Antibiotic Resistance and Its Relationship to Antibiotic Use

Antibiotic Resistance and Its Relationship to Antibiotic Use Antibiotic Stewardship Curriculum Developed by: Vera P. Luther, M. D. Christopher A. Ohl, M. D. Wake Forest School of Medicine With Support from the Centers for Disease Control and Prevention

Objectives 1. Define antibiotic susceptibility, antibiotic resistance and breakpoint 2. List four methods for determining antibiotic susceptibility 3. Discuss factors that contribute to antibiotic resistance 4. List five bacterial resistance mechanisms and the antibiotic classes each affects 5. Understand the clinical implications of antibiotic resistance for Staphylococcus aureus, Streptococcus pneumoniae and gram-negative organisms

Outline • • Introduction Key Terms Susceptibility Testing Methods Factors Contributing to Antibiotic Resistance Mechanisms of Resistance Clinical Examples Conclusion

Introduction • Since the first use of antibiotics in the 1930 s and 1940 s, bacteria quickly adapted and developed mechanisms to escape their effects • Over the following decades, new antibiotics were developed to overcome resistance • Since the 1990 s, new antibiotic development has fallen sharply while bacterial resistance continues to increase • Antibiotic resistance is responsible for countless human deaths and billions of dollars in healthcare expenses

Introduction Resistance Beyond Typical Bacteria • Imidazole-resistant Candida spp. • Multidrug-resistant tuberculosis • Multidrug-resistant malaria • Anti-viral resistant influenza

Outline • • Introduction Key Terms Susceptibility Testing Methods Factors Contributing to Antibiotic Resistance Mechanisms of Resistance Clinical Examples Conclusion

Key Terms • Antibiotic = A drug that kills or inhibits the growth of microorganisms • Resistant = Somewhat arbitrary designation that implies that an antimicrobial will not inhibit bacterial growth at clinically achievable concentrations • Susceptible = Somewhat arbitrary designation that implies that an antimicrobial will inhibit bacterial growth at clinically achievable concentrations

Key Terms • MIC = Minimal inhibitory concentration. Lowest concentration of antimicrobial that inhibits growth of bacteria. Commonly used in clinical lab • MBC = Minimal bactericidal concentration. Concentration of an antimicrobial that kills bacteria. Used clinically only in special circumstances • Breakpoint = The MIC that is used to designate between susceptible and resistant. Arbitrarily set by a committee

Outline • • Introduction Key Terms Susceptibility Testing Methods Factors Contributing to Antibiotic Resistance Mechanisms of Resistance Clinical Examples Conclusion

Minimum Inhibitory Concentration MIC = 6. 25 mcg/m. L

Automated Methods Well Plate for MIC Testing Many Labs Use Automated Testing

Other Methods for Determining Susceptibility E-test® Kirby-Bauer Disk Diffusion Agar dilution

Concept of Breakpoint to Determine Susceptibility EXAMPLE: Susceptibility testing for a single isolate of Pseudomonas aeruginosa -Breakpoint for intermediate resistance for meropenem is 4 and for piperacillin/tazobactam (pip/tazo) 32 -Pip/tazo is the better choice between the two -Ciprofloxacin is a poor choice even though the MIC is lowest of the three Antibiotic Ampicillin Gentamicin Cephalothin Cefepime Cefotaxime Ceftazidime Aztreonam Ciprofloxacin Amp/Sulbactam Meropenem Pip/tazo MIC >16 2 >16 8 16 2 4 2 >16 4 8 Breakpoint 8 4 N/A 32 16/32 32 16 2 8 4/8 32 -64/128 Susceptibility Resistant Susceptible Intermediate Susceptible Resistant Intermediate Susceptible

Outline • • Introduction Key Terms Susceptibility Testing Methods Factors Contributing to Antibiotic Resistance Mechanisms of Resistance Clinical Examples Conclusion

Antibiotic Use Leads to Antibiotic Resistance Inpatient Agriculture Outpatient

Reasons for Antibiotic Overuse : Conclusions from 8 Focus Groups Patient Concerns • Want clear explanation • Green nasal discharge • Need to return to work Physician Concerns • Patient expects antibiotic • Diagnostic uncertainty • Time pressure Antibiotic Prescription Barden L. S. Clin Pediatr 1998; 37: 665

