Vol. 17 •Issue 24 • Page 12
The Learning Scope
Battling Antibiotic Resistance in a Healthcare Center
Upon completion of this course, the participant will be able to:
1. Explain contributing factors that lead to antibiotic resistance.
2. Compare and contrast case histories and “selective resistance.”
3. Explain extended spectrum beta-lactamase (ESBL)-producing bacteria and explain the enzymes defining them.
4. Explain the steps in laboratory detection and confirmation of ESBL-producing or multidrug resistant bacteria.
5. Explain prevention and control measures for combating antibiotic drug resistance.
Note: This article is limited to gram-negative nosocomial infection.
Editor’s note: This Learning Scope article offers a unique opportunity for clinical laboratory personnel to earn continuing education credit. It is offered to our subscribers six times a year. Simply read the peer-reviewed article and send your answers to the questions that follow to the American Society for Clinical Laboratory Science (ASCLS). As does this one, most Learning Scope articles provide 0.1 CEU or 1 contact hour if you score 70 or above. The credit is issued through ASCLS’ P.A.C.E. program. The ASCLS is the oldest and largest non-registry, non-profit professional membership association representing non-physician clinical laboratory practitioners. You don’t need to be a member to earn the credit. Additional details concerning the CEU offer are listed to the left of the answer sheet. Tests may be submitted up to 2 years following publication in ADVANCE. The answer sheet may be copied for a fellow laboratorian to submit for credit.
Nosocomial (hospital-acquired) infection that results from antibiotic resistance–sepsis, pneumonia, urinary tract and post-surgical infection–is considered a public health hazard by the CDC. The problem has been described as “alarming, formidable, appalling,” but 10 years after third-generation cephalosporin resistance appeared in Klebsiella spp., little has been accomplished in the prevention and control of antibiotic resistance resulting from gram-negative nosocomial infection. The cost to defeat multidrug resistance in gram-negative infection, in lives and dollars, has reached 90,000 deaths and $4.5 billion per year.1
According to the Clinical Laboratory Standards Institute (CLSI), multidrug resistance has been defined as the resistance of a microorganism to three or more of the antibiotics tested. Resistance due to extended spectrum beta-lactamase (ESBL) production is defined as resistance to both cefotaxime and ceftazidime.2
Among the most significant factors that have contributed to the present crisis are the following:
• Inappropriate use of broad-spectrum antibiotics; first the cephalosporins, then the fluoroquinolones.
• Use of invasive devices commonly associated with infection: mechanical ventilators and nosocomial pneumonia, indwelling catheters and urinary tract infection (UTI), central lines and sepsis.
• Continued noncompliance by healthcare providers with infection control guidelines; despite the addition of alcohol-based hand sanitizers to physician offices, hospital and clinic compliance averages only 48 percent.
• Decreases in staffing, particularly in the intensive care units (ICU), increase the risk of transmitting resistant microorganisms to susceptible patients by limiting time for appropriate hygiene
• New antibiotic agents have been developed for gram-positive super-bugs (methicillin-resistant Staphylococcus aureus or MRSA; vancomycin-resistant Enterococcus faecalis or VRE; vancomycin-resistant Staphylococcus aureus or VRSA [e.g., linezolid, daptomycin]), but not for resistant gram negatives.3,4
An intercontinental study of hospitalized patients by four European countries, Canada and the U.S. provided susceptibility data from 2000 to 2001 on more than 125,000 isolates of gram-negative bacteria. Among nosocomial infection types, catheter-related UTIs prevailed at 40 percent and pneumonia at 15 percent to 20 percent. Bloodstream or sepsis infection resulting from nosocomial infection was identified as a leading cause of death in the U.S.
