Microorganisms Profile and their Antimicrobial Resistance Pattern Isolated from the Lower Respiratory Tract of Mechanically Ventilated Patients in the Intensive Care Unit of A Tertiary Care Hospital in Dhaka

Objective: Aim of the study was to know the microorganisms profile and determine the antibiotic resistance pattern of the LRT isolates from mechanically ventilated (MV) patients admitted to the ICU. This prospective observational study was done in Department of Critical Care Medicine (ICU) of BIRDEM General Hospital Dhaka from July, 2011 to December, 2011. Methods: Blind Tracheal Aspirate or Broncho Alveolar Lavage or both from 110 consecutive patients (total 130 samples) admitted to the ICU requiring MV were cultured, identified, and antibiotic sensitivity was performed by standard methods. Results: A total of 130 samples were analyzed. Growth was obtained in 93.8% of the samples yielding 143 organisms. Many (21 samples) yielded more than one organism. The major organism isolated were Acinetobacter sp. (54.5%), Pseudomonas sp.(14.7%), Klebsiella sp. (7.7%).Candida sp. (7.0%), Staphylococcus aureus(7.0%), Escherichia coli (4.9%).Proteus and Flavobacterium accounted for 4.2% of the isolates. All the isolates were highly resistant (>90%) to cephalosporins and >70% to fluoroquinolones. The frequency of third generation cephalosporin resistant E. coli, Klebsiellaand imipenem resistant Pseudomonas and Acinetobacter were>90%. Acinetobacter was remarkably resistant to most antibiotics including imipenem (>90% resistant) and Piperacillin+Tazobactum (>85% resistant), but most of the members of the Enterobacteriacae group and Acinetobacter showed maximum sensitivity to colistin (80%-100%). Conclusion: Nonfermenters Gram Negative Bacilli (GNB)-Acinetobacter sp. & Pseudomonas sp. are the most common etiological agents of LRT infections in ICU. There is an alarmingly high rate of resistance to cephalosporin and 2β-lactamase inhibitor group of drugs. Colistin was found to be the most sensitive drug against all GNB.


Introduction:
Critically ill patients admitted in ICUs are always at a higher risk of developing nosocomial infections with resistant strains. 1 Patients admitted in ICUs have an increased susceptibility to infection because of decreased mobility and increased use of invasive devices. 2 LRTIs are the most common bacterial infections among patients in ICUs occurring in 10-25% of all ICU patients and resulting in high overall mortality, which may range from 22-71%. 3,4ost common bacterial agents of LRTI in the ICUs are Pseudomonas sp., Acinetobacter sp., Klebsiella sp., Citrobacter sp., Escherichia coli. 5,6,7In almost all cases, there is a need to initiate empirical antimicrobial treatment before obtaining the microbial culture results, but the situation is further complicated by the emergence of multiple beta lactamase producers and MDR pathogens.In a recent report, Infectious Disease Society of America specifically addressed three categories of GNB, namely ESBL producing Escherichia coli, and Klebsiella sp., MDR Pseudomonas sp., and carbapenem resistant Acinetobacter sp., as high priority bacterial pathogens. 8Infections with resistant strains of microorganisms in the ICUs lead to increased mortality and cost. 9All these major reports indicate the need for obtaining data on prevalent strains in the ICU along with the susceptibility pattern, to help in revising antibiotic policy and guiding clinicians for the better management of patients.Prevalent flora and antimicrobial resistance pattern may vary from region to region depending upon the predominant antibiotic use in that locality.Presently, data on pattern of organisms and their antibiotic susceptibility in ICUs of large hospitals of our country are lacking.Therefore, the present study is designed to know the microorganisms profile and determine the antimicrobial resistance pattern isolated from LRT of mechanically ventilated patients admitted to the ICU of BIRDEM General Hospital.

Methods:
It was aprospective observational study done in Department of Critical Care Medicine (ICU) of BIRDEM General Hospital (Tertiary Care Hospital) in Dhaka.July, 2011 to December, 2011.Blind Tracheal Aspirate or Broncho Alveolar Lavage or both from 110 consecutive patients (total 130 samples) admitted to the ICU requiring MV were cultured, identified, and antibiotic sensitivity was performed by standard methods.SPSS software (Version-16) was used for calculation.

