In vitro biofilm formation by methicillin susceptible and resistant Staphylococcus aureus strains isolated from cystic fibrosis patients

Staphylococcus aureus is one of the most common pathogens isolated from respiratory tracts of Cystic Fibrosis patients (CF). The infection by this pathogen starts in early infancy, often preceding chronic infections by Pseudomonas aeruginosa. The infection and colonization by methicillin-resistant Staphylococcus aureus (MRSA) are, by then, events very frequent among CF patients and this bacterial isolation leads to complications in therapeutic management because of the limited treatment options. Strains of Staphylococcus aureus are able to produce biofilms on natural or synthetic surfaces. Biofilms are sophisticated communities of matrix-encased bacteria and infections by biofilm-producing bacteria are particularly problematic because sessile bacteria can often withstand host immune responses and are generally much more tolerant to antibiotics. The first aim of this work is to evaluate the ability of MRSA strains isolated from respiratory secretions of CF patients to develop biofilms in comparison with methicillin-sensitive Staphylococcus aureus (MSSA) strains obtained from respiratory secretions of CF patients.Therefore, our second aim is to evaluate the environmental influence on this ability. To evaluate the development of biofilm on solid matrix and the possible environmental influence,we applied the method described by Christensen et al. We found that a significantly higher number of MRSA strains were biofilm positive compared with MSSA strains (p<0.05).The presence of glucose did not influence the ability to form biofilm in our MRSA strains (p=0.165). MSSA strains are not strong biofilm-producers, but, when grown in TSB added with 0.25% glucose, the number of biofilm-forming strains increases, as expected. These data suggest a possible association between methicillin-resistance and biofilm formation

Serum In Vivo and In Vitro Activity of Single Dose of Ertapenem in Surgical Obese Patients for Prevention of SSIs

Background Despite progress made in the control of postoperative infections, the incidence of surgical site infections (SSIs) is still high. An improper perioperative antibiotic use can expose patients to the risk of resistant microorganisms, and, in surgical obese patients, the drug dosage and infusion time are critical points. The aim of our study was to evaluate the effectiveness of ertapenem in the prophylaxis of SSIs in obese patients undergoing general or bariatric surgery. Methods A total of 63 obese patients, candidates for several surgical interventions, were enrolled and divided into two groups. Patients received antibiotic prophylaxis before surgery: the case group received venous infusion of ertapenem; the control group received standard prophylaxis. Serum samples were tested for antimicrobial activity against Gram-positive and Gram-negative bacteria. Results After single-dose ertapenem in obese patients, we registered in vitro activity of sera against the growth of nonextended beta lactamase (ESBL)-producing Escherichia coli, Proteus mirabilis, Citrobacter freundii, Enterobacter cloacae, and non-ESBL-producing Klebsiella pneumoniae. Moreover, methicillin-sensitive Staphylococcus aureus and Streptococcus viridans were also inhibited. We found in vivo efficacy according to clinical monitoring: at the weekly and monthly follow-ups, one patient in the case group and six patients in the control group presented superficial incisional SSIs. Conclusions These preliminary results are suggestive of the efficacy of ertapenem in perioperative prophylaxis of SSIs in obese patients; however, they need to be confirmed by further investigations and more defined trials