Large Multicountry Outbreak of Invasive Listeriosis by a Listeria monocytogenes ST394 Clone Linked to Smoked Rainbow Trout, 2020 to 2021

Whole-genome sequencing (WGS) has revolutionized surveillance of infectious diseases. Disease outbreaks can now be detected with high precision, and correct attribution of infection sources has been improved. Listeriosis, caused by the bacterium Listeria monocytogenes, is a foodborne disease with a high case fatality rate and a large proportion of outbreak-related cases. Timely recognition of listeriosis outbreaks and precise allocation of food sources are important to prevent further infections and to promote public health. We report the WGS-based identification of a large multinational listeriosis outbreak with 55 cases that affected Germany, Austria, Denmark, and Switzerland during 2020 and 2021. Clinical isolates formed a highly clonal cluster (called Ny9) based on core genome multilocus sequence typing (cgMLST). Routine and ad hoc investigations of food samples identified L. monocytogenes isolates from smoked rainbow trout filets from a Danish producer grouping with the Ny9 cluster. Patient interviews confirmed consumption of rainbow trout as the most likely infection source. The Ny9 cluster was caused by a MLST sequence type (ST) ST394 clone belonging to molecular serogroup IIa, forming a distinct clade within molecular serogroup IIa strains. Analysis of the Ny9 genome revealed clpY, dgcB, and recQ inactivating mutations, but phenotypic characterization of several virulence-associated traits of a representative Ny9 isolate showed that the outbreak strain had the same pathogenic potential as other serogroup IIa strains. Our report demonstrates that international food trade can cause multicountry outbreaks that necessitate cross-border outbreak collaboration. It also corroborates the relevance of ready-to-eat smoked fish products as causes for listeriosis. IMPORTANCE Listeriosis is a severe infectious disease in humans and characterized by an exceptionally high case fatality rate. The disease is transmitted through consumption of food contaminated by the bacterium Listeria monocytogenes. Outbreaks of listeriosis often occur but can be recognized and stopped through implementation of whole-genome sequencing-based pathogen surveillance systems. We here describe the detection and management of a large listeriosis outbreak in Germany and three neighboring countries. This outbreak was caused by rainbow trout filet, which was contaminated by a L. monocytogenes clone belonging to sequence type ST394. This work further expands our knowledge on the genetic diversity and transmission routes of an important foodborne pathogen.

A Novel Lineage of Ceftriaxone-resistant Salmonella Typhi From India That Is Closely Related to XDR S. Typhi Found in Pakistan

Two MDR Salmonella Typhi isolates from India were found by whole genome sequencing to be closely related to the 2016 XDR S. Typhi outbreak strain from Pakistan. The Indian isolates have no chromosomal antimicrobial resistance cassette but carry the IncY plasmid p60006. Both isolates are susceptible to chloramphenicol, azithromycin, and carbapenems.

Mycobacterial infections in wild boars (Sus scrofa) from Southern Switzerland: Diagnostic improvements, epidemiological situation and zoonotic potential

The occurrence of mycobacterial infections in different hosts and their implication as obligate or opportunistic pathogens remain mainly unclear. In addition to the well-known pathogenic members of the Mycobacterium tuberculosis - complex (MTBC), over 180 non-tuberculous mycobacteria (NTM) species have been described. Although the large majority of the NTM is assumed to be non-pathogenic to most individuals, an increasing trend in NTM infections has been observed over the last decades. The reasons of such augmentation are probably more than one: improved laboratory diagnostics, an increasing number of immunocompromised patients and individuals with lung damage are some of the possible aspects. Mandibular lymph nodes of 176 hunted wild boars from the pre-Alpine region of Canton Ticino, Switzerland, were collected. Following gross inspection, each lymph node was subjected to culture and to an IS6110 based real-time PCR specific for MTBC members. Histology was performed of a selection of lymph nodes (n = 14) presenting gross visible lesions. Moreover, accuracy of matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) species identification was compared with sequence analysis of a combination of housekeeping genes. Mycobacteria of the MTBC were detected in 2.8% of the wild boars (n = 5; CI_95% 1.2-6.5) and were all confirmed to be Mycobacterium microti by molecular methods. In addition, based on the examined lymph nodes, NTM were detected in 57.4% (n = 101; CI_95% 50.0-64.5) of the wild boars originating from the study area. The 111 isolates belonged to 24 known species and three potentially undescribed Mycobacterium species. M. avium subsp. hominissuis thereby predominated (22.5%) and was found in lymph nodes with and without macroscopic changes. Overall, the present findings show that, with the exception of undescribed Mycobacterium species where identification was not possible (3.6%; 4/111), MALDI-TOF MS had a high concordance rate (90.1%; 100/111 isolates) to the sequence-based reference method.

