Bacteria on shoes could help forensic teams catch suspects
鞋子上的細菌也許有助鑑識小組抓到嫌犯
作者／Stefano Vanin (哈德斯菲爾德大學法醫生物學系)
譯者／吳京
Prospective criminals should take note: bacteria are everywhere. A small pilot study has shown that the germs on personal belongings such as shoes and mobile phones are actually a useful way of tracing a person’s whereabouts – something that may prove useful in forensic investigations.
蠢蠢欲動的犯罪者請注意：人間處處有細菌。一個小型的前導研究指出，鞋子、手機等個人物品上的微生物竟可洩漏一個人的行跡，這對法證識別而言應該很實用。
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| credit:Gideon Chilton |
Microorganisms like bacteria are small, diverse and often specific to certain environments, organisms or individuals. This is also what makes them excellent as a forensic tool. In fact, like DNA and fingerprints, a suspect can unknowingly leave microbes behind on a crime scene or victim, providing useful information about the identity or origin of the suspect for forensic scientists. One day, such microbial signatures of individuals may prove as important as DNA or fingerprints, although a lot more research is needed to get there.
細菌之類的微生物雖小，但種類俱全，往往生存於特定的環境、生物群或個體上，讓牠們可望成為出色的鑑識工具。就如同DNA和指紋一般，罪犯會在犯罪現場或被害人身上留下微生物而渾然不覺，提供鑑識科學有用的資訊，能追溯來源並辨視身份。雖然這項技術仍需更多研究驗證，但假以時日，個體的「微生物簽名」也可能像DNA及指紋一樣重要。
The age of bacteria
細菌時代
Biology books typically state that we are living in the “age of mammals” that has followed the “age of dinosaurs” and the “age of the bacteria”. But, there are loads more species of bacteria than there are species of mammals. Looking at these numbers, along with the distribution and adaptability of the species, it seems we are still in the age of the bacteria.
Bacteria are the most abundant and genetically diverse organisms that we know. These germs ubiquitously inhabit the environment, including many extreme places like the glaciers in the high altitude, polar regions, or very hot thermal springs. Moreover, bacteria are present on different regions of the animal and human body, especially skin, mouth and the gastrointestinal tract. These body regions are home of diverse communities of bacteria and other microorganisms that can change depending on the health status and age of the host.
生物教科書上通常這麼說，我們正處於「哺乳類時代」，在此之前的是「恐龍時代」，更早則是「細菌時代」。然而，現存細菌的種類比哺乳類還多，看看細菌的數量、分佈及對環境的適應力，說我們尚處於細菌時代也不為過。
細菌是我們所知遺傳多樣性最豐富的物種，細菌無所不在，冷若高海拔的冰河裡，熱似滾燙的溫泉中，都有他們的身影，除了這些極端的環境，細菌還會存在於動物及人體上，特別是在皮膚、口腔和消化器官中。這些身體區域成為細菌及微生物的溫床，滋養著族繁不及備載的物種，種類還會隨著宿主健康狀況及年齡而改變。
Several studies have been carried out to describe the human microbiome, which is the collection of bacteria we are associated with, and to verify that the microbial signature can be used in the investigative field and, at the end of the legal process, in the court as proper evidence.
為了解析人體微生物的狀況，有好幾個研究已在進行，旨在搜整與人體相關的細菌資料，想要證明微生物簽名可用於犯罪偵查，並透過合法的程序成為呈堂證供。
When arriving at a crime scene, the suspect usually has to walk. This was the starting point for the study, which tried to determine the possibility to trace people’s origin using the microbial community of their shoes.
由於大部份的嫌犯是「走」到犯罪現場的，著眼於此，有一個研究試著找出「利用鞋子的微生物族群來追溯宿主背景」的可能性。
This team looked at shoes from 89 participants randomly selected from attendees at three different scientific conferences in the US. They found that the shoes could be divided into three different groups according to the geographic locations of the conferences. This is because shoes that have travelled on different types of surfaces show distinct microbial signatures, in addition to a “core microbiome” belonging to an individual. This is obviously useful to forensic teams as it reveals the microbial signature of the owner as well as demonstrating where they have been before the sampling.
這個研究團隊從三場在美國舉辦得科學會議場合中，隨機抽樣了89位參與者來看看他們的鞋。他們發現這些鞋子根據會議地點的不同也可分成三類，行經不同之地會造就鞋上明顯不同的微生物族群，除此之外，還有一些「核心微生物群」是因人而異的。這對科學鑑識小組而言明顯有用，這種樣本不但帶有原宿主的微生物簽名，還透露了他們曾去過哪些地方。
The team also showed that one of the most common objects that we use every day, the mobile phone, could also be of used in this way. They demonstrated that the pattern of microbes found on a telephone is unique. There are also differences between the front and the back since the back is mainly in contact with the hands and the front comes into contact with the face, and particularly with the mouth. These observations are supported by previous studies that demonstrated how different microbial communities are from different body parts – and that the personal microbial signature is unique.