Before empiric therapy is considered, clinicians must first evaluate the rates of antimicrobial resistance in a particular hospital environment. Results from the exhaustive intercontinental study analysis determined that the effectiveness of antibiotics against the Entero-bacteriaceae family and Pseudomonas aeruginosa was decreasing, particularly with the fluoroquinolones (ciprofloxacin and levofloxacin). But in 2001, rates of susceptibility to third-generation cephalosporins (ceftriaxone and cefotaxime), known to induce ESBL enzymes in Escherichia coli, Klebsiella pneumoniae and Proteus mirabilis, continued to have in vitro activity against them.5
In the United States, susceptibility to ceftriaxone, piperacillin/ tazobactam, imipenem and aminoglycosides appeared to be stable from 1996 to 2001 within the family of Enterobacteriaceae. However, ESBL producers and hyper-producing chromosomal beta-lactamases were emerging in isolates of E. coli and Klebsiella oxytoca. According to The Surveillance Network USA database, evidence was seen in the increased minimal inhibitory concentration (MIC) to ceftazidime from 0.9 percent to 1.6 percent for “intermediate susceptibility” and from 2.9 percent to 5.9 percent for “resistance” during the period from 1996-2000.5
Because of their extensive use, the fluoroquinolones soon were added to the expanding list of resistant drugs. The National Nosocomial Infections Surveillance (NNIS) System Report summarized data from 300 hospitals during the period from 1992 to 2004. Data on ICU patients with nosocomial infection was analyzed and the rates of antibiotic resistance were compared. Most notable among the results was the continuing increase in cases of MRSA. That is, resistance in S. aureus to methicillin, oxacillin and nafcillin, which saw an increase of 60 percent for the period of January through December in 2003. A frightening change also was seen in K. pneumoniae to third-generation cephalosporins–a 50 percent increase in resistance between 2002 and 2003.6
The severity of nosocomial infection and the antibiotic dilemma that clinicians face is illustrated by the patient histories that follow. Chosen because of their microbiology cultures that grew antibiotic-resistant organisms, the cases are presented here. A tabulation of antibiotic susceptibility reports demonstrates the occurrence of “selective resistance,” i.e., resistance that bacteria acquire in adapting to an antibiotic-ridden environment. The microorganisms to be discussed belong to the Enterobacteriaceae family and are either ESBL producers or, having failed the test for those enzymes, are designated multidrug resistant.
Case No. 1
A male, age 59, was diagnosed with insulin-dependent type II diabetes, as well as neurological, renal and ophthalmologic manifestations. The patient had hypertension and required hemodialysis for end-stage renal disease. Earlier, he experienced a cerebral-vascular accident. After a below-knee amputation in March, he was boarded at the rehabilitation/homecare ward where he developed a sacral ulcer, stage II type wound.
In mid-April, the patient became febrile with temperatures to 102û F and drenching sweats. Wound and blood cultures were taken in the emergency department where he was treated with Zosyn (trade name for piperacillin/tazobactam). Known as a beta-lactamase inhibitor, the drug is given empirically to treat gram-negative infection when suspicion of multidrug resistance exists.
Upon entering the hospital, the patient’s antibiotic regimen was switched to vancomycin for a MRSA infection and metronidazole for Clostridium difficile diarrhea. Blood cultures drawn in mid-April grew an ESBL-producing K. pneumoniae. A 4-week course of imipenem was ordered via an intravenous peripherally-inserted central catheter (PICC) line. A member of the carbapenem family, this drug was highly effective against resistant P. aeruginosa infection; hence, presumed ideal for ESBL producers in the blood.3
Determining, after less than 2 weeks, that the bloodstream infection was transient, the infectious disease (ID) team ordered the IV stopped and the PICC line removed. By the end of April, four blood cultures were negative and the sacral ulcer, apparently a decubitus or bed sore, had healed well.
Cultures of the sacral wound from March had grown four different organisms including two gram-negative rods, both ESBL producers. Because one had the same susceptibility pattern as the blood culture isolate, the K. pneumoniae found in April was the presumed source of the bloodstream infection. The second ESBL producer, Citrobacter amalonaticus, was isolated in March from the wound and also from a urine culture. Review of the April susceptibility results showed the pattern was unchanged for C. amalonaticus, but the ESBL-producing K. pneumoniae, identified in the previous blood culture isolate, was no longer present. The April isolate had the susceptibility pattern of a typically sensitive K. pneumoniae. Thus, the diagnosis of transient bacteremia followed by curtailment of the imipenem and removal of the PICC line was well justified. Susceptibility results are presented in Tables 1 and 2.
