Phenotypic detection of methicillin resistance in Staphylococcus aureus by disk diffusion testing and Etest on Mueller-Hinton agar

On-site detection of methicillin-resistant Staphylococcus aureus (MRSA) utilizing G-quadruplex based isothermal exponential amplification reaction (GQ-EXPAR)

Methicillin-resistant Staphylococcus aureus (MRSA) has a high incidence in infectious hospitals and communities, highlighting the need for early on-site detection due to its resistance to methicillin antibiotics. The present study introduces a highly sensitive detection system for mecA, a crucial methicillin marker, utilizing an RCA-based isothermal exponential amplification reaction. The G-quadruplex-based isothermal exponential amplification reaction (GQ-EXPAR) method designs probes to establish G-quadruplex secondary structures incorporating thioflavin T for fluorescence. The system, unlike conventional genetic detection methods, works with portable isothermal PCR devices (isoQuark), facilitating on-site detection. A detection limit of 0.1 fmol was demonstrated using synthetic DNA, and effective detection was proven using thermal lysis. The study also validated the detection of targets swabbed from surfaces within bacterial 3D nanostructures using the GQ-EXPAR method. After applying complementary sequences to the padlock probe for the target, the GQ-EXPAR method can be used on various targets. The developed method could facilitate rapid and accurate diagnostics within MRSA strains.

Novel synergistic interactions between monolaurin, a mono-acyl glycerol and β lactam antibiotics against Staphylococcus aureus: an in vitro study

BACKGROUND

A major worldwide health issue is the rising frequency of resistance of bacteria.Drug combinations are a winning strategy in fighting resistant bacteria and might help in protecting the existing drugs.Monolaurin is natural compound extracted from coconut oil and has a promising antimicrobial activity against Staphylococcus.aureus. This study aims to examine the efficacy of monolaurin both individually and in combination with β-lactam antibiotics against Staphylococcus aureus isolates.

METHODS

Agar dilution method was used for determination of minimum inhibitory concentration (MIC) of monolaurin against S.aureus isolates. Scanning electron microscope (SEM) was used to detect morphological changes in S.aureus after treatment with monolaurin. Conventional and Real-time Polymerase chain reaction (RT-PCR) were performed to detect of beta-lactamase (blaZ) gene and its expressional levels after monolaurin treatment. Combination therapy of monolaurin and antibiotics was assessed through fractional inhibitory concentration and time-kill method.

RESULTS

The antibacterial activity of monolaurin was assessed on 115 S.aureus isolates, the MIC of monolaurin were 250 to 2000 µg/ml. SEM showed cell elongation and swelling in the outer membrane of S.aureus in the prescence of 1xMIC of monolaurin. blaZ gene was found in 73.9% of S.aureus isolates. RT-PCR shows a significant decrease in of blaZ gene expression at 250 and 500 µg/ml of monolaurin. Synergistic effects were detected through FIC method and time killing curve. Combination therapy established a significant reduction on the MIC value. The collective findings from the antibiotic combinations with monolaurin indicated synergism rates ranging from 83.3% to 100%.In time-kill studies, combination of monolaurin and β-lactam antibiotics produced a synergistic effect.

CONCLUSION

This study showed that monolaurin may be a natural antibacterial agent against S. aureus, and may be an outstanding modulator of β-lactam drugs. The concurrent application of monolaurin and β-lactam antibiotics, exhibiting synergistic effects against S. aureus in vitro, holds promise as potential candidates for the development of combination therapies that target particularly, patients with bacterial infections that are nearly incurable.

Nanofibers of N,N,N-trimethyl chitosan capped bimetallic nanoparticles: Preparation, characterization, wound dressing and in vivo treatment of MDR microbial infection and tracking by optical and photoacoustic imaging

Recent advancements in wound care have led to the development of interactive wound dressings utilizing nanotechnology, aimed at enhancing healing and combating bacterial infections while adhering to established protocols. Our novel wound dressings consist of N,N,N-trimethyl chitosan capped gold‑silver nanoparticles (Au-Ag-TMC-NPs), with a mean size of 108.3 ± 8.4 nm and a zeta potential of +54.4 ± 1.8 mV. These optimized nanoparticles exhibit potent antibacterial and antifungal properties, with minimum inhibitory concentrations ranging from 0.390 μg ml-1 to 3.125 μg ml-1 and also exhibited promising zones of inhibition against multi-drug resistant strains of S. aureus, E. coli, P. aeruginosa, and C. albicans. Microbial transmission electron microscopy reveals substantial damage to cell walls and DNA condensation post-treatment. Furthermore, the nanoparticles demonstrate remarkable inhibition of microbial efflux pumps and are non-hemolytic in human blood. Incorporated into polyvinyl alcohol/chitosan nanofibers, they form Au-Ag-TMC-NPs-NFs with diameters of 100-350 nm, facilitating efficient antimicrobial wound dressing. In vivo studies on MDR microbial-infected wounds in mice showed 99.34 % wound healing rate within 12 days, corroborated by analyses of wound marker protein expression levels and advanced imaging techniques such as ultrasound/photoacoustic imaging, providing real-time visualization and blood flow assessment for a comprehensive understanding of the dynamic wound healing processes.

A synergistic investigation of azo-thiazole derivatives incorporating thiazole moieties: a comprehensive exploration of their synthesis, characterization, computational insights, solvatochromism, and multimodal biological activity assessment

In the present study, a novel series of azo-thiazole derivatives (3a-c) containing a thiazole moiety was successfully synthesized. The structure of these derivatives was examined by spectroscopic techniques, including 1H NMR, 13C NMR, FT-IR, and HRMS. Further, the novel synthesized compounds were evaluated for their in vitro biological activities, such as antibacterial and anti-inflammatory activities, and an in silico study was performed. The antibacterial results demonstrated that compounds 3a and 3c (MIC = 10 μg mL-1) have a notable potency against Staphylococcus aureus compared to azithromycin (MIC = 40 μg mL-1). Alternatively, compound 3b displayed a four-fold higher potency (24 recovery days, 1.83 mg day-1) than Hamazine (28 recovery days, 4.14 mg day-1) in promoting burn wound healing, and it also exhibited a comparable inhibitory activity against screened bacterial pathogens compared to the reference drug. Docking on 1KZN, considering the excellent impact of compounds on the crystal structure of E. coli1KZN, a 24 kDa domain, in complex with clorobiocin, indicated the close binding of compounds 3a-c with the active site of the 1KZN protein, which is consistent with their observed biological activity. Additionally, we conducted molecular dynamics simulations on the docked complexes of compounds 3a-c with 1KZN retrieved from the PDB to assess their stability and molecular interactions. Furthermore, we assessed their electrochemical characteristics via DFT calculations. Employing PASS and pkCSM platforms, we gained insights into controlling the bioactivity and physicochemical features of these compounds, highlighting their potential as new active agents.

