What Is LA-MRSA?
Worldwide focus has recently been on two types of antimicrobial resistant bacteria derived from livestock, which are mcr-1-positive colistin-resistant Escherichia coli, and livestock-associated methichilin-resistant Staphylococcus aureus, LA-MRSA. MRSA has been isolated from not only humans, but also various animals such as dogs, cats, cattle, swine, and birds, however, detailed analysis was not performed and the origin was not clarified. In 2003, a different type of MRSA was isolated from a four-year-old girl of a Dutch family engaging in pig breeding. Then, it was confirmed that this MRSA can be isolated from livestock, especially from swine, and resides in a high of employees in the livestock industry. LA-MRSA is not defined clearly, however, is considered to be involved in livestock and to be distinguished from genotypes of Hospital (Healthcare)-acquired MRSA；HA-MRSA and Community-acquired MRSA; CA-MRSA. In major genotype, MLST（multi locus sequence typing）is ST398, spa types which were subjected to S. aureus protein A (spa) sequence typing are t001 or t034, and SCCmec types are SCCmec IVa and SCCmec V. Moreover, ST9, Clonal Complex (CC) 398, CC97, and CC9 have been reported. The isolation rate from swine nasal cavities was reported to be over 40% in Europe. Medical personnel were surprised that most of MRSA which was isolated at hospitals in Netherlands and Germany was LA-MRSA, and high MRSA isolation rates in these hospitals were involved in people in the livestock industry. On the other hand, it was reported that LA-MRSA was isolated from cattle and milk in bulk tank, however, the effect on human health is not clear.
How about the isolation state in Japan? We are worried about the spread of LA-MRSA in Europe, and reported the result of a survey about the isolation state from swine nasal cavities at 23 farms in eastern Japan in 2010. The results showed, ST221/t-002 which is different from the prevalent clone in Europe. Then, we also surveyed 100 samples of swabs from nasal cavities of swine which were shipped from 21 farms to a slaughterhouse in Kanto area in 2015. In the result, 5 strains of ST97/spa t1236/SCCmec V and 3 strains of ST5/spa t002/atypical SCCmec type were isolated from 3 farms. Thus, there are no reports of the isolation of ST398 from Japanese swine at this point, however, it will be a matter of time that LA-MRSA is introduced in Japan from Europe. Therefore, we need to monitor the trend of LA-MRSA under the monitoring system of antimicrobial resistance based on One Health. Once the increasing trend is confirmed, risk management measures are needed to prevent the spread in humans. Considering these states, the Ministry of Agriculture, Forestry and Fisheries decided to add LA-MRSA to the Japanese Veterinary Antimicrobial Resistance Monitoring System (JVARM) as an objective bacteria. Infiltration states throughout Japan will be clarified from now on. Although MRSA isolated from the strains of humans is needed molecular biological testing, only genotype is used for discrimination, thus, the development of novel clinical examinations for differential diagnosis is immediately needed.