Lincomycin Resistance in Methicillin-Resistant Staphylococcus aureus Strains of Hospital Origin

Summary

A total of 170 Staphylococcus aureus strains isolated during a one-year period at the University Hospital of Patras Medical School were examined for resistance to a battery of antimicrobial agents by disk diffusion and minimum inhibitory concentration (MIC) determination. Fifty-five isolates were lincomycin- and methicillin-resistant (LMRSA). In the group of 55 LMRSA isolates 13 were also resistant to vancomycin. All the LMRSA isolates were not typed by the international set and the experimental phages 88A and 25 at routine typing dilution (RTD), while 18 isolates were lysed by phages at 100XRTD and 1000XRTD. Reverse phage-typing and heat shock treatment of the LMRSA isolates had no effect on their typability. Plasmid profiles coupled with restriction endonuclease analysis of plasmid DNA established that the LMRSA isolates represent different strains. Membrane-protein profiles by polyacrylamide gel electrophoresis (PAGE) showed that LMRSA strains could belong to one group. This method proved useful and sensitive for characterization of LMRSA.     

病灶残腔灭活治疗软骨肉瘤的近远期效果分析

目的 探讨病灶残腔灭活治疗软骨肉瘤的近远期效果.方法 收治软骨肉瘤患者72例,根据治疗方法的不同分为观察组与对照组各36例,对照组采用手术治疗,观察组采用病灶残腔灭活治疗,观察与记录两组的近远期预后.结果 对照组平均手术时间为(290.42±56.24)min,出血量为(1622.94±451.92) ml;而观察组平均手术时间为(182.44±44.92) min,出血量为(432.11±111.84)ml,观察组均明显低于对照组(P＜0.05).观察组术后3个月的深部感染、深静脉血栓、血肿、皮缘坏死等并发症发生率为8.3％,对照组为36.1％,观察组明显低于对照组(P＜0.05).观察组与对照组术后3个月的肢体功能优良率分别为36.1％和8.3％,观察组的优良率明显高于对照组(P＜0.05).随访至今,观察组与对照组的中位生存时间分别为(78.24±11.48)个月和(59.24±10.42)个月,观察组的中位生存时间明显长于对照组(P＜0.05).结论 病灶残腔灭活治疗软骨肉瘤具有很好的微创性,在近期能提高肢体功能,降低并发症的预防,在远期能延长患者的生存时间,有很好的应用价值.     

Frequency and Transferability of Trimethoprim and Sulfonamide Resistance in Methicillin-Resistant Staphylococcus aureus and Staphylococcus epidermidis

A total of 374 Staphylococcus aureus and 126 Staphylococcus epidermidis strains from 14 countries were studied for their resistance to methicillin, trimethoprim (Tp) and sulfonamides (Su), alone and combined (TpSu). The frequency of resistance to Tp, Su and TpSu was much higher in methicillin-resistant S. epidermidis (MRSE) than in methicillin-resistant S. aureus (MRSA). Considerable differences, however, existed in isolates from different countries. Resistance to Tp, Su or TpSu in MRSA was low or absent in isolates from Switzerland, Spain, Japan, Mexico, Argentina and Chile, but high in isolates from Germany and Brazil. High level Tp resistance mostly resided on large plasmids. It could be transferred in 17 out of 97 strains. Su resistance was never cotransferred. Strains cured of their large Tp resistance plasmids remained Su-resistant, which suggests a chromosomal location of Su resistance.     

p73基因失活在儿童急性淋巴细胞白血病发病和预后中的意义

目的 探讨p73基因mRNA失表达与儿童急性淋巴细胞白血病(ALL)的发病和预后的关系。方法 采用反转录聚合酶链反应(RT-PCR)方法检测了34例ALL患儿骨髓单个核细胞内p73 mRNA的表达情况，并分析了p73 mRNA失表达与化疗的反应及复发的关系。结果 儿童ALL患者中p73 mRNA失表达率达26．5％(9/34)，且与诱导缓解治疗的反应和复发显著相关(P＜0．05)。结论 p73m RNA失表达在小儿ALL的发病过程中起重要作用，p73 mRNA检测对评估儿童ALL预后，指导临床治疗有一定临床意义。     

