Antibiotic Resistance Patterns of Serratia marcescens

Introduction

• Study on antibiotic resistance patterns of clinical isolates of Serratia marcescens.

• Conducted by Robert C. Cooksey, Edward R. Bannister, and W. Edmund Farrar, Jr. at the Medical University of South Carolina.

• 102 strains isolated from three medical centers; analyzed using disk sensitivity and agar dilution methods.

Key Findings on Antibiotic Resistance

• Least resistance observed against:

  • Gentamicin

  • Nalidixic acid

  • Chloramphenicol

  • Sulfisoxazole

  • All inhibited more than 80% of strains.

• Total resistance:

  • Cephalothin was completely ineffective (100% resistance).

  • Ampicillin and Tetracycline had over 90% resistance.

• Effective drugs recognized (demonstrated by minimum inhibitory concentration):

  • Nalidixic acid

  • Gentamicin

  • Tobramycin

  • Chloramphenicol

  • Inhibitory concentrations achieved fall within therapeutically attainable levels.

Patterns of Resistance

• Uniformity of resistance against ampicillin, cephalothin, and tetracycline across three hospitals.

• Hospital-specific patterns noted for other antibiotics.

• 11 isolates were pigmented, resistant to multiple drugs, similar resistance patterns with nonpigmented strains.

• Multiple drug resistance:

  • 50% of strains were resistant to five or more antibiotics.

• Problems associated with hospital infections include:

  • Meningitis

  • Pulmonary infections

  • Septicemia

  • Endocarditis

Antibiotic Efficacy and MIC Results

• Table 1 shows resistance percentages for various strains:

  • All strains: 100% resistant to Cephalothin.

  • 93% resistance to Ampicillin and Tetracycline.

  • Resistance rates for others (e.g., 14% for Gentamicin, 8% for Nalidixic acid).

• Resistance varied by hospital:

  • M. D. Anderson Hospital: more resistant across all tested drugs (except colistin & cephalothin).

  • Emory University: higher resistance to colistin.

• Notable findings on pigmented strains:

  • Resistant to Streptomycin, Colistin, and Tobramycin.

Discussion Points

• Gentamicin, chloramphenicol, sulfisoxazole, and nalidixic acid remain the most effective agents against Serratia at therapeutic doses.

• Ineffective agents:

  • Ampicillin, cephalothin, tetracycline, and colistin showed no efficacy and should not be used for treatment.

• Characteristic resistance patterns suggest ongoing evaluation of antibiotic susceptibility is needed due to:

  • Rapid development of resistance.

  • Changes over short periods of time.

• R factors:

  • Transferable resistance among strains contributing to increased resistance to selected antibiotics.

Acknowledgments

• Thanks to Dieter Groschel and Jonas Shulman for bacterial strains provided for study.

Conclusion

• The ongoing study of antibiotic resistance patterns in S. marcescens is crucial given the organism's opportunistic nature and rapid adaptability in clinical settings.

• Study on antibiotic resistance patterns of clinical isolates of Serratia marcescens.

• Conducted by Robert C. Cooksey, Edward R. Bannister, and W. Edmund Farrar, Jr. at the Medical University of South Carolina.

• 102 strains isolated from three medical centers; analyzed using disk sensitivity and agar dilution methods.

Key Findings on Antibiotic Resistance

• Least resistance observed against:- Gentamicin

  • Nalidixic acid

  • Chloramphenicol

  • Sulfisoxazole

  • All inhibited more than 80% of strains.

• Total resistance:- Cephalothin was completely ineffective (100% resistance).

  • Ampicillin and Tetracycline had over 90% resistance.

• Effective drugs recognized (demonstrated by minimum inhibitory concentration):- Nalidixic acid

  • Gentamicin

  • Tobramycin

  • Chloramphenicol

  • Inhibitory concentrations achieved fall within therapeutically attainable levels.

Patterns of Resistance

• Uniformity of resistance against ampicillin, cephalothin, and tetracycline across three hospitals.

• Hospital-specific patterns noted for other antibiotics.

• 11 isolates were pigmented, resistant to multiple drugs, similar resistance patterns with nonpigmented strains.

• Multiple drug resistance:- 50% of strains were resistant to five or more antibiotics.

• Problems associated with hospital infections include:- Meningitis

  • Pulmonary infections

  • Septicemia

  • Endocarditis

Antibiotic Efficacy and MIC Results

• Table 1 shows resistance percentages for various strains:- All strains: 100% resistant to Cephalothin.

  • 93% resistance to Ampicillin and Tetracycline.

  • Resistance rates for others (e.g., 14% for Gentamicin, 8% for Nalidixic acid).

• Resistance varied by hospital:- M. D. Anderson Hospital: more resistant across all tested drugs (except colistin & cephalothin).

  • Emory University: higher resistance to colistin.

• Notable findings on pigmented strains:- Resistant to Streptomycin, Colistin, and Tobramycin.

Discussion Points

• Gentamicin, chloramphenicol, sulfisoxazole, and nalidixic acid remain the most effective agents against Serratia at therapeutic doses.

• Ineffective agents:- Ampicillin, cephalothin, tetracycline, and colistin showed no efficacy and should not be used for treatment.

• Characteristic resistance patterns suggest ongoing evaluation of antibiotic susceptibility is needed due to:- Rapid development of resistance.

  • Changes over short periods of time.

• R factors:- Transferable resistance among strains contributing to increased resistance to selected antibiotics.

Acknowledgments

• Thanks to Dieter Groschel and Jonas Shulman for bacterial strains provided for study.

Conclusion

• The ongoing study of antibiotic resistance patterns in S. marcescens is crucial given the organism's opportunistic nature and rapid adaptability in clinical settings.

Cooksey, R. C., Bannister, E. R., & Farrar, W. E. (1975). Study on antibiotic resistance patterns of clinical isolates of *Serratia marcescens*. *Medical University of South Carolina*, Volume XX, Issue YY, Location: Charleston, SC.