Molecular characterization of enterotoxin genes in methicillin-resistant S. aureus isolated from food poisoning outbreaks in Egypt

BACKGROUND

Staphylococcus aureus (S. aureus), especially methicillin-resistant S. aureus (MRSA), is a known disease-causing bacteria with many associated health hazards. Staphylococcal food poisoning can result from staphylococcal enterotoxins (SEs).

METHODS

In this study, 50 S. aureus isolates were isolated from the gastrointestinal tract (GIT) clinical samples of patients with food poisoning in clinical laboratories at Mansoura University Hospital, Egypt. For determination their antibiogram, these isolates were tested for antimicrobial sensitivity against 12 antimicrobial agents using the agar disk diffusion test. After DNA extraction from the isolates, conventional polymerase chain reaction (PCR) was used to detect mecA and SEs genes.

RESULTS

As a result, all isolates were ampicillin and cefoxitin-resistant, while 86% (43 of 50) of the tested isolates exhibited multidrug resistance (MDR). In contrast, the highest sensitivity was confirmed against vancomycin, linezolid and quinolones, namely ciprofloxacin and norfloxacin. Although 100% of the isolates were mecA positive, staphylococcal enterotoxin genes set-A, set-B, set-C, set-G, set-M, and set-O genes were detected in 56%, 20%, 8%, 32%, 16%, and 24%, of the tested isolates, respectively. Finally, isolates encompassing SEs genes were used to validate a microarray chip, indicating its potential for a better methodological approach for detecting and identifying SEs in human samples.

CONCLUSION

The genotypic findings of this study may help explain the enterotoxigenic patterns in S. aureus among Egyptian patients with food poisoning.

Enhancing the Antibacterial Activity of Erythromycin with Titanium Dioxide Nanoparticles against MRSA

BACKGROUND

Staphylococcus aureus (S. aureus) is the most common infectious agent in the community and hospitals. Infections with S. aureus are now becoming difficult to be treated by using conventional antibiotics due to its emerging methicillin-resistant S. aureus (MRSA) strain.

OBJECTIVE

In the present study, MRSA was isolated from clinical samples and evaluated for resistance against different antibiotics, TiO2 nanoparticles, and their combinations.

METHODS

Clinical samples were collected from Ayub Medical Complex (AMC), Abbottabad, Pakistan, and identified by different biochemical tests and polymerase chain reactions (PCR). Kirby-Bauer disk diffusion method was performed to evaluate antimicrobial susceptibility. Minimum Inhibitory Concentration (MIC) of ampicillin, ciprofloxacin, erythromycin, and vancomycin was found out by agar dilution method while the broth dilution method was used for the MIC of TiO2 nanoparticles and their combinations with erythromycin.

RESULTS

All 13/100 (13%) MRSA were successfully identified. All isolates were susceptible to quinupristin/ dalfopristin, teicoplanin, and vancomycin, while the highest resistance was seen with erythromycin, penicillin, and tetracycline. MIC showed high resistance against ampicillin (0.25-512 mg/L) and erythromycin (0.25-1024 mg/L).

CONCLUSION

The MIC value of 2 mM TiO2 nanoparticles was found to be the most effective concentration after 12 h of incubation, while the combination of erythromycin with 3 mM TiO2 nanoparticles was found to be more potent which significantly lowered down the MIC of erythromycin to 2-16 mg/L.

Characterization of methicillin-resistant Staphylococcus aureus through genomics approach

In the present study, a total of 35 S. aureus isolates collected from two different geographical locations viz., Germany and Hungary were tested for their methicillin-resistant phenotype which revealed a high incidence of methicillin-resistant S. aureus. The quantitative test for biofilm production revealed that 73.3% of isolates were biofilm producers. The isolates were further characterized using a set of biochemical and genotypic methods such as amplification and analysis of S. aureus species-specific sequence and mecA gene. The 33 mecA positive isolates were then characterized by the amplification of SCCmec and pvl toxin genes. Further, based on the biofilm-forming phenotype, 15 isolates were selected and characterized through PCR–RFLP of coa gene, polymorphism of spa gene and amplification of biofilm-associated genes. The dendrogram prepared from the results of both biochemical and genotypic analyses of the 15 isolates showed that except for the isolates SA G5 and SA H29, the rest of the isolates grouped themselves according to their locations. Thus, the two isolates were selected for further characterization through whole-genome sequencing. Comparative genome analysis revealed that SA G5 and SA H29 have 97.20% ANI values with 2344 gene clusters (core-genome) of which 16 genes were related to antibiotic resistance genes and 57 genes encode virulence factors. The highest numbers of singleton genes were found in SA H29 that encodes proteins for virulence, resistance, mobile elements, and lanthionine biosynthesis. The high-resolution phylogenetic trees generated based on shared proteins and SNPs revealed a clear difference between the two strains and can be useful in distinguishing closely related genomes. The present study demonstrated that the whole-genome sequence analysis technique is required to get a better insight into the MRSA strains which would be helpful in improving diagnostic investigations in real-time to improve patient care.

Penicillin-binding protein PBP2a provides variable levels of protection toward different β-lactams in Staphylococcus aureus RN4220

Methicillin-resistant Staphylococcus aureus (MRSA) is resistant to most β-lactams due to the expression of an extra penicillin-binding protein, PBP2a, with low β-lactam affinity. It has long been known that heterologous expression of the PBP2a-encoding mecA gene in methicillin-sensitive S. aureus (MSSA) provides protection towards β-lactams, however, some reports suggest that the degree of protection can vary between different β-lactams. To test this more systematically, we introduced an IPTG-inducible mecA into the MSSA laboratory strain RN4220. We confirm, by growth assays as well as single-cell microfluidics time-lapse microscopy experiments, that PBP2a expression protects against β-lactams in S. aureus RN4220. By testing a panel of ten different β-lactams, we conclude that there is also a great variation in the level of protection conferred by PBP2a. Expression of PBP2a resulted in an only fourfold increase in minimum inhibitory concentration (MIC) for imipenem, while a 32-fold increase in MIC was observed for cefaclor and cephalexin. Interestingly, in our experimental setup, PBP2a confers the highest protection against cefaclor and cephalexin-two β-lactams that are known to have a high specific affinity toward the transpeptidase PBP3 of S. aureus. Notably, using a single-cell microfluidics setup we demonstrate a considerable phenotypic variation between cells upon β-lactam exposure and show that mecA-expressing S. aureus can survive β-lactam concentrations much higher than the minimal inhibitory concentrations. We discuss possible explanations and implications of these results including important aspects regarding treatment of infection.

