Mechanisms of Antibiotic Resistance in Corynebacterium spp. Causing Infections in People

In recent years we can observe an increasing number of publications describing different incidents of infections, where species of Corynebacterium are isolated as the etiological factor of infection (Anderson et al., 2008; Campanile et al., 2009; Chiner et al., 1999; Dela et al., 2008; Fernandez-Roblas et al., 2009; Funke et al., 1997a; Funke et al., 1997b; Lagrou et al., 1998; Otsuka et al., 2005; Ostuka et al., 2006; Williams et al., 1993). It is a large and very diverse group of microorganisms, in which Corynebacterium diphtheriae is the most important species, with the most important human-pathogenic significance (Gomes et al., 2009; Wagner et al., 2011; Wilson, 1995). Strains of this species produce a strong exotoxine and are responsible for causing diphtheria. Well-developed procedures for diagnosis of diphtheria and conducted large-scale vaccinations resulted in erradication of diphtheria in most countries. Beside the typical human-pathogenic C. diphtheriae, the genus Corynebacterium comprises more than 85 different species of pathogenic significance. This type includes species pathogenic for animals, e.g. C. pseudotuberculosis (Baird & Fontanie, 2007; Nieto et al., 2009), C. kutscheri (Amao et al., 2008; Suzuki et al., 1988), C. canis (Funke et al., 2009) and a very large group of species colonizing the skin and mucous membranes of man, which in favorable circumstances, may become the cause of serious infections in humans. These opportunistic organisms, e.g. C. jeikeium (Ifantidou et al., 2010; Pitcher et al., 1990; Rosato et al., 2001), C. urealyticum (Funke et al., 1997b; Garcia-Bravo et al. 1996; Lopez-Medrano et al., 2008), C. amycolatum (Anderson et al., 2008; Dela et al., 2008; Funke et al., 1997b), C. striatum (Campanile et al., 2009; Funke et al., 1997b; Martinem-Martinez et al., 1995; Ostuka et al., 2006; Roberts et al., 1992), C. pseudodiphtehriticum (Chiner et al., 1999; Dorello et al., 2006; Freman et al., 1994; Olender & Niemcewicz, 2010), may cause infections of various course: mild, chronic and acute, as well as of invasive nature, life-threatening to a patient. The genus Corynebacterium includes also species unrelated to the human organism, e.g. C. glutamicum, producing L-glutamic acid and lysine, used in biotechnological processes on the industrial scale and in genetic studies (Katsumata et al., 1984; Serwold-Davis et al., 1987; Tauch et al., 1998; Wendisch et al., 2006; Valbuena et al., 2007, Yague Guirao et al., 2005).

Many opportunistic strains of the genus Corynebacterium, isolated from clinical materials, belong to species whose characteristics determining the pathogenic effect on the human body have not been thoroughly recognised and characterized yet.Therefore, the assessment of their role as pathogens is often very difficult.Undoubtedly, the common occurrence of coryneform on mucous membranes and the skin may cause doubts in interpretation of their contribution to infections, especially when the material is sampled from places non-sterile physiologically and there might be a suspicion of its contamination.
An increasing number of recognized and described incidents of infections and the observed increase in the number of publications on this topic is probably connected with the microbiological diagnostics currently carried out at a higher level and development of quick commercial tests for identification of species based on their biochemical properties.In reference to strains difficult to identify or requiring verification of uncertain biochemical determination, oftener methods of molecular biology are used, which has resulted in detection of new species and the reclassification of ones previously poorly assayed.
Infections caused by opportunistic Corynebacterium spp.generally refer to a group of people, who experience symptoms of immunodeficiency.The group of patients with a particular risk of infection includes primarily people with immunodeficiency due to disorders of bone marrow activity, the ongoing processes of cancer, post surgery or urological surgery, invasive diagnostic procedures and patients with AIDS.The risk of infection is increased by long-term hospitalization, antibiotic therapy, radiotherapy, treatment with cytostatics or steroids.A disturbing fact is occurrence of such infections in a group of people called "immunocompetent", in whom no symptoms of immunodeficiency were reported before (Chiner et al., 1999;Frejman et al., 1994).
