UNLABELLED:Immunocompromised hosts are subjects of predilection to bloodstream infections. The global mortality is high. Bacterial strains are frequently multiresistant; fungemias are almost always deadly, in spite of the susceptibility of the fungus.OBJECTIVE:to evaluate the positive blood cultures in patients with malignant and non-malignant diseases and to determine the resistance mechanisms with the Vitek2.MATERIAL AND METHOD:a 29 months study--181 episodes of invasive infections--168 patients. The blood culture vials were Bactec Plus. The isolates were identified using Api galleries and with the Vitek 2. The susceptibility was tested by the disk-diffusion method (Oxoid Ltd.). Minimal inhibitory concentrations: Vitek2.INTERPRETATION:EUCAST 2008 standard.RESULTS:overall mortality: 27%. Gram-negative bacilli: 59.4% and 48.5% Gram-positive cocci. Klebsiella pneumoniae and Escherichia coli isolates accounted for 16.43% and 71.23%respectively; 25% of E. coli strains and 33% of K. pneumoniae respectively, produced extended-spectrum beta-lactamases. Oxacillin resistance: 54.4% of S. aureus isolates. No resistance to carbapenems in enterobacteria.CONCLUSIONS:Bacterial resistance is not likely to decrease, if at all; Death produced by infections is an event that can be prevented. Molecular determinations should be performed to assess the role of the virulence genes and of the resistance mechanisms and to help the better understanding of the interractions between bacteria and the human organism.
Yeast biodiversity represents a dynamic scientific domain characterized by permanent emerging theories and accumulation of new data. Identification of genome structure for a number of yeast species and elucidation of regulatory pathways for species-specific metabolic networks, lead to development of numerous applications of yeasts in industry, biotechnology, therapeutics and bioremediation. The studies of the scientific community were long time focused on Saccharomyces cerevisae due mainly to its use in food production. Therefore, the species belonging to Saccharomyces genus became reference points for genomics and biodiversity studies. During last decades there is a growing interest for yeast species able to produce biomass by assimilating or degrading various compounds such as methanol, hydrocarbons, wood hydrolisates and other residues or by-products from different industries.
A large distributed bacterium, Listeria monocytogenes has been isolated from water and fresh vegetables, raw meat and processed meat (all types), and raw, salted and smoked fish. L. monocytogenes grows at low oxygen concentrations and at low temperatures, surviving for a long time in the environment, in the processing plant, as well as on the equipment, instruments and during storage at the refrigeration temperature. L. monocytogenes causes invasive listeriosis, often affecting immunocompromised individuals. Epidemiologically, listeriosis appears as sporadic cases and outbreaks, with an incidence of 3-8 cases/1000000 inhabitants, run-down in most countries, reflecting the measures compulsory in food processing industry. The purpose of this review is to describe the measures regarding the implementation of Current Good Manufacturing Practice (CGMP), to protrude the integrity of cold chain through preparing, packing and holding food, including household refrigerating, and to increase a good communication, particularly for consumers at increased risk of listeriosis.
For a long period of time, microbiological analysis of samples gathered from individuals, food and environment was based on culture techniques which were considered "gold standard". These conventional methods are yet time-consuming (with respect to germ identification and characterization), cumulative costs are huge, which made research focus on obtaining methods with a rapidity / cost ratio higher than that of classical methods. Rapid diagnostic became as well a priority in the case of food-borne diseases determined by Salmonella spp. These methods of rapid diagnostic are based on phenotypic or molecular techniques for identification and typing, as well as on tests using biosensors and DNA chips, which are under development, and which use the capacity of real-time monitoring of the presence of multiple pathogens in food. With the continuous development of new molecular technologies allowing the rapid detection of food pathogens, the future of conventional microbiological methods looks rather insecure, the more so as there is continuous interest in improving the performances of genotypic methods regarding easy handling, reliability and low costs. The work reviews the panoply of Salmonella identification and typing tests available in the present.