Discussion:
Our study included types and antibiotic susceptibility pattern of organisms isolated from the lower respiratory tract of mechanically ventilated patients in the intensive care unit, but it did not attempt to investigate the underlying disease condition of patients or their sources of infection.
In this study, growth was obtained from 93.8% samples (T/ A, BAL) which probably were due to the fact that most patients either had prior respiratory problems or were in ventilators.
Gram negative bacteria were isolated at a significantly higher rate (86%) than gram positive bacteria and Candida.Acinetobacter, Pseudomonas, Klebsiella, E.coliand Candida were the most prevalent pathogens recovered from our ICU patients (Table-II).The predominant bacterial isolates reported in the Jordanian, Indian and European studies were almost similar to our results. 9,10,11,12 Retion in antimicrobial resistance in the ICUs has been a goal for all intensive care units as it improves the outcome and reduces total expenses as well as duration of ICU stay.The extreme antibiotic use results in the emergence of MDR microorganisms in the ICU environment.The present study revealed high prevalence of antibiotic resistant organisms in our ICU.More than 90% Pseudomonas sp.showed resistance to 3 rd generation cephalosporins and >70% resistance to fluoroquinolons.In 2005 & 2006-2007, two study conducted in the same ICU reported >80% of Pseudomonas was resistant to 3 rd generation cephalosporins. 13,14But it has been observed that the frequency of fluoroquinolon and imipenem resistant

Table-III
The antibiotic resistance pattern of major organisms isolated from the lower respiratory tract of mechanically ventilated patients in intensive care unit.

Antibiotics Percent isolates showing antibiotic resistance
Acinetobacter sp Pseudomonas sp Klebsiella sp E.coli Pseudomonas (71.4% and 95.2%) has increased in the present study compared to that of 2005 (48% and 36% respectively).In present study, colistin was the most effective drug (>80%sensitive) against pseudomonas followed by piperacillin+tazobactum combination (>75% sensitive).
In present study, Acinetobactersp was the commonest (54.5%) organism isolated from LRT specimen but in the study conducted in the same ICU in 2006-2007 Acinetobacterwas isolated only 27.5%. 14Though this is commonly isolated from skin and throat of healthy people, it is also known to colonize respirators, respiratory tubing and intravenous catheters in ICU causing serious and often fatal opportunistic infections.They are generally resistant to most classes of antimicrobials and emergence of imipenem resistant strains in many parts of the world is alarming and a threat to the effective management of these infections. 15In our study, Acinetobacterwas remarkably resistant to most antibiotics including imipenem (93.6% resistance) and piperacillin+tazobactum (89.5% resistance) but Acinetobacterand most of the members of the Enterobacteriacaegroup like E.coli, Klebsiella were maximally susceptible to colistin (>98% sensitive).The susceptibility of these bacteria to cephalosporins was uniformly poor in our study (>90% resistant).This was probably due to over use of cephalosporins in the indoor and ICU patients.Resistance pattern of these organisms to aminoglycosides showed marked variability ranging from 57.1% to 100%.
Candida species was the fourth frequently isolated organism in our ICU.Both C. albican and non-albican Candida species were found.High number isolation of Candida might be due to the presence of underlying conditions like poor nutritional status, diabetes mellitus and the use of steroids and broad spectrum antibiotics.

Conclusion
We conclude that GNB are the most common etiological agents of LRTIs in our ICU.Acinetobacter& Pseudomonas species hold the top of the list.There is an alarmingly majority of the isolates showed high resistance to cephalosporins, aminoglycosides & quinolones.Compared to previous two studies, overall resistance pattern of Pseudomonas & Acinetobacter to carbapenem became worse.Colistin was found to be the most sensitive drug against all GNB.The findings of this study might help clinicians to formulate their first line empirical antibiotic treatment regimens for the patients admitted in ICUs and judicious use of antimicrobial agents is essential to prevent the emergence of MDR bacteria in the ICUs.

Table - I
Sample profile and rate of positive culture from lower respiratory tract specimen.
Note: Many samples yielded more than one organism.