Epidemiological Aspects and Antibiotic Resistance Profile of Pseudomonas aeruginosa in Fann CHNU

Research Article

J Bacteriol Mycol. 2020; 7(1): 1125.

Epidemiological Aspects and Antibiotic Resistance Profile of Pseudomonas aeruginosa in Fann CHNU

Ka R1,2*, Diagne R2, Niang AA1,3, Ndiaye M1, Diop A3, Dièye B3, Dia ML1,3, Sow AI1,3

¹Laboratoire de Bactériologie, CHU de Fann, Dakar, Sénégal

²UFR des Sciences de la Santé, Université de Thiès, Fann, Dakar, Sénégal

³Faculté de Médecine, Pharmacie et Odontologie, UCAD, Fann, Dakar, Sénégal

*Corresponding author: Pr Roughyatou Ka, Laboratoire de Bactériologie, CHU de Fann. BP 15117 Dakar Fann, Dakar, Sénégal

Received: April 09, 2020; Accepted: May 01, 2020; Published: May 09, 2020


Pseudomonas aeruginosa is a gram-negative bacillus, opportunistic pathogen, saprophyte of humid environments in hospitals. This bacteria, naturally resistant to several antibiotics, is often involved in the occurrence of care-associated infections.

P.aeruginosa is notorious for being intrinsically resistant to many structurally unrelated antimicrobial agents. These bacteria is one of those bacteria which are listed in the antimicrobial resistance survey. The objective of our study was to study the frequency of isolation of P. aeruginosa and to determine the evolution of antibiotic resistance in CHNU de Fann between 2012 and 2016. This is a retrospective, descriptive study of strains of Pseudomonas aeruginosa isolated from the Bacteriology Laboratory of Fann’s Hospital. Bacteria were isolated according to current procedures. For each isolated strain, an antibiogram was performed following the recommendations of the CA-SFM. The average number of strains found was 151 per year. Most of them were isolated from patients over the age of sixty. The isolates came mainly from suppurations samples (49.1%) followed by urines (26.8%) and respiratory samples (16.2%). The study of global resistance showed rates of 40.6% for ticarcillin, 36.1% for gentamicin, 22.3% for ceftazidime, 25% for imipenem and 10% for ciprofloxacin. Regarding the sensitivity according to the pathological product, there was no noticeable difference for beta-lactams, whereas for aminoglycosides, isolated strains of blood cultures had higher resistance levels. Pseudomonas aeruginosa is a pathogen that is increasingly isolated in the laboratory. Its many virulence factors and its multi-resistance to antibiotics justify the surveillance that is essential to update the therapeutics protocols.

Keywords: Pseudomonas aeruginosa; Multi-Drug Resistant Bacteria; Antibiotics; Nosocomial Infections; Senegal


Pseudomonas aeruginosa, also known as pyocyanic bacteria, is a non-fermentative, Gram-negative and a rode-shaped bacteria associated with a large variety of infections. It is an opportunistic pathogen, commonly found in the moist environments in the hospital, where it is often involved in the occurrence of nosocomial infections [1].

P. aeruginosa displays natural resistance to a large variety of antibiotics that belong to a broad range of families. This natural resistance is often associated with lower outer membrane permeability, efflux pumps that physically sequester incoming antibiotics and expel them out of the cell [2], or production of antibiotic inactivating enzymes [2]. Hence, antibiotic resistance, acquired through mutational changes or horizontal transfer of antimicrobial resistance genes, have also been described with P. aeruginosa [3]. Moreover, P. aeruginosa induces adaptive antimicrobial resistance by producing a biofilm that act as protective barriers against antibiotic penetration [4,5]. In addition, this adaptive resistance is often associated with generation, in the biofilm, of bacterial persister cells, tolerant to high concentrations of antibiotic, that contribute to the recalcitrance of P. aeruginosa caused chronic infections [6]. The multiplicity of the pathways employed by this bacteria to develop antibiotic resistance could explain the high frequency of the occurrence of acquired antipseudomonal resistance. This P. aeruginosa -mediated antimicrobial resistance could lead to a drastic therapeutic resource limitation drawback as very few or no conventional antibiotics are still effective in infections caused by multiresistant strains of P. aeruginosa [7]. Intriguingly, this hurdle appears difficult to overcome as the discovery of news drug is still very slow whereas the emergence of P. aeruginosa Multi-Drug-Resistant (MDR) strains is overwhelming [8]. Therefore, this bacteria rises a major public health concern and is thus, listed by the World Health Organization (WHO), among the pathogens to be monitored in the context of antimicrobial resistance surveillance [9].

Even though P. aeruginosa is increasingly isolated in the Fann University Hospital’s laboratory, nationwide studies addressing its epidemiological characteristics, its antibiotic susceptibility profile as well as its spread conditions in the hospitals are still lacking in Senegal. Therefore, there is a crucial need to launch studies that address the mechanism that underline this striking phenomenon and its epidemiological aspects. Such studies would rule out the impact of P. aeruginosa mediated antibiotic resistance in patient’s clinical outcomes.

