Development of bacterial resistance to the third generation cephalosporins and their clinical use

Multidrug resistant Acinetobacter baumannii isolates from a teaching hospital

Abstract Acinetobacter baumannii is the most common nosocomial pathogen among all Acinetobacter spp. A. baumannii tend to be resistant to multiple antibiotics, and represent a severe threat in the treatment of hospitalized patients. The purpose of this study was to evaluate the prevalence, biotyping, and antibiotic resistance status of A. baumannii isolates recovered from submitted hospital clinical specimens. The in-vitro activity of 29 currently used antimicrobial agents was studied in 180 isolates of A. baumannii. The prevalence was higher in wound exudates (32%) and urine samples (22%) than in other specimens. Forty-six percent of the isolates were of biotype 9. The evolution of resistance from November 1996 through October 1998 was studied. More than 75% of the isolates were multidrug resistant (MDR) and more than 70% were #-lactamase producers. Amikacin, ampicillin + sulbactam, and imipenem are still effective antimicrobial agents, but a steady rise in the values of the minimum inhibitory concentration at which 50% of the isolates were inhibited (MIC50 )and MIC90 was observed. Resistance to aztreonam (60%), enrofloxacin (60%), imipenem (29%), moxalactam (73%), and sparfloxacin (25%) was noted; enrofloxacin and sparfloxacin are not generally used in this hospital. From the findings of the present study, no single drug appears to be suitable for empirical therapy for this nosocomial pathogen. Abstract Acinetobacter baumannii is the most common nosocomial pathogen among all Acinetobacter spp. A. baumannii tend to be resistant to multiple antibiotics, and represent a severe threat in the treatment of hospitalized patients. The purpose of this study was to evaluate the prevalence, biotyping, and antibiotic resistance status of A. baumannii isolates recovered from submitted hospital clinical specimens. The in-vitro activity of 29 currently used antimicrobial agents was studied in 180 isolates of A. baumannii. The prevalence was higher in wound exudates (32%) and urine samples (22%) than in other specimens. Forty-six percent of the isolates were of biotype 9. The evolution of resistance from November 1996 through October 1998 was studied. More than 75% of the isolates were multidrug resistant (MDR) and more than 70% were #-lactamase producers. Amikacin, ampicillin + sulbactam, and imipenem are still effective antimicrobial agents, but a steady rise in the values of the minimum inhibitory concentration at which 50% of the isolates were inhibited (MIC50) and MIC90 was observed. Resistance to aztreonam (60%), enrofloxacin (60%), imipenem (29%), moxalactam (73%), and sparfloxacin (25%) was noted; enrofloxacin and sparfloxacin are not generally used in this hospital. From the findings of the present study, no single drug appears to be suitable for empirical therapy for this nosocomial pathogen.

Study of an outbreak of Enterobacter cloacae sepsis in a neonatal intensive care unit: the application of epidemiologic chromosome profiling by pulsed-field gel electrophoresis

OBJECTIVE

From October 1996 to March 1997, a cluster of 11 cases of neonatal sepsis caused by Enterobacter cloacae with similar antimicrobial susceptibility patterns occurred in a neonatal intensive care unit. This outbreak prompted an investigation.

METHOD

Twelve isolates obtained from 6 neonatal patients who developed E cloacae sepsis during the outbreak were analyzed. Four E cloacae isolates from 2 preterm neonates without E cloacae infection on the same ward, and 1 isolate from the hands of a nurse, were also examined. No E cloacae were isolated from the environment. Bacterial DNA digested with XbaI or NotI was analyzed with pulsed-field gel electrophoresis.

RESULT

Three distinct banding patterns were identified by pulsed-field gel electrophoresis. Of the 6 preterm infants with sepsis, strain I was identified in 1, strain II in 2, a mixed infection of strains I and II in 2, and strain III was found in only 1 infant. An isolate from the hands of a nurse was identified as strain II, as were the 4 isolates from the 2 preterm neonates without E cloacae infection. Thus, this outbreak of sepsis was caused by 2 genotypes of E cloacae.

CONCLUSION

This study demonstrates that pulsed-field gel electrophoresis with restriction enzyme digestion is a valuable tool for genetic characterization of multidrug-resistant E cloacae strains during outbreaks.

Geographic variations in activity of broad-spectrum beta-lactams against Pseudomonas aeruginosa: summary of the worldwide SENTRY Antimicrobial Surveillance Program (1997-2000)

With reports of increasing resistance to antimicrobial agents among Pseudomonas aeruginosa clinical isolates worldwide, the activities of cefepime and eight other broad-spectrum beta-lactams against 6969 isolates collected during 1997-2000 from the four regions of the SENTRY Antimicrobial Surveillance Program. P. aeruginosa isolates were tested by the reference broth microdilution method against nine beta-lactam antimicrobial agents (aztreonam, cefepime, ceftazidime, imipenem, meropenem, piperacillin +/- tazobactam, ticarcillin +/- clavulanate), three aminoglycosides (amikacin, gentamicin, tobramycin), and two fluoroquinolones (ciprofloxacin, levofloxacin). The strains were contributed by more than 100 medical centers. National Committee for Clinical Laboratory Standards criteria were used to identify susceptible and resistant isolates. P. aeruginosa strains from Latin America were generally the most resistant to all classes of antimicrobials, compared with strains from other regions. The beta-lactams exhibited a wide range of potency, with carbapenems most active (meropenem, 80-91% susceptible; imipenem, 76-88% susceptible). Piperacillin/tazobactam was the most active penicillin (77-80% susceptible), and cefepime (67-83% susceptible) had an average 2% (range, 0.7-3.5%) greater susceptibility rate than ceftazidime (66-80% susceptible) across all regions. The rank order of beta-lactam activity according to percent resistant isolates in North American P. aeruginosa strains was: meropenem (4.8% resistant) > cefepime (6.8%) > imipenem (8.6%) > piperacillin/tazobactam (10.3%) > piperacillin (12.9%). Only 2.3% and 6.5% of isolates were resistant to amikacin or tobramycin, respectively, and nearly 16% of P. aeruginosa strains were resistant to ciprofloxacin. Compared with other geographic regions, strains of P. aeruginosa remain most susceptible in North America. In all regions, aminoglycosides in combination with carbapenems, cefepime, or piperacillin/tazobactam would provide more potential antipseudomonal activity than fluoroquinolone combinations for wide-spectrum empiric regimens.