Antibiotic Resistance Profile of Bacteria Isolated at the Central Laboratory of the National Hospital Center of Nouakchott

Sample Collection

Our samples were collected at the bacteriology laboratory of the Centre Hospitalier National de Nouakchott;

Patients come from all the medical facilities in the city of Nouakchott: private facilities, outpatient clinics and the hospitalization departments of the various hospitals. Study period: Our study was spread over a two-year period from the beginning of January 2020 to the end of December 2021. Type of study: Our study was retrospective. Data were collected from the department’s registers. Sampling: Strains were isolated from a variety of samples: urine, suppuration, genital swabs, puncture fluid and blood cultures. Study population: All patients of either sex and of any age who presented to the above laboratory for antibiotic susceptibility testing during this period. Inclusion criteria: All patients with a positive culture and antibiogram were included in our study. Exclusion criteria:

• All patients with negative culture or incomplete antibiogram.
• Duplicate strains isolated in the same patient from the same anatomical site.
• Incomplete or poor-quality samples.

Bacterial identification: Depending on their nature and site of infection, samples are inoculated onto culture media (CLED, EMB, blood agar, Chapman agar). Identification of bacterial strains was based on morphological, cultural and biochemical characteristics. For biochemical identification, bacterial strains were identified by VITEK® 2 (Biomerieux®) or API 20 E (Biomerieux)® Antibiogram: Antimicrobial susceptibility testing was performed using VITEK® 2 Compact or the agar diffusion technique, in accordance with the recommendations of the French Microbiology Society’s Committee on Antimicrobial Susceptibility Testing (CA-SFM) and the European Committee on Antimicrobial Susceptibility Testing (EUCAST) [4].

Distribution of Germs by Species and Site of Infection

Gram-negative bacteria (GNB) accounted for 78.3% of isolates, while Gram-positive cocci (GPC) accounted for 21.7% of strains. GNB were mainly represented by enterobacteria (98.0%), and Escherichia coli was the most frequently isolated species (54.8%). The Gram-positive cocci were mainly Staphylococcus aureus (17.8%). The 511 strains isolated were distributed as follows: 387 from urine, 99 from suppurations, 18 from vaginal swabs, 5 from punctures and 2 from blood cultures: The distribution of species according to the pathological product is presented in Table I The distribution of germs by infectious site is shown in Table I.

Antibiotic Resistance in Bacteria

Escherichia coli: Antibiotic resistance rates in Escherichia coli strains: The rate of antibiotic resistance in Escherichia coli is shown in Figure 1.

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Antibiotic Resistance Rates of Klebsiella Pneumoniae Strains

The rate of antibiotic resistance in Klebsiella pneumoniae is shown in Figure 2.

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Other Germs

Resistance rates for Enterobacter cloacae, Proteus mirabilis, Serratia marcescens and Citrobacter sp are shown in Table 2.

BLSE-secreting Enterobacteria

Of 392 enterobacterales isolated, ESBL-secreting enterobacterales accounted for 14.5%. The percentage of ESBL strains within each enterobacterium is shown in Table 3.

Pseudomonas Aeruginosa, Acinetobacter Baumannii and Stenotrophomonas Maltophilia

Antibiotic resistance rates for strains of Pseudomonas aeruginosa, Acinetobacter baumannii and Stenotrophomonas maltophilia are shown in Table IV.

Resistance rate of Staphylococcus aureus strains

Staphylococcus aureus resistance rates are shown in Figure 3.

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Streptococcus spp and Enterococcus faecalis Antibiotic resistance rates for Streptococcus spp and Enterococcus faecalis are shown in Table 5.

Enterobacterales Resistance Profile

Of all the enterobacterales (strains) isolated, Escherichia coli was the most frequently isolated species (280/392) or 71.4%, followed by Klebsiella pneumoniae (71/392) or 18.1%. These results were comparable with those reported by Nadmia, et al. in Morocco, where Escherichia coli was the most frequently isolated species (80%), followed by Klebsiella (13%) [7], and with those reported by Nijssen, et al. in Europe, Escherichia coli (3325/5000) followed by Klebsiella pneumoniae (505/5000) [8]. Of the 392 enterobacterales identified, 57 (14.5%) were ESBL-producing strains. Our results were lower than those reported by Zahir, et al. (39%) in Morocco [9], and higher than those reported by Baizet, et al. (5.1%) in France [10]. In our study, the proportion of ESBL-producing strains of Klebsiella pneumoniae (17/71 or 23.9%) was higher than that of ESBL-producing strains of Escherichia coli (37/280 or 13.2%), a result in line with that of Baizet, et al. [10] and that reported by Guillard, et al. [11].