Antimicrobial and Insecticidal: Cyclic Lipopeptides and Hydrogen Cyanide Produced by Plant-Beneficial Pseudomonas Strains CHA0, CMR12a, and PCL1391 Contribute to Insect Killing

Particular groups of plant-beneficial fluorescent pseudomonads are not only root colonizers that provide plant disease suppression, but in addition are able to infect and kill insect larvae. The mechanisms by which the bacteria manage to infest this alternative host, to overcome its immune system, and to ultimately kill the insect are still largely unknown. However, the investigation of the few virulence factors discovered so far, points to a highly multifactorial nature of insecticidal activity. Antimicrobial compounds produced by fluorescent pseudomonads are effective weapons against a vast diversity of organisms such as fungi, oomycetes, nematodes, and protozoa. Here, we investigated whether these compounds also contribute to insecticidal activity. We tested mutants of the highly insecticidal strains Pseudomonas protegens CHA0, Pseudomonas chlororaphis PCL1391, and Pseudomonas sp. CMR12a, defective for individual or multiple antimicrobial compounds, for injectable and oral activity against lepidopteran insect larvae. Moreover, we studied expression of biosynthesis genes for these antimicrobial compounds for the first time in insects. Our survey revealed that hydrogen cyanide and different types of cyclic lipopeptides contribute to insecticidal activity. Hydrogen cyanide was essential to full virulence of CHA0 and PCL1391 directly injected into the hemolymph. The cyclic lipopeptide orfamide produced by CHA0 and CMR12a was mainly important in oral infections. Mutants of CMR12a and PCL1391 impaired in the production of the cyclic lipopeptides sessilin and clp1391, respectively, showed reduced virulence in injection and feeding experiments. Although virulence of mutants lacking one or several of the other antimicrobial compounds, i.e., 2,4-diacetylphloroglucinol, phenazines, pyrrolnitrin, or pyoluteorin, was not reduced, these metabolites might still play a role in an insect background since all investigated biosynthetic genes for antimicrobial compounds of strain CHA0 were expressed at some point during insect infection. In summary, our study identified new factors contributing to insecticidal activity and extends the diverse functions of antimicrobial compounds produced by fluorescent pseudomonads from the plant environment to the insect host.

Insect pathogenicity in plant-beneficial pseudomonads: phylogenetic distribution and comparative genomics

Bacteria of the genus Pseudomonas occupy diverse environments. The Pseudomonas fluorescens group is particularly well-known for its plant-beneficial properties including pathogen suppression. Recent observations that some strains of this group also cause lethal infections in insect larvae, however, point to a more versatile ecology of these bacteria. We show that 26 P. fluorescens group strains, isolated from three continents and covering three phylogenetically distinct sub-clades, exhibited different activities toward lepidopteran larvae, ranging from lethal to avirulent. All strains of sub-clade 1, which includes Pseudomonas chlororaphis and Pseudomonas protegens, were highly insecticidal regardless of their origin (animals, plants). Comparative genomics revealed that strains in this sub-clade possess specific traits allowing a switch between plant- and insect-associated lifestyles. We identified 90 genes unique to all highly insecticidal strains (sub-clade 1) and 117 genes common to all strains of sub-clade 1 and present in some moderately insecticidal strains of sub-clade 3. Mutational analysis of selected genes revealed the importance of chitinase C and phospholipase C in insect pathogenicity. The study provides insight into the genetic basis and phylogenetic distribution of traits defining insecticidal activity in plant-beneficial pseudomonads. Strains with potent dual activity against plant pathogens and herbivorous insects have great potential for use in integrated pest management for crops.

