Antimicrobial resistance in Brachyspira pilosicoli with special reference to point mutations in the 23S rRNA gene associated with macrolide and lincosamide resistance

A point mutation in the 23S rRNA gene causes macrolide and lincosamide resistance in Brachyspira hyodysenteriae. The possible occurrence of a similar mutation in Brachyspira pilosicoli was studied and the MICs of six antimicrobial agents for Swedish field isolates of B. pilosicoli were determined. Of 10 isolates with high MICs of macrolide and lincosamide antibiotics, six had a mutation in nucleotide position 2058 or 2059 in the 23S rRNA gene as compared to the wild type of Escherichia coli, whereas none of 10 tylosin-susceptible isolates were mutated in this region. The mutations found in position 2058 were A --> T transversions, and in position 2059 either A --> G transitions or A --> C transversions. The MICs at which 90% of the B. pilosicoli field isolates were inhibited by tylosin, erythromycin, clindamycin, virginiamycin, tiamulin, and carbadox, were >256, >256, >4, 4, 2, and 0.125 microg/ml, respectively. In conclusion, point mutations in positions 2058 and 2059 of the 23S rRNA gene can cause macrolide and lincosamide resistance in B. pilosicoli. Macrolide resistance is widespread among Swedish field isolates of B. pilosicoli. Notably also a few isolates with elevated MICs of tiamulin were found.     

Utility of Sequencing the erm(41) Gene in Isolates of Mycobacterium abscessus subsp. abscessus with Low and Intermediate Clarithromycin MICs

The erm(41) gene confers inducible macrolide resistance in Mycobacterium abscessus subsp. abscessus, calling into question the usefulness of macrolides for treating M. abscessus subsp. abscessus infections. With an extended incubation (14 days), isolates with MICs of ≥8 μg/ml are considered macrolide resistant by current CLSI guidelines. Our goals were to determine the incidence of macrolide susceptibility in U.S. isolates, the validity of currently accepted MIC breakpoints, and the erm(41) sequences associated with susceptibility. Of 349 isolates (excluding those with 23S rRNA gene mutations), 85 (24%) had clarithromycin MICs of ≤8 μg/ml. Sequencing of the erm(41) genes from these isolates, as well as from isolates with MICs of ≥16 μg/ml, including ATCC 19977^T, revealed 10 sequevars. The sequence in ATCC 19977^T was designated sequevar (type) 1; most macrolide-resistant isolates were of this type. Seven sequevars contained isolates with MICs of >16 μg/ml. The T28C substitution in erm(41), previously associated with macrolide susceptibility, was identified in 62 isolates (18%) comprising three sequevars, with MICs of ≤2 (80%), 4 (10%), and 8 (10%) μg/ml. No other nucleotide substitution was associated with macrolide susceptibility. We recommend that clarithromycin susceptibility breakpoints for M. abscessus subsp. abscessus be changed from ≤2 to ≤4 μg/ml and that isolates with an MIC of 8 μg/ml have repeat MIC testing or erm sequencing performed. Our studies suggest that macrolides are useful for treating approximately 20% of U.S. isolates of M. abscessus subsp. abscessus. Sequencing of the erm gene of M. abscessus subsp. abscessus will predict inducible macrolide susceptibility.     

Erythromycin-resistant genes in group A β-haemolytic Streptococci in Chengdu,Southwestern China

