Induction of clindamycin resistance in erythromycin-resistant, clindamycin susceptible and methicillin-resistant clinical Staphylococcal isolates

To demonstrate the in vitro ability of erythromycin to induce clindamycin in erythromycin resistant and clindamycin susceptible clinical isolates of Staphylococci. 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. 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]. 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

Prevalence and antimicrobial susceptibility of exended spectrum beta-lactamase-producing Escherichia coli and Klebsiella Pneumoniae in a general hospital

The prevalence of extended-spectrum beta-lactamases [ESBLs] varies between countries and institutions. We studied the prevalence of ESBL among clinical isolates of Escherichia coli and Klebsiella pneumoniae and analyzed patterns of susceptibilities to different antimicrobial agents in a general hospital in Saudi Arabia over a 15-month period. A total of 2455 clinical isolates of E. coli and K. pneumoniae were tested for ESBL production by double-disk diffusion. The minimum inhibitory concentration to imipenem, meropenem, piperacillin-tazobactam, cefepime, ciprofloxacin, gentamicin and amikacin were determined by the agar dilution method. Of the 2455 isolates of E. coli and K. pneumoniae tested, 268 [11%] produced ESBL. The ESBL phenotype was detected in 10.3% of 1674 E. coli isolates and 12.2% of 781 K. pneumoniae isolates. The majority of these isolates were from urine [57.5%] and wounds [17%]. Only 7% of the blood culture isolates were ESBL-producing. Overall, carbapenems [imipenem and meropenem] had good activity against the ESBL-producing isolates tested [over 92% of isolates were susceptible]. There was no difference in the activity of imipenem and meropenem against the ESBL-producing E. coli or K. pneumoniae. Over 66% of the isolates were susceptible to piperacillin-tazobactam. Susceptibilities of the isolates to amikacin varied, ranging from 72.8% for E. coli to 62% for K. pneumoniae. Gentamicin, ciprofloxacin and cefepime were active against 58.6%, 55% and 22.8% of the isolates, respectively. Our findings demonstrate the increasing incidence of infection with ESBL-producing bacteria, and the high rates of antimicrobial resistance encountered among them. Clinicians should be familiar with the clinical importance of these enzymes and potential strategies for dealing with them