Burkholderia cepacia complex

Authors: David A. Pegues, M.D.

MICROBIOLOGY

The taxonomy of Burkholderia (formerly Pseudomonascepacia complex currently consists of 18 distinct bacterial species with a wide environmental distribution in soil and plants, especially the underground stem (rhizome) (Table 1) (6373) . B. cepaciacomplex species are obligate aerobic gram-negative rods that do not ferment glucose and are catalase positive. The organism can proliferate under conditions of minimal nutrition and can survive in the presence of certain disinfectants.

EPIDEMIOLOGY

Although B. cepacia complex strains are frequently isolated from the natural environment, common environmental species are infrequently associated with human infection. Historically regarded as an organism of low pathogenicity, B. cepacia complex can be transmitted person to person in both healthcare and non-healthcare settings, and both direct and indirect contact with infectious secretions and droplet spread have been implicated in transmission (2531323963).  B. cepacia complex can survive for long periods in water or disinfectants, and healthcare-associated outbreaks of B. cepacia complex infection have been linked to contaminated nebulized and intravenous medications and solutions, including compounded and commercially distributed products, skin care products, disinfectants, and to inadequate disinfection of reusable medical devices (20474958).

B. cepacia complex emerged in the late 1970s as a cystic fibrosis respiratory pathogen, associated with accelerated decline in pulmonary functions and reduced survival, especially among those with more advanced lung disease or who had undergone lung transplantation (161934).  According to the U.S. Cystic Fibrosis Foundation’s 2012 National Patient Registry, 2.6 percent of all persons with cystic fibrosis were infected with B. cepacia complex compared to 3.1% in 2005 (1). The prevalence increases with age and varies widely between cystic fibrosis centers. In the United States, B. multivorans and B. cenocepacia account for ~70% of patient isolates, and the incidence of new infection with B. multivorans relative to B. cenocepacia has increased in recent years (40).  In comparison, in Canada and some European countries, B. cenocepacia is the predominant species. Molecular typing and epidemiologic investigations support person-to-person transmission of B. cepacia complex during hospitalization, while attending ambulatory clinics, and during social gatherings (254057).  Transmission is facilitated by prolonged close contact between cystic fibrosis patients, sharing of equipment and personal care items, and by bacterial virulence factors. Transmission of B. cepacia complex among cystic fibrosis patients has been reduced in recent years by stringent infection prevention and control efforts, supported by the finding that the majority of new B. cepacia complex infections involve acquisition of unique strains likely from independent environmental sources (63).

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CLINICAL MANIFESTATIONS

B. cepacia complex has been associated with both sporadic infections and outbreaks in hospitals and other health-care settings, including device-associated bloodstream infection in immunocompromised patients (454756), lower respiratory tract infection, particularly associated with nebulized medications and mechanical ventilation (273855), urinary tract infection, neonatal meningitis and brain abscess (29), wound infection, peritonitis, septic arthritis, and ocular infections. B. cepacia complex is an important cause of chronic respiratory infection among persons with cystic fibrosis (40) and of pneumonia, septicemia, and soft tissue abscesses among persons with chronic granulomatous disease (5259).  Among persons with cystic fibrosis, B. cepacia complex is associated with five clinical syndromes: transient colonization; persistent colonization without clinical deterioration; persistent infection with clinical deterioration similar to that seen with Pseudomonas aeruginosa infection; persistent infection with frequent exacerbations and marked clinical deterioration; and the “cepacia” syndrome with persistently positive blood cultures and death.

LABORATORY DIAGNOSIS

B. cepacia complex grow well on standard laboratory media, and isolation from clinical specimens with mixed respiratory flora is enhanced by use of selective media, such as BCSA, OFPBL and PC agar ). Of these, BCSA agar is the most useful in supporting the growth of B. cepacia complex and suppressing the growth of other organisms. B. cepacia complex isolates are frequently misidentified in the clinical laboratory by conventional manual biochemical or automated testing methods. In contrast, MALDI-ToF instruments can correctly identify most B. cepacia complex isolates to the species level, although 23.1% of isolates were not correctly identified related, in part, to close genetic homology  (21) . Confirmation of identification, speciation, and molecular typing of epidemiologically important B. cepacia complex isolates should be performed at a reference laboratory.