Context: The management of Group A β-haemolytic Streptococci (Streptococcus pyogenes or GAS) infection include the use of penicillins, cephalosporins or macrolides for treatment. A general increase in macrolides resistance in GAS has been observed in recent years. Differences in rates of resistance to these agents have existed according to geographical location and investigators. Aims: To investigate the antibiotic pattern and erythromycin-resistant genes of GAS isolates associated with acute tonsillitis and scarlet fever in Chengdu, southwestern China. Settings and Design: To assess the macrolide resistance, phenotype, and genotypic characterization of GAS isolated from throat swabs of children suffering from different acute tonsillitis or scarlet fever between 2004 and 2011 in the city of Chengdu, located in the southwestern region of China. Materials and Methods: Minimal inhibitory concentration with seven antibiotics was performed on 127 GAS isolates. Resistance phenotypes of erythromycin-resistant GAS isolates were determined by the double-disk test. Their macrolide-resistant genes (mefA, ermB and ermTR) were amplified by PCR. Results: A total of 98.4% (125/127) of the isolates exhibited resistance to erythromycin, clindamycin and tetracycline. All isolates were sensitive to penicillin G and cefotaxime. Moreover, 113 ermB-positive isolates demonstrating the cMLS phenotype of erythromycin resistance were predominant (90.4%) and these isolates showed high-level resistance to both erythromycin and clindamycin (MIC₉₀ > 256 μg/ml); 12 (9.6%) isolates demonstrating the MLS phenotype of erythromycin resistance carried the mefA gene, which showed low-level resistance to both erythromycin (MIC₉₀ = 8 μg/ml) and clindamycin (MIC₉₀ = 0.5 μg/ml); and none of the isolates exhibited the M phenotype. Conclusions: The main phenotype is cMLS, and the ermB gene code is the main resistance mechanism against macrolides in GAS. Penicillin is the most beneficial for treating GAS infection, and is still used as first-line treatment. And macrolide antibiotics are not recommended for treatment of GAS infection in children because of the high rates of antimicrobial resistance in mainland China.     

Trends in the susceptibility of methicillin-resistant Staphylococcus aureus to nine antimicrobial agents,including ceftobiprole,nemonoxacin, and tyrothricin: results from the Tigecycline In Vitro Surveillance in Taiwan (TIST) study, 2006–2010

This study investigated the in vitro susceptibilities of methicillin-resistant Staphylococcus aureus (MRSA) to nine antimicrobial agents in Taiwan. A total of 1,725 isolates were obtained from 20 hospitals throughout Taiwan from 2006 to 2010. The minimum inhibitory concentrations (MICs) of the nine agents were determined by the agar dilution method. The MICs of mupirocin and tyrothricin were determined for 223 MRSA isolates collected from 2009 to 2010. For vancomycin, 99.7 % were susceptible; however, 30.0 % (n?=?517) exhibited MICs of 2 μg/ml and 0.3 % (n?=?6) demonstrated intermediate susceptibility (MICs of 4 μg/ml). Nearly all isolates (≥99.9 %) were susceptible to teicoplanin, linezolid, and daptomycin. The MIC₉₀ values were 2 μg/ml for ceftobiprole and 1 μg/ml for nemonoxacin. The MIC₉₀ values of mupirocin and tyrothricin were 0.12 and 4 μg/ml, respectively. MIC creep was noted for daptomycin during this period, but not for vancomycin, teicoplanin, linezolid, or tigecycline. For isolates with vancomycin MICs of 2 μg/ml, the MIC₉₀ values were 2 μg/ml for teicoplanin, 0.5 μg/ml for daptomycin, and 0.5 μg/ml for tigecycline. Those values were four- to eight-fold higher than those among isolates with vancomycin MICs of 0.5 μg/ml (2, 0.06, and 0.12 μg/ml, respectively). Of the nine MRSA isolates exhibiting non-susceptibility to vancomycin (n?=?6), teicoplanin (n?=?1), daptomycin (n?=?2), or tigecycline (n?=?1), all had different pulsotypes, indicating the absence of intra-hospital or inter-hospital spread. The presence of a high proportion of MRSA isolates with elevated MICs (2 μg/ml) and MIC creep of daptomycin might alert clinicians on the therapy for serious MRSA infections in Taiwan.     

