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High-level resistance to gentamicin in Streptococcus faecalis: risk factors and evidence for exogenous acquisition of
Abstract:
Between November 1981 and October 1984, 48 of 3,456 clinical isolates of Streptococcus faecalis that were studied showed high-level (greater than 2,000 micrograms/ml) resistance to gentamicin. A case-control study comparing patients with gentamicin-susceptible (MIC less than 64 micrograms/ml) and -resistant S. faecalis infections showed significant associations (P less than .01) between the development of infection with highly gentamicin-resistant S. faecalis and prior antimicrobial therapy (particularly with cephalosporins or aminoglycosides), perioperative antibiotic prophylaxis, prior surgical procedures, and longer hospitalization. All highly resistant strains appeared to be nosocomial since 12 cases were clustered on a surgical floor and in a burn unit. In vitro transfer of gentamicin resistance by filter mating was observed for 44 of 48 isolates. The use of plasmid content as an epidemiological marker suggested nosocomial transmission and exogenous acquisition of S. faecalis.
Insights
High-level gentamicin resistance in Streptococcus faecalis is linked to prior antibiotic use and hospital stays. This resistance can be transferred between bacteria, suggesting nosocomial spread.
Area of Science:
- Clinical microbiology
- Infectious diseases
- Antimicrobial resistance
Background:
- Streptococcus faecalis (now Enterococcus faecalis) is a common cause of nosocomial infections.
- High-level aminoglycoside resistance (HLAR) in enterococci can lead to treatment failures, particularly with gentamicin.
- Understanding the epidemiology and transmission of HLAR strains is crucial for infection control.
Purpose of the Study:
- To investigate the prevalence and risk factors associated with high-level gentamicin-resistant Streptococcus faecalis infections.
- To determine the mechanisms of gentamicin resistance transfer and potential for nosocomial transmission.
- To identify epidemiological markers for tracking resistant strains.
Main Methods:
- A case-control study was conducted comparing patients with gentamicin-susceptible and -resistant S. faecalis infections.
- Risk factors such as prior antimicrobial therapy, surgical procedures, and hospitalization duration were analyzed.
- In vitro filter mating experiments were performed to assess the transferability of gentamicin resistance.
- Plasmid content analysis was used as an epidemiological marker.
Main Results:
- 48 of 3,456 clinical isolates (1.4%) exhibited high-level gentamicin resistance (>2,000 µg/ml).
- Significant associations were found between HLAR S. faecalis infections and prior antibiotic use (cephalosporins, aminoglycosides), perioperative prophylaxis, surgery, and prolonged hospitalization (P < .01).
- All resistant strains appeared nosocomial, with clusters in surgical and burn units.
- Gentamicin resistance was transferable in vitro for 44 of 48 isolates (91.7%).
Conclusions:
- Prior antimicrobial exposure and healthcare-associated factors are significant risk factors for developing high-level gentamicin-resistant S. faecalis infections.
- The high rate of in vitro resistance transfer and plasmid analysis suggests that nosocomial transmission and exogenous acquisition of these resistant strains are common.
- These findings underscore the importance of antimicrobial stewardship and infection control measures to prevent the spread of resistant enterococci.