Case No. 2
A male, age 56, who tested positive for HIV and hepatitis C virus (HCV), was known to have long-term drug and alcohol addiction. In 2002 and in 2004, he was treated with 3TC/ddI/TDF/EFV, the recommended pharmaceutical “cocktail” for HIV. Working toward recovery, he participated in the rehabilitation program for alcohol and drug addiction. In 2002, however, he underwent surgery for a spinal abscess that resulted in L>R paraplegia. Afterward, he became a patient in the spinal cord institute section of the healthcare center. Incontinence resulted from the paraplegia and was controlled via a foley catheter for 6 months. Notorious for harboring bacteria, this type of indwelling catheter contributes to chronic UTIs. In Dec. 2004, his urine culture grew four organisms, one of which was the gram negative rod, K. pneumoniae. The organism was susceptible to all generations of cephalosporins and aztreonam, and, therefore, was not an ESBL producer.
The foley was removed and he was switched to a condom catheter. Eventually, he was able to manage self-catheterization with a straight catheter. In March 2005, urinary tract infection recurred with an ESBL-producing K. pneumoniae along with a less-resistant E. coli isolated. The E. coli was resistant only to ampicillin, aminoglycosides and trimethoprim/sulfamethoxazole. He was treated at the end of March with tobramycin IV for the ESBL producer and Ancef (oral cephalosporin) for the E. coli.
After ordering a supra-pubic catheter placed in his bladder, the ID team stopped the IV. He was discharged only with Ancef when a subsequent susceptibility test showed the remaining E. coli was not multi-drug resistant (Table 3).
Case No. 3
A male paraplegic, age 48, with multiple sclerosis, malnutrition and a history of kidney stones was discharged from the spinal cord institute section of the hospital in 2005 after a 2-year stay. A susceptible E. coli had been isolated from his urine during the years from 1992 to 1997. This organism had selected for resistance to ampicillin and piperacillin when cultures were repeated in 1998 and, in 2001, several other organisms also were present in his urine. At that time, the E. coli had become resistant to the fluoroquinolones and trimethoprim/sulfamethoxazole. From 2002 to 2003, the selective resistance continued until cefazolin, tobramycin and aztreonam were all resistant. In 2003, the patient became septic, but blood cultures unexpectedly grew a strain of E. coli that was neither ESBL-producing nor multidrug resistant. Susceptibility tests wound and urine cultures also proved the E. coli was sensitive, and he was treated with Zosyn for 6 weeks (Table 4).
For some time, he suffered chronic pressure ulcers in the ischial region where both gram-positive and gram-negative organisms had been found. Included was a multidrug resistant E. coli with similar susceptibility pattern to one isolated from his urine in March 2004. Susceptibility was limited to imipenem and Zosyn. In Feb. 2005, E. coli was isolated from his urine and from an ischial wound. Clinicians determined that only the UTI appeared to be a true infection and he was treated with Macrodantin (trade name for nitrofurantoin), an oral antibiotic specifically targeted for treating urinary tract infections (Table 4).
First reported in 1983 in K. pneumoniae, ESBL enzymes evolved from previous TEM-1, TEM-2 and SHV-1 or broad-spectrum beta-lactamases with varying substrate affinity and enzyme kinetics that hydrolyze penicillins, cephalosporins and aztreonam.
