Macrolide-lincosamide-streptogramin B Research Articles

Novel erm (T)-Carrying Multiresistance Plasmids from Porcine and Human Isolates of Methicillin-Resistant Staphylococcus aureus ST398 That Also Harbor Cadmium and Copper Resistance Determinants

This study describes three novel erm(T)-carrying multiresistance plasmids that also harbor cadmium and copper resistance determinants. The plasmids, designated pUR1902, pUR2940, and pUR2941, were obtained from porcine and human methicillin-resistant Staphylococcus aureus (MRSA) of the clonal lineage ST398. In addition to the macrolide-lincosamide-streptogramin B (MLSB) resistance gene erm(T), all three plasmids also carry the tetracycline resistance gene tet(L). Furthermore, plasmid pUR2940 harbors the trimethoprim resistance gene dfrK and the MLSB resistance gene erm(C), while plasmids pUR1902 and pUR2941 possess the kanamycin/neomycin resistance gene aadD. Sequence analysis of approximately 18.1 kb of the erm(T)-flanking region from pUR1902, 20.0 kb from pUR2940, and 20.8 kb from pUR2941 revealed the presence of several copies of the recently described insertion sequence ISSau10, which is probably involved in the evolution of the respective plasmids. All plasmids carried a functional cadmium resistance operon with the genes cadD and cadX, in addition to the multicopper oxidase gene mco and the ATPase copper transport gene copA, which are involved in copper resistance. The comparative analysis of S. aureus RN4220 and the three S. aureus RN4220 transformants carrying plasmid pUR1902, pUR2940, or pUR2941 revealed an 8-fold increase in CdSO4 and a 2-fold increase in CuSO4 MICs. The emergence of multidrug resistance plasmids that also carry heavy metal resistance genes is alarming and requires further surveillance. The colocalization of antimicrobial resistance genes and genes that confer resistance to heavy metals may facilitate their persistence, coselection, and dissemination.

Inducible clindamycin resistance among clinical isolates of Staphylococcus aureus

Introduction: The resistance to antimicrobial agents among staphylococci is an increasing problem. This has led to renewed interest in the usage of macrolide-lincosamide-streptogramin B (MLSB) antibiotics to treat Staphylococcus aureus infections. Clinical failure has been reported due to multiple mechanisms that confer resistance to MLSB antibiotics. The present study was aimed to detect inducible clindamycin resistance among S. aureus isolates and to study the relationship between clindamycin and methicillin resistance. Materials and Methods: During a period of 1 year, a total of 593 S. aureus isolates from various clinical specimens were included in the study. Antimicrobial susceptibility test was done by Kirby-Bauer's disc diffusion method as per Clinical and Laboratory Standards Institute (CLSI) guidelines. For detection of inducible clindamycin resistance, D test using erythromycin and clindamycin as per CLSI guidelines was performed, and three different phenotypes were interpreted as methicillin-sensitive (MS) phenotype (D test negative), inducible MLSB (iMLSB) phenotype (D test positive), and constitutive MLSB phenotype. Results: Of the total 593 S. aureus isolates, majority were obtained from pus (31.1%) followed by blood and body fluids (27.3%). All the isolates were sensitive to vancomycin, teicoplanin, and linezolid. Out of 306 (51.7%) erythromycin resistant isolates, 280 (91.5%) were methicillin-resistant S. aureus (MRSA) and 26 (8.5%) were methicillin-sensitive S. aureus (MSSA). iMLSB phenotype in 33.3%, MS phenotype in 44.8%, and constitutive MLSB phenotype was observed in 21.9% of isolates. Inducible clindamycin resistance was almost equal among MRSA and MSSA isolates. Conclusion: D test should be included as a mandatory method in routine disc diffusion testing to detect inducible clindamycin resistance in staphylococci for the optimum treatment of patients.

