resistant” isolates. When using antibiotics with a wide “toxic/therapeutic ratio,” i.e., beta-
lactams, many “relatively resistant” or resistant GNBs may be effectively eradicated at most
body sites with usual or higher doses. An infectious disease consultation can be useful in
properly interpreting the subtleties of susceptibility testing vis-a-vis achievable antibiotic
optimizing antibiotic therapy dosing to assess the probability of eradication of MDR GNB
isolates at infected sites (1–6).
THE MAJOR PROBLEMATIC MDR GRAM-NEGATIVE BACILLI (GNBs)
IN CRITICAL CARE
MDRP. aeruginosa
Epidemiological Considerations
P. aeruginosais a water-borne aerobic GNB. In the CCU environment, it is a common colonizer
of body fluids, i.e., respiratory secretions, wounds, irrigation solutions, and urine.P. aeruginosa
in the CCU commonly colonizes fluids used in the CCU, i.e., intravenous fluids, irrigation
fluids, nebulizer fluids; therefore,P. aeruginosais prevalent in the CCU aquatic environment.
With the exception of nosocomial pneumonia (NP),P. aeruginosais a highly virulent organism;
it has limited invasive ability in non-immunocompromised hosts. Excluding NP, also known
as hospital-acquired pneumonia (HAP) or in ventilated patients known as ventilator-
associated pneumonia (VAP),P. aeruginosaonly causes infection in neutropenic patients,
those with chronic bronchiectasis/cystic fibrosis, and those with extensive burn wounds.
P. aeruginosa nosocomial urosepsis not uncommonly is a complication of urological
procedures/instrumentation.P. aeruginosais not a common cause of IV line infections, skin/
soft tissue infections, central nervous system (CNS) infections, gastrointestinal/pelvic
infections, bone/joint infections. Pseudomonas is not an infrequent colonizer of the urine in
patients with indwelling urinary catheters, i.e.,P. aeruginosacatheter-associated bacteriuria
(CAB). CAB is an example of colonization of the urinary tract and is not a urinary tract
infection (UTI) per se. Pseudomonas may colonize body fluids or other fluids used in the CCU
by person-to-person or fomite transmission.P. aeruginosastrains that colonize the CCU may be
of the sensitive or MDR variety (1,2).
Non-MDRP. aeruginosaisolates are usually susceptible to one or more aminoglycosides,
anti-pseudomonal penicillins, anti-pseudomonal cephalosporins (cefoperazone or cefepime),
azthreonam, anti-pseudomonal penicillins, and meropenem and carbapenems, excluding
ertapenem. MDRP. aeruginosamay be defined as aP. aeruginosaisolate resistant to three or
more different classes of antibiotics to which it is normally susceptible. MDRP. aeruginosa
strains may occur as the result of mutation and be spread clonally within the unit. These
strains should be identified as such and their spread limited by effective infection-control
containment measures. Ultimately, MDR resistance may be antibiotic mediated using “high
resistance” potential anti-pseudomonal antibiotics extensively in the CCU, i.e., imipenem,
ciprofloxacin, ceftazidime. The therapeutic approach for non-MDRP. aeruginosausually can be
treated effectively with various “low resistance” potential anti-P. aeruginosaantibiotics. In
contrast, MDRP. aeruginosais a definite problem because, by definition, there are few
antibiotics effective against such pan-resistant strains (1,2).
Aside from preferentially using “low-resistance” potential anti-P. aeruginosaantibiotics in
preference to “high-resistance” potential anti-P. aeruginosaantibiotics, the next most important
therapeutic consideration is to avoid using antibiotics to treat antibiotic colonization.
Colonization is more difficult to eradicate than infection. The reason for this is that colonizing
strains exist in sites where the concentration of antibiotics may be subtherapeutic. All other
things being equal, subtherapeutic concentrations of antibiotics are more likely to predispose
to resistance than our supra therapeutic concentrations. If at all possible, avoid treating
colonization versus infection. It is important to differentiate colonization from infection to
avoid needless antibiotic use (3–6).
Nosocomial Pneumonia (NP)/Ventilator Associated Pneumonia (VAP)
The typical CCU dilemma is in evaluating the clinical significance ofP. aeruginosaisolates in
respiratory secretions of ventilated patients. Because it is well known that the single most
514 Cunha