Prevalence of Multidrug-Resistant Pseudomonas aeruginosa and Risk Factors for their Infections at Intensive Care Units of a Tertiary Hospital in Southern China

Research Article

J Bacteriol Mycol. 2022; 9(1): 1193.

Prevalence of Multidrug-Resistant Pseudomonas aeruginosa and Risk Factors for their Infections at Intensive Care Units of a Tertiary Hospital in Southern China

Liu J1,4,5, Guo H-W4, Pan Q3, Fu M-Z4, Qiu Y-K4, Wong N-K2 and Huang Y-C4*

1Department of Clinical Laboratory, The First Affiliated Hospital of Hunan University of Medicine, China

2Department of Infection Diseases, Shenzhen Third People’s Hospital, The Second Hospital Affiliated to Southern University of Science and Technology, China

3Shenzhen Key Laboratory of Microbial Genetic Engineering, College of Life Sciences and Oceanology, Shenzhen University, China

4Microbiology Division, Department of Clinical Laboratory, The First Affiliated Hospital of Shantou University Medical College, China

5Department of Clinical Laboratory, Huaihua First People’s Hospital, Huaihua Hospital Affiliated to Nanhua University, China

*Corresponding author: Yuan-Chun Huang, Department of Clinical Laboratory, The First Affiliated Hospital of Shantou University Medical College, No. 57, Changping Road, Shantou, Guangdong, China

Received: December 20, 2021; Accepted: January 24, 2022; Published: January 31, 2022


Pseudomonas aeruginosa (PA) is highly significant opportunistic pathogens causing healthcare associated infections (HAIs) in hospital settings, notably at intensive care units (ICUs). The aim of this study was to retrospectively analyze the infection status, prevalence and antimicrobial resistance (AMR) of PA at ICUs of a tertiary care hospital in southern China during a one-year period (2016) and examine the clinical risk factors for HAIs by PA. Multiple-locus variablenumber tandem-repeat (VNTR) analysis (MLVA) method was employed to analyze clonality of the strains. Our results suggested that the resistance of PA in ICUs were higher than in other wards. In terms of resistance to carbapenems, the resistance gene island (blaOXA-1+blaIMP+ant(2’’)-Ia+aac(6’)-Ib) carried in IntI was a salient feature among AMR genes. While PA infections at local ICUs seemed frequent, there were no obvious trends suggestive of outbreaks. Some epidemic strains have apparently thrived locally for substantial periods, as carriers of major AMR genes and virulence factors. For risk factors for HAIs, inappropriate treatment was found to impact empiric antibiotic therapy of PA infections, especially in the case of carbapenems, where patients often did not get proper treatment during hospitalization of more than 30 days. Multifactor analysis shows that ventilator-associated pneumonia (VAP) was an independent risk factor for increasing the 30-day mortality rate in patients. In addition, the use of antimicrobials, duration of hospitalization and use of mechanical ventilation before isolation were independent risk factors for HAIs.

Keywords: Pseudomunas aeruginosa; Antimicrobial resistance; Virluence; Clinical risk factors; Intensive care units (ICUs)


PA: Pseudomunas aeruginosa; HAIs: Healthcare-Associated Infection; ICUs: Intensive Care Units; MDR PA: Multidrug- Resistant PA; AMR: Antimicrobial Resistance; TTSS: The Type III Secretion System; MV: Mechanical Ventilation; CLSI: The Clinical and Laboratory Standard Institute; VNTR: Variable-Number Tandem-Repeat; MLVA: Multiple-Locus Tandem-Repeat; UPGMA: Unweighted Pair Group Method with Arithmetic Mean; SD: Standard Deviation; HCAI: Healthcare Associated Infection; VAP: Ventilator-Associated Pneumonia


Pseudomunas aeruginosa (PA) represents an important cause of healthcare-associated infection (HAIs) in intensive care units (ICUs) [1,2]. Owing to its extraordinary ability to form biofilm and efficiently develop resistance towards broad-spectrum antibiotics, PA has contributed to significant mortality and morbidity in HAIs and thus a heavy burden to health care systems in developed and developing countries alike, including China [3].