Antimicrobial susceptibility and resistance mechanisms of clinical Clostridium difficile from a Chinese tertiary hospital

Clostridium difficile is a predominant cause of antibiotic-associated diarrhoea. It is increasingly difficult to treat C. difficile infection efficiently owing to its multidrug resistance. In the present study, 60 clinical C. difficile isolates were collected and analysed for their genotype, antimicrobial susceptibility and resistance mechanisms. Tandem repeat sequence typing (TRST) generated 21 types, including the epidemic clone tr017. Antimicrobial susceptibility testing of eight antibiotics was performed by the agar dilution method. Rifampicin, metronidazole and vancomycin remained the most potent agents in vitro, whilst the resistance rates of other agents such as ciprofloxacin, cefoxitin, clindamycin, tetracycline and moxifloxacin varied from 30% to 100%. 73.33% of the strains were multiresistant to at least three classes of antibiotics, and tr017 strains made up the greatest proportion of multidrug resistance. By further investigating the resistance mechanisms, amino acid substitutions in target enzymes encoded by gyrA/gyrB and rpoB were observed in fluoroquinolone- and rifampicin-resistant strains, respectively. The erm(B) gene was the most prevalent in macrolide–lincosamide–streptogramin B (MLSB)-resistant strains, and the ErmB determinant ‘Erj2’, a novel genetic organisation identified in this study, plays a central role in conferring resistance, especially in epidemic strains. Moreover, transposon Tn916 carrying the tet(M) gene is more common than Tn5397 in tetracycline resistance.

903 Multidrug Resistant Clones of Ca-Mrsa Isolated from Chinese Children and the Resistance Determinants to Clindamycin and Mupirocin

This study aims to correlate the multidrug resistance (MDR) and ST clones of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA), to identify the genes responsible for clindamycin and mupirocin resistance in Staphylococcus...

Phenotypical examination of the macrolide-lincosamide-streptogramin B resistance in Staphylococcus isolates

The aim of the present study was to evaluate the phenotypic characteristics of the macrolide-lincosamide-streptogramin B (MLSB) resistance in Staphylococcus aureus and coagulase-negative staphylococci (CNS) strains isolated from various clinical samples in our hospital. The study was conducted on 516 Staphylococcus isolates isolated from various clinical samples in Microbiology Laboratory of Diyarbakir State Hospital between January, 2009 and December, 2009. After the identification of microorganisms via conventional methods and the evaluation of their methicillin resistance profile, disk approximation test was performed using erythromycin (15 μg) and clindamycin (2 μg) disks in order to determine MLSB resistance phenotypes. Of 516 Staphylococcusisolates, 208 were determined to be S. aureus and 308 were CNS. The MLSB resistance of isolates was 56.2%, whereas the resistance due to the efflux pump was determined to be 3.5%. The MLSB resistance phenotype was determined in 38% of S. aureus strains and 68.5% of CNS strains. The presence of MLSB resistance was determined to be higher in methicillin-resistant group (74.7%) compared to the methicillin-susceptible group (23.9%). While constitutive MLSB resistance (cMLSB) and inducible MLSB resistance (iMLSB) were determined in 48.9 and 19.1% of methicillin-resistant S. aureus strains, respectively, these rates were 2.6 and 10.5% for methicillin-susceptible strains, respectively. The rate of constitutive resistance was determined to be 41.5% in methicillin resistant CNS, whereas the rate of inducible resistance was determined to be 35.9%. In methicillin-susceptible CNS group, cMLSB and iMLSB resistances were determined to be 17.6 and 23%, respectively. The cMLSB phenotype was more common among methicillin-resistant S. aureus and CNS group, whereas iMLSB phenotype was more common among methicillin-susceptible S. aureus strains. In conclusion, we suggest that the determination and reporting of the presence of inducible resistance is of great importance regarding the success of therapy; therefore, it would be beneficial to use D test in routine antibiogram studies. Key words: Staphylococcus aureus, coagulase-negative staphylococci, macrolide-lincosamide-streptogramin B

Detection of various types of resistance patterns and their correlation with minimal inhibitory concentrations against clindamycin among methicillin-resistant Staphylococcus aureus isolates