PATHOGENESIS

B. cepacia complex form biofilms in vitro and in vivo in the lungs of cystic fibrosis patients, potentially contributing to reduced antimicrobial susceptibility, treatment failure and persistent infection (950) . Compared to MICs for planktonic B. cepacia complex isolates, biofilm inhibitory concentrations are substantially higher for most β-lactam agents (9). Other putative virulence factors, include regulated gene expression by quorum sensing, exopolysaccharide production associated with the mucoid phenotype that promotes evasion of the host response and persistence, and lipopolysaccharide that contributes to immune-mediated tissue damage. There is an inverse correlation between the quantity of mucoid exopolysaccharide production by B. cepacia strains and rate of decline in cystic fibrosis lung function, likely related to increased surface expression of virulence factors in non-mucoid strains (76) . Epidemic transmission of B. cenocepacia strains among both cystic fibrosis and non-cystic fibrosis patients has been associated with two genetic markers, cable pilin subunit (cblA) that promotes respiratory colonization by binding the abnormal cystic fibrosis respiratory mucin (66)  and the transcriptional regulator Burkholderia cepacia epidemic strain marker (BCESM) (43). However, the low frequency of both markers suggests that other factors are involved in B. cepacia complex virulence and transmissibility.

The pathogenicity of B. cepacia complex in persons with chronic granulomatous disease appears due to the ability of the organism to resist neutrophil-mediated non-oxidative killing and to induce neutrophil necrosis (859). Clinical isolates from the same B. cepacia complex species display different virulence phenotypes likely related to differential expression of virulence factors that promote intracellular survival. In contrast to chronic B. cepacia complex infection in persons with cystic fibrosis that typically is associated with persistence of a single strain type, recurrent B. cepacia complex infection in persons with chronic granulomatous disease is usually caused by a new strain (26).

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SUSCEPTIBILITY IN VITRO AND IN VIVO

Single Drug

B. cepacia complex strains are intrinsically resistant to a wide range of antimicrobial agents, including aminoglycosides, polymyxin, first and second generation cephalosporins, and carboxypenicillins (5154) . Antimicrobial agents that are effective against B. cepacia complex in vitro include trimethoprim-sulfamethoxazole, ceftazidime, carbapenems, ureidopenicillins, fluoroquinolones, minocyline, and chloramphenicol. The antibacterial activity of cefoperazone/sulbactam is comparable to that of ceftazidime against B. cepacia complex and both compounds are more active than cefepime or cefaperazone (22).  Meropenem and doripenem have greater activity in vitro against B. cepacia complex than imipenem or ertapenam (111267).  Temocillin, a 6-a-methoxy derivative of ticarcillin, has orphan drug status for the treatment of B. cepacia complex infection in Europe and is more active in vitro than meropenem and ceftazidime (72).  Aztreonam is poorly active in vitro against B. cepacia with MIC50 values ranging from 32 mg/mL to128 mg/mL (2440).  Of fluoroquinolones, clinafloxacin has the greatest activity against susceptible and efflux-mediated multidrug-resistant B. cepacia complex strains  (74) .  Tigecycline is variably active in vitro due to efflux-mediated resistance and clinical experience is limited (1248).

Resistance to β-lactam agents is most commonly mediated by constitutively expressed or inducible chromosomal β lactamases or efflux pumps (68). The variable ability of novel b-lactamase inhibitors to restore the in vitro activity of ceftazidime may be related to the relative prevalence of b lactamase- versus efflux-mediated resistance in clinical B. cepacia complex isolates (50). Less commonly, resistance is due to plasmid-mediated β-lactamases of the TEM class (cephalosporinases) or to alterations in the penicillin-binding proteins that confer piperacillin resistance. Resistance to β-lactam drugs also can be increased in vitro by incubation in 5% CO2, a condition that may mimic the milieu of the cystic fibrosis lung (17).

Emerging resistance to carbapenems and trimethoprim-sulfamethoxazole are of increasing clinical concern, especially among cystic fibrosis patients with B. cepacia complex respiratory infection where only 26% and 5% of over 2600 strains tested were susceptible to these two agents, respectively (75).  Carbapenem resistance is conferred metallo-β-lactamses that are particularly effective in hydrolyzing imipenem or to efflux pumps (68).  Resistance to trimethoprim is mediated by production of dyhydrofolate reductase or acquisition of outer membrane antibiotic efflux pumps that confer cross resistance to chloramphenicol and fluoroquinolones (7).