The basis for treatment of infections caused by Corynebacterium spp. is taking up of an effective antibiotic therapy.For this group of microorganisms, until recently an obstacle in the evaluation of drug resistance was use of different criteria of interpretation that were recommended for other groups of microorganisms and determination of drug resistance with various methods, yet results presented by different authors have become the basis for information about occurrence of strains with high resistance to antibiotics among opportunistic Corynebacterium spp., which indicate existence of different mechanisms of resistance in these strains.

Mechanisms of resistance to antibiotics most commonly occurring in
Corynebacterium spp.
The conducted study characterizing resistance to antibiotics isolated from clinical material of different species of the genus Corynebacterium (Anderson et al., 2008;Fernandez-Roblas et al., 2009;Funke et al., 1997a;Funke et al., 1997b;Garcia-Bravo et al., 1996;Gomez-Garceset al., 2007;Martinem-Martinez et al., 1995;Otsuka et al., 2006;Roberts et al., 1992, Troxler R et al., 2001, Weiss et al., 1996 ) draw attention to the most frequently occuring mechanisms of resistance to antibiotics in this group of microorganisms.The results show participation of extrachromosomal genetic elements in transmission of resistance genes in both pathogenic and potentially pathogenic -opportunistic and typically nonpathogenic ones, e.g.present in the soil or strains of Corynebacterium spp.(Kono et al., 1983;Vertes et al., 2005).

Resistance to macrolides, lincosamides and streptogramins B
The occurrence of simultaneous resistance to three groups of antibiotics: macrolides, lincosamides and streptogramins B, determined in short as MLSB, is characteristic mainly of staphylococci and streptococci.It is connected with occurrence of three different mechanisms of the effects of activity: modification of the ribosome binding site associated with methylation or mutation, the mechanism of active efflux of antibiotic from the cell and the least significant -enzymatic inactivation of the antibiotic.The first two MLSB resistance mechanisms are of the highest importance.
Methylation of the binding site causes conformational changes of the subunit 23S rRNA, which prevents binding of the antibiotic molecules in the peptidyltransferase center within the 50S ribosome subunit and leads to the blockade of the mRNA translation and inhibition of bacterial protein synthesis.In species of the genus Corynebacterium it is connected with presence of genes belonging to class erm (erythromycin ribosome methylation), encoding the rRNA methylase enzyme, which causes dimethylation of adenine present in the 23S rRNA (Arthur et al., 1990).The gene erm occurring in Corynebacterium spp, responsible for this mechanism of resistance has been classified as class X of genes erm (Roberts et al., 1999).Despite a high degree of homology between genes ermX isolated from different species of Corynebacterium (C. diphtheriae, C. jeikeium and C. xerosis), it has been found that they exhibit different locations.The gene ermX in C. diphtheriae was found within the 14.5-kbp plasmid pNG2 (Coyle et al., 1979), while the gene ermX in C. xerosis turned out to be located on transposon Tn5432, whose carrier is the 50-kbp plasmid pTP10 (Delal et al., 2008).In the strain C. jeikeium (Pitcher et al., 1990) and C. striatum (Roberts et al., 1992), the gene ermX was found on the chromosome, which has been confirmed also in other analysed strains of C. jeikeium (Rosato et al., 2001).Despite detection of different locations of genes ermX in certain strains of C. jeikeium and C. xerosis, it is assumed that its most typical location is primarily the transposon Tn5432.At the same time in other examined Corynebacterium spp., in which the MLSB mechanism is not related to the location of genes ermX on transposon Tn5432, interesting results of research were obtained, indicating the possibility of reorganization of fragments of the transposon Tn5432 and presence of all its components in the strain genome (Hall et al., 1999).