National surveillance programme on susceptibility patterns of respiratory pathogens in South Africa: moxifloxacin compared with eight other antimicrobial agents

AIMS: The susceptibility patterns of Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis, Klebsiella pneumoniae, and Streptococcus pyogenes isolated from specimens submitted to 12 private laboratories in South Africa were determined. METHODS: Minimum inhibitory concentration (MIC) determinations were performed on the isolates in the microbiology laboratory at Tygerberg Hospital according to the recommendations of the National Committee for Clinical Laboratory Standards (NCCLS). RESULTS: According to the NCCLS breakpoints, 24% of 729 S pneumoniae isolates were sensitive, 30% intermediate, and 46% resistant to penicillin. Rates of macrolide resistance were high, with 61% of the pneumococci being resistant to clarithromycin and azithromycin. Co-trimoxazole resistance was also high, with 28% of pneumococcal strains being sensitive, 21% intermediate, and 51% resistant. beta Lactamase was produced by 7% of 736 H influenzae isolates and 91% of 256 M catarrhalis isolates. The quinolones, moxifloxacin and levofloxacin, were universally active against all isolates tested, which included S pneumoniae, H influenzae, M catarrhalis, K pneumoniae, and S pyogenes. CONCLUSIONS: Haemophilus influenzae and S pneumoniae were the most commonly isolated organisms. Resistance to penicillin was one of the highest reported in the world (76%) in S pneumoniae, as was macrolide resistance in pneumonocci, although surprisingly, only 14% of S pyogenes were resistant. The quinolones, moxifloxacin and levofloxacin, were active against all organisms tested, including the penicillin and macrolide resistant strains and moxifloxacin was more active than levofloxacin against pneumococci.     

Dissemination of High-Level Penicillin-, Extended-Spectrum Cephalosporin-, and Erythromycin-Resistant Streptococcus pneumoniae Clones in Taiwan

Sixty-seven clinical isolates of Streptococcus pneumoniae (40 of serotype 23F, 19 of serotype 19F, and 8 of serotype 6B) with decreased susceptibilities to penicillin and erythromycin were characterized by antimicrobial susceptibility patterns; DNA restriction endonuclease cleavage profiles of the penicillin-binding protein genes pbp1a, pbp2b, and pbp2x; random amplified polymorphic DNA (RAPD) patterns generated by arbitrarily primed PCR; and chromosomal macrorestriction profiles based on pulsed-field gel electrophoresis. A total of 22 clones (identical or closely related pulsotypes and identical RAPD patterns) were identified; 14 clones of 23F, 6 of 19F, and 2 of 6B. Three 23F clones (26 isolates) and one 19F clone (9 isolates) expressed high-level resistance to penicillin, cefotaxime, and erythromycin (MICs ≥ 256 μg/ml). These data strongly suggest that multiple high-level penicillin-, extended-spectrum cephalosporin-, and macrolide-resistant clones of S. pneumoniae have been disseminated in Taiwan.     

ermA, ermC , tetM and tetK are essential for erythromycin and tetracycline resistance among methicillin-resistant Staphylococcus aureus strains isolated from a tertiary hospital in Malaysia

The objective of this study was to determine the expression and transferability of tetracycline and erythromycin resistance among 188 MRSA strains from a Malaysian tertiary hospital. The minimum inhibitory concentrations (MICs) for oxacillin, erythromycin, tetracycline and ciprofloxacin ranged from 4 to 512 μg/ml, 0.25 to 256 μg/ml, 0.5 to 256 μg/ml and 0.5 to 512 μg/ml, respectively. Tetracycline-resistant strains showed co-resistance towards ciprofloxacin and erythromycin. There was a significant increase (P<0.05) of high-level tetracycline (≥MIC 256 μg/ml) and erythromycin (≥MIC 128 μg/ml) resistant strains in between the years 2003 and 2008. All erythromycin-resistant strains harboured ermA or ermC gene and all tetracycline-resistant strains harboured tetM or tetK gene. The blaZ was detected in all MRSA strains, whereas ermA, tetM, ermC, tetK and msrA genes were detected in 157 (84%), 92 (49%), 40 (21%), 39 (21%) and 4 (2%) MRSA strains, respectively. The blaZ, tetM, ermC and tetK genes were plasmid-encoded, with ermC gene being easily transmissible. Tn5801-like transposon was present in 78 tetM-positive strains. ermA and tetM genes were the most prevalent erythromycin and tetracycline resistance determinants, respectively, in MRSA strains. The association of resistance genes with mobile genetic elements possibly enhances the spread of resistant traits in MRSA.     

