Meticillin-resistant S. Aureus Strains Research Articles

Brief communication: Carrier rate, antimicrobial resistance and molecular typing of Staphylococcus aureus and Staphylococcus pseudintermedius in healthy dogs from Morogoro, Tanzania.

Staphylococcus pseudintermedius and S. aureus are important pathogens in dogs. This study established carrier rates, strain diversity and antimicrobial resistance of these bacteria among healthy dogs in Tanzania. Based on cultures of mouth and perineal swabs, 11.3% and 50.3% of 151 healthy dogs were carriers of S. aureus and S. pseudintermedius, respectively. Only four dogs (3%) carried meticillin-resistant S. aureus (MRSA), while none of the S. pseudintermedius strains were meticillin-resistant. 12 of 19 S. aureus strains tested were resistant to penicillin G, and resistance to enrofloxacin and tetracycline was also commonly detected. The most common resistances in 103 S. pseudintermedius strains tested were to penicillin G (28.2%) and tetracycline (22.3%). S. pseudintermedius strains showed 65 different random amplified polymorphic DNA (RAPD) fingerprints, and S. aureus strains belonged to eight different spa types, including two novel types (t18988 and t18989). MRSA strains carried SCCmec type V. Healthy dogs in Tanzania were carriers of MRSA at low frequency, and half of the dogs carried S. pseudintermedius with high strain diversity.

P.8.b.008 How pregnancy changes psychoactive drugs – pharmacokinetic implications in clinical practice

The emergence of glycopeptide reduced susceptibility and resistance in Staphylococcus aureus strains is a growing clinical problem that poses significant clinical challenges in treatment. Its development is a complex and novel process involving many subtle physiological changes in the micro-organism. Daptomycin is the first cyclic lipopeptide approved for clinical use. Unlike most other antimicrobials, a trend towards increased daptomycin resistance has not been reported, although several cases of daptomycin non-susceptibility have been reported. The present review will present the available evidence on daptomycin resistance of S. aureus, with particular attention to its development. In addition to a literature overview, we have compiled the reported cases of daptomycin non-susceptibility to shed light on possible clinical mechanisms of resistance. In the 36 reports describing 62 clinical cases, infections caused by meticillin-resistant S. aureus (MRSA) strains with a vancomycin minimum inhibitory concentration (MIC) between 1 mg/L and 2 mg/L often led to vancomycin treatment failure, which may be associated with the development of non-susceptibility to daptomycin. Additional evidence suggests that underdosage of daptomycin is an important clinical aspect that merits further study. The current analysis highlights the importance of determining the MIC when using vancomycin to treat patients with severe S. aureus infections and that when failure is suspected, testing for heterogeneous vancomycin-intermediate S. aureus (hVISA) may also be necessary. Whilst further investigation is needed, it can be hypothesised that MRSA strains become hVISA during prolonged bacteraemia, which may predispose to the development of daptomycin resistance.

Genotype-specific prevalence of heterogeneous vancomycin-intermediate Staphylococcus aureus in Asian countries

Although heterogeneous vancomycin-intermediate Staphylococcus aureus (hVISA) has been increasingly reported, the true prevalence of hVISA is unclear, especially in Asia. In this study, the genotype-specific prevalence of hVISA among meticillin-resistant S. aureus (MRSA) clinical isolates collected from Asian countries was determined. Among MRSA collections from South Korea, Taiwan, Hong Kong, Thailand, the Philippines, Vietnam, India and Sri Lanka in the ANSORP surveillance study during 2004 and 2006, isolates with a vancomycin minimum inhibitory concentration of ≥0.25mg/L were randomly selected. After screening by macro Etest, hVISA was confirmed using the modified population analysis profile method. MRSA isolates were typed by spa tying and multilocus sequence typing (MLST). Among 462 MRSA isolates, 16 (3.5%) were confirmed as hVISA. The proportion of hVISA was highest in South Korea and Vietnam (both 7.0%), followed by Thailand (3.2%) and Taiwan (1.9%). spa type t601 belonging to clonal complex (CC) 5 showed the highest proportion of hVISA (33.3%), and hVISA accounted for 6.9% among isolates of t002 belonging to CC5. Among CC239 isolates, only those of t037 were hVISA (1.6%). Among isolates of community-associated MRSA genotypes, hVISA was found only in those of t437 (4.8%) belonging to CC59, and no hVISA was found among those of CC30 or CC72. The prevalence of hVISA in the Asian region differed by country and was dependent upon the genotype of MRSA strains. It suggests that differences in hVISA prevalence between countries can be affected by the genotype distribution of MRSA strains.

