Potent In Vitro Bactericidal Activity of Polymyxin B against Methicillin-Resistant Staphylococcus aureus (MRSA)

Eradication of methicillin-resistant Staphylococcus aureus (MRSA) carried by inpatients or healthy hospital personnel by topical use of antibiotics is an important step for preventing outbreak of MRSA nosocomial infection. In the screening of the antibiotic best suited for this purpose, we have found that polymyxin B, a commonly used antibiotic for gram-negative infection, had an unexpected strong cytokilling activity towards MRSA clinical strains, which was more potent than that of vancomycin or gentamicin. The data suggested that polymyxin B could be an antibiotic of choice in the treatment of topical carriage of or infection caused by MRSA.     

Evaluation of a New Bactericidal Spray Effective against Staphylococcus aureus

A new germicidal spray consisting of an active ingredient, 2-chloro-4-phenylphenol, solvent, and propellant was evaluated against aerosols of Staphylococcus aureus and spores of Bacillus subtilis. The method of evaluation consisted of determining the decay rate of the bacterial aerosols in a small chamber, with and without the aerial germicide present. The method is unique in that the effect of very short exposures of airborne bacteria to aerial germicides can be measured accurately. By use of the method outlined, extremely potent aerial germicides may be evaluated against highly sensitive organisms. The 2-chloro-4-phenylphenol spray was found to be extremely effective against S. aureus but only moderately effective against spores of B. subtilis.     

Comparison of the Virulence of Methicillin-Resistant and Methicillin-Sensitive Staphylococcus aureus

The virulence of methicillin-resistant Staphylococcus aureus (MRSA) was compared with that of methicillin-sensitive S. aureus (MSSA), using 13 MRSA and 7 MSSA strains isolated from clinical specimens. The infectivity and lethality of the two groups were examined as to the inoculum required to infect 50% of guinea pigs (ID₅₀) and to kill 50% of mice (LD₅₀), respectively. The mean ID₅₀ [log₁₀ colony forming units (CFU)] for MRSA strains was 7.1 ± 0.60 standard deviation, which was 1.5 higher than that for MSSA strains (P < 0.001). The mean LD₅₀ (log₁₀ CFU) for MRSA strains was 9.0 ± 0.42, being 1.1 higher than that for MSSA strains (P = 0.001). Pretreatment of mice with cyclophosphamide decreased the mean LD₅₀ for MRSA strains more than that for MSSA strains, resulting in the difference in the mean LD₅₀ being insignificant (P = 0.502). These results indicate that MRSA is less virulent than MSSA in normal hosts, but that they are equally virulent in immunocompromised hosts. The growth of MRSA strains was much slower than that of MSSA strains in the lag phase, although their growth rates were almost the same in the exponential growth phase, suggesting that the difference in virulence between them may be at least partly due to such a difference in growth.     

Silver Nanoparticles Toxicity and Bactericidal Effect Against Methicillin-Resistant Staphylococcus aureus: Nanoscale Does Matter

Silver nanoparticles, which are being used increasingly as antimicrobial agents, may extend its antibacterial application to methicillin-resistant Staphylococcus aureus (MRSA), the main cause of nosocomial infections worldwide. To explore the antibacterial properties of silver nanoparticles against MRSA, the present work includes an analysis of the relation between nanosilver effect and MRSA’s resistance mechanisms, a study of the size dependence of the bactericidal activity of nanosilver and a toxicity assessment of nanoparticles against epithelial human cells. Minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and MBC/MIC ratio of silver nanoparticles were quantified by using a luciferase-based assay. The cytotoxic effect (CC₅₀ and CC₉₀) of three different nanosilver sizes (10, 30–40, and 100 nm) were assessed in HeLa cells by a similar method. The therapeutic index was used as an indicator of nanosilver overall efficacy and safety. Silver nanoparticles inhibited bacterial growth of both MRSA and non-MR S. aureus in a bactericidal rather than a bacteriostatic manner (MBC/MIC ratio?≤?4). Silver nanoparticle’s therapeutic index varied when nanoparticle’s size diminished. At the same dose range, 10 nm nanoparticles were the most effective since they did not affect HeLa’s cell viability while inhibiting a considerable percentage of MRSA growth. Silver nanoparticles are effective bactericidal agents that are not affected by drug-resistant mechanisms of MRSA. Nanosilver size mediates MRSA inhibition and the cytotoxicity to human cells, being smaller nanoparticles the ones with a better antibacterial activity and nontoxic effect.     

