Bhargava Nidhi, Sharma Prince, Capalash Neena
Department of Biotechnology, Panjab University, Chandigarh, India.
Department of Microbiology, Panjab University, Chandigarh, India.
Infect Immun. 2014 Aug;82(8):3417-25. doi: 10.1128/IAI.01600-14. Epub 2014 Jun 2.
Acinetobacter baumannii and Pseudomonas aeruginosa are nosocomial pathogens with overlapping sites of infection. This work reports that the two can coexist stably in mixed-culture biofilms. In a study intended to improve our understanding of the mechanism of their coexistence, it was found that pyocyanin, produced by P. aeruginosa that generally eliminates competition from other pathogens, led to the generation of reactive oxygen species (ROS) in A. baumannii cells, which in response showed a significant (P ≤ 0.05) increase in production of enzymes, specifically, catalase and superoxide dismutase (SOD). This work shows for the first time that the expression of catalase and SOD is under the control of a quorum-sensing system in A. baumannii. In support of this observation, a quorum-sensing mutant of A. baumannii (abaI::Km) was found to be sensitive to pyocyanin compared to its wild type and showed significantly (P ≤ 0.001) lower levels of the antioxidant enzymes, which increased on addition of 5 μM N-(3-hydroxydodecanoyl)-l-homoserine lactone. Likewise, in wild-type A. baumannii, there was a significant (P < 0.01) decrease in the level of anti-oxidant enzymes in the presence of salicylic acid, a known quencher of quorum sensing. In the presence of amikacin and carbenicillin, A. baumannii formed 0.07 and 0.02% persister cells, which increased 4- and 3-fold, respectively, in the presence of pyocyanin. These findings show that pyocyanin induces a protective mechanism in A. baumannii against oxidative stress and also increases its persistence against antibiotics which could be of clinical significance in the case of coinfections with A. baumannii and P. aeruginosa.
鲍曼不动杆菌和铜绿假单胞菌是感染部位重叠的医院病原体。这项研究报告称,二者能够在混合培养生物膜中稳定共存。在一项旨在加深我们对它们共存机制理解的研究中发现,通常会消除其他病原体竞争的铜绿假单胞菌产生的绿脓菌素,会导致鲍曼不动杆菌细胞中产生活性氧(ROS),作为响应,鲍曼不动杆菌细胞中过氧化氢酶和超氧化物歧化酶(SOD)等酶的产量显著增加(P≤0.05)。这项研究首次表明,鲍曼不动杆菌中过氧化氢酶和SOD的表达受群体感应系统调控。为支持这一观察结果,发现鲍曼不动杆菌的群体感应突变体(abaI::Km)与野生型相比对绿脓菌素敏感,且抗氧化酶水平显著降低(P≤0.001),添加5μM N-(3-羟基十二烷酰基)-L-高丝氨酸内酯后抗氧化酶水平升高。同样,在野生型鲍曼不动杆菌中,已知的群体感应淬灭剂水杨酸存在时,抗氧化酶水平显著降低(P<0.01)。在阿米卡星和羧苄青霉素存在的情况下,鲍曼不动杆菌形成0.07%和0.02%的持留菌,在绿脓菌素存在时分别增加4倍和3倍。这些发现表明,绿脓菌素在鲍曼不动杆菌中诱导了一种针对氧化应激的保护机制,还增加了其对抗生素的耐受性,这在鲍曼不动杆菌和铜绿假单胞菌合并感染的情况下可能具有临床意义。