Evidence for a LOS and a capsular polysaccharide in Capnocytophaga canimorsus

Capsular polysaccharide determines the serotyping of Riemerella anatipestifer

IMPORTANCE

Riemerella anatipestifer (R. anatipestifer) is one of the most important veterinary pathogens with at least 21 serotypes. However, the exact polysaccharide(s) that determine R. anatipestifer serotype is still unknown. This study has provided a preliminary exploration of the relationship between capsular polysaccharides and serotyping in R. anatipestifer and suggests possible directions for further investigation of the genetic basis of serotypes in this bacterium.

Capnocytophaga canimorsus Infection in a 38-Year-Old Male after a Dog Bite

Here, we present a unique case of a 38-year-old male with a history of alcohol use disorder and multiple sexual partners, who presented with fulminant sepsis with shock, multiorgan failure, and livedo racemosa after a dog bite the week prior. The patient was intubated on arrival and was started on vasopressors and antibiotics. Eventually, the patient's clinical status improved, and he was transferred out of the intensive care unit. Blood cultures tested positive for oxidase-positive Gram-negative rods two days after collection, and species identification showed Capnocytophaga canimorsus.

Culture-negative Capnocytophaga canimorsus meningitis diagnosed by 16s ribosomal RNA polymerase chain reaction in an immunocompetent veterinarian and a review of the literature

Capnocytophaga canimorsus is a fastidious, capnophilic and facultative anaerobic Gram-negative rod found commonly in the oral flora of dogs that may cause zoonotic infections such as cellulitis and eye infections. In immunocompromised patients, it may cause fulminant sepsis. Meningitis due to C. canimorsus is, however, a rare manifestation. This is the first reported case of C. canimorsus meningitis in Australia in an immunocompetent veterinarian diagnosed by 16s ribosomal RNA polymerase chain reaction.

Lethal Waterhouse-Friderichsen syndrome caused by Capnocytophaga canimorsus in an asplenic patient

Background

Capnocytophaga canimorsus, a Gram-negative rod, belongs to the Flavobacteriaceae family and colonizes the oropharynx of dogs and cats. Infections with C. canimorsus are rare and can induce a systemic infection with a severe course of the disease. So far, only five case reports of C. canimorsus infections associated with Waterhouse–Friderichsen Syndrome (WFS) have been reported with only two of the patients having a history of splenectomy.

Case presentation

Here, we report a fatal case of WFS due to C. canimorsus bacteremia and mycetal superinfection in a 61-year-old female asplenic patient. Despite extensive therapy including mechanical ventilation, antibiotic coverage with meropenem, systemic corticosteroids medication, vasopressor therapy, continuous renal replacement therapy, therapeutic plasma exchange, multiple transfusions of blood products and implantation of a veno-arterial extracorporeal membrane oxygenation the patient died 10 days after a dog bite. The autopsy showed bilateral hemorrhagic necrosis of the adrenal cortex and septic embolism to heart, kidneys, and liver. Diagnosis of C. canimorsus was prolonged due to the fastidious growth of the bacteria.

Conclusions

The occurrence of a severe sepsis after dog bite should always urge the attending physician to consider C. canimorsus as the disease-causing pathogen. A therapeutic regimen covering C. canimorsus such as aminopenicillins or carbapenems should be chosen. However, despite maximum therapy, the prognosis of C. canimorsus-induced septic shock remains very poor. Asplenic or otherwise immunocompromised patients are at higher risk for a severe course of disease and should avoid exposure to dogs and cats and consider antibiotic prophylaxis after animal bite.

A case of septic arthritis caused by Capnocytophaga canimorsus in an HIV patient

Invasive infections caused by Capnocytophaga canimorsus, a Gram-negative rod found in the oral cavity of healthy dogs and cats, are rare but they are increasing worldwide. We report a case of septic arthritis in a native knee joint due to this micro-organism. A 57-year-old man, with a well-controlled chronic HIV infection, attended the Emergency Department because of left knee pain and shivering without measured fever. A knee arthrocentesis and a computed tomography scan were performed, revealing septic arthritis with collections in the left leg posterior musculature. He was admitted to the Infectious Diseases Department for antibiotic treatment. Initial synovial fluid was inoculated in blood culture bottles, and the anaerobic one was positive after 63 h. Gram stain revealed fusiform Gram-negative rods, identified as C. canimorsus by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF) directly from the bottle. Identification was confirmed by 16S rRNA sequencing and serotyping was performed by PCR, with serovar A as the outcome. Due to an unfavourable clinical course, the patient required two surgical cleanings and after appropriate antibiotic treatment he was discharged 2 months later.

