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LETTER TO EDITOR  
Year : 2011  |  Volume : 54  |  Issue : 2  |  Page : 432-433
Bacteriology profile among patients with ventilator-associated pneumonia from a medical intensive care unit at a tertiary care center in Mumbai


Department of Microbiology, T. N. Medical College, Mumbai - 400 008, India

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Date of Web Publication27-May-2011
 

How to cite this article:
Set R, Bobade O, Shastri J. Bacteriology profile among patients with ventilator-associated pneumonia from a medical intensive care unit at a tertiary care center in Mumbai. Indian J Pathol Microbiol 2011;54:432-3

How to cite this URL:
Set R, Bobade O, Shastri J. Bacteriology profile among patients with ventilator-associated pneumonia from a medical intensive care unit at a tertiary care center in Mumbai. Indian J Pathol Microbiol [serial online] 2011 [cited 2019 Dec 15];54:432-3. Available from: http://www.ijpmonline.org/text.asp?2011/54/2/432/81622


Sir,

Ventilator-associated pneumonia (VAP) is an important form of health care-associated pneumonia, specifically refers to pneumonia developing in a mechanically ventilated (MV) patient more than 48 h after tracheal intubation or tracheostomy. Due to increasing incidence of multidrug-resistant (MDR) organisms in intensive care units (ICU), early and correct diagnosis of VAP is an urgent challenge for optimal antibiotic treatment. The hypothesis behind the proposed study was to find whether such potential MDR organisms were a threat in our MICU. We also felt that the knowledge of local antimicrobial susceptibility patterns would surely guide the physician in the initial prophylactic treatment planning for patients on MV in our MICU.

The aim of the present study was to assess the incidence of VAP in the 15 bedded MICU of our tertiary care center. This prospective study was done from January to September 2005, enrolling patients undergoing MV for more than 48 h. Endotracheal aspirates (EA) were collected from the patients with suspected VAP, using a sterile mucus extractor and were sent to the microbiology laboratory immediately. A smear was prepared from the purulent portion of the sample and stained by Gram stain for semi-quantitative grading of polymorphonuclear neutrophils. [1] Hundred microliters of the homogenized sample was added to 100 mL of sterile normal saline. Diluted samples were inoculated onto blood agar, MacConkeys agar, and chocolate agar by using a 4-mm nichrome wire loop, which holds 0.01 mL of sample. The plates were incubated overnight at 37°C. The chocolate agar plate was incubated in a candle jar at 37°C. Colony-forming units (CFU) were calculated by counting the number of colonies on the blood agar plate and multiplying it with the dilution factor and the inoculation factor. For definitive diagnosis of VAP, quantitative culture threshold was considered as 10 5 CFU/mL. A Gram-stained smear was prepared from each type of colony. Depending on the smear findings the organism was identified further by standard laboratory methods. [2] Antimicrobial susceptibility testing was done as per CLSI guidelines. All isolates of  Escherichia More Details coli, Klebsiella pneumoniae, and other Gram-negative bacilli were tested for extended spectrum beta-lactamase (ESBL) production by using the CLSI screening test (double disc diffusion method). Ceftazidime (30 μg) and ceftazidime-clavulanic acid (30 μg/10 μg) combination were used for identification of ESBL producers. Metallo-beta-lactamase-producing Pseudomonas aeruginosa were identified by imipenem ethylene diamine tetraacetic acid disc synergy test. [3] All the isolates of Staphylococcus aureus were tested for methicillin resistance by using 1-μg oxacillin disc diffusion test.

