Narrow Results

The response of bacterial populations to antibiotic treatment is often a function of a diverse range of interacting factors. In order to develop strategies to minimize the spread of antibiotic resistance in pathogenic bacteria, a sound theoretical understanding of the systems of interactions taking place within a colony must be developed. The agent-based approach to modeling bacterial populations is a useful tool for relating data obtained at the molecular and cellular level with the overall population dynamics. Here we demonstrate an agent-based model, called Micro-Gen, which has been developed to simulate the growth and development of bacterial colonies in culture. The model also incorporates biochemical rules and parameters describing the kinetic interactions of bacterial cells with antibiotic molecules.

Simulations were carried out to replicate the development of methicillin-resistant S. aureus (MRSA) colonies growing in the presence of antibiotics. The model was explored to see how the properties of the system emerge from the interactions of the individual bacterial agents in order to achieve a better mechanistic understanding of the population dynamics taking place. Micro-Gen provides a good theoretical framework for investigating the effects of local environmental conditions and cellular properties on the response of bacterial populations to antibiotic exposure in the context of a simulated environment.

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Photodynamic inactivation of microorganisms known as antibacterial photodynamic therapy (APDT) is one of the most promising and innovative approaches for the destruction of pathogenic microorganisms. Among the photosensitizers (PSs), compounds based on cationic porphyrins/metalloporphyrins are most successfully used to inactivate microorganisms. Series of meso-substituted cationic pyridylporphyrins and metalloporphyrins with various peripheral groups in the third and fourth positions of the pyrrole ring have been synthesized in Armenia. The aim of this work was to determine and test the most effective cationic porphyrins and metalloporphyrins with high photoactivity against Gram negative and Gram positive microorganisms. It was shown that the synthesized cationic pyridylporphyrins/metalloporphyrins exhibit a high degree of phototoxicity towards both types of bacteria, including the methicillin-resistant S. aureus strain. Zinc complexes of porphyrins are more phototoxic than metal-free porphyrin analogs. The effectiveness of these Zn–metalloporphyrins on bacteria is consistent with the level of singlet oxygen generation. It was found that the high antibacterial activity of the studied cationic porphyrins/metalloporphyrins depends on four factors: the presence in the porphyrin macrocycle of a positive charge (+4), a central metal atom (Zn${}^{2+})$ and hydrophobic peripheral functional groups as well as high values of quantum yields of singlet oxygen. The results indicate that meso-substituted cationic pyridylporphyrins/metalloporphyrins can find wider application in photoinactivation of bacteria than anionic or neutral PSs usually used in APDT.

Photodynamic inactivation of microorganisms known as antibacterial photodynamic therapy (APDT) is one of the most promising and innovative approaches for the destruction of pathogenic microorganisms. Among the photosensitizers (PSs), compounds based on cationic porphyrins/metalloporphyrins are most successfully used to inactivate microorganisms. Series of meso-substituted cationic pyridylporphyrins and metalloporphyrins with various peripheral groups in the third and fourth positions of the pyrrole ring have been synthesized in Armenia. The aim of this work was to determine and test the most effective cationic porphyrins and metalloporphyrins with high photoactivity against Gram negative and Gram positive microorganisms. It was shown that the synthesized cationic pyridylporphyrins/metalloporphyrins exhibit a high degree of phototoxicity towards both types of bacteria, including the methicillin-resistant S. aureus strain. Zinc complexes of porphyrins are more phototoxic than metal-free porphyrin analogs. The effectiveness of these Zn–metalloporphyrins on bacteria is consistent with the level of singlet oxygen generation. It was found that the high antibacterial activity of the studied cationic porphyrins/metalloporphyrins depends on four factors: the presence in the porphyrin macrocycle of a positive charge (+4), a central metal atom (Zn²⁺) and hydrophobic peripheral functional groups as well as high values of quantum yields of singlet oxygen. The results indicate that meso-substituted cationic pyridylporphyrins/metalloporphyrins can find wider application in photoinactivation of bacteria than anionic or neutral PSs usually used in APDT.

Methicillin-resistant Staphylococcus aureus (MRSA) now becomes a global health concern. It costs 3 d-4 d to finish MRSA detection procedure using conventional methods, also it may have false positive or false negative. Thus, developing an accurate and rapid method in MRSA detection and infection control becomes necessary. This study aimed to develop and establish a multiplex PCR assay for rapid and sensitive detection of MRSA. Four genetic loci were selected to be detected in one amplification system, 16S rRNA of Staphylococcus genus, femA of S. aureus, mecA of methicillin-resistance and orfX of SCCmec. The PCR reaction was finished within 3 h. The specificity of multiplex PCR was brought out with the evaluation using four different kinds of reference strains including MSCNS, MRCNS, MSSA and MRSA. The diagnostic evaluation was brought out with the appliance of 33 clinical MRSA strains. The results showed that the sensitivity and diagnostic rate of multiplex PCR was 100% and without false negative or false positive. To sum up, this rapid detection method has the potential in the diagnosing and infection control of MRSA.

