Biotyping, serotyping and ribotyping as epidemiological tools in the evaluation of Acinetobacter baumannii dissemination in hospital units, Sorocaba, São Paulo, Brazil

Suitable restriction enzyme for standardization of pulsed-field gel electrophoresis protocol and interlaboratory comparison of Acinetobacter baumannii

BACKGROUND/PURPOSE

Interlaboratory comparison of pulsed-field gel electrophoresis (PFGE) patterns is difficult. A key reference of standardized PFGE protocol for Acinetobacter baumannii may address this issue. This study aimed to determine restriction enzymes with rare cutting sites on A baumannii genomes and evaluate their cost-effectiveness, discriminatory power, and interlaboratory consistence of band assignments.

METHODS

There were 42 A baumannii isolates collected, including nine from three hospital outbreaks and 33 sporadic isolates. The numbers of cutting sites for the restriction enzymes were explored using the "Restriction Digest and PFGE" program. The cost-effectiveness for PFGE analysis was evaluated for the tested restriction enzymes, while its discriminatory ability was expressed through a discriminatory index and 95% confidence interval. The interlaboratory consistence of band assignments was evaluated for the 42 A baumannii isolates.

RESULTS

ApaI was the most cost-effective restriction enzyme for a PFGE protocol for A baumannii. Both AscI and AsiSI were reasonable in terms of costs. ApaI, AscI, and AsiSI exhibited similar discriminatory indices. ApaI generated more than 40 fragments that were close and not easy to resolve, resulting in less consistence of band assignments. AscI and AsiSI generated 10-20 fragments that were clearly resolved, resulting in higher consistence of band assignments. AscI exhibited a close discriminatory power to that of AsiSI and at half of the cost of AsiSI for PFGE analysis.

CONCLUSION

We recommend AscI as the primary enzyme and AsiSI as the secondary enzyme for standardizing the PFGE protocol and interlaboratory comparisons of A baumannii.

The increasing role of Acinetobacter species as nosocomial pathogens

Among gram-negative organisms playing a significant role in nosocomial infections, Acinetobacter species have attracted increasing attention in intensive care units during the past two decades. Acinetobacter species are implicated in a wide spectrum of infections (eg, bacteremia, nosocomial pneumonia, urinary tract infections, secondary meningitis, superinfections in burn patients). One of the most striking features of Acinetobacter species is their extraordinary ability to develop multiple resistance mechanisms against major antibiotic classes. They have become resistant to broad-spectrum β-lactams (third-generation cephalosporins, carboxypenicillins, and increasingly to carbapenems); they produce a wide range of aminoglycoside-inactivating enzymes; and most strains are resistant to fluoroquinolones. In Acinetobacter nosocomial infections, the major problems confronting clinicians in intensive care units are related to the severity of Acinetobacter nosocomial infections and to resistance to major antibiotic classes of these organisms.

Resistance trends of Acinetobacter spp. in Latin America and characterization of international dissemination of multi-drug resistant strains: five-year report of the SENTRY Antimicrobial Surveillance Program

OBJECTIVES

To analyze the antimicrobial susceptibility of Acinetobacter spp. isolates collected from Latin American medical centers as part of the SENTRY Antimicrobial Surveillance Program and also to evaluate the dissemination of multi-drug resistant Acinetobacter spp. strains in the region.

METHODS

A total of 826 isolates of Acinetobacter spp. from multiple infection sites were collected from January 1997 to December 2001 in ten medical centers and susceptibility tested to >25 selected agents by broth microdilution. Multi-drug resistant Acinetobacter spp. isolates were molecular typed.

RESULTS

Resistance rates to carbapenems varied significantly among countries. A continued annual increase occurred in the Argentinean medical centers. In contrast, carbapenem resistance was rare in Chilean centers, and decreased significantly in the Brazilian institutions. Acinetobacter spp. isolates recovered from lower respiratory tract and bloodstream infections were associated with lower antimicrobial susceptibility rates. Resistance rates to imipenem were higher among isolates collected from intensive care units (13.5%) than among isolates from other units. A major ribogroup pattern (521-1) was detected among eight Acinetobacter spp. strains isolated from three distinct Latin American countries.

CONCLUSIONS

This study found that antimicrobial resistance is still a major issue among Acinetobacter spp. isolates collected from some Latin American countries. The dissemination of a major bacterial cluster in different regions reinforces the importance of longitudinal surveillance programs, such as SENTRY, as valuable tools for monitoring antimicrobial susceptibility rates and guiding local interventions.