Echinocandin susceptibility testing of Candida isolates collected during a 1-year period in Sweden

The susceptibilities of Candida isolates to the echinocandins anidulafungin, caspofungin, and micafungin were determined by using the recently revised CLSI breakpoints and Etest on 238 clinical bloodstream Candida isolates collected between September 2005 and August 2006. The isolates represent approximately 95% of all non-albicans Candida bloodstream infections and one-third of Candida albicans bloodstream infections during this 1-year period in Sweden. The collection included 81 C. albicans, 81 C. glabrata, 36 C. parapsilosis, 14 C. dubliniensis, 8 C. tropicalis, 8 C. lusitaniae, 5 C. krusei, 2 C. guilliermondii and 2 C. inconspicua isolates as well as 1 C. pelliculosa isolate. The MICs were largely consistent with the global epidemiology of bloodstream Candida isolates. All C. albicans and C. glabrata isolates were susceptible to all 3 echinocandins (MIC ≤ 0.016 μg/ml in all instances). Resistance (MIC ≥ 8 μg/ml) to anidulafungin alone was observed for 4 (11.1%) C. parapsilosis isolates and for 1/2 C. guilliermondii isolates. Intermediate susceptibility to caspofungin alone was observed for 2/5 C. krusei isolates. One of the eight C. tropicalis isolates was classified as being intermediately susceptible to micafungin (MIC, 0.5 μg/ml) and as being resistant to anidulafungin and caspofungin (MIC ≥ 1 μg/ml). This isolate harbored a heterozygous FKS1 hot spot mutation (S80P) known to confer echinocandin resistance. This first study to apply the revised CLSI breakpoints for Etest endpoints showed that the breakpoints worked successfully in detecting an isolate with a hot spot mutation. Acquired echinocandin resistance is rare in Sweden. Echinocandin MICs against C. parapsilosis and C. guilliermondii were lowest for micafungin.     

Divergent rifamycin susceptibilities of Clostridium difficile strains in Canada and Italy and predictive accuracy of rifampin Etest for rifamycin resistance

We tested the activities of rifampin (RIF) and rifaximin (RFX) against 180 Clostridium difficile clinical isolates selected from Canadian and Italian culture collections. MICs were determined by CLSI agar dilution for both drugs and by Etest for RIF. Sixteen of 85 Italian isolates (18.8%) showed high-level resistance to both rifamycins (MICs, >16 μg/ml), compared to 2 of 95 (2.1%) Canadian isolates. Two new rpoB mutations were identified in rifamycin-resistant isolates. RIF susceptibility by Etest correlated completely with susceptibility to both rifamycins determined by agar dilution.     

Use of clindamycin disks To detect macrolide resistance mediated by ermB and mefE in Streptococcus pneumoniae isolates from adults and children

We studied 198 macrolide-resistant S. pneumoniae isolates obtained from adults and children to evaluate whether 2-microgram clindamycin disks can distinguish between isolates manifesting ermB- versus mefE-mediated resistance to clarithromycin and to determine the relative frequency with which each resistance mechanism occurred in these populations. The mefE gene was predominant among 109 isolates from children, occurring in 73.4% versus 50.6% of 89 isolates from adults. Three isolates (1.5%) did not amplify either gene. Among 125 mefE(+) isolates, the MIC of clarithromycin at which 90% of the isolates tested were inhibited, determined by Etest, was 32 microgram/ml versus >256 microgram/ml in 70 ermB(+) isolates. All ermB(+) isolates were highly resistant to clindamycin (MICs >256 microgram/ml), whereas all mefE(+) isolates were susceptible to clindamycin using the 2-microgram disk. Testing S. pneumoniae from the respiratory tract for susceptibility to clindamycin by agar disk diffusion is an easy and inexpensive method to estimate the frequency of resistance mediated by ermB in specific patient populations. Macrolide resistance mediated by ermB is usually of greater magnitude than that due to mefE. Clinical studies are needed to determine the significance of high- versus low-level macrolide resistance in S. pneumoniae.     

