Prevalence and Molecular Characterization of Tetracycline Resistance in Enterococcus Isolates from Food

Abstract

In the present study, a collection of 187 Enterococcus food isolates mainly originating from European cheeses were studied for the phenotypic and genotypic assessment of tetracycline (TC) resistance. A total of 45 isolates (24%) encompassing the species Enterococcus faecalis (n ‫؍‬ 33), E. durans (n ‫؍‬ 7), E. faecium (n ‫؍‬ 3), E. casseliflavus (n ‫؍‬ 1), and E. gallinarum (n ‫؍‬ 1) displayed phenotypic resistance to TC with MIC ranges of 16 to 256 g/ml. Eight of these strains exhibited multiresistance to TC, erythromycin, and chloramphenicol. By PCR detection, TC resistance could be linked to the presence of the tet(M) (n ‫؍‬ 43), tet(L) (n ‫؍‬ 16), and tet(S) (n ‫؍‬ 1) genes. In 15 isolates, including all of those for which the MIC was 256 g/ml, both tet(M) and tet(L) were found. Furthermore, all tet(M)-containing enterococci also harbored a member of the Tn916-Tn1545 conjugative transposon family, of which 12 erythromycin-resistant isolates also contained the erm(B) gene. Filter mating experiments revealed that 10 E. faecalis isolates, 3 E. durans isolates, and 1 E. faecium isolate could transfer either tet(M), tet(L), or both of these genes to E. faecalis recipient strain JH2-2. In most cases in which only tet(M) was transferred, no detectable plasmids were acquired by JH2-2 but instead all transconjugants contained a member of the Tn916-Tn1545 family. Sequencing analysis of PCR amplicons and evolutionary modeling showed that a subset of the transferable tet(M) genes belonged to four sequence homology groups (SHGs) showing an internal homology of >99.6%. Two of these SHGs contained tet(M) mosaic structures previously found in Tn916 elements and on Lactobacillus and Neisseria plasmids, respectively, whereas the other two SHGs probably represent new phylogenetic lineages of this gene.As lactic acid bacteria, enterococci are natural inhabitants of the gastrointestinal systems of mammals, but they are also known to occur in soil and fecally polluted surface waters and on plants and vegetables (26,31,35). Because of their high prevalence in the gastrointestinal tracts of many food animals, it is often unavoidable that these organisms enter the human food chain via contamination of raw milk or raw meat. For many years, the presence of enterococci in foods has been highly controversial. On the one hand, Enterococcus strains can harbor specific biochemical traits that are essential in the manufacturing of various fermented milk products, and some strains are technologically exploited as functional starters or probiotics (12, 17). On the other hand, enterococci have also been implicated in the spoilage of processed meats (14, 51) and include strains that have been recognized as emerging human pathogens mostly in nosocomial but also in community-acquired infections (for a review, see reference 29).Triggered by the apparent duality between their beneficial and harmful properties, a lot of research has focused on the potential role of food enterococci as reservoirs and/or vehicles of antibiotic resistance (AR) and viru...

Prevalence and Antibiotic-Resistance Characteristics of Enterococcus Spp. Isolated From Free-Living and Captive Raptors in Central Illinois

“…have demonstrated inducible resistance to antimicrobials such as chloramphenicol, enrofloxacin, erythromycin, and tetracycline (Huys et al, 2004;Leener et al, 2005). Many of these resistance genes are located on transferable sections of DNA (plasmids), which can be exchanged between different Enterococcus isolates (Huys et al, 2004). Although determining specific resistance genes for antimicrobial agents was outside the scope of this study, the phenotypic resistance characteristics seen in this study closely parallel previously reported genetic characteristics of Enterococcus.…”

“…In addition to innate resistance, Enterococcus spp. have demonstrated inducible resistance to antimicrobials such as chloramphenicol, enrofloxacin, erythromycin, and tetracycline (Huys et al, 2004;Leener et al, 2005). Many of these resistance genes are located on transferable sections of DNA (plasmids), which can be exchanged between different Enterococcus isolates (Huys et al, 2004).…”

Detection and characterization of tet(M) in tetracycline-resistant Listeria strains from human and food-processing origins in Belgium and France

“…Purified tet(M) amplimers were sequenced directly with the DI, DII and TetM-R primers (Gevers et al, 2003;Huys et al, 2004) in order to obtain a 1420 bp partial sequence (74 % of the 1920 bp open reading frame) of the tet(M) gene. Sequencing was performed with a BigDye Terminator version 2 Ready Reaction cycle sequencing kit (Applied Biosystems) on an ABI Prism 310 Genetic Analyzer (Applied Biosystems).…”

“…In previous studies, it has been shown that the tet(M) gene can display several mosaic structures, leading to the recognition of at least five different sequence homology groups (SHGs I-V) (Gevers et al, 2003;Huys et al, 2004). In order to investigate whether any of these SHGs are also represented in the four tet(M)-containing Listeria strains of this current study, the open reading frame of this gene was partially sequenced and aligned with a selection of tet(M) reference sequences (Fig.…”

Safety Evaluation Of Sjenica Cheese With Regard To Coagulase-Positive Staphylococci And Antibiotic Resistance Of Lactic Acid Bacteria And Staphylococci

“…Hence, the investigation of LAB antibiotic resistance patterns may represent an effi cient tool in predicting the antibiotic resistance among clinical pathogens. Extensive literature data pointed out that genes conferring resistance to several antimicrobials (i.e., chloramphenicol, erythromycin, streptomycin, tetracycline, and vancomycin), hosted on mobile genetic elements, have been characterized in lactococci [44], lactobacilli [45,46] and enterococci [47,48] from food.…”