Transmission of Mycobacterium chimaera from Heater-Cooler Units during Cardiac Surgery despite an Ultraclean Air Ventilation System

All such units should be separated from air that can gain access to sterile areas.

Heater–cooler units (HCUs) were recently identified as a source of Mycobacterium chimaera causing surgical site infections. We investigated transmission of this bacterium from HCUs to the surgical field by using a thermic anemometer and particle counter, videotape of an operating room equipped with an ultraclean laminar airflow ventilation system, and bacterial culture sedimentation plates in a nonventilated room. Smoke from the HCU reached the surgical field in 23 s by merging with ultraclean air. The HCU produced on average 5.2, 139, and 14.8 particles/min in the surgical field at positions Off, On/oriented toward, and On/oriented away, respectively. Culture plates were positive for M. chimaera<5 m from the HCU in the test room. These experiments confirm airborne transmission of M. chimaera aerosols from a contaminated HCU to an open surgical field despite ultraclean air ventilation. Efforts to mitigate infectious risks during surgery should consider contamination from water sources and airflow-generating devices.

Aggregatibacter aphrophilus ventriculitis following C1-C2 transarticular screw fixation

OBJECTIVE

Central nervous system (CNS) infections after cervical spine surgery are a rare but serious complication and may be caused by uncommon pathogens. We report the case of a 57-year-old male who developed slowly progressive mental confusion with headaches, increased daytime sleepiness and mild gait disturbance within the last 3 weeks. Six weeks prior to admission to our department, he underwent an atlantoaxial fusion by C1-C2 transarticular screw fixation for rheumatoid arthritis related C1-C2 multidirectional instability.

METHODS

We analyzed clinical and neuroradiological findings.

RESULTS

The findings were consistent with communicating hydrocephalus secondary to ventriculitis and the left C1-C2 screw was found to be misplaced with perforation of the dura. The situation was interpreted as implant related surgical site infection of the cerebrospinal fluid followed by ventriculitis and hydrocephalus. Bacterial broad range 16S rRNA gene PCR from the cerebrospinal fluid (CSF) followed by sequencing identified Aggregatibacter aphrophilus as the causative agent, while conventional cultures remained negative due to its fastidious growth. The patient was successfully treated with a lumbar drain and intravenous ceftriaxone.

CONCLUSIONS

To our knowledge, this is the first report of Aggregatibacter aphrophilus ventriculitis following C1-C2 transarticular screw fixation.

Hepatitis From Spiroplasma sp. in an Immunocompromised Patient

A 70-year-old lung transplant recipient patient was admitted with fever, nausea, abdominal pain, peripheral edema and pronounced weakness. An initial work-up for presumed infection revealed cholestatic hepatitis, leukocytosis and thrombocytopenia, but failed to detect a pathogen. An increased glucose uptake exclusively in the liver was demonstrated by positron emission tomography. Liver biopsy showed basophilic inclusions in the cytoplasm of hepatocytes. Broad- range 16S rRNA gene PCR followed by sequence analysis yielded Spiroplasma sp. in two independent blood samples and the liver biopsy, confirming Spiroplasma sp. as the causative agent. Antibiotic treatment with doxycycline and azithromycin led to complete recovery.

Evolutionary patchwork of an insecticidal toxin shared between plant-associated pseudomonads and the insect pathogens Photorhabdus and Xenorhabdus

BACKGROUND

Root-colonizing fluorescent pseudomonads are known for their excellent abilities to protect plants against soil-borne fungal pathogens. Some of these bacteria produce an insecticidal toxin (Fit) suggesting that they may exploit insect hosts as a secondary niche. However, the ecological relevance of insect toxicity and the mechanisms driving the evolution of toxin production remain puzzling.

