Conjugal Transfer of the Tn916-like Transposon TnFO1 from Enterococcus faecalis Isolated from Cheese to Other Gram-positive Bacteria

Survival strategies of Listeria monocytogenes to environmental hostile stress: biofilm formation and stress responses

Listeria monocytogenes is a critical foodborne pathogen that causes listeriosis and threatens public health. This pathogenic microorganism forms a transmission cycle in nature, food industry, and humans, expanding the areas of contamination among them and influencing food safety. L. monocytogenes forms biofilms to protect itself and promotes survival through stress responses to the various stresses (e.g., temperature, pH, and antimicrobial agents) that may be inflicted during food processing. Biofilms and mechanisms of resistance to hostile external or general stresses allow L. monocytogenes to survive despite a variety of efforts to ensure food safety. The current review article focuses on biofilm formation, resistance mechanisms through biofilms, and external specific or general stress responses of L. monocytogenes to help understand the unexpected survival rates of this bacterium; it also proposes the use of obstacle technology to effectively cope with it in the food industry.

Novel macrolide-lincosamide-streptogramin B resistance gene erm(56) in Trueperella pyogenes

Whole-genome sequence analysis of a macrolide, lincosamide, streptogramin B (MLSB)-resistant Trueperella pyogenes from a dog revealed a new 23S ribosomal RNA methylase gene erm(56). Expression of the cloned erm(56) confers resistance to MLSB in T. pyogenes and Escherichia coli. The erm(56) gene was flanked by two IS6100 integrated on the chromosome next to a sul1-containing class 1 integron. GenBank query revealed additional erm(56)-containing elements in another T. pyogenes and in Rothia nasimurium from livestock. IMPORTANCE A novel 23S ribosomal RNA methylase gene erm(56) flanked by insertion sequence IS6100 was identified in a Trueperella pyogenes isolated from the abscess of a dog and was also present in another T. pyogenes and in Rothia nasimurium from livestock. It was shown to confer resistance to macrolide, lincosamide, streptogramin B antibiotics in T. pyogenes and E. coli, indicating functionality in both Gram-positive and Gram-negative bacteria. The detection of erm(56) on different elements in unrelated bacteria from different animal sources and geographical origins suggests that it has been independently acquired and likely selected by the use of antibiotics in animals.

Genome analysis of probiotic bacteria for antibiotic resistance genes

To date, probiotic bacteria are used in the diet and have various clinical applications. There are reports of antibiotic resistance genes in these bacteria that can transfer to other commensal and pathogenic bacteria. The aim of this study was to use whole-genome sequence analysis to identify antibiotic resistance genes in a group of bacterial with probiotic properties. Also, this study followed existing issues about the importance and presence of antibiotic resistance genes in these bacteria and the dangers that may affect human health in the future. In the current study, a collection of 126 complete probiotic bacterial genomes was analyzed for antibiotic resistance genes. The results of the current study showed that there are various resistance genes in these bacteria that some of them are transferable to other bacteria. The tet(W) tetracycline resistance gene was more than other antibiotic resistance genes in these bacteria and this gene was found in Bifidobacterium and Lactobacillus. In our study, the most numbers of antibiotic resistance genes were transferred with mobile genetic elements. We propose that probiotic companies before the use of a micro-organism as a probiotic, perform an antibiotic susceptibility testing for a large number of antibiotics. Also, they perform analysis of complete genome sequence for prediction of antibiotic resistance genes.

Listeria monocytogenes Virulence, Antimicrobial Resistance and Environmental Persistence: A Review

Listeria monocytogenes is a ubiquitous opportunistic pathogen responsible for the well-known listeriosis disease. This bacterium has become a common contaminant of food, threatening the food processing industry. Once consumed, the pathogen is capable of traversing epithelial barriers, cellular invasion, and intracellular replication through the modulation of virulence factors such as internalins and haemolysins. Mobile genetic elements (plasmids and transposons) and other sophisticated mechanisms are thought to contribute to the increasing antimicrobial resistance of L. monocytogenes. The environmental persistence of the pathogen is aided by its ability to withstand environmental stresses such as acidity, cold stress, osmotic stress, and oxidative stress. This review seeks to give an insight into L. monocytogenes biology, with emphasis on its virulence factors, antimicrobial resistance, and adaptations to environmental stresses.

