''Lactococcus garvieae'' is a known fish
pathogen
In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ ...
affecting saltwater fish in the Far East, specifically in
rainbow trout
The rainbow trout (''Oncorhynchus mykiss'') is a species of trout native to cold-water tributaries of the Pacific Ocean in Asia and North America. The steelhead (sometimes called "steelhead trout") is an anadromous (sea-run) form of the coasta ...
, Japanese
yellowtail,
Cobia
The cobia (''Rachycentron canadum'') is a species of carangiform marine fish, the only extant representative of the genus ''Rachycentron'' and the family Rachycentridae. Other common names include black kingfish, black salmon, ling, lemonfis ...
(''Rachycentron canadum'') and
grey mullet Grey mullet can mean any of several fish in the family ''Mugilidae'' (the mullets) and having a greyish hue:
* Flathead grey mullet, ''Mugil cephalus''
* Thicklip grey mullet, ''Chelon labrosus''
* Boxlip grey mullet, ''Oedalechilus labeo
The bo ...
(''Mugil cephalus''). This bacteria causes lesions in the vascular endothelium, leading to
hemorrhages
Bleeding, hemorrhage, haemorrhage or blood loss, is blood escaping from the circulatory system from damaged blood vessels. Bleeding can occur internally, or externally either through a natural opening such as the mouth, nose, ear, urethra, vagi ...
and petechias at the surface of internal organs.
As few as 10 bacterial cells per fish can cause an infection. ''L. garvieae'' is isolated in saltwater fish in the
Far East
The ''Far East'' was a European term to refer to the geographical regions that includes East and Southeast Asia as well as the Russian Far East to a lesser extent. South Asia is sometimes also included for economic and cultural reasons.
The ter ...
and specifically in European
Rainbow Trout
The rainbow trout (''Oncorhynchus mykiss'') is a species of trout native to cold-water tributaries of the Pacific Ocean in Asia and North America. The steelhead (sometimes called "steelhead trout") is an anadromous (sea-run) form of the coasta ...
.
Host range
''Lactococcus garvieae'' is usually identified within aquatic species. However, it has also been found in subclinical intramammary infections in cows, subclinical mastitis in water buffalos, poultry meat, raw cow's milk, meat products, porcine blood from industrial abattoirs and from cat and dog tonsils.
History
''Lactococcus garvieae'' was first discovered in
rainbow trout
The rainbow trout (''Oncorhynchus mykiss'') is a species of trout native to cold-water tributaries of the Pacific Ocean in Asia and North America. The steelhead (sometimes called "steelhead trout") is an anadromous (sea-run) form of the coasta ...
raised on a Japanese fish farm in the 1950s. In 1988, ''L. garvieae'' was identified in the rainbow trout from Spanish fish farms as well. In later years, ''L. garvieae'' was isolated from several septicemic processes in fish and phenotypical and molecular taxonomic studies confirmed the same agent as ''E. seriolicida''. This species was reclassified as a junior synonym of ''L. garvieae''.
Culture and morphology
''Lactococcus garvieae'' is a facultatively
anaerobic
Anaerobic means "living, active, occurring, or existing in the absence of free oxygen", as opposed to aerobic which means "living, active, or occurring only in the presence of oxygen." Anaerobic may also refer to:
* Anaerobic adhesive, a bonding a ...
, non-motile, non-spore forming,
Gram-positive
In bacteriology, gram-positive bacteria are bacteria that give a positive result in the Gram stain test, which is traditionally used to quickly classify bacteria into two broad categories according to their type of cell wall.
Gram-positive bacte ...
ovoid
coccus
A coccus (plural cocci) is any bacterium or archaeon that has a spherical, ovoid, or generally round shape. Bacteria are categorized based on their shapes into three classes: cocci (spherical-shaped), bacillus (rod-shaped) and spiral ( of whi ...
, occurring in pairs and short chains. It can produce
α-hemolysis on
blood agar
An agar plate is a Petri dish that contains a growth medium solidified with agar, used to Microbiological culture, culture microorganisms. Sometimes selective compounds are added to influence growth, such as antibiotics.
Individual microorganism ...