Malaria is the most common disease in the tropical areas and the most common imported disease in the non endemic areas, being considered by WHO a public health issue. About half of the world population lives in zones where there is a malaria risk, and in 2008 were reported 243 million malaria cases and 863.000 deaths. Europe was declared "malaria-free" by WHO in 1975. However there are still cases, most of them imported due to migration and travelling to high risk zones. In 2008 in Europe were reported 5848 imported cases in 25 countries. In recent years there were sporadic indigenous cases in Spain (2009) and Greece (2009, 2011), but the risk of malaria transmission in Europe is considered low in present. In Romania since 1961 indigenous transmission was interrupted, and starting with 1963 we are in the maintenance phase of malaria eradication. in the period 2007-2010 were reported 68 cases of malaria, all imported (24 cases in 2007, 13 cases in 2008, 12 cases in 2009 and 19 cases in 2010) and one death in 2007 (to a man aged 40 years infected in Uganda and who developed a toxic form of malaria with Plasmodium falciparum). Most cases of malaria (94.1%) were recorded in men who have traveled for work in Africa (83.8%), and who were infected with Plasmodium falciparum (67.7% of cases). Occurrence of malaria cases in non endemic areas is possible by the increasing number of people who travel in the risk areas and/ or ignoring and not following prevention measures, respectively chemoprophylaxis and personal protective measures against mosquito's bites.
Since 2005 a sentinel system for surveillance of nosocomial diseases has been introduced in Romania which had, among other objectives, the evaluation of antibiotic resistance. The surveillance methodology was shared annually, the number of participants varying between 12 and 40 hospitals. During 2005-2008 the Reference Laboratory for Nosocomial Infections and Antibiotic Resistance in the "Cantacusino" NIRDMI received 1481 bacterial strains, comprising 531 S. aureus, 486 Pseudomonas aeruginosa, 439 enterobacteria and 25 enterococci strains. The resistance percents widely differred for some species, especially regarding the type of hospital unit that sent the strains (ex., Pseudomonas aeruginosa isolated form patients with burns). A great variability was noted concerning the manner in which nominalized hospitals responded to the solicitations in the methodology that was shared. especially regarding participation to a national bank for bacterial strains. Only for 5 out of the 40 hospitals that participated along the 4 years in the sentinel programme the annual comparative evaluations of antibiotic resistance were achieved. for a small number of microorganisms that underwent surveillance (S. aureus, E. coli). Among the strong points of the system we can point out: unity in methodology; working protocols for microbiological investigation given to all the participants; special forms for reporting. Among the weak points, we consider: modification in the number of participant hospitals during the program: unequal participation of hospitals, with unwanted effects on the sample representativity of analysed microbial strains; difficulties in stocking and processing laboratory data. In order to increase the quality of data provided, we consider the following as useful: harmonization of the objectives regarding integrated surveillance of nosocomial infections and antibiotic resistance in hospital environment, correlated with the ECDC demands and recommendations; inclusion in the system of sanitary units that fit the needs of the program fir microbiological identification and investigation of nosocomial infections; intensification of the training activities of persons involved in the program, regardless of the level of responsibility and the acknowledgement of each person's responsibilities in nosocomial infection monitoring; external and internal control implementation in the laboratories: selection of aspects concerning the emergence and spread of antibiotic resistance that come out during surveillance in order to be studied using molecular methods for the emphasizing of mechanisms and causes, in view of implementing measures for prevention and control; evaluation of the necessity for molecular investigation in view of identifying resistant bacterial clones in the hospitals in Romania etc.
UNLABELLED:Enterococci are a frequent cause of a variety of human infections, the most common being urinary tract infection followed by bacteraemia, meningitis and endocarditis from hospitalized patients.OBJECTIVE:The study and monitoring of antibiotic resistance of enterococci strains isolated and confirmed in 2009.MATERIALS AND METHODS:Identification of 30 strains received in 2009 was based on phenotypic characteristics (microscopy, culture and biochemical characters); antibiotic susceptibility testing was performed according to CLSI standards 2009 by diffusion test and MIC by agar dilution and E-test.RESULT:The strains belonged to the following species: E. faecalis (18), E. faecium (6), E. gallinarum (5), and E. durans (1), and were isolated from: blood cultures, urine, pus-wound, cerebrospinal fluid (CSF) and catheter. Antibiotic susceptibility testing showed susceptibility to different antibiotics depending on the species and also on the type of clinical samples.CONCLUSIONS:Due to the small number of strains, no resistance phenotypes could be determined. As emergence of antibiotic resistant enterococci is well known, continuous surveillance of antibiotic susceptibility and molecular study of this issue are required.
