Bartolomeu Maria, Rocha Sónia, Cunha Ângela, Neves M G P M S, Faustino Maria A F, Almeida Adelaide
Departamento de Biologia and Centro de Estudos do Ambiente e do Mar, University of Aveiro Aveiro, Portugal.
Departamento de Química and Unidade de Investigação em Química Orgânica, Produtos Naturais e Agroalimentares, University of Aveiro Aveiro, Portugal.
Front Microbiol. 2016 Mar 7;7:267. doi: 10.3389/fmicb.2016.00267. eCollection 2016.
Staphylococcus aureus is a Gram-positive bacterium that is present in the human microbiota. Nevertheless, these bacteria can be pathogenic to the humans. Due to the increasing occurrence of antibiotic-resistant S. aureus strains, new approaches to control this pathogen are necessary. The antimicrobial photodynamic inactivation (PDI) process is based in the combined use of light, oxygen, and an intermediary agent (a photosensitizer). These three components interact to generate cytotoxic reactive oxygen species that irreversibly damage vital constituents of the microbial cells and ultimately lead to cell death. Although PDI is being shown to be a promising alternative to the antibiotic approach for the inactivation of pathogenic microorganisms, information on effects of photosensitization on particular virulence factors is strikingly scarce. The objective of this work was to evaluate the effect of PDI on virulence factors of S. aureus and to assess the potential development of resistance of this bacterium as well as the recovery of the expression of the virulence factors after successive PDI cycles. For this, the photosensitizer 5,10,15,20-tetrakis(1-methylpyridinium-4-yl)porphyrin tetra-iodide (Tetra-Py(+)-Me) and six strains of S. aureus [one reference strain, one strain with one enterotoxin, two strains with three enterotoxins and two methicillin resistant strains (MRSA) - one with five enterotoxins and the other without enterotoxins] were used. The effect of photosensitization on catalase activity, beta hemolysis, lipases, thermonuclease, enterotoxins, coagulase production, and resistance/susceptibility to methicillin was tested. To assess the development of resistance after successive cycles of treatment, three strains of S. aureus (ATCC 6538, 2065 MA, and SA 3 MRSA) were used. The surviving colonies of a first cycle of PDI were collected from the solid medium and subjected to further nine consecutive cycles of PDI. The results indicate that the expression of some external virulence factors is affected by PDI and enterotoxin producing strains were more susceptible to PDI than non-toxigenic strains. The surviving bacteria did not develop resistance. PDI, contrarily to traditional antibiotics, inhibited the expression of virulence factors, efficiently inactivating either highly virulent strains and low virulent S. aureus strains, inactivating also antibiotic susceptible and resistant strains, without development of photoresistance after at least 10 consecutive cycles of treatment, and so this therapy may become a strong promising alternative to antibiotics to control pathogenic microorganisms.
金黄色葡萄球菌是一种存在于人类微生物群中的革兰氏阳性细菌。然而，这些细菌可能对人类致病。由于耐抗生素金黄色葡萄球菌菌株的出现日益增多，因此需要新的方法来控制这种病原体。抗菌光动力灭活（PDI）过程基于光、氧和一种中间剂（一种光敏剂）的联合使用。这三种成分相互作用产生细胞毒性活性氧，不可逆地损伤微生物细胞的重要成分，最终导致细胞死亡。尽管PDI已被证明是一种有前景的替代抗生素方法用于灭活致病微生物，但关于光致敏对特定毒力因子影响的信息却极为匮乏。这项工作的目的是评估PDI对金黄色葡萄球菌毒力因子的影响，并评估该细菌耐药性的潜在发展以及在连续PDI循环后毒力因子表达的恢复情况。为此，使用了光敏剂5,10,15,20-四（1-甲基吡啶鎓-4-基）卟啉四碘化物（四吡啶（+）-甲基）和六株金黄色葡萄球菌[一株参考菌株、一株产一种肠毒素的菌株、两株产三种肠毒素的菌株以及两株耐甲氧西林菌株（MRSA）——一株产五种肠毒素，另一株不产肠毒素]。测试了光致敏对过氧化氢酶活性、β溶血、脂肪酶、耐热核酸酶、肠毒素、凝固酶产生以及对甲氧西林的耐药性/敏感性的影响。为了评估连续治疗循环后耐药性的发展，使用了三株金黄色葡萄球菌（ATCC 6538、2065 MA和SA 3 MRSA）。从固体培养基中收集第一个PDI循环的存活菌落，并对其进行另外九个连续的PDI循环。结果表明，一些外部毒力因子的表达受PDI影响，产肠毒素菌株比不产毒菌株对PDI更敏感。存活的细菌未产生耐药性。与传统抗生素相反，PDI抑制毒力因子的表达，能有效灭活高毒力菌株和低毒力金黄色葡萄球菌菌株，也能灭活抗生素敏感和耐药菌株，在至少连续10个治疗循环后未产生光耐药性，因此这种疗法可能成为控制致病微生物的一种非常有前景的替代抗生素的方法。