Bactericidal Silver Nanoparticles by Atmospheric Pressure Solution Plasma Processing

Silver nanoparticles have applications in plasmonics, medicine, catalysis and electronics. We report a simple, cost-effective, facile and reproducible technique to synthesise silver nanoparticles via plasma-induced non-equilibrium liquid chemistry with the absence of a chemical reducing agent. Silver nanoparticles with tuneable sizes from 5.4 to 17.8 nm are synthesised and characterised using Transmission Electron Microscopy (TEM) and other analytic techniques. A mechanism for silver nanoparticle formation is also proposed. The antibacterial activity of the silver nanoparticles was investigated with gram-positive and gram-negative bacteria. The inhibition of both bacteria types was observed. This is a promising alternative method for the instant synthesis of silver nanoparticles, instead of the conventional chemical reduction route, for numerous applications.

Current and Emerging Methods of Antibiotic Susceptibility Testing

Antibiotic susceptibility testing (AST) specifies effective antibiotic dosage and formulates a profile of empirical therapy for the proper management of an individual patient's health against deadly infections. Therefore, rapid diagnostic plays a pivotal role in the treatment of bacterial infection. In this article, the authors review the socio-economic burden and emergence of antibiotic resistance. An overview of the phenotypic, genotypic, and emerging techniques for AST has been provided and discussed, highlighting the advantages and limitations of each. The historical perspective on conventional methods that have paved the way for modern AST like disk diffusion, Epsilometer test (Etest), and microdilution, is presented. Several emerging methods, such as microfluidic-based optical and electrochemical AST have been critically evaluated. Finally, the challenges related with AST and its outlook in the future are presented.

Genome analysis of methicillin resistance in Macrococcus caseolyticus from dairy cattle in England and Wales

Species of the genus Macrococcus are widespread commensals of animals but are becoming increasingly recognised as veterinary pathogens. They can encode methicillin resistance and are implicated in its spread to the closely-related, but more pathogenic, staphylococci. In this study we have identified 33 isolates of methicillin-resistant Macrococcus caseolyticus from bovine bulk tank milk from England and Wales. These isolates were characterised to provide insight into the molecular epidemiology of M. caseolyticus and to discern the genetic basis for their methicillin resistance. Antimicrobial susceptibility testing was performed by Vitek2 and disc diffusion. Isolates were whole-genome sequenced to evaluate phylogenetic relationships and the presence of methicillin resistance determinants, mecA–D. All 33 isolates were phenotypically methicillin-resistant according to cefoxitin disc diffusion, cefoxitin Etest and oxacillin resistance assessed by Vitek2. In contrast only a single isolate was resistant in the Vitek2 cefoxitin screen. Twenty-seven isolates were positive for mecD and six were positive for mecB. mecA and mecC were not detected. The results of phylogenetic analysis indicated that these methicillin-resistant isolates represented a heterogeneous population with both mecB and mecD found in diverse isolates. Isolates had a widespread distribution across the sampled region. Taken together with the role of M. caseolyticus in veterinary infections, including bovine mastitis, and in the potential spread of methicillin resistance to more pathogenic staphylococci, this work highlights the need to better understand their epidemiology and for increased awareness among veterinary microbiology laboratories.

Activity of siderophores against drug-resistant Gram-positive and Gram-negative bacteria

Infections by drug-resistant bacteria are life-threatening. As iron is a vital element for the growth of bacteria, iron-chelating agents (siderophores) can be used to arrest their multiplication. Exogenous siderophores - exochelin-MS and deferoxamine-B - were evaluated for their inhibitory activity against methicillin-resistant Staphylococcus aureus and metallo-β-lactamase producers - Pseudomonas aeruginosa and Acinetobacter baumannii - by disc diffusion, micro-broth dilution, and turbidimetric growth assays. The drug-resistant isolates were inhibited by the synergistic activity of siderophores and antibiotics. Minimum inhibitory concentration of exochelin-MS+ampicillin for different isolates was between 0.05 and 0.5 mg/mL. Minimum inhibitory concentration of deferoxamine-B+ampicillin was 1.0 mg/mL and greater. Iron-chelation therapy could provide a complementary approach to overcome drug resistance in pathogenic bacteria.

Isolation, purification, structural elucidation and antimicrobial activities of kocumarin, a novel antibiotic isolated from actinobacterium Kocuria marina CMG S2 associated with the brown seaweed Pelvetia canaliculata

AIMS

Screening of seaweed-associated bacteria capable of producing antimicrobials.

METHODS AND RESULTS

Fifteen microbial strains, associated to the brown seaweed Pelvetia canaliculata (Linnaeus) attached to the rocks of Sonmiani Beach (Karachi, Pakistan), were screened. Crude extract filtrates of CMG S2 strain grew on Zobell marine agar (ZMA) had the most remarkable antimicrobial activity. Based on its phenotypic aspects (e.g. Gram-positive, microccoid form), biochemical characteristics (e.g. halotolerance) and genetic analyses, CMG S2 is identified as a putatively new Kocuria marina type strain belonging to the actinobacteria's class and micrococcaceae family. Thereby, the nucleotide sequence analysis of its full-length 16S ribosomal ribonucleic acid (rRNA) gene (GenBank accession number EU073966.1) displayed highest identity (i.e. 99%) and score (2630) with K. marina KMM 3905. Phylogenic trees analysis using the neighbor-joining method showed closest evolutionary distance of CMG S2 with KMM 3905 strain and K. carniphila (DC2201) specie. Interestingly, a unique ultraviolet (UV)-bioactive compound was purified from CMG S2 crude extracts by flash silica gel column and thin-layer chromatography (TLC) techniques. Its chemical structure was unraveled as 4-[(Z)-2 phenyl ethenyl] benzoic acid (PEBA, later named kocumarin) by nuclear magnetic resonance (NMR) spectroscopy techniques. Importantly, kocumarin demonstrated prominent and rapid growth inhibition against all tested fungi and pathogenic bacteria including methicillin-resistant Staphylococcus aureus (MRSA), with a minimal fungal inhibitory concentration (MFC) of 15-25μg/mL and a minimal (bacterial) inhibitory concentration (MIC) of 10-15μg/mL.