Resistance Profile of Escherichia coli Strains

Amoxicillin and clavulanic acid: Amoxicillin resistance for Escherichia coli was 80.1%. This result was comparable with the result of Hailaji, et al. 2014 in Nouakchott-Mauritania, 82.1% [12]. and 80% the studies of Zahir H, et al. in Morocco

2017 [9].

In the presence of clavulanic acid, resistance fell to 63.9%. Our study showed an increase in resistance compared with the study by Hailaji, et al. where resistance to AMC for Escherichia coli in 3 medical analysis laboratories in the city of Nouakchott, including CHN, in 20014 was 28.2% [12]. This increase in resistance was probably linked to the more frequent use of this antibiotic.

Cephalosporins: In our study, Escherichia coli resistance rates were 63.9%, 18.6% and 26.3% respectively for cefalotin, cefoxitin and cefotaxime. This rate was comparable with that reported by Hailaji, et al. for cefalotin and cefoxitin: 60.9% and 19.8% respectively, and lower than the 18.4% resistance rate for cefotaxime. The number of ESBL-producing strains in our study was 14.0% versus 10.4% in the Hailaji, et al. survey [12].

3rd-generation cephalosporins (C3G) remain active, and resistance is mainly due to ESBL production. However, in terms of antibiotic sparing, they are only indicated for probabilistic treatment of acute pyelonephritis [13].

Carbapenems: Escherichia coli were resistant to imipenem in 0.8% of cases, a result comparable with the 1.0% reported by Hailaji, et al. [12]. Our result was superior to that reported by Baizet, et al. France 2014, who found no imipenem- resistant strains [10].

Carbapenem-resistant enterobacteriaceae are a global concern in both hospital and community settings. Patients with carbapenem-resistant enterobacterial infections are three times more likely to die than patients with non- carbapenem-resistant enterobacterial infections [14] with an estimated mortality of 70% [15]. Rapid and accurate identification of carbapenem-resistant enterobacteriaceae is essential for infection prevention, as well as for guiding appropriate treatment. Once a patient has a confirmed carbapenem-resistant enterobacterial infection, additional precautions, including patient isolation, screening of other at-risk patients and monitoring of the spread of infection are warranted [16].

Aminoglycosides: In our study, the aminoglycosides remained active, mainly amikacin and to a lesser extent gentamicin, with resistance rates of 6.8% and 18.2% respectively. This result was superior to that of Hailaji, et al. 2014 in Nouakchott-Mauritania with a resistance rate of around 1% to amikacin and 13.5% to gentamicin [12]. and that of Smaoui, et al. in Tunisia, with a resistance rate of 1.1% to amikacin and 7.7% to gentamicin [17]. Our results were lower than those reported by Ebongue, et al. 27.5% for gentamicin and 14.1% for amikacin [6].

However, the activity of amikacin was better than that of gentamicin. This result is in line with the findings of some authors Hamouche, et al. [6, 18].

Quinolones: In our study, resistance to nalidixic acid was 41.7%. This result was comparable to the 40.6% reported in the 2014 study by Hailaji et al. in Nouakchott-Mauritania [12]. This rate is higher than 19.4% and 20.9% reported respectively by Garnotel, et al. in France [13]. and Smaoui, et al. in Tunisia [17]. Fluoroquinolones were more active: with a resistance rate of 33.6% for ciprofloxacin. This result was higher than that reported by Hailaji, et al. 28.6% [12], Smaoui, et al. 16.2% [17] and Guillard, et al. 15.9% [11]. Our rates remain low compared with those reported by Goro, et al. 65.92% [19]. Acquired resistance to quinolones is essentially linked to chromosomal mutations [20]. Resistance to fluoroquinolones is cross-linked between the different molecules, but its level of expression can vary for each molecule. Escherichia coli strains sensitive to nalidixic acid are also sensitive to other fluoroquinolones. On the other hand, resistance to nalidixic acid is frequently accompanied by reduced sensitivity to fluoroquinolones. This may correspond to low-level resistance mutants that can easily evolve to high-level resistance under the selection pressure exerted by this class of antibiotics. The appearance of resistance to nalidixic acid therefore appears to be a step in the evolution towards fluoroquinolone resistance, with a consequent risk of therapeutic failure [21].

Cotrimoxazole: Cotrimoxazole, a widely prescribed antibiotic, was resistant in 59.5%. This rate is comparable to 58.4% Hailaji, et al. in Mauritania in 2014 [12]. and lower compared to Fabre, et al. in France 19.3% [22]. The EAU (European Association of Urology) recommendations state that cystitis in men without prostate involvement is rare. Consequently, treatment with prostate-penetrating antimicrobials such as cotrimoxazole and fluoroquinolones is required in men with signs of UTI [23].

