Bovine Lactoferrin and Hen Ovotransferrin Affect Virulence Factors of Acute Hepatopancreatic Necrosis Disease (AHPND)-Inducing Vibrio parahaemolyticus Strains

Lactoferrin impairs pathogen virulence through its proteolytic activity

Antibiotics, often hailed as 'miracle drugs' in the 20th century, have revolutionised medicine by saving millions of lives in human and veterinary medicine, effectively combatting bacterial infections. However, the escalating global challenge of antimicrobial resistance and the appearance and spread of multidrug-resistant pathogens necessitates research into alternatives. One such alternative could be lactoferrin. Lactoferrin, an iron-binding multifunctional protein, is abundantly present in mammalian secretions and exhibits antimicrobial and immunomodulatory activities. An often overlooked aspect of lactoferrin is its proteolytic activity, which could contribute to its antibacterial activity. The proteolytic activity of lactoferrin has been linked to the degradation of virulence factors from several bacterial pathogens, impeding their colonisation and potentially limiting their pathogenicity. Despite numerous studies, the exact proteolytically active site of lactoferrin, the specific bacterial virulence factors it degrades and the underlying mechanism remain incompletely understood. This review gives an overview of the current knowledge concerning the proteolytic activity of lactoferrins and summarises the bacterial virulence factors degraded by lactoferrins. We further detail how a deeper understanding of the proteolytic activity of lactoferrin might position it as a viable alternative for antibiotics, being crucial to halt the spread of multi-drug resistant bacteria.

Genomic mining of Vibrio parahaemolyticus highlights prevalence of antimicrobial resistance genes and new genetic markers associated with AHPND and tdh + /trh + genotypes

BACKGROUND

Acute Hepatopancreatic Necrosis Disease (AHPND) causes significant mortality in shrimp aquaculture. The infection is primarily instigated by Vibrio parahaemolyticus (Vp) strains carrying a plasmid encoding the binary toxin PirAB. Yet, comprehension of supplementary virulence factors associated with this relatively recent disease remains limited. Furthermore, the same holds for gastroenteritis in humans caused by other Vp genotypes. Additionally, given the prevalent use of antibiotics to combat bacterial infections, it becomes imperative to illuminate the presence of antimicrobial resistance genes within these bacteria.

RESULTS

A subsampled number of 1,036 Vp genomes was screened for the presence of antimicrobial resistance genes, revealing an average prevalence of 5 ± 2 (SD) genes. Additional phenotypic antimicrobial susceptibility testing of three Vp strains (M0904, TW01, and PV1) sequenced in this study demonstrated resistance to ampicillin by all tested strains. Additionally, Vp M0904 showed multidrug resistance (against ampicillin, tetracycline, and trimethoprim-sulfamethoxazole). With a focus on AHPND, a screening of all Vibrio spp. for the presence of pirA and/or pirB indicates an estimated prevalence of 0.6%, including four V. campbellii, four V. owensii, and a Vibrio sp. next to Vp. Their pirAB-encoding plasmids exhibited a highly conserved backbone, with variations primarily in the region of the Tn3 family transposase. Furthermore, an assessment of the subsampled Vp genomes for the presence of known virulence factors showed a correlation between the presence of the Type 3 Secretion System 2 and tdh, while the presence of the Type 6 Secretion System 1 was clade dependent. Furthermore, a genome-wide association study (GWAS) unveiled (new) genes associated with pirA, pirB, tdh, and trh genotypes. Notable associations with the pirAB genotype included outer membrane proteins, immunoglobulin-like domain containing proteins, and toxin-antitoxin systems. For the tdh + /trh + genotypes (containing tdh, trh, or both genes), associations were found with T3SS2 genes, urease-related genes and nickel-transport system genes, and genes involved in a 'minimal' type I-F CRISPR mechanism.

CONCLUSIONS

This study highlights the prevalence of antimicrobial resistance and virulence genes in Vp, identifying novel genetic markers associated with AHPND and tdh + /trh + genotypes. These findings contribute valuable insights into the genomic basis of these genotypes, with implications for shrimp aquaculture and food safety.