It is possible that mobile transpositional elements IS1249 containing ermX may create new composite transposons containing other multidrug-resistant genes.This phenomenon is particularly disturbing since transposition of the insertional sequence IS1249 is known for its capabilities to insert and transfer Tn5432 from genomes of unrelated bacteria (Rosato et al., 2001).
Different results of studies suggesting different locations of the detected genes ermX referred to the species of Corynebacterium, which were isolated from strains coming from different geographical regions, which may explain such diversified locations in the genome.The strain of C. diphthariae, containing pNG2 and C. striatum came from patients from the northwestern USA (Coyle et al., 1979;Hodgson et al., 1990;Roberts et al., 1992), C. xerosis from pTP10 from Japan (Tauch et al.1995), C. jeikeium from France (Rosato et al.2001) and C. jeikeium and C. amycolatum from Spain (Yague Guirao et al., 2005).
It is very likely that different locations of genes ermX may indicate the possibility of acquiring resistance genes by multidrug-resistant strains of Corynebacterium spp.from microorganisms colonizing the skin or mucous membranes.ErmX occurring in C. diphtheriae is contained in plasmid pNG2, similar to plasmids isolated from Corynebacterium spp.occurring on the skin (Serwold-Davis & Groman, 1986).The replicon 2.6-kb EcoRI-ClaI fragment (oriR) may be possessed by many microorganisms, including a popular commensal E. coli (Deb & Nath, 1999;Serwold-Davis et al., 1990;Serwold-Davis et al., 1987).
At the same time, as research indicates, the plasmid pNG2 seems an unlikely place of origin for genes erm occurring in Corynebacterium spp.More likely is transposon Tn5432 associated with the chromosome, which may be mobile (Trauch et al., 1995).Tn5432 was also found in the occuring on the skin strains of Propionibacterium acnes, P. granulosum and P. avidum, which suggests that multidrug -resistant strains of the genus Corynebacterium may be an important source in horizontal transfer of resistance genes to other human pathogens (Ross et al., 2002).Another source, from which strains may be derived or to which they may arrive, is bacterial flora occurring in animals.It may be confirmed by detection of gene ermX in the strain of Corynebacterium spp.isolated from pasteurized milk.It showed resistance to erythromycin and/or spiromycin (Perrin-Guyomard et al., 2005).
Beside gene ermX, in strains of Corynebacterium Group A with the MLSB mechanism of resistance, also gene erm class B has been found (Luna et al., 1999), which occurs in Enterococcus spp.and Streptococcus spp., which may also suggest the participation of these microorganisms in spread of the MLSB mechanism in Corynebacterium spp.
The expression of the MLSB resistance may be constitutive or induced.In the case of the constitutive type of resistance, active mRNA, permitting synthesis of methylase, is created without an inducer, while the induced MLSB -inactive mRNA is synthesized, which is activated only under the influence of an inducer, which allows synthesis of the enzyme.Occurrence of the constitutive MLSB resistance mechanism is very popular in strains of C. pseudodiphtheriticum, present in mucous membranes of the upper respiratory tract in humans (Olender & Niemcewicz, 2010).
Formation of cross-resistance associated with the MLSB mechanism is also accompanied by the process of active efflux of antibiotic from the cell.In staphylococci they are transporters of the membrane protein nature (ETP -binding cassette), encoded by genes msrA (macrolide streptogramin resistance), carried on plasmids.These transporters act as a specific pump removing macrolides of 14 -and 15-membered lactone ring and streptogramins B from the bacterial cell.Macrolides of 16-membered lactose ring, lincosamides and telithromycin are not transported.In this case, this mechanism is referred to as MSB (Leclercq, 2002;Douthwaite &Champney, 2001) It was found that presence of gene msrA is also associated with resistance to macrolides and streptogramins B in strains of Corynebacterium spp.(Ojo et al., 2006) and similarly with production of an active transport system of the antibiotic pumped out from the cell (macrolide efflux proteins).Gene msrA had been previously found only in Staphylococcus spp.(Roberts et al., 1999).It encodes the ATP relay needed by the cell to gain energy from hydrolysis ATP for active transport of erythromycin and streptogramin B, and enables synthesis of the ABC family of transporters, i.e. multiprotein systems to actively pump out the antibiotic from the cell.