Purpose: The macrolide lincosamide streptogramin B (MLSB) family of antibiotics serves as an alternative for the treatment of skin and soft tissue infections caused by methicillin-resistant Staphylococcus aureus (MRSA). However, resistance to clindamycin too has emerged, which is of two types, inducible and constitutive. Therapeutic failure is common with inducible type of clindamycin resistance. This study was done to determine the various clindamycin resistance patterns in MRSA isolates and to compare them with minimal inhibitory concentration (MIC) of clindamycin. Materials and Methods: Fifty MRSA isolates were studied by disc approximation test (D test) to detect inducible iMLSB resistance and MIC by agar dilution technique. Results: Of the 50 isolates, 34 were sensitive to both clindamycin and erythromycin. 16 isolates showed different sensitivity patterns; nine of these were positive for D zone indicating inducible iMLSB resistance, five were positive for constitutive MLSB resistance and two showed possible efflux mechanism for macrolide resistance. Out of the 34 sensitive isolates, 5 showed isolated colonies (subpopulation) inside the clindamycin-sensitive zone. When these sub-populations were tested further, two were constitutive MLSB phenotypes, two were inducible iMLSB and one was HD (hazy D zone), which is D+ with growth up to clindamycin disc (which is also considered as constitutive MLSB phenotype). Seven isolates showed an MIC of ≥4 μg/ml to clindamycin in spite of being susceptible to both erythromycin and clindamycin by Kirby Bauer disc diffusion technique. Out of these seven isolates, five were those which grew as subpopulation inside the clindamycin-sensitive zone. Conclusion: Detection of iMLSB resistance among MRSA helps to avoid treatment failure with clindamycin. Studying the subpopulation inside the clindamycin-sensitive zone raises the question of existence of hetero-resistance or some other mechanism, which needs further study.

Penicillin Susceptibility and Macrolide-Lincosamide-Streptogramin B Resistance in Group BStreptococcusIsolates from a Canadian Hospital

Intrapartum antibiotic prophylaxis (IAP) is recommended for pregnant women who test positive for group B Streptococcus (GBS) in their genitourinary tract to prevent GBS-induced neonatal sepsis. Penicillin G is used as the primary antibiotic, and clindamycin or erythromycin as the secondary, if allergies exist. Decreased susceptibility to penicillin G has occasionally been reported; however, clindamycin and erythromycin resistance is on the rise and is causing concern over the use of clindamycin and erythromycin IAP. Antibiotic resistance was characterized phenotypically using a D-Test for erythromycin and clindamycin, while an E-Test (E-strip) was used for penicillin G. GBS was isolated from vaginal-rectal swabs and serologically confirmed using Prolex (Pro-Lab Diagnostics, Canada) streptococcal grouping reagents. Susceptibility testing of isolates was performed according to the Clinical Laboratory Standards Institute guidelines. All 158 isolates were penicillin G sensitive. Inducible macrolide-lincosamide-streptogramin B (MLSB) resistance was observed in 13.9% of isolates. Constitutive MLSB resistance was observed in 12.7% of isolates. M phenotype resistance was observed in 6.3% of isolates. In total, erythromycin resistance was present in 32.9% of the GBS isolates, while clindamycin resistance was present in 26.6%. The sampled GBS population showed no sign of reduced penicillin susceptibility, with all being well under susceptible minimum inhibitory concentration values. These data are congruent with the large body of evidence showing that penicillin G remains the most reliable clinical antibiotic for IAP. Clindamycin and erythromycin resistance was higher than expected, contributing to a growing body of evidence that suggests the re-evaluation of clindamycin and erythromycin IAP is warranted.

The strongest resistance of Staphylococcus aureus to erythromycin is caused by decreasing uptake of the antibiotic into the cells

The consequence of excessive use of macrolides is a high occurrence of mechanisms responsible for resistance to these drugs. Of 97 erythromycin-resistant bacterial strains gathered in the Wrocław area in Poland, 60% exhibited very high resistance, and those with the inducible MLSB (macrolide-lincosamide-streptogramin B) resistance phenotype predominated. Direct genetic investigation revealed that the erm genes coding for ribosomal methylases are the most frequently occurring erythromycin resistance-determining genes. No genetic resistance determinant was detected in 13% of the erythromycin-resistant strains. The efflux mechanism occurs in strains isolated from the nasopharyngeal cavity twice as often as in those isolated from other material, where the mechanism connected with target site modification predominates. Measurements of radiolabelled antibiotic accumulation inside bacterial cells revealed that in highly resistant strains (MIC > 1024 μg/ml), an important factor responsible for the resistance is the permeability barrier at the cell wall level. This would be a hitherto unknown mechanism of resistance to erythromycin in Staphylococcus aureus.