(BA). It has the ability to grow at 4-45 °C in media containing 6.5% sodium chloride (NaCl) at pH 9.6. Its optimal growth temperature is 37 °C for a 24‑hour period, while at 4 °C it needs between 12 and 15 days for premium growth. It also grows rapidly in rich media, such as
brain heart infusion agar (BHIA),
trypticase soy agar
Trypticase soy agar or tryptone soya agar (TSA) and Trypticase soy broth or tryptone soya broth (TSB) with agar are growth media for the culturing of bacteria. They are general-purpose, nonselective media providing enough nutrients to allow for ...
(TSA), BA,
trypticase soy broth
Tryptic soy broth or Trypticase soy broth (frequently abbreviated as TSB) is used in microbiology laboratories as a culture broth to grow aerobic bacteria. It is a complex, general purpose medium that is routinely used to grow certain pathogenic b ...
(TSB), and
bile esculin agar
Bile Esculin Agar (BEA) is a selective differential agar used to isolate and identify members of the genus ''Enterococcus'', formerly part of the "group D streptococci" (enterococci were reclassified in their own genus in 1984).
Composition and ...
(BEA). Conversely, ''L. garvieae'' does not grow on
McConkey agar or ''
Enterococcus
''Enterococcus'' is a large genus of lactic acid bacteria of the phylum Bacillota. Enterococci are gram-positive cocci that often occur in pairs (diplococci) or short chains, and are difficult to distinguish from streptococci on physical charact ...
''
agar
Agar ( or ), or agar-agar, is a jelly-like substance consisting of polysaccharides obtained from the cell walls of some species of red algae, primarily from ogonori (''Gracilaria'') and "tengusa" (''Gelidiaceae''). As found in nature, agar is ...
. Optimum conditions for colony growth exists within
brain heart infusion broth (BHIB) where conditions include a pH range of 7-8 and a temperature range of 25-30 °C.
Epidemiology
In fish models, all clinical forms of
lactococcosis show an absence of clinical symptoms and mortalities in fish weighing under 80 grams. Smaller fish can be infected experimentally. In a follow-up study of the
pathogenicity
In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ ...
of ''L. garvieae'', younger fish at 50 grams underwent a higher mortality than older fish at about 100 grams and the acute period of the disease was reported to be longer in young fish.
Numerous investigations of ''L. garvieae'' pathogenicity have confirmed that capsulated strains, commonly classified as serotype KG−, are more virulent than non-capsulated strains, commonly classified as serotype KG+. The appearance of the disease is affected specifically by factors of the aquatic environment such as temperature and water quality.
Water temperature affects the disease seasonally as the climate changes, specifically when the water temperature is over .
Infection
An infection is the invasion of tissues by pathogens, their multiplication, and the reaction of host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmissible disease or communicable dise ...
is linked to water temperatures over 18 °C, although acute outbreaks have been discovered in water temperatures of 14–15 °C.
Low water quality caused by poor sanitary conditions has been shown to influence evolution of infection. The disease becomes more distinct when the immediate aquatic environment is poor, and oxygen deficiency increases virulence of the agent. Likewise, excessive
ammonium
The ammonium cation is a positively-charged polyatomic ion with the chemical formula or . It is formed by the protonation of ammonia (). Ammonium is also a general name for positively charged or protonated substituted amines and quaternary a ...
concentration causes an increase in mortality of fish.
Virulence
Several virulence experiments have been performed in order to determine the possible correlation between
pathogenicity
In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ ...
of ''L. garvieae'' in
rainbow trout
The rainbow trout (''Oncorhynchus mykiss'') is a species of trout native to cold-water tributaries of the Pacific Ocean in Asia and North America. The steelhead (sometimes called "steelhead trout") is an anadromous (sea-run) form of the coasta ...
and the two antigenic profiles (KG- and KG+). The results revealed that capsulated strains (KG-) were more virulent than non-capsulated (KG+), showing LD50 values as low as 102 bacteria per fish. The KG− type strain was more virulent than the KG+ because when the surface morphologies of the KG− and KG+
phenotypes
In genetics, the phenotype () is the set of observable characteristics or traits of an organism. The term covers the organism's morphology or physical form and structure, its developmental processes, its biochemical and physiological proper ...
were differentiated by
scanning electron microscopy, KG− cells were found to be more hydrophilic than KG+ cells. The immune response of
Japanese yellowtail following injection of the two phenotypes varied with higher adhering titers in the KG+ phenotype compared to the KG-.