In turn in reference to S.pneumoniae, S. pyogenes, S. agalactiae and other species of streptococci and enterococci, the efflux mechanism is associated with presence of the MCF transporters (macrolide-specific efflux) and refers only to macrolites with 14 -and 15-membered lactose rings.It does not apply to macrolites with a 16-membered lactose ring, ketolides, linkosamides and streptogramin B. It is associated with low levels of resistance to macrolides (Appelbaum, 2002).
Gene mef, causing active efflux of macrolides from the bacterial cell was also found in Corynebacterium group A, C. jeikeium and strains of Corynebacterium spp.(Luna et al., 1999).

Resistance to fluoroquinolones
In species of the genus Corynebacterium, resistance has been also observed to fluoroquinolones.It is associated with point mutations within the structural gene region of the gyrase subunit A, which is defined as the region determining resistance to quinolones (QRDR -quinolone resistance determining region).
Mutations are of the spontaneous nature, leading to changes in the amino acid sequences, on which depends the range of resistance to certain fluoroquinolones.The resulting level of resistance depends largely on the type of the amino acid that has been built-in as a result of mutation in place of the pre-existing one.Some of them cause a small loss of affinity and a slight decrease in sensitivity, other reduce potently the affinity and activity of fluoroquinolones.It is confirmed by studies of strains of C. macginleyi, in which resistance has been found to norfloxacin, ciprofloxacin and levofloxacin.By analyzing gene gyraA encoding the gyrase subunit A, a change of the amino acid in position 83 in the QRDR region was found (Serine to Arginine), which resulted in resistance in C. macginleyi to norfloxacin.A double mutation has been also found, leading to amino acid changes in positions 83 and 87, which conditioned resistance to all fluoroquinolones.It was observed that double mutations occurred in Ser-83 and Asp-87 in all strains of C. macginleyi with a high level of resistance (Eguchi et al., 2008).
Studies of the gene gyrA sequence were also conducted in strains of C. striatum and C. amycolatum (Sierra et al., 2005).A high resistance to quinolones in C.amycolatum resulted from a double mutation and amino acid changes in positions 87 and 97 or 87 and 88 (unusual location of mutation in gyrA).In the case of C. striatum mutations of amino acids in positions 87 and 91 occurred in gyrA, corresponding to resistance characterized by very high MIC values for ciprofloxacin and levofloxacin, while only moderately increased MIC values for moxifloxacin.
These studies showed various complex and intricate mechanisms of resistance to quinolones in the studied species of Corynebacterium spp.(Sierra et al., 2005), which depend on the number of mutations and the type of changed amino acids.

Resistance to tetracyclines
Phenotypic studies constituted the basis for detection of resistance to tetracycline in Corynebacterium spp.In the case of C. striatum, it was found in 97% of the tested strains (Martinem-Martinez, 1995).These observations were confirmed by detection of the gene tetM, responsible for resistance to all tetracyclines, which is due to the protective effect on the protein ribosome with the mass of about 72-72.5 kDa (Roberts et al., 1992).
In strains of C. striatum M82B resistance to tetracycline is associated with the region 50-kb Rplasmid pTP10.An analysis of the nucleotide sequence revealed two reading frames called tetA and tetB.For analysis of the tetAB genes function, their expression in C. glutamicum was used and thus it was confirmed that they are responsible for resistance to tetracycline, oxytetracycline, and at a low level to other derivatives, such as chlortetracycline, minocycline and doxycycline.At the same an increased MIC value for oxacycline was found in this strain.This effect is associated with participation of the tetAB genes that determine resistance of the transport nature.It creates a powerful mechanism of active transport (efflu) causing pumping out of drugs from the cell via specific transport protein localized in the cytoplasmic membrane (Tauch et al., 1999).R-plasmid pTP10 found in C. xerosis also contains determinants of resistance to tetracycline with parallel resistance to other antibiotics, such as chloramphenicol, kanamycin and erythromycin (Kono et al., 1983;Tauch et al., 1995) whereas, in strains of C. melassecola, the species used to produce glutamate, the resistance gene to tetracycline was found on another mobile element -plasmid pAG1 (Deb & Nath, 1999).

