Rate Of Inducible Resistance Research Articles

P122 A high rate of inducible resistance against clindamycin in Staphylococcus aureus isolates in children: A multicenter study in Japan

P122 A high rate of inducible resistance against clindamycin in Staphylococcus aureus isolates in children: A multicenter study in Japan

Phenotypical examination of the macrolide-lincosamide-streptogramin B resistance in Staphylococcus isolates

The aim of the present study was to evaluate the phenotypic characteristics of the macrolide-lincosamide-streptogramin B (MLSB) resistance in Staphylococcus aureus and coagulase-negative staphylococci (CNS) strains isolated from various clinical samples in our hospital. The study was conducted on 516 Staphylococcus isolates isolated from various clinical samples in Microbiology Laboratory of Diyarbakir State Hospital between January, 2009 and December, 2009. After the identification of microorganisms via conventional methods and the evaluation of their methicillin resistance profile, disk approximation test was performed using erythromycin (15 μg) and clindamycin (2 μg) disks in order to determine MLSB resistance phenotypes. Of 516 Staphylococcusisolates, 208 were determined to be S. aureus and 308 were CNS. The MLSB resistance of isolates was 56.2%, whereas the resistance due to the efflux pump was determined to be 3.5%. The MLSB resistance phenotype was determined in 38% of S. aureus strains and 68.5% of CNS strains. The presence of MLSB resistance was determined to be higher in methicillin-resistant group (74.7%) compared to the methicillin-susceptible group (23.9%). While constitutive MLSB resistance (cMLSB) and inducible MLSB resistance (iMLSB) were determined in 48.9 and 19.1% of methicillin-resistant S. aureus strains, respectively, these rates were 2.6 and 10.5% for methicillin-susceptible strains, respectively. The rate of constitutive resistance was determined to be 41.5% in methicillin resistant CNS, whereas the rate of inducible resistance was determined to be 35.9%. In methicillin-susceptible CNS group, cMLSB and iMLSB resistances were determined to be 17.6 and 23%, respectively. The cMLSB phenotype was more common among methicillin-resistant S. aureus and CNS group, whereas iMLSB phenotype was more common among methicillin-susceptible S. aureus strains. In conclusion, we suggest that the determination and reporting of the presence of inducible resistance is of great importance regarding the success of therapy; therefore, it would be beneficial to use D test in routine antibiogram studies. Key words: Staphylococcus aureus, coagulase-negative staphylococci, macrolide-lincosamide-streptogramin B

Inducible Clindamycin Resistance and Molecular Epidemiologic Trends of Pediatric Community-Acquired Methicillin-Resistant Staphylococcus aureus in Dallas, Texas

Community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) infection occurs commonly in children. Clindamycin resistance may be inducible or constitutive, and the rates of inducible resistance in CA-MRSA that could produce clindamycin treatment failures vary worldwide. The double-disk test was performed in 197 erythromycin-resistant and clindamycin-susceptible CA-MRSA strains from children in Dallas, Texas, from 1999 to 2002 to determine inducible clindamycin resistance. Resistance mechanisms were studied by PCR; epidemiologic trends were studied by pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST). Inducible resistance was demonstrated in 28 (93%+/-6%) of 30 tested isolates in 1999, 21 (64%, +/-11%) of 33 in 2000, 12 (23%+/-7%) of 52 in 2001, and 6 (7%+/-3%) of 82 in 2002. All noninducible strains had the msr(A) gene. Among inducible resistant strains, 31 had erm(B), 24 had erm(C), and 12 had erm(A) genes. Two distinct pulsed types were the most prevalent; one of them was the most common pulsed type in 1999, whereas in 2002 a different pulsed type was prevalent. MLST analyses determined that ST-8 was the most common type, with 76%+/-5% found in 2002. All but one of these clindamycin-susceptible, erythromycin-resistant ST-8 strains showed no induction of clindamycin resistance. We conclude that, among erythromycin-resistant, clindamycin-susceptible CA-MRSA strains isolated from children in Dallas, inducible methylase resistance became less common from 1999 to 2002 (P<0.001). The phenotype of strains was associated with their sequence type. Our results demonstrate a clonal shift in CA-MRSA in Dallas children from 1999 to 2002.