RESULTS

Screening a large collection of plant-associated pseudomonads for insecticidal activity and presence of the Fit toxin revealed that Fit is highly indicative of insecticidal activity and predicts that Pseudomonas protegens and P. chlororaphis are exclusive Fit producers. A comparative evolutionary analysis of Fit toxin-producing Pseudomonas including the insect-pathogenic bacteria Photorhabdus and Xenorhadus, which produce the Fit related Mcf toxin, showed that fit genes are part of a dynamic genomic region with substantial presence/absence polymorphism and local variation in GC base composition. The patchy distribution and phylogenetic incongruence of fit genes indicate that the Fit cluster evolved via horizontal transfer, followed by functional integration of vertically transmitted genes, generating a unique Pseudomonas-specific insect toxin cluster.

CONCLUSIONS

Our findings suggest that multiple independent evolutionary events led to formation of at least three versions of the Mcf/Fit toxin highlighting the dynamic nature of insect toxin evolution.

Healthcare-associated prosthetic heart valve, aortic vascular graft, and disseminated Mycobacterium chimaera infections subsequent to open heart surgery

AIMS

We identified 10 patients with disseminated Mycobacterium chimaera infections subsequent to open-heart surgery at three European Hospitals. Infections originated from the heater-cooler unit of the heart-lung machine. Here we describe clinical aspects and treatment course of this novel clinical entity.

METHODS AND RESULTS

Interdisciplinary care and follow-up of all patients was documented by the study team. Patients' characteristics, clinical manifestations, microbiological findings, and therapeutic measures including surgical reinterventions were reviewed and treatment outcomes are described. The 10 patients comprise a 1-year-old child and nine adults with a median age of 61 years (range 36-76 years). The median duration from cardiac surgery to diagnosis was 21 (range 5-40) months. All patients had prosthetic material-associated infections with either prosthetic valve endocarditis, aortic graft infection, myocarditis, or infection of the prosthetic material following banding of the pulmonary artery. Extracardiac manifestations preceded cardiovascular disease in some cases. Despite targeted antimicrobial therapy, M. chimaera infection required cardiosurgical reinterventions in eight patients. Six out of 10 patients experienced breakthrough infections, of which four were fatal. Three patients are in a post-treatment monitoring period.

CONCLUSION

Healthcare-associated infections due to M. chimaera occurred in patients subsequent to cardiac surgery with extracorporeal circulation and implantation of prosthetic material. Infections became clinically apparent after a time lag of months to years. Mycobacterium chimaera infections are easily missed by routine bacterial diagnostics and outcome is poor despite long-term antimycobacterial therapy, probably because biofilm formation hinders eradication of pathogens.

Prolonged Outbreak of Mycobacterium chimaera Infection After Open-Chest Heart Surgery

BACKGROUND

Invasive Mycobacterium chimaera infections were diagnosed in 2012 in 2 heart surgery patients on extracorporeal circulation. We launched an outbreak investigation to identify the source and extent of the potential outbreak and to implement preventive measures.

METHODS

We collected water samples from operating theaters, intensive care units, and wards, including air samples from operating theaters. Mycobacterium chimaera strains were characterized by randomly amplified polymorphic DNA polymerase chain reaction (RAPD-PCR). Case detection was performed based on archived histopathology samples and M. chimaera isolates since 2006, and the patient population at risk was prospectively surveyed.

RESULTS

We identified 6 male patients aged between 49 and 64 years with prosthetic valve endocarditis or vascular graft infection due to M. chimaera, which became clinically manifest with a latency of between 1.5 and 3.6 years after surgery. Mycobacterium chimaera was isolated from cardiac tissue specimens, blood cultures, or other biopsy specimens. We were able also to culture M. chimaera from water circuits of heater-cooler units connected to the cardiopulmonary bypass, and air samples collected when the units were in use. RAPD-PCR demonstrated identical patterns among M. chimaera strains from heater-cooler unit water circuits and air samples, and strains in 2 patient clusters.

CONCLUSIONS

The epidemiological and microbiological features of this prolonged outbreak provided evidence for the airborne transmission of M. chimaera from contaminated heater-cooler unit water tanks to patients during open-heart surgery.