Resistance to beta-lactam antibiotics
The common susceptibility to penicillin in toxic and nontoxic strains of C. diphtheriae made it one of the most frequently prescribed antibiotics in treatment of diphtheria (Wilson, 1995).Despite this opinion, there have been cases observed in which it showed no efficacy.Phenotypic tests consisuted the basis (Von Hunostein et al., 2002), in which penicillin sensitivity of 24 nontoxic strains of C. diphtheriae biotype gravis was determined in the broth microdilution method and by Etests.The research conducted with two methods showed a high 98% consistency of results.MIC values for penicillin were in the range from 0.064 to 0.250 mg/l, with simultaneous very low values for erythromycin (MIC  0.016 mg/l), whereas MBC (Minimal Bactericidal Concentaration) -MBC50 and MBC90 for penicillin were respectively 2.0 and 8.0 mg/l and 17.0 and 24.0.In 71% of the tested strains the ratio MBC/MIC was ≥ 32.The results of the study indicated the insensitivity (tolerance) to penicillin, which was confirmed by a lack of a positive effect of treatment despite the MIC values indicating sensitivity of the tested strains to this antibiotic.Such an effect was also observed in the case of tolerance to amoxicillin in the strain C. diphtheriae isolated from the case of endocarditis (Dupon et al., 1995).
In other strains of Corynebacterium spp. a similar situation was found, i.e. creation of insensitivity to oxacillin with low MIC values.This effect was not associated with the existing mechanism of resistance to beta-lactam antibiotics, but with a very high phenotypic expression and activity of a pair of genes tetA and tetB present on the Tn3598-transposon Class II -12kb, which determined resistance to tetracycline.The activity of these genes, which consists of powerful active pumping, resulted also in removal of a structurally different antibiotic, which was oxacillin (Tauch et al., 2000).

Resistance to glycopeptides
An antibiotic recommended by many authors in the empirical treatment of invasive infections caused by species of the genus Corynebacterium is vancomycin.It is connected with the common sensitivity to this antibiotic of even multidug-resistant species, which pose the greatest problems in infections.It refers to such species as C. jeikeium, C. resistant, C. amycolatum and C. striatum (Wiliams et al., 1993).Unfortunately, still cases of isolated strains of C. aquaticum and C. group B1 resistant to vancomycin have been reported.Only single cases are described, in treatment of which other alternative antibiotics give very good results.An example might be a case of infection in a 44-year-old patient with endocarditis 4 months after a prosthetic mitral valve (Barnas et al., 1991).The strain of Corynebacterium spp.isolated from the blood turned out resistant to vancomycin and penicillin G, erythromycin, gentamicin and rifampicin.The use of imipenem and ciprofloxacin resulted in an effective cure of the infection.
In related species of Coryneform Oerskovia turbata 892 and Arcanobacterium (former Corynebacterium) haemolyticum 872, resistance to vancomycin and teicoplanin was found of the constitutive nature.Presence of the VanA gene detected, found on plasmids of 15 and 20 kb.In strains of A. haemolyticum 872 the VanA gene sequence turned out the same as in vancomycin-resistant Enterococcus faecium BM4147.In the case of O. turbata 892 a change of sequence occurred in three points.Species A. haemoliticum and O. turbata show a natural sensitivity to vancomycin and teicoplanin, and resistance found in the tested strains resulted from presence of the VanA gene (Power et al., 1995).The resistance phenotype associated with presence of the VanA gene is characterized by a high degree of resistance to vancomycin and teicoplanin.