The increase of incidence of resistance to the antibiotics became the most worrisome subject within the clinical and research communities in the medical fields. Intrinsic resistance genetic mutations, horizontal transfer of mobile structures carrying genes coding for resistance to the antibiotics within the pan-microbial genome are representing the bacterial resistome which is bearing the genetic information regarding the defensive mechanisms developed by micro-organisms to protect themselves against antibiotics. Rice in the resistance of enteric bacteria, pathogens involved in a large number of human infections, to the cephalosporin of last generation and to the fluoroquinolones is a very actual subject in the medical area. Production of beta-lactamases with extended spectrum is the most important enzymatic defence system, developed by micro-organisms, consisting in the inactivation of beta-lactam antibiotics by destroying the beta-lactam ring. Enterobacteria are able to produce beta-lactamases of type TEM, SHV and/or CTX-M. Punctual mutations in nucleotide structure of bla genes, coding for beta-lactamases synthesis, are leading on production of a large diversity of enzymes with enlarged spectrum of activity (ESBL). At the beginning of 90's the first beta-lactamases resistance to clavulanic acid were detected and in our days more then 170 TEM, 120 SVH and 90 CTX-MESBLs are known. Escherichia coli strains are producing, firstly, TEM ESBLs, Klebsiella pneumoniae SHV ESBLs. and both are producing CTX-M type ESBLs, are resistant to the fluoroquinolones due to punctual mutations in nucleotide structure of gyr gene coding for gyrases production, enzymes involved in nucleic acids replication. Resistance to the antibiotics with extended activity is a public health threat due to their capacity of large spreading within bacterial population, when the coding structures are located on mobile genetic structures. The menace increase when genes coding for fluoroquinolones resistance (qnr) are identified on such of structures.
According to the resolution adopted by the Member States in the "Microbial threat" Conference, Copenhaga, 1988. antimicrobial resistance surveillance is one of the four pillars of the control strategy of this increasingly serious public health problem, coming together with the antimicrobial consumption surveillance, intersectoral actions and antibiotics prudent use promotion. Seventeen years ago, O'Brien and col. were describing the current degree of the antimicrobial resistance surveillance as follow: "There are no reliable data in this area--simply fragments of information and anecdotes that we use to draw an overall picture" (Diagnostic Microbiology and Infectious Diseases, 1992, 15.53S-60S). Ten years later, Morris and Masterton were showing that there were reports underlying the big volume of activity delivered in the field of antimicrobial resistance surveillance during that time, but there were no major changes in respect of the data quality (JAC,. 2002, 49, 7-10). According to the WHO definition, surveillance, as continuous and systematic process of data collection, data analysis and data reporting, is reaching it's scope only if it is able to provide information valuable for action. Though it is by excellence a type of surveillance based on the microbiology laboratory activity, antimicrobial resistance surveillance is not coming to be useful according to the WHO and EUCAST (European Committee for Antimicrobial Susceptibility Testing) acception without using the epidemiology methods in order to make possible the adoption of a clear strategy, starting from the definition of the type of information that we want to obtain. Pending on the scope and taking into account the preexisting premises for setting up a surveillance network, we need to select the appropriate surveillance methods, in respect of data and strains collection and storage, data reporting, appropriate denominators (population categories. admission days, patient days etc.), data stratifying etc. In Romania there are few data on antimicrobial resistance surveillance which could resist to a critical evaluation of representativity, reporting to adequate denominators, stratifying methodologies which would allow to follow trends, comparing data by wards, hospitals, counties, intercomparing data with other countries etc. Contacting the European Antimicrobial Resistance Surveillance System in 2001 was an initial modality to decrease the huge gap existing by that time, but could not remain the unique solution to develop in this direction. On the other hand, participating in the European Antimicrobial Resistance Surveillance System is enforcing the involvement of all implicated professional categories, improving logistic and interdisciplinary collaboration, in order to set up a systematic surveillance. We are supporting the initiative of a critical evaluation of the existing situation, as of setting up a surveillance strategy in accordance with the targetted goals, starting from the recent recommendations of WHO and ESCMID Antimicrobial Resistance Surveillance Study Group. This initiative could contribute, together with the participation in the European antimicrobial resistance surveillance program, to the efficient turning account of the resources and uncoordinated and sometimes redundant efforts of different working groups including prestigious microbiology, infectious diseases and epidemiology specialists.
