ABSTRACT

Corresponding Author:
Dr. Chithra Jayaprakash,
Associate Professor,
Department of Microbiology,
MOSC Medical College, Kolenchery,
Ernakulam-682311, Kerala.
E-mail: chithrasc@yahoo.com

ABSTRACT

BACKGROUND

Lower Respiratory Tract Infections (LRTIs) is one of the leading infective health problems worldwide. The inappropriate use of antibiotics for these infections has led to a dramatic increase in antibiotic resistance among the respiratory pathogens. The choice of antibiotics for the treatment of LRTIs has become limited.

AIM

To isolate the bacterial pathogens from the lower respiratory tract specimens, identify them and elaborate their antibiotic susceptibility profile using disc diffusion method.

METHODS

During the study period, 54 respiratory samples (27 sputum and 27 endotracheal secretions) were processed by following standard methods. The bacterial isolates were identified by standard biochemical reactions and their susceptibility testing done by Kirby-Bauer disc diffusion method. The results were interpreted as per CLSI (Clinical and Laboratory Standards Institute) guidelines.

RESULTS

Out of the 54 samples processed, 31 yielded significant growth (57.4%). Only gram-negative bacterial pathogens (37 isolates, 68.52%) were obtained during the study. The most common bacterial pathogen isolated was Pseudomonas aeruginosa (32.43%), Klebsiella pneumoniae (27.03%) ranking second; 59.45% of the bacterial isolates were multidrug resistant. The overall susceptibility of the gram-negative isolates was highest for colistin (94.11%) followed by tigecycline (71.40%) and co-trimoxazole (64.70%). 22 (59.46%) bacterial isolates were multidrug resistant.

CONCLUSION

The study yielded only gram-negative bacterial isolates, susceptibility being highest for colistin. Regular determination of the type of bacterial pathogens and their antibiotic resistance trends must be followed in every institution to aid in better patient management by helping the clinician in the judicious use of antibiotics.

KEYWORDS

Bacterial Pathogens, Lower Respiratory Infections, Drug Resistance.

INTRODUCTION

Lower Respiratory Tract Infections (LRTIs) are one of the main infective causes of morbidity and mortality in the world.⁽¹⁾ LRTIs though common in the general population, occur most frequently among patients in Intensive Care Units (ICUs). The LRTIs include bronchitis, bronchiectasis, bronchiolitis, emphysema, lung abscess, pleural effusion and pneumonia. Each type of LRTI vary in the epidemiology, pathogenesis, clinical presentation, and outcome.⁽²⁾ The factors that contribute to the rising incidence of LRTIs in hospitals include underlying lung diseases, diabetes mellitus, malignancy, immunosuppressant drugs, inappropriate

DISCUSSION

Many studies have reported male predominance in LRTIs.^(12,16) In our study, 40 samples were from male patients (74%) and 14 from female patients (25.9%). In a study by Purti et al⁽²⁾ 67.74% of the respiratory samples were from male patients and 32.26% from females. Shrestha et al⁽¹⁷⁾ also reported a predominance of male patients in their study. Majority of accepted samples were from inpatients (94.4%). This is in accordance with a study by Purti et al⁽²⁾;81.48% patients received at least one antibiotic prior to sample collection, which might interfere in the recovery of the pathogen if the organism is susceptible; 8 (14.81%) samples did not yield any growth and 13 (24.07%) samples were observed to have no significant growth/normal flora. In the study by Akter et al⁽¹⁶⁾, 50 out of 105 sputum samples yielded no growth and they attributed this to viruses and previous treatment with antibiotics. Mishra et al⁽⁴⁾ also highlighted the finding of culture negativity in their study, imparting this to the use of antibiotics; 57.4% of samples yielded predominant/significant growth of pathogens. The isolation rates are comparatively lower in other studies - 42.2% in a study by Purti et al⁽²⁾,31.2% by Navaneeth et al⁽⁵⁾ and 34.5% by Jethwani et al⁽¹⁸⁾, Navaneeth et al⁽⁵⁾ report that 53.6% of samples in their study yielded normal pharyngeal flora and 15.1% did not yield any growth, whereas Jethwani et al⁽¹⁸⁾ report that 65.5% of samples yielded no growth. In our work, polymicrobial growth was obtained in 6 (11.11%) of samples. This rate can be compared with the finding of Mishra et al (9%).⁽⁴⁾ and Purti et al (13.37%).⁽²⁾

Only Gram-negative bacteria were obtained in our study. Many other studies have obtained the similar results.^{(4,7,17,18,19,20)} The Gram-negative predominance in our study might partly be due to the unequal distribution of patients with community-acquired and hospital-acquired infections and also due to the spread of antibiotic resistance in hospital setting. The most common bacteria isolated in our study were Pseudomonas aeruginosa (32.43%), Klebsiella pneumoniae (27.03%) and Acinetobacter spp. (21.62%), which is similar to many studies.^{(5,8,9,12,17,19,21)} The only possible reason for not recovering Gram-positive bacteria in our study could be the small number of outpatient samples (5.55%). Purti et al⁽²⁾,Ahmed et al⁽¹²⁾,Ramana et al⁽¹⁹⁾ and Egbe et al⁽²²⁾ have reported K. pneumoniae as the predominant isolate in their studies. Mishra et al⁽⁴⁾,Shrestha et al⁽¹⁸⁾ and Jafari et al⁽²³⁾ have P. aeruginosa as the most common bacterial isolate in their works.