The distribution of pathogenic and toxigenic genes among MRSA and MSSA clinical isolates

Staphylococcus aureus (S. aureus) is considered as a notorious nosocomial pathogen among hospitalized patients and community-dwelling subjects. Its increasing morbidity and mortality is believed to be due to antibiotic resistance. However, the data concerning molecular properties of infecting strains are few.In this study, a total of 192 S. aureus strains, including 88 (45.8%) meticillin-sensitive S. aureus (MSSA) and 104 (54.2%) meticillin-resistant S. aureus (MRSA) were recovered from clinical samples. The prevalence of subtypes containing staphylococcal cassette chromosome mec (SSCmec), staphylococcal enterotoxins (SEs), toxic shock syndrome toxin (TSST) and exfoliative toxin was assessed by PCR. Antibiotic susceptibility pattern and vancomycin resistance of each isolate were evaluated by disk diffusion method and micro-dilution method, respectively.9 (2.3%) strains required MIC > 2 mg/l of vancomycin, which significantly increased among multi drug resistant (MDR), MRSA and SCCmec type III strains (p < 0.05). 171 (89%), 140 (72.91%), 7 (3.6), 78 (48.6%), 5 (2.6%), 151 (78.64%), 129 (67.18%), 178 (92.7%) and 15 (7.8%) of 192 isolates harbored mecA, entA, entB, entC, entD, entE, eta, etb and tsst-1 genes, respectively. 31 (16.14%), 5 (2.6%), 95 (49.48%) and 7 (3.64%) of 192 isolates carried SCCmec type I, II, III and IV, respectively. We found a significantly higher rate of MRSA and resistance to all tested antibiotics, except to penicillin G, kanamycin and linezolide among the SCCmec type III class (p < 0.05).According to our findings, MSSA isolates should be taken as seriously as MRSA strains due to the potential presence of broad spectrum virulence factor genes.

Activity of the antiseptic polyhexanide against meticillin-susceptible and meticillin-resistant Staphylococcus aureus.

Staphylococcus aureus is one of the most important pathogens, with increasing emergence of meticillin-resistant S. aureus (MRSA) strains. This is associated not only with multiresistance to antibiotics but also with increasing resistance to topical antibiotics and antiseptics. As the antiseptic polyhexanide has only a low risk of emergence of resistant strains, the aim of the study was to obtain data on the sensitivity of S. aureus towards polyhexanide. The effect of polyhexanide was tested against 80 meticillin-susceptible S. aureus (MSSA) and 80 MRSA strains from sporadic cases as well as against 6 MRSA outbreak strains. The clonal diversity of the 166 strains was proven by pulsed-field gel electrophoresis (PFGE). Minimum inhibitory concentrations (MICs) and minimum bactericidal concentrations (MBCs) were determined by the serial broth microdilution technique according to DIN 58940. Time-kill studies were performed for reference strains MSSA ATCC 29213 and MRSA ATCC 33591. MICs and MBCs in the range of 0.5-2mg/L were found. According to a created epidemiological cut-off (ECOFF) value of 4mg/L, all strains were regarded as susceptible to polyhexanide, including MRSA epidemic strains and MSSA and MRSA sporadic strains with various antibiotic susceptibility patterns. Addition of up to 4% albumin to the test medium did not change the MICs and MBCs. Time-kill studies showed reduction rates of 4log10CFU/mL for 200mg/L and 5log10CFU/mL for 400mg/L polyhexanide within 5-30min. It is concluded that polyhexanide is suitable for topical eradication of S. aureus.

Prevalence and resistance of commensal Staphylococcus aureus, including meticillin-resistant S aureus, in nine European countries: a cross-sectional study

Information about the prevalence of Staphylococcus aureus resistance to antimicrobial drugs has mainly been obtained from invasive strains, although the commensal microbiota is thought to be an important reservoir of resistance. We aimed to compare the prevalence of nasal S aureus carriage and antibiotic resistance, including meticillin-resistant S aureus (MRSA), in healthy patients across nine European countries. In this cross-sectional study, nasal swabs were obtained from 32,206 patients recruited by family doctors participating in existing nationwide family doctor networks in Austria, Belgium, Croatia, France, Hungary, Spain, Sweden, the Netherlands, and the UK. Eligible patients were aged 4 years or older (≥ 18 years in the UK) and presented with a non-infectious disorder. Swabs were sent to national microbiological laboratories for identification and isolation of S aureus. Antibiotic resistance testing was done at one central microbiological laboratory. We established the genotypic structure of the isolated MRSA strains with the spa typing method. S aureus was isolated from 6956 (21 · 6%) of 32,206 patients swabbed. The adjusted S aureus prevalence for patients older than 18 years ranged from 12 · 1% (Hungary) to 29 · 4% (Sweden). Except for penicillin, the highest recorded resistance rate was to azithromycin (from 1 · 6% in Sweden to 16 · 9% in France). In total, 91 MRSA strains were isolated, and the highest MRSA prevalence was reported in Belgium (2 · 1%). 53 different spa types were detected-the most prevalent were t002 (n = 9) and t008 (n = 8). The prevalence of S aureus nasal carriage differed across the nine European countries assessed, even after correction for age, sex, and family doctor. Generally, the prevalence of resistance, including that of MRSA, was low. The MRSA strains recorded showed genotypic heterogeneity, both within and between countries. European Commission, 7th Framework Programme(grant agreement 223083).