Antibiotic Use Leads to Antibiotic Resistance • Resistant bacteria or their genetic determinates are selected when colonizing or infecting bacteria are exposed to antibiotics • Resistant bacteria can then be transmitted between patients • Highest risk patients: – Immunocompromised – Hospitalized – Invasive devices (central venous catheters)

• • • Outline Introduction Key Terms Susceptibility Testing Methods Factors Contributing to Antibiotic Resistance Mechanisms of Resistance – Overview – Specific Examples 1. 2. 3. 4. Antibiotic Degrading Enzymes Decreased Permeability Efflux Pumps Target Alterations • Clinical Examples • Conclusion

Cycle of Antibiotic Resistance Acquisition: Bacterial Selection Under increasing antibiotic selection pressure: 1. Bacteria resistant to a particular drug are selected and replicate 2. Different antibiotics select different bacteria but can select resistant phenotypes to other drugs as well 3. This results in multidrug-resistant (MDR) organisms and increases their total number R Selection by Drug X Replication Selection by Drug Y Replication Resistance to: Drug X Drug Y Drug Z

Antibiotic Mechanism of Action Linezolid Daptomycin

Mechanisms Of Antibiotic Resistance • Bacteria are capable of becoming resistant through several mechanisms • One or many mechanisms may exist in an organism • Multidrug-resistant bacteria often have multiple mechanisms • Genes encoding resistance may exist on plasmid or chromosome Decreased Permeability Alteration in Target Molecule

Mechanisms of Resistance Antibiotic Degrading Enzymes • Sulfonation, phosphorylation, or esterifictation – Especially a problem for aminoglycosides • β-lactamases – Simple, extended spectrum β-lactamases (ESBL), cephalosporinases, carbapenemases – Confer resistance to some, many, or all beta-lactam antibiotics – May be encoded on chromosome or plasmid – More potent in gram-negative bacteria – Examples: S. aureus, H. influenzae, N. gonorrhoeae, E. coli, Klebsiella sp. , Enterobacter sp. , Serratia sp. , other enteric bacteria, anaerobes

Extended Spectrum -lactamases • -lactamases capable of hydrolysing extended spectrum cephalosporins, penicillins, and aztreonam • Most often associated with E. coli and Klebsiella pneumoniae but spreading to other bacteria • Usually plasmid mediated • Aminoglycoside, ciprofloxacin and trimethoprimsulfamethoxazole resistance often encoded on same plasmid • Has become a significant resistance determinate in acute and long-term care facility enteric pathogens

Class A Carbapenemases • Most common in Klebsiella pneumoniae (KPC) • Also seen in E. coli, Enterobacter, Citrobacter, Salmonella, Serratia, Pseudomonas and Proteus spp. • Very often with multiple other drug resistance mechanisms, resistance profile similar to ESBL but also carbapenem resistant • Became problem in New York City first in 2002 -2003 and is being increasingly recognized in Mid-Atlantic US. • Spreading across species to other gram-negatives and enterobacteriaceae • Emerging in long-term care facilities

Mechanisms of Resistance Decreased Permeability • Pseudomonas spp. • Affects many antibiotics including carbapenems Efflux Pumps • Pseudomonas spp. (multiple antibiotics) • Tetracyclines • Macrolides

Mechanisms of Resistance Target Alteration • DNA gyrase • Fluoroquinolones • Many gram-negatives, S. pneumoniae • Penicillin-binding protein • Methicillin-resistant S. aureus (MRSA) • Penicillin-resistant S. pneumoniae • Gram positive cell wall • Vancomycin • Enterococcus spp.

Mechanisms of Resistance Target Alteration (cont’d) • Ribosome • Tetracyclines • Macrolides • S. pneumoniae, Staphylococcus sp. , N. gonorrhoeae, enteric gram-negative rods

Outline • • • Introduction Key Terms Susceptibility Testing Methods Factors Contributing to Antibiotic Resistance Mechanisms of Resistance Clinical Examples – Staphylococcus aureus – Streptococcus pneumoniae – Escherichia coli • Conclusion

Illustrative Case 1 • A 50 y. o. female with type 2 diabetes mellitus was admitted for an elective total knee replacement. Postoperative day 4: fever to 39ºC and a gray, purulent wound discharge • Gram stain of the exudate showed neutrophils and gram positive cocci in clusters • She was started on IV cefazolin. After two days of therapy she remained febrile and her wound showed little improvement