Infections with the tick-borne bacterium "Candidatus Neoehrlichia mikurensis" mimic noninfectious conditions in patients with B cell malignancies or autoimmune diseases

BACKGROUND

Candidatus Neoehrlichia mikurensis is a newly discovered noncultivatable bacterium spread among ticks and rodents in Europe and Asia that can infect humans, particularly immunocompromised patients.

METHODS

We compiled clinical and laboratory data from 11 patients with hematological malignances or autoimmune diseases who were diagnosed with Candidatus N. mikurensis infection in Europe 2010-2013. Both published (6) and unpublished cases (5) were included.

RESULTS

The patients had a median age of 67, were mostly male (8/11), and resided in Sweden, Switzerland, Germany, and the Czech Republic. All but one had ongoing or recent immune suppressive treatment and a majority were splenectomized (8/11). Less than half of them recalled tick exposure. The most frequent symptoms were fever (11/11), localized pain afflicting muscles and/or joints (8/11), vascular and thromboembolic events (6/11), that is, deep vein thrombosis (4), transitory ischemic attacks (2), pulmonary embolism (1), and arterial aneurysm (1). Typical laboratory findings were elevated C-reactive protein, leukocytosis with neutrophilia, and anemia. Median time from onset of symptoms to correct diagnosis was 2 months. In at least 4 cases, the condition was interpreted to be due to the underlying disease, and immunosuppressive therapy was scheduled. All patients recovered completely when doxycycline was administered.

CONCLUSIONS

Candidatus N. mikurensis is an emerging tick-borne pathogen that may give rise to a systemic inflammatory syndrome in persons with hematologic or autoimmune diseases that could be mistaken for recurrence of the underlying disease and/or unrelated arteriosclerotic vascular events. Awareness of this new pathogen is warranted among rheumatologists, hematologists, oncologists, and infectious disease specialists.

[A rare cause of recurrent monarthritis of the knee]

Isolated monarthritis caused by Tropheryma whipplei without involvement of the gastrointestinal tract is rare but is nowadays often described as an early manifestation of the disease. In a male patient with recurrent knee joint arthritis for several years, we could ultimately diagnose Whipple's disease based on PCR positive biopsies of synovial tissue and fluid. Furthermore, the patient was found to be an asymptomatic T. whipplei carrier. With adequate antibiotic therapy the patient has meanwhile fully recovered.

Surveillance of bovine tuberculosis and risk estimation of a future reservoir formation in wildlife in Switzerland and Liechtenstein

Bovine tuberculosis (bTB) caused by Mycobacterium bovis or M. caprae has recently (re-) emerged in livestock and wildlife in all countries bordering Switzerland (CH) and the Principality of Liechtenstein (FL). Comprehensive data for Swiss and Liechtenstein wildlife are not available so far, although two native species, wild boar (Sus scrofa) and red deer (Cervus elaphus elaphus), act as bTB reservoirs elsewhere in continental Europe. Our aims were (1) to assess the occurrence of bTB in these wild ungulates in CH/FL and to reinforce scanning surveillance in all wild mammals; (2) to evaluate the risk of a future bTB reservoir formation in wild boar and red deer in CH/FL. Tissue samples collected from 2009 to 2011 from 434 hunted red deer and wild boar and from eight diseased ungulates with tuberculosis-like lesions were tested by direct real-time PCR and culture to detect mycobacteria of the Mycobacterium tuberculosis complex (MTBC). Identification of suspicious colonies was attempted by real-time PCR, genotyping and spoligotyping. Information on risk factors for bTB maintenance within wildlife populations was retrieved from the literature and the situation regarding identified factors was assessed for our study areas. Mycobacteria of the MTBC were detected in six out of 165 wild boar (3.6%; 95% CI: 1.4-7.8) but none of the 269 red deer (0%; 0-1.4). M. microti was identified in two MTBC-positive wild boar, while species identification remained unsuccessful in four cases. Main risk factors for bTB maintenance worldwide, including different causes of aggregation often resulting from intensive wildlife management, are largely absent in CH and FL. In conclusion, M. bovis and M. caprae were not detected but we report for the first time MTBC mycobacteria in Swiss wild boar. Present conditions seem unfavorable for a reservoir emergence, nevertheless increasing population numbers of wild ungulates and offal consumption may represent a risk.

