European Journal of Cardiovascular Medicine

Ventilator-associated pneumonia (VAP) is defined as pneumonia that arises more than 48–72 hours after endotracheal intubation and mechanical ventilation. It is one of the most common and serious healthcare-associated infections in critically ill patients, accounting for nearly 25% of all ICU-acquired infections [1].

The pathophysiology of VAP involves colonization of the aerodigestive tract and subsequent aspiration into the lower respiratory tract. Several risk factors include prolonged mechanical ventilation, prior antibiotic exposure, severity of underlying illness, re-intubation, and poor infection control practices [2,3].

Antibiotic resistance in VAP pathogens is of growing concern, especially in tertiary care centers where empirical use of broad-spectrum antibiotics is frequent. The emergence of multidrug-resistant (MDR) pathogens such as Acinetobacter baumannii, Klebsiella pneumoniae, and Pseudomonas aeruginosa complicates treatment and increases mortality [4,5].

This study was undertaken to identify the bacterial pathogens involved in VAP and to assess their antibiotic resistance patterns, with a view to guide empirical therapy and inform infection control practices.

Study Design and Setting

A hospital-based, prospective observational study was conducted over 12 months (January 2024–December 2024) in the medical and surgical ICUs of a tertiary care hospital in Northern India.

Inclusion Criteria

• Patients ≥18 years old.
• Intubated and on mechanical ventilation for >48 hours.
• Clinical suspicion of VAP based on:
• Fever >38°C or hypothermia <36°C,
• Leukocytosis (>12,000/mm³) or leukopenia (<4,000/mm³),
• Purulent tracheal secretions,
• New or progressive infiltrates on chest radiograph.

Exclusion Criteria

• Pneumonia diagnosed before mechanical ventilation.
• Patients with immunosuppressive conditions or malignancy.

Sample Collection and Processing

Endotracheal aspirates and/or bronchoalveolar lavage (BAL) specimens were collected using aseptic precautions. Samples were processed within 2 hours of collection. A semi-quantitative culture method was used.

Bacterial Identification and Antibiotic Susceptibility Testing

Bacterial isolates were identified using standard biochemical tests and automated VITEK 2 systems. Antibiotic susceptibility was determined using the Kirby-Bauer disc diffusion method and interpreted as per Clinical and Laboratory Standards Institute (CLSI) 2023 guidelines.

Antibiotics tested included:

• β-lactams (ampicillin, piperacillin-tazobactam)
• Cephalosporins (cefotaxime, ceftazidime, cefepime)
• Carbapenems (imipenem, meropenem)
• Aminoglycosides (gentamicin, amikacin)
• Fluoroquinolones (ciprofloxacin, levofloxacin)
• Colistin and tigecycline

MDR was defined as resistance to at least one agent in three or more antimicrobial classes.

Ethical Consideration

The study was approved by the Institutional Ethics Committee. Informed consent was waived due to the observational nature of the study.

Table 1: Demographic and Clinical Characteristics of VAP Patients (n = 150)

Inference:
Most patients affected by VAP were elderly males with significant comorbidities. The average ventilation duration suggests a critical illness burden. The mortality rate (27.3%) underscores the clinical severity and impact of VAP in ICU settings.

Table 2: Distribution of Bacterial Isolates (n = 134)

Inference:
The predominance of Acinetobacter baumannii and Pseudomonas aeruginosa highlights their importance in ICU-acquired infections. These are well-known for their MDR profiles, warranting vigilant infection control and treatment strategies.

Table 3: Antibiotic Resistance Pattern of Acinetobacter baumannii (n = 47)

Inference:
Acinetobacter baumannii exhibits extensive resistance to most conventional antibiotics, including carbapenems. Colistin remains the most effective agent, with tigecycline showing partial efficacy. This pattern indicates a crisis of limited therapeutic options.

Table 4: Resistance Pattern of Gram-negative Bacteria Combined (n = 118)

Inference:
The majority of Gram-negative isolates demonstrate high resistance to key antibiotic classes. The low resistance to colistin may reflect its limited usage or preserved activity, but caution is required due to potential nephrotoxicity and emerging resistance.

