associated brain lesions (EABLs). The brains of 20 slaughter pigs with spontaneously arising LSVE and 11 controls were examined by sectioning half of a formalin-fixed brain into 4mm slices for histological examination. The aetiology of the endocarditis was determined by bacteriological and, in some cases, by fluorescence in-situ hybridization examinations. These examinations identified 11 cases of Streptococcus suis, six cases of Erysipelothrix rhusiopathiae, one Streptococcus spp. and two cases that remained aetiologically undetermined. One of the S. suis cases had a dual infection with S. suis in the aortic valve lesions and Streptococcus dysgalactiae subsp. equisimilis in the atrioventricular valve lesions. Renal infarcts were present in eight cases. Focal encephalitis was found in 12 cases, with the number of lesions ranging from one to 11. Most pigs had less than four microscopical lesions. Acute lesions were characterized by focal microabscesses without observable bacteria. Chronic lesions were characterized by astrocytosis and focal accumulation of mononuclear leucocytes. An infarct was observed in one animal. Perivascular inflammation was seen in 14 cases, mostly as two or three lesions, while focal leptomeningitis was found in eight cases. EABLs are therefore common in slaughter pigs with LSVE. The number of lesions per animal is small, which may explain the limited attention paid to this sequela of LSVE. EABLs have rarely been reported in domestic animals and mostly in patients with neurological signs. The frequent occurrence of EABLs in slaughter pigs suggests that this pathology should be investigated in other animal species with LSVE.