Continuous feeding of antimicrobial growth promoters to commercial swine during the growing/finishing phase does not modify faecal community erythromycin resistance or community structure

To investigate the effect of continuous feeding of antimicrobial growth promoters (tylosin or virginiamycin) on the swine faecal community. The study consisted of two separate on-farm feeding trials. Swine were fed rations containing tylosin (44 or 88 mg kg(-1) of feed) or virginiamycin (11 or 22 mg kg(-1) of feed) continuously over the growing/finishing phases. The temporal impact of continuous antimicrobial feeding on the faecal community was assessed and compared to nondosed control animals through anaerobic cultivation, the analysis of community 16S rRNA gene libraries and faecal volatile fatty acid content. Feeding either antimicrobial had no detectable effect on the faecal community. Erythromycin methylase genes encoding resistance to the macrolide-lincosamide-streptogramin B (MLS(B) ) antimicrobials are present at a high level within the faecal community of intensively raised swine. Continuous antimicrobial feeding over the entire growing/finishing phase had no effect on community erm-methylase gene copy numbers or faecal community structure. Antimicrobial growth promoters are believed to function by altering gut bacterial communities. However, widespread MLS(B) resistance within the faecal community of intensively raised swine likely negates any potential effects that these antimicrobials might have on altering the faecal community. These findings suggest that if AGP-mediated alterations to gut communities are an important mechanism for growth promotion, it is unlikely that these would be associated with the colonic community.

Antimicrobial Resistance among Respiratory Pathogens in Spain: Latest Data and Changes over 11 Years (1996-1997 to 2006-2007)

A nationwide multicenter susceptibility surveillance study (Susceptibility to the Antimicrobials Used in the Community in España [SAUCE] project), SAUCE-4, including 2,559 Streptococcus pneumoniae, 2,287 Streptococcus pyogenes, and 2,736 Haemophilus influenzae isolates was carried out from May 2006 to June 2007 in 34 Spanish hospitals. Then, the results from SAUCE-4 were compared to those from all three previous SAUCE studies carried out in 1996-1997, 1998-1999, and 2001-2002 to assess the temporal trends in resistance and the phenotypes of resistance over the 11-year period. In SAUCE-4, on the basis of the CLSI breakpoints, penicillin (parenteral, nonmeningitis breakpoint) and cefotaxime were the antimicrobials that were the most active against S. pneumoniae (99.8% and 99.6%, respectively). Only 0.9% of isolates had a penicillin MIC of > or = 2 microg/ml. In S. pyogenes, nonsusceptibility to erythromycin was observed in 19.4% of isolates. Among the H. influenzae isolates, a beta-lactamase-positive prevalence of 15.7% was found. A statistically significant temporal decreasing trend over the 11-year period was observed for nonsusceptibility (from 60.0% to 22.9%) and resistance (from 36.5% to 0.9%) to penicillin and for the proportion of erythromycin-resistant isolates of S. pneumoniae of the macrolide-lincosamide-streptogramin B (MLS(B)) phenotype (from 98.4% to 81.3%). A similar trend was observed for the prevalence of ampicillin resistance (from 37.6% to 16.1%), beta-lactamase production (from 25.7% to 15.7%), and beta-lactamase-negative ampicillin resistance (BLNAR) in H. influenzae (from 13.5% to 0.7%). Among erythromycin-resistant isolates of S. pyogenes, a significant increasing trend in the prevalence of MLS(B) was observed (from 7.0% to 35.5%). SAUCE-4 confirms a generalized decline in the resistance of the main respiratory pathogens to the antimicrobials as well as a shift in their resistance phenotypes.

Antimicrobial characterisation of CEM-101 activity against respiratory tract pathogens, including multidrug-resistant pneumococcal serogroup 19A isolates

