[Clindamycin-colitis].

OBJECTIVES: To demonstrate the in vitro ability of erythromycin to induce clindamycin in erythromycin resistant and clindamycin susceptible clinical isolates of Staphylococci. METHODS: We studied 291 clinical isolates of erythromycin-resistant (ER-R) clindamycin-susceptible Staphylococci (CL-S) at Almana General Hospitals, Al-Khobar, Dammam, Saudi Arabia during the period from June 2004 to May 2005. The isolates included 70 Staphylococcus aureus, 81 Methicillin Resistant Staphylococcus aureus (MRSA) and 140 coagulase-negative Staphylococci (CNS). We examined these isolates for inducible clindamycin resistance (ICR) by erythromycin induction test using double disc susceptibility test (D-test). Strains producing ICR show flattening of the clindamycin disc zone adjacent to the erythromycin disc. RESULTS: Of the 291 ER Staphylococci studied, 82 (28%) demonstrated constitutive clindamycin resistance [2 (2.9%) S. aureus, 43 (53%) MRSA and 37 (26%) CNS]. Inducible clindamycin resistance was demonstrated in 113 (38.8%) of Staphylococcal isolates, including 84 (28.9%) from adult patients and 29 (10%) from pediatric patients. The incidence of ICR was 49 (70%) for S. aureus, 35 (43%) for MRSA and 29 (20.7)% for CNS. Overall, 96 (33%) of the isolates remained susceptible to clindamycin and were negative for clindamycin induction [19 (27%) S. aureus, 3 (3.7%) MRSA and 74 (52.8%) CNS]. CONCLUSION: We conclude that a significant number of ER-R CL-S staphylococcal isolates studied were positive for ICR. These isolates should be reported as clindamycin resistant. Given the high rate of inducible resistance to clindamycin in the staphylococcal isolates, we recommend that microbiology laboratories perform erythromycin induction test on all ER-R CL-S staphylococcal isolates prior to reporting clindamycin susceptibility.

Clindamycin↗

PubMed2004

Isolation of antibiotic resistance mutations in the rRNA by using an in vitro selection system.

Genetic, biochemical, and structural data support an essential role for the ribosomal RNA in all steps of the translation process. Although in vivo genetic selection techniques have been used to identify mutations in the rRNAs that result in various miscoding phenotypes and resistance to known ribosome-targeted antibiotics, these are limited because the resulting mutant ribosomes must be only marginally disabled if they are able to support growth of the cell. Furthermore, in vivo, it is not possible to control the environment in precise ways that might allow for the isolation of certain types of rRNA variants. To overcome these limitations, we have developed an in vitro selection system for the isolation of functionally competent ribosomal particles from populations containing variant rRNAs. Here, we describe this system and present an example of its application to the selection of antibiotic resistance mutations. From a pool of 4,096 23S rRNA variants, a double mutant (A2058U/A2062G) was isolated after iteration of the selection process. This mutant was highly resistant to clindamycin in in vitro translation reactions and yet was not viable in Escherichia coli. These data establish that this system has the potential to identify mutations in the rRNA not readily accessed by comparable in vivo systems, thus allowing for more exhaustive ribosomal genetic screens.

Clindamycin↗