Failure of Clindamycin Treatment of Methicillin-Resistant Staphylococcus aureus Expressing Inducible Clindamycin Resistance In Vitro

Abstract

We report a case of a surgical site infection caused by clindamycin-susceptible, erythromycin-resistant methicillin-resistant Staphylococcus aureus (MRSA) that did not respond to treatment with clindamycin. The MRSA isolate obtained after treatment was resistant to clindamycin but was found to be identical by pulsed-field gel electrophoresis to the clindamycin-susceptible isolate obtained before treatment. A post hoc erythromycin-induction test (D test) confirmed the presence of in vitro inducible macrolide-lincosamide-streptogramin B resistance (iMLS) in the pretreatment isolate. Erythromycin induction testing confirmed in vitro iMLS in 90 (56%) of 161 erythromycin-resistant, clindamycin-susceptible clinical S. aureus isolates overall and in a significantly higher proportion (78%) of methicillin-susceptible S. aureus isolates from pediatric patients. Our clinical laboratory currently tests all S. aureus isolates for iMLS before reporting clindamycin susceptibility.

Prevalence and Anti-Microbial Susceptibility of Methicillin Resistant <i>Staphylococcus aureus</i> at Moi Teaching and Referral Hospital Eldoret

“…There was significant clindamycin resistance as well as shown by the positive D-test at 74%. This inducible resistance has also been shown by other studies [23]- [25].…”

A report on infection dynamics of inducible clindamycin resistance of Staphylococcus aureus isolated from a teaching hospital in India

“…Among 244 clinical isolates of staphylococci reported from Karnataka, India, 13.1% strains had inducible clindamycin resistance with the MLSB phenotype; among them, 10 isolates were MRSA (38.4% of the total MRSA), 16 were MSSA (12.9% of the total MSSA) and 6 were "coagulasenegative staphylococci" or CONS, i.e., 6.3% of the total isolated CONS [17] . In another laboratory from Karnataka, 10% isolates had inducible clindamycin resistance, 9% had constitutive resistance and 8% had MS phenotype.…”

“…In the presence of erythromycin, the strain with the MLSB gene induces resistance to clindamycin in the "Er-r, Cd-s" strain, conferring clindamycin resistance to the original Cd-s strain, eventually causing the wellknown flattening of the clindamycin inhibition zone towards the erythromycin disc, so that the shape "D" is seen in the clindamycin zone or "D-test positivity" (Figure 1). Since, failure in the therapy with clindamycin used against S. aureus had been frequently met [4,6] , the D-test procedure is often recommended for checking the efficacy of the empiric use of clindamycin against isolated staphylococci in most hospitals to avoid the unbeknown pervasive error in the therapy, due to MLSB resistance. Admittedly, it is the standard procedure, being simple for checking the inducible erm mediated MLSB resistance in MRSA and other staphylococci.…”

Detection and prevalence of inducible clindamycin resistance in staphylococci

“…CL is a good alternative for the treatment of both meticillin-resistant and -susceptible staphylococcal infections (Fiebelkorn et al, 2003). CL-R can develop in staphylococcal isolates with the inducible phenotype, and spontaneous constitutively resistant mutants have been selected from such isolates both in vitro and in vivo during CL therapy (Drinkovic et al, 2001;Panagea et al, 1999;Siberry et al, 2003 (Rao, 2000).…”