Pseudomonas aeruginosa is a non-fermentative, aerobic, motile, Gram-negative bacillus belonging to the family Pseudomonadaceae. It was first isolated from green pus in 1882. More than half of all clinical isolates produce the characteristic blue-green pigment, pyocyanin[1] [2]. As an opportunistic pathogen, it frequently causes nosocomial infections, particularly among patients in intensive care units (ICUs). Its ability to survive in environments with limited nutrients, grow at temperatures ranging between 40-42°C, and adhere to medical equipment and hospital surfaces significantly contributes to its pathogenicity, especially in immunocompromised patients[3] [4].

According to the National Nosocomial Infection Surveillance System, P. aeruginosa is the second leading cause of nosocomial pneumonia (17%), the third most common cause of urinary tract infections (7%), the fourth most common cause of surgical site infections (8%), the seventh most frequent pathogen isolated from bloodstream infections (2%), and the fifth most common isolate overall (9%). Antimicrobial therapy remains the primary approach for managing infections caused by various microbial pathogens[5] [6].

The antimicrobial resistance mechanisms of P. aeruginosa include acquisition of resistance genes encoding enzymes such as beta-lactamases and aminoglycoside-modifying enzymes[7]. Biofilm formation further contributes to resistance, especially in pulmonary infections associated with cystic fibrosis. Multidrug-resistant (MDR) strains of P. aeruginosa produce enzymes like extended-spectrum beta-lactamases (ESBLs) and metallo-β-lactamases (MBLs), conferring resistance against beta-lactams and carbapenems. ESBL-producing P. aeruginosa strains emerged in Western Europe in the mid-1980s, and MBL-producing strains were first reported in Japan in 1991. The MDR phenotype is defined by resistance to three or more classes of anti-Pseudomonal antimicrobial agents (carbapenems, fluoroquinolones, penicillins/cephalosporins, and aminoglycosides). The increasing prevalence of MDR P. aeruginosa significantly limits therapeutic options, underscoring the importance of monitoring antimicrobial susceptibility patterns. This study aimed to determine the current antimicrobial susceptibility profiles of P. aeruginosa isolates at GMC, Ongole, Andhra Pradesh.

Study Design: Retrospective study

Study Location: Department of Microbiology, Government Medical College, Ongole, Andhra Pradesh.

Sample Size: A total of 500 clinical samples, including pus (n=223), urine (n=183), sputum (n=60), and blood samples (n=34), were collected and analyzed.

Inclusion Criteria: Patients of all age groups and both sexes.

Exclusion Criteria: Clinical isolates other than Pseudomonas aeruginosa.

Methodology: All clinical samples were cultured on Nutrient Agar, Blood Agar, and MacConkey Agar plates. Plates were incubated overnight at 37°C for 24 hours. Colonies suggestive of Pseudomonas aeruginosa were identified based on colony morphology, pigment production (pyocyanin), characteristic grape-like odor, oxidase positivity, motility, Gram-negative staining reaction, ability to reduce nitrates to nitrites, non-fermentative metabolism, arginine dihydrolysis capability, and growth at 42°C

Antibiotic Susceptibility Testing (AST): The antibiotic susceptibility profiles of identified P. aeruginosa isolates were determined using the Kirby-Bauer disc diffusion method on Mueller–Hinton agar, according to Clinical and Laboratory Standards Institute (CLSI) guidelines. Antibiotic discs from Hi-media were used, which included cefepime (30 µg), gentamicin (10 µg), amikacin (30 µg), piperacillin/tazobactam (100/10 µg), imipenem (10 µg), ciprofloxacin (5 µg), ceftazidime (30 µg), meropenem (10 µg), cefixime (10 µg), cefoperazone/sulbactam (30 µg), piperacillin (30 µg), tobramycin (10 µg), colistin (10 µg) and polymyxin-B (10 µg). Pseudomonas aeruginosa ATCC 27853 strain served as a quality control reference throughout the study.