SIGNIFICANCE AND IMPACT OF THE STUDY

Kocumarin represents a new promising natural antibiotic for in vivo and environmental applications.

Determination of antimicrobial susceptibility patterns in Staphylococcus aureus strains recovered from patients at two main health facilities in Kabul, Afghanistan

Background

Staphylococcus aureus (S. aureus) is a major pathogen implicated in skin and soft tissue infections, abscess in deep organs, toxin mediated diseases, respiratory tract infections, urinary tract infections, post-surgical wound infections, meningitis and many other diseases. Irresponsible and over use of antibiotics has led to an increased presence of multidrug resistant organisms and especially methicillin resistant Staphylococcus aureus (MRSA) as a major public health concern in Afghanistan. As a result, there are many infections with many of them undiagnosed or improperly diagnosed. We aimed to establish a baseline of knowledge regarding the prevalence of MRSA in Kabul, Afghanistan, as well as S. aureus antimicrobial susceptibility to current available antimicrobials, while also determining those most effective to treat S. aureus infections.

Methods

Samples were collected from patients at two main Health facilities in Kabul between September 2016 and February 2017. Antibiotic susceptibility profiles were determined by the disc diffusion method and studied using standard CLSI protocols.

Results

Out of 105 strains of S. aureus isolated from pus, urine, tracheal secretions, and blood, almost half (46; 43.8%) were methicillin-sensitive Staphylococcus aureus (MSSA) while 59 (56.2%) were Methicillin-resistant Staphylococcus aureus (MRSA). All strains were susceptible to vancomycin. In total, 100 (95.2%) strains were susceptible to rifampicin, 96 (91.4%) susceptible to clindamycin, 94 (89.5%) susceptible to imipenem, 83 (79.0%) susceptible to gentamicin, 81(77.1%) susceptible to doxycycline, 77 (77.1%) susceptible to amoxicillin + clavulanic acid, 78 (74.3%) susceptible to cefazolin, 71 (67.6%) susceptible to tobramycin, 68 (64.8%) susceptible to chloramphenicol, 60 (57.1%) were susceptible to trimethoprim-sulfamethoxazole, 47 (44.8%) susceptible to ciprofloxacin, 38 (36.2%) susceptible to azithromycin and erythromycin, 37 (35.2%) susceptible to ceftriaxone and 11 (10.5%) were susceptible to cefixim. Almost all (104; 99.05%) were resistant to penicillin G and only 1 (0.95%) was intermediate to penicillin G. Interestingly, 74.6% of MRSA strains were azithromycin resistant with 8.5% of them clindamycin resistant. Ninety-six (91.4%) of the isolates were multi-drug resistant.

Conclusions

There was a high rate of Methicillin resistance (56.2%) among S. aureus strains in the samples collected and most (91.4%) were multidrug resistant. The most effective antibiotics to treat Staph infections were vancomycin, rifampicin, imipenem, clindamycin, amoxicillin-clavulanic acid, cefazolin, gentamicin and doxycycline. The least effective were azithromycin, ceftriaxone, cefixim and penicillin. We recommend that, where possible, in every case of S. aureus infection in Kabul, Afghanistan, Antibiotic susceptibility testing (AST) should be performed and responsible use of antibiotics should be considered.

pH-Dependent Antimicrobial Properties of Copper Oxide Nanoparticles in Staphylococcus aureus

The antimicrobial properties of CuO nanoparticles have been investigated, but the underlying mechanisms of toxicity remain the subject of debate. Here, we show that CuO nanoparticles exhibit significant toxicity at pH 5 against four different Staphylococcus aureus (S. aureus) strains, including Newman, SA113, USA300, and ATCC6538. At this pH, but not at pH 6 and 7, 5 mM CuO nanoparticles effectively caused reduction of SA113 and Newman cells and caused at least 2 log reduction, whereas 20 mM killed most strains but not USA300. At 5 mM, the nanoparticles were also found to dramatically decrease reductase activity in SA113, Newman, and ATCC6538 cells, but not USA300 cells. In addition, analysis of X-ray absorption near-edge structure and extended X-ray absorption fine structure confirmed that S. aureus cells exposed to CuO nanoparticles contain CuO, indicating that Cu²⁺ ions released from nanoparticles penetrate bacterial cells and are subsequently oxidized intracellularly to CuO at mildly acidic pH. The CuO nanoparticles were more soluble at pH 5 than at pH 6 and 7. Taken together, the data conclusively show that the toxicity of CuO nanoparticles in mildly acidic pH is caused by Cu²⁺ release, and that USA300 is more resistant to CuO nanoparticles (NPs) than the other three strains.

Carriage, Clinical Microbiology and Transmission of Staphylococcus aureus

Staphylococcus aureus is one of the most important bacterial pathogens in clinical practice and a major diagnostic focus for the routine microbiology laboratory. It is carried as a harmless commensal in up to two-thirds of the population at any one time predominantly not only in the anterior nares, but also in multiple other sites such as the groin, axilla, throat, perineum, vagina and rectum. It colonizes skin breach sites, such as ulcers and wounds, and causes superficial and deep skin and soft tissue infections and life-threatening deep seated infections particularly endocarditis and osteomyelitis. S. aureus is constantly evolving through mutation and uptake of mobile genetic elements that confer increasing resistance and virulence. Since the 1960s, hospitals have had to contend with emergence of methicillin-resistant S. aureus (MRSA) strains that spread better in hospitals than methicillin-susceptible S. aureus (MSSA) and are harder to treat. Since the 1980s, distinct community MRSA strains have also emerged that cause severe skin and respiratory infections. Conventional identification of MSSA and MRSA in the microbiology laboratory involves microscopy, culture and biochemical analysis that for most samples is straightforward but slow, taking at least 48 h. This delay has significant consequences for individual patient care and public health, through inadequate or excessive empiric antibiotic use, and failure to implement appropriate infection control measures for MRSA-colonized patients during those first 48 h. This unmet need has driven development of rapid molecular diagnostics that either complement or replace conventional culture techniques in the laboratory, or can be placed in the clinical environment as point-of-care (POC) devices. These new technologies provide results to clinicians anything from within an hour to 24 h, depending on sample and clinical setting, and should transform management of patients with S. aureus and other bacterial diseases; however, uptake is often slow due to the disruptive effect of new technologies, costs of transition and uncertainty of the optimal solution given successive advances. More evidence of the health economic, clinical and antimicrobial resistance benefit will help support introduction of these new technologies. Finally, preventing MRSA transmission has been a priority for healthcare organizations for many years. There have been significant recent reductions in transmission following local and national campaigns to re-enforce basic and heightened infection control interventions such as universal hand hygiene, barrier nursing, decolonization and isolation of MRSA-colonized patients detected through routine culture or screening policies. Developments in whole genome sequencing are providing greater insight into reservoirs and routes of transmission that should help better target interventions to ensure sustainable control of endemic strains and to identify and prevent emergence of new strains.