Staphylococcal skin disease in livestock

This review covers cutaneous manifestations of staphylococcal infection in livestock species. CATTLE: In cattle, staphylococcal infections may present as folliculitis or as impetigo. Both may present as mild forms of a group of conditions loosely termed udder dermatitis, which has various clinical presentations and does not always involve staphylococci. GOATS: In goats, staphylococcal infection may be secondary to chorioptic mange or contagious pustular dermatitis (parapox virus infection). While Staphylococcus aureus is usually implicated, infection with Staphylococcus chromogenes and Staphylococcus hyicus have also been reported. SHEEP: Ovine staphylococcal dermatitis typically involves the head. Trauma due to the close contact of heads over feeding troughs and abrasive plants at pasture may be predisposing factors. PIGS: In pigs, the most common cause of staphylococcal skin disease is S. hyicus, although other bacteria, including Staphylococcus sciuri, Staphylococcus chromogenes and meticillin-resistant S. aureus (MRSA), have also been isolated from some cases of greasy pig disease (exudative epidermitis). Routine culture methods are increasingly supplemented by molecular methods to characterize staphylococci. As commensal bacteria, staphylococcal skin infection is presumed to develop because of predisposing factors. While topical and systemic therapies can be effective, it is important to control for predisposing factors so that recurrences can be prevented. LIVESTOCK-ASSOCIATED MRSA: In recent years, MRSA strains have emerged, particularly in pigs and cattle. While they rarely cause skin disease, they do pose a significant concern for public health authorities. Studies on livestock-associated MRSA may help to progress our understanding of staphylococci in livestock, especially how they spread between animals and humans.

Phagocytosis and intracellular killing of heterogeneous vancomycin-intermediate Staphylococcus aureus strains

Risk factors for invasive infections by heterogeneous vancomycin-intermediate Staphylococcus aureus (hVISA) may involve resistance to opsonophagocytosis and bacterial killing. hVISA strains typically have a thickened cell wall with altered peptidoglycan cross-linking. To determine whether hVISA may be endowed with an increased resistance to phagocytosis, this study assessed the characteristics of uptake and killing by granulocytes of three hVISA strains. All isolates were analysed by multilocus sequence typing and staphylococcal chromosome cassette mec typing. One of the strains belonged to the Hungarian meticillin-resistant S. aureus (MRSA) clone ST239-MRSA-III and the other two to the New York/Japan MRSA clone ST5-MRSA-II. In the presence of 10 % normal serum, the extent of phagocytosis and killing by blood granulocytes was equivalent for hVISA, MRSA and meticillin-sensitive S. aureus (MSSA) strains. Using granulocytes and serum from one patient who survived hVISA infection, the rate of phagocytosis and killing was also found to be comparable to that by control cells in the presence of 10 % serum. However, phagocytosis and killing of hVISA and MRSA (ATCC 25923) strains by normal granulocytes was markedly decreased in the presence of low concentrations (1 and 2.5 %) of serum from the patient who survived hVISA infection compared with that found with normal human serum. These data suggest that hVISA and MRSA isolates may be more resistant to opsonophagocytosis and bacterial killing than MSSA isolates, at least in some cases.

Decline of meticillin-resistant Staphylococcus aureus in Oxfordshire hospitals is strain-specific and preceded infection-control intensification

BackgroundIn the past, strains of Staphylococcus aureus have evolved, expanded, made a marked clinical impact and then disappeared over several years. Faced with rising meticillin-resistant S aureus (MRSA) rates, UK...

Changing epidemiology of meticillin-resistant S. aureus in Queensland, Australia, 2000–2006: use of passive surveillance of susceptibility phenotypes

The epidemiology of meticillin-resistant S. aureus (MRSA) infection has changed remarkably in recent years with the appearance of new MRSA strains causing infections in the community. These strains have now begun to cause healthcare-associated infections. The ability to track such changes is necessary to guide clinical and public health action. Here we report passive surveillance of all public laboratory susceptibility data in Queensland to track changes in MRSA phenotypes corresponding to the major epidemic strains from 2000 to 2006. The inpatient rate of MRSA isolation from pus, tissue and fluid (PTF) and blood culture (BC) specimens declined by 26% and 35%, respectively. The rate of isolation of the AUS-2/3-like phenotype (corresponding to ST239-MRSA-III) decreased from 651 to 242 isolates per million accrued patient days in inpatient PTF and BC, whereas that for non-multiresistant MRSA (nmMRSA, corresponding to community MRSA strains) increased from 71 to 315. The overall outpatient rate of MRSA isolation from PTF and BC increased by 224% and 31%, respectively. The rate of AUS-2/3-like isolates in outpatient PTF decreased from 131 to 60 per million outpatient occasions of service while the nmMRSA rate increased from 52 to 490. Surveillance of phenotypes derived from routine susceptibility data is a useful tool for tracking changes in the epidemiology of MRSA over large geographical regions.