Cellulitis and transient bacteremia by Capnocytophaga canis after a cat scratch in an immunocompetent patient

Capnocytophaga canis is still a rare cause of infection. We present a case of an immunocompetent patient admited in the hospital with functional impotence, pain and erythema in his left leg after suffering two scratches from his cat 48 h ago. After obtaining blood and wound cultures, broad-spectrum antimicrobial therapy with intravenous amoxicillin clavulanate was initiated. After 1 day and with a clear improvement of the symptoms the patient was discharged from the hospital with cellulitis and transient bacteremia as diagnosis and completing 1 week of antimicrobial therapy orally. After 80 and 92 h of incubation, both anaerobic flasks were positive. In the Gram-stain Gram-negative rod-shaped bacteria could be observed. Despite subculturing in brucella blood agar, tripticase soy agar with 5 % of sheep blood and chocolate agar, in both anaerobic and microaerophilic conditions, the strain could not be recovered. However, these Gram-negative rods could be identified as C. canis by 16S rRNA sequencing, Capsular typing was performed to study the strain, but none of the studied capsule-types tested positive. C. canis is still a rare cause of human infection, but it must be considered in the differential diagnosis of infections related to bites, scratches and licks from dogs or cats.

Complete Lipopolysaccharide of Piscirickettsia salmonis Is Required for Full Virulence in the Intraperitoneally Challenged Atlantic Salmon, Salmo salar, Model

Bacterial cell envelopes play a critical role in host-pathogen interactions. Macromolecular components of these structures have been closely linked to the virulence of pathogens. Piscirickettsia salmonis is a relevant salmonid pathogen with a worldwide distribution. This bacterium is the etiological agent of piscirickettsiosis, a septicemic disease that causes a high economic burden, especially for the Chilean salmon farming industry. Although P. salmonis has been discovered long ago, its pathogenicity and virulence mechanisms are not completely understood. In this work, we present a genetic approach for producing in-frame deletion mutants on genes related to the biosynthesis of membrane-associated polysaccharides. We provide a detailed in vitro phenotype description of knock-out mutants on wzx and wcaJ genes, which encode predicted lipopolysaccharide (LPS) flippase and undecaprenyl-phosphate glucose phosphotransferase enzymes, respectively. We exhibit evidence that the wzx mutant strain carries a defect in the probably most external LPS moiety, while the wcaJ mutant proved to be highly susceptible to the bactericidal action of serum but retained the ability of biofilm production. Beyond that, we demonstrate that the deletion of wzx, but not wcaJ, impairs the virulence of P. salmonis in an intraperitoneally infected Atlantic salmon, Salmo salar, model of piscirickettsiosis. Our findings support a role for LPS in the virulence of P. salmonis during the onset of piscirickettsiosis.

Integrative Genomics Sheds Light on Evolutionary Forces Shaping the Acidithiobacillia Class Acidophilic Lifestyle

Extreme acidophiles thrive in environments rich in protons (pH values <3) and often high levels of dissolved heavy metals. They are distributed across the three domains of the Tree of Life including members of the Proteobacteria. The Acidithiobacillia class is formed by the neutrophilic genus Thermithiobacillus along with the extremely acidophilic genera Fervidacidithiobacillus, Igneacidithiobacillus, Ambacidithiobacillus, and Acidithiobacillus. Phylogenomic reconstruction revealed a division in the Acidithiobacillia class correlating with the different pH optima that suggested that the acidophilic genera evolved from an ancestral neutrophile within the Acidithiobacillia. Genes and mechanisms denominated as "first line of defense" were key to explaining the Acidithiobacillia acidophilic lifestyle including preventing proton influx that allows the cell to maintain a near-neutral cytoplasmic pH and differ from the neutrophilic Acidithiobacillia ancestors that lacked these systems. Additional differences between the neutrophilic and acidophilic Acidithiobacillia included the higher number of gene copies in the acidophilic genera coding for "second line of defense" systems that neutralize and/or expel protons from cell. Gain of genes such as hopanoid biosynthesis involved in membrane stabilization at low pH and the functional redundancy for generating an internal positive membrane potential revealed the transition from neutrophilic properties to a new acidophilic lifestyle by shaping the Acidithiobacillaceae genomic structure. The presence of a pool of accessory genes with functional redundancy provides the opportunity to "hedge bet" in rapidly changing acidic environments. Although a core of mechanisms for acid resistance was inherited vertically from an inferred neutrophilic ancestor, the majority of mechanisms, especially those potentially involved in resistance to extremely low pH, were obtained from other extreme acidophiles by horizontal gene transfer (HGT) events.

The use of eculizumab in Capnocytophaga canimorsus associated thrombotic microangiopathy: a case report

BACKGROUND

The use of complement inhibition is well established for complement mediated thrombotic microangiopathy, but its role in secondary forms of thrombotic microangiopathy is debated. We here present a case of thrombotic microangiopathy triggered by Capnocytophaga canimorsus, illustrating the diagnostic difficulties in discriminating between different thrombotic microangiopathies, and the dilemmas regarding how to treat this disease entity.

