|Year : 2013 | Volume
| Issue : 3 | Page : 102-106
Bacterial isolates from the bronchoalveolar lavage fluid of patients with pneumonia not responding to initial antimicrobial therapy
Rahul Magazine1, Bharti Chogtu2, Shobitha Rao1, Kiran Chawla3
1 Department of Pulmonary Medicine, Kasturba Medical College, Manipal University, Manipal, Karnataka, India
2 Department of Pharmacology, Kasturba Medical College, Manipal University, Manipal, Karnataka, India
3 Department of Microbiology, Kasturba Medical College, Manipal University, Manipal, Karnataka, India
|Date of Web Publication||22-Nov-2013|
Department of Pulmonary Medicine, Kasturba Medical College, Manipal University, Manipal, Karnataka - 576 104
Background: Patients with community-acquired pneumonia (CAP) who are admitted in a hospital but do not respond to initial antimicrobial therapy pose a challenge to the attending physician. The knowledge of the likely pathogens and their sensitivity pattern can help the clinicians to better manage such cases. Aims and Objectives: To study the spectrum of the bacterial isolates and to determine the antimicrobial sensitivity pattern obtained from the bronchoalveolar lavage (BAL) fluid of CAP patients who did not respond to initial antimicrobial therapy. Setting and Design: A retrospective study of 87 patients who were admitted in the medical wards of a tertiary care teaching hospital in South India with the diagnosis of CAP and were not responding to initial antimicrobial therapy. Materials and Methods: The patient-related data were obtained from the case records and entered on a pre-designed proforma. This included demographic characteristics and reports of relevant clinical tests. The BAL culture and sensitivity results were also noted on the proforma. Results: The mean age of the patients was 49.28 ± 16.61 years (mean ± SD, range 17-80 years). Fifty-seven patients (65.5%) of were male. Also, 98 bacterial isolates were obtained from the BAL fluid of 87 patients. The most prevalent bacterial isolates included Pseudomonas aeruginosa (n = 35, 35.7%), Klebsiella pneumoniae (n = 19, 19.4%), Staphylococcus aureus (n = 15, 15.3%) and Acinetobacter species (n = 11, 11.2%). Most bacterial isolates tested showed 100% sensitivity to meropenem except Acinetobacter species (25%). Conclusion: P. aeruginosa and K. pneumoniae were the most common bacterial pathogens isolated from the BAL fluid. The isolates tested showed 100% sensitivity to meropenem except Acinetobacter species. All the methicillin-resistant S. aureus isolates displayed sensitivity to vancomycin, linezolid and teicoplanin.
Keywords: Antimicrobial sensitivity, bacterial isolates, bronchoalveolar lavage, pneumonia
|How to cite this article:|
Magazine R, Chogtu B, Rao S, Chawla K. Bacterial isolates from the bronchoalveolar lavage fluid of patients with pneumonia not responding to initial antimicrobial therapy. Sahel Med J 2013;16:102-6
|How to cite this URL:|
Magazine R, Chogtu B, Rao S, Chawla K. Bacterial isolates from the bronchoalveolar lavage fluid of patients with pneumonia not responding to initial antimicrobial therapy. Sahel Med J [serial online] 2013 [cited 2020 May 27];16:102-6. Available from: http://www.smjonline.org/text.asp?2013/16/3/102/121914
| Introduction|| |
The distribution of bacterial isolates and their antibiotic sensitivity patterns in patients suffering from community-acquired pneumonia (CAP), healthcare-associated pneumonia or hospital-acquired pneumonia (HAP) have been reported in the literature.  Clinicians are faced with scenarios where patients initially diagnosed with CAP are admitted in the hospital for treatment but do not respond to initial empirical antibiotic therapy.  The possible reasons for this lack of response could be inappropriate choice of antibiotics, acquisition of drug-resistant pathogens from the community or development of superimposed infection due to hospital-acquired pathogens.  This situation is further complicated if either the sputum culture report is inconclusive or the patient does not respond to the antibiotics to which the organisms were reported to be sensitive according to the sputum sensitivity report. In hospitals with bronchoscopy facilities, it is possible to obtain bronchoalveolar lavage (BAL) samples and isolate the specific bacterial pathogen(s) to guide therapy.  This information can help the physicians in understanding the bacterial pathogens. Each healthcare facility will have a different antibiotic sensitivity pattern among the various isolates. This study provides data from our tertiary care hospital.