Comparison of Real-Time PCR with Disk Diffusion, Agar Screen and E-test Methods for Detection of Methicillin-Resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) is a nosocomial pathogen. Our main objective was to compare oxacillin disk test, oxacillin E-test, and oxacillin agar screen for detection of methicillin resistance in S. aureus, using real-time PCR for mecA as the “gold standard” comparison assay. 196 S. aureus isolates were identified out of 284 Staphylococcus isolates. These isolates were screened for MRSA with several methods: disk diffusion, agar screen (6.0 μg/ml), oxacillin E-test, and real-time PCR for detection of mecA gene. Of the 196 S. aureus isolates tested, 96 isolates (49%) were mecA-positive and 100 isolates (51%) mecA-negative. All methods tested had a statistically significant agreement with real-time PCR. E-test was 100% sensitive and specific for mecA presence. The sensitivity and specificity of oxacillin agar screen method were 98 and 99%, respectively and sensitivity and specificity of oxacillin disk diffusion method were 95 and 93%, respectively. In the present study, oxacillin E-test is proposed as the best phenotypic method. For economic reasons, the oxacillin agar screen method (6.0 μg/ml), which is suitable for the detection of MRSA, is recommended due to its accuracy and low cost.     

Comparison of Two Commercial PCR Methods for Methicillin-Resistant Staphylococcus aureus (MRSA) Screening in a Tertiary Care Hospital

Nose/throat-swabs from 1049 patients were screened for MRSA using CHROMagar MRSA, LightCycler Advanced MRSA, and Detect-Ready MRSA. Results were compared to the CHROMagar MRSA results, which was set as reference system. MRSA was detected in 3.05% of the patients with CHROMagar MRSA. LightCycler MRSA Advanced showed a higher clinical sensitivity (84.38%) than Detect-Ready MRSA (57.69%).The negative predictive values were high for both tests (>98%). The specificity and the positive predictive value were higher for the Detect-Ready MRSA test than for the LightCycler MRSA test (99.59% and 78.95% versus 98.52% and 64.29%). For routine screening LightCycler MRSA Advanced proved to be more efficient in our clinical setting as the clinical sensitivity was much higher than the sensitivity of Detect-Ready MRSA. CHROMagar MRSA detected more MRSA positive samples than both PCR methods, leading to the conclusion that the combination of PCR with cultural screening is still the most reliable way for the detection of MRSA. LightCycler MRSA Advanced was faster and needed less hands-on time. The advantage of Detect-Ready MRSA was the additional identification of methicillin-sensitive S.aureus (here in 34.63% of the samples), an information which can be possibly used for reducing the risk of postoperative infections in surgical patients in future.     

Antibacterial Activity of THAM Trisphenylguanide against Methicillin-Resistant Staphylococcus aureus