Detection of Staphylococcus aureus isolates with heterogeneous intermediate-level resistance to vancomycin in the United States

The prevalence of heterogeneous intermediate-level resistance to vancomycin (hVISA) in Staphylococcus aureus was assessed by screening a large collection of recent isolates. Susceptibility testing by the Clinical and Laboratory Standards Institute broth microdilution method and the Etest GRD (glycopeptide resistance detection) method (bioMérieux) was performed on 4,210 clinically significant S. aureus isolates obtained in 2009 from 43 U.S. centers. Isolates with Etest GRD-positive results for hVISA were evaluated further by repeat GRD testing and population analysis profiling-area under the curve (PAP-AUC) analysis. No VISA (vancomycin MIC, 4 to 8 μg/ml) or vancomycin-resistant (MIC ≥ 16 μg/ml) strains were detected. The Etest GRD screen for hVISA was initially positive for 68 isolates (1.6%; all by teicoplanin MIC ≥ 8 μg/ml at 24 or 48 h). Among those 68 isolates, 45 were reproducibly GRD positive. PAP-AUC testing confirmed only 11 isolates as hVISA (all had reproducible GRD-positive results). The 11 hVISA isolates were from nine medical centers and appeared genetically diverse (ten different PFGE types). The rates of resistance (including intermediate) for hVISA were as follows: oxacillin, 82%; erythromycin, 82%; clindamycin, 73%; levofloxacin, 73%; trimethoprim-sulfamethoxazole, 9%; and daptomycin, 9%. All hVISA isolates were susceptible to linezolid, tigecycline, and ceftaroline. Our data suggest that the overall prevalence of hVISA in the United States is low (0.3%). The hVISA isolates represented 10.5% of isolates with vancomycin MICs of 2 μg/ml and 0.1% of isolates with vancomycin MICs of 1 μg/ml. The positive predictive value of GRD Etest for hVISA was 16.2% for initial screen positive and 24.4% for reproducibly positive results.     

Emergence of rifampin-resistant Rhodococcus equi with several types of mutations in the rpoB gene among AIDS patients in northern Thailand

The antimicrobial susceptibilities of 30 Rhodococcus equi isolates obtained from 30 patients between 1993 and 2001 in northern Thailand were investigated. The MICs showed a tendency toward resistance to various antibiotics but sensitivity to imipenem, minocycline, vancomycin, and teicoplanin (MICs, /=64 micro g/ml) to rifampin. PCR amplification and DNA sequencing of the rpoB gene and molecular typing by pulsed-field gel electrophoresis (PFGE) were performed for eight R. equi isolates from eight AIDS patients with pneumonia or lung abscess caused by R. equi between 1998 and 2001, including one low- and three high-level rifampin-resistant isolates. As a result, two high-level rifampin-resistant strains with PFGE pattern A had a Ser531Trp (Escherichia coli numbering) mutation, and one high-level rifampin-resistant strain with PFGE pattern B had a His526Tyr mutation, whereas one low-level rifampin-resistant strain with PFGE pattern C had a Ser509Pro mutation. Four rifampin-susceptible strains with PFGE patterns D and E showed an absence of mutation in the rpoB region. Our results indicate the presence of several types of rifampin-resistant R. equi strains among AIDS patients in northern Thailand.     

Detection of amphotericin B resistance in Candida haemulonii and closely related species by use of the Etest, Vitek-2 yeast susceptibility system, and CLSI and EUCAST broth microdilution methods