Marbofloxacin-encapsulated microparticles provide sustained drug release for treatment of veterinary diseases

Fluoroquinolone antibiotics with concentration-dependent killing effects and a well-established broad spectrum of activity are used commonly to treat infectious diseases caused by bacteria. However, frequent and excessive administration of these antibiotics is a serious problem, and leads to increased number of drug-resistant bacteria. Thus, there is an urgent need for novel fluoroquinolone antibiotic formulations that minimize the risk of resistance while maximizing their efficacy. In this study, we developed intramuscularly injectable polymeric microparticles (MPs) that encapsulated with marbofloxacin (MAR) and were composed of poly(D,L-lactide-co-glycolic acid) (PLGA) and poloxamer (POL). MAR-encapsulated MP (MAR-MP) had a spherical shape with particle size ranging from 80 μm to 120 μm. Drug loading efficiency varied from 55 to 85% (w/w) at increasing amount of hydrophilic agent, POL. Drug release from MAR-MP demonstrated a significant and sustained increase at increased ratios of POL to PLGA. These results indicate that MAR-MP is an improved drug delivery carrier for fluoroquinolone antibiotics, which can reduce the number of doses needed and sustain a high release rate of MAR for 2-3 days. As a novel and highly effective drug delivery platform, MAR-MP has great potential for use in a broad range of applications for the treatment of various veterinary diseases.

Detection of mecA and enterotoxin genes in Staphylococcus aureus isolates associated with bovine mastitis and characterization of Staphylococcal cassette chromosome mec (SCCmec) in MRSA strains

BACKGROUND AND OBJECTIVES

Staphylococcus aureus is one of the main causatives of bovine mastitis. Resistance of some strains to methicillin, can complicate the treatment of its infections. On the other hand, enterotoxin production is also important. Therefore, the aim of our study was to investigate the methicillin resistance and enterotoxin production in S. aureus isolates caused bovine mastitis.

MATERIALS AND METHODS

Four hundred and fifty milk samples were collected. After isolation of Staphylococcus aureus, MRSA strains were detected by cefoxitin disc diffusion and oxacillin agar screening methods. DNA was extracted by phenol - chloroform method and PCR was applied for mecA, sea and seb genes. SCCmec types of mecA gene were identified using multiplex-PCR.

RESULTS

Fifty-four (12%) S. aureus were isolated. Out of these, 10 and 9 MRSA strains identified by cefoxitin disc diffusion and oxacillin agar screening methods, respectively. All 10 MRSA isolates identified by cefoxitin disc diffusion, were positive for mecA gene and all of them belonged to SCCmec type IV. The sea genes were detected in 19 isolates and only two isolates were positive for seb genes. One isolate possessed both sea and seb genes.

CONCLUSION

Findings of this study indicated that results of cefoxitin disc diffusion test is in concordance with the PCR for mecA gene and has a higher sensitivity compared to oxacillin agar screening method. Finally, Our findings suggest that enterotoxin A is the dominant type.

Rapid optical determination of β-lactamase and antibiotic activity

BACKGROUND

The absence of rapid tests evaluating antibiotic susceptibility results in the empirical prescription of antibiotics. This can lead to treatment failures due to escalating antibiotic resistance, and also furthers the emergence of drug-resistant bacteria. This study reports a rapid optical method to detect β-lactamase and thereby assess activity of β-lactam antibiotics, which could provide an approach for targeted prescription of antibiotics. The methodology is centred on a fluorescence quenching based probe (β-LEAF--β-Lactamase Enzyme Activated Fluorophore) that mimics the structure of β-lactam antibiotics.

RESULTS

The β-LEAF assay was performed for rapid determination of β-lactamase production and activity of β-lactam antibiotic (cefazolin) on a panel of Staphylococcus aureus ATCC strains and clinical isolates. Four of the clinical isolates were determined to be lactamase producers, with the capacity to inactivate cefazolin, out of the twenty-five isolates tested. These results were compared against gold standard methods, nitrocefin disk test for β-lactamase detection and disk diffusion for antibiotic susceptibility, showing results to be largely consistent. Furthermore, in the sub-set of β-lactamase producers, it was demonstrated and validated that multiple antibiotics (cefazolin, cefoxitin, cefepime) could be assessed simultaneously to predict the antibiotic that would be most active for a given bacterial isolate.

CONCLUSIONS

The study establishes the rapid β-LEAF assay for β-lactamase detection and prediction of antibiotic activity using S. aureus clinical isolates. Although the focus in the current study is β-lactamase-based resistance, the overall approach represents a broad diagnostic platform. In the long-term, these studies form the basis for the development of assays utilizing a broader variety of targets, pathogens and drugs.

Antibiotic resistance and molecular characterization of ophthalmic Staphylococcus pseudintermedius isolates from dogs

The prevalence, virulence potential, and antibiotic resistance of ophthalmic Staphylococcus pseudintermedius (SP) isolated from dogs were examined. Sixty-seven Staphylococcus species were isolated from ophthalmic samples and surveyed for species-specific sequences in the Staphylococcus intermedius group (SIG) nuclease gene (SInuc), exfoliative toxin gene for SIG (siet), and antibiotic resistance genes (blaZ and mecA). PCR-restriction fragment length polymorphism analysis of the pta gene was also performed. Fifty isolates were identified as SIG strains, all of which were found to be SP. The blaZ gene was detected in 42 of the 50 SP strains and mecA gene was observed in 18 of the 50 SP strains. The 50 SP strains were most susceptible to amoxicillin/clavulanic acid (94%) and chlorampenicol (70%), and highly resistant to tetracycline (94%) and penicillin (92%). It was also found that 16 (88.9%) mecA-positive SP strains were resistant to oxacillin, tetracycline and penicillin. All mecA-positive SP were resistant to more than four of the eight tested antibiotics and therefore considered SP with multi-drug resistance (MDR). Our results indicate a high prevalence of antibiotic resistance genes in ophthalmic SP along with a close relationship between MDR SP strains and the mecA gene. Based on our findings, judicious administration of antibiotics to companion dogs is necessary.

Phenotypic detection of mecC-MRSA: cefoxitin is more reliable than oxacillin

OBJECTIVES

To investigate the reliability of cefoxitin and oxacillin for the detection of mecC-positive Staphylococcus aureus.

