Chromobacterium haemolyticum Pneumonia Associated with Near-Drowning and River Water, Japan

Pathogenic and transmissional potentials of a Chromobacterium haemolyticum isolate from a hydroponic farm

AIMS

This study aims to investigate the in vitro pathogenicity of Chromobacterium haemolyticum strain WI5 toward the intestinal tract, its resistance to water treatments, and its potential for foodborne transmission through leafy greens produced in hydroponic systems.

METHODS AND RESULTS

C. haemolyticum WI5 caused cytopathic effects in human colon cells HCT116 and exhibited an 8.2-fold higher cell attachment compared to Salmonella serotype Typhimurium. It showed comparable resistance to sodium hypochlorite (NaOCl) and ultraviolet (UV) treatments as Escherichia coli O157: H7 and Pseudomonas aeruginosa but was more susceptible to desiccation. On lettuce, C. haemolyticum WI5 failed to persist, with counts decreasing below the detection limit (≥4 log reductions) after 3 and 2 days at 4 and 25°C, respectively.

CONCLUSIONS

C. haemolyticum WI5 demonstrated considerable virulence features and high in vitro pathogenicity toward the intestinal tract. NaOCl and UV treatments were effective in disinfecting C. haemolyticum in water. Due to its high susceptibility to desiccation and poor survivability on lettuce, the foodborne transmission potential of C. haemolyticum is considered limited.

Chromobacterium haemolyticum infection from hot springs near Yellowstone National Park: a case report

BACKGROUND

Chromobacterium haemolyticum is a gram-negative anaerobic sporulated rod and was only first identified in 2008. It is very rare in people with only a handful of cases having been diagnosed around the world.

CASE PRESENTATION

After suffering a fall near Yellowstone National Park, a white male patient in his 50 s presented to a hospital in Eastern Idaho. With many unexplained symptoms, several changes in patient stability and recovery, over a course of 18 days in the hospital, the infecting organism could not be easily identified. Labs in the hospital, state, and eventually outside of the state were consulted for pathogen identification, which was only accomplished after the patient was discharged.

CONCLUSIONS

To our knowledge, this is only the seven reported human infection with Chromobacterium haemolyticum. This bacterium is difficult to identify and may be occur in rural areas without the proper testing facilities to quickly identify the pathogen, which is essential to timely treatment.

Meningitis caused by Chromobacterium haemolyticum suspected to be derived from a canal in Japan: a case report

BACKGROUND

The genus Chromobacterium, of which 12 species have been recognized, comprises bacteria that reside in tropical and subtropical environments. Of these species, Chromobacterium violaceum and Chromobacterium haemolyticum are known to cause infections in humans. There have been few reports of infections caused by Chromobacterium haemolyticum.

CASE PRESENTATION

Chromobacterium haemolyticum was detected in spinal fluid and blood samples isolated from a 73-year-old Japanese male patient who fell into a canal in Kyoto City, Japan and developed bacteremia and meningitis. Although meropenem and vancomycin were administered, this patient died 9 days after admission. Although the infection was misidentified as being caused by Chromobacterium violaceum by conventional identification methods, average nucleotide identity analysis revealed that the causative pathogen was Chromobacterium haemolyticum. The same bacteria were also detected in the canal in which the accident occurred. Phylogenetic analysis of the strain isolated from the patient and the strain isolated from the canal suggested that the two strains were very closely related.

CONCLUSIONS

Chromobacterium haemolyticum can be misidentified as Chromobacterium violaceum by conventional identification methods and tends to be more resistant to β-lactams than Chromobacterium violaceum. Pigment production and β-hemolysis on blood sheep agar can provide clues for the early identification of Chromobacterium haemolyticum.

Outbreak of Fatal Piglet Diarrhea Caused by Chromobacterium haemolyticum in China

Chromobacterium haemolyticum is a fatal Gram-negative bacterium which could infect human beings. Our investigation found severe piglet diarrhea in one farm; the morbidity rate of piglets was 30.65%. Then, we isolated a nonpigmented, β-hemolytic Gram-negative bacillus from the clinical samples of this farm, which was designated GDHYZ30 strain. The 16S rRNA gene sequence indicated it was most closely related to Chromobacterium haemolyticum. Similar clinical symptoms were successfully reproduced in experimental piglets with this isolate, and the isolate was also subjected to whole genome-sequencing. It is worth noting that this Chromobacterium haemolyticum has been isolated from several other pig farms with diarrhea of unknown causes. To our knowledge, this is the first report that discusses Chromobacterium haemolyticum as a new pathogen causing diarrhea and death in piglets and transmitting through water sources, and it provides a reference for the prevention and control of human/animal infections as well as food safety.

Bacterial Antagonism of Chromobacterium haemolyticum and Characterization of its Putative Type VI Secretion System

This study reports the isolation of a new Chromobacterium haemolyticum strain named WI5 from a hydroponic farming facility. WI5 exhibited remarkable bacterial antagonistic properties, eliminating Salmonella, Escherichia coli, Listeria monocytogenes and Staphylococcus aureus (initial inoculum load ∼10⁵ CFU/ml) in dual-species co-culture biofilms. Antagonism was strictly contact-dependent and highly influenced by nutrient availability. Next, we identified a complete suite of putative Type VI secretion system (T6SS) genes in the WI5 genome, annotated the gene locus architecture, and determined the crystal structure of hallmark T6SS tube protein Hcp1, which revealed a hexameric ring structure with an outer and inner diameter of 77 and 45Å, respectively. Structural comparison with homologs showed differences in the key loops connecting the β-strands in which the conserved residues are located, suggesting a role of these residues in the protein function. The T6SS is well-known to facilitate interbacterial competition, and the putative T6SS characterized herein might be responsible for the remarkable antagonism by C. haemolyticum WI5. Collectively, these findings shed light on the nature of bacterial antagonism and a putative key virulence determinant of C. haemolyticum, which might aid in further understanding its potential ecological role in natural habitats.