The novel macrolide-Lincosamide-Streptogramin B resistance gene erm(44) is associated with a prophage in Staphylococcus xylosus

A novel erythromycin ribosome methylase gene, erm(44), that confers resistance to macrolide, lincosamide, and streptogramin B (MLSB) antibiotics was identified by whole-genome sequencing of the chromosome of Staphylococcus xylosus isolated from bovine mastitis milk. The erm(44) gene is preceded by a regulatory sequence that encodes two leader peptides responsible for the inducible expression of the methylase gene, as demonstrated by cloning in Staphylococcus aureus. The erm(44) gene is located on a 53-kb putative prophage designated ΦJW4341-pro. The 56 predicted open reading frames of ΦJW4341-pro are structurally organized into the five functional modules found in members of the family Siphoviridae. ΦJW4341-pro is site-specifically integrated into the S. xylosus chromosome, where it is flanked by two perfect 19-bp direct repeats, and exhibits the ability to circularize. The presence of erm(44) in three additional S. xylosus strains suggests that this putative prophage has the potential to disseminate MLSB resistance.

New MLSB resistance gene erm(43) in Staphylococcus lentus

The search for a specific rRNA methylase motif led to the identification of the new macrolide, lincosamide, and streptogramin B resistance gene erm(43) in Staphylococcus lentus. An inducible resistance phenotype was demonstrated by cloning and expressing erm(43) and its regulatory region in Staphylococcus aureus. The erm(43) gene was detected in two different DNA fragments, of 6,230 bp and 1,559 bp, that were each integrated at the same location in the chromosome in several S. lentus isolates of human, dog, and chicken origin.

New transposon Tn6133 in methicillin-resistant Staphylococcus aureus ST398 contains vga(E), a novel streptogramin A, pleuromutilin, and lincosamide resistance gene

A novel streptogramin A, pleuromutilin, and lincosamide resistance determinant, Vga(E), was identified in porcine methicillin-resistant Staphylococcus aureus (MRSA) ST398. The vga(E) gene encoded a 524-amino-acid protein belonging to the ABC transporter family. It was found on a multidrug resistance-conferring transposon, Tn6133, which was comprised of Tn554 with a stably integrated 4,787-bp DNA sequence harboring vga(E). Detection of Tn6133 in several porcine MRSA ST398 isolates and its ability to circularize suggest a potential for dissemination.

Identification of tet(M) in two Lactococcus lactis strains isolated from a Spanish traditional starter-free cheese made of raw milk and conjugative transfer of tetracycline resistance to lactococci and enterococci

Specific PCR and sequencing showed that a tet(M) gene was present in two tetracycline-resistant Lactococcus lactis strains isolated from a raw milk, starter-free cheese. Hybridisation experiments using as a probe an internal segment of the gene obtained by PCR associated tet(M) with plasmids of around the same size (30 kbp) in both strains. Molecular analysis of the tetracycline resistance loci, including the upstream and downstream regions of the genes, showed them to be identical to one other and to the tet(M) encoded by the conjugative transposon Tn916. Amplification of Tn916-derived segments suggested the transposon was complete in the two L. lactis strains. Further, curing of the tetracycline resistance was accompanied by a reduction in size of the plasmids comparable to that expected for Tn916. Tetracycline resistance could be transferred by conjugation to plasmid-free Lactococcus and Enterococcus strains. However, no plasmid DNA was detected among the transconjugants while both tet(M) and transposon-related sequences were amplified by PCR. This suggested that only the transposon was mobilized.