METHODS

The susceptibility to cefoxitin and oxacillin of 62 mecC-positive S. aureus isolates was investigated using broth microdilution, agar dilution, Etest and disc diffusion on different types of media. The data were interpreted for the utility of cefoxitin and oxacillin in conjunction with the stated methodologies for the detection of mecC-positive isolates.

RESULTS

Cefoxitin with Mueller-Hinton media from Becton Dickinson and Oxoid detected all mecC-positive isolates when tested by broth microdilution, agar dilution and disc diffusion. By Etest, one isolate was falsely susceptible. Mueller-Hinton agar from bioMérieux was substantially less able to detect these isolates. One isolate was falsely susceptible by agar dilution when using Iso-Sensitest and Columbia agar. Disc diffusion using cefoxitin on Iso-Sensitest agar missed 29% of the isolates. For oxacillin, only agar dilution on Columbia agar + 2% NaCl was able to detect all mecC-positive isolates successfully.

CONCLUSIONS

Cefoxitin used with EUCAST methodology and oxacillin used with agar dilution on Columbia agar + 2% NaCl detected all mecC-positive isolates. These methods with their concomitant agars should be preferred over Iso-Sensitest, which is recommended by the BSAC. It should be noted that for disc diffusion Mueller-Hinton media from bioMérieux performed poorly, with 26%-47% of mecC isolates being falsely susceptible.

Phenotypic and molecular characteristics of methicillin-resistant Staphylococcus aureus isolates from Ekiti State, Nigeria

Introduction

The characteristics and antimicrobial resistance profiles of Staphylococcus aureus differs according to geographical regions and in relation to antibiotic usage. The aim of this study was to determine the biochemical characteristics of the prevalent S. aureus from Ekiti State, Nigeria, and to evaluate three commonly used disk diffusion methods (cefoxitin, oxacillin, and methicillin) for the detection of methicillin resistance in comparison with mecA gene detection by polymerase chain reaction.

Materials and methods

A total of 208 isolates of S. aureus recovered from clinical specimens were included in this study. Standard microbiological procedures were employed in isolating the strains. Susceptibility of each isolate to methicillin (5 μg), oxacillin (1 μg), and cefoxitin (30 μg) was carried out using the modified Kirby–Bauer/Clinical and Laboratory Standard Institute disk diffusion technique. They were also tested against panels of antibiotics including vancomycin. The conventional polymerase chain reaction method was used to detect the presence of the mecA gene.

Results

Phenotypic resistance to methicillin, oxacillin, and cefoxitin were 32.7%, 40.3%, and 46.5%, respectively. The mecA gene was detected in 40 isolates, giving a methicillin-resistant S. aureus (MRSA) prevalence of 19.2%. The S. aureus isolates were resistant to penicillin (82.7%) and tetracycline (65.4%), but largely susceptible to erythromycin (78.8% sensitive), pefloxacin (82.7%), and gentamicin (88.5%). When compared to the mecA gene as the gold standard for MRSA detection, methicillin, oxacillin, and cefoxitin gave sensitivity rates of 70%, 80%, and 100%, and specificity rates of 76.2%, 69.1%, and 78.5% respectively.

Conclusion

When compared with previous studies employing mecA polymerase chain reaction for MRSA detection, the prevalence of 19.2% reported in Ekiti State, Nigeria in this study is an indication of gradual rise in the prevalence of MRSA in Nigeria. A cefoxitin (30 μg) disk diffusion test is recommended above methicillin and oxacillin for the phenotypic detection of MRSA in clinical laboratories.

Methicillin-resistant Staphylococcus aureus diagnostics: state of the art

INTRODUCTION

Methicillin-resistant Staphylococcus aureus (MRSA) is among the most common causes of community- and healthcare-acquired infections, accounting for > 80,000 invasive infections in the United States in 2010 according to the Center for Disease Control and Prevention's Active Bacterial Core Surveillance data. Control and treatment of MRSA depend on reliable identification, which is challenging. This article reviews the current status of detection and identification of MRSA.

AREAS COVERED

Publications since 2001, guidelines from the Clinical Laboratory Standards Institute and the European Committee on Antimicrobial Susceptibility Testing, common microbiology laboratory practices for identification and characterization of MRSA in human samples, and recent publications that assessed patient care outcomes of various detection and intervention strategies were surveyed for this review.

EXPERT OPINION

Given the predilection of Staphylococcus aureus to modify its genetic characteristics, thereby enabling the species to stay one step ahead of laboratory detection systems, phenotypic methods for detection of antibiotic resistance mechanisms, especially those directed against the beta-lactam family, will continue to be required, in some situations, for the foreseeable future. Molecular methods are now the gold standard for surveillance, yielding higher sensitivity than the slower, culture-based methods. The newer molecular surveillance methods for detecting methicillin-resistant S. aureus (MRSA) colonization and for rapid and accurate identification of S. aureus from growth in culture systems have revolutionized patient care, enabling rapid interventions that lead to better individual patient outcomes, such as fewer postsurgical site infections, and better overall institutional infection control (fewer healthcare-associated MRSA infections).

Evaluation of Clearview Exact PBP2a, a new immunochromatographic assay, for detection of low-level methicillin-resistant Staphylococcus aureus (LL-MRSA)

We evaluated the performance of a new immunochromatographic assay (ICA), the Clearview Exact PBP2a, for rapid detection of penicillin-binding protein 2a (PBP2a) in a challenge set of Staphylococcus aureus strains showing MICs to oxacillin of ≤16 mg/liter. The sensitivity and specificity of the ICA were 96.6% and 100%, respectively.

In vitro activity of beta-lactam antibiotics to community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA)

Community-associated (CA) MRSA often display low MIC values against oxacillin. The in vitro activity of various beta-lactam antibiotics against heterogeneous CA-MRSA (n = 98) isolated in a low endemic area was determined by Etest, and Mueller-Hinton agar (MUHAP) was compared with Mueller-Hinton agar supplemented with 2% NaCl (MUHSP). In general, the CA-MRSA isolates showed higher MIC values for the various beta-lactam antibiotics on MUHSP compared with MUHAP. MIC values for oxacillin ranged from 1 to >256 mg/L on MUHSP. Cephalothin, representing the first generation of cephalosporins, showed MICs from 0.75 to 96 mg/L and the MIC(50) and MIC(90) for cefuroxime, cefotaxime and cefepime, representing the second, third and fourth generations, respectively, were rather high. However, the MIC(50) and MIC(90) for ceftobiprole (fifth generation) were 1.5 and 2 mg/L, respectively, on MUHSP. The MIC(50) and MIC(90) for imipenem were 0.75 and 2 mg/L, respectively, on MUHSP. Only 3/98 (3%) CA-MRSA isolates showed a MIC >4 mg/L. Consequently, low MIC values for imipenem, lower than those of the newly developed fifth generation cephalosporins, were found among CA-MRSA. These findings may be considered for further studies including clinical trials in order to evaluate carbapenems as a potential treatment option for infections caused by CA-MRSA.

