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Stenotrophomonas maltophilia is increasingly being isolated from the respiratory tract of individuals with cystic fibrosis, and, because of its multidrug-resistant nature, the selection of suitable treatment regimens can be problematical. Etest methodology was used to facilitate MIC and antimicrobial combination testing on 80 isolates of S. maltophilia cultured from the respiratory tract of Scottish individuals with cystic fibrosis between 2001 and 2010. The overall rate of susceptibility for the 1,410 MIC tests was 23.1%, and resistance was 68.9%. The most active antimicrobials were minocycline, co-trimoxazole, and doxycycline, with 92.4%, 87.3%, and 58.8% of isolates being susceptible, respectively. Of the 517 combinations, 13.2% were synergistic, with the most synergistic being ticarcillin/clavulanate plus aztreonam (91.7% synergistic), ticarcillin/clavulanate plus colistin (40%), and ticarcillin/clavulanate plus levofloxacin (19.4%). Colistin plus tobramycin was the only antagonistic combination (0.2%). By the median susceptible breakpoint index, the most active combinations were minocycline plus co-trimoxazole (median index, 20), minocycline plus piperacillin-tazobactam (median, 20), and co-trimoxazole plus ceftazidime (median, 16.5). The increasing problem of multidrug resistance in organisms recovered from the respiratory tracts of individuals with cystic fibrosis is not going to go away. Current susceptibility testing methods do not address the slow-growing organisms associated with chronic infection, and interpretive standards are based on achievable blood levels of antimicrobials. Addressing these issues specifically for organisms recovered from the respiratory tracts of individuals with cystic fibrosis should lead to better therapeutic outcomes and improved wellbeing of individuals with cystic fibrosis.

The Etest is a useful tool for determining MICs and testing antimicrobial combinations. The SBPI is more discriminatory than the FICI, allowing easy ranking of the combinations, and is likely to have clinical relevance.

12Emergence of Staphylococcus isolates with reduced susceptibility to chlorhexidine is being 13 increasingly reported. We present an update to a previous report showing continuing efficacy 14 of chlorhexidine-based infection control measures against Staphylococcus aureus over six 15 years. We screened qacA/B genes in Staphylococcus isolates collected over another six 16 years in the same intensive therapy unit in Scotland where chlorhexidine baths form an 17 essential component of long-term control of nosocomial infections. Consistent with our 18 previous study we report minimal presence of qacA/B in S. aureus strains from screening 19 samples and bacteraemia patients but the new finding of a high proportion of qacA/B 20 carriage in Staphylococcus epidermidis associated to reduced susceptibility to chlorhexidine. potentially associated with resistance. Qac genes encode for proton-dependent efflux pumps 48 which are known to bind a variety of lipophilic cations including quaternary ammonium 49 compounds such as chlorhexidine. Of the genes known to be associated with biocide 50 resistance, qacA has been more strongly associated with decreased susceptibility to 51 chlorhexidine in Staphylococcus (8, 12). The QacB efflux pump carries amino acid 52 differences compared with QacA including a substitution from Asp to Ala which determines 53 inability to bind divalent cations (13). QacA/B genes are located on mobile genetic elements 54and their co-presence on plasmids with antibiotic resistance genes has pointed to the 55 possibility of cross-resistance between biocides and antibiotics in Staphylococcus (10, 14). 56However, it is yet unclear whether or not the presence of qac genes selects for the presence 57 of antibiotic resistance genes. 58Another medically important Staphylococcus species is Staphylococcus epidermidis. While 59 previously considered to be a non-pathogenic skin commensal, it is now recognized a key 60 opportunistic pathogen associated with nosocomial infections including bacteraemias. selected from patients screened at multiple body sites on admission over the whole period of 78 the study. Forty-one strains were obtained from blood cultures and comprised sixteen strains 79 of S. aureus and twenty-five strains of S. epidermidis. This was a random collection of strains 80 representing 12% and 32% of the total number of bacteraemias related to S. aureus and S. 81 epidermidis, respectively, that occurred over the study time period. For both screening 82 samples and blood cultures one isolate per patient was included in the study. The MRSA 83 infection control measures following screening have already been described (17). Bacterial 84 isolation and characterisation was carried out as previously described (17). 85 2.2DNA extraction: Genomic DNA was extracted from overnight pure cultures of the 86 Staphylococcus isolates using the High Pure PCR template preparation kit (Roche 87 Diagnostics, Germany) following the manufacturer's instructions. Samples were pre-treated 88 with 5µl of Lysozyme (Sigma,...