Prevalence of multidrug-resistant PA (MDR PA) is on the rise across the globe, with various mechanisms being attributed to the development of antimicrobial resistance (AMR) in MDR PA. The prevalence rates of MDR PA range between 15% and 30%in some geographical areas [4,5]. Of note, the genes of ant(2”)-Ia and aac(6’)- Ib carried by PA lead to increased aminoglycoside resistance [6], while the class B enzymes MBL (IMP) and class D OXA beta-lactamases were the most common ESBLs reported in PA [4,7]. OprD2 protein forms part of the specific pathway for imipenem to enter into PA, and it has ligand specificity with loci specific binding of the imipenem [8]. Among the multitude of virulence determinants of PA, the type III secretion system (TTSS) has been identified as an important contributor to cytotoxicity and PA invasion during infections [9]. TTSS occurs as four cytotoxin genes (exoS, exoU, exoY and exoT), among which the impact of exoS and exoU on pathogen virulence is deemed crucial, whereas exoY and exoT supposedly have minor effects on virulence. The toxA gene is reputedly a principal virulence factor of this bacterium with ADP-ribosylation activity that could halt host protein synthesis and eventually lead to cell death [10]. The frequency of both toxA & exoS genes has been reported to be significantly higher in MDR PA strains isolates from patients with burnt injuries [11]. Additionally, genes carried by integrons usually encode molecules that mediate a variety of resistance mechanisms. Among integrons found in clinically important Gram negative bacteria such as PA, class 1 integron is most common [12].

In terms of risk factors for HAIs, over-prescription and inappropriate use of antimicrobials in the hospital environment clearly drive the development of antibiotic resistance [13]. Inappropriate empiric antimicrobial therapy adversely affected the outcomes of in patients diagnosed with PA infections [14,15]. In this study, we investigated the prevalence of drug-resistant PA in a coastal region (Chaoshan) of southern China, focusing on carriage status of AMR genes and virulence factors, and related clinical data including risk factors of HAIs with PA.

Materials and Methods

Patients and research settings

Databases at the Microbiology Division, Department of Clinical Laboratory, The First Affiliated Hospital of Shantou University Medical College, Shantou City, Guangdong, China, were reviewed to identify patients with PA infections in three types of intensive care units (namely, comprehensive, cardiovascular, and neurosurgery ICUs) within the period of January to December 2016. For patients with multiple episodes of PA infections, only first episodes were analyzed.

Ethical approval

The ethics committee on medical research of the First Affiliated Hospital of Shantou University had evaluated and approved the experimental design of this study.

Study design and clinical data collection

This study was designed as a retrospective study aiming to determine the prevalence, virulence genes and resistance genes in PA isolates as well as PA infection rates, based on data collected by the Department of Clinical Laboratory. Furthermore, we analyzed the impact of inappropriate therapy on patients with PA infections at the ICUs. The main outcome was patient mortality, measured on the basis of 30-day mortality rates. We also assessed secondary outcomes, including the duration of hospitalization and use of invasive procedures. For each patient studied, the following characteristics were recovered from their clinical records: age, gender, date of hospital admission, treatment outcomes as discharge or death (within 30 days from admission), length of total hospital stay, surgery, invasive procedures such as mechanical ventilation (MV), central venous line, urinary catheter, tracheostomy, haemodialysis, catheter enteral or gastric nutrition, and surgical drain during the current hospitalization, underlying conditions such as diabetes mellitus, chronic renal failure, heart failure and cancer, sources of infection, antibiotic use during the current hospitalization, and cases of inappropriate antimicrobial therapies. Antimicrobial therapy was considered to be “appropriate” if the initial antimicrobials, which were administered within 24 hours of acquisition of a culture sample, included at least one antibiotic that was active in vitro. As a universal consensus considered to be lacking, the definition of antibiotic appropriateness used in this study relies on the authoritative guidelines and previous works elsewhere [16].

Identification of isolates and antimicrobial susceptibility testing

A total of 70 non-duplicated strains of PA were used in this study. All isolates were identified by the VITEK 2 COMPACT system (BioMérieux, France) and antimicrobial susceptibility tests were performed with its assemble kit of AST 09 card with the following antibiotics: aminoglycosides (gentamicin, amikacin, tobramycin), carbapenems (imipenem, meropenem), cephalosporins (ceftazidime, cefepime), fluoroquinolones (ciprofloxacin, levofloxacin), penicillins plus Β-lactamase inhibitors (piperacillin-tazobactam), monobactams (aztreonam). PA strains that showed intermediate susceptibility were considered to be resistant. Quality-control protocols were used according to the 2016 guidelines of the Clinical and Laboratory Standard Institute (CLSI). PA ATCC 27853 was used as a quality control strain.

Characterization of drug resistance phenotypes and genotypes

The presence of virulence genes (including exoS, exoU, toxA), class I integron gene, aminoglycoside resistance genes (including ant(2’’)-Ia, aac(6’)-Ib) and Β-lactamase genes (including IMP, OXA, OprD2) were tested by PCR. All primers were based on previously published works as summarized in Table 1. The amplified gene products were sequenced by Sanger method and compared to the sequences deposited in GenBank ( gene/).