The emerging fungal pathogens Candida haemulonii and Candida pseudohaemulonii often show high-level resistance to amphotericin B (AMB). We compared the utilities of five antifungal susceptibility testing methods, i.e., the Etest using Mueller-Hinton agar supplemented with glucose and methylene blue (Etest-MH), the Etest using RPMI agar supplemented with glucose (Etest-RPG), the Vitek-2 yeast susceptibility system, and the Clinical and Laboratory Standards Institute (CLSI) and European Committee on Antimicrobial Susceptibility Testing (EUCAST) broth microdilution methods, for the detection of AMB-resistant isolates of C. haemulonii and closely related species. Thirty-eight clinical isolates (8 C. haemulonii, 10 C. pseudohaemulonii, and 20 Candida auris isolates) were analyzed. Of the 18 C. haemulonii and C. pseudohaemulonii isolates, 18, 15, 18, 10, and 9 exhibited AMB MICs of >1 μg/ml by the Etest-MH, Etest-RPG, Vitek-2, CLSI, and EUCAST methods, respectively. All 20 C. auris isolates showed AMB MICs of ≤1 μg/ml by all five methods. Of the methods, the Etest-MH generated the broadest distribution of AMB MICs for all 38 isolates and showed the best discrimination between the C. haemulonii and C. pseudohaemulonii isolates (4 to 32 μg/ml) and those of C. auris (0.125 to 0.5 μg/ml). Taking the Etest-MH as the reference method, the essential agreements (within two dilutions) for the Etest-RPG, Vitek-2, CLSI, and EUCAST methods were 84, 92, 55, and 55%, respectively; the categorical agreements were 92, 92, 79, and 76%, respectively. This study provides the first data on the efficacy of the Etest-MH and its excellent agreement with Vitek-2 for discriminating AMB-resistant from AMB-susceptible isolates of these Candida species.     

Development of Doxycycline MIC and Disk Diffusion Interpretive Breakpoints and Revision of Tetracycline Breakpoints for Streptococcus pneumoniae

A study was performed to derive susceptibility testing interpretive breakpoints for doxycycline with Streptococcus pneumoniae and to reassess breakpoints for tetracycline using the requirements defined in Clinical and Laboratory Standards Institute (CLSI) document M23-A3. Tetracycline and doxycycline MICs and disk diffusion zone sizes were determined on 189 isolates selected from the 2009-2010 CDC Active Bacterial Core surveillance strain collection according to the testing methods described in CLSI documents M07-A8 and M02-A10. Tetracycline and doxycycline MICs and zones were compared to each other directly, and the reproducibility of MICs and zone diameters for both drugs was determined. Scattergrams of tetracycline MICs versus corresponding zone diameters and doxycycline MICs versus zones were prepared, and analysis indicated that the present CLSI tetracycline MIC and disk breakpoints did not fit the susceptibility data for doxycycline. Doxycycline was 1 to 3 dilutions more potent than tetracycline, especially in strains harboring the tetM resistance determinant. tetM was detected in ≥90% of isolates having tetracycline MICs of ≥4 μg/ml and in ≥90% with doxycycline MICs of ≥1. Limited pharmacokinetic/pharmacodynamic (PK/PD) data coupled with application of the error-rate bounded method of analysis suggested doxycycline-susceptible breakpoints of either ≤0.25 μg/ml or ≤0.5 μg/ml, with intermediate and resistant breakpoints 1 and 2 dilutions higher, respectively. The disk diffusion zone diameter correlates were susceptible at ≥28 mm, intermediate at 25 to 27 mm, and resistant at ≤24 mm. Revised lower tetracycline MIC breakpoints were suggested as susceptible at ≤1 μg/ml, intermediate at 2 μg/ml, and resistant at ≥4 μg/ml. Suggested tetracycline disk diffusion zones were identical to those of doxycycline.     

Genomic Epidemiology and Molecular Resistance Mechanisms of Azithromycin-Resistant Neisseria gonorrhoeae in Canada from 1997 to 2014