CEM-101 is a novel fluorinated macrolide–ketolide with potent activity against bacterial pathogens that are susceptible or resistant to other macrolide–lincosamide–streptogramin B (MLSB)–ketolide agents. CEM-101 is being developed for oral and parenteral use in moderate to moderately severe community-acquired bacterial pneumonia. The objective of this study was to assess the activity of CEM-101 and comparators against contemporary respiratory tract infection (RTI) isolates. A worldwide sample of organisms was used, including Streptococcus pneumoniae [n=168; 59.3% erythromycin-resistant and 18 multidrug-resistant (MDR) serogroup 19A strains], Moraxella catarrhalis (n=21; 11 β-lactamase positive), Haemophilus influenzae (n=100; 48 β-lactamase positive), Haemophilus parainfluenzae and Haemophilus haemolyticus (n=12), and Legionella pneumophila (n=30). Testing and interpretation were performed using reference Clinical and Laboratory Standards Institute methods. CEM-101 was very potent against S. pneumoniae [minimum inhibitory concentration for 90% of the organisms (MIC90)=0.25mg/L; highest MIC at 0.5mg/L] and was 2- and ≥32-fold more active than telithromycin and clindamycin, respectively. CEM-101 also demonstrated potent activity against S. pneumoniae MDR-19A strains (MIC90=0.5mg/L). CEM-101 was the most potent antimicrobial agent tested against L. pneumophila, with all MIC values at ≤0.015mg/L (telithromycin MIC90=0.03mg/L). CEM-101 was as potent as azithromycin against Haemophilus spp. RTI pathogens (MIC90=2mg/L), with no variations for β-lactamase production. CEM-101 MIC values against M. catarrhalis were all at ≤0.5mg/L. Interestingly, CEM-101 potency was ca. 6log2 dilutions greater than telithromycin MIC results among 44 β-haemolytic streptococci having telithromycin MICs ≥2mg/L. CEM-101 exhibited the greatest potency and widest spectrum of activity against RTI pathogens among the tested MLSB–ketolide agents (azithromycin, clarithromycin, erythromycin, telithromycin, clindamycin and quinupristin/dalfopristin) and was comparable overall with levofloxacin.

Distribution of Serotypes, Genotypes, and Resistance Determinants among Macrolide-Resistant Streptococcus pneumoniae Isolates

Macrolide resistance in Streptococcus pneumoniae has emerged as an important clinical problem worldwide over the past decade. The aim of this study was to analyze the phenotypes (serotype and antibiotic susceptibility), genotypes (multilocus sequence type [MLST] and antibiotic resistance gene/transposon profiles) among the 31% (102/328) of invasive isolates from children in New South Wales, Australia, in 2005 that were resistant to erythromycin. Three serotypes--19F (47 isolates [46%]), 14 (27 isolates [26%]), and 6B (12 isolates [12%])--accounted for 86 (84%) of these 102 isolates. Seventy four (73%) isolates had the macrolide-lincosamide-streptogramin B (MLS(B)) resistance phenotype and carried Tn916 transposons (most commonly Tn6002); of these, 73 (99%) contained the erythromycin ribosomal methylase gene [erm(B)], 34 (47%) also carried the macrolide efflux gene [mef(E)], and 41 (55%) belonged to serotype 19F. Of 28 (27%) isolates with the M phenotype, 22 (79%) carried mef(A), including 16 (57%) belonging to serotype 14, and only six (19%) carried Tn916 transposons. Most (84%) isolates which contained mef also contained one of the msr(A) homologues, mel or msr(D); 38 of 40 (95%) isolates with mef(E) (on mega) carried mel, and of 28 (39%) isolates with mef(A), 10 (39%) carried mel and another 11(39%) carried msr(D), on Tn1207.1. Two predominant macrolide-resistant S. pneumoniae clonal clusters (CCs) were identified in this population. CC-271 contained 44% of isolates, most of which belonged to serotype 19F, had the MLS(B) phenotype, were multidrug resistant, and carried transposons of the Tn916 family; CC-15 contained 23% of isolates, most of which were serotype 14, had the M phenotype, and carried mef(A) on Tn1207.1. Erythromycin resistance among S. pneumoniae isolates in New South Wales is mainly due to the dissemination of multidrug-resistant S. pneumoniae strains or horizontal spread of the Tn916 family of transposons.