Do biofilm formation and interactions with human cells explain the clinical success of Acinetobacter baumannii?

Background

The dramatic increase in antibiotic resistance and the recent manifestation in war trauma patients underscore the threat of Acinetobacter baumannii as a nosocomial pathogen. Despite numerous reports documenting its epidemicity, little is known about the pathogenicity of A. baumannii. The aim of this study was to obtain insight into the factors that might explain the clinical success of A. baumannii.

Methodology/Principal Findings

We compared biofilm formation, adherence to and inflammatory cytokine induction by human cells for a large panel of well-described strains of A. baumannii and compared these features to that of other, clinically less relevant Acinetobacter species. Results revealed that biofilm formation and adherence to airway epithelial cells varied widely within the various species, but did not differ among the species. However, airway epithelial cells and cultured human macrophages produced significantly less inflammatory cytokines upon exposure to A. baumannii strains than to strains of A. junii, a species infrequently causing infection.

Conclusion/Significance

The induction of a weak inflammatory response may provide a clue to the persistence of A. baumannii in patients.

Isolation and characterization of antagonistic Bacillus subtilis strains from the avocado rhizoplane displaying biocontrol activity

AIM

This study was undertaken to isolate Bacillus subtilis strains with biological activity against soil-borne phytopathogenic fungi from the avocado rhizoplane.

METHODS AND RESULTS

A collection of 905 bacterial isolates obtained from the rhizoplane of healthy avocado trees, contains 277 gram-positive isolates. From these gram-positive isolates, four strains, PCL1605, PCL1608, PCL1610 and PCL1612, identified as B. subtilis, were selected on the basis of their antifungal activity against diverse soil-borne phytopathogenic fungi. Analysis of the antifungal compounds involved in their antagonistic activity showed that these strains produced hydrolytic enzymes such as glucanases or proteases and the antibiotic lipopeptides surfactin, fengycin, and/or iturin A. In biocontrol trials using the pathosystems tomato/Fusarium oxysporum f.sp. radicis-lycopersici and avocado/Rosellinia necatrix, two B. subtilis strains, PCL1608 and PCL1612, both producing iturin A, exhibited the highest biocontrol and colonization capabilities.

CONCLUSIONS

Diverse antagonistic B. subtilis strains isolated from healthy avocado rhizoplanes have shown promising biocontrol abilities, which are closely linked with the production of antifungal lipopeptides and good colonization aptitudes.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is one of the few reports dealing with isolation and characterization of B. subtilis strains with biocontrol activity against the common soil-borne phytopathogenic fungi F. oxysporum f.sp. radicis-lycopersici and R. necatrix.

Use of green fluorescent protein color variants expressed on stable broad-host-range vectors to visualize rhizobia interacting with plants

We developed two sets of broad-host-range vectors that drive expression of the green fluorescent protein (GFP) or color variants thereof (henceforth collectively called autofluorescent proteins [AFPs]) from the lac promoter. These two sets are based on different replicons that are maintained in a stable fashion in Escherichia coli and rhizobia. Using specific filter sets or a dedicated confocal laser scanning microscope setup in which emitted light is split into its color components through a prism, we were able to unambiguously identify bacteria expressing enhanced cyan fluorescent protein (ECFP) or enhanced yellow fluorescent protein (EYFP) in mixtures of the two. Clearly, these vectors will be valuable tools for competition, cohabitation, and rescue studies and will also allow the visualization of interactions between genetically marked bacteria in vivo. Here, we used these vectors to visualize the interaction between rhizobia and plants. Specifically, we found that progeny from different rhizobia can be found in the same nodule or even in the same infection thread. We also visualized movements of bacteroids within plant nodule cells.