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A methicillin-resistant Staphylococcus aureus (MRSA) referred to as livestock-associated (LA-MRSA) has recently emerged in farm animals, particularly in pigs. Strains of this MRSA variant from Europe and North America mostly belong to clonal complex (CC) 398. Generally LA-MRSA cause asymptomatic colonization among pigs, but also in veal calves, broiler chickens, turkeys, and horses. People in contact with livestock animals are at high risk of asymptomatic colonization or infection with these bacteria. In previous years, the impact of LA-MRSA on human health was considered small. However, LA-MRSA has become more prevalent among people without direct livestock contact, especially in areas with a high density of pig production. As a result of horizontal gene transfer S. aureus CC398 strains are constantly evolving. The adaptive power of S. aureus to new hosts and acquisition of resistance to antibiotics may cause the emergence of new, more virulent clones. LA-MRSA has evolved from human-adapted methicillin-susceptible S. aureus CC398, which was proved by comparative genome analysis. The adaptation to livestock was associated with several genetic changes. The most worrying aspect of MRSA CC398 seems to be its ability to spread to humans. For this reason, continuous surveillance of further genetic changes is recommended.
Zbadano częstość występowania szczepów opornych na kotrimoksazol wśród Staphylococcus aureus i koagulazo-ujemnych gronkowców opornych na meticylinę izolowanych z próbek materiału klinicznego w latach 2001-2003 w Szpitalu Uniwersyteckim im. A. Jurasza Collegium Medicum w Bydgoszczy UMK w Toruniu. W kolejnych latach szczepy oporne stanowiły: wśród szczepów MRCNS 52,8%, 51,4%, 63,9%, natomiast wśród szczepów MRSA 23,4%, 19,5%, 16,8%.
The first meticillin-resistant strains of Staphylococcus aureus (MRSA) emerged in the early 1960s after the introduction β-lactamases, semi-synthetic penicillins, such as methicillin. For nearly 30 years the incidence was confined to the hospital environment (hospital-associated MRSA, HA-MRSA), which have a selective advantage over strains of S. aureus sensitive to methicillin (meticillin-susceptible Staphylococcus aureus, MSSA). CA-MRSA strains, as well as hospital strains, are capable of inducing a variety of infections; they are frequently responsible for the initial infection of the skin and soft tissues as well as necrotizing pneumonia. The factors that predispose the occurrence of MRSA are: diabetes mellitus, intravenous drug abuse, chronic hemodialysis, the colonization of the skin lesions, specific immunotherapy, neutropenia, increased IgE level, hemodialysis, surgical wound infections, stays in hospitals and nursing homes. The first reports of MRSA occurring in cattle took place in Belgium in 1972. MRSA strains have also been identified in horses, pigs, dogs, poultry and turtles. The common coexistence of VRE and MRSA can lead to the formation of MDR (multidrug resistant) strains of S. aureus. The emergence of multidrug-resistant strains is a major problem for MRSA eradication, and therefore it is necessary to discover antibacterial substances reducing the activity of the pathogens.
The objectives of this review were to characterize published data on the prevalence and epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) infection and colonization in the following animals: cats, dogs, horses and food animals, especially swine. The mentioned reservoir was evaluated in relation to the possibility people in contact with animals becoming infected. This was enabled by using such molecular typing methods as: pulsed field gel electrophoresis (PFGE), multilocus sequence typing (MLST), SCCmec, spa typing and multiplex PCR. Basing on these tests for the species Staphylococcus aureus and particularly MRSA strains, sequence types and clonal lineages or genetic clones were differentiated. This enabled the identification of strains primarily originating from animals and humans infected from this source, or vice versa. In many publications the clonal complex ST398 of MRSA strains has been found to be an important reservoir in pigs, horses, poultry, dogs and cats. This MRSA clone has also been shown to be capable of infecting humans, therefore it is called zoonotic. Since the pig reservoir of the mentioned MRSA clone seems to be of particular importance for public health, the European Food Safety Authority of the European Union has decided to start a survey in 2008 on the prevalence of methicillin resistant Staphylococcus aureus in breeding pigs with the participation of EU member countries, including Poland. It is anticipated that all participants will use the same methodology.
Due to the widespread prevalence of methicillin-resistant Staphylococcus aureus (MRSA) it has been included in the group of microorganisms causing severe human and animal infections. These bacteria occur in cattle, sheep, pigs, horses, dogs, cats, rabbits and poultry. The main diseases that are caused by S. aureus are dermatosis, mastitis, arthritis and urinary tract infections. People may develop more serious complications; e.g. pneumonia, endocarditis, bacteraemia. Moreover, these microorganisms are frequently connected with postoperative wound infections. The first MRSA strains emerged in the early 1960s after the acquisition of the methicillin resistance gene mecA, which is carried by the staphylococcal chromosomal cassette mec (SCCmec). The mecA gene encodes for a penicillin-binding protein (PBP2a) which has a low affinity to β-lactam antibiotics. Epidemiological data suggests that MRSA isolates from various animal species are genetically very similar or even indistinguishable from human isolates. The transfer of MRSA strains can occur between animals and humans as well as vice versa. The antibiotics that are effective for the treatment of infections caused by MRSA are still glycopeptides: vancomycin and teicoplanin, mupirocin and linezolid. However, there are already strains resistant to all known antibiotic groups. MRSA may be a source of antibiotic resistance genes and contribute to the spread of drug-resistance genetic elements to other disease-causing microorganisms.
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