Evaluation of six agglutination tests for Staphylococcus aureus identification depending upon local prevalence of meticillin-resistant S. aureus (MRSA)

Most routine laboratory detection of Staphylococcus aureus isolates is based on rapid agglutination test systems. Failure of agglutination assays to identify meticillin-resistant S. aureus strains (MRSA) has been demonstrated. The aim of this study was to evaluate six commercially available agglutination tests for the detection of meticillin-sensitive S. aureus (MSSA) and mecA-positive MRSA strains. The Dry Spot Staphytect Plus test (Oxoid), the Pastorex Staph Plus test (Bio-Rad), the Slidex Staph-Kit and Slidex Staph Plus test (bioMérieux), the Staphaurex Plus test (Remel) and the Staphylase Test (Oxoid) were used. As determined by pulsed field gel electrophoresis, 52 distinct MRSA strains from five countries, 83 MSSA strains and 150 coagulase-negative staphylococci were included. Species identification and determination of susceptibility patterns were performed using colony morphology, Gram stain, catalase testing, tube coagulase testing, DNase testing, mannitol fermentation, susceptibility testing towards oxacillin by Etest, coagulase gene PCR, fibrinogen receptor gene PCR and PCR of the mecA gene. Sensitivity of the agglutination tests ranged from 82.7 to 100.0 % for MRSA strains and 92.8 to 100.0 % for MSSA strains, respectively. Specificity of the test systems ranged from 91.3 to 99.1 %. None of the six agglutination assays produced correct reactions for all staphylococci tested. Only the Dry Spot Staphytect Plus test correctly identified all 52 MRSA strains. For the other tests kits, sensitivity of MRSA detection was lower than for MSSA isolates. Depending upon the local MRSA prevalence and the parameter of interest (sensitivity or specificity), these test systems may be useful for routine diagnostic purposes.

Antibiotic resistance in Staphylococcus aureus and its relevance in therapy

Staphylococcus aureus is a major cause of infections. Only ∼ 20% of the strains remain sensitive to penicillin. β-lactamase stable penicillins such as flucloxacillin form the mainstay of treatment of staphylococcal infection. Meticillin-resistant S. aureus (MRSA) are resistant to all β-lactam antibiotics. Glycopeptide antibiotics are effective against most MRSA strains but, in the last few years, isolates of MRSA that have reduced susceptibility to glycopeptides (glycopeptide-intermediate S. aureus) have been isolated. Some strains exhibit frank resistance to glycopeptides (vancomycin-resistant S. aureus). Infections due to these strains are difficult to treat. This review summarises the therapeutic options for MRSA, glycopeptide-intermediate S. aureus and vancomycin-resistant S. aureus. Novel therapeutic strategies such as immunotherapy and vaccines are also discussed.

Résistance au linézolide de Staphylococcus aureus avant inscription au livret du médicament

Resistance to antibiotics is a global problem in geriatric centres. Objective. – The aim of this study was to determine the frequency of the resistance to linezolid in Staphylococcus aureus strains before its release in a geriatric centre. Method. – From 03-01-01 to 03-04-30 linezolid was included in the panel of antibiotics tested in S. aureus strains. The susceptibilities were estimated by the disk diffusion test in routine clinical microbiology practice. Results. – A total of 213 strains of S. aureus was analysed. All of them were susceptible to the following antibiotics: linezolid, cotrimoxazol, fosfomycin, and glycopeptides. The meticillin-resistant S. aureus (MRSA) represented 67.1% (60.3–73.3) strains. The resistance to pefloxacin, tobramycin and erythromycin concerned 92.3% (86.3–95.9), 73.4% (65.3–80.3) and 31.5% (24.1–39.8) of MRSA strains respectively. The MRSA strains were less resistant to the following antimicrobial drugs: gentamicin 7.0% (3.6–12.8), fusidic acid 2.1% (0.5–6.5) and rifampicin 1.4% (0.2–5.5). The resistance concerning at the same time gentamicin, pefloxacin and fucidic acid represented 2.1% (0.5–6.5) of SARM strains, rifampicin was not interested. Conclusion. – Linezolid was effective in vitro in S. aureus strains regardless their susceptibilities in meticillin. According to its effectiveness in vivo, linezolid may be of use for the treatment of infections due to MRSA. However, there has been two reports of resistance of MRSA in clinical infections. The use of linezolid has to follow the instructions and it should be carefully monitored.