INTRODUCTION:The alarming increase of cases of tuberculosis with resistant germs renders compulsory the orientation towards rapid and cheap methods that would allow large-scale testing of mycobacterial strains.AIM:Evaluation of the performances of two phenotypic methods for mycobacteria sensitivity testing. nitrate reductase and absolute concentrations.MATERIAL AND METHOD:In two different laboratories we tested the same set of 20 mycobacterial strains from the 2008/2009 international panel and an additional 10 strains isolated in the second laboratory, using the absolute concentration method as standard and the nitrate reductase method, both using Lowenstein Jensen medium with rifampicine and isoniaside incorporated The results obtained in both laboratories are concordant for both methods and show sensitivity and specificity of 100% for nitrate reductase method compared to absolute concentration method The results obtained using the two methods in the two laboratories also showed a 100% reproducibility.CONCLUSIONS:Nitrate reductase method is easy to perform and to acknowledge. It does not require special equipment, besides what is usually found in the laboratory. It showed a 100% sensitivity and specificity. The 100% reproducibility and repetability of results can represent arguments for a possible use of the methods in all the laboratories belonging to the national network of mycobacteriology laboratories, in order to screen for multiresistant strains.
EARSS (European Antimicrobial Resistance Surveillance System) is the biggest antimicrobial resistance surveillance project in the world financed from public finds, aiming to provide validated and comparable official data on antimicrobial resistance of invasive microbial strains (isolated from blood and CSF), belonging to 6 indicator bacterial species, i.e.: S. aureus, E. coli, E. faecium/faecalis, Str. pneumoniae, Ps. aeruginosa, K. pneumoniae. Romania reported data to EARSS since 2002 so far. Though the number of participating laboratories increased progressively from 12 to 35, the number of hospitals which reported for EARSS. as the number of strains included in the data base remained steady and relatively low. This issue is related to the particular position of Romania in the European context, in respect of the very low number of blood cultures performed in hospitals. Our paper is presenting the trends of antimicrobial resistance in the indicator strains in the 2002-2008 interval. During the 2002-2008 interval, Romania reported to EARSS a total number of 1276 bacterial strains, distributed by species as follows: 513 S aureus, 369 E. coli, 128 Streptococcus pneumoniae, 127 Enterococcus spp.. 71 Klebsiella pneumoniae, 68 Pseudomonas aeruginosa. Klebsiella pneumoniae and Pseudomonas aeruginosa were reported, according to the EARSS protocol, only for the 2005-2008 interval. It is difficult to describe trends, specially in Enterococcus, Streptococcus pneumonaie and the 2 species collected only since 2005, because of the low number of isolates, but there are several results that are supporting us to claim that antimicrobial resistance in invasive isolates is a real problem in Romanian hospitals, like in other Central, Southern and South Eastern European countries: more than 25% of S. aureus strains resistant to methicilline, with more than 50% in some years, high aminoglycozides resistance in more than 70-80% of Enterococcus faecium invasive strains, more than 80% of strains resistant to 3rd generation cephalosporines etc.
One of the major causes leading to increased antibiotic resistance is excess antimicrobial consumption. We have analysed the correlation between antibiotic use and frequency of carbapenem-resistant Pseudomonas aeruginosa (CRPA) strains in the general intensive care unit of a university hospital Antibiotic use was expressed as number DDD (daily defined doses)/100 occupied hospital bed-days (BD). CRPA incidence rates were determined by number of unique isolates reported to 100,000 BD. The average use of antibiotics between January and August 2008 was 174 DDD/100 BD. The first four most frequently prescribed antibiotics were as follows: first and second generation cephalosporins (47 DDD/100 BD), carbapenemns (29 DDD/100 BD), fluoroquinolones (26 DDD/100 BD) and glycopeptids (20 DDD/100 BD). Average monthly incidence rate of CRPA was 546/100,000 BD (319-773/100,000 BD. CI 95%). There was a correlation between CRPA incidence rate and carbapenem plus fluoroquinolone use (Pearson coefficient of correlation r = 0.7, p < 0.05). Our data showed that the evolution of CRPA incidence rates was related to carbapenem and fluoroquinolone use.
