Aeromonas hydrophila meningitis and fulminant sepsis in preterm newborn: A case report and review of literature

Case Report: A rare infection of multidrug-resistant Aeromonas caviae in a pediatric case with acute lymphoblastic leukemia and review of the literature

Aeromonas caviae infection of the bloodstream and intestine is a rare and severe opportunistic infection in immunocompromised people. In Southwest China, we first reported a case of bloodstream and intestinal infection with multidrug-resistant (MDR) Aeromonas caviae in a 4-year-old child with T-cell acute lymphoblastic leukemia. Blood and stool cultures were used to identify the infection. The selection of antibiotics was based on clinical expertise and medication sensitivity tests. We used linezolid, levofloxacin, and polymyxin B to treat the patient aggressively. Aeromonas caviae infection is uncommon in juvenile acute lymphoblastic leukemia. Doctors should be aware of the likelihood of opportunistic infection during the post-chemotherapy bone marrow suppression period. We further conducted a review of the literature and performed a detailed analysis of Aeromonas infection in pediatric leukemia. It is becoming increasingly apparent that antibiotic is abused domestically and abroad, resulting in the sharp increase of MDR bacteria. In general, most of the Aeromonas isolates are susceptible to third- or fourth-generation cephalosporins, aminoglycosides, quinolones, and carbapenem, but drug-resistant strains are being reported increasingly. We summarized the drug resistance rate of Aeromonas caviae and Aeromonas hydrophila in China in the last 10 years. Early recognition and effective treatment will improve prognosis and reduce mortality.

Probable Role of Type IV Pili of Aeromonas hydrophila in Human Pathogenicity

BACKGROUND

Aeromonas hydrophila is a widely recognized broad-spectrum pathogen that primarily targets the gastrointestinal tract. Type IV pili (T4P) are proteinaceous nano-machines located on the bacterial cell surface, playing a crucial role in host colonization and infection. Regrettably, the T4P systems of A. hydrophila remain largely underexplored.

METHODS

A. hydrophila genomes with complete genome assembly and annotation reports up to 31 March 2023, were obtained from the NCBI Genome database or KEGG genome database, followed by a global search for T4P secretion system genes. Protein sequences of these manually curetted genes were used as secondary quarry for Synteny analysis. Protein-protein interaction analysis was performed by string analysis and in silico study of genomic islands.

RESULTS

We identified 27 orthologs of type IV pili (T4P) nano-machine components in A. hydrophila. These orthologs are primarily distributed across three operons: pilABCD, pilMNOPQ, and pilVWXY. While the first two operons are commonly found in all experimental genomes, the presence of the pilVWXY operon, coding for 11 orthologs, is reported here for the first time in A. hydrophila. Notably, the complete pilVWXY operon is absent in nonvirulent strains. A genomic islands study between a nonvirulent and hypervirulent strain also confirms absence of most of the genes coded by pilVWXY in nonvirulent strain. Interestingly, among the 51 experimental genomes analyzed, the pilVWXY operon was completely absent in 10 strains, most of which are categorized as nonvirulent; Conclusions: The distribution of two major type IV pili (T4P) nano-machines, PilABCDMNOPQ and PilVWXY, is reported here for the first time in A. hydrophila. Additionally, this study suggests a potential role for the PilVWXY nano-machine in establishing human disease.

Metabolite features of serum and intestinal microbiota response of largemouth bass (Micropterus salmoides) after Aeromonas hydrophila challenge

The enteric morphology, enteric microbiota structure and serum metabolomics of M. salmoides before and after infected by A. hydrophila were analysed to explore the pathogenic mechanism of A. hydrophila infection in M. salmoides. The results revealed that, after the infection of A. hydrophila, the villus boundary of largemouth bass became less obvious; the relative abundance of Proteobacteria and decreasing relative abundance of Tenericutes were increasing; genera relative abundance of putatively beneficial bacteria (Mycoplasma) were decreasing, whereas the genus Aeromonas increased after infection; serum metabolomic analysis showed that infection with A. hydrophila caused disorder to the metabolic processes of largemouth bass, particularly amino acid metabolism, and caused inflammation; several potential pathogen infection-related and significantly differential intestinal microbiota-related metabolite markers were identified, such as 6-hydroxy-5-methoxyindole glucuronide, zalcitabine, bilirubin, aciclovir. This study may provide new insights into the potential association between enteric microbiota and serum metabolism and the pathogenic mechanism of M. salmoides infected by A. hydrophila, providing a scientific basis for disease control in largemouth bass breeding.