This study investigated the potential antibacterial activity of three series of compounds synthesized from 12 linear and branched polyamines with 2–8 amino groups, which were substituted to produce the corresponding guanides, biguanides, or phenylguanides, against Acinetobacter baumannii, Enterococcus faecalis, Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus. Antibacterial activity was measured for each compound by determining the minimum inhibitory concentration against the bacteria, and the toxicity towards mammalian cells was determined. The most effective compound, THAM trisphenylguanide, was studied in time-to-kill and cytoplasmic leakage assays against methicillin-resistant Staphylococcus aureus (MRSA, USA300) in comparison to chlorhexidine. Preliminary toxicity and MRSA challenge studies in mice were also conducted on this compound. THAM trisphenylguanide showed significant antibacterial activity (MIC ∼1 mg/L) and selectivity against MRSA relative to all the other bacteria examined. In time-to-kill assays it showed increased antimicrobial activity against MRSA versus chlorhexidine. It induced leakage of cytoplasmic content at concentrations that did not reduce cell viability, suggesting the mechanism of action may involve membrane disruption. Using an intraperitoneal mouse model of invasive MRSA disease, THAM trisphenylguanide reduced bacterial burden locally and in deeper tissues. This study has identified a novel guanide compound with selective microbicidal activity against Staphylococcus aureus, including a methicillin-resistant (MRSA) strain.     

Synergism between Medihoney and Rifampicin against Methicillin-Resistant Staphylococcus aureus (MRSA)

Skin and chronic wound infections caused by highly antibiotic resistant bacteria such as methicillin-resistant Staphylococcus aureus (MRSA) are an increasing and urgent health problem worldwide, particularly with sharp increases in obesity and diabetes. New Zealand manuka honey has potent broad-spectrum antimicrobial activity, has been shown to inhibit the growth of MRSA strains, and bacteria resistant to this honey have not been obtainable in the laboratory. Combinational treatment of chronic wounds with manuka honey and common antibiotics may offer a wide range of advantages including synergistic enhancement of the antibacterial activity, reduction of the effective dose of the antibiotic, and reduction of the risk of antibiotic resistance. The aim of this study was to investigate the effect of Medihoney in combination with the widely used antibiotic rifampicin on S. aureus. Using checkerboard microdilution assays, time-kill curve experiments and agar diffusion assays, we show a synergism between Medihoney and rifampicin against MRSA and clinical isolates of S. aureus. Furthermore, the Medihoney/rifampicin combination stopped the appearance of rifampicin-resistant S. aureus in vitro. Methylglyoxal (MGO), believed to be the major antibacterial compound in manuka honey, did not act synergistically with rifampicin and is therefore not the sole factor responsible for the synergistic effect of manuka honey with rifampicin. Our findings support the idea that a combination of honey and antibiotics may be an effective new antimicrobial therapy for chronic wound infections.     

Pitfalls in Identification of Methicillin-Resistant Staphylococcus aureus

Media and techniques for in vitro testing with respect to screening for methicillin-resistant Staphylococcus aureus are discussed.     

耐甲氧西林金黄色葡萄球菌的分子流行病学研究

了解我院患者耐甲氧西林金黄色葡萄球菌（MRSA）的分子流行病学特点,为临床抗感染治疗提供依据。收集2007年1月~2008年9月我院分离的耐甲氧西林金黄色葡萄球菌共54株,采用PCR进行SCCmec基因分型、葡萄球菌A蛋白（SPA）分型,并检测杀白细胞毒素（PVL）基因,同时应用脉冲场凝胶电泳（PFGE）进行同源性分析。54株MRSA菌株SCCmec基因分型为SCCmecⅡ型17株,SCCmecⅢ型33株,SCCmecⅣ型2株,SCCmecⅤ型2株;SPA基因分型将28株归属为t030,9株为t002,8株为t037,5株为t570,2株为t437,t163和t796各1株;PVL毒素检测只有2株SCCmecⅣ型菌株阳性;PFGE证实院内MRSA感染主要为2种克隆株传播,同时还有其他型别出现。本院MRSA流行传播的SCCmec基因型主要以Ⅲ型占优势,同时发现有携带PVL毒素的CA-MRSA分离株流行,应引起密切关注。     

Computational Ranking of Yerba Mate Small Molecules Based on Their Predicted Contribution to Antibacterial Activity against Methicillin-Resistant Staphylococcus aureus