Successively, 24 isolates of ''L. garvieae'' from different fish species and geographic origin were studied by
slide cohesion tests. These tests were conducted using rabbit antisera against representative strains with diverse origins and by Dot blot assays. These results endorsed the establishment of two different groups of isolates, but a correlation between serological group and geographic origin or host source could not be determined.
Barnes and Ellis serologically compared 17 geographically distinct strains of ''L. garvieae'' isolated from diseased
rainbow trout
The rainbow trout (''Oncorhynchus mykiss'') is a species of trout native to cold-water tributaries of the Pacific Ocean in Asia and North America. The steelhead (sometimes called "steelhead trout") is an anadromous (sea-run) form of the coasta ...
, finding that sera raised against capsule deficient isolates did not agglutinate capsulated isolates, whereas all antisera against capsulated strains cross reacted with non-capsulated isolates. The results determine that ''L. garvieae'' can be differentiated serologically into three different serotypes: a European capsulated serotype, a Japanese capsulated serotype and a non-capsulated serotype from both the European and Japanese regions.
The comparative analysis of genomes of a virulent strain Lg2 (KG-) and a non-virulent strain ATCC 49156 (KG+) of ''L. garvieae'' revealed that the two strains shared a high degree of sequence identity, but Lg2 had a 16.5-kb capsule gene cluster that is absent in ATCC 49156.
The capsule gene cluster of Lg2 may be a genomic island from several features such as the presence of insertion sequences flanked on both ends, different GC content from the chromosomal average, integration into the locus syntenic to other lactococcal genome sequences, and distribution in human gut microbiomes.
Signs and symptoms in fish
In fish, the incubation period of ''L. garvieae'' is very brief and the microorganism performs with high virulence. In an experimental infection by intraperitoneal route in
Japanese yellowtail, it caused symptoms 2–3 days post-inoculation, while intramuscular infection in
grey mullet Grey mullet can mean any of several fish in the family ''Mugilidae'' (the mullets) and having a greyish hue:
* Flathead grey mullet, ''Mugil cephalus''
* Thicklip grey mullet, ''Chelon labrosus''
* Boxlip grey mullet, ''Oedalechilus labeo
The bo ...
(''
Mugil cephalus
The flathead grey mullet (''Mugil cephalus'') is an important food fish species in the mullet family Mugilidae. It is found in coastal tropical and subtropical waters worldwide. Its length is typically . It is known with numerous English names, ...
'') produced its first symptoms and fatalities two days post-inoculation. Correspondingly, intraperitoneal experimental infection in
rainbow trout
The rainbow trout (''Oncorhynchus mykiss'') is a species of trout native to cold-water tributaries of the Pacific Ocean in Asia and North America. The steelhead (sometimes called "steelhead trout") is an anadromous (sea-run) form of the coasta ...
caused the first symptoms and deaths three days post-inoculation.
Warm water lactococcosis has been detected in a variety of host organisms, including cage cultured cobia, grey mullet, freshwater prawn and Tilapia.
The gross pathology of
lactococcosis arises with the presence of a rapid and general
anorexia
Anorexia nervosa, often referred to simply as anorexia, is an eating disorder characterized by low weight, food restriction, body image disturbance, fear of gaining weight, and an overpowering desire to be thin. ''Anorexia'' is a term of Gre ...
,
melanosis
Melanosis is a form of hyperpigmentation associated with increased melanin.
It can also refer to:
* Melanism
* Ocular melanosis
* Smoker's melanosis
* Oral melanosis
* Riehl melanosis
See also
* List of cutaneous conditions
Many skin cond ...
,
lethargy
Lethargy is a state of tiredness, sleepiness, weariness, fatigue, sluggishness or lack of energy. It can be accompanied by depression, decreased motivation, or apathy. Lethargy can be a normal response to inadequate sleep, overexertion, overwo ...