The emergence of Neisseria gonorrhoeae strains with decreased susceptibility to cephalosporins and azithromycin (AZM) resistance (AZM^r) represents a public health threat of untreatable gonorrhea infections. Genomic epidemiology through whole-genome sequencing was used to describe the emergence, dissemination, and spread of AZM^r strains. The genomes of 213 AZM^r and 23 AZM-susceptible N. gonorrhoeae isolates collected in Canada from 1989 to 2014 were sequenced. Core single nucleotide polymorphism (SNP) phylogenomic analysis resolved 246 isolates into 13 lineages. High-level AZM^r (MICs ≥ 256 μg/ml) was found in 5 phylogenetically diverse isolates, all of which possessed the A2059G mutation (Escherichia coli numbering) in all four 23S rRNA alleles. One isolate with high-level AZM^r collected in 2009 concurrently had decreased susceptibility to ceftriaxone (MIC = 0.125 μg/ml). An increase in the number of 23S rRNA alleles with the C2611T mutations (E. coli numbering) conferred low to moderate levels of AZM^r (MICs = 2 to 4 and 8 to 32 μg/ml, respectively). Low-level AZM^r was also associated with mtrR promoter mutations, including the −35A deletion and the presence of Neisseria meningitidis-like sequences. Geographic and temporal phylogenetic clustering indicates that emergent AZM^r strains arise independently and can then rapidly expand clonally in a region through local sexual networks.     

Characterization of In Vivo acquired resistance of Mycoplasma hyopneumoniae to macrolides and lincosamides

Macrolides and related antibiotics are used to control mycoplasma infections in the pig industry worldwide. Some porcine mycoplasmas, however, survive these treatments by acquiring resistance. The mechanism of acquired resistance to macrolides and lincosamides was studied in more detail for Mycoplasma hyopneumoniae by comparing both the phenotype and genotype of a resistant field isolate to five susceptible isolates. The MICs were significantly higher for the resistant strain for all antibiotics tested. The MICs for the 16-membered macrolide tylosin ranged from 8 to 16 microg for the resistant strain and from 0.03 to 0.125 microg/ml for the five susceptible strains. The MICs for the 15-membered macrolides and lincosamides were higher than 64 microg/ml for the resistant strain while only 0.06 to 0.5 microg/ml for the susceptible strains. Mycoplasma hyopneumoniae strains are intrinsically resistant to the 14-membered macrolides due to a G 2057 A transition (E. coli numbering) in their 23S rDNA. Therefore, high MICs were observed for all strains, although the MICs for the resistant strain were clearly increased. An additional, acquired A 2058 G point mutation was found in the 23S rRNA gene of the resistant strain. No differences linked to resistance were found in the ribosomal proteins L4 and L22. The present study showed that 23S rRNA mutations resulting in resistance to macrolides and lincosamides as described in other Mycoplasma spp. also occur under field conditions in M. hyopneumoniae.     

解脲脲原体Parvo和T960生物群msr基因的检测

目的 检测解脲脲原体(Uu)是否携带介导对红霉素耐药的msr基因,并分析其在Uu两生物群间分布的差异.方法 采用微量肉汤稀释法测定72株Uu临床株对红霉素的体外耐性,PCR检测msrA、msrB、msrG、msrD基因,并对Uu进行PCR分群.结果 72株Uu的最低抑菌浓度(MIC)范围是≤0.125 μg/ml≥128 μg/ml,MIC_(50)为32 μg/ml,MIC_(90)≥128μg/ml.分群结果示Parvo生物群51株,占70.83%,T960生物群21株,占29.17%.共检测到msrD基因的Uu24株,msrB基因12株,msrA基因1株,没有发现Uu菌株携带msrC基因.5株Uu同时检测到msrB和msrD基因,1株Uu同时检测到msrA、msrB和msrD基因.以MIC≥8μg/ml为耐药判定值时,两生物群对红霉素耐药性无显著差异,msrB基因主要分布在T960生物群.结论 Uu临床菌株携带对大环内酯类耐药的msr基因(包括msrA、msrB、msrP),msrB基因主要分布在T960生物群.     