Field size dependence of radiation sensitivity and dose fractionation response in skin

Four sets of data from the literature were analyzed to assess the effects of field size on dose tolerance and dose fraction size dependence in irradiated skin. The data consisted of combinations of total dose and dose per exposure (or number of fractions) required to yield a given degree of visible damage to the skin, for fields of different sizes. Putative cell survival curves were constructed, under the assumptions that the isoeffect represents a fixed cell survival, and that each exposure during a course of fractionated irradiation has equal effect on cell survival. The analysis showed that overall sensitivity to radiation, and dependence on dose per exposure, both increase with field size. To account for these results we describe a model that can be qualitatively related to the geometric properties of the dermal vascular network. First, vascular function after irradiation should depend on the length of the vessels exposed to the radiation. This directly predicts an increasing sensitivity in large irradiated fields. Furthermore, if vascular function determines radiation response, the shape of the shoulder (low-dose) region of the effective survival curve will depend on the average number of vessels nourishing each cell, with a more pronounced shoulder for a high multiplicity of vessels. The model predicts a greater fractionation sensitivity in large than in small fields, in agreement with our analysis of the isoeffect data. It is therefore possible that the advantages of hyperfractionation in reducing late effects in normal tissues may be related to vascular architecture, and not to inherent differences between late and acutely responding cell populations.     

Comparison of teicoplanin and vancomycin in vitro activity on clinical isolates of Staphylococcus aureus

Abstract

Ninety-one clinical isolates of Staphylococcus aureus have been tested with the Kirby Bauer and the Etest® method to determine the susceptibility to glycopeptides in the 2007–2010 period. Five strains (5·5%) were resistant to vancomycin and nine (9·9%) to teicoplanin. Teicoplanin showed a median minimal inhibitory concentration (MIC) of 1 mg/l (range 0·125–24 mg/l), an MIC50 of 1 mg/l, and an MIC90 of 2 mg/l; vancomycin had a median MIC of 1·5 mg/l (range 0·38–4 mg/l), an MIC50 of 1·5 mg/l, and an MIC90 of 2 mg/l. More isolates were distributed on higher values of MIC for vancomycin. Inhibition halos induced by vancomycin-impregnated paper diskettes were slightly larger than those by teicoplanin. Glycopeptide resistance among methicillin-resistant Staphylococcus aureus in Italy is an underestimated phenomenon, possibly due to the described underestimation of glycopeptides MICs by the automatic broth microdilution method, when compared to agar MIC assays. A teicoplanin MIC creep, as reported for vancomycin, cannot be assumed.     

Lysogeny of Methicillin-Resistant Staphylococcus aureus and the Role of Prophages in Transfer of Conjugative and Non-Conjugative Plasmids

Summary

The lysogcnicity of 49 strains of methicillin-resistant S. aureus (MRSA) isolated in Moscow clinics in the 1970s and 80s was studied by the method of mitomycin C induction. It was found that one strain had phage of serogroup B, 33 strains had serogroup F phages and 15 strains had phages of both serogroups. In the course of genetic crossing on nitrocellulose filters it was demonstrated that serogroups B and F prophages contained in recipient cells 1) increase the frequency of transfer of conjugative plasmid pG873 and 2) mobilize transfer of non-conjugative plasmids pE994 and rms7.     