Case 1 Gram Stain

Illustrative Case 1 (cont’d) • Wound cultures yielded S. aureus resistant to penicillin, methicillin, all cephalosporins, erythromycin, tetracycline, gentamicin and ciprofloxacin • The wound was débrided and she was started on IV vancomycin with improvement • After 4 days of vancomycin she was discharged on oral trimethoprim/sulfamethoxazole for 2 weeks • 3 months later she experienced a recurrence of symptoms after initial improvement and was diagnosed as having a deep prosthetic joint infection due to MRSA

Increase in MRSA Prevalence in US Comparison to Other Drug-Resistant Organisms Wenzel et. al. ICHE 2008; 29; 1012

Surgical Site Infections Impact of Resistance on Clinical Outcomes MSSA (N=165) MRSA (N=121) P Value 6. 7% 20. 7% P<. 001 After surgery 14 (7 -25) 23 (12 -38) P<. 001 After infection 10 (4 -17) 15 (7 -30) P=. 001 Unadjusted Mortality, 90 -day Length of stay: median days Adjusted* mortality for MRSA (P=0. 003) *Adjusted for other predictors of mortality: age, physical status, duration of surgery. Engemann JJ, et al. Clin Infect Dis. 2003; 36: 592 -598.

Glycopeptide Resistant S. aureus • Glycopeptide Intermediate Resistance: – – First reported in Japan Vancomycin MIC 8μg/m. L Still uncommon All with prolonged vancomycin use due to persistent S. aureus infections • Glycopeptide High Level Resistance: – – First report in Michigan in June 2002 Vancomycin MIC >128 ug/ml Diabetic with peripheral vascular disease and chronic renal failure Resistance determinant acquired from Vancomycin-resistant Enterococcus (VRE) – Very uncommon MMWR 2002; 51: 565 -7 MMWR 2000; 48: 1165 -7 Smith TL et al. NEJM 1999; 340: 493 -501

Illustrative Case 2 • 67 y. o. man with chronic lymphocytic leukemia admitted with sudden onset high fever, rigors, pleuritic chest pain and productive cough • Physical exam and chest x-ray confirmed pneumonia • Started on IV azithromycin

Illustrative Case 2 (cont) • Gram stain showed numerous neutrophils and sheets of lancet shaped gram positive diplococci • After 48 hours the patient was still febrile and developed progressive respiratory tract failure • Blood culture from admission yielded S. pneumoniae resistant to penicillin, ceftriaxone, erythromycin and clindamycin Gram stain

2009 S. pneumoniae Susceptibility CDC ABC surveillance Network Invasive Isolates (Meningitis, bacteremia, etc. ) http: //www. cdc. gov/abcs/reports-findings/survreports/spneu 09. pdf

Macrolide-Resistant S. pneumoniae Prevalence is Increasing in US Jenkins S. et al Emerg Infect Dis. 2009; 5: 1260 Hicks L et. Al. Emerg Infect Dis. 2010; 16: 896

Decreased Susceptibility of S. pneumoniae to Fluoroquinolones (FQRSP) in Canada Relationship of Resistance to Antibiotic Use Chen et. al. , NEJM 1999; 341: 233 -9

Illustrative Case 3 • 45 y. o. female seen in clinic for urinary urgency, frequency and dysuria. Her urinalysis is positive for leukocyte esterase and 31 -40 white blood cells. A urine gram stain was performed and showed 2+ white blood cells and many gramnegative rods • Urine culture reveals E. coli, which is resistant to ciprofloxacin and trimethoprim-sulfamethoxazole, but is sensitive to ceftriaxone

Community-Acquired Resistant E. Coli • Mostly UTIs • Young healthy women in addition to the elderly • 10 -20% now resistant to fluoroquinolones • 30 -50% resistant to trimethoprimsulfamethoxazole • CTX-M β-lactamases becoming more common – Cause cephalosporin resistance

Outline • • Introduction Key Terms Susceptibility Testing Methods Factors Contributing to Antibiotic Resistance Mechanisms of Resistance Clinical Examples Conclusion

Conclusion • Inappropriate and excessive use of antibiotics is a major factor contributing to emerging antibiotic resistance • Determinants of resistance are selected for by antibiotic use • Multiple mechanisms exist for bacteria to become resistant to antibiotics • Antibiotic resistance is a problem in outpatient and inpatient settings and is a factor in a wide variety of infections • Antibiotic resistance continues to emerge as a serious threat to public health