Intrinsic resistance of B. cepacia complex strains to aminoglycosides and polymyxin results from decreased site-specific drug binding of these cationic drugs to lipopolysaccharide, reduced outer membrane permeability, and efflux pumps. One specific species,B. vietnamiensis, is susceptible to aminoglycosides but resistant to other polycationic antimicrobials. In cystic fibrosis patients with B. vietnamiensis pulmonary infection, aminoglycoside or azithromycide therapy has been associated with emergence of aminoglycoside resistance via induction of active drug efflux  (33).  Efflux-mediated tobramycin resistance can potentially be overcome in the lung alveoli by efficient delivery of tobramycin inhalation powder by a podhaler device (21).

B. cepacia complex isolates from patients with cystic fibrosis are generally substantially more resistant than are isolates from non-cystic fibrosis patients, a finding that likely reflects the both prior parenteral, oral, and nebulized antimicrobial exposure and differences in the distribution of the B. cepacia complex species among the patient populations (41).  In the few studies that compared B. cepacia complex isolates from cystic fibrosis and non-cystic fibrosis patients, the cystic fibrosis isolates were less susceptible to all antibiotics tested, including carbapenems, ceftazidime, chloramphenicol, fluoroquinolones, piperacillin, and trimethoprim-sulfamethoxazole (3765).  Meropenem, ceftazidime, minocycline, temocillin, and piperacillin/tazobactam appear to have the greatest activity in vitro against B. cepacia complex isolates from patients with cystic fibrosis (Table 2) (75).  Among cystic fibrosis patients, pan-resistant B. cepacia complex isolates are of increasing concern. In a study of 119 multidrug-resistant B. cepacia complex isolates from 59 patients in 17 geographically dispersed cystic fibrosis centers, 50% of the isolates were resistant to all single drug and 8% to all two-drug combinations tested (3). In a larger and more generalizable study of approximately one-third of US cystic fibrosis patients harboring B. cepacia complex, 18% of strains were resistant to all single agents tested (75).

Despite in vitro susceptibility, antimicrobial agents are very ineffective in eradicating chronic B. cepacia complex pulmonary infection from patients with cystic fibrosis (62).  This discrepancy between in vitro susceptibility and the clinical response may be due to a variety of factors in cystic fibrosis patients including: altered pharmacokinetics, failure to deliver drug to the bronchiectatic lung, failure to penetrate across the bronchial mucosa in sufficient concentration into abnormally viscous bronchial secretions, high colony counts of organisms (>107 cfu/mL), biofilm resistance, and local factors such as decreased pH and increased concentration of divalent cations that impair phagocytic activity in the lung. Attempts to eradicate new B. cepacia pulmonary infection, typically with a combination of intravenous and nebulized antimicrobials, are increasingly used, particularly at UK adult cystic fibrosis centers (30).  These efforts are unsuccessful in the majority of cases, and spontaneous clearance of early infection can also occur, confounding interpretation of early eradication therapy.

Combination Drugs

Because of intrinsic and acquired resistance of B. cepacia complex strains from cystic fibrosis patients, combination antimicrobial susceptibility testing has become widely performed although evidence of clinical efficacy is lacking (375).  Typically, broth micro- or macrodilution checkerboard MIC testing has been utilized to identify synergistic and bactericidal antimicrobial combinations against B. cepacia complex strains. Checkerboard MIC testing using two-drug combinations appears to have limited utility in designing treatment regimens for cystic fibrosis patients with multiply-resistant B. cepacia complex (1875).   Among 2,621 B. cepacia complex isolates from US cystic fibrosis patients, synergy was uncommon (range, 1% to 15% of isolates per two-drug combination) and antagonistic combinations were identified for up to 9% of isolates (75).  The use of combinations of e-test strip and breakpoint combination susceptibility testing are simpler and more rapid methods to assess synergy for two-drug combinations against B. cepaciacomplex and have good correlation with but also the same potential clinical limitations as checkerboard MIC testing (4670).

Multiple-combination bactericidal testing (MCBT) allows rapid bactericidal determination for up to three drug combinations using 12 antibiotics arranged in 298 total combinations in microtiter trays (2).  The triple antimicrobial combination of meropenem, high-dose tobramycin (200  µg/mL, achievable by aerosol administration), and a third antibiotic were bactericidal against 81%-93% of 191 multidrug-resistant B. cepacia complex isolates from cystic fibrosis patients (2).  Using this method, antagonism was common (47%) for two drug combinations, especially meropenem-tobramycin, but could be overcome by adding a third drug. Instructions on how to ship bacterial isolates for MCBT can be obtained by emailing cheomcbt@cheo.on.ca. In a more recent report, the three-drug combination of high-dose tobramycin, meropenem, and a third agent—either piperacillin-tazobactam, ceftazidime, trimethoprim-sulfamethoxazole, or amikacin, was active in vitro against half of 47 multidrug-resistant biofilm-grown B. cepacia complex isolates (18,).