CASE PRESENTATION

A previously healthy 56-year-old woman presented with fever and confusion. She was diagnosed with sepsis from Capnocytophaga canimorsus and thrombotic microangiopathy. Marked activation of both T-cells, endothelium and complement were documented. She was successfully treated with antimicrobial therapy, the complement inhibitor eculizumab and splenectomy. After several weeks, a heterozygote variant in complement factor B was localized, potentially implying the diagnosis of a complement mediated TMA over an isolated infection related TMA.

CONCLUSIONS

We discuss the possible interactions between complement activation and other findings in severe infection and argue that complement inhibition proved beneficial to this patient's rapid recovery.

Structure of the capsule and lipopolysaccharide O-antigen from the channel catfish pathogen, Aeromonas hydrophila

A hypervirulent A. hydrophila (vAh) pathotype has been identified as the etiologic agent responsible for disease outbreaks in farmed carp species and channel catfish (Ictalurus punctatus) in China and the Southeastern United States, respectively. The possible route of infection has previously been unknown; however, virulence is believed to be multifactorial, involving the production/secretion of several virulence factors, including a high molecular weight group 4 capsular polysaccharide. Here we present chemical structural evidence of a novel capsule- and LPS-associated O-antigen found present in vAh isolated during these disease outbreaks. In this study, the chemical structure of the vAh O-antigen was determined by chemical analysis, Smith degradation, mass spectrometry, and 2D proton and carbon nuclear magnetic resonance (NMR) spectroscopy and found to be unique among described bacterial O-antigens. The O-antigen consists of hexasaccharide repeating units featuring a 4)-α-l-Fucp-(1-3)-β-d-GlcpNAc-(1-4)-α-l-Fucp-(1-4)-β-d-Glcp-(1- backbone, substituted with single residue side chains of α-d-Glcp and α-d-Quip3NAc linked to O-3 of the two fucose residues. The polysaccharide is partially O-acetylated on O-6 of the 4-substituted β-Glcp residue.

Capnocytophaga canimorsus Capsular Serovar and Disease Severity, Helsinki Hospital District, Finland, 2000-2017

We assembled a collection of 73 Capnocytophaga canimorsus isolates obtained from blood cultures taken from patients treated at Helsinki University Hospital (Helsinki, Finland) during 2000–2017. We serotyped these isolates by PCR and Western blot and attempted to correlate pathogen serovar with patient characteristics. Our analyses showed, in agreement with previous research, that 3 C. canimorsus serovars (A–C) caused most (91.8%) human infections, despite constituting only 7.6% of isolates found in dogs. The 3 fatalities that occurred in our cohort were equally represented by these serovars. We found 2 untypeable isolates, which we designated serovars J and K. We did not detect an association between serovar and disease severity, immune status, alcohol abuse, or smoking status, but dog bites occurred more frequently among patients infected with non-A–C serovars. Future research is needed to confirm serovar virulence and develop strategies to reduce risk for these infections in humans.

Repeated evolutionary transitions of flavobacteria from marine to non-marine habitats

The taxonomy of marine and non-marine organisms rarely overlap, but the mechanisms underlying this distinction are often unknown. Here, we predicted three major ocean-to-land transitions in the evolutionary history of Flavobacteriaceae, a family known for polysaccharide and peptide degradation. These unidirectional transitions were associated with repeated losses of marine signature genes and repeated gains of non-marine adaptive genes. This included various Na⁺ -dependent transporters, osmolyte transporters and glycoside hydrolases (GH) for sulfated polysaccharide utilization in marine descendants, and in non-marine descendants genes for utilizing the land plant material pectin and genes facilitating terrestrial host interactions. The K⁺ scavenging ATPase was repeatedly gained whereas the corresponding low-affinity transporter repeatedly lost upon transitions, reflecting K⁺ ions are less available to non-marine bacteria. Strikingly, the central metabolism Na⁺ -translocating NADH: quinone dehydrogenase gene was repeatedly gained in marine descendants, whereas the H⁺ -translocating counterpart was repeatedly gained in non-marine lineages. Furthermore, GH genes were depleted in isolates colonizing animal hosts but abundant in bacteria inhabiting other non-marine niches; thus relative abundances of GH versus peptidase genes among Flavobacteriaceae lineages were inconsistent with the marine versus non-marine dichotomy. We suggest that phylogenomic analyses can cast novel light on mechanisms explaining the distribution and ecology of key microbiome components.