Evaluation of different methods for detecting methicillin resistance in Staphylococcus aureus isolates in a university hospital located in the Northeast of Brazil

Many methods have been described for the detection of methicillin-resistant Staphylococcus aureus (MRSA), but the heterogeneous expression of methicillin resistance affects the reliability of these methods. The aim of the present study was to evaluate some methods for detecting methicillin resistance in Staphylococcus aureus isolates in a university hospital located in the Northeast of Brazil. Among the isolates, 15 were methicillin-susceptible and 45 were methicillin-resistant, including low-level heterogeneous resistance strains. Both the 30 ηg-cefoxitin disk and PBP2a test had 100% sensibility/specificity and appear to be good options for the detection of MRSA in the clinical laboratory.

Comparative evaluation of five culture media with triplex PCR assay for detection of methicillin-resistant Staphylococcus aureus

The emergence of methicillin-resistant Staphylococcus aureus (MRSA) is responsible for nosocomial and community-acquired infections. Hence, rapid and accurate laboratory diagnosis of MRSA is a vital constituent of control measures. The present study evaluated five different methods for the identification of MRSA. A total of 207 S. aureus clinical isolates that consisted of 89 MRSA and 118 methicillin-susceptible S. aureus (MSSA) strains confirmed by PCR were tested. MRSA strains were evaluated by five different methods: chromogenic MRSA agar (CMRSA), oxacillin resistance screening agar base (ORSAB), mannitol salt oxacillin agar (MSO), mannitol salt cefoxitin agar with two different concentrations of cefoxitin [4 microg/ml (MSC-4) and 6 microg/ml (MSC-6)]. The results of the different methods were compared to mecA PCR as the gold standard. MSC-6 showed only six false-positive MRSA in comparison with PCR. The sensitivities and specificities of MSC-6, MSC-4, MSO-4, ORSAB, and CMRSA were as follows: 98.9/94.9%, 100/83.1%, 89.9/87.3%, 97.8/96.6%, and 95.5/94.9%, respectively. In comparison with PCR, it was found that both MSC-6 and ORSAB were relatively the least expensive screening tests ($0.70 and $1.00, respectively). In conclusion, all methods were comparable, but MSC-6 was the least expensive medium for MRSA screening.

Comparison of different methods for detecting methicillin resistance in MRSA isolates belonging to international lineages commonly isolated in the American continent

The aim of the present paper was to compare different methods for detecting methicillin resistance in Staphylococcus aureus. Among the isolates analyzed, 52 belonged to MRSA international lineages commonly detected in the American continent and 14 to sporadic MRSA clones. Both 30 microg-cefoxitin disk and PBP2a had 100% sensibility/specificity when the low-level heterogeneous isolates were tested and, thus, are highly recommended.

Agar dilution and agar screen with cefoxitin and oxacillin: what is known and what is unknown in detection of meticillin-resistant Staphylococcus aureus

In this study we evaluated the performance of the oxacillin agar screen test, and agar dilution tests using cefoxitin and oxacillin antimicrobials, to detect meticillin resistance in Staphylococcus aureus isolates. The presence of the mecA gene, detected by PCR, was used as the standard to which agar screen and agar dilution tests were compared. The best performance was obtained using the agar dilution test (99.4 % accuracy) with breakpoints of 4 mug ml(-1) for oxacillin and 8 mug ml(-1) for cefoxitin, and using the oxacillin agar screen test. Also, a strong correlation between MIC values of cefoxitin and oxacillin permits the use of either drug for detection of meticillin resistance.

Evaluation of new Vitek 2 card and disk diffusion method for determining susceptibility of Staphylococcus aureus to oxacillin

Detection of methicillin resistance in Staphylococcus aureus is a challenge, especially low-level resistance, which is often misdiagnosed. The aim of this study was to compare the diagnostic accuracies of the automated Vitek 2 system and disk diffusion tests, using cefoxitin and moxalactam, for the detection of methicillin resistance in S. aureus strains. Four sets of genotypically diverse isolates were selected from a national reference collection, including mecA-negative S. aureus isolates (n = 56), hospital-acquired (n = 88) and community-acquired (n = 40) S. aureus isolates, and heterogeneous methicillin-resistant S. aureus isolates (n = 29). Oxacillin susceptibility was tested by the Vitek 2 system with the AST P549 card and by disk diffusion methods using 10, 30, and 60 microg cefoxitin and 30 microg moxalactam. Oxacillin resistance was confirmed by PCR for the mecA gene. The overall sensitivities for oxacillin resistance detection were 97.5% for the Vitek 2 automated system, 98.7% for 60-microg cefoxitin and moxalactam disk diffusion, and 99.6% for 10- and 30-microg cefoxitin disks, respectively. Methicillin-susceptible S. aureus isolates were correctly reported as susceptible by all methods. The median times for methicillin testing were 7 h for the Vitek 2 system versus 24 h for disk diffusion methods. In conclusion, the cefoxitin and moxalactam disk diffusion methods and the Vitek 2 automated system are highly accurate methods for methicillin resistance detection, including a range of representative Belgian methicillin-resistant S. aureus strains and unusual strains exhibiting cryptic or low-level oxacillin resistance.

Fatal necrotizing pneumonia due to a Panton-Valentine leukocidin positive community-associated methicillin-sensitive Staphylococcus aureus and Influenza co-infection: a case report

Recent studies have described a number of fatalities due to methicillin-resistant Staphylococcus aureus (MRSA) and influenza virus co-infection. MRSA isolates provide a challenge to caregivers due to inherent wide range antibiotic resistance. Many facilities have instituted screening methods, based on the presence of antibiotic resistance genes, to identify MRSA positive patients upon admission. However, the resistance profile of the pathogen does not necessarily determine the severity of disease caused by that organism.

We describe a fatal case of necrotizing pneumonia in a patient co-infected with Influenza B and a community-associated, PVL-positive methicillin-susceptible Staphylococcus aureus (MSSA).