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ANTIMICROBIAL THERAPY

Drug of Choice

Clinical studies comparing the various agents in the treatment of B. cepacia complex infection are largely limited to uncontrolled case series, especially among patients who do not have cystic fibrosis (438).  A recent systematic review of patients with B. cepacia complex infection treated with systemic antimicrobials other than trimethoprim-sulfamethoxazole included 8 cohort studies with 125 patients both with and without cystic fibrosis found that ceftazidime and meropenem were the most effective agents (4).  Cure was reported in 77.8% (42/54) of patients receiving ceftazidime [4 studies; monotherapy (33 patients), combination therapy (21 patients)] and 66.7% (11/15) of patients treated with a carbapenem [2 studies; meropenem monotherapy (9 patients); imipenem + ceftazidime (6 patients)]. Given the many methodological limitations of the primary studies, data is insufficient to determine the relative clinical efficacy of these agents or the benefit of combination therapy for serious B. cepaciacomplex infection.

Based upon in vitro susceptibility data, meropenem, ceftazidime, piperacillin, temocillin, and trimethoprim-sulfamethoxazole have the greatest activity against B. cepacia (Table 2). Data from synergy studies and the potential for emergence of resistance while on monotherapy suggest that therapy of serious B. cepacia complex infection should include at least two parenteral antimicrobial agents administered at standard doses. The choice of agents should be guided by results of in vitro susceptibility testing, and the duration of therapy should be based upon assessment clinical and microbiologic response. For serious infection with susceptible strains, a two-drug combination of parenteral trimethoprim-sulfamethoxazole (5 mg/kg trimethoprim component every 6-12 hr) plus a β-lactam (e.g., ceftazidime, piperacillin, meropenem) or a fluoroquinolone should be utilized. For serious infection with trimethoprim-sulfamethoxazole-resistant strains or sulfa drug allergy, combination therapy guided by in vitro susceptibility results should be administered.

Special Situations

Cystic Fibrosis

Each year, approximately 3% of all US patients with cystic fibrosis have B. cepacia isolated from respiratory secretions, almost all of whom are previously colonized with mucoid Pseudomonas aeruginosa (63).  Pulmonary infection of cystic fibrosis patients with B. cepacia complex most often results in chronic endobronchial colonization with a large numbers of organisms (107cfu/mL). Despite the low prevalence of B. cepacia complex infection among cystic fibrosis patients, the organism has a major impact on morbidity and mortality (139), especially when associated with epidemic strains that may be enhanced in virulence  (34).

Patients with cystic fibrosis experience periodic exacerbations of pulmonary infections that are typically manifested by increased pulmonary symptoms and sputum production and decline in pulmonary function. A 2011 systematic review did not identify any randomized trials of therapies for treating pulmonary exacerbations in cystic fibrosis patient chronically infected with B. cepaciacomplex, concluding that clinicians must continue to assess each patient individually, taking into consideration in vitrosusceptibility results, previous clinical response, and clinical experience (73).  Typical therapy for exacerbations associated with B. cepacia complex includes 14-21 days of parenteral therapy with at least two antimicrobials, intensified chest physiotherapy to promote airway clearance, and bronchodilator administration (60). For treatment of pulmonary exacerbations for susceptible strains of B. cepacia complex two-drug therapy is recommended with meropenem (40 mg/kg IV every 8 hours) plus one of the following: tobramycin (10 mg/kg IV once daily) or amikacin (20 mg/kg IV once daily); ceftazidime (50 mg/kg IV every 8 hours; or trimethoprim-sulfamethoxazole (5 mg/kg trimethoprim component every 12 hours)  (13).

