Intervention points for community- acquired methicillin- resistant Staphylococcus aureus colonization and load in healthy population of lesser Himalayan Belt, South Asia, India

OBJECTIVES： To trace the critical practicing, clinical and epidemiological risk factors in bacterial load and points of intervention in spread of community-acquired methicillin resistant Staphylococcus aureus （CA-MRSA） in healthy community. STUDY DESIGN： 2872 individuals with no prominent clinical features were enrolled and administered a pre-tested questionnaire prepared on the basis of outcome of a prior pilot study in same region. Swab samples from skin, throat and nasal nares were tested for MRSA and molecular identification was done to track the strains moving from hospital to community. METHODS： Swab samples from skin, throat and nasal nares were tested for MRSA culture followed by molecular characterization of isolates and antimicrobial resistance pattern. Bacterial load was estimated to better understand the burden in different categories. Statistical analysis was done using SPSS 16.0 version. RESULTS： History of prior infection （OR 3.9, 95% CI 1.363 - 5.793）, habit of self remedy （OR 3.2, 95% CI 0.991 1.473） and incomplete treatment （OR 0.26, 95% CI 0.08 - 0.80） （P 〈 0.05 for each） were the predominant factors that contributed to spread of CA-MRSA. Increased drug resistance in CA-MRSA was observed for 4 different clones： SCCmec^＋ IVa/PVL^＋, SCCmec^＋ IVa/PVL^- and SCCmec^＋ IVc/PVL^＋, SCCmec^＋ IVc/PVL . Bacterial load was found significantly high in below poverty line dwellers and drug abusers （P 〈 0.05）. CONCLUSION： We identified habit of self remedy, drug abusing and incomplete treatment as practicing risk factors where interventions can be made to manage the dissemination of CA-MRSA in rural population.

Community and hospital acquired methicillin resistant Staphylococcus aureus efficiently retain the Van A determinant

Dissemination of vancomycin resistance from hospital to community strains is a serious threat to public health. Our study aimed to provide evidence for transmission of Van A type resistance from the hospital to the community. Wild-type community and hospital associated methicillin resistant Staphylococcus aureus strains were studied in vitro and in a model that mimicked a natural environment to ascertain their ability to acquire and maintain the vancomycin resistance determinant （Van A gene） from vancomycin resistant Enterococcus faecalis. Fitness was assessed and the cost of Van A acquisition and retention was estimated. In vitro mating experiments were carried out using a filter mating technique and a model of a natural water body environment. Transfer of resistance was carried out in two different conditions： restricted and favorable. Transconjugants were confirmed by E test and PCR using specific primer sets. Growth kinetics and fitness measurements were done by spectrometric analysis. Using the in vitro filter mating technique, high transfer frequencies that ranged from 0.7 × 10^-3（0.0006） to 3.1 ×10^-4（0.00011） were recorded, with the highest transfer frequencies for CA MRSA （thermosensitively homogenous） （0.7 × 10^- 3）, and 1.2 × 10^-4 to 2.4 × 10^-4 in the model. HA MRSA （homogenous） showed a greater capacity （3.6 ×10^-4） to receive the Van A gene, while CA MRSA showed a reduced ability to maintain the gene after serial subcultures. CA and HA thermosensitively heterogeneous MRSA transconjugants exhibited higher growth rates. The present study provides evidence for the enhanced ability of CA and HA MRSA clones to acquire and maintain Van A type resistance.