Aims and objectives
The aims and objectives of this study were:
- To study the spectrum of bacterial isolates obtained from the BAL fluid samples of CAP patients who did not respond to initial empirical antimicrobial therapy
- To study the sensitivity pattern of these bacterial isolates.
| Materials and Methods|| |
This study was conducted at a 2050-bed tertiary care teaching hospital attached to a medical college in South India. The hospital provides health care services to the surrounding urban, semiurban and rural areas. This retrospective cohort study was started after taking clearance from the institutional ethics committee. In our institution, it is mandatory to seek such clearance prior to starting any study. The case records of 129 consecutive in-patients, admitted in medical wards with a diagnosis of CAP, who underwent flexible fiberoptic bronchoscopy (FOB), between 1 January 2009 and 31 December 2012, were accessed from the medical records department of the hospital. The cases of CAP who underwent FOB were identified from the bronchoscopy register maintained in the hospital, and all such cases were screened for inclusion in the study. CAP was defined as per the following criteria: (a) symptoms such as cough with or without expectoration, shortness of breath or pleuritic chest pain for less than 1 week, (b) one or more systemic features (temperature >37.7°C, chills and rigors and/or severe malaise), (c) new focal signs on chest examination (bronchial breath sounds and/or crackles) and (d) new chest X-ray opacity for which there was no other explanation.  Diagnosed cases of CAP having received at least 3 days of antibiotic therapy in the ward without any improvement in clinical condition (i.e. persistence or worsening of initial symptoms and signs as described above), and with the availability of a BAL fluid bacterial culture and sensitivity report, were included in the study. Patients with history suggestive of healthcare-associated pneumonia or HAP prior to admission at our center, admission in an Intensive Care Unit, human immunodeficiency virus infection or patients on immunosuppressive drugs were excluded from the analysis. Using these criteria, 42 patients were excluded from the study. The data of 87 patients who met the study criteria were noted on a pre-designed proforma and were finally used for the analysis. The demographic details regarding age, sex, clinical diagnosis and comorbidities and viral serology (including human immunodeficiency virus, hepatitis B and hepatitis C virus) were recorded. Chest roentgenogram reports were also noted. The bronchoscopy was performed by the physician via the transnasal route using a Pentax video bronchoscope. All the samples were cultured on McConkey agar, sheep blood agar and sheep chocolate agar. Plates were incubated at 37°C overnight. The next day, the growth on the Petridishes was observed and bacterial isolates were identified according to standard protocol. Sensitivity to various antibiotics was assessed using the disk-diffusion method by Kirby-Bauer.  The isolates that were resistant to commonly used antibiotics were tested with reserved antibiotics such as aztreonam, cefoperazone-sulbactum, cefpirome, cefepime, imipenem, meropenem, piperacillin-tazobactum, vancomycin, teicoplanin and linezolid. The data were analyzed using SPSS 16.0 by descriptive statistics and are presented in the form of tables and figures, showing percentages.
