Antimicrobe.org: Lactococcus species (Lactococci)
drsuryabrata@gmail.comGENERAL DESCRIPTION
Microbiology Guided Medline Search
Lactococci are gram-positive cocci that arrange in pairs and short chains with a tendency to an ovoid shape in the direction of the chain. They grow in catalase-negative, non-pigmented, generally non-hemolytic colonies on blood agar, similar to oral streptococci. Previously classified as group N streptococci, 16S rRNA sequencing and DNA-DNA relatedness studies, as well as physiologic criteria, have elevated these organisms to a separate genus, which also includes organisms previously classified as lactobacilli (15). Seven strains are currently recognized, although only Lactococcus lactis subspecies lactis and Lactococcus garvieae have been isolated with any regularity from human sources (3). One infection due to Lactococcus lactis subspecies cremoris has been recently reported (13). Lactococci have been misidentified as enterococci, since they are usually PYRase positive, usually grow 6.5% NaCl in and may grow in bile esculin (3, 5). Misidentification as oral streptococci is common after susceptibility testing is reviewed.
Epidemiology Guided Medline Search
Lactococcus lactis species are important in starter cultures of cheese and fermented milk products and only recently have been recognized as probable human pathogens. It is not clear whether or not lactococci are a part of normal oral flora, but they can be isolated from the mouth. They can remain in colonic flora for several days after consumption, but their numbers disappear with time (10). Lactococcus garvieae is a mastitis pathogen in cows and buffaloes and a fatal pathogen to fish, reaching an economic importance in trout farming (16). Human infections with lactococci have been anecdotally linked to fermented milk product consumption (1, 2, 17).
Clinical Manifestations Guided Medline Search
Five cases of subacute, infectious endocarditis due to Lactococcus garvieae have been reported, with 4 of the cases occurring on prosthetic valves (6, 7, 9). Two cases of suspected subacute, infectious endocarditis due to Lactococcus lactis subspecies lactis have been reported (11, 17). Lactococcus garvieae has been reported to cause a case of vertebral discitis and osteomyelitis (9) and a case of a liver abscess in the setting a biliary stent (12). Lactococcus lactis subspecies lactis was reported to cause a case of septic hip arthritis, which evolved into osteomyelitis (1). Twenty-one other isolates of lactococci have been reported from blood cultures, 4 from the urinary tract, 2 from wounds and one each from pleural fluid, brain abscess material, eye, and skin (3, 5). No deaths have been directly attributed to a lactococcus infection, although deaths have occurred during active infections (6, 12).
Laboratory Diagnosis Guided Medline Search
Lactococci are readily grown on media routinely used in clinical microbiology laboratories. The physiologic criteria for identifying Lactococcus species have been described (3, 4, 5), although there are discrepancies between physiologic findings and genetic identification methods (4). The reliability of commercial physiologic testing systems is unproven, although some success has been reported with API rapid 32 strep (bioMérieux) (9, 12). The identification of Lactococcus species may be missed in many clinical laboratories due to limited physiologic testing performed upon isolates resembling enterococci or oral streptococci. The greater susceptibility to antimicrobial agents of lactococci in comparison to enterococci should aid in their differentiation, although the common use of automated restricted susceptibility reporting for items presumed to be enterococci may hide these differences. Antimicrobial susceptibility studies can also help speciation between L. garvieae and L. lactis subspecies lactis by their differing clindamycin susceptibilities (4).
Pathogenesis Guided Medline Search
Lactococci seem to be of low pathogenic potential, apparently similar to or less virulent than oral streptococci. Lactococcus garvieae seems to be the more pathogenic of the species encountered due to its more frequent clinical isolation and its pathogenic potential in fish and animals. Considering the frequent enteral exposure to Lactococcus lactis species in commercial food products, relatively few infections have been noted.