Effects of air exposure stress on crustaceans: Histopathological changes, antioxidant and immunity of the red swamp crayfish Procambarus clarkii

Air exposure stress may result in oxidative damage and ultimately disease or death in crustaceans. Using the Procambarus clarkia, one of the main commercial aquaculture species in China, as a study model, the molecular mechanism including histopathological changes, antioxidant capacity and immunity response under the air exposure stress were firstly evaluated. Results showed that the surfaces of gill were wrinkled while the morphologies of the nuclei and mitochondria in the hepatopancreas were altered after 48 h of air exposure stress, and the damage of mitochondria was more serious after additional bacterial infection. Moreover, the activity of antioxidant enzymes increased at first and then decreased along with increasement of air exposure time. The concentration of malondialdehyde (MDA) in hepatopancreas was significantly increased under the air exposure stress, while the bacterial infection further aggravated such oxidative damage. The transcriptome analysis exhibited that the stress- and immunity-related genes in hepatopancreas altered when response to the air exposure stress. This study could help uncover the mechanisms of aerial exposure stress responses in Procambarus clarkii.

Synergistic Inhibition of Plantaricin E/F and Lactic Acid Against Aeromonas hydrophila LPL-1 Reveals the Novel Potential of Class IIb Bacteriocin

Plantaricin E/F (PlnEF) is a pair of two-component class IIb bacteriocin produced by lactic acid bacteria. PlnEF commonly displays potent antimicrobial activity against certain Gram-positive organisms. In this study, we investigated the synergistic activity of PlnEF combined with lactic acid against Gram-negative food and aquaculture potential pathogen Aeromonas hydrophila LPL-1, which is naturally resistant to PlnEF. We applied SDS-PAGE, wavelength-scanning, laser confocal microscopy, flow cytometer, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and two-dimensional electrophoresis to investigate their synergistic inhibitory activities. The results showed that L-lactic acid drove the release of LPS from A. hydrophila, making it possible for PlnEF to contact the inner cell membrane of A. hydrophila. Besides, co-treatment of lactic acid and PlnEF caused severe morphological and intracellular changes of A. hydrophila, including blebs on the cell surface, abnormal cell elongation, inner membrane disruption, pore-forming through the outer and inner membrane, coagulation of the cytoplasm, and structural transformation of DNA. Protein profile analysis revealed that combined treatment of lactic acid and PlnEF inhibited the energy metabolism, protein synthesis, protein folding, and DNA replication in A. hydrophila. These findings proved that PlnEF combined with lactic acid was efficient against A. hydrophila and shed light on bacteriocin’s potential and a new inhibition mechanism against A. hydrophila.

Empyema and bacteremia caused by Aeromonas hydrophila: Case report and review of the literature

INTRODUCTION

Despite the advance in antibiotics and widespread chest tube drainage, acute empyema still shows a high mortality rate, accounting for 10-25%. We experienced a case of acute empyema caused by A. hydrophila, which is extremely uncommon, and reviewed all previously published articles.

CASE PRESENTATION

A 76-year older man with a medical history of liver cirrhosis (LC) due to chronic hepatitis C and hepatic cell carcinoma was admitted to our institute. Elevated inflammatory reaction and effusions on chest CT were seen, and he was suspected of having acute empyema. Although an empiric antibiotic therapy of meropenem with chest tube drainage was performed as an initial treatment, he died within 8 hours of admission. Postmortem, both blood and left pleural fluid cultures yielded Aeromonas hydrophila. The final diagnosis was acute empyema caused by A. hydrophila. We reviewed previously reported empyema caused by Aeromonas species cases (4 A. hydrophila, and 1 A. veronii) in 4 previous reports written in English, including ours. Of 5, all were male, and the mean age was 52 years (range 27-76 years). All patients had LC due to alcohol or viral infections. As for antibiotics initially prescribed, third-generation cephalosporins were most frequently used in 3/5 (60%). Thoracentesis was performed in all patients (100%). As for prognosis, 2 (40%) survived, and 3 (60%) died.

CONCLUSION

Physicians should be aware of the possibility of acute empyema caused by A. hydrophila among patients with chronic hepatic disease.

Molecular and Functional Characterization of a Novel Plasmid-Borne bla NDM-Like Gene, bla AFM-1, in a Clinical Strain of Aeromonas hydrophila

Purpose

An increasing frequency of antibiotic resistance has been observed in both clinical and environmental Aeromonas hydrophila isolates in recent years. However, there are still very few in-depth studies regarding the role of plasmids in the antibiotic resistance of A. hydrophila. Hence, we investigated the molecular and functional characterization of a multidrug-resistant plasmid encoding an NDM-like metallo-β-lactamase, AFM-1, in the clinical A. hydrophila isolate SS332.

Methods

The minimum inhibitory concentrations (MICs) of 24 antibiotics against A. hydrophila SS332 were measured by the agar dilution method. The genome of A. hydrophila SS332 was sequenced with PacBio and Illumina platforms. Six plasmid-borne antimicrobial resistance genes were chosen for cloning, including bla_AFM-1, bla_OXA-1, msr(E), mph(E), aac(6ʹ)-Ib10, and aph(3ʹ)-Ia. Phylogenetic analysis, amino acid sequence alignment, and comparative genomic analysis were performed to elucidate the active site requirements and genetic context of the bla_AFM-1 gene.