Genetic diversity among Enterococcus faecalis

Enterococcus faecalis, a ubiquitous member of mammalian gastrointestinal flora, is a leading cause of nosocomial infections and a growing public health concern. The enterococci responsible for these infections are often resistant to multiple antibiotics and have become notorious for their ability to acquire and disseminate antibiotic resistances. In the current study, we examined genetic relationships among 106 strains of E. faecalis isolated over the past 100 years, including strains identified for their diversity and used historically for serotyping, strains that have been adapted for laboratory use, and isolates from previously described E. faecalis infection outbreaks. This collection also includes isolates first characterized as having novel plasmids, virulence traits, antibiotic resistances, and pathogenicity island (PAI) components. We evaluated variation in factors contributing to pathogenicity, including toxin production, antibiotic resistance, polymorphism in the capsule (cps) operon, pathogenicity island (PAI) gene content, and other accessory factors. This information was correlated with multi-locus sequence typing (MLST) data, which was used to define genetic lineages. Our findings show that virulence and antibiotic resistance traits can be found within many diverse lineages of E. faecalis. However, lineages have emerged that have caused infection outbreaks globally, in which several new antibiotic resistances have entered the species, and in which virulence traits have converged. Comparing genomic hybridization profiles, using a microarray, of strains identified by MLST as spanning the diversity of the species, allowed us to identify the core E. faecalis genome as consisting of an estimated 2057 unique genes.

Antibiotic resistance in non-enterococcal lactic acid bacteria and bifidobacteria

Over the last 50 years, human life expectancy and quality of life have increased dramatically due to improvements in nutrition and the use of antibiotics in the fight against infectious diseases. However, the heyday of antibiotic treatment is on the wane due to the appearance and spread of resistance among harmful microorganisms. At present, there is great concern that commensal bacterial populations from food and the gastrointestinal tract (GIT) of humans and animals, such as lactic acid bacteria (LAB) and bifidobacteria, could act as a reservoir for antibiotic resistance genes. Resistances could ultimately be transferred to human pathogenic and opportunistic bacteria hampering the treatment of infections. LAB species have traditionally been used as starter cultures in the production of fermented feed and foodstuffs. Further, LAB and bifidobacteria are normal inhabitants of the GIT where they are known to exert health-promoting effects, and selected strains are currently been used as probiotics. Antibiotic resistance genes carried by LAB and bifidobacteria can be transferred to human pathogenic bacteria either during food manufacture or during passage through the GIT. The aim of this review is to address well-stated and recent knowledge on antibiotic resistance in typical LAB and bifidobacteria species. Therefore, the commonest antibiotic resistance profiles, the distinction between intrinsic and atypical resistances, and some of the genetic determinants already discovered will all be discussed.

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

In the present study, three Listeria monocytogenes strains and one Listeria innocua strain out of a collection of 241 Listeria isolates from human and food-processing sources were found to display resistance to tetracycline (TC) due to the presence of the tet(M) gene. Through sequence analysis, it was shown that tet(M) genes in two of the isolates belong to sequence homology group (SHG) II, a group comprising chromosomally encoded tet(M) genes previously found in Staphylococcus aureus and in lactobacilli. The tet(M) genes of the two other L. monocytogenes strains were associated with a member of the Tn916-Tn1545 family of conjugative transposons and were closely related to SHG III, which harbours enterococcal tet(M) genes associated with Tn916. One of these transposon-containing strains was able to transfer the tet(M) gene to Enterococcus faecalis recipient strain JH2-2. Collectively, these sequence and conjugation data indicate that the acquisition of tet(M) by Listeria strains may be triggered by successive transfers between other Gram-positive organisms.

Antibiotic resistance in food lactic acid bacteria--a review

Antibiotics are a major tool utilized by the health care industry to fight bacterial infections; however, bacteria are highly adaptable creatures and are capable of developing resistance to antibiotics. Consequently, decades of antibiotic use, or rather misuse, have resulted in bacterial resistance to many modern antibiotics. This antibiotic resistance can cause significant danger and suffering for many people with common bacterial infections, those once easily treated with antibiotics. For several decades studies on selection and dissemination of antibiotic resistance have focused mainly on clinically relevant species. However, recently many investigators have speculated that commensal bacteria including lactic acid bacteria (LAB) may act as reservoirs of antibiotic resistance genes similar to those found in human pathogens. The main threat associated with these bacteria is that they can transfer resistance genes to pathogenic bacteria. Genes conferring resistance to tetracycline, erythromycin and vancomycin have been detected and characterized in Lactococcus lactis, Enterococci and, recently, in Lactobacillus species isolated from fermented meat and milk products. A number of initiatives have been recently launched by various organizations across the globe to address the biosafety concerns of starter cultures and probiotic microorganisms. The studies can lead to better understanding of the role played by the dairy starter microorganisms in horizontal transfer of antibiotic resistance genes to intestinal microorganisms and food-associated pathogenic bacteria.