Noted somewhat later, in 1988, in E. coli, another beta-lactamase, a plasmid-mediated AmpC presumed to have transferred from chromosomal genes onto plasmids, was found in other strains of E. coli, K. pneumoniae, Salmonella spp., Citrobacter freundii, Enterobacter aerogenese and P. mirabilis. In 1996, a mechanism responsible for the increase in ceftazidime resistance in Klebsiella spp. and E. coli that caused the production of ESBL was explained. The enzymes giving these organisms resistance to third-generation cephalosporins, aztreonam or even piperacillin/tazobactam, but not to the second-generation cephalosporins were found to be both strain and enzyme distinct/dependent.3,7
By 2003, it was apparent that the increase in multi-drug resistance to non-beta-lactam drugs (e.g., aminoglycosides) resulted from the genes carried on the same plasmid with the ESBL gene. In 2004, another plasmid-mediated ESBL, a cefotaxime (CTX)-m beta-lactamase, was found in strains from Asia, Eastern Europe and Latin America. That resistance was also thought to result from genes residing on the same plasmid with the ESBL and AmpC enzymes. At the 2005 meeting of the European Congress of Clinical Microbiology and Infectious Diseases, presentations of investigative work indicated that the CTX-m type of ESBL predominated. Results further showed that E. coli was the most common organism to carry the plasmid. Added to the growing concern of clinical specialists, was information implicating another group of resistance enzymes found in gram-negative bacteria. These enzymes appearing in Europe are known as metallo-beta-lactamases.7,9
Able to transfer between organisms via transposons, mobile genetic elements, CTX-m enzymes can hydrolyze cefotaxime and ceftriaxone more readily than ceftazidime. Because laboratories may not have screened for these enzymes in the past, the likelihood exists that a greater prevalence of ESBL producers may exist. However, newer guidelines (CLSI 2005) for laboratory testing that include both cefotaxime and ceftazidime predict that better detection of these resistant bugs will follow.3,7
Because they colonize the gastrointestinal tract, resistant enteric bacteria are easily transferred among healthcare workers and patients. Moreover, their continuous presence contributes to the opportunistic outbreak of nosocomial infection. Furthermore, resistance to non-beta- lactam antibiotics, such as trimethoprim/sulfamethoxazole, aminoglycosides and even the fluoroquinolones, may be encoded on the same plasmid with ESBL enzymes. Treatment options then become severely limited. Isolation, detection and susceptibility testing of these bacteria become critical elements in diagnosis.
To determine the presence of an ESBL producer, the following review by the microbiology laboratory is paramount: MIC or disk diffusion susceptibility test results must be scrutinized in all species of Enterobacteriaceae for resistance to aztreonam, cefotaxime, ceftazidime, ceftriaxone or cefpodoxime. CLSI recommends an ESBL screen for any of these antibiotics if MIC results are ³ 2µg/mL or zone diameters are ² 22mm for cefpodoxime or ceftazidime, ² 27mm for aztreonam and ² 25 mm for ceftriaxone.8
Both screening and confirmation tests are performed with cation-adjusted Mueller-Hinton broth (CAHMB) or agar (CAHMA), using a standard broth or agar dilution.8
|Initial Screen||Antibiotic Concentration||Results|
|cefpodoxime||4 µg/mL||Any growth may indicate|
|ceftazidime||1 µg/mL||ESBL production; e.g.,|
|aztreonam 1 µg/mL||cefpodoxime MIC > 8 µg/mL;|
|cefotaxime||1 µg/mL||others, MIC > 2 µg/mL|
Note: Use of more than one agent (above) will improve detection sensitivity.
|ceftazidime||0.25-128 µg/mL||>3 log2 dilution decrease in MIC|
Note: Screening breakpoints for P. mirabilis are unlike those for E .coli and K. pneumoniae shown above.
CAMHA plates are inoculated with a standard dilution (0.5 McFarland-adjusted turbidity) of both patient and quality control (QC) organisms as directed for a disk diffusion susceptibility test. Both ceftazidime/ceftazidime-clavulanic acid (TZ/TZL) and cefotaxime/cefotaxime-clavulanic acid (CT/CTL) impregnated strips are placed on the inoculated agar according to the Etest” package insert procedure.
After overnight incubation at 35û C, reading and interpretation of results follow. Explanation and examples of various growth-inhibition patterns with MIC ratios are given in the package insert and appear in Figures 1-3.
1. > 3 log2 dilution or a 2-fold concentration decrease in MIC for either TZ or CT combined with clavulanic acid compared to either drug alone.
2. Both strips TZ/TZL and CT/CTL must be tested together.
3. When confirmed, ESBL producers should be reported “resistant” to all penicillins, cephalosporins and aztreonam.
4. The following (limitations) are examples of Etest® pattern results (see AB BIODISK package insert at www.abbiodisk.com).