A total of 190 samples were collected from 90 patients who were on MV. Of these 90 patients, 25 developed VAP as per the diagnostic criteria used. The incidence of VAP was observed to be 27.77%. Early-onset VAP occurs within the first 4 days of ventilation and late-onset VAP occurs thereafter. Out of 25 VAP patients, 17 (68%) developed late onset, whereas 8 (32%) had early-onset VAP. Dey et al's study shows the incidence of VAP to be 45.4%, which is much higher probably due to comorbid conditions of their patients, the commonly isolated pathogens being Acinetobacter species and P. aeruginosa. [4] In the present study a total of 96 isolates were obtained from the 25 patients diagnosed as VAP. Frequently isolated were either K. pneumoniae constituting 33.33% or P. aeruginosa 31.25% of the isolates. Of the K. pneumoniae, 93.75% were ESBL producers. S. aureus constituted 9.37% of the isolates and all were methicillin-resistant S. aureus (MRSA). In a study by Joseph et al, ESBL were produced by 67% of K. pneumoniae, and 43% of S. aureus were MRSA. [5] In the present study, the patients on ventilation had been administered a combination of second-generation cephalosporin, amikacin, and metronidazole. This explains the predominance of ESBL producers, such as K. pneumoniae, P. aeruginosa, and also MRSA in VAP. This study clearly indicates that previous antibiotic use is a risk factor for VAP by these resistant organisms.

[Table 1] shows the antibiotic resistance patterns of predominant Gram-negative bacilli from cases of VAP. Presently there is concern about the acquisition of plasmid-mediated metallo-beta-lactamases active against carbapenems, anti-pseudomonal penicillins, and cephalosporins. Among the 30 isolates of P. aeruginosa, 3 (10%) were resistant to carbapenems. All the above 3 isolates were metallo-beta-lactamase producers. All isolates of MRSA were resistant to penicillin, gentamicin, cefazolin, and erythromycin. No resistance was seen to vancomycin, teicoplanin, ampicillin sulbactam, and amoxicillin clavulanic acid. The increased resistance pattern among the isolates might be due to inadvertent empirical use of higher antibiotics without the previous knowledge of the organism and also due to transferable ESBL production. This suggests that administration of broad spectrum antibiotics, such as third-generation cephalosporins, leads to the colonization of the respiratory tract of MV patients by the resistant strains of K. pneumoniae, P. aeruginosa, Acinetobacter species, and S. aureus.
Table 1: Antibiotic resistance patterns of predominant Gram negative bacilli from VAP cases

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Therefore, in conclusion, the inadvertent empirical use of broad spectrum antibiotics should be discouraged. The selection of antibiotic treatment should be based on predominant organisms isolated and their antibiotic sensitivity pattern. This will improve the overall antibiotic utilization and will reduce the emergence of MDR organisms.

 
   References Top

1.Albert S, Kirchner J, Thomas H, Behne M, Schur J, Brade V. Role of quantitative cultures and microscopic examinations of endotracheal aspirates in the diagnosis of pulmonary infections in ventilated patients. J Hosp Infect 1997;37:25-37.  Back to cited text no. 1
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2.Koneman EW, Allen SD, Janda WM, Schreckenberger PC, Winn WC Jr. Color atlas and textbook of diagnostic microbiology. 5 th ed. Philadelphia: Lippincott; 1997.  Back to cited text no. 2
    
3.Yong D, Lee K, Yum JH, Shin HB, Rossolini GM, Chong Y. Imipenem EDTA disk method for differentiation of Metallobetalactamase producing clinical isolates of Pseudomonas spp. and Acinetobacter spp. J Clin Microbiol 2002;40:3798-801.  Back to cited text no. 3
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4.Dey A, Bairy I. Incidence of multidrug resistant organisms causing ventilator associated pneumonia in a tertiary care hospital. A nine months prospective study. 2007;2:52-7.  Back to cited text no. 4
    
5.Joseph NM, Sistla S, Dutta TK, Badhe AS, Rasitha D, Parija SC. Ventilator associated pneumonia in a tertiary care hospital in India: Role of multidrug resistant pathogens. J Infect Dev Ctries 2010;4:218-25.  Back to cited text no. 5
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Correspondence Address:
Reena Set
Department of Microbiology, T. N. Medical College, Mumbai-400 008
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0377-4929.81622

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