Microbial Pattern of Tracheal Aspirate in Tracheostomized Patients in a Tertiary Care Center and Its Clinical Implications

Aerobic Organisms Isolated In Aspirate

In the present study P. aeruginosa is the most common organism isolated in tracheal aspirate specimens on day 1 and day 8, post tracheostomy followed by K. pneumoniae and Citrobacter species. S. aureus which was found on day 1 specimens was not isolated on day 8. Enterococcus species and MRSA were isolated only on day 8. The isolation of aerobic gram-negative bacteria (AGNB) increased from 21 (75%) on day 1 to 25 (86%) on day 8 of the aspirate. The aerobic gram positive cocci (GPC) which includes S. aureus, Coagulase negative Staphylococcus, MRSA, and Enterococcus species reduced from six (21%) to four (14%) of isolates from day 1 to day 8 post tracheostomy. P. aeruginosa persisted in six (20%) of the patients from day 1 to day 8. K. pneumoniae and Enterococcus species persisted in one (3%) of patients.

In a study conducted by Koirala et al. in 2010, P. aeruginosa and enteric gram-negative bacteria (Escherichia coli, K. pneumoniae, Klebsiella oxytoca, and Enterobacter cloacae) were most predominant followed by S. aureus, other gram negative bacteria, and Viridans streptococci. The P. aeruginosa constituted 27 (40%) of the total 67 isolates. The K. pneumoniae was 11 (17%) and the other enteric gram-negative bacteria were 16 (24%). Hence the total aerobic gram negative bacteria was 54 (81%) which correlates well with the present study. The S. aureus was present in seven (10%) isolates as compared to three (11%) in the present study on day 1 but the same was not seen on day 8 with increase in duration of tracheostomy.⁸

In a study conducted by Siddiqui et al. in 2011, P. aeruginosa and K. pneumonia were the predominant organisms (32 and 28% respectively) which correlate with the present study. MRSA was isolated in three (6%) of patients as compared to one (4%) patient in the present study.⁹

Studying 101 individuals in a surgical intensive care unit after a recent tracheostomy, Bryant et al. found that 94 had lower-airway colonization with potential pathogens, most often with P. aeruginosa or other EGNB.¹² Brook conducted a 1 year survey of less acutely ill tracheostomized pediatric patients with severe neurologic disease, using biweekly tracheal cultures and all of 27 patients had a microflora, again most often consisting of P. aeruginosa and other EGNB. When P. aeruginosa was present, it remained in the tracheal aspirates longer than any other organism and could not be eradicated by aminoglycoside therapy.⁴

A national nosocomial infections study conducted in United States reported that aerobic gram-negative bacilli (AGNB) cause more than 60% of nosocomial chest infections of which P. aeruginosa is the most common organism.¹³

The possible reason for the predominant aerobic gram-negative bacterial colonization (AGNB) of lower airways could be that macrophages are thought to release elastase in response to these underlying chronic diseases. The elastase is subsequently released in saliva and denudes the mucosa of fibronectin, making receptor sites available for aerobic gram-negative bacilli.¹⁴ The fibronectin also possesses attachment sites for community bacteria, including S. pneumoniae and S. aureus. ¹⁵

Antimicrobial Sensitivity Pattern of Aerobic Organisms from Tracheal Aspirate

In the present study P. aeruginosa, the most common organism in tracheal aspirate, was 100% sensitive to Piperacillin + Tazobactum on day 1 but was 71% sensitive on day 8. The sensitivity to Amikacin was 70% on day 1 and 56% on day 8. The organism showed 100% resistance to amoxicillin + clavulanate on both day 1 and day 8. Antibiotics like ciprofloxacin (63 and 57%), Ceftazidime (67 and 55%), and Levofloxacin (67 and 34%) showed intermediate sensitivity to P. aeruginosa on day 1 and day 8. Gentamicin showed 63 and 60% sensitivity to P. aeruginosa on day 1 and day 8 following tracheostomy, respectively. There was an overall decrease in sensitivity of P. aeruginosa even to the most effective antibiotics available.

In the present study K. pneumonia, the next most common organism showed 67% sensitivity to Piperacillin on day 1 whereas on day 8 it was only 37% sensitive to Piperacillin + Tazobactum. The organism showed 100% sensitivity to Amikacin on day 1 but became 50% sensitive on day 8. It was 100% resistant to amoxicillin + clavulanate combination on day 1 and day 8. The organism was 100% sensitive to Levofloxacin on day1 but reduced to 37% on day 8. Meropenam had 100% sensitivity on day 1 and day 8 following tracheostomy.

