Characterisation of Listeria monocytogenes isolates from cattle using a bovine caruncular epithelial cell model

Abstract

Listeria monocytogenes is an important foodborne pathogen in human and veterinary health, causing significant morbidity and mortality including abortion. It has a particular tropism for the gravid uterus, however, the route of infection in reproductive tissues of ruminants (i.e. placentome), is much less clear. In this study, we aimed to investigate a bovine caruncular epithelial cell (BCEC) line as a model for L. monocytogenes infection of the bovine reproductive tract. The BCEC infection model was used to assess the ability of 14 different L. monocytogenes isolates to infect these cells. Lysozyme sensitivity and bacterial survival in 580 μg lysozyme/ml correlated with attenuated ability to proliferate in BCEC (p = 0.004 and p = 0.02, respectively). Four isolates were significantly attenuated compared to the control strain 10403S. One of these strains (AR008) showed evidence of compromised cell wall leading to increased sensitivity to ß-lactam antibiotics, and another (7644) had compromised cell membrane integrity leading to increased sensitivity to cationic peptides. Whole genome sequencing followed by Multi Locus Sequence Type analysis identified that five invasive isolates had the same sequence type, ST59, despite originating from three different clinical conditions. Virulence gene analysis showed that the attenuated isolate LM4 was lacking two virulence genes ( uhpT , virR ) known to be involved in intracellular growth and virulence. In conclusion, the BCEC model was able to differentiate between the infective potential of different isolates. Moreover, resistance to lysozyme correlated with the ability to invade and replicate within BCEC, suggesting co-selection for surviving challenging environments as the abomasum.

Listeria monocytogenesat the interface between ruminants and humans: A comparative pathology and pathogenesis review

“…Clinically associated strains, however, often display marked lysozyme resistance together with enhanced invasiveness. 22,302 It has therefore been speculated that these strains might better survive abomasal passage and are more efficient in invading conjunctival and caruncular epithelial tissues.…”

“…1). 22,79,220,221,277 However, the cause for the epidemiologically evident predominance of a limited number of subtypes in clinical cases of both humans and ruminants is not exactly understood. Host-associated hypervirulent clones have been shown to possess conserved virulence genes, 17,149,192,199 whereas environmental clones may harbor inactivating mutations of such genes, making them hypovirulent and potentially accounting for their sporadic association with disease.…”

“…5,42,49,209,216 Notably, lesions appear to be continuous along the neuraxis, with generally higher severity and chronicity in the pontomedullary area than in other brain regions (Figs. [16][17][18][19][20][21][22]. 42,209 Microabscesses can range from small, delineated lesions to large coalescing areas, occurring both in gray and white matter.…”

“…97 The role of the previously mentioned virulence factors in ruminants has not been characterized, as in vitro models of ruminant placental infection are only recently being developed. 22,249,253,254 As hypervirulent strains (CC1, CC4-CC217, CC6, 221 CC14, 277 CC59 22 ) are associated with abortions, knowledge on pathomechanisms of fetoplacental infection in ruminants might benefit from investigation of such strains in these in vitro systems.…”