Results

A. hydrophila SS332 showed high levels of resistance to 15 antibiotics, especially those with MIC levels at or above 1024 μg/mL, including ampicillin, cefazolin, ceftriaxone, aztreonam, spectinomycin, and roxithromycin. Six plasmid-borne resistance genes from A. hydrophila were verified to be functional in E. coli DH5α. AFM-1 shared 86% amino acid identity with NDM-1 and showed resistance to ampicillin, cefazolin, cefoxitin, and ceftazidime. In addition, the bla_AFM-1 gene was associated with three different novel ISCR19-like elements, designated ISCR19-1, ISCR19-2 and ∆ISCR19-3, which may be involved in the acquisition and mobilization of the bla_AFM-1 gene.

Conclusion

Our investigation showed that plasmid-borne resistance genes can contribute to antibiotic resistance in A. hydrophila SS332. A novel bla_NDM-like gene, bla_AFM-1, was verified to be functional and associated with novel ISCR19-like elements. This fact indicated the risk of spread of bla_AFM-1 genes and ISCR19-like elements.

Urinary tract infection due to Aeromonas species: An uncommon causative agent

BACKGROUND

Members of the genus Aeromonas are Gram-negative bacilli, belonging to family Aeromonadaceae, and are widely found in various aquatic environments. The most common species associated with human infections are A. hydrophila, A. caviae, and A. veronii biovar sobria. Aeromonas species are recognized as emerging opportunistic pathogens in humans mainly causing gastrointestinal infections and wound infections with or without progression to septicaemia. Aeromonas organisms rarely cause urinary tract infection (UTI) and are not known uropathogens.

CASE

We report a series of UTI due to Aeromonas species in three adult patients, specifically identified as A. veronii biovar sobria in two patients and A. hydrophila in one patient. Two patients had history of occupational exposure to aquatic environment.

CONCLUSIONS

The cases highlight another expanded range of infections caused by Aeromonas spp. that can be encountered in a community setting and indicate that infections with Aeromonas spp. should be kept in mind while investigating for the etiology of UTI, especially in adult patients with occupational exposure to aquatic ecosystems.

Bacteriological, Clinical and Virulence Aspects of Aeromonas-associated Diseases in Humans

Aeromonads have been isolated from varied environmental sources such as polluted and drinking water, as well as from tissues and body fluids of cold and warm-blooded animals. A phenotypically and genotypically heterogenous bacteria, aeromonads can be successfully identified by ribotyping and/or by analysing gyrB gene sequence, apart from classical biochemical characterization. Aeromonads are known to cause scepticemia in aquatic organisms, gastroenteritis and extraintestinal diseases such as scepticemia, skin, eye, wound and respiratory tract infections in humans. Several virulence and antibiotic resistance genes have been identified and isolated from this group, which if present in their mobile genetic elements, may be horizontally transferred to other naive environmental bacteria posing threat to the society. The extensive and indiscriminate use of antibiotics has given rise to many resistant varieties of bacteria. Multidrug resistance genes, such as NDM1, have been identified in this group of bacteria which is of serious health concern. Therefore, it is important to understand how antibiotic resistance develops and spreads in order to undertake preventive measures. It is also necessary to search and map putative virulence genes of Aeromonas for fighting the diseases caused by them. This review encompasses current knowledge of bacteriological, environmental, clinical and virulence aspects of the Aeromonas group and related diseases in humans and other animals of human concern.

Etiology of bacterial meningitis: a cross-sectional study among patients admitted in a semi-urban hospital in Nairobi, Kenya

Introduction

bacterial meningitis, responsible for childhood morbidity and mortality, can also lead to permanent neurological disability among survivors. This study conducted from January to December, 2015 used standard bacteriological and molecular methods to investigate the etiology of three common causes of bacterial meningitis among hospitalized patients admitted at a semi-urban hospital in Nairobi, Kenya.

Methods

a total of 196 patients admitted at Mama Lucy Kibaki with clinically diagnosed meningitis were recruited into this cross-sectional study. Participants’ information was collected through patient interviews and abstraction of health records. Bacterial culture, gram stains and multiplex polymerase chain reaction (PCR) were used to investigate causes of bacterial meningitis from cerebrospinal fluid (CSF) samples. Characteristics such as age, gender, occupation, underlying conditions of patients with laboratory confirmed bacterial meningitis infection are described.

Results

among the 196 patients diagnosed with bacterial meningitis, the median age was 1 year (range 1 to 36 years) with 87.2% aged 1 to 4 years; 54.6% were males. Using PCR, 22 out of 196 (11.2%) samples had evidence suggesting a bacterial infection. These included 12/22 (54.5%) S. pneumonia, 7/22 (31.8%) N. meningitides and 3/22 (13.6%) H. influenza. From bacterial culture, four of 196 (2.1%) samples grew S. pneumonia. All three samples found positive for H. influenza were from male patients aged between 1 to 4 years.

Conclusion

of the three common causes evaluated, S. pneumonia was the most common cause of bacterial meningitis among patients from this region, particularly among infants. One older patient was diabetic, thereby highlighting the importance of pre-existing conditions. Although serotyping of bacteria was not done, under-vaccination might have played a role in the cases identified and ensuring complete and timely vaccination may prevent further cases of bacterial meningitis.