Prevalence of phenotypic resistance of Staphylococcus aureus isolates to macrolide, lincosamide, streptogramin B, ketolid and linezolid antibiotics in Turkey

The incidence of drug-resistant pathogens differs greatly between countries according to differences in the usage of antibiotics. The purpose of this study was to investigate the phenotypic resistance of 321 methicillin resistance Staphylococcus aureus (MRSA) and 195 methicillin susceptible S. aureus (MSSA) in a total of 516 S. aureus strains to macrolide, lincosamide, streptogramin B (MLSB), ketolid, and linezolid. Disk diffusion method was applied to determine MLSB phenotype and susceptibility to different antibiotic agents. It was found that 54.6% of the isolates were resistant to erythromycin (ERSA), 48% to clindamycin, 55% to azithromycin, 58.7% to spiramycin, 34.7% to telithromycin, and 0.4% to quinupristin-dalfopristin, respectively. No strain resistant to linezolid was found. The prevalence of constitutive (cMLSB), inducible (IMLSB), and macrolides and type B streptogramins (M/MSB) among ERSA isolates (237 MRSA, 45 MSSA) was 69.6%, 18.2%, and 12.2% in MRSA and 28.9%, 40%, and 31.1% in MSSA, respectively. In conclusions, the prevalence of cMLSB was predominant in MRSA; while in MSSA strains, iMLSB and M/MSB phenotype were more higher than cMLSB phenotype resistance. The resistance to quinupristindalfopristin was very low, and linezolid was considered as the most effective antibiotic against all S.aureus strains.

Phenotypic characterization of nosocomial isolates of Staphylococcus aureus with reference to MRSA

Apart from being a major cause of mortality, nosocomial infections due to Staphylococcus aureus have been imposing a burden on patients, hospitals and health care systems. The present study was designed to determine the prevalence of methicillin resistant S. aureus (MRSA) among nosocomial isolates along with their phenotypic characterization. MRSA and methicillin sensitive S. aureus (MSSA) were determined by performing four different tests viz: disc diffusion, oxacillin screen agar test, MRSA latex agglutination test, and MIC of oxacillin by E test. Of the 149 S. aureus nosocomial isolates, 44.9% were MRSA, which included 82.1% of homogeneous MRSA and 17.9% of heterogeneous MRSA. Association of MRSA infection was found to be significantly higher in skin and lower respiratory tract infections. Of the MRSA isolates, 65 were multiresistant oxacillin resistant Staphylococcus aureus (MORSA) and 2 were nonmultiresistant oxacillin resistant Staphylococcus aureus (NORSA). D tests performed on 136 isolates showed that Inducible macrolide-lincosamide-streptogramin B (MLSB) and constitutive MLSB resistance were found to be associated with MRSA. On the contrary, susceptibility to both erythromycin and clindamycin was found to be associated with MSSA. However, MSB (macrolide-streptogramin B) resistance was not found associated either with MRSA or MSSA. Furthermore, both inducible and constitutive MLSB were found to be associated with only homogenous MRSA. D tests may be made mandatory in all S. aureus isolates as inducible MLSB resistance cannot be detected in routine susceptibility test unless erythromycin and clindamycin are placed 15-26 mm apart.

Macrolide Resistance in Microorganisms at Antimicrobial-Free Swine Farms

To investigate the relationship between agricultural antimicrobial use and resistance, a variety of methods for quantification of macrolide-lincosamide-streptogramin B (MLS(B)) resistance were applied to organic swine farm manure samples. Fluorescence in situ hybridization was used to indirectly quantify the specific rRNA methylation resulting in MLS(B) resistance. Using this method, an unexpectedly high prevalence of ribosomal methylation and, hence, predicted MLS(B) resistance was observed in manure samples from two swine finisher farms that reported no antimicrobial use (37.6% +/- 6.3% and 40.5% +/- 5.4%, respectively). A culture-based method targeting relatively abundant clostridia showed a lower but still unexpectedly high prevalence of resistance at both farms (27.7% +/- 11.3% and 11.7% +/- 8.6%, respectively), while the prevalence of resistance in cultured fecal streptococci was low at both farms (4.0%). These differences in the prevalence of resistance across microorganisms suggest the need for caution when extrapolating from data obtained with indicator organisms. A third antimicrobial-free swine farm, a breeder-to-finisher operation, had low levels of MLS(B) resistance in manure samples with all methods used (<9%). Tetracycline antimicrobials were detected in manure samples from one of the finisher farms and may provide a partial explanation for the high level of MLS(B) resistance. Taken together, these findings highlight the need for a more fundamental understanding of the relationship between antimicrobial use and the prevalence of antimicrobial resistance.