In Vitro Activity of Amikacin against Isolates of Mycobacterium avium Complex with Proposed MIC Breakpoints and Finding of a 16S rRNA Gene Mutation in Treated Isolates

Amikacin is a major drug used for the treatment of Mycobacterium avium complex (MAC) disease, but standard laboratory guidelines for susceptibility testing are not available. This study presents in vitro amikacin MICs for 462 consecutive clinical isolates of the MAC using a broth microdilution assay. Approximately 50% of isolates had amikacin MICs of 8 μg/ml, and 86% had MICs of ≤16 μg/ml. Of the eight isolates (1.7%) with MICs of 64 μg/ml, five had an MIC of 32 μg/ml on repeat testing. Ten isolates (2.1%) had an initial amikacin MIC of >64 μg/ml, of which seven (1.5%) had MICs of >64 μg/ml on repeat testing. These seven isolates had a 16S rRNA gene A1408G mutation and included M. avium, Mycobacterium intracellulare, and Mycobacterium chimaera. Clinical data were available for five of these seven isolates, all of which had received prolonged (>6 months) prior therapy, with four that were known to be treated with amikacin. The 16S mutation was not detected in isolates with MICs of ≤64 μg/ml. We recommend primary testing of amikacin against isolates of the MAC and propose MIC guidelines for breakpoints that are identical to the CLSI guidelines for Mycobacterium abscessus: ≤16 μg/ml for susceptible, 32 μg/ml for intermediate, and ≥64 μg/ml for resistant. If considered and approved by the CLSI, this will be only the second drug recommended for primary susceptibility testing against the MAC and should facilitate its use for both intravenous and inhaled drug therapies.     

In vitro antimicrobial susceptibility of viridans streptococci isolated from blood cultures

The susceptibility of 211 viridans streptococci isolated from blood cultures to eight antimicrobial agents was determined. All the isolates were susceptible to cefotaxime, ceftriaxone, imipenem and vancomycin. Thirty eight percent of the isolates were resistant to penicillin (MICs 0.25 µg/ml). Tetracycline resistance was found in 41 % of the isolates and in 7 % of these strains tetracycline resistance was combined with erythromycin resistance. FiveStreptococcus mitis isolates exhibited increased (MIC 64 µg/ml and 128 µg/ml) or high-level (MIC 500 µg/ml) resistance to gentamicin, kanamycin and tobramycin. Four of these isolates were also resistant to penicillin (MICs 16–32 µg/m). In vitro synergy was not demonstrated for combinations of penicillin and gentamicin against threeStreptococcus mitis isolates with gentamicin MICs of 1000, 128 and 64 µg/ml. Results of this study indicate the importance of monitoring antibiotic resistance trends in viridans streptococci particularly with respect to penicillin and aminoglycoside resistance.     

Penicillin susceptibility breakpoints for Streptococcus pneumoniae and their effect on susceptibility categorisation in Germany (1997–2013)

Continuous nationwide surveillance of invasive pneumococcal disease (IPD) was conducted in Germany. From July 1, 1997, to June 30, 2013, data on penicillin susceptibility were available for 20,437 isolates. 2,790 of these isolates (13.7 %) originate from patients with meningitis and 17,647 isolates (86.3 %) are from non-meningitis cases. A slight decline in isolates susceptible at 0.06 and 0.12 μg/ml can be noticed over the years. Overall, 89.1 % of the isolates had minimum inhibitory concentrations (MICs) of ≤0.015 μg/ml. In 2012/2013, the first three isolates of Streptococcus pneumoniae with MICs of 8 μg/ml were found. The application of different guidelines with other MIC breakpoints for the interpretation of penicillin resistance leads to differences in susceptibility categorisation. According to the pre-2008 Clinical and Laboratory Standards Institute (CLSI) interpretive criteria, 5.3 % of isolates overall were intermediate and 1.4 % were resistant to penicillin. Application of the 2008–2014 CLSI interpretive criteria resulted in 7.6 % resistance among meningitis cases and 0.5 % intermediate resistance in non-meningitis cases. Referring to the 2009–2014 European Committee on Antimicrobial Susceptibility Testing (EUCAST) breakpoints, 7.6 % of the isolates in the meningitis group were resistant to penicillin. In the non-meningitis group, 6.1 % of the isolates were intermediate and 0.5 % were resistant. These differences should be kept in mind when surveillance studies on pneumococcal penicillin resistance are compared.