SUSCEPTIBILITY IN VITRO AND IN VIVO Guided Medline SearchIn Vitro and In Vivo
Single Drug
Limited information is available on in vitro susceptibility of lactococci. Table 1 reports the extent of known susceptibility ranges L. lactis ss. lactis and L. garvieae. As noted, the antimicrobial susceptibility patterns of lactococci are similar to those of oral streptococci. Aminoglycoside sensitivity has been variable in non-clinical isolates of lactococci (14). Of note are the differences in clindamycin susceptibility in most known strains of L. garvieae from L. lactis ss. lactis, with L. garvieae being clindamycin-resistant, a feature proposed to help in these species differentiation (4). Vancomycin resistance has not been detected; reevaluation of the bacteria previously reported as vancomycin-resistant lactococci (8) revealed that they were actually Pediococcus species (4).
Combination Drugs
There is no data on post-antibiotic effect, antimicrobial synergy, or bactericidal activity on lactococci, except for a report of strong serum bactericidal activity with penicillin and gentamicin against a single isolate of Lactococcus lactis subspecies lactis (11).
ANTIMICROBIAL THERAPY Smart search
Drug of Choice Guided Medline Search
Available data suggests that penicillin is the drug of choice for infections due to Lactococcus species. Penicillin therapy resolved an infectious hip arthritis with osteomyelitis even without surgery (1). Penicillin and aminoglycosides cured 2 cases of endocarditis (11, 17). Teichoplanin cured a case of intervertebral discitis/osteomyelitis (9) and cefotaxime and amikacin were used successfully in a bacteremia of unclear source (2).
Special Infections
Endocarditis: Guided Medline Search
Due to antimicrobial susceptibility similarities to oral streptococci it is tempting to use aminoglycosides in an attempt to achieve synergistic bactericidal activity in cases of endocarditis due to lactococci. Data supporting this recommendation is not available, other than the strong serum bactericidal activity reported in one case (11) and the clinical success of combination therapy in 2 cases (11, 17). Efforts should be made to assure bactericidal antimicrobial activity in cases of endocarditis, either by in vitro methods or by serum bacteristatic and bactericidal titers. Treatment should be continued at least as long as that for similar infections due to oral streptococci.
Underlying Diseases
Lactococci have shown no particular predilection to any underlying condition, although 2 cases have occurred in patients with illnesses requiring corticosteroids (2, 12). All cases have been acquired in the community; no cases have been nosocomial.
Alternative Therapy
In situations where penicillin cannot be used, vancomycin, erythromycin or possibly trimethoprim/sulfamethoxazole are reasonable alternatives for infections due to lactococci. Clinical data on alternative therapies is limited and is described above. In vitro susceptibility testing results should be used to direct therapy. Susceptibility testing should be required for clindamycin before it is used in lactococcal infections, due to consistent resistance in Lactococcus garvieae.
Combination Therapy: As mentioned above under the special situation of endocarditis, the antimicrobial sensitivity and physiologic similarities of lactococci to oral streptococci bring penicillin/aminoglycoside combination therapy to mind in serious infections due to lactococci. Penicillin/aminoglycoside combination therapy has been effective in 2 cases of endocarditis (11, 17) and a cephalosporin/aminoglycoside combination was used successfully in a bacteremia (2).
(Printable Version of Antimicrobial Therapy for Lactococcus)
ADJUNCTIVE THERAPY Guided Medline Search
Adjunctive therapies are not necessary.
ENDPOINTS FOR MONITORING THERAPY Guided Medline Search
There are no specific endpoints due to the low virulence of these bacteria.
VACCINES Guided Medline Search
There are no vaccines in use or in development against lactococci.
PREVENTION Guided Medline Search Smart search
There are no special preventive measures.
TABLE 1.The MIC Range (mgml) of 6 Strains of L. lactis ss. lactis and 13 Strains of L. garvieae (4).