| Results|| |
The mean age of the patients was 49.28 ± 16.61 years (range 17-80 years). Fifty-seven patients (65.5%) were male. The patients were subjected to FOB as the sputum culture reports were inconclusive and the patients were not responding to empirical antibiotic therapy. All the cases were being managed in the wards, and all patients had a CURB-65 score of 2 or less. The procedure was performed after Day 3 of starting empirical antibiotics (range 4-6 days). Serology for human immunodeficiency virus, hepatitis B virus and hepatitis C virus was negative for all subjects. The comorbidities seen in the study population were diabetes mellitus [15 (17.2%) patients], hypertension [14 (16%) patients], bronchial asthma [11 (12.6%) patients], chronic obstructive pulmonary disease [3 (3.4%) patients], dyslipidemia [2 (2.3%) patients] and heart disease [2 (2.3%) patients]. The chest radiographs of the subjects showed features suggestive of consolidation on the right side (37%), left side (41%) and bilateral involvement (9%). A total of 98 bacterial isolates were obtained from the BAL fluid of 87 subjects. The spectrum of bacterial isolates obtained from the BAL fluid is shown in [Table 1]. Pseudomonas aeruginosa was the most common isolate obtained. Five (33%) of the 15 isolates of Staphylococcus aureus obtained from the BAL fluid were methicillin-resistant Staphylococcus aureus (MRSA). The empirical antibiotics received by the subjects prior to flexible FOB included ceftriaxone or cefotaxine [79 (91%) patients], azithromycin [51 (59%) patients], levofloxacin or moxifloxacin [11 (13%) patients] and aminoglycoside [21 (24%) patients]. Two antibiotics (which included a cephalosporin) were combined in the prescription of 75 patients and 12 patients were given monotherapy. Patients on empirical monotherapy were given a quinolone (n = 8) or a cephalosporin (n = 4). Antimicrobial resistance among Gram positive and Gram negative organisms in isolates from BAL fluid are shown in [Table 2] and [Table 3], respectively. It was observed that Staphylococcus and Streptococcus isolates showed a high degree of resistance to macroclides. However, all isolates of Staphylococcus were sensitive to second-line antibiotics such as linezolid, etc., All isolates of Streptococcus were sensitive to ciprofloxacin. Most of the Gram negative isolates displayed a high percentage of resistance to beta lactam antibiotics. However, all except Acinetobacter were sensitive to meropenem.
|Table 2: Antimicrobial sensitivity pattern of gram positive isolates from BAL fluid|
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|Table 3: Antimicrobial sensitivity pattern of gram negative isolates from BAL fluid|
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| Discussion|| |
To determine the bacterial etiology and antimicrobial sensitivity patterns, in CAP treatment failures, can help clinicians in managing such cases better. In our study, P. aeruginosa (35.7%) was the most common bacterial isolate followed by Klebsiella (19.4%). In a review of various studies, which were conducted on hospitalized patients admitted with a diagnosis of CAP, it was noted that 82% of the patients had bacterial infection and that Streptococcus pneumoniae was the most common typical bacterium isolated, followed by Haemophilus influenzae.  In a study performed at a medical college in Shimla, India, involving 70 patients of CAP, the investigators observed that the most common isolate was Streptococcus pneumoniae (35.8%), followed by K. pneumoniae (22%) and S. aureus (17%).  Investigators from a tertiary care center in New Delhi studied samples from 124 cases of CAP at the Medicine and Paediatric Department and found that the bacterial pathogens in CAP were Streptococcus pneumoniae (35.3%) S. aureus (23.5%), K. pneumoniae (20.5%) and H. influenzae (8.8%).  Our results are different from that of the above studies, and the reason for this could be the fact that in these studies, routine cases of CAP were included and not the special subset of CAP patients who are treatment failures. Hence, the spectrum and distribution of bacterial pathogens may not be similar to CAP patients who show favorable response to initial antimicrobial treatment. In a study from Spain, investigators have reported that, initially, the most common bacterium cultured from their CAP patients prior to treatment failure was Streptococcus pneumonia, followed by P. aeruginosa. However, after failing treatment, from among a variety of isolated pathogens, P. aeruginosa and Streptococcus pneumoniae were the most common isolates, and both had the same frequency of occurrence. Although P. aeruginosa was the most common bacterium isolated in our study as well, Streptococcus pneumoniae isolates formed only a small fraction of the isolates. 