Microarray-based detection of 90 antibiotic resistance genes of gram-positive bacteria

A disposable microarray was developed for detection of up to 90 antibiotic resistance genes in gram-positive bacteria by hybridization. Each antibiotic resistance gene is represented by two specific oligonucleotides chosen from consensus sequences of gene families, except for nine genes for which only one specific oligonucleotide could be developed. A total of 137 oligonucleotides (26 to 33 nucleotides in length with similar physicochemical parameters) were spotted onto the microarray. The microarrays (ArrayTubes) were hybridized with 36 strains carrying specific antibiotic resistance genes that allowed testing of the sensitivity and specificity of 125 oligonucleotides. Among these were well-characterized multidrug-resistant strains of Enterococcus faecalis, Enterococcus faecium, and Lactococcus lactis and an avirulent strain of Bacillus anthracis harboring the broad-host-range resistance plasmid pRE25. Analysis of two multidrug-resistant field strains allowed the detection of 12 different antibiotic resistance genes in a Staphylococcus haemolyticus strain isolated from mastitis milk and 6 resistance genes in a Clostridium perfringens strain isolated from a calf. In both cases, the microarray genotyping corresponded to the phenotype of the strains. The ArrayTube platform presents the advantage of rapidly screening bacteria for the presence of antibiotic resistance genes known in gram-positive bacteria. This technology has a large potential for applications in basic research, food safety, and surveillance programs for antimicrobial resistance.

Detection of tet(M) gene from raw milk by rapid DNA extraction followed by a two-step PCR with nested primers

The likelihood that milk and milk products may act as a vehicle for antibiotic-resistant bacterial genes has become a concern to the food industry and a public health issue, and the demand for rapid tests has increased. The purity of DNA extracted from food samples is a key issue in the sensitivity and usefulness of biological analyses, such as PCR for pathogens and nonpathogens. A rapid, phenol-chloroform free method based on a modification of a sodium iodide DNA extraction, followed by a two-step PCR was developed for direct detection of the tet(M) gene in milk samples within a single working day. This study compares the proposed method with a traditional phenol solvent extraction method and with a commercial kit (QIAamp DNA blood mini kit, Qiagen). The three DNA extraction methods were used to ensure access to the tet(M) gene from 1 ml of raw milk, inoculated with a strain of Enterococcus faecalis, which carries the tet(M) gene. The proposed method, followed by a two-step PCR with nested primers specific for the tet(M) gene, was able to reach a detection limit below 10 CFU/ml in less than 4 h, including the two amplification cycles, thus outperforming in sensitivity and rapidity both the traditional and the commercial method.

Prevalence and molecular characterization of tetracycline resistance in Enterococcus isolates from food

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 microg/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 micro 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 > or = 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.

Molecular structure and evolution of the conjugative multiresistance plasmid pRE25 of Enterococcus faecalis isolated from a raw-fermented sausage