The aqueous extract of yerba mate, a South American tea beverage made from Ilex paraguariensis leaves, has demonstrated bactericidal and inhibitory activity against bacterial pathogens, including methicillin-resistant Staphylococcus aureus (MRSA). The gas chromatography-mass spectrometry (GC-MS) analysis of two unique fractions of yerba mate aqueous extract revealed 8 identifiable small molecules in those fractions with antimicrobial activity. For a more comprehensive analysis, a data analysis pipeline was assembled to prioritize compounds for antimicrobial testing against both MRSA and methicillin-sensitive S. aureus using forty-two unique fractions of the tea extract that were generated in duplicate, assayed for activity, and analyzed with GC-MS. As validation of our automated analysis, we checked our predicted active compounds for activity in literature references and used authentic standards to test for antimicrobial activity. 3,4-dihydroxybenzaldehyde showed the most antibacterial activity against MRSA at low concentrations in our bioassays. In addition, quinic acid and quercetin were identified using random forests analysis and 5-hydroxy pipecolic acid was identified using linear discriminant analysis. We also generated a ranked list of unidentified compounds that may contribute to the antimicrobial activity of yerba mate against MRSA. Here we utilized GC-MS data to implement an automated analysis that resulted in a ranked list of compounds that likely contribute to the antimicrobial activity of aqueous yerba mate extract against MRSA.     

Eugenol: A Phyto-Compound Effective against Methicillin-Resistant and Methicillin-Sensitive Staphylococcus aureus Clinical Strain Biofilms

Background

Inhibition and eradication of Staphylococcus aureus biofilms with conventional antibiotic is difficult, and the treatment is further complicated by the rise of antibiotic resistance among staphylococci. Consequently, there is a need for novel antimicrobials that can treat biofilm-related infections and decrease antibiotics burden. Natural compounds such as eugenol with anti-microbial properties are attractive agents that could reduce the use of conventional antibiotics. In this study we evaluated the effect of eugenol on MRSA and MSSA biofilms in vitro and bacterial colonization in vivo.

Methods and Results

Effect of eugenol on in vitro biofilm and in vivo colonization were studied using microtiter plate assay and otitis media-rat model respectively. The architecture of in vitro biofilms and in vivo colonization of bacteria was viewed with SEM. Real-time RT-PCR was used to study gene expression. Check board method was used to study the synergistic effects of eugenol and carvacrol on established biofilms. Eugenol significantly inhibited biofilms growth of MRSA and MSSA in vitro in a concentration-dependent manner. Eugenol at MIC or 2×MIC effectively eradicated the pre-established biofilms of MRSA and MSSA clinical strains. In vivo, sub-MIC of eugenol significantly decreased 88% S. aureus colonization in rat middle ear. Eugenol was observed to damage the cell-membrane and cause a leakage of the cell contents. At sub-inhibitory concentration, it decreases the expression of biofilm-and enterotoxin-related genes. Eugenol showed a synergistic effect with carvacrol on the eradication of pre-established biofilms.

Conclusion/Major Finding

This study demonstrated that eugenol exhibits notable activity against MRSA and MSSA clinical strains biofilms. Eugenol inhibited biofilm formation, disrupted the cell-to-cell connections, detached the existing biofilms, and killed the bacteria in biofilms of both MRSA and MSSA with equal effectiveness. Therefore, eugenol may be used to control or eradicate S. aureus biofilm-related infections.     

Bactericidal activity of ethanolic extracts of propolis against Staphylococcus aureus isolated from mastitic cows