Characterization of three strains of Capnocytophaga canis isolated from patients with sepsis

Capnocytophaga canimorsus and Capnocytophaga cynodegmi, both commensal bacteria in the oral cavities of dogs and cats, are zoonotic pathogens. In particular, C. canimorsus causes sepsis and fatal septic shock. Recently, a novel Capnocytophaga species, C. canis, was isolated from the oral cavities of healthy dogs. It is reportedly oxidase-negative and therefore considered avirulent in humans. In the present study, three strains of C. canis were isolated from Japanese patients with sepsis. All three strains, HP20001, HP33001 and HP40001, were oxidase-positive. Nucleotide sequence identities of the 16S rRNA gene of the three strains to the C. canimorsus type strain ATCC35979, C. cynodegmi type strain ATCC49044 and C. canis type strain LMG29146 were 96.9-97.0%, 96.9-97.0% and 99.7-99.8%, respectively. Multi-locus sequence analysis based on seven house-keeping genes, dnaJ, fumC, glyA, gyrB, murG, trpB and tuf, revealed that the oxidase-positive C. canis strains isolated in Japan and oxidase-negative strains of C. canis from canine oral cavities in Switzerland were clustered in different genetic subgroups. These results indicate that the virulence of C. canis strains in humans is associated with oxidase activity.

Capsular serovars of virulent Capnocytophaga canimorsus are shared by the closely related species C. canis and C. cynodegmi

Capnocytophaga canimorsus is a dog oral commensal bacterium that causes rare but life-threatening generalized infections in humans who have been in contact with its animal hosts. Two other dog commensals, Capnocytophaga canis and Capnocytophaga cynodegmi, cause rare, mild local infections. To date, nine capsular serovars have been described in C. canimorsus. Here, we serotyped 112 strains of Capnocytophaga spp. isolated from human infections. The C. canimorsus strains (86 of 96, 89.6%) belonged to serovars A, B, or C with relative frequencies of approximately 30% for each serovar. The high prevalence of the A, B, and C serovars in strains isolated from humans, compared to the previously described low prevalence of these serovars among dog isolates (7.6%), confirms that these three serovars are more virulent to humans than other serovars and suggests that the low incidence of disease may be linked to the low prevalence of the A, B, and C serovars in dogs. We serotyped six strains of C. canis and ten strains of C. cynodegmi and, surprisingly, found one C. canis and three C. cynodegmi strains to be of capsular serovar B. This observation prompted us to test 34 dog-isolated C. canis and 16 dog-isolated C. cynodegmi strains. We found four C. canis strains belonging to serovar A and one belonging to serovar F. In contrast, no dog-isolated C. cynodegmi strain could be typed with the available antisera. This work demonstrates that virulence-associated capsular polysaccharides (A, B, and C) are not specific to the C. canimorsus species.

Identification of a wza-like gene involved in capsule biosynthesis, pathogenicity and biofilm formation in Riemerella anatipestifer

Duck infectious serositis is the most serious bacterial disease of ducks. It is caused by Riemerella anatipestifer (RA) infection. The capsule plays an important role in virulence of many pathogenic bacteria. In addition, the capsule has some key biological features. However, few studies have explored the characteristics of the RA capsule. In this study, we mainly constructed a capsular mutants of RA by inactivating the wza gene using homologous recombination. We found that the mutant was failed to produce a capsule layer. The mutant was less resistant to killing by the host complement or by desiccation and oxidative stress. Furthermore, the mutant strain was more hydrophobic, more able to auto-aggregate and underwent increased biofilm formation. Moreover, the mutant was less virulent than the wild-type in vivo studies. In summary, we found that the RA capsule was involved in the desiccation and oxidative stress, surface hydrophobicity, complement-mediated killing, biofilm formation, and virulence.

Identification of Virulent Capnocytophaga canimorsus Isolates by Capsular Typing

Capnocytophaga canimorsus is a dog oral commensal that causes rare but severe infections in humans. C. canimorsus was recently shown to be endowed with a capsular polysaccharide implicated in resistance to the innate immune system of the host. Here, we developed the first C. canimorsus capsular serotyping scheme. We describe nine different serovars (A to I), and this serotyping scheme allowed typing of 25/25 isolates from human infections but only 18/52 isolates from dog mouths, indicating that the repertoire of capsules in the species is vast. However, while only three serovars (A, B, and C) covered 88% of the human isolates tested (22/25), they covered only 7.7% of the dog isolates (4/52). Serovars A, B, and C were found 22.9-, 14.6-, and 4.2-fold more often, respectively, among human isolates than among dog isolates, with no geographical bias, implying that isolates endowed with these three capsular types are more virulent for humans than other isolates. Capsular serotyping would thus allow identification of virulent isolates in dogs, which could contribute to the prevention of these infections. To this end, we developed a PCR typing method based on the amplification of specific capsular genes.