Oxacillin- and Mupirocin-Resistant Staphylococcus aureus: In vitro Activity of Silver Sulphadiazine and Cerium Nitrate in Hospital Strains

Abstract

Nasal carriage is an important reservoir of oxacillin-resistant Staphylococcus aureus (ORSA). Mupirocin is a topical drug used to remove S. aureus from nares. However, isolates resistant to mupirocin have been reported all over the world. Silver sulphadiazine (SSD) is a topical agent, which when associated with cerium nitrate (CN), has been shown to be useful in the treatment of burn infections and could be an alternative drug for patient decolonization. Susceptibility to oxacillin in 203 S. aureus isolates was evaluated by the agar diffusion test, while the agar diffusion and agar dilution methods were used for mupirocin. A PCR-multiplex method was performed to detect the mecA and ileS-2 genes. Minimum inhibitory concentration (MICs) to SSD and CN, used alone or in association, were determined by the agar dilution method. One hundred and sixty-three (80.3%) strains were oxacillinresistant, and 37 (18.2%) were mupirocin resistant. The MIC of SSD alone or in association with CN was 64 μg/mL, while for CN alone was 2,048 μg/mL for all isolates. SSD presented anti-staphylococcal activity at concentrations (64 μg/mL) much lower than those commonly used in commercial preparations (10 mg/g) and had good activity against mupirocin-resistant strains, showing that this drug could be used for nasal decolonization in ORSA carries.     

In vitro activity of ceftaroline and ceftobiprole against methicillin-resistant Staphylococcus aureus with decreased susceptibility to vancomycin isolated in paediatric patients

Minimal inhibitory concentrations (MIC, mg/l) of ceftaroline and ceftobiprole were evaluated over 70 methicillin-resistant Staphylococcus aureus (MRSA) strains with vancomycin MIC ≥1 isolated in a paediatric hospital. The proportion of non-wild-type strains (MIC?>?epidemiological cut off) was 18% for ceftobiprole and 64% for ceftaroline. Only 1.4% of strains was resistant to ceftobiprole, and none to ceftaroline. These results are worrisome, since show the presence of non-negligible proportions of MRSA strains with high MIC values for ceftaroline and ceftobiprole in a setting where both drugs were never used.     

Pharmacokinetically-based prediction of the effects of antibiotic combinations on resistant Staphylococcus aureus mutants: in vitro model studies with linezolid and rifampicin

To explore if combinations of linezolid (L) with rifampicin (R) are able to restrict Staphylococcus aureus resistance, the enrichment of L- and R-resistant mutants was studied in an in vitro dynamic model. L- and R-resistant mutants were enriched in all single drug treatments. In contrast, L-resistant mutants were not enriched and R-resistant mutants were similar to baseline amounts with only minimal regrowth at the end of the combination treatments. These effects appear to be explained by lowering the mutant prevention concentration (MPC) for L+R combinations (MPC_L+R) compared to the MPCs of L and R alone (MPC_L and MPC_R) and thereby the longer times above MPC_L+R (73–100% of the dosing interval for L and 42–58% for R) compared to the times above MPC_L (0–44%) and MPC_R (0%). These findings provide an opportunity to predict the selection of S. aureus resistance in L+R treatments using MPC_L+Rs.     

Multicentric study in five African countries of antibiotic susceptibility for three main pathogens: Streptococcus pneumoniae,Staphylococcus aureus,and Pseudomonas aeruginosa

Antibiotic resistance is a growing clinical and epidemiological problem. We report on the antibiotic susceptibility of three pathogens isolated from patients in Algeria, Egypt, Morocco, Senegal, and Tunisia during 2010–2011. In total, 218 Streptococcus pneumoniae, 428 Staphylococcus aureus, and 414 Pseudomonas aeruginosa strains were collected. S. pneumoniae resistance was noted against penicillin (30.2%), erythromycin (27.4%), cefpodoxime (19.1%), amoxicillin (12.0%), cefotaxime (7.4%), and levofloxacin (3.2%). All the strains were teicoplanin susceptible. Staphylococcus aureus methicillin resistance differed between countries, from 5.0% in Senegal to 62.7% in Egypt. Levofloxacin resistance was low in all countries, and the highest rate (in Egypt) was still only 13.6% for intermediate and resistant strains combined. Most strains were susceptible to fosfomycin (99.3%) and pristinamycin (94.2%). P. aeruginosa resistance was found against levofloxacin (30.4%), ciprofloxacin (29.9%), tobramycin (19.7%), ceftazidime (19.2%), and imipenem (17.9%), but not colistin. Antibiotic susceptibility varied widely between countries, with resistance typically most prevalent in Egypt.     