Staphylococcus aureus is an important pathogen for both humans and animals, and it has been an ubiquitous etiological agent of bovine mastitis in dairy farms worldwide. Elimination of S. aureus with classic antibiotics is difficult, and the current study aimed to evaluate the efficacy of ethanolic extracts of propolis (EEP) against S. aureus cultivated in complex media or milk. EEP (0–0.5 mg ml⁻¹) decreased growth of S. aureus in BHI media and 1 mg ml⁻¹ was bactericidal against washed cell suspensions (10⁷ CFU ml⁻¹). Propolis extracts also killed S. aureus cells resuspended in milk, but the bactericidal dose was at least 20-fold greater. Cultures that were transferred for at least 60 generations with sub-lethal doses of propolis did not change much their sensibility to EEP. Atomic force microscopy images revealed changes in morphology and cell size of S. aureus cells exposed to EEP (0.5 mg ml⁻¹). Our results indicate that propolis extracts might be effective against mastitis-causing S. aureus strains in vivo, but milk constituents affect the inhibitory activity of propolis. Considering that propolis-resistance appears to be a phenotype not easily selected, the use of EEP combined or not with other antimicrobial agents might be useful for mastitis control in vivo.     

Occurrence and Molecular Characteristics of Methicillin-Resistant Staphylococcus aureus and Methicillin-Resistant Staphylococcus pseudintermedius in an Academic Veterinary Hospital

Recently, methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-resistant Staphylococcus pseudintermedius (MRSP) have been increasingly isolated from veterinarians and companion animals. With a view to preventing the spread of MRSA and MRSP, we evaluated the occurrence and molecular characteristics of each in a veterinary college. MRSA and MRSP were isolated from nasal samples from veterinarians, staff members, and veterinary students affiliated with a veterinary hospital. Using stepwise logistic regression, we identified two factors associated with MRSA carriage: (i) contact with an identified animal MRSA case (odds ratio [OR], 6.9; 95% confidence interval [95% CI], 2.2 to 21.6) and (ii) being an employee (OR, 6.2; 95% CI, 2.0 to 19.4). The majority of MRSA isolates obtained from individuals affiliated with the veterinary hospital and dog patients harbored spa type t002 and a type II staphylococcal cassette chromosome mec (SCCmec), similar to the hospital-acquired MRSA isolates in Japan. MRSA isolates harboring spa type t008 and a type IV SCCmec were obtained from one veterinarian on three different sampling occasions and also from dog patients. MRSA carriers can also be a source of MRSA infection in animals. The majority of MRSP isolates (85.2%) carried hybrid SCCmec type II-III, and almost all the remaining MRSP isolates (11.1%) carried SCCmec type V. MRSA and MRSP were also isolated from environmental samples collected from the veterinary hospital (5.1% and 6.4%, respectively). The application of certain disinfection procedures is important for the prevention of nosocomial infection, and MRSA and MRSP infection control strategies should be adopted in veterinary medical practice.Methicillin-resistant Staphylococcus aureus (MRSA) is an important cause of nosocomial infections in human hospitals. The prevalence of hospital-acquired MRSA (HA-MRSA) infection among inpatients in intensive care units (ICUs) continues to increase steadily in Japan. Recently, cases of community-acquired MRSA (CA-MRSA) have been documented in persons without an established risk factor for HA-MRSA infection (14, 32, 36, 49).There has also been an increase in the number of reports of the isolation of MRSA from veterinarians and companion animals (5, 21, 23-26, 28, 31, 34, 38, 44, 50, 51, 53). Values reported for the prevalence of MRSA among veterinary staff include 17.9% in the United Kingdom (21), 10% in Japan (38), 3.9% in Scotland (13), and 3.0% in Denmark (28). Loeffler et al. reported that the prevalence of MRSA among dog patients and healthy dogs owned by veterinary staff members was 8.9% (21). In Japan, an MRSA isolate was detected in only one inpatient dog (3.8%) and could not be detected in any of 31 outpatient dogs (38). In the United States, MRSA isolates were detected in both dog (0.1%) and cat (0.1%) patients (31). The prevalence of MRSA among healthy dogs has been reported to be 0.7% (5). Hanselman et al. suggested that MRSA colonization may be an occupational risk for large-animal veterinarians (12). Recently, Burstiner et al. reported that the frequency of MRSA colonization among companion-animal veterinary personnel was equal to the frequency among large-animal veterinary personnel (6).In addition, other methicillin-resistant coagulase-positive staphylococci (MRCPS), such as methicillin-resistant Staphylococcus pseudintermedius (MRSP) and methicillin-resistant Staphylococcus schleiferi (MRSS), isolated from dogs, cats, and a veterinarian have been reported (11, 31, 38, 40, 52). MRSP isolates have also been detected among inpatient dogs (46.2%) and outpatient dogs (19.4%) in a Japanese veterinary teaching hospital (38). In Canada, however, MRSP and MRSS isolates were detected in only 2.1% and 0.5% of dog patients, respectively (11).Methicillin-resistant staphylococci produce penicillin-binding protein 2′, which reduces their affinity for β-lactam antibiotics. This protein is encoded by the mecA gene (48), which is carried on the staphylococcal cassette chromosome mec (SCCmec). SCCmec is a mobile genetic element characterized by the combination of the mec and ccr complexes (16), and it is classified into subtypes according to differences in the junkyard regions (43). SCCmec typing can be used as a molecular tool (22, 27, 30, 33, 36, 55) for examining the molecular epidemiology of methicillin-resistant staphylococci.In this study, we investigated the occurrence and characteristics of MRCPS isolates in a veterinary hospital in order to establish the transmission route of MRCPS in a veterinary hospital and with a view to preventing the spread of MRCPS infection. In addition, we evaluated the factors associated with MRCPS. Further, as Heller et al. have reported the distribution of MRSA within veterinary hospital environments and suggested the necessity to review cleaning protocols of hospital environments (13), we also attempted to isolate MRCPS from environmental samples collected in a veterinary hospital for an evaluation of MRSA transmission cycle though environmental surfaces in the veterinary hospital.     