The isolates of P. aeruginosa in our study had a higher level of resistance to cepahalosporins as compared with the other antibiotics that were tested. It is noteworthy that in our study, all the isolates of P. aeruginosa were sensitive to meropenem.
The fluoroquinolones are widely used in our country for different indications and, in a study from the Indian state of Andhra Pradesh, the overall sensitivity of ciprofloxacin among various isolates has been reported to be 35.5%.  Overall, the ciprofloxacin-sensitive isolates in our study comprised 52 (59.1%) patients. Investigators from Italy have reported that isolates of K. pneumoniae from the respiratory tract showed an increase in carbapenem resistance from 5.3% in 2009 to 38.5% in 2012.  This finding is contrary to the results of our study, with all isolates being sensitive to meropenem.
Seventy-five percent of the isolates of Acinetobacter spp was resistant to meropenem in our study, and this is in contrast to the findings of a retrospective study conducted in the Department of Microbiology in a tertiary care teaching hospital at Rohtak, India, where the investigators reported that the samples obtained from the lower respiratory tract of ventilated patients revealed that 25.6% of the isolates of Acinetobacter species, 22.8% the isolates of P. aeruginosa and 9% of the isolates of Klebsiella species were resistant to meropenem.  This difference could be due to the difference in the site of care of the two study populations. In our study, despite being managed in the wards, patients developed infection with Acinetobacter species, which had a high percentage of carbapenem resistance. It is possible that the isolates of Acinetobater in our study were hospital acquired and hence had a high level of meropenem resistance.
In a study performed at a university hospital in Turkey, the investigators found that among various aminoglycosides, the isolates of Acinetobacter displayed the highest sensitivity (97%) to netilmicin. This is similar to the result obtained in our study, where 80% of the isolates showed netilmicin sensitivity.  One should bear in mind that the two study populations were different. Although all Gram negative isolates were sensitive to meropenem, the fact that there was high level of resistance to Acinetobacter is a worrisome trend.
A study from a hospital in Korea has demonstrated very high levels of resistance to erythromycin and ciprofloxacin among the isolates of MRSA but a 100% sensitivity to vancomycin.  All isolates of MRSA in our study that were tested for sensitivity to vancomycin, teicoplanin and linezolid were found to be sensitive. This is similar to the study of El Amin et al. (2012), who also reported the MRSA isolates from skin and soft tissue infections as being 100% sensitive to these three antibiotics. 
We cannot comment on the usefulness of BAL versus tracheal aspirate in this sub-population of CAP patients as the latter procedure is performed on intubated patients. Moreover, to the best of our knowledge, we could not find a study comparing BAL with tracheal aspirate in CAP patients managed in the wards without mechanical ventilation.
While considering resistance to each antimicrobial among all the isolates put together, we noted that isolates exhibited highest resistance to aztreonam, followed by ampicillin and cephalosporins [Figure 1]. The reason for such high a percentage of beta lactam-resistant organisms could be the frequent use of cephalosporins in the empirical antibiotic regimens. Most of the patients in our study received cephalosporins, and initial resistance to this group of antibiotics could also contribute to treatment failure. At the same time, we could not differentiate between inadequate antibiotics usage and delayed response as a cause of treatment failure. The reason for this was that the initial sputum culture report was inconclusive and hence we did not know the spectrum of the infecting organisms at presentation.
|Figure 1: Overall sensitivity to various antimicrobials among the bacterial isolates|
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The limitation of this study was that the relative contribution of community-acquired and hospital-acquired pathogens to the overall spectrum of bacterial isolates could not be differentiated. However, it is well established that Gram negative pathogens and S. aureus are frequently associated with HAP. Also, the frequency of occurrence of atypical bacterial pathogens was not evaluated in this study.
| Conclusion|| |
Patients admitted in wards with CAP but not responding to initial antimicrobial regimen may predominantly harbor drug-resistant Gram negative organisms. Meropenem can be effective if the isolates do not display sensitivity to other commonly used antimicrobials.
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[Table 1], [Table 2], [Table 3]