Nitrofurans, fosfomycin: In this context, molecules with urinary specificity are of particular interest. Indeed, they are effective: nitrofurans and fosfomycin (resistance 7.2% and 14.1% respectively for the two molecules). This rate was higher than that reported by Fabre, et al. in France (1.9% and 4.3% respectively [22]) and by Smaoui, et al. [17] in Tunisia (1% and 0% respectively. Our results differed from those reported by de Hailaji, et al. in 2014: nitrofurans were resistant in 7.2% versus 38.9% and fosfomycin in 14.1% versus 4.3% [12].

Nitrofurantoin, due to its limited use and highly specific mechanism of action (reduction of NO2 groups, leading to bacterial DNA damage), prevents cross-resistance. It retains good activity.

Fosfomycin also retains its activity for the same reasons. It is frequently prescribed because of its ease of use in single- dose form and good tolerance.

The characteristics of these antibiotics make them first-line probabilistic treatments for uncomplicated and gestational cystitis [23, 24].

Resistance profile of Klebsiella pneumoniae strains: In our study we observed an increase in Klebsiella pneumoniae resistance to amoxicillin-clavulanic acid 59.6% versus 35.1% in the survey by Hailaji, et al. in Nouakchott 2014 [12]. This rate was higher than the 23.6% reported by Smaoui, et al. in Tunisia [17].

Resistance to 3rd generation cephalosporins was 35.4% for cefotaxime, comparable with 37.9% in the study by Hailaji, et al. in Nouakchott 2014 [12] and with that of Hamouche, et al. in 2009 in France 32.3% [18] and higher than that of Smaoui, et al. in Tunisia 17.3% [17].

In our study ESBL-producing Klebsiella pneumoniae strains were 23.9% versus 20.4% isolated in 2014 [12].

In our study we noted imipenem resistance of 4.8% this result was higher than that reported by Hailaji, et al. in 2014 who reported no imipenem resistance in Klebsiella pneumoniae strains [12].

Aminoglycosides maintained good activity in our study, with the rate of resistance to amikacin and gentamicin reaching 1.6% and 14.5% respectively, a result comparable to that of Smaoui, et al. (3% and 16.2%) respectively [17]. Our result was lower than the rate reported by Hailaji, et al. in 2014 (19.5%) of gentamicin resistance [12].

In our study, the rate of quinolone resistance was lower than the results reported by Hailaji, et al. in 2014 in Nouakchott, with nalidixic acid resistance at 32.2% versus

48.0% in 2014 and ciprofloxacin resistance at 27.4% versus 33.6% in 2014 [12].

In our study, Klebsiella pneumoniae had a cotrimoxazole resistance rate of 50.0%. This rate was higher than the 44.6%, 40.0% and 40.1% reported respectively by Haylaji, et al. [12]. Hamouche, et al. in 2009 in France [18] and Smaoui, et al. Tunisia [17].

Resistance profile of Staphylococcus aureus strains: In our study, the penicillin G resistance rate was 95.0%, comparable to 97.2% reported by Salem, et al. [25] and higher than that found by Elhamzaoui, et al. in Morocco (86.8%) [26].

The rate of methicillin resistance in S. aureus was 46.6%, higher than that found in the study by Salem et al. 26.3% and Elhamzaoui, et al. in Morocco 19.3% [25, 26].

In our study, gentamicin resistance was found to be 3.3%, a lower rate than that reported by Salem, et al. in Nouakchott, Mauritania (6.85% [25]) and by Maiga, et al. in Mali (5.1% [27]).

In our study, cotrimoxazole was resistant in 15.0% of cases. this rate was lower than that noted by Salem, et al. with a resistance of 75% [25] and higher than that reported by Maiga, et al. 8,5% [27].

Resistance to fluoroquinolones was 6.6%, which is high compared with Salem, et al. in Nouakchott [25].

In our study, resistance to erythromycin and lincomycin was 13.3% and 11.6% respectively, higher than that reported by Maiga, et al. [27].

The diminished sensitivity of Staphylococcus aureus to glycopeptides is a current problem. In our study, we found 1.6% resistance to vancomycin. Our results differ from those reported by Salem, et al. in Mauritania, Nouakchott [25], and Elhamzaoui, et al. in Morocco [26], where all strains were sensitive to vancomycin.

It should be noted that this resistance of staphylococci to glycopeptides needs to be confirmed in staphylococci reference centers.