Plasmid pRE25 from Enterococcus faecalis transfers resistances against kanamycin, neomycin, streptomycin, clindamycin, lincomycin, azithromycin, clarithromycin, erythromycin, roxithromycin, tylosin, chloramphenicol, and nourseothricin sulfate by conjugation in vitro to E. faecalis JH2-2, Lactococcus lactis Bu2, and Listeria innocua L19. Its nucleotide sequence of 50237 base pairs represents the largest, fully sequenced conjugative multiresistance plasmid of enterococci (Plasmid 46 (2001) 170). The gene for chloramphenicol resistance (cat) was identified as an acetyltransferase identical to the one of plasmid pIP501 of Streptococcus agalactiae. Erythromycin resistance is due to a 23S ribosomal RNA methyl transferase, again as found in pIP501 (ermB). The aminoglycoside resistance genes are packed in tandem as in transposon Tn5405 of Staphylococcus aureus: an aminoglycoside 6-adenyltransferase, a streptothricin acetyl transferase, and an aminoglycoside phosphotransferase.). Identical resistance genes are known from pathogens like Streptococcus pyogenes, S. agalactiae, S. aureus, Campylobacter coli, Clostridium perfringens, and Clostridium difficile. pRE25 is composed of a 30.5-kbp segment almost identical to pIP501. Of the 15 genes involved in conjugative transfer, 10 codes for putative transmembrane proteins (e.g. trsB, traC, trsF, trsJ, and trsL). The enterococcal part is joined into the pIP501 part by insertion elements IS1216V of E. faecium Tn1545 (three copies), and homologs of IS1062 (E. faecalis) and IS1485 (E. faecium). pRE25 demonstrates that enterococci from fermented food do participate in the molecular communication between Gram-positive and Gram-negative bacteria of the human and animal microflora.

Effect of raw-milk cheese consumption on the enterococcal flora of human feces

Enterococci are one of the major facultative anaerobic bacterial groups that reside in the human gastrointestinal tract. In the present study, the composition of the enterococcal fecal flora in three healthy humans was analyzed before, during, and after the daily consumption of approximately 125 g of a raw-milk Cheddar-type cheese containing 3.2 x 10(4) enterococci/g of cheese. Enterococcal counts ranged between 1.4 x 10(2) and 2.5 x 10(8) CFU/g of feces and differed from subject to subject and from week to week. The cheese contained mainly Enterococcus casseliflavus and a small population of Enterococcus faecalis. Clonal relationships were determined by pulsed-field gel electrophoresis. Before and after consumption of the cheese, samples from humans contained mainly Enterococcus faecium, with some of the clones being resident. During consumption of the cheese, one particular transient clone of E. faecalis, clone Fs2, which was present in small numbers in the cheese, largely dominated the feces. Two clones of E. casseliflavus from the cheese were also found in the feces of one of the subjects during cheese consumption. These results suggest that a clone need not be present in a food in high numbers to establish itself in the intestine.

Influence of the culture medium on antibiotic susceptibility testing of food-associated lactic acid bacteria with the agar overlay disc diffusion method

AIMS

To investigate the influence of the culture medium on antibiotic susceptibility testing of food-associated lactic acid bacteria (LAB) with the agar overlay disc diffusion (DD) method.

METHOD

The antibiotic resistance profile of 39 food-associated lactobacilli and enterococci was determined with the agar overlay DD method using a defined medium (i.e. Iso-sensitest agar; ISA) or an undefined medium (i.e. de Man, Rogosa, Sharpe or MRS agar).

RESULTS

The study revealed that ampicillin discs and, although to a lesser extent, also tetracycline discs consistently produced larger zones on MRS medium compared to ISA medium. For the antibiotics gentamicin, bacitracin and erythromycin, the radius of the inhibition zones produced on MRS medium was significantly smaller in relation to ISA. For categorizing LAB isolates into resistant, intermediate and susceptible groups, it was demonstrated that major errors can occur in determining bacitracin and gentamicin resistance if MRS medium instead of ISA medium is used. On the other hand, the performance of both media was found to be equivalent for testing tetracycline resistance.

CONCLUSIONS, SIGNIFICANCE AND IMPACT OF THE STUDY

Despite the fact that MRS medium generally supports the growth of lactic acid bacteria much better than the nutrient-poor ISA medium, the present study clearly demonstrates that both media are not compatible in susceptibility testing against various classes of antibiotics. These results may stimulate future discussions on a generally recommended DD method for susceptibility testing of food LAB strains.