Table 5: Methicillin Resistance in Staphylococcus aureus (n = 8)

Inference:
MRSA was found in 75% of the S. aureus isolates, indicating the need for empirical MRSA coverage in suspected Gram-positive VAP. However, the absence of vancomycin resistance provides some reassurance regarding treatment options.

This study underscores the alarming rate of multidrug resistance among pathogens isolated from VAP patients. The most common isolates were Acinetobacter baumannii and Pseudomonas aeruginosa, which aligns with studies conducted in similar tertiary settings in India and globally [6,7].

Acinetobacter baumannii, notorious for its ability to acquire resistance mechanisms rapidly, showed >90% resistance to carbapenems, confirming its role as a critical MDR organism. This trend mirrors findings by Gupta et al. [8], who reported similar resistance patterns in their multicenter ICU study.

Pseudomonas aeruginosa, although less resistant to carbapenems than Acinetobacter, still posed a challenge due to its inherent resistance and ability to develop efflux pumps and beta-lactamases [9].

Klebsiella pneumoniae, a known ESBL producer, exhibited high resistance to third-generation cephalosporins and moderate resistance to carbapenems. The emergence of carbapenemase-producing strains is a growing public health threat [10].

The presence of MRSA in 75% of S. aureus isolates further complicates empirical treatment strategies. However, vancomycin and linezolid remained effective against MRSA in this study, which is consistent with other Indian ICU reports [11].

Colistin retained its efficacy against most Gram-negative isolates, yet its toxicity profile and potential for future resistance stress the need for judicious use [12]. Tigecycline was moderately effective but not universally reliable, especially in bloodstream infections.

The overall ICU mortality of 27.3% is comparable to global VAP-related mortality rates ranging from 20–50% [13]. Inappropriate initial antibiotic therapy has been strongly linked to increased mortality, emphasizing the role of local antibiograms in guiding empirical regimens [14].

The study highlights the critical need for:

• Antibiotic stewardship programs,
• Implementation of VAP prevention bundles,
• Routine surveillance of resistance trends,
• Education and training of ICU staff on infection control practices.

This study revealed a high prevalence of MDR pathogens among VAP patients in our tertiary ICU. Acinetobacter baumannii, Pseudomonas aeruginosa, and Klebsiella pneumoniae were the predominant isolates with alarming resistance profiles. Continuous monitoring of resistance patterns, strict infection control, and evidence-based antibiotic use are essential to manage VAP effectively.

This study reveals a disturbing prevalence of multidrug-resistant organisms, particularly Acinetobacter baumannii, Pseudomonas aeruginosa, and Klebsiella pneumoniae, among patients diagnosed with VAP in the ICU. The patterns of antibiotic resistance observed suggest a dwindling arsenal of effective antimicrobial agents, with colistin and tigecycline often remaining as the last lines of defense.

Our data demonstrate that:

• More than 80% of Gram-negative isolates are resistant to cephalosporins and fluoroquinolones.
• Carbapenem resistance is alarmingly high, particularly among Acinetobacter and Klebsiella strains.
• Colistin retained good in-vitro activity, although its use must be cautious and reserved for confirmed MDR infections.
• A significant proportion (75%) of Staphylococcus aureus isolates were MRSA, highlighting the importance of covering for MRSA in empirical regimens.

These findings stress the urgent need for robust antimicrobial stewardship, the implementation of VAP prevention bundles, and regular surveillance of local resistance trends to guide empirical therapy. Training and awareness for ICU staff, timely microbiological evaluation, and rational antibiotic prescription based on antibiogram data should form the backbone of any VAP control program.

Ultimately, the battle against VAP and antimicrobial resistance is one of vigilance, science-based protocols, and collaboration between microbiologists, intensivists, and infection control teams. The findings of this study contribute valuable local data that can inform both policy and clinical practice in tertiary care ICU settings.

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