Introduction

Mycoplasma hyopneumoniae is a species of bacteria

Bacteria

Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...

 known to cause the disease Porcine Enzootic Pneumonia, a highly contagious and chronic disease affecting pigs (Whittlestone, 1979). As with other mollicutes

Mollicutes

The Mollicutes are a class of bacteria distinguished by the absence of a cell wall. The word "Mollicutes" is derived from the Latin mollis , and cutis . They are parasites of various animals and plants, living on or in the host's cells. Individuals are very small, typically only 0.2–0.3 μm in size...

, M. hyopneumoniae is gram positive, small in size (400 - 1200 nm), has a small genome

Genome

In modern molecular biology and genetics, the genome is the entirety of an organism's hereditary information. It is encoded either in DNA or, for many types of virus, in RNA. The genome includes both the genes and the non-coding sequences of the DNA/RNA....

 (893 - 920 kilo-base pairs (kb)) and lacks a cell wall

Cell wall

The cell wall is the tough, usually flexible but sometimes fairly rigid layer that surrounds some types of cells. It is located outside the cell membrane and provides these cells with structural support and protection, and also acts as a filtering mechanism. A major function of the cell wall is to...

 (Tajima et al., 1982). It is considered to be difficult to grow in laboratories due to its complex nutritional requirements and the high chances of contamination associated with mycoplasma culture. To successfully grow the bacterium, an environment of 5-10% carbon dioxide is required, and the medium should demonstrate an acid colour shift.

This bacterium is a concern in the livestock industry as it causes a significant reduction in the growing weight of pigs. Losses in the U.S.A. have been previously estimated at 200 million to 1 billion dollars per annum (Clark et al., 1991). Porcine enzootic pneumonia is endemic worldwide and M. hyopneumoniae is present in almost every pig herd (Minion, 2002). Treatment of this disease is limited to antibiotics, which are currently ineffective as they do not completely remove the infection. Vaccines have been found to reduce the severity of the disease but do not prevent the disease from occurring in infected pigs (Haesebrouck, et al., 2004).

Pathogenesis

M. hyopneumoniae has been found to attach to the cilia of epithelial cells in the lungs of swine. They cause cilia to stop beating (ciliostasis), clumping and loss of cilia, eventually leading to epithelial cell death; which is the source of the lesions found in the lungs of pigs with porcine enzootic pneumonia. This damage impedes normal ciliary clearance and often secondary infections develop. On a cellular level, mononuclear infiltration of peribronchiolar and perivascular areas occurs.

Sadly, the immune response caused by the presence of M. hyopneumoniae in pigs is slow and ineffective (Minion, 2002); it is also believed to cause much of the damage that is seen in pigs with the disease. This mycoplasma

Mycoplasma

Mycoplasma refers to a genus of bacteria that lack a cell wall. Without a cell wall, they are unaffected by many common antibiotics such as penicillin or other beta-lactam antibiotics that target cell wall synthesis. They can be parasitic or saprotrophic. Several species are pathogenic in humans,...

 is not known to produce any specifically harmful toxin

Toxin

A toxin is a poisonous substance produced within living cells or organisms; man-made substances created by artificial processes are thus excluded...

 like many other disease-causing bacteria

Bacteria

Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...

, but some mildly toxic by-products have been observed (Geary et al., 1985).

Conclusions

Mycoplasma hyopneumoniae has been a topic of interest in the scientific community due to the economic impact of porcine enzootic pneumonia. Three separate strains

Strain (biology)

In biology, a strain is a low-level taxonomic rank used in three related ways.-Microbiology and virology:A strain is a genetic variant or subtype of a micro-organism . For example, a "flu strain" is a certain biological form of the influenza or "flu" virus...

 (232, J & 7448) of this mycoplasma

Mycoplasma

Mycoplasma refers to a genus of bacteria that lack a cell wall. Without a cell wall, they are unaffected by many common antibiotics such as penicillin or other beta-lactam antibiotics that target cell wall synthesis. They can be parasitic or saprotrophic. Several species are pathogenic in humans,...

 have had their genomes sequenced, making it the most sequenced mycoplasma

Mycoplasma

Mycoplasma refers to a genus of bacteria that lack a cell wall. Without a cell wall, they are unaffected by many common antibiotics such as penicillin or other beta-lactam antibiotics that target cell wall synthesis. They can be parasitic or saprotrophic. Several species are pathogenic in humans,...

 (Minion et al., 2004; Vasconcelos et al., 2005). Research has been mainly focused on identifying adhesin

Adhesin

Adhesins are cell-surface components or appendages of bacteria that facilitate bacterial adhesion or adherence to other cells or to inanimate surfaces. Adhesins are a type of virulence factor....

s with a final goal of developing an effective vaccine

Vaccine

A vaccine is a biological preparation that improves immunity to a particular disease. A vaccine typically contains an agent that resembles a disease-causing microorganism, and is often made from weakened or killed forms of the microbe or its toxins...

 that prevents M. hyopneumoniae from attaching to lung cilia.