Ciprofloxacin-resistant methicillin-resistant Staphylococcus aureus in an acute-care hospital

Abstract

Use of ciprofloxacin as an alternative to vancomycin for treatment of methicillin-resistant Staphylococcus aureus infection has been paralleled by the emergence of resistant strains. This phenomenon has also been noticed in our hospital. To confirm our observation, methicillin and ciprofloxacin susceptibilities were tested by disk diffusion and broth microdilution techniques. We studied 83 methicillin-resistant Staphylococcus aureus isolates obtained from various sources over a 4-month period. Ciprofloxacin resistance (MIC, >2 ,Ig/ml) was detected in 69 isolates (83%). Prior use of ciprofloxacin was reported for 24 of 69 patients with ciprofloxacinresistant strains and 0 of 14 patients with ciprofloxacin-susceptible strains. The day of detection during the hospital stay and the location of the source patient were not significantly different between resistant and susceptible strains. Bacteriophage typing showed a higher occurrence of nontypeable strains among ciprofloxacin-resistant strains (54%). Review of our microbiology register showed a progressive increase in the rate of resistance to ciprofloxacin during the first year of use, with initial rates being about 10% and recent rates being higher than 80%. On the other hand, methicillin-susceptible S. aureus remained uniformly susceptible to ciprofloxacin (98.4%). We conclude that prior use of ciprofloxacin is an important factor for the selection of ciprofloxacin-resistant strains and that ciprofloxacin has limited usefulness against methicillin-resistant S. aureus.

Antibiotic Resistance in the Environment, with Particular Reference to MRSA

“…The antibiotic resistance patterns of pig MRSA, other than to methicillin, reflect the antibiotics used in veterinary medicine: tetracycline resistance is very common, whereas ciprofloxacin resistance has been found to be completely absent (de Neeling et al, 2007). This is very different to the situation in nosocomial MRSA strains, in which over 80% of MRSAs may be resistant to ciprofloxacin (Marangon et al, 2004;Raviglione et al, 1990), perhaps suggesting that ST398 is circulating in pigs and only infecting humans occasionally, or that pigs are an emerging reservoir of MRSA.…”

Comparative prophylactic efficacies of ciprofloxacin, ofloxacin, cefazolin, and vancomycin in experimental model of staphylococcal wound infection

“…A concern about the clinical use of quinolones has been the rapid increase in resistance to ciprofloxacin in S. aureus, in particular MRSA, when ciprofloxacin has been introduced into widespread use within a medical center (9,36). In some institutions, most strains of MRSA are now quinolone resistant.…”

“…For example, similar reductions in bacterial counts within valvular vegetations occur following treatment of experimental endocarditis caused by methicillin-susceptible S. aureus or MRSA with ofloxacin and with vancomycin (20). On the other hand, the rapid emergence of quinolone-resistant strains associated with quinolone use in some institutions raises concerns about the role of these agents in staphylococcal infection (8,36 In vivo procedures. Details of this small-inoculum prophylaxis model have been described previously (22,25,26).…”

In vitro and in vivo evaluations of A-80556, a new fluoroquinolone

“…The initial concern that resistance in the gram-negative genera would emerge as a result of the introduction of the fluoroquinolones (for urinary tract infections) has not been borne out with the extensive use of this class for gram-negative infections (7). However, the increased use of the fluoroquinolones has apparently led to a dramatic increase in quinolone resistance among the staphylococci, particularly methicillinresistant S. aureus and Staphylococcus epidermidis (7,14). It has been suggested that this rise in resistance is due to the moderate activity of these drugs against staphylococci coupled with the low levels attainable in serum (4,7).…”

“…A. (4,7,14), have pointed to the need to develop compounds with improved activity against S. pneumoniae and S. aureus. The insufficient activity of commercially available fluoroquinolones against anaerobes has precluded their use in infections caused by these organisms.…”