Bactericidal activity of catechin-copper (II) complexes against Staphylococcus aureus compared with Escherichia coli

The bactericidal activity of catechin-copper (II) complexes against Staphylococcus aureus compared with Escherichia coli was investigated in relation to the generation of hydrogen peroxide and the binding of Cu(II) ion onto the bacteria. The bactericidal activity of catechin-Cu(II) complexes against Staph. aureus (Gram-positive) was much lower than that against E. coli (Gram-negative), suggesting that the binding of copper ions to the surface of bacterial cells plays an important role in the bactericidal activity of catechin-Cu(II) complexes.     

Nasal Carriage of Methicillin-Resistant Staphylococcus aureus among Pediatricians in Taiwan

Background

Health care workers (HCWs) are at the interface between hospitals and communities. The survey for methicillin-resistant Staphylococcus aureus (MRSA) carriage among HCWs has mostly been conducted to investigate outbreaks or endemics. Community-associated MRSA are prevalent among children in Taiwan. We conducted this study to better understand the carriage rate of MRSA among pediatricians in non-outbreak situations in Taiwan,.

Methods

A total of 220 pediatricians from Taiwan who attended the annual meeting of Taiwan Pediatric Association in April, 2010 were recruited to participate in this study and were sampled from the nares for the detection of MRSA by polymerase chain reaction (PCR) and further by culture. The following molecular analyses were performed, including pulsed-field gel electrophoresis (PFGE), multilocus sequence typing (MLST), typing of staphylococcal cassette chromosome mec (SCCmec) and the presence of Panton-Valentine leukocidin (PVL) genes.

Results

MRSA was detected from 15 attendees (6.8%) by PCR. MRSA-colonized attendees had a significantly lower rate (0.041) of working in the medical center, while borderline significantly higher rate of working in the Regional Hospital (p=0.056), than those without MRSA colonization. From those 15 samples, 12 MRSA isolates were identified by culture and molecularly characterized. Three PFGE patterns, two sequence types (ST 59, ST 508), and two SCCmec types (IV and V_T) were identified, respectively. Five isolates, including three carrying SCCmec types V_T, were PVL-positive. All 12 isolates were susceptible to vancomycin, teicoplanin, linezolid, fusidic acid, trimethoprim/sulfamethoxazole, and doxycyclin, and resistant to penicillin.