, loss of orientation, and irregular swimming. Typical external symptoms include
exophthalmia and the presence of hemorrhages in the periorbital and
intraocular area, the base of fins, the perianal region, the opercula and the
buccal region. In further studies, swollen abdomens and
anal prolapsus have been observed. Due to infection, fish have produced lesions in the
vascular
The blood vessels are the components of the circulatory system that transport blood throughout the human body. These vessels transport blood cells, nutrients, and oxygen to the tissues of the body. They also take waste and carbon dioxide away f ...
endothelium
The endothelium is a single layer of squamous endothelial cells that line the interior surface of blood vessels and lymphatic vessels. The endothelium forms an interface between circulating blood or lymph in the lumen and the rest of the vessel ...
that cause
blood
Blood is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells, and transports metabolic waste products away from those same cells. Blood in the c ...
extravasation
__NOTOC__
Extravasation is the leakage of a fluid out of its container into the surrounding area, especially blood or blood cells from vessels. In the case of inflammation, it refers to the movement of white blood cells from the capillaries to the ...
, leading to
hemorrhages
Bleeding, hemorrhage, haemorrhage or blood loss, is blood escaping from the circulatory system from damaged blood vessels. Bleeding can occur internally, or externally either through a natural opening such as the mouth, nose, ear, urethra, vagi ...
and
petechia
A petechia () is a small red or purple spot (≤4 mm in diameter) that can appear on the skin, conjunctiva, retina, and Mucous membrane, mucous membranes which is caused by haemorrhage of capillaries. The word is derived from Italian , 'freckle,' ...
e at the surface of internal organs. The main organs affected are the
spleen
The spleen is an organ found in almost all vertebrates. Similar in structure to a large lymph node, it acts primarily as a blood filter. The word spleen comes . ,
liver
The liver is a major Organ (anatomy), organ only found in vertebrates which performs many essential biological functions such as detoxification of the organism, and the Protein biosynthesis, synthesis of proteins and biochemicals necessary for ...
,
brain
A brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as vision. It is the most complex organ in a v ...
,
stomach
The stomach is a muscular, hollow organ in the gastrointestinal tract of humans and many other animals, including several invertebrates. The stomach has a dilated structure and functions as a vital organ in the digestive system. The stomach i ...
,
kidney
The kidneys are two reddish-brown bean-shaped organs found in vertebrates. They are located on the left and right in the retroperitoneal space, and in adult humans are about in length. They receive blood from the paired renal arteries; blood ...
and
heart
The heart is a muscular organ in most animals. This organ pumps blood through the blood vessels of the circulatory system. The pumped blood carries oxygen and nutrients to the body, while carrying metabolic waste such as carbon dioxide t ...
.
Macroscopic lesions in affected fish are typical of acute systemic disease with strong congestion in the internal organs and different levels of hemorrhages in the swim bladder, intestine, liver, peritoneum, spleen and kidney. Also, enlargement of the spleen, focal areas of necrosis in the liver and spleen, pericarditis, hemorrhagic fluid in the intestine, and yellowish exudate covering the brain surface are typically observed.
Histopathology
Histopathology (compound of three Greek words: ''histos'' "tissue", πάθος ''pathos'' "suffering", and -λογία '' -logia'' "study of") refers to the microscopic examination of tissue in order to study the manifestations of disease. Spe ...
is found mainly in the eyes and internal organs’ capsules. Lesions on the ocular area consist of extensive
fibroplasias with inflammatory cells penetration. In the brain, lesions exist in the cerebrum and cerebellum. Diseased fish typically show signs of acute meningitis, consisting of an exudate covering the brain surface. In the heart, lesions are usually signified by
fibroplasias,
macrophage
Macrophages (abbreviated as M φ, MΦ or MP) ( el, large eaters, from Greek ''μακρός'' (') = large, ''φαγεῖν'' (') = to eat) are a type of white blood cell of the immune system that engulfs and digests pathogens, such as cancer cel ...
, and
lymphocyte
A lymphocyte is a type of white blood cell (leukocyte) in the immune system of most vertebrates. Lymphocytes include natural killer cells (which function in cell-mediated, cytotoxic innate immunity), T cells (for cell-mediated, cytotoxic ad ...
. In kidneys, the renal tubules have hyaline droplet deposition in the epithelia and hyaline casts in the lumen.
