Natural ingredients for a bacteria-free library collection

Introduction

Most of the insect species that are likely to infest paper collections are attracted to paper because of its size and the adhesives and starches that are used, which all provide food for various insects. Many chemical methods are used regularly to control pests such as silverfish, firebrats, psocids (also known as booklice) and cockroaches. However, paper, being organic in nature, can also be a feeding ground for microorganisms. Moreover, packed bookshelves may obstruct airflow and allow airborne microorganisms to settle and grow on books. Countries like India have a warm and humid climate, which encourages the growth of microorganisms that degrade paper.

The control of these microorganisms is a challenging task as they do not respond to the regular cleaning and pest-control methods of a library. The library environment offers optimal conditions for the proliferation of microorganisms, and this contamination not only has adverse effects on the life of books, but can also affect the health of users along with the air quality of the library.

A study was undertaken to identify the microorganisms growing on paper that had been put through regular biannual pest control. Based on the presence of microorganisms, the action of naturally occurring substances on these microorganisms was studied.

Need for the study

Various library studies carried out across the world have found the existence of bacteria-contaminated collections, despite all the precautions taken against this (Hempel et al., 2014; Leite et al., 2012; Singh, et al., 2011 and Skóra, et al., 2015). Such contamination can also have adverse effects on the health of library users. Hence, the researchers were interested in verifying the bacterial contamination found in a library collection and studying the impact of various natural ingredients on these microorganisms. For this study, commonly occurring substances such as pepper powder, cinnamon powder, neem oil, clove powder and a mixture of all of these were used to study their inhibitory effects.

Method and observation

The researchers have backgrounds in analytical and medicinal chemistry and organic chemistry, respectively, and were keen to undertake the present study. They sought guidance and support from the Biotechnology Department at the SIES College of Arts, Science and Commerce, which is the parent body of one of the researchers. The college is located in the heart of Mumbai, India, and known as a well-respected institution that has served the ever-growing educational needs of students from the north and central Mumbai suburbs since 1960. The Biotechnology Department was established in 2002 and offers courses for undergraduate, postgraduate and PhD students; it is equipped with a state-of-the-art laboratory and other required facilities (such as Polymerase Chain Reaction Instrument and a spectrophotometer). The Biotechnology Department was used to conduct the tests as the materials and instruments required for this study were readily available. The late Dr Rajalaxmi Amudan, an experienced biotechnologist and faculty member of the SIES College of Arts, Science and Commerce, mentored the experimental study.

All of the books selected for the study were subjected to chemical pest control three times a year. However, the samples collected from these books showed the presence of microorganisms. These microorganisms were identified as belonging to the Bacillus species by 16S ribosomal RNA tests. The subsequent step was to try and inhibit the growth of these microorganisms with the available resources. Naturally occurring substances like neem, cinnamon, cloves and pepper are readily available and used in day-to-day life. Further, they are known for their medicinal properties. It was therefore decided to study the inhibitory effects of these substances.

To study the effect of naturally occurring substances like neem, cinnamon, cloves and pepper, books belonging to different accession numbers were selected with the view that older books may have more contamination compared to newly acquired books. A ditch-plate method was used to check the inhibitory action of neem oil, cinnamon powder, clove powder and pepper powder. This method consisted of preparing a ditch in a sterile nutrient agar plate. The ditch was then filled with the substance mixed in nutrient agar and kept till set. The organisms were streaked evenly across the ditch and incubated for 24 hours at 37°C. The observed zones of inhibition provided the measurable sensitivity of the bacteria to the antimicrobial substance. The entire procedure was done under sterile conditions to prevent contamination.

A microbial inhibitory count for neem oil was performed in order to confirm its inhibitory action by using slants (5 ml) of nutrient broth and neem oil (1 ml to 3 ml). It was observed that 3 ml of neem oil had the maximum inhibitory effect. Further, to confirm inhibitory action, pellets were made of an equal proportion of wheat flour and cinnamon powder, wheat flour and pepper powder, wheat flour and neem oil, wheat flour and clove powder, and wheat flour and a mixture of all of the above. These pellets were put in boxes containing eight books each, and a standard without any inhibitory agent was also maintained. Swabs were taken before placing the pellets in their respective boxes and after 1 day and 23 days. The microbial counts were compared, and it was observed that there was a reduction in growth.

The results of a paired t test to test for a significant drop in the number of microorganisms for all five methods are shown in Table 1.

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Table 1.

T Test results for Microbial Count

Box number	1	2	3	4	5
Combination of Natural Inhibitors used	Wheat flour + cinnamon powder	Wheat flour + pepper powder	Wheat flour + Neem Oil	Wheat flour + clove powder	Wheat flour + a mixture of all the herbs and spices
p value	.033947	.008919	.249982	.386154	.157923

All of the boxes showed a reduction in the number of microorganisms. However, Box 1 and Box 2 – that is, wheat flour + cinnamon powder and wheat flour + pepper powder – showed the greatest reduction in the number of microorganisms over the 1–23-day period. The box without any inhibitory agent showed an increase (matlike appearance) in the number of microorganisms.

Findings and suggestions

Even though neem, cinnamon, cloves and pepper all exhibited inhibitory properties, neem oil was the most effective. However, a dusting of neem powder on books would leave a residue and stick to the hands of users. Neem oil could therefore be mixed with methanol and placed in small bottles on bookshelves; being volatile, it would evaporate and inhibit the growth of microorganisms. A mixture of neem oil and methanol in the proportion of 3:2 could be sprayed on shelves or cotton-wool balls dipped in neem oil could be placed on shelves. A further detailed study is required to determine the best method of application.

Components such as cinnamon powder, pepper powder and clove powder, and a mixture of all four herbs and spices, displayed a considerable reduction in microbial activity. Hence, placing pellets made by mixing equal proportions of wheat flour with cinnamon powder, pepper powder, clove powder or a mixture of all four herbs and spices (and water, and then drying them) among book stacks can restrict the growth of microorganisms.