High frequency of macrolide resistance mechanisms in clinical isolates of Corynebacterium species.

The genus Corynebacterium includes a high number of species that are usually isolated from human skin as saprophytes. However, these microorganisms have also been reported as infectious agents in a broad group of patients and have showed broad-spectrum resistance. We studied the susceptibility profiles against macrolides, clindamycin, and streptogramins of 254 clinical strains belonging to the species Corynebacterium urealyticum (120), Corynebacterium amycolatum (66), Corynebacterium jeikeium (17), Corynebacterium striatum (20), Corynebacterium coyleae (12), Corynebacterium aurimucosum (11), and Corynebacterium afermentans subsp. afermentans (8). The MLS(B) phenotype was detected in 186 strains and was associated with the presence of methylase enzymes codified by the erm(X) gene in 171 strains. The erm(B) gene was only detected in two C. urealyticum strains. Fourteen strains showed macrolide resistance, but they did not carry erm genes. mef genes were not detected despite eight C. amycolatum strains showed the M phenotype. Also, the presence of hydrolytic enzymes codified by ere(B) was evaluated, but all results were negative. Resistance to macrolide in Corynebacterium sp. is mainly due to the presence of erm(X) methylase, although other resistance mechanisms could be involved.

Influence of surface porosity and pH on bacterial adherence to hydroxyapatite and biphasic calcium phosphate bioceramics.

Hydroxyapatite (HA) and biphasic calcium phosphate (BCP) ceramic materials are widely employed as bone substitutes due to their porous and osteoconductive structure. Their porosity and the lowering of surrounding pH as a result of surgical trauma may, however, predispose these materials to bacterial infections. For this reason, the influence of porosity and pH on the adherence of common Gram-positive bacteria to the surfaces of these materials requires investigation. Mercury intrusion porosimetry measurements revealed that the pore size distribution of both bioceramics had, on a logarithmic scale, a sinusoidal frequency distribution ranging from 50 to 300 nm, with a mean pore diameter of 200 nm. Moreover, total porosity was 20 % for HA and 50 % for BCP. Adherence of Staphylococcus aureus and Staphylococcus epidermidis was studied at a physiological pH of 7.4 and at a pH simulating bone infection of 6.8. Moreover, the effect of pH on the zeta potential of HA, BCP and of both staphylococci was evaluated. Results showed that when pH decreased from 7.4 to 6.8, the adherence of both staphylococci to HA and BCP surfaces decreased significantly, although at the same time the negative zeta-potential values of the ceramic surfaces and both bacteria diminished. At both pH values, the number of S. aureus adhered to the HA surface appeared to be lower than that for BCP. A decrease in pH to 6.8 reduced the adherence of both bacterial species (mean 57 %). This study provides evidence that HA and BCP ceramics do not have pores sufficiently large to allow the internalization of staphylococci. Their anti-adherent properties seemed to improve when pH value decreased, suggesting that HA and BCP bioceramics are not compromised upon orthopaedic use.

Biofilm development by potentially pathogenic non-pigmented rapidly growing mycobacteria.

BACKGROUND: A study to evaluate the biofilm-development ability in three different media (Middlebrook 7H9, sterile tap water and PBS-5% glucose) was performed with 19 collection strains from 15 different species on non-pigmented rapidly growing mycobacteria (NPRGM). A microtiter plate assay was developed to evaluate the percentage of covered surface of the microtiter plate wells in different days from day 1 to day 69. RESULTS: All strains were able to develop biofilm in all the tested media. Middlebrook 7H9 showed the fastest growth, followed by sterile tap water and PBS-5% glucose. A sigmoid growth curve was detected in all the strains both in Middlebrook 7H9 and in sterile tap water. A difference could be detected for Mycobacterium abscessus in tap water, where it showed faster growth than all the other strains. CONCLUSION: Biofilm development seems to be a property of all the species of NPRGM and it depends on the nutrients present in the medium. The microtiter plate assay described here is a useful tool to evaluate differences in biofilm development among the different species of rapidly growing mycobacteria.