Bacteriological Profile of Endotracheal Aspirates and their Antibiotic Susceptibility Pattern

Early onset Ventilator associated pneumonia (VAP) is usually less severe, associated with a better prognosis, and is more likely caused by antibioticsensitive bacteria. Late-onset VAP, is usually caused by multidrug resistant (MDR) pathogens and is associated with increased morbidity and mortality. Therefore, the local microbial flora causing VAP needs to be studied and appropriate therapy based on the early endotracheal (ET) aspirate culture report can help managing this group of patients. The present study was carried out in the department of Microbiology, JSS Hospital, Mysore from January 2017 to December 2017. Bacterial pathogens and antibiotic resistance pattern of isolates from ET aspirates of patients on mechanical ventilation in Intensive care units were source of data. A total number of 1432 samples were received in the lab for ET aspirate culture. Among these 1432 samples, 1055 showed growth ranging from 10 2to 106 colony forming units/ml (CFU/ml), 124 had no growth at all and 253 had no significant growth (<102 CFU/ml) Out of 1055 isolates,1023 were Gram negative bacteria and 32 were Gram positive cocci . Acinetobacter, Pseudomonas and Klebsiella were the major pathogens in our study. Majority of them being MDR, maximum sensitivity was observed for Tigecycline and colistin in these isolates. Knowledge of causative microbial flora of VAP along with information on the susceptibility patterns will help in selection of the appropriate antibiotic for therapeutic use for better outcome.


INTRODUCTION
Ventilator associated pneumonia (VAP) is a globally known notorious nosocomial infection that occurs more than 48 hours after a patient begins mechanical ventilation (MV)making recovery more difficult for patients who are already critically ill. 1 Early onset VAP is usually less severe, associated with a better prognosis, and is more likely to be caused by antibiotic-sensitive bacteria. Late-onset VAP, is usually caused by multidrug resistant (MDR) pathogens and is associated with increased morbidity and mortality 2,3 . VAP results from microaspiration, which is primary route of bacterial entry into respiratory tract . The ET tube acts as an obstacle to host defences by inhibiting the action of cilia, swallowing, and spontaneous coughing by the patients. Risk factors that are associated with increased incidence of VAP are body position, state of consciousness, enteral nutrition, prior exposure to antibiotics, use of a nasotracheal tube and pre-existing conditions such as acute respiratory distress syndrome 4 .
Typically, diagnosis includes clinical, radiologic and microbiologic evidence of infection. However, the exact criteria for diagnosis varies widely among institutions and thus results in a wide range of reported VAP mortality rates, which is stated to be anywhere from 0-76% 5,6,7 . Many studies from India have investigated the causative organisms of VAP. Pseudomonas species, Acinetobacter species, Escherichia coli, Klebsiella pneumoniae and Staphylococcus aureus are the common pathogens with varying prevalence and quite often being MDR 6,8,9 . Therefore, the local microbial flora causing VAP needs to be studied and an appropriate therapy based on the early ET aspirate report can reduce the mortality and cost in managing this group of patients Aim In view of increasing incidence of VAP and MDR nature of pathogens in our hospital, this study was taken up to detect the bacteriological profile and sensitivity pattern of isolates from Endotracheal aspirates

MATERIALS AND METHODS
The present study was carried out in the Department of Microbiology, JSS Hospital, Mysore, Karnataka, for a period of 1 year from January 2017 to December 2017. This was a prospective study. ET aspirates sent from various intensive care units sent to Microbiology laboratory formed the material of our study

Bacterial identification and isolation
The ET samples received in the Microbiology lab were subjected to microscopy and culture. Gram stain of Lower respiratory tract secretions is an immediate procedure that can guide management and it has a reasonable correlation with culture results Semiquantitative culture was done on blood agar and MacConkey agar and incubated overnight at 37°C for 24 to 48 hrs for bacterial growth and isolation. The isolated organisms were processed with Vitek 2 systems for identification as well as Antibiotic susceptibility testing. Colony count of 10 6 CFUml or more was considered significant for VAP . ET aspirates yielding growth between 10 2 to 10 6 CFU/ ml, whose microscopy revealed moderate to plenty of inflammatory cells were also processed.

RESULTS
A total number of 1432 samples were received in the lab for ET aspirate culture. Among these 1432 samples, 1055 showed growth ranging from 10 2 to 10 6 CFU/ml or more, 124 had no growth at all and 253 had no significant growth (<10 2 CFU/ml) Among 1055 bacterial growth isolates, 377 isolates showed growth 10 6 CFUml or more which is considered significant for VAP and 731 isolates ranging 10 2 to 10 6 CFU/ml.

DISCUSSION
Prompt identification of organisms from ET aspirates in ventilated patients and accurate selection of antimicrobial agents, based on MIC represent important clinical goals in prevention of VAP. Sound knowledge of susceptibility pattern of the locally prevalent pathogens is necessary for choosing the appropriate antibiotics.
In our study, overall, Gram-negative bacilli predominated over Gram-positive cocci. Acinetobacter spp, Klebsiella spp followed by Pseudomonas were the most common isolates identified. Other significant Gram negative isolates were E.coli, Serratia, Stenotrophomonas, Enterobacter, Citrobacter, Proteus and Burkholderia. Among Gram positive organisms Staphylococcus aureus was most common. The antibiogram pattern of isolates showed that Maximum resistance of Acinetobacter spp and Pseudomonas were seen in Aztreonam, Cefipime, Doripenem, Imipenem, Ciprofloxacin, Piperacillin/ Tazobactum. Maximum sensitivity was observed with Colistin, Tigecycline and Minocycline. Our findings were similar to the other studies 6,7,8,9 In last two decades, Gram negative bacteria have become important nosocomial pathogens throughout the world and is a leading problem in treatment owing to its multidrug resistance. Colistin, which is an old antimicrobial agent, is very active against these. Susceptibility to Colistin was reported as 97.9-100% in various studies. There was least resistance to Colistin in our study. It appeared to be a good option apart from Tigecycline, in the treatment of VAP developed with MDR pathogens.

CONCLUSION
We conclude that VAP in mechanically ventilated patients is on rise and has been continually associated with indiscriminate and irrational use of antibiotics which contribute to emergence of drug resistant strains. Knowledge of their causative microbial flora in a local setting along with information on the susceptibility patterns will help in selection of the appropriate antibiotic for therapeutic use and a better outcome. It is clear that Tigecycline and Colistin become the last resort antibiotics in most cases. Within no time in future, we can expect resistance to these antibiotics also making us reach the dead end. Hence, resistance rates should be pursued closely. Newer alternative drugs revealing promising results to solve the problem is the need of the hour.