Results of the Etest are used to detect an ESBL producer and do not indicate therapy with an agent combined with clavulanic acid. The test only provides information that cephalosporins should not be used to treat the patient. Use of Etest” strips separately is not recommended.
Illustrated among the case presentations are examples of carefully selected, optimal antibiotic therapy. Information provided by antimicrobial susceptibility testing that included the screening and confirmation of ESBL-producing bacteria was responsible for the correct diagnosis and treatment. To reduce selection for resistance, prevent nosocomial infection and target specific microorganisms require culture, isolation and susceptibility testing are necessary by the microbiology laboratory.
In case No. 1, the imipenem IV antibiotic was stopped and the PICC line removed when the ID team determined that the patient’s symptoms resulted from a (transient) bacteremia. Intravascular devices have been documented as the primary cause of bacteremia. Consultation with the ID service is notable in this case because the patient’s workup included cultures growing different organisms with varying susceptibility patterns. When symptoms and culture results present conflicting data, expertise may be required to determine the difference between true infection and contamination from a line or an intravascular device such as the PICC line (Table 1).
In case No. 2, physicians discontinued the IV tobramycin and ordered removal of the foley catheter, the presumed source of contamination with an ESBL producer. Placement of a supra-pubic catheter directly into the bladder was a better solution to deter chronic infection. Repeated cultures proved the ESBL producer was gone. The patient then could be discharged with a more “side-effect friendly” oral cephalosporin to treat the E. coli.
In case No. 3, the patient had a long history of increased selection for resistance by E. coli. Treatment with IV Zosyn was indicated when a positive blood culture together with symptoms of sepsis occurred. His wound infections, the presumed result of colonization, were not treated. On the other hand, a persistent E. coli, which had been isolated from repeated urine cultures, was treated as a true infection with a simpler, oral antibiotic.
Prevention and Control
First, consider the prognosis of each of the cases presented here. Then, consider the implications for the spread of resistant microorganisms in the particular setting:
• a homecare rehabilitation unit where both elderly and immunocompromised patients reside;
• the spinal cord institute that houses both paraplegic and quadriplegic patients, who may return to the community for short periods; and
• an ICU ward, where patients are in close association with each other and the nursing staff who cares for them.
Added to the ease of transmission inherent in an institutional environment are nosocomial infections that result from bacterial selection for antibiotic resistance. Common among them are: ventilator-associated pneumonia, sepsis or bloodstream infection, catheter-associated UTI and surgical-site infection. Avoiding unnecessary therapy and attention to the administration of antibiotic therapy also play essential roles in the prevention of developing resistance. Improved empiric therapy, therapy of shorter duration and targeting a specific organism are factors noted in a 2005 presentation to address the prevention of infection by resistant bacteria.4
In an effort to reduce infection and ultimately improve hospital care, the Society for Healthcare Epidemiology (SHEA) has encouraged public disclosure of data concerning hospital-acquired infection. Healthcare providers are concerned about the method of collecting the data, the uniformity of that collection across the U.S. and the statistical reliability, not to mention the cost of undertaking such a task.
A SHEA 1995 survey found there were 13 states providing data on their hospital-acquired infection rate based on “quality indicators,” or factors relating to the quality of care. The earlier programs were not mandatory, and results were disclosed only to the individual hospital, not to the public for the purpose of comparing rates of healthcare-associated infection (HAI). The newer 2004 legislation was enacted in only a few states, but requires hospitals to collect and report this data to a state-wide office. The legislation was passed by the California legislature but not signed by Gov. Schwarzenegger. Attention would not be on the providers, but rather on the healthcare institutions themselves. However, the debate over “public disclosure” continues among insurance companies, HMOs and their providers.