The clinical impact of combination antimicrobial therapy against B. cepacia complex has been studied most commonly in small, uncontrolled series of cystic fibrosis patients and assessment of clinical response potentially was confounded by co-infection with P. aeruginosa (4).  In a prospective open-label study of combination therapy, 14 cystic fibrosis patients with pulmonary exacerbations associated with B. cepacia complex were treated with 14 days of meropenem 40 mg/kg IV up to 2 gm every 8 hours and tobramycin every eight hours (adjusted to achieve a peak >8 mcg/mL and trough <2 mcg/mL) (6). Treatment was associated with a small but significant improvement from baseline in pulmonary function (13% improvement in FEV1% predicted), clinical status, and a mean 1.8 log reduction in sputum bacterial burden. No meropenem resistant B. cepacia complex strains were cultured at the end of treatment compared to 5 of 14 strains resistant to meropenem before therapy. This study emphasizes that antimicrobials to which B. cepacia complex strains are resistant as single agent in vitro may have clinical benefit in treating chronic endobronchial infection when used in combination.

In a large, prospective randomized trial, use of MCBT to guide combination antimicrobial therapy did not result in better clinical and bacteriologic response compared to standard culture and sensitivity testing in a group of 251 patients with routine exacerbations of cystic fibrosis associated with multiply-resistant bacteria, including 21.5% with B. cepacia complex (3). Whether MCBT is of benefit for guiding therapy in the subset of the sickest patients who have failed to improve after a course of empiric antimicrobial therapy cannot be determined from this trial. Despite these findings, based upon the goals of reducing bacterial density, virulence factor production, and airway inflammation and potentially limiting the risk of emergence of resistance on therapy, cystic fibrosis patients with pulmonary exacerbations associated with B. cepacia complex should receive combination therapy. For patients with multidrug- or pan-resistant B. cepacia complex strains, two- or three-drug combination bactericidal therapy should be utilized, especially for severe infections. Drug selection should be guided by MCBT testing to avoid the substantial risk of antagonism with two-drug combinations (2) . Temocillin has been used as salvage therapy for multidrug-resistant B. cepacia infection. In an uncontrolled, retrospective study, combination therapy with temocillin (mean dose 4 gm/day) and an aminoglycoside for 14 days resulted in objective improvement in clinical status and pulmonary functions in 18 (56.2%) of 32 treatment courses administered to 20 cystic fibrosis patients with B. cepacia complex infection (36). However, eight patients died during therapy, including three in whom the strain had become resistant during therapy.

The role of maintenance oral therapy in reducing the incidence of exacerbations of pulmonary infections associated with B. cepacia complex has not been defined. Trimethoprim-sulfamethoxazole (children: 4-5 mg/kg trimethoprim component every 12 hours; adults: 160 mg trimethoprim and 800 mg sulfamethoxazole every 12 hours) has been recommended when oral therapy is used (2360).  For patients colonized with trimethoprim-sulfamethoxazole-resistant strains, oral minocycline (4 mg/kg initial dose followed by 2 mg/kg twice a day) or doxycycline (5 mg/kg initial dose followed by 2.5 mg/kg twice a day) may have some clinical benefit, but emergence of resistance and toxicity, including dental and skin discoloration, are of concern (3559).

Chronic Granulomatous Disease

B. cepacia complex also has emerged as an important cause of infection among patients with chronic granulomatous disease, in part related to the ability of the organism to resist neutrophil-mediated non-oxidative killing (59).  Because B. cepacia survives intracellularly, it may be difficult to isolate and to identify early in the course of invasive infection in patients with chronic granulomatous disease. It is important to consider B. cepaciacomplex, especially in cases of culture-negative pneumonia. The initial empiric antimicrobial regimen for with invasive infections in a patient with chronic granulomatous disease should include trimethoprim-sulfamethoxazole (5 mg/kg trimethoprim component every 6 hours) and ceftazidime or a similar agent with broad spectrum antimicrobial activity. Prophylactic antimicrobial therapy benefits patients with chronic granulomatous disease, and oral trimethoprim-sulfamethoxazole (children: 4-5 mg/kg trimethoprim component every 12 hours; adults: 160 mg trimethoprim and 800 mg sulfamethoxazole every 12 hours) is the regimen of choice.

Other Special Situations

Data is limited on the treatment of central nervous system infections with B. cepacia complex, but based upon in vitro susceptibility and pharmacokinetics, meropenem may be a particularly useful agent for this indication. Optimal management of B. cepacia complex infection associated with indwelling medical devices, including central venous catheters and central nervous system shunts, requires removal of the device in addition to directed antimicrobial therapy (5356).