Predicting effects of antibiotic combinations using MICs determined at pharmacokinetically derived concentration ratios: in vitro model studies with linezolid- and rifampicin-exposed Staphylococcus aureus

To predict the effects of combined use of antibiotics on their pharmacodynamics, the susceptibility of Staphylococcus aureus to linezolid–rifampicin combinations was tested at concentration ratios equal to the ratios of 24-area under the concentration–time curve (AUC₂₄) simulated in an in vitro dynamic model. The linezolid MICs in combination with rifampicin decreased 8- to 67-fold. The rifampicin MICs were similar with or without linezolid. The enhanced activity of linezolid combined with rifampicin increased the AUC₂₄/MIC ratios and provided more pronounced antibacterial effects compared with single treatments. The areas between the control growth and time-kill curves (ABBCs) determined in combined and single treatments with linezolid were plotted against AUC₂₄/MIC on the same graph (r² 0.94). These findings suggest that the effects of linezolid–rifampicin combinations can be predicted by AUC₂₄/MICs of linezolid using its MIC determined at pharmacokinetically derived linezolid-to-rifampicin concentration ratios.     

Genetic lineages and antimicrobial resistance genotypes in Staphylococcus aureus from children with atopic dermatitis: detection of clonal complexes CC1, CC97 and CC398

The objective was to analyse the genetic lineages of Staphylococcus aureus recovered from nasal and skin samples of atopic dermatitis (AD) paediatric patients, and to characterize the antimicrobial resistance phenotype–genotype and the immune-evasion-cluster (IEC) type of isolates. Forty S. aureus isolates from 35 patients (skin: 26; nasal samples: 14) were characterized. Isolates were submitted to spa-, agr- and multilocus sequence typing. All S. aureus strains analyzed were methicillin-susceptible (MSSA). High genetic diversity was detected among the 40 MSSA isolates (especially among skin isolates), with detection of 27 different spa-types, 20 sequence-types and 16 clonal complexes (CCs). Lineages CC30 and CC5 were predominant among nasal isolates (71% vs 23% skin). Thirteen different CCs were detected among skin isolates, with detection of clades CC1, CC9 and CC398. Antimicrobial resistance rates detected were higher in skin than in nasal isolates, especially for macrolides, aminoglycosides, lincosamides and mupirocin. MSSA strains were characterized into five IEC-types, being A, B and F the predominant ones. MSSA strains of lineages CC45 and CC5 were detected in almost all cases in AD patients with severe Scoring Atopic Dermatitis (SCORAD) and lineages CC8, and CC30 in those with mild or moderate one. As conclusion, high-clonal-diversity was detected among MSSA from AD patients, especially in skin-isolates. Colonization with S. aureus of some CCs seems more associated with AD severity than other lineages.     

A novel parameter to predict the effects of antibiotic combinations on the development of Staphylococcus aureus resistance: in vitro model studies at subtherapeutic daptomycin and rifampicin exposures

The search for optimal predictors of anti-mutant effects remains a pressing problem in studies of antibiotic-associated bacterial resistance. To relate the emergence of bacterial resistance with the antibiotic mutant prevention concentration (MPC), a novel integral parameter – the area around the resistance threshold, i.e. MPC level (AAMPC) is proposed. The AAMPC is the algebraic sum of the area under the antibiotic concentration–time curve that is above the MPC (positive area) and the area above the concentration–time curve that is under the MPC (negative area). To assess the predictive performance of AAMPC, the enrichment of resistant Staphylococcus aureus was studied by simulating treatment with daptomycin and rifampicin alone and in combination in an in vitro dynamic model. The enhanced anti-mutant effects of the antibiotic combinations were due to lowering the negative 24-h AAMPCs. These findings suggest that a novel MPC-related parameter is a reliable predictor of mutant enrichment.     

