PubMed · 6846380
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B Hollingsworth, J Hudson. 1983. Microbiology problem.. https://pubmed.ncbi.nlm.nih.gov/6846380/
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BACKGROUND: Aeromonas species are ubiquitous aquatic bacteria that have emerged as significant foodborne enteric pathogens worldwide, yet their genomic landscape in clinical settings remains poorly delineated, particularly in Beijing. METHODS: To address this gap, we performed active surveillance for Aeromonas among 691 consecutive diarrheal outpatients in a Beijing district from January to December 2024. Isolates were recovered using enrichment culture coupled with PCR screening and identified by MALDI-TOF MS. Antimicrobial susceptibility was tested against 17 agents. Whole-genome sequencing was conducted on all isolates, enabling average nucleotide identity (ANI) analysis, comprehensive annotation of antimicrobial resistance and virulence genes, multilocus sequence typing (MLST), and core-genome SNP (cgSNP)-based phylogenetics. RESULTS: Aeromonas was detected in 3.3% (23/691) of patients, with Aeromonas veronii (56.52%, 13/23) and Aeromonas caviae (26.09%, 6/23) predominating. Co-infections with other enteric pathogens occurred in 65.2% of positive cases. Resistance rates were notably high for ampicillin/ampicillin-sulbactam (78.26%), nalidixic acid (56.52%), and ertapenem (21.73%), and 65.21% of isolates were multidrug-resistant. Genotypic-phenotypic concordance was robust, with β-lactamase genes ampS (60.87%) and blaCEPH-A3 (47.83%) being most prevalent. Strikingly, mcr-3.25 and mcr-3.3, which belong to the mcr family (originally described as mobile colistin resistance genes), were identified in 8.70% of isolates, exhibiting perfect correlation with phenotypic resistance. Plasmer analysis suggested both mcr genes to be chromosomally encoded. Comparative genomic analysis of virulence-associated genes revealed striking species-specific specialization: A. veronii predominantly carried complete T3SS clusters (61.5%), A. caviae and Aeromonas enteropelogenes were enriched in T6SS genes, and a single A. dhakensis isolate possessed an extensive arsenal including T3SS, T6SS, and a full RTX toxin cluster. MLST resolved the 23 isolates into 22 sequence types, 18 of which were novel. Phylogenetic reconstruction identified a tight monophyletic cluster of three A. veronii isolates (9-27 SNP differences) recovered within a 96-h window, suggestive of a potential cluster that warrants further epidemiological investigation. Comparative genomic analysis of the rare species Aeromonas allosaccharophila demonstrated that the Beijing clinical isolate S14 differs from the U.S. clinical strain ATCC 35942 by 42,099 SNPs, confirming its distinct genetic lineage. CONCLUSION: Collectively, this study delineates high genetic diversity, emerging chromosomal colistin resistance, and species-specific virulence specialization among Aeromonas isolates from diarrheal patients in Beijing. The detection of a potential outbreak cluster and a rare clinical isolate underscores the power of genomics-based surveillance for detecting and mitigating foodborne pathogen threats.
The Aeromonas salmonicida (As) exe gene cluster, an additional member of the pul-related operon family required for general signal-sequence-dependent secretion of proteins from Gram- bacteria, was cloned in the broad-host-range cosmid pLAFR3. Twelve genes, exeC-N, were identified by partial nucleotide (nt) sequence analyses (exeE-N) or determination of the complete sequence (exeC and exeD). The organisation of the exeC-N genes is similar to that of several other operons of this family. These genes are arranged contiguously and are apparently transcribed in the same direction. On alignment of As and A. hydrophila exe sequences a 73-bp 'silent' deletion was identified close to the end of the As exeF gene. No gene encoding prepilin peptidase (the PulO homolog) was detected in this region. The exeN gene is evidently the last gene of this operon; it is followed by an ORF encoding a putative transcription regulator.
The Aeromonas salmonicida Tn5 mutant, A449-TM1, is unable to secrete the surface layer protein (A-protein) through the outer membrane. Immunogold labeling of thin sections of A449-TM1, with polyclonal antisera against the A-protein, showed the accumulation of large quantities of A-protein in an enlarged periplasm. The majority of the labeled A-protein could be seen at the poles of the cells. The ability of A449-TM1 to secrete other extracellular proteins such as hemolysin and protease was not impaired by the Tn5 insertion, which indicates that the mutation in A449-TM1 interferes with a secretion pathway specifically for the translocation of the A-protein through the outer membrane. The mutant, A449-TM1, was shown to be avirulent for fish. A cosmid clone from a gene library of A449-TM1, which contains the Tn5 insertion from the chromosome, was used to identify a 1.4 kb SaII/ClaI fragment from immediately adjacent to the Tn5 insertion. This fragment was used to identify and clone a 4 kb HindIII fragment from a chromosomal DNA digest from the wild-type strain, A449. DNA sequence analysis of this clone identified an open reading frame (ORF) of 1656 bp. The deduced product of this ORF showed sequence similarity to a family of ATP-binding secretion proteins, but appeared to be phylogenetically distinct from these proteins, consistent with its participation in a secretory pathway specific for surface layer protein.