The SHEA 2005 publication on public disclosure emphasized the importance of statistical accuracy and measurement of rates based on the use of “process indicators” instead. Hand hygiene when a catheter line is inserted or isolation precautions to prevent transmission are better evaluators. The use of “outcome indicators” has been recommended to measure infection rates by the Hospital Infection Control Practice Advisory Committee (HICPAC). These measurements are defined as infections that are device- or catheter-related, from surgical-site or blood stream infections.10
CMS began a serious effort in 2004 to require information in the areas of myocardial infarction, heart failure and community-acquired pneumonia as criteria to structure its reimbursement program. Hospitals that do not report data were to receive less funding. At present, CMS is working with the states to improve and develop other “indicators,” particularly related to outcome of the infection control process. Indicators recommended by HICPAC eventually may become mandatory on a national level for a hospital to receive reimbursement.10
With the crisis escalating in both the U.S. and Europe, the status of antibiotic resistance would seem compelling enough for pharmaceutical research and development companies to concentrate their efforts in the field of infectious diseases. However, analysis of reports from University of California, Los Angeles, and the FDA from 1998 to 2002 concluded that only seven new antibiotic drugs out of a total of 225 were available. In 2002, no antibiotics were developed and in 2003 only gemifloxacin and daptomycin for gram-positive infection were approved. Others were antifungal, antiparasitic and antiviral—a total of 13 drugs—but none for the nosocomial multidrug resistant gram negatives and ESBL producers. Thus, the need for antibiotics to treat infection with multiresistant bacteria has become desperate.2,11
Despite pleas for funding by the Infectious Disease Society of America, pharmaceutical companies have focused on more lucrative drug development, such as treatment of chronic diseases and long-term conditions proven to be “cost effective.” The struggle to prioritize antibiotic resistance when the emphasis is geared toward the wealth of the pharmaceutical companies, rather than a public health and epidemiologic need in a sinking healthcare economy, has created an ongoing saga of perpetual crisis.
1. Medscape Medical News 2005. Available at: www.cdc.gov/ncidod/hip/PublicReportingGuide.pdf. Last accessed Nov. 15, 2005.
2. National Committee for Clinical Laboratory Standards. Performance standards for antimicrobial susceptibility testing-14th informational supplement, approved standard M 100-S14. Wayne (PA): The Committee; 2004.
3. Villegas MV, Quinn JP. An update on antibiotic resistant gram negative bacteria. Infectious Medicine 2004;212(12):595-599.
4. Kollef MH, Leeper, KV Jr. Prevention of infection due to antibiotic-resistant bacteria. Accreditation Council for Continuing Medical Education (ACCME), May 20, 2005.
5. Wenzel RP, Sahm DF, Thornsberry C, et al. In vitro susceptibilities of gram-negative bacteria isolated from hospitalized patients in four European countries, Canada, and the United States in 2000-2001 to expanded-spectrum cephalosporins and comparator antimicrobials: implications for therapy. Antimicrob Agents Chemother 2003 Oct;47(10):3089-3098.
6. National Nosocomial Infections Surveillance (NNIS) Summary Report. October 2004. Division of Healthcare Quality Promotion, National Center for Infectious Diseases, Centers for Disease Control and Prevention, Public Health Service, U.S. Department of Health and Human Services, Atlanta, Georgia.
7. Thomson KS. Thomson KS. Controversies about extended-spectrum and AmpC beta-lactamases. Emerg Infect Dis 2001 Mar-Apr;7(2):333-336.
8. Clinical Laboratory Science Institute (CLSI/NCCLS). Performance standards for antimicrobial susceptibility testing. 15th edition, M100-515. CLSI/NCCLS, Wayne, PA, 2005.
9. Goossens H. Resistant bacteria in Europe: evolving toward the level in the United States? Highlights of the 15th European Congress on Clinical Microbiology and Infectious Diseases. 2005. Available at: www.medscape.com/viewarticle/504969 (registration required).
10. Wong ES, Rupp ME, Mermel L, et al. Public disclosure of healthcare-associated infections: the role of the Society for Healthcare Epidemiology of America. Infect Control Hosp Epidemiol 2005 Feb;26(2):210-212.
11. Spellberg B, Powers JH, Brass EP, et al. Trends in antimicrobial drug development: implications for the future. Clin Infect Dis 2004 May 1;38(9):1279-1286.
Cynthia Schofield is retired from the VA San Diego Healthcare System. The author would like to acknowledge the VA San Diego Healthcare System, microbiology department, and Joshua Fierer, chief of infectious diseases, with particular thanks to Janice Kaping, supervisor, and Tracey Grosser, MT(ASCP).