Multiple drug resistance is a growing concern among respiratory pathogens, particularly those causing hospital-acquired infections. Of the 37 bacterial isolates, 22 (59.45%) were MDR organisms; 15 out of the 22 MDR organisms were recovered from ICU patients. Faimow and Nahra.⁽¹⁵⁾ state that the highest rates of MDR bacteria are found in the ICUs and

selective pressures from intense antimicrobial exposure contributes to the emergence of MDR bacteria. De-escalation

after receiving the culture and sensitivity reports is also not done in many ICUs, thus compounding the problem. The common MDR isolates in our study were K. pneumoniae (36.36%) and Acinetobacter spp. (36.36%). P. aeruginosa was comparatively more susceptible to antibiotics. Vishwanath et al⁽⁹⁾ conducted a detailed study on MDR Gram negative bacilli causing lower respiratory infections. They had K. pneumoniae and Acinetobacter spp. as the commonest MDR isolates. Another salient issue is the growing predominance of MDR Acinetobacter species in our study (21.62%). Acinetobacter species have emerged as a major cause of healthcare-associated infections, particularly hospital-acquired and ventilator-associated pneumonia.⁽²⁴⁾

Colistin, Carbapenems, Tigecycline and Cotrimoxazole showed the highest in vitro efficacy against the coliform isolates in our study. P. aeruginosa also was highly susceptible to colistin followed by aminoglycosides. Colistin (Polymyxin E) was re-introduced in the context of multiple drug resistance among Gram-negative bacteria and lack of new antibiotics.⁽²⁵⁾ Tigecycline, a glycylcycline antibiotic, has in vitro activity against gram-positive and gram-negative bacteria including drug-resistant bacteria.⁽²⁶⁾ Carbapenems have been used as the last resort for infections caused by resistant Enterobacteriaceae. But Carbapenem-Resistant Enterobacteriaceae (CRE) have now been increasingly reported worldwide.⁽²⁷⁾ Kanj et al⁽²⁸⁾ pointed that aminoglycosides, fluoroquinolones and cotrimoxazole must be used with caution in serious infections even when they are active in vitro.

In a study by Ahmed et al⁽¹²⁾,K. pneumoniae exhibited a higher susceptibility to Imipenem followed by Piperacillin/tazobactam. P. aeruginosa displayed less resistance to fluoroquinolones. In our study, only 30% of K. pneumoniae strains were susceptible to Piperacillin/tazobactam and 60% susceptible to Carbapenem. High rates of resistance to cephalosporins was noticed in several studies.^(12,20) Our observation about cephalosporins match with their findings. This might be due to the extensive use of 3^rd generation cephalosporins in hospitals. P. aeruginosa has 66.66% susceptibility to Meropenem and Imipenem each, whereas all the 8 Acinetobacter spp. were resistant to carbapenems. There are several antibiotic-resistance mechanisms working in P. aeruginosa and Acinetobacter spp. Moreover, high colonisation rates have been observed in the ICU setting, particularly in the respiratory tract.

LIMITATIONS

A distinction between community-acquired and hospital-acquired infections could not be made. A complete data regarding the predisposing conditions could not be collected.

CONCLUSION

Antimicrobial resistance, initially associated with hospital-acquired infections, has now extended into the community also. In intensive care units and critical care units, antibiotic resistance rates are escalating to the point of complete resistance. With strategies such as ‘antibiotic cycling’ and ‘antibiotic stewardship’ gaining much importance now, it has become necessary to conserve the already available antibiotics. Hospitals should have an ‘antibiotic policy’ and facilities for proper monitoring of antibiotic usage along with effective infection control practices to curb the issue of antibiotic resistance worldwide. Moreover, determination of the type of bacterial pathogens and their antibiotic resistance trends aid in better patient management by helping the clinician in the judicious use of antibiotics.

ACKNOWLEDGEMENTS

We acknowledge the ICMR for granting the Short Term Studentship (STS) 2015 (Reference ID 2015-01395). We are thankful to the Dean and to the Management of MOSC Medical College for their encouragement and support. We also thank Dr. Anna Mathew, Research Co-ordinator, MOSC Medical College, for her constant support throughout the study. The contribution of Mr. Saravanan Velusamy (Biostatistician) in statistical analysis is also acknowledged.

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