OBJECTIVE:The aim of the this study was the analysis of the resistance to antibiotics of Streptococcus pneumoniae isolated in last years.METHODS:328 S. pneumoniae strains, coming from blood, CSF tracheal aspirate (TA), or sputum, pleural fluid (PL) and other samples (ear and sinus fluid) isolated in 2006-2008, were analyzed at INCDMI "Cantacuzino", National Reference Center for Streptococcus pneumoniae. Strains were tested for susceptibility to by agar diution method (minimal inhibitory concentration-MIC) to the following antibiotics: penicillin (Pc), erythromycin (Em), cephalothin (Kf). cefuroxim (Cxm), cefotaxim (Ctx), trimethoprim/sulfamethoxazol (Sxt), ofloxacin (Ojx), amoxicillin (Amx). tetracycline (Te), cloramphenicol (Cm), vancomycin (Va).RESULTS:The analysis of the results was done according to CLSI 2009. Pneumococci strains isolated from blood, CSF, TA or sputum and PL showed lower resistance level to antibiotics (38.8% Pc, 9.3% Cxm. 4.1% Ctx, 2.7% Amx. 24% Em, 2.4% Ofx, 68% Sxt) against those isolated from ear ans sinus fluid which revealed high levels of resistance (70% Pc, 11.2 % Cxm, 5.9 % Ctx, 3.4% Amx, 58.4 % Em. 3.8% Ofx, 73% Sxt). Strains resistant to penicillin, isolated from blood and CSF revealed the following aspects: 17% low level of resistance and 11 % high level of resistance. CONCLUSIONS. The most efficient antibiotics were Ctx, Amx and Oft. A continuous surveillance of pneumococci strains resistant to antibiotics is needed, as well as the use of an pneumococcal efficient vaccine.
AIM:Testing antibiotic resistance of bacterial strains (compulsor, reported for EARSS surveillance) isolated from patients hospitalised for systemic infection in the "Dr. V. Babe" Hospital for Infectious and Tropical Diseases during 01.01.2005-11.11.2009, for a dynamic evaluation and for the surveillance of resistance emergence for certain classes of antibiotics.MATERIAL AND METHODS:Bacterial isolation: BacT/ALERT system; strain identification in classic and automated system (ATB Expression. VITEK 2C): antibioresistance: disk-difussion method (NCCLS 2005--CLSI 2009), MIC (E-Test, ATB/ Expression, VITEK 2C). Screening of ESBL-producing strains performed with double disk-difussion method (DDD). Reference strains used: S. aureus ATCC 25923, S. pneumoniae ATCC 49619, E. coli A TCC 25922, Enterococcus fiecalis ATCC 29212.RESULTS:During the studied period, 245 bacterial strains have been isolated, identified and tested (Staphylococcus aureus / 70, Streptococcus pneumoniae / 61, Enterococcus faecalis / 18, Enterococcus faecium / 5, Neisseria meningitidis / 18, E. coli / 73). out of 166 hemocultures and 79 cerebrospinal fluids / CSF. The average incidence of MRSA strains in systemic infections was 34.28%. 44.28% of the S. aureus strains were resistant to erythromycin, 17.14% to cyprofloxacyne, 15.71% to rifampicine, 14.49% to gentamycine. No strain resistant to vancomycine and linezolide. Streptococcus pneumoniae presented an average high resistance to penicillin G of 11.47%. and a 1.63% resistance to third generation cephalosporines. 0% resistance to vancomycine and rifampicine. 7/ 18 Enterococcus faecalis strains and 4/5 Enterococcus faecium strains presented high level resistance to gentamycine (CN 120 microg/disk) and no strain was resistant to vancomycine, teicoplanin or linezolid. The 18 Neisseria meningitidis strains were all sensitive to beta-lactams, macrolides, fluoroquinolones and cloramphenicol. For the 73 Escherichia coli strains, the average incidence of ESBL-producing isolates was 10.95%, the average resistance to ampicillin was 58.90%, to gentamycine--13.88% and to cyprofloxacin--20.83%. No strain resistant to carbapenemes and amikacine.CONCLUSIONS:For the systematic surveillance of antibiotic resistance there is a need for a harmonised protocol of data gathering and strain selection and the rigurous implementation of correct evaluating methods for antibiotic resistance in the microbiology laboratory. Carbapenemes. glycopeptides and oxazolidinones still present a major effectiveness in the first intention treatment of systemic infections.