Pseudomonas aeruginosa producing greenish pigmentation on nutrient agar

Pseudomonas aeruginosa producing NLF colonies

INDOLE- NOT PRODUCED,

CITRATE -UTILISED,

UREA – NOT HYDROLYSED,

TSI -K/K ,NO GAS,NO H2S

Pseudomonas aeruginosa producing greenish pigmentation on AST

Of the total 500 clinical samples analyzed, 256 samples (51%) yielded positive cultures, while the remaining 244 samples (49%) were sterile. Among the 256 positive cultures, 223 isolates (87.1%) were identified as Pseudomonas aeruginosa using standard microbiological techniques.

Antibiotic susceptibility testing revealed varied resistance patterns. The isolates showed significant resistance rates to cefoperazone/sulbactam (65%), cefixime (60%), ciprofloxacin (50%) and ceftazidime (15%). Conversely, high sensitivity rates were observed for polymyxin-B (80%), cefepime (78%), meropenem (75%), tobramycin (70%), piperacillin-tazobactam (68%), amikacin (50%), gentamicin (42%), and imipenem (65%). Detailed antibiogram results are presented graphically to highlight the sensitivity and resistance patterns clearly.

AGE WISE DISTRUBUTION OFCULTURE WISE SAMPLES

Pseudomonas aeruginosa is increasingly recognized as a significant pathogen responsible for healthcare-associated infections globally. In our study, out of 256 positive clinical samples, 223 isolates (87.1%) were identified as Pseudomonas aeruginosa. This prevalence is considerably higher than that reported in other studies, such as those conducted by Alyahawi et al. (9%) [1] and Maharjan (19.6%) [12]. Variability in prevalence rates observed across different studies could be due to diverse geographical locations, patient demographics, hospital infection control protocols, and diagnostic methods used [12,14].

In our study, urine samples accounted for the highest number of P. aeruginosa isolates, followed by pus, sputum, and blood samples. The high isolation rate from urine aligns with previous findings by Shenoy et al. [8] and Harsh et al. [14], who also reported significant isolation from urinary samples. The organism's ability to colonize urinary tracts, especially in patients with indwelling urinary catheters, explains this observation. Additionally, a notable number of isolates from pus samples is consistent with findings by Kaushik et al. [9], highlighting the organism's role in severe wound infections, particularly among burn patients and individuals undergoing surgical procedures.

The observed antibiotic resistance patterns in our study indicate a significant clinical challenge. P. aeruginosa isolates showed high sensitivity to polymyxin-B (80%), cefepime (78%), and meropenem (75%), corroborating results from other studies emphasizing these antibiotics as effective options [11,13]. Conversely, imipenem exhibited notably lower sensitivity (6%), reflecting similar concerns documented by Raja and Singh [13] and Harsh et al. [14], who emphasized the clinical challenge posed by resistance to carbapenems. 

The rising prevalence of multidrug-resistant (MDR) P. aeruginosa isolates necessitates continuous monitoring and periodic antibiotic susceptibility assessments. Such surveillance enables clinicians to adopt targeted antimicrobial therapy, thereby reducing the spread of resistant strains and improving patient outcomes [10,11,14].

In this study, Pseudomonas aeruginosa was successfully isolated from various clinical specimens collected at Government General Hospital, Ongole, Andhra Pradesh, reinforcing its role as a significant opportunistic pathogen within healthcare settings. The antimicrobial susceptibility testing conducted highlighted extensive resistance patterns among the isolates, underscoring the critical and escalating challenge posed by multidrug-resistant P. aeruginosa. The observed resistance, particularly against frequently prescribed antibiotics, emphasizes the urgent need for ongoing surveillance programs, stringent infection control protocols, and cautious, evidence-based antibiotic stewardship. Such measures are essential to effectively manage infections, mitigate the emergence of resistant strains, and enhance patient outcomes.

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