Sequence of the 50-kb conjugative multiresistance plasmid pRE25 from Enterococcus faecalis RE25

The complete 50,237-bp DNA sequence of the conjugative and mobilizing multiresistance plasmid pRE25 from Enterococcus faecalis RE25 was determined. The plasmid had 58 putative open reading frames, 5 of which encode resistance to 12 antimicrobials. Chloramphenicol acetyltransferase and the 23S RNA methylase are identical to gene products of the broad-host-range plasmid pIP501 from Streptococcus agalactiae. In addition, a 30.5-kb segment is almost identical to pIP501. Genes encoding an aminoglycoside 6-adenylyltransferase, a streptothricin acetyltransferase, and an aminoglycoside phosphotransferase are arranged in tandem on a 7.4-kb fragment as previously reported in Tn5405 from Staphylococcus aureus and in pJH1 from E. faecalis. One interrupted and five complete IS elements as well as three replication genes were also identified. pRE25 was transferred by conjugation to E. faecalis, Listeria innocua, and Lactococcus lactis by means of a transfer region that appears similar to that of pIP501. It is concluded that pRE25 may contribute to the further spread of antibiotic-resistant microorganisms via food into the human community.

Mutagenesis in the post genomics era: tools for generating insertional mutations in the lactic acid bacteria

The increasing availability of whole genome sequences has increased the demand for effective tools to generate insertional mutations in the lactic acid bacteria (LAB). Several novel approaches, such as shuttle-, transposome- and intron-based mutagenesis methods, are possible additions to the existing repertoire of transposon- and recombination-based tools available for mutagenesis of LAB.

Enterococci at the crossroads of food safety?

Enterococci are gram-positive bacteria and fit within the general definition of lactic acid bacteria. Modern classification techniques resulted in the transfer of some members of the genus Streptococcus, notably some of the Lancefield's group D streptococci, to the new genus Enterococcus. Enterococci can be used as indicators of faecal contamination. They have been implicated in outbreaks of foodborne illness, and they have been ascribed a beneficial or detrimental role in foods. In processed meats, enterococci may survive heat processing and cause spoilage, though in certain cheeses the growth of enterococci contributes to ripening and development of product flavour. Some enterococci of food origin produce bacteriocins that exert anti-Listeria activity. Enterococci are used as probiotics to improve the microbial balance of the intestine, or as a treatment for gastroenteritis in humans and animals. On the other hand, enterococci have become recognised as serious nosocomial pathogens causing bacteraemia, endocarditis, urinary tract and other infections. This is in part explained by the resistance of some of these bacteria to most antibiotics that are currently in use. Resistance is acquired by gene transfer systems, such as conjugative or nonconjugative plasmids or transposons. Virulence of enterococci is not well understood but adhesins, haemolysin, hyaluronidase, aggregation substance and gelatinase are putative virulence factors. It appears that foods could be a source of vancomycin-resistant enterococci. This review addresses the issue of the health risk of foods containing enterococci.

Antibiotic resistance genes in coagulase-negative staphylococci isolated from food

Coagulase-negative staphylococci were isolated from different raw milk cheeses and raw meat products and screened for their antibiotic resistances. They were identified as Staphylococcus xylosus, S. lentus, S. caprae, S. epidemidis and S. haemolyticus. The most frequent resistances found were those to chloramphenicol, tetracycline, erythromycin and lincomycin. They have been characterized on the molecular level. The chloramphenicol resistance genes were localized in several S. xylosus and S. caprae on plasmids with sizes ranging from 3.8-kb to 4.3-kb and were identified as chloramphenicol acetyltransferase (cat). All the tetracycline resistant strains were identified as S. xylosus and harboured a 4.4-kb plasmid carrying the tetracycline efflux resistance gene (tetK). The two erythromycin/lincomycin resistant S. caprae and S. epidermidis strains did not hybridize with the MLSB resistance genes ermAM, ermA, ermB and ermC. Three erythromycin resistant Staphylococcus sp. strains harboured an erythromycin efflux resistance gene (msr) localized twice on a 18-kb plasmid and once on the chromosome. A S. haemolyticus strain showing resistance to both lincomycin and clindamycin harboured a linA gene-carrying 2.2-kb plasmid. Further resistances to gentamicin, penicillin and kanamycin were less frequently observed and yet not characterized on a molecular level.