The objective this study was to detect methicillin-resistant Staphylococcus aureus (MRSA) in clinical and/or surveillance cultures of patients seen at a Brazilian teaching hospital and to associate their detection with the prevalence of resistance and virulence factors. The genotypic resistance and virulence profiles of 212 S. aureus strains were analyzed by PCR for detection of the mecA gene and positive strains were subtyped for the staphylococcal cassette chromosome (SCCmec) by multiplex PCR. Investigation of the mecA gene revealed 134 (63.2%) MRSA strains and the characterization of SCCmec showed the presence of SCCmec type III or variations of type III in 104 (77.6%) strains, SCCmec type I or IA in 23 (17.2%), SCCmec type IV in 4 (3%), and SCCmec type II in 3 (2.2%). Analysis of the virulence profile showed no significant difference in the presence of genes encoding biofilm production (icaA and/or icaD), delta hemolysin (hld), alpha hemolysin (hla), or enterotoxin A (sea) or B (seb) between MRSA and MSSA. However, the enterotoxin C gene (sec-1) was more frequent in MRSA strains.

Human beta-defensins (hBDs) are an intrinsic part of the innate immune response. These peptides have been shown to possess varying potencies against a wide spectrum of bacteria, viruses and fungi. Due to increasing resistance to traditional antimicrobials, interest is being shown in these peptides as possible therapeutic molecules. In this study, the bactericidal activity of two peptides (human beta defensin-2: hBD-2, and human beta defensin-3: hBD-3) was assessed against a range of Staphylococcus aureus (S. aureus) strains, including MRSA, using a standard bactericidal assay. The antibiotic sensitive strains of S. aureus were more susceptible to killing and exhibited a dose response to the test peptides reaching 99% kill at the highest concentration. In comparison the MRSA clinical isolates although still susceptible to the peptides showed lower percentage kill at all the concentrations examined, reaching a maximum at 68% kill. Importantly, here we show for the first time a clear and significant difference in bactericidal activity of defensins towards Methicillin sensitive and Methicillin resistant strains of S. aureus.

Methicillin-resistant Staphylococcus aureus (MRSA) is a highly pathogenic multiple-drug resistant (MDR) microorganism that is most prevalent in the community. It has been found that MRSA strains can also contain genes that encode the panton valentine leukocidin toxin (PVL) and several genes that confer resistance to a various number of antimicrobial agents. The aim of this study was to determine the presence of MRSA (mecA gene) and PVL toxin genes (lukS-PV and lukF-PV) in strains isolated from two hospitals. The susceptibility to a various number of antimicrobial agents was tested and its clonality also studied. The results indicated a frequency of approximately 50% of MRSA and a frequency of 9% of isolates carrying the lukFS-PVL gene. Regarding the susceptibility patterns of isolates under study it was concluded that for most antimicrobial agents used MRSA strains reveal to be resistant to more antimicrobials than the isolates that lack mecA gene. Regarding fingerprinting method it was possible to observe a quite fixed number of strains among pathogen causing hospital-acquiring infection. The explanation for these findings is complex and multi-factorial. The high diversity of clones suggests diverse genetic backgrounds rather than the global spread of a single clone.

The occurrence of Panton Valentin leukocidin in 99 invasive MRSA strains isolated from hospitalized patients was shown to be around 9,1 %. Five of nine PVL positive strains had SCCmec type IV casette. The predominating SCCmec type in PVL negative and SCCmec typable MRSA was II. Such strains were simultaneously resistant to erythromycin, clindamycin and ciprofloxacin. The linezolid resistance in invasive MRSA strains from Slovak hospital was not recorded. The MLVA characterization of 8 PVL positive isolates from various locations has demonstrated three different patterns. Except one hospital, isolates from over the country expressed the same MVLA pattern.

The prevalence of Staphylococcus aureus carriage among healthy children from four kindergartens located in the North of Portugal and antibiotic resistance of the isolates were evaluated. Nasal swabs were collected from 296 healthy children aged 3 to 6 year. 144 were carriers of S. aureus; 15% of the strains were multidrug resistant. Resistance to gentamicin, chloramphenicol, rifampicin, oxacillin, nitrofurantoin, tetracycline, erythromycin, ampicillin and penicillin were determined to be 1.5, 2.2, 2.2, 9.7, 19, 34.1, 73.3, 84.4 and 91.1%, respectively. All the strains were sensitive to vancomycin. Our study reveals a high prevalence of healthy children carrying S. aureus (49%), including MRSA (9%), in the nasal cavity.