It is in this particular context that we set to conduct this study that aimed at: (i) determining the frequency of isolation of the strains of P. aeruginosa circulating in the Fann University Hospital, (ii) establishing their epidemiological (iii) and their antibiotic susceptibility profiles.

Material and Method

To reach the goals assigned above, we conducted a retrospective cross-sectional study on the strains of P. aeruginosa isolated in the Bacteriology Laboratory of the Fann University Hospital (Dakar, Senegal) from January 2012 to December 2016.


The study was approved by the Institutional Ethics committee of the “Université Cheikh Anta Diop de Dakar”. As the data was collected as part of routine laboratory tests, informed consent was waived. No additional risk was possessed on behalf of the patients and all precautions needed was taken to keep their identification unrevealed.


All patients (inpatients and outpatients) attending the microbiology laboratory of the Fann University Hospital, to whom a cytobacteriological examination was prescribed, during the time of our study, were enrolled.


All the specimens including inter alia suppurations, blood, urine, respiratory specimen, harvested from the patients involved in our study, were used.

Isolation and identification of Pseudomonas aeruginosa

The isolation of the strains from the pathological products was performed by inoculating the clinical samples onto Mueller Hinton (MH) agar (BIORAD) and Eosin Methylene Blue (EMB) selective agar plates (BIORAD). The cultures were then grown at 37°C for 18-24 hours. Subsequent to that, the plates were observed and the bacteria that form big, irregular, flat and translucent single colonies with a green fluorescent pigment which diffuses through the culture medium, and have a syringe-like odor, were assumed P. aeruginosa. To further identify the isolated colonies, to genus and species level, the suspected ones were peaked and used to perform Gram staining, motility test and biochemical tests (oxidase tests, sugar fermentation tests etc.). Ultimately, the aforementioned presumptive isolates were identified as P. aeruginosa based on their cultural and biochemical characteristics.

Susceptibility testing

The susceptibility to antipseudomonal drugs was carried out on Mueller Hinton agar, according to the Bauer-Kirby disc diffusion method [10] with respect to the National Committee for Clinical Laboratory Standards (NCCLS) [10]. To this end, the isolated colonies from the culture conditions described above, were picked and suspended in a tube containing 2-3 ml of a 0.85% sterile saline solution. The turbidity was then adjusted to 0.5 McFarland standards. This preparation was thereafter spread uniformly onto the Mueller Hinton agar (BIORAD) using sterile cotton swabs. The antibiotics discs were placed on the plates following a setting that allows for direct detection of a potential extended spectrum beta-lactamase. These latter were then inverted and incubated at 35-37°C for 16 to 18 hours. Following overnight incubation, a bacterial lawn appeared on the plates with zones of inhibition around the antibiotic discs. The diameters of the inhibition zones were measured and the results were recorded as susceptible (S) intermediate (I) and resistant (R). The data were interpreted according to the 2017 CA-SFM recommendations [10]. A systematic search for extended spectrum beta-lactamase was done using the synergy test.

The following antibiotics all purchased from BIORAD, were used at the indicated concentrations, in our study: Ticarcillin (TIC; 75 μg), Ticarcillin-clavulanic acid (TCC; 75-10 μg), Aztreonam (ATM; 30 μg), Cefepime (FEP; 30 μg), Ceftazidine (CAZ; 10 μg), Ciprofloxacin (CIP; 100 μg), Colistin (CST; 10 μg), Imipenem (IPM; 10 μg), Piperacillin (PIP; 100 μg), Fosfomycin (FOS; 200 μg), Kanamycin (K; 30 μg), Piperacilline+tazobactam (PPT; 30/06 μg), Gentamicine (GN; 10 μg), Tobramycine (TM; 10 μg), Amikacin (AK; 30 μg), Levofloxacin (LEV; 5 μg). P. aeruginosa ATCC 27853 was used as quality control reference strain for the verification of our procedures.

Statistical analysis

Data were collected and analyzed using the Excel and the GraphPad Prism softwares. Discrete variables were expressed as frequencies and percentages. The chi-squared test was used at 5% (P ≤ 0.05) significance level, to compare proportions of categorical variables.



A total of 755 patients with a yearly average number of 148 ± 28 strains were involved in our study. The year 2015 was the year with the highest number of patients (199 patients) registered (Figure 1). Our patients included outpatients (20%; n=152) and inpatients (80%; n=603). Among them, 60.2% (n=455) were males and 39.8% (n=300) were females displaying thereby, a male preponderancy translated into a sex ratio of 1.5. The mean age was 46 ± 16 years with ages ranging from 1 month to 85 years while the median age was 49 years. Hence, 29% (n=219) of the patients were in the 40-60 years age groups while 37.8% (n=283) of the patients aged over 60 years (Figure 2).