Conclusion/significance

Around seven percent of pediatricians in Taiwan harbored CA-MRSA in their nares.     

Efficacy of Combined Vancomycin and Fosfomycin against Methicillin-Resistant Staphylococcus aureus in Biofilms In Vivo

Infection by methicillin-resistant Staphylococcus aureus (MRSA) is a life-threatening condition, and formation of biofilms can lead to treatment failure in a clinical setting. The aim of this study was to demonstrate the in vivo bactericidal effects of a combination of vancomycin (VAN) and fosfomycin (FOS) against MRSA in a rat carboxymethyl cellulose-pouch biofilm model. The results of the time-kill assay showed that the combination therapy was capable of killing at low minimal inhibitory concentrations (MIC) (½× MIC VAN +1× MIC FOS and 1× MIC VAN + 1× MIC FOS). In the in vivo study, a synergistically bactericidal effect was observed when using the combination therapy on MRSA embedded in the mature biofilm model. In comparison with the untreated control group and the groups receiving either VAN or FOS alone, the rats treated with combination therapy had lower MRSA colony counts in exudates from the pouch, lower white blood cell and neutrophil counts, and C-reactive protein (CRP) in peripheral blood. Furthermore, histological analysis of the pouch wall indicated combination therapy resulted in disappearance of biofilm-like structures, marked decrease in necrosis, and formation of granular tissue. In conclusion, the combination of VAN with FOS had a synergistic bactericidal effect on chronic MRSA infection embedded in biofilm, providing an alternative approach to treating this condition.     

Bactericidal effect of photodynamic therapy against methicillin-resistant Staphylococcus aureus strain with the use of various porphyrin photosensitizers

Photodynamic therapy (PDT) is based on photosensitizers activated by light of appropriate wavelength. Their activation leads to generation of singlet oxygen and free radicals responsible for the cytotoxic effect. The aim of this project was to compare the bactericidal effect of PDT using different porphyrin photosensitizers against a methicillin-resistant Staphylococcus aureus strain. Exogenous sensitizers (protoporphyrin IX and newly synthesized derivative, protoporphyrin diarginate) induced a 3 log10-unit reduction in bacterial viable counts. With the use of endogenous, ALA-induced porphyrins, a 1.6 log10-unit reduction was obtained. The sensitizers tested executed their antibacterial activity with no essential change in the antibiotic resistance pattern of the studied strain.     

Molecular Epidemiology of Methicillin-Resistant Staphylococcus aureus Isolated from Australian Veterinarians

This work investigated the molecular epidemiology and antimicrobial resistance of methicillin-resistant Staphylococcus aureus (MRSA) isolated from veterinarians in Australia in 2009. The collection (n = 44) was subjected to extensive molecular typing (MLST, spa, SCCmec, dru, PFGE, virulence and antimicrobial resistance genotyping) and antimicrobial resistance phenotyping by disk diffusion. MRSA was isolated from Australian veterinarians representing various occupational emphases. The isolate collection was dominated by MRSA strains belonging to clonal complex (CC) 8 and multilocus sequence type (ST) 22. CC8 MRSA (ST8-IV [2B], spa t064; and ST612-IV [2B], spa variable,) were strongly associated with equine practice veterinarians (OR = 17.5, 95% CI = 3.3–92.5, P < 0.001) and were often resistant to gentamicin and rifampicin. ST22-IV [2B], spa variable, were strongly associated with companion animal practice veterinarians (OR = 52.5, 95% CI = 5.2–532.7, P < 0.001) and were resistant to ciprofloxacin. A single pig practice veterinarian carried ST398-V [5C2], spa t1451. Equine practice and companion animal practice veterinarians frequently carried multiresistant-CC8 and ST22 MRSA, respectively, whereas only a single swine specialist carried MRSA ST398. The presence of these strains in veterinarians may be associated with specific antimicrobial administration practices in each animal species.