Determining the prevalence of SCCmec polymorphism,virulence and antibiotic resistance genes among methicillin-resistant Staphylococcus aureus (MRSA) isolates collected from selected hospitals in west of Iran

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the most important pathogens worldwide and compared to other staphylococcal species that are associated with higher mortality rate. A total of 500 Staphylococcus spp. was collected from selected hospitals in Ilam, Kermanshah, Khorram Abad and Hamadan cities and, via phenotypic and genotypic methods, was assessed to find MRSA. The presence or absence of prevalent antibiotic resistance genes and virulence genes was evaluated among MRSA isolates, using polymerase chain reaction (PCR) method, and then the SCCmec typing of these isolates was assayed by multiplex PCR. A total of 372 (74.4%) Stapylococcus spp. isolates were identified as S. aureus, among which 200 (53.8%) possessed the mecA gene and were distinguished as MRSA. All of MRSA isolates contained blaZ gene. The frequency of ermA and ermC genes among erythromycin-resistant MRSA isolates was 21.6% and 66.7%, respectively. The frequency of the virulence genes eta, hla and sea among MRSA isolates was 10%, 80.5% and 100%, respectively. SCCmec type IV accounted for 30.6% of the MRSA isolates and SCCmec type III, SCCmec type II and SCCmec type I accounted for 30%, 22% and 17.5% of the isolates, respectively. The antibiotic resistance genes and the virulence genes of blaZ, hla, sea, eta and ermC had high frequencies among the MRSA isolates. This study showed that the antibiotic resistance genes had higher frequencies among SCCmec types I and IV, which confirms the previous reports in this field.     

Characteristics and Outcomes of Methicillin‐Resistant Staphylococcus aureus Bloodstream Infections in Patients with Cancer Treated with Vancomycin: 9‐Year Experience at a Comprehensive Cancer Center

Background.

Methicillin-resistant Staphylococcus aureus (MRSA) bloodstream infections (BSIs) can cause significant morbidity and mortality in patients with cancer. However, data on outcomes of patients treated with vancomycin are lacking.

Methods.

We identified 223 patients with cancer who developed MRSA BSIs between January 2001 and June 2009 and were treated with vancomycin. Treatment failure was defined as death within 60 days of infection, persistent bacteremia ≥5 days, fever ≥4 days, recurrence or relapse, and secondary MRSA infection.

Results.

The treatment failure rate was 52% (116 of 223 patients). These patients were more likely to have been hospitalized, been treated with steroids within the previous 3 months, developed acute respiratory distress syndrome, required mechanical ventilation, required intensive care unit care, and community-onset infections (all p < .05). Risk factors for MRSA-associated mortality (27 of 223 patients; 12%) included hematologic malignancy and hematopoietic stem cell transplantation, community-onset infection, secondary BSI, MRSA with minimum inhibitory concentration (MIC) ≥2.0 μg/mL, mechanical ventilation, and a late switch to an alternative therapy (≥4 days after treatment failure; all p < .05). On multivariate analysis, mechanical ventilation and recent hospitalization were identified as independent predictors of vancomycin failure, and community-onset infection, secondary BSIs, and MIC ≥2 μg/mL were identified as significant predictors of MRSA-associated mortality.

Conclusions.

We found a high treatment failure rate for vancomycin in patients with cancer and MRSA BSIs, as well as a higher mortality. A vancomycin MIC ≥2 μg/mL was an independent predictor of MRSA-associated mortality. An early switch to an alternative therapy at the earliest sign of failure may improve outcome.