Impact of Modified Nonmeningeal Streptococcus pneumoniae Interpretive Criteria (NCCLS M100-S12) on the Susceptibility Patterns of Five Parenteral Cephalosporins: Report from the SENTRY Antimicrobial Surveillance Program (1997 to 2001)

Abstract

The revised interpretive criteria for Streptococcus pneumoniae recently published in the NCCLS M100-S12 informational supplement provide two sets of breakpoints for some cephalosporins: one set for meningeal infection isolates and a new set for nonmeningeal infection isolates. The net effect of these changes was to increase the reported rates of susceptibility of S. pneumoniae to the more active parenteral cephalosporins, such as cefepime, cefotaxime, and ceftriaxone, by 9.1 to 13.0%, bringing their in vitro rates much closer to those of amoxicillin (modified in an earlier NCCLS publication). These revised breakpoints will assist the rational prescribing of antimicrobial agents for the treatment of pneumococcal infections for specific types of infection and establish a greater correlation with clinical outcomes.The revised interpretive MIC breakpoints for Streptococcus pneumoniae in NCCLS document M100-S10 (3) resulted in an anomalous situation in which more isolates would be reported as intermediate or resistant to broad-spectrum parenteral cephalosporins than to orally administered amoxicillin despite the twofold greater potency of agents such as ceftriaxone (6) and their superior bioavailability. This inconsistency was caused because the amoxicillin and amoxicillin-clavulanate breakpoints were based on their use in nonmeningeal infections, while those of the cephalosporins were set conservatively on the basis of their use in meningeal infections with limited associated bioavailability (4). Recently revised guidelines provide interpretive MIC breakpoints for some parenterally delivered cephalosporins for both meningeal and nonmeningeal (example: pneumonia with or without bacteremia) isolates of S. pneumoniae (5).By using data covering the period of 1996 to 2000 from their surveillance network database, Sahm and colleagues (7) have estimated that the new guidelines will reduce the number of isolates reported as either intermediate or resistant to cefotaxime and ceftriaxone by 10% and 3 to 4%, respectively. However, other clinically usable parenteral cephalosporins were not addressed, including cefepime, a relatively new cephalosporin with an extended spectrum of activity that includes many species resistant to cefotaxime or ceftriaxone. Using fiveyear results (1997 to 2001) for the United States from the SENTRY Antimicrobial Surveillance Program, we were able to compare the rates of susceptibility to five cephalosporins (cefepime, cefotaxime, ceftazidime, ceftriaxone, and cefuroxime), penicillin, erythromycin, and vancomycin by applying the M100-S11 (4) and M100-S12 (5) criteria for nonmeningeal isolates of S. pneumoniae.A total of 7,938 nonmeningeal infection isolates were selected for the period of 1997 to 2001 from the U.S. region of the SENTRY Antimicrobial Surveillance Program. These were consecutive prevalence study strains without preselection bias (7). The susceptibility criteria from M100-S11 and M100-S12 were identical for penicillin, erythromycin, and vancomycin (4, 5) and also remained unchanged for...

The epidemiology of antibiotic resistance in Streptococcus pneumoniae and the clinical relevance of resistance to cephalosporins, macrolides and quinolones

“…In contrast, when the new breakpoints were used, only 3.6% of isolates had intermediate resistance and none were fully resistant [96]. This confirms findings reported by others [97].…”

Tracking the implementation of NCCLS M100-S12 expanded-spectrum cephalosporin MIC breakpoints for nonmeningeal isolates of Streptococcus pneumoniae by clinical laboratories in the United States during 2002 and 2003

“…Continued use of the M100-S11 breakpoints for expanded-spectrum cephalosporins may lead to the reporting of false in vitro non-susceptibility of nonmeningeal S. pneumoniae isolates. Application of the new interpretative criteria, with higher breakpoints for nonmeningeal isolates, will result in an increase in the number of S. pneumoniae isolates reported as susceptible to cefotaxime and ceftriaxone (Table 2) [2,4]. Based on analysis of data from January 2002 to June 2003, approximately 10–15% more nonmeningeal isolates will be reported as susceptible when the M100-S12 breakpoints are used.…”

“…A previous study based on historical data showed the M100-S12 ceftriaxone and cefotaxime interpretive breakpoints for nonmeningeal isolates decreased the number of S. pneumoniae isolates interpreted as intermediate by 10% and as resistant by 3 to 4% [3]. A second study, by Jones and colleagues, showed a 9.1 to 13.0% increase in susceptibility to cefotaxime, ceftriaxone, and cefepime using the M100-S12 nonmeningeal interpretive criteria [4]. The current study was conducted to determine the rate at which a set of clinical laboratories in the United States adopted the M100-S12 interpretive breakpoint changes from January 2002 to June 2003.…”

Clinical Isolates of Streptococcus pneumoniae with Different Susceptibilities to Ceftriaxone and Cefotaxime

“…These differences were generally of one doubling dilution and were attributable to lower ceftriaxone MICs than cefotaxime MICs for penicillin-resistant isolates. Given that ceftriaxone and cefotaxime MICs and MIC interpretations are rarely reported together, the prevalence of such phenotypes is largely unknown (8,13,21,25). Available data suggest that isolates with different ceftriaxone and cefotaxime MICs and MIC interpretative phenotypes do exist (13,21), although their prevalence is low (2.6% in the present study [ Fig.…”