B. cepacia complex is often resistant in vitro (MIC >256  mg/mL) to concentrations of tobramycin achieved by nebulization of solution (54). Although high-dose nebulized tobramycin is often synergistic in vitro with one- or two-additional drugs based on MCBT results, evidence of clinical efficacy is lacking (2). Delivery of tobramycin inhalation powder by the podhaler device results very high sputum concentrations (up to 2000 mg/gm), which may overcome some of this resistance (61). A clinical trial of tobramycin inhalational powder in cystic fibrosis patients infected with B. cepacia complex is pending enrollment as of August 2014 (clinicaltrials.gov identifier NCT02212587).

A recent placebo, controlled trial of 24 weeks of continuous nebulized aztreonam for chronic B. cepacia complex pulmonary infection in cystic fibrosis found no benefit in improving pulmonary function tests or other clinical or microbiologic endpoint (69). In addition, at 24 weeks the B. cepacia MIC50 increased 4 fold compared to baseline in the nebulized aztreonam arm but was unchanged in the placebo arm. Although the concomitant use of non-study antibiotics in both arms may have confounded the results, current evidence does not support the use of nebulized aztreonam for prevention or treatment of pulmonary exacerbations associated with B. cepacia complex respiratory infections in cystic fibrosis.

Strategies that alter membrane permeability or decrease drug efflux have been investigated for the potential treatment of B. cepacia complex infection. Nebulized amiloride or verapamil inhibit the B. cepacia multidrug-resistance efflux pump, and both appear to potentiate the effect of tobramycin in vitro (1415). However, in two small, uncontrolled series, the continuous use of nebulized amiloride four times daily and nebulized tobramycin twice daily for up to 6 months eradicated B. cepacia complexin only 1 of 29 cystic fibrosis patients with chronic pulmonary infection (571). Fosmidomycin is an antibacterial and antiparasitic agent that inhibits isoprenoid biosynthesis, a precursor to hopanoids that are involved in membrane stability.  Although B. cepacia complex are highly resistant to both fosmidomycin and colistin in vitro, fosmidomycin decreased the colistin MIC up to 64-fold to as low as 8 mg/mL in checkerboard MIC assays, a concentration achievable by inhalational therapy (44).

Two recent studies examined the efficacy of B. cenocepacia-specific phage therapy in a mouse model of pulmonary infection. In the first, systemic phage therapy delivered intraperitoneally was more effective than intranasal delivery in reducing pulmonary bacterial density and inflammatory markers (10). In contrast, other investigators found aerosol phage delivery was associated with significant reductions in pulmonary bacterial loads whereas intraperitoneal delivery was not (64). These differences potentially were related to the more widespread and uniform particle delivery to the lungs by aerosolization compared to intranasal administration and to the aspiration of intranasal phage particles into the stomach. Aerosol phage therapy warrants additional study in the treatment of multidrug-resistant B. cepacia complex pulmonary infection.

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ENDPOINTS OF THERAPY

Among cystic fibrosis patients, objective response to therapy for exacerbations of pulmonary infection associated with B. cepaciacan be monitored by improved pulmonary functions, decreased inflammatory markers such as white blood count, ESR, and c-reactive protein, and weight gain. Compared to treatment of exacerbations associated with P. aeruginosa, a decrease in of the density of B. cepacia in the sputum is limited, and eradication of chronic endobronchial B. cepacia infection is rarely achieved. Although information about the treatment of pulmonary B. cepacia infection in cystic fibrosis therapy is limited, several conclusions can be drawn: 1) multidrug-resistant strains and frequent in vitro antagonism between agents make empiric therapy problematic; 2) bactericidal, two-or three-drug antimicrobial combinations should be administered with choice of agents guided by a combination susceptibility testing method; and 3) clinical response may be observed in the absence of bacteriologic response.

PREVENTION AND INFECTION CONTROL

Epidemic transmission of B. cepacia complex among persons with cystic fibrosis has most commonly been associated with B. cenocepacia strains, including ET12 (dominant in eastern Canada and the United Kingdom), PHDC (prevalent in the US mid-Atlantic region) and the Midwestern clone (39). Recently, B. delosa strain SLC6 caused a large outbreak of B. cepacia complex infection among pediatric and adult patients at a large US cystic fibrosis care center (34). These epidemic strains may be more transmissible or better adapted to cause human infection and have been associated with poorer clinical outcome  (1734).