In a study conducted in India in 2009 by Goel et al. transtracheal or bronchial aspirates from 207 patients admitted to the ICU were cultured, identified, and antibiotic sensitivity was performed by standard methods. The resistance patterns observed by them were almost similar to the present study especially for P. aeruginosa and K. pneumonia.¹⁶

In another study conducted in India by Gagneja et al. the authors observed a changing trend in the antibiotic susceptibility pattern over 5 years in gram negative bacilli (GNB). In the study during phase I, high level of resistance was observed to ampicillin (97–98%), cefuroxime (90–93%), gentamicin (79–80%), and amikacin (70–71%) against all the GNB, so during phase II some new drugs such as ceftriaxone, ceftazidime, and amoxicillin-clavulanic acid were added to the panel for GNB other than P. aeruginosa. For P. aeruginosa, other additional drugs tested were ofloxacin, piperacillin, piperacillin/tazobactam, netilmycin, and aztreonam. They observed an alarming increasing trend of resistance to third-generation cephalosporins and amoxicillin/clavulanic acid during phase II (2006–2009). During 2006–2007, piperacillin and piperacillin/tazobactam were found to be relatively effective against P. aeruginosa with susceptibility ranging from 52.95 to 55.89%, but susceptibility rapidly decreased to 20.99 and 23.46%, respectively, in 2008–2009. Another important observation of this study was increasing sensitivity trend of aminoglycosides against majority of GNB. During phase I, almost 70–80% of isolates were resistant to aminoglycosides, whereas during phase II about 50–60% isolates were resistant to aminoglycosides.¹⁷

In a study conducted at Kathmandu by Koirala et al. in 2010, P. aeruginosa were most sensitive to the Amikacin (n = 22, 81.4%) and Ciprofloxacin (n = 19, 70.3%). All pseudomonal isolates were resistant to the Cefotaxime. Enteric gram-negative bacteria (EGNB) were most sensitive to Amikacin and Chloramphenicol (20, 74.0%) and all were resistant to Ampicillin and Cephalexin.⁸

In a study conducted in Pakistan by Siddiqui et al. the highest mean resistance among GNB of tracheal aspirates was noted to be amoxiciclav (augmentin) and cefaclor (100%). The lowest mean resistance of tracheal aspirate isolates was to be piperacillin + tazobactam (7.7%) followed by Imipenam (20.6%), cefoperazone + sulbactum (23.7%), and amikacin (26.3%). MRSA showed 100% sensitivity to vancomycin as well as fusidic acid.⁹

In the present study S. aureus was isolated only on day 1 and it was 100% sensitive to Erythromycin and 50% sensitive to Amoxicillin + Clavulanate and Cotrimoxazole. The organism had 67% sensitivity to ciprofloxacin.

Only one isolate of MRSA was present in the tracheal aspirate on day 8 and it was sensitive only to Linezolid and resistant to all other antibiotics including Vancomycin. This is in contrast to study conducted in Pakistan in 2011 where MRSA showed 100% sensitivity to Vancomycin.⁹

The antimicrobial susceptibility pattern of organisms isolated from the tracheal aspirate showed alarming decrease in the sensitivity to the most effective antibiotics with increase in duration of tracheostomy. The possible reasons could be the hospital acquired resistance and prolonged duration of ICU stay.

Hence a meticulously chosen antibiotic based on evidence based medicine, tracheal aspirate culture along with a broad overview of the systemic condition of the patient is the key to successful management of a tracheostomized patient especially in situations like ICU. However, the importance of a good tracheostomy care should never be underestimated and should not be compromised.

Anaerobic Isolates in Tracheal Aspirate

In the present study there was one isolate of B. fragilis and P. assacharolyticus each on day 1, whereas on day 8, 1 isolate of P. assacharolyticus and Prevotella species each were present. This could be because of pre-existing colonization of the lower airways since these patients were on long-term intubation prior to tracheostomy.

In a study conducted in Baltimore by Bartlett in 1993, 193 cases of pleuropulmonary infections involving anaerobic bacteria were reviewed, the predominant clinical syndromes were aspiration pneumonia, lung abscess, and empyema. Transtracheal aspiration was the procedure most commonly used to obtain uncontaminated specimens for anaerobic culture. The dominant pathogens were Peptostreptococcus, Bacteroides, Prevotella, and Fusobacterium species. Although clindamycin is widely considered to be the antibiotic of choice, proper therapeutic trials would probably prove many antibiotics to be effective for the treatment of anaerobic pleuropulmonary infections.¹⁸

In a study conducted in Chicago by Verma the author suggested that anaerobic organisms play a major role in pleuropulmonary infections. Implicated pathogens are usually of endogenous origin. Laboratory diagnosis of anaerobic pleuropulmonary infections is based on recovering the etiological agent from clinical specimens. Appropriate specimens include pleural fluid, transtracheal aspirates, transthoracic aspirates, and fiberoptic bronchoscopic aspirates. Collection and transport of uncontaminated specimens is crucial to the recovery of the causative agents which was meticulously followed in our present study. Evaluation of a Gram’s stain of clinical material provides a guide to initial therapy. Pigmented and nonpigmented Prevotella species, Fusobacterium nucleatum, Peptostreptococcus species, and Bacteriodes species are the most commonly recovered anaerobes in pleuropulmonary infections. Successful treatment of anaerobic pleuropulmonary infections requires a combination of antibiotic therapy and surgical interventions. The author also suggested that routine susceptibility testing of recovered isolates is rarely warranted.¹⁹ We also do agree with this opinion of the author.