研究團隊表示還有一個物品也有同樣的效用，即我們每天使用的手機。他們指出每個手機上的微生物特徵都不同，甚至同一隻手機的正、反兩面就會有兩種特微。因為反面通常是手持端，而正面通常與臉部(特別是口部)接觸。過去的一些研究曾說明不同的身體部位會滋養不同的微生物，而每個人的微生物簽名都是獨一無二的，這也支持了研究團隊的觀察結果。
But the microbiome could have other uses in forensics than locating suspects. In the past few years a lot of work has been done in order to use the changes in the biome associated with decomposing bodies, called “necrobiome”, to estimate the time since death. The idea behind this approach follows what is already known and applied in another forensic discipline: forensic entomology. Insects, which colonise a cadaver in specific waves, are used in this field to give answers to one of the most crucial question on a homicide: when? This is because insects colonise a body in predictable waves, so the study of insects on cadavers tells us something about the minimum time since death.
話說回來，除了找出嫌犯的位置外，微生物在鑑識科學方面還有其他的應用。在過去幾年中，許多心血投入在「死屍寄生物」(necrobiome)相關的研究，即利屍體腐化時，其上微生物族群的變化情況來估算死亡時間。這種方法背後的原理可和另一門較成熟的鑑識科學「法醫昆蟲學」一以貫之，寄居於屍首上的蟲子數種有特定的起伏，能用來判定殺人案的關鍵因素之一：何時？由於寄生於死者上的蟲子變化是可預測的，籍此能推測死亡時間至少過了多久。
The small study is important but will not be seen as a revolution by those working in forensics. It is simply the extension of “Locard’s exchange principle, one of the most robust pillars of the forensic work, to the microbial level: “Every contact leaves a trace”. More work is needed to determine the practical use of it in the future. A first step would be to scale up the experiment to include more people.
這個小型研究雖重要，但對鑑識科學而言也還談不上革命性的工作。這只是「羅卡定律」在微生物角度下的一種延伸；羅卡定律是鑑識科學的基石之一，告訴我們「凡接觸必留下痕跡」。未來我們還需要更多的努力來決定這方面的研究是否實用，努力的第一步是招集更多人(的鞋子?)來擴大實驗。
研究團隊表示還有一個物品也有同樣的效用，即我們每天使用的手機。他們指出每個手機上的微生物特徵都不同，甚至同一隻手機的正、反兩面就會有兩種特微。因為反面通常是手持端，而正面通常與臉部(特別是口部)接觸。過去的一些研究曾說明不同的身體部位會滋養不同的微生物，而每個人的微生物簽名都是獨一無二的，這也支持了研究團隊的觀察結果。
Hurdles to overcome
仍有窒礙難行處
However the authors also pointed to some difficulties in implementing the research. The microbiome on our soles typically changes throughout the day, which could make it hard to pinpoint the places we’ve been if we have walked around a lot. In the same way, the microbiome of a certain floor is also altered if a lot of people walk on it.
仍有窒礙難行處
However the authors also pointed to some difficulties in implementing the research. The microbiome on our soles typically changes throughout the day, which could make it hard to pinpoint the places we’ve been if we have walked around a lot. In the same way, the microbiome of a certain floor is also altered if a lot of people walk on it.
不過，該報告的作者同時指出這個研究成果在執行面的難處。我們足底的微生物群通常還會逐日改變，在我們足履四方後，想要籍此標定出我們去過哪些地方是很因難的；相對的，一個現場若被許多人踩踏後，想要找出有用的那一組微生物，也沒那麼簡單啊！
話說回來，除了找出嫌犯的位置外，微生物在鑑識科學方面還有其他的應用。在過去幾年中，許多心血投入在「死屍寄生物」(necrobiome)相關的研究，即利屍體腐化時，其上微生物族群的變化情況來估算死亡時間。這種方法背後的原理可和另一門較成熟的鑑識科學「法醫昆蟲學」一以貫之，寄居於屍首上的蟲子數種有特定的起伏，能用來判定殺人案的關鍵因素之一：何時？由於寄生於死者上的蟲子變化是可預測的，籍此能推測死亡時間至少過了多久。
The small study is important but will not be seen as a revolution by those working in forensics. It is simply the extension of “Locard’s exchange principle, one of the most robust pillars of the forensic work, to the microbial level: “Every contact leaves a trace”. More work is needed to determine the practical use of it in the future. A first step would be to scale up the experiment to include more people.
這個小型研究雖重要，但對鑑識科學而言也還談不上革命性的工作。這只是「羅卡定律」在微生物角度下的一種延伸；羅卡定律是鑑識科學的基石之一，告訴我們「凡接觸必留下痕跡」。未來我們還需要更多的努力來決定這方面的研究是否實用，努力的第一步是招集更多人(的鞋子?)來擴大實驗。
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