Recommendations to prevent transmission of epidemiologically important pathogens among patients with cystic fibrosis were updated recently (63).  In addition to observing contact and standard precautions when caring for a cystic fibrosis patient who is coughing and infected with B. cepacia complex, segregation of patients with B. cepacia complex from other cystic fibrosis patient in inpatient, ambulatory care, and social settings is recommended.

CONTROVERSIES, CAVEATS, AND COMMENTS

Although much has been learned recently about the taxonomy, epidemiology and pathogenicity of B. cepacia complex, particularly among cystic fibrosis patients, further investigation is needed to define differences in pathogenicity, transmissibility, and antimicrobial susceptibility of B. cepacia complex, the relationship between in vitro susceptibility and clinical response to therapy, the role of novel parenteral and inhaled agents and local host factors in treating endobronchial infection, and the optimal selection of agents for two- and three-drug combination therapy. Development of new agents with in vitro and in vivo activity against B. cepacia complex remain an important goal in advancing the management of patients with B. cepacia complex infection.

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Tables

Table 1. Taxonomy and Sources of Isolation of Burkholderia cepacia Complex Species. Adapted from (63,73)

Species Former genomovar
designation
Habitat
B ubonensis Human (non CF), soil
B. ambifaria VII Human (CF and non CF), soil
B. anthina VIII Human (CF), turtle, soil, plant, water, industrial contaminant
B. arboris Human (CF), turtle, soil, water, industrial contaminant
B. cenocepacia III Human (CF and non CF), soil, plant, water, industrial contaminant
B. cepacia I Human (CF and non CF), soil, plant, water
B. contaminans Human (CF and non CF), sheep, plant
B. diffusa Human (CF and non CF), soil
B. delosa VI Human (CF), soil, plant
B. lateens Human (CF)
B. lata Human (CF and non CF), soil, plant, water, industrial contaminant
B. metallica Human (CF)
B. multivorans II Human (CF and non CF), soil, plant, water
B. pyrrocinia IX Human (CF and non CF), soil, water
B. seminalis Human (CF and non CF), soil, plant
B. stabilis IV Human (CF and non CF), plant, hospital contaminant
B. uronensis Human (non CF), soil
B. vietnamiensis V Human (CF and non CF), soil, plant, water, industrial contaminant

CF = cystic fibrosis

Table 2. Summary of Data From Selected Studies of the In Vitro Activity of Selected Antimicrobial Agents for Isolates of B. cepacia Complex from Non-Cystic Fibrosis and Cystic Fibrosis Patients.

      MIC (mg/mL)  
Agent  Isolate Source Number tested   MIC50   MIC90 MIC Range Ref
Amikacin Cystic fibrosis 59 128 >256 4->256 (42)
Ceftazidime Cystic fibrosis 59 2 >256 0.5->256 (42)
  Non-cystic fibrosis 66 8 64 2-128 (68)
  Reference strains* 38 8 32 2->128 (54)
 Chloramphenicol Non-cystic fibrosis 66 16 64 4-128 (68)
 Ciprofloxacin Cystic fibrosis 59 128 >256 8->256 (42)
Reference strains 38 1 16 <0.25-128 (54)
Colistin Cystic fibrosis 59 >256 >256 16->256 (42)
 Gentamicin Cystic fibrosis 59 128 >256 4->256 (42)
 Imipenem Cystic fibrosis 59 16 64 <0.25-128 (42)
 Levofloxacin Non-cystic fibrosis 66 2 4 0.25-64 (54)
 Meropenem Cystic fibrosis 59 2 8 <0.25-128 (42)
  Non-cystic fibrosis 66 4 16 1-128 (68)
Reference strains 38 4 16 0.5-32 (54)
Minocycline Non-cystic fibrosis 66 1 4 0.5-64 (68)
  Reference strains 38 2 8 <0.25-16 (54)
 Piperacillin Reference strains 38 4 >256 0.5->256 (54)
 Ticarcillin-clavulanic acid Non-cystic fibrosis 66 128/2 >128/2 >128/2 (68)
Tobramycin Reference strains 38 64 256 2-1024 (54)
 Trimethoprim-sulfamethoxazole Cystic fibrosis 59 <0.5/9.5 4 2/38-32/608 (42)
Non-cystic fibrosis 66 <0.5/9.5 1/19 <0.5/9.5-4/76 (68)
  Reference strains 38 4/76 32/608 0.25/4.75->128/2432 (54)

*Reference strains of 17 different B. cepacia complex species

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