Effect of the presence of the antimicrobial tylosin in swine waste on anaerobic treatment

An anaerobic sequencing batch reactor (ASBR), seeded with a biomass inoculum that previously had not been exposed to the macrolide antimicrobial tylosin (mixture of Tylosin A, B, C, and D), was operated for 3 months with swine waste without Tylosin A and for 9 months with swine waste containing Tylosin A at an average concentration of 1.6mg/L. When swine waste with tylosin was fed to the ASBR, methane production and volatile solids removal did not appear to be inhibited and a methane yield of 0.47L methane per gram volatile solids fed to the ASBR was observed. Throughout the operating period, Tylosin A levels in ASBR biomass and effluent were below the detection limit of 0.01mg/L. However, during the first 3 months of operation, the levels of macrolide–lincosamide–streptogramin B (MLSB)-resistant bacteria in the ASBR biomass increased substantially as determined by hybridizations with oligonucleotide probes designed to target MLSB-resistant bacteria. Since no Tylosin A was present in the swine waste during the initial 3 months, the presence of MLSB-resistant bacteria in the swine waste was likely the reason for the increase in resistance. Subsequently, the levels of MLSB-resistant bacteria in ASBR biomass stabilized with an average of 44.9% for the 9 months of operation with swine waste containing Tylosin A. The level of MLSB-resistant bacteria in the swine waste fed to the ASBR during this period averaged 18.0%. The results indicate that anaerobic treatment of a waste stream containing tylosin was effective (based on reactor performance) and that the level of resistant bacteria in the ASBR was substantially higher than in the waste stream fed to this system.

Distributions of Macrolide-Lincosamide-Streptogramin B Resistance Phenotypes in Clinical Isolates of Staphylococi

Background: Increased resistance rates to macrolide-lincosamide-streptogramin B (MLSB) antibiotics among clinical isolates of staphylococci are considered as a consequence of an expanded use of these antibiotics in the treatment of Gram-positive infections. The proportion of MLSB resistance phenotypes of staphylococci is quite different by geographical variations and study periods. The aim of the present study was to determine the distribution of MLSB resistance phenotypes among clinical isolates of staphylococci in a university hospital. Methods: The MLSB resistance phenotypes of clinical isolates of staphylococci were investigated by the double-disk diffusion test using erythromycin and clindamycin disks. Results: Of 7,916 isolates, 55.7% exhibited a constitutive resistance phenotype (cMLSB) whereas 8.1% expressed an inducible resistance phenotype (iMLSB). Among 3,419 coagulase-negative staphylococci (CNS), 32.6% and 10.0% exhibited cMLSB and iMLSB resistance phenotypes, respectively. Of 4,497 Staphylococcus aureus isolates, 73.1% and 6.8% were cMLSB and iMLSB resistance phenotypes, respectively. cMLSB was detected among 90.2% of methicillin-resistant S. aureus (MRSA), 46.5% of methicillin-resistant CNS (MRCNS), 3.2% of methicillin-susceptible CNS (MSCNS), and 2.2% of methicillin-susceptible S. aureus (MSSA). iMLSB was detected among 16.5% of MSSA, 11.5% of MRCNS, 6.7% of MSCNS, and 4.4% of MRSA. Conclusion: MLSB resistance was more prevalent among S. aureus isolates than CNS strains. Although cMLSB was the most frequently detected resistance phenotype among the total staphylococcal isolates, methicillin-susceptible strains exhibited somewhat higher iMLSB resistance rates compared with methicillin-resistant strains. (Korean J Clin Microbiol 2008; 11:78-83)

Differences in Potential for Selection of Clindamycin-Resistant Mutants Between Inducible erm (A) and erm (C) Staphylococcus aureus Genes