Resistance to chloramphenicol
Resistance genes to chloramphenicol were detected on plasmids -in the strain Corynebacterium spp. on the pXZ10145 plasmid -5.3 kb and in C. xerosis on pTP10 -45.0 kb (Deb & Nath, 1999).In C. striatum strain M82B (former C. xerosis M82B) (Tauch et al., 1998) chloramphenicol resistance gene cmx (chloramphenicol and exports) was detected as an integral part of the transposon Tn5564, which contains a complete copy of the insertion sequence IS1513.The cmx gene is responsible for encoding of a specific protein (transmembran chloramphenicol efflux protein), which inhibits the passage of the antibiotic into the cytoplasm, and gives the bacetrial cell resistance to chloramphenicol.

Problems with diagnostic of infection by coryneform
The increasing isolation of multidrug-resistant strains of the genus Corynebacterium from clinical materials draws attention to the emerging issues related to treatment of infections caused by this group of opportunistic bacteria.The problem is all the more important since the infections often concern diagnostically difficult cases, long-hospitalized patients, the chronically ill, often with an accompanying disease causing immunosuppression.The underrated contribution of coryneform in infections may lead to therapeutic errors.Their common occurrence on the mucous membranes and skin causes doubts about their recognition as the etiologic factor of the infection.
The next problem, that may determine the accuracy of microbiology result as well as confirmation of the presence of opportunistic Corynebacterium spp. in infection, is a choice of appropriate culture method -bacterial culture media, which composition supports the growth of different coryneforms species.It is applied mostly for lipophilic species, as C. jeikeium, C. urealyticum.It is very important to identify the isolated strains precisely, as this enables tracking multi drug-resistance in specific strains, their existence on specific areas and routes of transmission.These informations are specifically important for hospital areas, facilitating to make proper decision on limiting these types of infections.
Accurate microbiological diagnostics of infections caused by species of the genus Corynebacterium, identification of strains of the isolated species and determination of antibiotic susceptibility with methods enabling determination of the MIC values permit assessment of the existing and emerging mechanisms drug resistance and result in making right decisions about the most appropriate antibiotic therapy for a given case.It is extremely important to apply correct interpretation criteria of the determined drug resistance for species of the genus Corynebacterium, specific for this group of microorganisms, based on the established and generally accepted recommendations (Clinical and Laboratory Standards Institute [CLSI], 2006;Łętowska & Olender, 2010).Application of methods of molecular biology and examination of resistance genes, their locations and transmission paths is a very important direction of research on monitoring of resistance mechanisms in coryneform and gives the ability to track and determine their role in transmission of genes also among other species.

Antibiotic therapy used in infections of Corynebacterium spp.
The basis for monitoring of the emerging multi-drug resistant strains for all bacteria, as well as species of the genus Corynebacterium, is conducting research characterizing their sensitivity to antibiotics, which is potentially useful in treating infections.Publication of such data is extremely important due to tips received about the most effective antibiotic therapy for a given group of microorganisms.
An analysis of sensistivity to antibiotics of a large group of strains of C. urealyticum, C. amycolatum, C. jeikeium, C. coyleae, C. striatum, C. aurimucosum and C. afermentans was conducted with assays using Etests (Fernandez-Roblas et al., 2009).The authors found that strains of all tested species were susceptible to glycopeptides, linezolid, chinupristin/dalphopristin and daptomycin, which was also confirmed in other studies (Funke et al., 1997a;Funke et al., 1997b).
The results obtained from research done in Italy, involving strains of C. striatum isolated from different infections, also indicated the need of analysis of drug resistance in Corynebacterium.Genetic studies of strains of C. striatum MDR (multidrug-resistant) revealed presence of a multidrug-resistant clone, whose strains isolated from cases of pneumonia, catheter related bacteremia and wound infections showed, despite resistance to other classes of antibiotics, susceptibility to glycopeptides, tigecyclin, chinupristyn/dalphopristin, daptomycin and linezolid (Campanile et al., 2009).
