Abstract

Staphylococcus aureus is one of the most common causes of life-threatening bacterial infections.

It is the cause of 241,188 illnesses, 1,064 hospitalizations, and 6 deaths per year. Roughly

400,000 hospital patients are infected by Staphylococcus aureus. Approximately 100,000 of these

patients die from complications due to their infections. Staphylococcus aureus is a Gram-

positive, oxidase-negative, non-motile microorganism and facultative anaerobic.

Staphylococcus aureus is one of about 32 species in the Staphylococcus genus of bacteria. Most

of the other species are found only in other mammals and do not infect humans. The origin of

Staphylococcus aureus is not well understood, but current theories suggest that it evolved from

prehistoric soil bacteria. Staphylococcus aureus was first conclusively described by German

physician Anton Rosenbach in 1884. It is a nonmotile bacterium that grows in clusters just like

the grapes. Staphyleis is a Greek word for “bunch of grapes,” and cocci, means “spherical

bacteria." The name aureus, which is Latin for “gold,” was given to the bacteria because it

grows in large yellow colonies. The cells are about 1 micrometer in diameter; so 1,000 cells

lined up next to each other would cover a distance of only 1 millimetre. This experiment was

carried out for a comparison of the growth rate of S. aureus grow on soft (camembert) & hard

(cheddar) cheeses as well as to assess the effect of the cheese handling, storage temperature and

time on the growth rate of Staphylococcus aureus.

Introduction

Staphylococcus aureus has been recognized and described only 125 years ago, but it has almost

certainly been infecting and killing humans for thousands of years. As a nitrogen source,

Staphylococcus aureus needs thiamine, nicotic acid, salts (inorganic) and amino acids

For growth it requires B vitamins (nicotic acid, thiamine), amino acids and inorganic salts as a

nitrogen source, although cystein, valine, Glutamic acid, agrinine, and tyrosine do not help in its

growth but important source of enterotoxin production. Boils, which are common S. Aureus skin

infections, are mentioned in the Bible. Staphylococcus aureus is extremely durable. It grows in a

wide temperature range, it's Mesophilic; 7- 47.8°C (opt. 35°C); pH: 4.5- 9.3 (opt. 7.0-7.5). Low

levels of water activity (aw) 0.83 (Opt.>0.99). If conditions for growth (i.e. temperature or

nutrient supply) are not favourable, Staphylococcus aureus can exist for years in a dormant state

(essentially, being inactive and lying in wait for a good time to begin growing). Later, the

bacteria can start growing again when conditions are more favourable. One reason why

Staphylococcus aureus is so resilient is that its cell wall is extremely thick compared with the cell

walls of other bacteria. This thickness allows Staphylococcus aureus to exist with the highest

internal pressure of any type of bacteria. S. aureus is nothing if not opportunistic. The biggest

problem with S. aureus wound infections is the dramatic increase in the number of such

infections that are caused by antibiotic-resistant S. aureus. These infections might be easily

treated if the bacteria were sensitive to the first antibiotic used, but they can become much more

serious before an appropriate antibiotic is found. Because of this, many patients today die from

infections that were once easily cured. Sometimes dairy products, like cheese also causes food

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poisoning, which is due to the presence of S. aureus. In dairy products like cheese, where the

presence of staphylococcal enterotoxins act, as causative agent of outbreaks of staphylococcal

food poisoning in humans. About 90% of S. aureus strains are currently resistant to penicillin. S.

aureus produces a wide range of virulence factors—proteins that help the bacteria sustain an

infection and damage human host cells. These virulence factors help the bacteria attach to the

host cells, specifically attack and damage them, and prevent the immune system from responding

to the bacteria. The characteristics of S.aureus are mentioned as under:

Gram-positive

Non- motile

Facultative anaerobic

Catalase-positive

Cocci in pairs, short chains, or bunched in grape-like clusters

Ubiquitous

Usually found in foods due to environmental, animal and human contamination.

Heat stable enterotoxins

Kousta et al. (51) studied that in both pasteurized and unpasteurized milk cheese did not meet the

EU regulations for Staphylococcus aureus where its presence was detected in 13-20% of samples

or 35-45% and even in 70-80%. Cheese production has its own critical factors of safety like the

natural contamination in milk, type of cheese and its nature, kind of starter culture. The aim of

this project is to study the comparison of the growth rate of S. aureus growth on soft

(camembert) & hard (cheddar) cheeses as well as to find out the effect of cheese handling,

storage temperature and time on the growth rate of Staphylococcus aureus.

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Methods and Materials

Response of growth of Staphylococcus aureus as affected by NaCl concentration, pH value and

storage temperature were studied in laboratory medium.

For the detection, enumeration and isolation of Staphylococcus aureus the direct plating method

was used. as it allows the placement of cheese slices directly on solidified agar media. This

process was used as it provides effective measure of inherent mycological quality while it also

helps assess the presence of mycotoxins:

Two type: Soft Cheese (Camembert) and hard cheese (Cheddar)

Two replicates for each type of cheese

Staphylococcus aureus (strain)

Low concentration for soft cheese (103 cfu/ml)

High concentration for hard cheese (107 cfu/ml)

Two type of media for direct plating method:

Nutrient Agar (NA) as non-selective medium and

Baird-Parker (BP) as selective medium

Storage temperature: 20 °C

For the past several decades, in the food science literature, the phenomenon denoted by the term

“aw” has been widely used to predict microbial growth as well as the relationship between many

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common food deterioration reactions and aw. Although RH is a better indicator of food stability

and safety than the water content of a system.

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Result

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Results in the present study showed that the contamination in cheese also can occur due to safety

lacks in the production process. For example at some stage during cheese production air control

points contain high mould counts. Which proves that air is an important factor in the

contamination of cheese; f the air is clean the mould contamination is reduced.

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ELISA based method: an immunological technique used to diagnose various infectious diseases of human, animals as well as plants which is more than 99% sensitive and specific than any other serological test (Kemeny & Challacombe, 1989). ELISA is used for the detection of Staphylococcus aureus which is Gram +ve bacteria; exist in pairs, short chains, bunched or grape like clusters and of golden yellow in colour.

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References

Gandhi, M & Chikindas, ML 2006, ‘Listeria: A foodborne pathogen that knows how to survive’, International Journal of Food Microbiology, vol. 113, pp. 1-15.

Kamal S, Rehman K, Zia A and Parvin B, International journal of agriculture and biology, Pakistan, viewed 18 June 2013, http://www.fspublishers.org/ijab/past-issues/IJABVOL_8_NO_1/17.pdf

Kousta (ed) 2008, Structure and Function of Food Engineering.

Medveďová A and Valík L 2012, ‘Staphylococcus aureus: Characterisation and Quantitative Growth Description viewed 18 June 2013. http://www.intechopen.com/books/structure-and-function-of-food-engineering/staphylococcus-aureus-characterisation-and-quantitative-growth-description-in-milk-and-artisanal-raw

Cynthia M. Stewart, Martin B. Cole 2002, ‘Staphylococcus aureus Growth Boundariesto Applied and Environmental Microbiology, vol. 68, no. 12, pp. 6405-6409.

Ryser, ET & Marth, EH (eds) 2007, Listeria, listeriosis and food safety, 3rd edn, CRC Press, US.

Sumner, J, Ross, T, Jenson, I & Pointon, A 2005, 'Staphylococcus aureus Growth Boundaries', Applied & Environmental Microbiology viewed on 18th June 2013 http://www.ncbi.nlm.nih.gov/pmc/articles/PMC123857/

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