In staphylococci, inducible macrolide-lincosamide-streptogramin B (MLS(B)) resistance is conferred by the erm(C) or erm(A) gene. This phenotype is characterized by the erythromycin-clindamycin "D-zone" test. Although clindamycin appears active in vitro, exposure of MLS(B)-inducible Staphylococcus aureus to this antibiotic may result in the selection of clindamycin-resistant mutants, either in vitro or in vivo. We have compared the frequencies of mutation to clindamycin resistance for 28 isolates of S. aureus inducibly resistant to erythromycin and bearing the erm(C) (n = 18) or erm(A) (n = 10) gene. Seven isolates susceptible to erythromycin or bearing the msr(A) gene (efflux) were used as controls. The frequencies of mutation to clindamycin resistance for the erm(A) isolates (mean +/- standard deviation, 3.4 x 10(-8) +/- 2.4 x 10(-8)) were only slightly higher than those for the controls (1.1 x 10(-8) +/- 6.4 x 10(-9)). By contrast, erm(C) isolates displayed a mean frequency of mutation to clindamycin resistance (4.7 x 10(-7) +/- 5.5 x 10(-7)) 14-fold higher than that of the S. aureus isolates with erm(A). The difference was also observed, although to a lower extent, when erm(C) and erm(A) were cloned into S. aureus RN4220. We conclude that erm(C) and erm(A) have different genetic potentials for selection of clindamycin-resistant mutants. By the disk diffusion method, erm(C) and erm(A) isolates could be distinguished on the basis of high- and low-level resistance to oleandomycin, respectively.

Clinical and Epidemiological Aspects of Invasive Streptococcus pyogenes Infections in Denmark during 2003 and 2004

Active surveillance of invasive group A streptococcal (GAS) infections was conducted in Denmark during 2003 and 2004 as a part of the Strep-EURO initiative. The main objective was to improve understanding of the epidemiology of invasive GAS disease in Denmark. During the 2 years, 278 cases were reported, corresponding to a mean annual incidence of 2.6 cases per 100,000 inhabitants. The vast majority of isolates, 253 (91%), were from blood, with the remaining 25 (9%) being from cerebrospinal fluid, joints, or other normally sterile sites. The mean case fatality rate (CFR) was 20%, with the rate being higher in patients more than 70 years of age (36.5%). For streptococcal toxic shock syndrome (STSS) and necrotizing fasciitis the CFRs were 53% and 25%, respectively. Out of 16 T types recorded, three predominated: T28 (23%), T1 (22%), and the cluster T3/13/B3264 (14%). Among 29 different emm types, emm28 and emm1 accounted for 51% of strains, followed by emm3 (11%), emm89 (7%), and emm12 (5.5%). Low resistance rates were detected for macrolide-lincosamide-streptogramin B (MLS(B)) antibiotics (3%) and tetracycline (8%); two isolates exhibited coresistance to tetracycline and macrolides. Of nine pyrogenic exotoxin (superantigen) genes examined, speA and speC were identified in 58% and 40% of the strains, respectively; either of the genes was present in all strains causing STSS. Most strains harbored speG (99%). ssa was present in 14% of the isolates only. In Denmark, as in comparable countries, GAS invasive disease shows a sustained, high endemicity, with involvement of both established and emerging streptococcal emm and T types.

Macrolide Resistance Trends in β-Hemolytic Streptococci in a Tertiary Korean Hospital

PurposeErythromycin-resistant β-hemolytic streptococci (BHS) has recently emerged and quickly spread between and within countries throughout the world. In this study, we evaluate the antimicrobial susceptibility patterns and erythromycin resistance mechanisms of BHS during 2003-2004.Materials and MethodsThe MICs of seven antimicrobials were determined for 204 clinical isolates of BHS from 2003 to 2004. Resistance mechanisms of erythromycin-resistant BHS were studied by the double disk test as well as by polymerase chain reaction (PCR).ResultsCompared with our previous study, resistance among Streptococcus pyogenes isolates to a variety of drugs decreased strikingly: from 25.7% to 4.8% in erythromycin; 15.8% to 0% in clindamycin; and 47.1% to 19.0% in tetracycline. The prevalent phenotypes and genotypes of macrolide-lincosamide-streptograminB (MLSB) resistance in Streptococcus pyogenes isolates have been changed from the constitutive MLSB phenotype carrying erm(B) to the M phenotype with mef(A) gene. In contrast with Streptococcus pyogenes, resistance rates to erythromycin (36.7%), clindamycin (43.1%), and tetracycline (95.4%) in Streptococcus agalactiae isolates did not show decreasing trends. Among the Streptococcus dysgalactiae subsp. equisimilis isolates (Lancefield group C, G), resistance rates to erythromycin, clindamycin, tetracycline and chloramphenicol were observed to be 9.4%, 3.1%, 68.8%, and 9.4%, respectively.ConclusionContinual monitoring of antimicrobial resistance among large-colony-forming BHS is needed to provide the medical community with current data regarding the resistance mechanisms that are most common to their local or regional environments.