One of the most resistant species, which causes the biggest problems in hospitals and is frequently isolated from infections in hospitalized patients, is C. jeikeium.The study of 66 strains of C. jeikeium (Johnson et al. 2004) showed resistance to penicillin in all of them, in 94% resistance to erythromycin, and in 74% to tetracycline.Twenty-two strains of other examined species of the genus Corynebacterium had a significantly lower level of the resistant.But what is extremely important, all examined strains were susceptible to vancomycin (MIC = 0.5-4.0mg/l), linezolid (MIC = 0.5-2.0mg/l) and daptomycin (MIC ≤ 1mg/l) with the exception of two isolates of C. auaticum, whose MIC for daptomycin was 8 mg/l.At the same time effecacy of daptomycin was confirmed in the successfully applied combination with rifampicin in a patient with endocarditis caused by C. amycolatum (Dala et al., 2008) i C. striatum (Shah & Murillo, 2005).
Linezolid, as shown in published works, was also characterized by a very good action.High activity of linezolid was found in studies of 190 strains of coryneform (Gomez-Garces et al.,2007).It confirmed the possibility of equally successful application this antibiotic in infections caused by Coryneform.
Diversity of antibiotic resistance in species of the genus Corynebacterium is strictly connected with the locations, in which the tested strains occur.As found in the conducted studies (Garcia-Bravo et al., 1996) strains of C. urealyticum coming from hospitalized patients show significantly higher resistance to antibiotics than those isolated from outpatients, from outside of the hospital environment.An analysis of frequency and duration of antibiotic therapy used in patients from both groups of respondents was conducted.It confirmed unequivocally that the hospital environment and more frequently used antibiotics in the hospitalized patients is conducive to occurence of multidrug-resistant strains, and the hospital environment in which such patients stay is the place from which strains of C. urealyticum came, causing infections in the hospitalized patients.At the same time considerably lower resistance to antibiotics of isolates coming from the outpatients indicates that the strains of C.urealyticum most likely are derived from microflora colonizing the skin of the examined outpatients.
A very disturbing fact is discovery of new multidrug-resistant species of the genus Corynebacterium, which suggests a progressive character of multidrug-resistance occurring in this group.It is confirmed by a description of a new multidrug-resistant species of C. resistens in 2005.It is lipophilic, with low fermentation properties (it ferments glucose), does not reduce nitrates, does not produce urease and pyrazinamidase.It is characterized by resistance to penicillin and cephalosporins (MIC  64 µg/ml), imipenem (MIC  32 µg/ml), aminoglycosides (MIC  3 µg/ml 2), macrolides (MIC  16 µg/ml), quinolones (MIC  32 µg/ml) and sensitivity to teicoplanin (MIC  0.5 µg/ml) and vancomycin (MIC = 2 µg/ml) (Otsuka et al., 2005).

Conclusion
Presented by several authors results of their studies on antibiotics resistance show, that even though Corynebacterium spp.are the members of the normal flora, they are not universally susceptible to antibiotics, as could be expected.Opportunistic Corynebacterium spp., until now considered as bacteria of low pathogenicity, may pose a diagnostic and therapeutic problems, as they are more and more commonly isolated from serious, life-threatening invasive infections.Observed in many cases multi drug-resistance may be connected with the possibility to acquire resistance genes by gene transfer within bacteria regarded as normal flora present in large number on a given body area (skin, mucous membranes).Drug resistance occurrence in opportunistic species is the result of antibiotics overuse.It is obvious that antibiotics used also influence on saprophytic bacteria.Resulting selection of resistant strains is commonly known and regarded as important process leading to multi drug-resistance.For these reasons, analysis of the process in opportunistic Corynebacterium is an important element in monitoring new multi drug-resistant strains derived from saprophytic flora, mostly in infections i n p a t i e n t s f r o m r i s k g r o u p s , u n d e r immunosuppression, hospitalized for long time.Studying mechanisms of drug resistance on the basis of phenotypic and genotypic expression is important for proper antibiotic therapies in infections caused by this group of microorganisms.