#lactococcus

Lactococcus garviae is a Gram positive coccus that somewhat resembles Enterococci. It is a known animal pathogen having originally been isolated from cases of bovine mastitis.  It also causes pneumonia in pigs, and haemorrhagic septicaemia in fish (Gibello, 2016).  Many recent publications in the literature relate to its impact on aquaculture where it is a major pathogen (Meyburgh, 2017).

I encountered my first clinical isolate of L. garviae (from the blood culture of a patient) in April 2012. A quick internet search found that L. garviae bacteraemia had been associated with raw fish consumption in Taiwan (Wang CY, 2007) and could lead to endocarditis. That of course captured my interest as I am a collector of exotic zoonotic pathogens. Our lab has been archiving any L. garviae we have isolated since then.

There have been 30 non-duplicate cases of L. garviae from 2012 to 2020. Most were isolated from blood (12), with the remainder from urine (6), wounds (4), bile (6), catheter (1), ear abscess (1). Often L. garviae was isolated with other bacteria in a mixed culture.

Of the wound isolates, three were from the finger, and in two cases where the mechanism of injury was documented, the patient had been chopping meat (not detailed).

Of the blood culture isolates, six were from post-mortem specimens and therefore of uncertain significance. Of the remaining six, three were from patients that underwent 2D-echo and had no evidence of endocarditis.  The remaining isolate was from a patient with a mitral valve bioprosthesis, who was managed for endocarditis even though no vegetations were seen on echo. Two patients did not have 2D-echo performed.

So L. garviae did not seem to be particularly associated with endocarditis in our local context but how were patients acquiring them? I knew from my studies on  Group B Streptococci that L. garviae are readily isolated from local fish.

In all our patients, there was no history of raw fish ingestion but taking an accurate food history in Singapore is a very fraught undertaking. There was also the possibility of other food sources given the animal reservoirs described above with L. garviae also being found in meat (Comi, 2020) and dairy (Scillieri, 2020) products.

With the help of 2 Ngee Ann Polytechnic students (Snow Lin and Kwek Kah Hao) we subjected all isolates in our archive collection from 2012-2018 to whole genome sequencing and compared them with whatever sequences of L. garviae that were available to see if we could find answers.

In total 11 local isolates were sequenced (Table).
 Virulence and antimicrobial resistance genes were identified. The strains were typed using multi-locus sequence typing (MLST) and compared with other published whole genome sequences from L. garvieae isolated overseas.

Local isolates had more resistance genes compared with the overseas isolates. 

Based on the MLST result, L. garviae can be divided into 3 lineages or genetic clusters (GC) (Figure). Non-human GC1 isolates overseas came from fish, meat and dairy sources.
 Non-human GC2 isolates overseas came from fish, plant and dairy sources.
 Most GC3 isolates overseas were from human sources (1 pork).
 We also noticed that some virulence genes (putative internalin and mucus adhesin) were present in GC2 and GC3, 
but not GC1. 


Local fish and human isolates were scattered across the 3GCs 
illustrating the heterogeneity of local isolates.
 

DB44798 from local human blood shared a common sequence type (ST) with isolate 138 from human urine in 
Spain and belonged to the same clonal complex (CC3) as FISH1 from local Cobia. Most CC3 
isolates overseas have so far been found in humans and dairy products.


DM12426 isolated from local human finger shared common ST41 with CT2 isolated from a local 
Bighead Carp.


Because the existing MLST database is not very discriminatory, we couldn’t really narrow down a specific food source for our human L garviae isolates, however it is also possible that they may really come from diverse sources.

This work has since been published (Lin YS, 2020).

 Gibello A, Galán-Sánchez F, Blanco MM, Rodríguez-Iglesias M, Domínguez L, Fernández-Garayzábal JF. The zoonotic potential of Lactococcus garvieae: An overview on microbiology, epidemiology, virulence factors and relationship with its presence in foods. Res Vet Sci. 2016 Dec;109:59-70.  (no free access)

Meyburgh CM, Bragg RR, Boucher CE. Lactococcus garvieae: an emerging bacterial pathogen of fish. Dis Aquat Organ. 2017 Feb 8;123(1):67-79.  (open access)

Wang CY, Shie HS, Chen SC, Huang JP, Hsieh IC, Wen MS, Lin FC, Wu D. Lactococcus garvieae infections in humans: possible association with aquaculture outbreaks. Int J Clin Pract. 2007 Jan;61(1):68-73. (no free access)

Comi G, Muzzin A, Corazzin M, Iacumin L. Lactic Acid Bacteria: Variability Due to Different Pork Breeds, Breeding Systems and Fermented Sausage Production Technology. Foods. 2020 Mar 13;9(3):338.  (open access)

Scillieri Smith JC, Moroni P, Santisteban CG, Rauch BJ, Ospina PA, Nydam DV. Distribution of Lactococcus spp. in New York State dairy farms and the association of somatic cell count resolution and bacteriological cure in clinical mastitis samples. J Dairy Sci. 2020 Feb;103(2):1785-1794. (open access)