REFERENCES
1. Campbell P, Dealler S, Lawton JO. Septic arthritis and unpasteurised milk. J Clin Pathol 1993;46:1057-1058. [PubMed]
2. Durand JM, Rousseau MC, Gandois JM, Kaplanski G, Mallet MN, Soubeyrand J. Streptococcus lactis septicemia in a patient with chronic lymphocytic leukemia. Am J Hematol 1995;50:64-65. [PubMed]
3. Elliott JA, Collins MD, Pigott NE, Facklam RR. Differentiation of Lactococcus lactis and Lactococcus garvieae from humans by comparison of whole - cell protein patterns. J Clin Microbiol 1991;29:2731-2734. [PubMed]
4. Elliott JA, Facklam RR. Antimicrobial susceptibilities of Lactococcus lactis and Lactococcus garvieae and a proposed method to discriminate between them. J Clin Microbiol 1996;34:1296-1298. [PubMed]
5. Facklam R, Elliott JA. Identification, classification, and clinical relevance of catalase-negative, gram-positive cocci, excluding the streptococci and enterococci. Clin Microbiol Rev 1995;8:479-495. [PubMed]
6. Fefer J, Ratzan KR, Sharp SE, Saiz E. Lactococcus garvieae endocarditis: report of a case and review of the literature. Diagn Microbiol Infect Dis 1998;32:127-130. [PubMed]
7. Furutan NP, Breiman RF, Fischer MA, Facklam RR. Lactococcus garvieae infections in humans: a cause of prosthetic valve endocarditis. Abstract 91st Gen Meet Am Soc Microbiol 1991;p109:C-297. American Society for Microbiology, Washington, D.C. [PubMed]
8. Green M, Wadowsky RM, Barbadora K. Recovery of vancomycin-resistant gram-positive cocci from children. J Clin Microbiol 1990;28:484-488. [PubMed]
9. James PR, Hardman SM, Patterson DL. Osteomyelitis and possible endocarditis secondary to Lactococcus garvieae: a first case report. Postgrad Med J 2000;76:301-303. [PubMed]
10. Klijn N, Weerkamp AH, de Vos WM. Genetic marking of Lactococcus lactis shows its survival in the human gastrointestinal tract. Appl Environ Microbiol 1995;61: 2771-2774. [PubMed]
11. Mannion PT, Rothburn MM. Diagnosis of bacterial endocarditis caused by streptococcus lactis and assisted by immunoblotting of serum antibodies. J Infection 1990; 21:317-326. [PubMed]
12. Mofredj A, Baraka D, Cadranel JF, LeMaitre P, Kloeti G, Dumont JL. Lactococcus garvieae septicemia with liver abscess in an immunosuppressed patient. Am J Med 2000:109:513-514. [PubMed]
13. Nakarai T, Morita K, Nojiri Y, Kawamori Y. Liver abscess due to Lactococcus lactis cremoris. Pediatr Int 2000;42:699-701. [PubMed]
14. Orberg PK, Sandine WE. Survey of antimicrobial resistance in lactic streptococci. Appl Environ Microbiol 1985;49:538-542. [PubMed]
15. Schleifer KH, Kraus J, Dvorak C, Kilpper-Balz R, Collins MD, Fischer W. Transfer of Streptococcus lactis and related streptococci to the genus Lactococcus gen nov. System Appl Microbiol 1985;6:183-195. [PubMed]
16. Vela AI, Vázquez J, Gibello A, Blanco MM, Moreno MA, Liébana P, Albendea C, Alcalá B, Mendez A, Domínguez L, Fernández-Garayzágal JF. Phenotypic and genetic characterization of Lactococcus garvieae isolated in Spain from lactococcosis outbreaks and comparison with isolated of other countries and sources. J Clin Microbiol 2000;38:3791-3795. [PubMed]
17. Wood HF, Jacobs K, McCarty M. Streptococcus lactis isolated from a patient with subacute bacterial endocarditis. Am J Med 1955;18:345-347. [PubMed]