Evaluation of phenotypic and molecular methods for screening and detection of methicillin-resistant Staphylococcus aureus

An in-house PCR was compared with the GenoType MRSA and the MRSA EVIGENE tests, both of which corresponded 100% with the results of in-house PCR. The cefoxitin disk diffusion method was superior to both the oxacillin disk diffusion and minimum inhibitory concentration tests for predicting the mecA status.

Comparison of mecA polymerase chain reaction with phenotypic methods for the detection of methicillin-resistant Staphylococcus aureus

In the present study, several conventional methods to detect methicillin-resistant Staphylococcus aureus (MRSA) were compared with polymerase chain reaction (PCR) detection of mecA gene-positive isolates. Cefoxitin E-test was also evaluated as a possible phenotypic method of MRSA detection. Oxacillin agar screen and PBP2' latex agglutination methods were found to be more sensitive than oxacillin and cefoxitin disk-diffusion methods. Cefoxitin disk diffusion was found to be the most specific. A combination of oxacillin agar screening with cefoxitin disk diffusion, or oxacillin disk diffusion with PBP2', improved sensitivity and specificity. Cefoxitin E-test with the current break points had low sensitivity and specificity (33.3% and 75%, respectively) for the detection of MRSA. However, changing the break points to <or= 4 microg/ml and to >or= 6 microg/ml for sensitive and resistant, respectively, greatly improved both. Changing the 30-microg cefoxitin disk-diffusion break points to <or= 21 mm for resistant slightly improved sensitivity but had no effect on specificity. It was therefore concluded that the use of more than one screening method is necessary to detect all MRSA isolates in clinical settings.

Recomendaciones para la selección de antimicrobianos en el estudio de la sensibilidad in vitro con sistemas automáticos y semiautomáticos

The number of clinical microbiology laboratories that have incorporated automatic susceptibility testing devices has increased in recent years. The majority of these systems determine MIC values using microdilution panels or specific cards, with grouping into clinical categories (susceptible, intermediate or resistant) and incorporate expert systems to infer resistance mechanisms. This document presents the recommendations of a group of experts designated by Grupo de Estudio de los Mecanismos de Acción y Resistencia a los Antimicrobianos (GEMARA, Study group on mechanisms of action and resistance to antimicrobial agents) and Mesa Española de Normalización de la Sensibilidad y Resistencia a los Antimicrobianos (MENSURA, Spanish Group for Normalizing Antimicrobial Susceptibility and Antimicrobial Resistance), with the aim of including antimicrobial agents and selecting concentrations for the susceptibility testing panels of automatic systems. The following have been defined: various antimicrobial categories (A: must be included in the study panel; B: inclusion is recommended; and C: inclusion is secondary, but may facilitate interpretative reading of the antibiogram) and groups (0: not used in therapeutics but may facilitate the detection of resistance mechanisms; 1: must be studied and always reported; 2: must be studied and selectively reported; 3: must be studied and reported at a second level; and 4: should be studied in urinary tract pathogens isolated in urine and other specimens). Recommended antimicrobial concentrations are adapted from the breakpoints established by EUCAST, CLSI and MENSURA. This approach will lead to more accurate susceptibility testing results with better detection of resistance mechanisms, and allowing to reach the clinical goal of the antibiogram.

In vitro activities of 18 antimicrobial agents against Staphylococcus aureus isolates from the Institut Pasteur of Madagascar

BACKGROUND

Staphylococcus aureus, one of the most frequently isolated pathogens in both hospitals and the community, has been particularly efficient at developing resistance to antimicrobial agents. In developed countries, as methicillin-resistant S. aureus (MRSA) has prevailed and, furthermore, as S. aureus with reduced susceptibility to vancomycin has emerged, the therapeutic options for the treatment of S. aureus infections have become limited. In developing countries and especially African countries very little is known concerning the resistance of S. aureus to antibiotics. In Madagascar no data exist concerning this resistance.

OBJECTIVE

To update the current status of antibiotic resistance of S. aureus in Antananarivo, Madagascar.

METHODS

Clinical S. aureus isolates were collected from patients at the Institut Pasteur of Madagascar from January 2001 to December 2005. Susceptibility tests with 18 antibiotics were performed by the disk diffusion method.

RESULTS

Among a total of 574 isolates, 506 were from community-acquired infections and 68 from nosocomial infections. There was no significant difference in the methicillin resistance rate between community-acquired strains (33 of 506; 6.5%) and nosocomial strains (3 of 68, 4.4%). Many MRSA isolates were resistant to multiple classes of antibiotics. Resistance to tetracyclin, trimethoprim-sulfamethoxazole and erythromycin was more common. Among MRSA isolates resistance rates to rifampicin, fusidic acid, gentamicin and ciprofloxacin were lower than that observed with other drugs easily available in Madagascar. No isolates were resistant to glycopeptides.

CONCLUSION

The rate of methicillin-resistant S. aureus is not different between community-acquired and nosocomial infections and is still rather low in Madagascar.

Comparison of four chromogenic media for culture-based screening of meticillin-resistant Staphylococcus aureus

Meticillin-resistant Staphylococcus aureus (MRSA) are responsible for nosocomial and community-acquired infections. Detection of MRSA is of utmost importance for the adaptation of infection control and therapeutic strategies. To date, selective agar plates constitute the standard routine method for reliable detection of this worldwide infectious problem. The performance of four different chromogenic media was evaluated in this study for MRSA detection and identification on >240 consecutive swab samples. The results indicate that primary plating on MRSASelect or MRSA ID is more sensitive than screening with oxacillin-based culture media. In addition, the utilization of cefoxitin- or cephamycin-containing plates reduces significantly the number of required confirmatory tests. Several selective agar plates allowing the identification of S. aureus are commercially available. However, their respective performances under real conditions of utilization are heterogeneous, underlining the absence of a gold standard medium for MRSA screening.

Retrospective detection of methicillin resistant and susceptible Staphylococcus aureus ST398 in Danish slaughter pigs

This retrospective study documents the first detection in Danish pigs of methicillin resistant and susceptible variants of the Staphylococcus aureus lineage ST398, which was previously described among pigs, pig farmers and veterinary staff in The Netherlands as well as in human patients and infected animals in Europe. Ten out of 100 pigs tested were shown to carry ST398 in the nasal cavity and two out of three farms tested were positive. The 10 porcine ST398 isolates had spa type t034 (n=9) and t1793 (n=1), and were resistant to erythromycin, clindamycin and tetracycline in addition to penicillin. The detection of ST398 in Danish pigs suggests that this new emerging zoonotic bacterium is rapidly spreading in the pig population in Europe.