OBJECTIVEAntibiotic resistance evaluation of Gram-positive cocci isolated in 2008.MATERIAL AND METHODSAntibiotic susceptibility testing was performed for 1044 strains: 610 Staphylococcus aureus (352 from patients, 258 from carriers), 203 Streptococcus pneumoniae (53 from patients, 150 from carriers), 144 Enterococcus faecalis. 57 Enterococcus faecium and 30 Streptococcus spp. using automatic systems Vitek 2 Compact. MicroScan, disc diffusion method and Etest according to 2008 CLSI. A number of 497 Streptococcus pyogenes strains were tested for eritromycin resistance.RESULTSThere were 33.2% MRSA for strains isolated from patients and 30.0% from carriers. From MRSA strains. 35.5% were resistant to gentamicin. 33.6% to ciprofloxacin, 74.3% to erythromycin and 30.5% to rifampin. There were no S. aureus strain resistant to vancomycin and linezolid. S. aureus strains isolated from wounds were more resistant to erythromycin (43.9%) than the strains isolated from systemic infections (12.1%). From 11 S. pneumoniae strains isolated from meningitis, 4 were resistant to penicillin. Neither S. pneumoniae strain isolated from other infections, nor those from carriers had MIC to penicillin more than 4 microg/ml. S. pneumoniae strains isolated from carriers were more resistant to erythromycin. clindamycin and tetracycline than the strains isolated from patients (66.7%, 54.1%, 54.2% vs. 27.4%, 22.6%, 33.9%). E. faecium was 95.9% resistant to penicillin, 90.2% to ampicillin, 64.7% to gentamicin, 72.0% to streptomycin and 78.4% to ciprofloxacin. F. faecalis was less resistant than E. faecium at most of the antibiotics: 32.4% to gentamicin, 59.6% to streptomycin, 28.5% to ciprofloxacin. Viridans group Streptococci, all isolated from blood culture were 92% susceptible to penicillin and ampicillin. To erythromycin, 12% of viridians group Streptococci were resistant. S. pyogenes resistance to eritromycin was 5.8%.CONCLUSIONSS. aureus strains showed a relatively high level of resistance to oxacillin (33.2%) and resistance in the same time to several antibiotics. S. pneumoniae can not be considered resistant to penicillin administrated parenteral, with exception of the strains isolated from meningitis. E. faecium had a higher resistance rate than E. faecalis.
C. difficile is recognised as the main cause for colitis in hospitalised patients which are treated with antibiotics, chemotherapics or other drugs that disturb intestinal microbiota. Thus, a rapid and correct diagnostic of Clostridium difficile infections is essential for preventing nosocomial infection spread. Empiric therapy, regardless of the laboratory investigation results, is inadequate, especially in epidemic situations, as not all the cases of diarrhoea are due to C. difficile infection. Other risk factors for CDAD (Clostridiumn difficile Associated Diseases might be: prolonged hospitalization or residency in an asylum, age, existence of a severe chronic disease in the background nasogastric intubation, anti-ulcer drugs, at less extent gastrointestinal surgery, other immunosuppresive compounds etc. In our country, C. difficile infection is rather frequent in adults, though it is not always reported by clinicians. The circulation of endemic rybotype 027 in Romania is not well documented, the rybotype being extremely virulent and spread in other European countries. Hence the importance of extending the diagnostic capacity of C. difficile infection in order to allow detection of this rybotype among the strains isolated in our country.
Macrolides, lincosamides and streptogramines are distinct antibiotic (AB) families, with different chemical structure, but with similar antibacterial spectre and mechanisms. Macrolides are natural products of secondary metabolism of several species of actynomyces; they represent a group of compounds with a lactonic ring of variable dimensions (12-22 atoms of C) that can bind, by means of glycosidic bonds, sacharridic and/or amino-sacharridic structures. Most of the MLS antibiotics are bacteriostatic. Their mechanisms consist in inhibiting protein synthesis. the target being 50 S subunit of the bacterial ribosome, the binding sites being different for the different MLS classes. Erythromycin (E) was introduced in therapy in 1952; quickly, several bacterial genera started developing resistance to E. Strains resistant to E were as well resistant to all macrolides and other antibiotics with different structures--lincosamides and streptogramines B--resistance phenotype called MLSB. The main molecular mechanisms for bacterial resistance to MLS are: (1) Target modification, coded by erm genes (>12 classes). In Gram-positive cocii MLSB resistance, regardless of erm gene, can be: inducible (i MLSB)--when the presence of the inductor AB is necessary for methylation enzyme production; constitutive (c MLSB)--when the methylation enzyme is continuously produced Distinction between iMLSB and cMLSB can be easily appreciated based on the phenotypic expression of bacteria. In streptococci--all MLSB antibiotics can act as methylase inductors. (2) The decrease of AB intracellular concentration by active efflux, coded by mef genes--also called M resistance phenotype, low level resistance (LLR). (3) AB inactivation (enzymatic modification of AB); there are different resistance phenotypes: MLSB +SA and L phenotype (in staphyilococci) or SA4 phenotype and L phenotype (in enterococci).
