Mammina Caterina, Aleo Aurora, Romani Cristina, Nastasi Antonino
Centre for Enteric Pathogens of southern Italy (CEPIM), Department of Hygiene and Microbiology G, D'Alessandro, University, Via del Vespro 133, 90127 Palermo, Italy.
BMC Infect Dis. 2006 Jul 17;6:117. doi: 10.1186/1471-2334-6-117.
Emergence and global dissemination of multiresistant strains of enteric pathogens is a very concerning problem from both epidemiological and Public Health points of view. Shigella sonnei is the serogroup of Shigella most frequently responsible for sporadic and epidemic enteritis in developed countries. The dissemination is associated most often to human to human transmission, but foodborne episodes have also been described. In recent years the circulation of multiresistant strains of S. sonnei biotype g carrying a class 2 integron has been reported in many countries worldwide. In southern Italy a strain with similar properties has been responsible for a large community outbreak occurred in 2003 in Palermo, Sicily. The objective of this study was to date the emergence of the biotype g strain carrying the class 2 integron in southern Italy and to evaluate the genetic heterogeneity of biotype g S. sonnei isolated throughout an extended interval of time.
A total of 31 clinical isolates of S. sonnei biotype g identified in southern Italy during the years 1971-2000 were studied. The strains were identified at the serogroup level, characterized by biochemical tests and submitted to antimicrobial susceptibility testing. Molecular typing was performed by pulsed field gel electrophoresis (PFGE) after digestion of DNA by XbaI. Carriage of class 2 integrons was investigated by polymerase chain reaction (PCR) with specific primers and confirmed by restriction endonuclease analysis of amplicons.
The 15 isolates of S. sonnei biotype g identified in the decade 1971-1980 showed highly heterogeneous drug resistance profiles and pulsotypes. None of the isolates was simultaneous resistant to streptomycin and trimethoprim and none was class 2 integron positive. On the contrary, this resistance phenotype and class 2 integron carriage were very common among the 16 strains of biotype g identified in the following two decades. Moreover, all the more recent isolates, but one, showed closely related pulsotypes.
Although our findings refer to a limited geographic area, they provide a snapshot of integron acquisition by an enteric pathogen responsible for several outbreaks in the years 2001-2003 in Italy. Molecular typing, indeed, suggests that the emergence of biotype g class 2 integron carrying S. sonnei in southern Italy should be backdated to at least the late 1980s. In the following decades, the circulation of biotype g appears to be sustained by multiresistant highly related strains. Similar trend are described in several countries, but the questions about mechanism of emergence and worldwide spread of this pathogen remain open.
从流行病学和公共卫生角度来看，肠道病原体多重耐药菌株的出现和全球传播是一个非常令人担忧的问题。宋内志贺菌是志贺菌属中在发达国家最常导致散发性和流行性肠炎的血清群。这种传播最常与人际传播有关，但也有食源性感染事件的报道。近年来，在世界许多国家都报告了携带2类整合子的宋内志贺菌生物型g多重耐药菌株的传播情况。在意大利南部，一种具有类似特性的菌株导致了2003年在西西里岛巴勒莫发生的大规模社区疫情。本研究的目的是确定携带2类整合子的生物型g菌株在意大利南部出现的时间，并评估在较长时间内分离出的生物型g宋内志贺菌的遗传异质性。
对1971年至2000年期间在意大利南部鉴定出的31株宋内志贺菌生物型g临床分离株进行了研究。这些菌株在血清群水平上进行了鉴定，通过生化试验进行了表征，并进行了药敏试验。在通过XbaI消化DNA后，通过脉冲场凝胶电泳（PFGE）进行分子分型。使用特异性引物通过聚合酶链反应（PCR）研究2类整合子的携带情况，并通过扩增子的限制性内切酶分析进行确认。
在1971 - 1980年这十年中鉴定出的15株宋内志贺菌生物型g分离株显示出高度异质的耐药谱和脉冲型。没有分离株同时对链霉素和甲氧苄啶耐药，也没有分离株为2类整合子阳性。相反，在接下来的二十年中鉴定出的16株生物型g菌株中，这种耐药表型和2类整合子携带情况非常普遍。此外，除了一株之外，所有较新的分离株都显示出密切相关的脉冲型。
尽管我们的研究结果仅涉及一个有限的地理区域，但它们提供了一幅肠道病原体获得整合子的快照，该病原体在2001 - 2003年期间在意大利引发了数次疫情。分子分型确实表明，在意大利南部携带2类整合子的生物型g宋内志贺菌的出现至少可以追溯到20世纪80年代末。在接下来的几十年中，生物型g的传播似乎由多重耐药的高度相关菌株维持。在几个国家也描述了类似的趋势，但关于这种病原体出现和全球传播机制的问题仍然悬而未决。
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