World impact of fish infection
According to a series of studies in 2006, ''L. garvieae'' is an emerging pathogen that is causing significant economic losses both in marine and freshwater aquaculture when water temperature increases over 16 °C in summer months. This pathogen causes serious economic losses due to three main factors: elevated rates of mortality have been investigated at 50% of fish, a decrease in the growth rates of fish due to infection, and unpleasant appearance of the infected fish which makes them unmarketable to consumers.
Eradication in fish
Several vaccines have been developed to tackle ''L. garvieae'' infection in the face of rising antibiotic resistance, with whole-cell killed cells being the most common.
Human pathogen
''Lactococcus garvieae'' in humans is a rare pathogen and of low virulence. More than 31 cases of infection in humans have been reported.
These include 25 cases of endocarditis and other infections like those related to peritoneal dialysis catheters, discitis, catheter associated UTI, post TURP infection, liver abscess in a patient with cholangiocarcinoma, AICD/Pacemaker related infections to name a few.
The signs and symptoms of United States cases ranges from urinary tract, blood, skin and pneumonic processes. In Canada, patients have been found with bacterial
endocarditis
Endocarditis is an inflammation of the inner layer of the heart, the endocardium. It usually involves the heart valves. Other structures that may be involved include the interventricular septum, the chordae tendineae, the mural endocardium, or the ...
. It is speculated that the infection followed the consumption of fresh seafood and is believed to be facilitated by
immunosuppression
Immunosuppression is a reduction of the activation or efficacy of the immune system. Some portions of the immune system itself have immunosuppressive effects on other parts of the immune system, and immunosuppression may occur as an adverse react ...
or
liver cirrhosis
Cirrhosis, also known as liver cirrhosis or hepatic cirrhosis, and end-stage liver disease, is the impaired liver function caused by the formation of scar tissue known as fibrosis due to damage caused by liver disease. Damage causes tissue repai ...
.
A patient with ''L. garvieae'' septicaemia in absence of infective endocarditis was successfully treated with a combination of
ampicillin
Ampicillin is an antibiotic used to prevent and treat a number of bacterial infections, such as respiratory tract infections, urinary tract infections, meningitis, salmonellosis, and endocarditis. It may also be used to prevent group B strepto ...
and
gentamicin
Gentamicin is an antibiotic used to treat several types of bacterial infections. This may include bone infections, endocarditis, pelvic inflammatory disease, meningitis, pneumonia, urinary tract infections, and sepsis among others. It is not e ...
and showed a favourable clinical course. Antibiotic therapy adapted to the
antibiogram
Antibiotic sensitivity testing or antibiotic susceptibility testing is the measurement of the susceptibility of bacteria to antibiotics. It is used because bacteria may have resistance to some antibiotics. Sensitivity testing results can allow ...
(
levofloxacin
Levofloxacin, sold under the brand name Levaquin among others, is an antibiotic medication. It is used to treat a number of bacterial infections including acute bacterial sinusitis, pneumonia, H. pylori (in combination with other medications), ...
,
amoxicillin
Amoxicillin is an antibiotic medication used to treat a number of bacterial infections. These include middle ear infection, strep throat, pneumonia, skin infections, and urinary tract infections among others. It is taken by mouth, or less c ...
, and
Clavulanic acid
Clavulanic acid is a β-lactam drug that functions as a mechanism-based β-lactamase inhibitor. While not effective by itself as an antibiotic, when combined with penicillin-group antibiotics, it can overcome antibiotic resistance in bacteria t ...
) for eight weeks and an oral anticoagulative therapy for three months.
Bacterial endocarditis
Infective endocarditis is an infection of the inner surface of the heart, usually the valves. Signs and symptoms may include fever, small areas of bleeding into the skin, heart murmur, feeling tired, and low red blood cell count. Complications ...
from ''L. garvieae'' is extremely rare and may actually be underreported due to its morphologic and biochemical similarities with enterococci.
The source of infection in many ''L. garvieae'' infected patients is unclear, where similar cases were identified and patients denied having contact with domestic animals or fish, or eating raw fish, milk or meat and dairy products. However, a few cases had known diverticulitis of the colon, which could provide a point of entry for ''L. garvieae'' infection.
References
External links
Type strain of ''Lactococcus garvieae'' at Bac''Dive'' - the Bacterial Diversity Metadatabase
{{Taxonbar, from=Q16984199
Streptococcaceae
Bacteria described in 1984