Microbes have the incredible ability to quickly respond to antibiotic pressures by developing various mechanisms of resistance. It is with increasing regularity that we read about the "super bugs" such as MRSA, VRE, and multiply resistant M. tuberculosis that are spreading throughout our communities and healthcare facilities. Multiple drug resistance is also becoming more common among enteric Gram negative rods.
Since the introduction in the late 1980s of extended-spectrum beta-lactam antibiotics that include the 3rd and 4th generation cephalosporins, as well as extended-spectrum penicillins such as ticarcillin and piperacillin, there has been a steady increase in resistance to these broad spectrum agents. This resistance is caused by the production of Extended-Spectrum Beta-Lactamase (ESBL) enzymes. While ESBL production is exhibited most frequently by E.coli, Klebsiella spp., and Proteus mirabilis, other Gram negative rods may also produce ESBLs.
MuirLab Microbiology routinely screens for and confirms the presence of ESBL for all clinically significant E.coli, Klebsiella spp., and Proteus mirabilis. For those isolates that are confirmed as having ESBL, the interpretation for all penicillins, cephalosporins and aztreonam are changed to Resistant even though these drugs may appear to be effective with in vitro testing. Cephamycins such as cefoxitin and cefotetan are not affected by ESBLs, although there are resistance mechanisms aside from ESBL that may cause these drugs to be ineffective as well.
ESBLs are of significant concern to infection control practitioners at acute care hospitals and long term care facilities because ESBL resistance is transmitted via plasmids from one organism to another, and thus, from one patient to another. ESBL producing Gram negative rods are generally treated with carbapenems (e.g., imipenem and meropenem), or with fluoroquinolones (e.g., levofloxacin and ciprofloxacin); however, there is every indication that resistance to these agents is also increasing.
This table lists the percentage of isolates that have been confirmed as ESBL producers at MuirLab Microbiology within the past few months.
|Patient location||% of E.coli that produce ESBL||% of Klebsiella spp. that produce ESBL||% of Proteus mirabilis that produce ESBL|
|Skilled nursing facility||10.1%||13.8%||3.9%|
|Acute care hospital||2.7%||13.4%||5.8%|