Salmonella enterica Isolated from Pigeon ( Columba livia ) in Egypt

Introduction

H uman salmonellosis has been found to be associated with direct contact with food animals, highlighting the possibility of increased transmission of these organisms to humans through the food chain (Hoelzer et al., 2011). Pigeons (Columba livia var. domestica) are widely distributed in urban and rural areas of Egypt, dairy farms, around mosques and churches, livestock premises, poultry farms, and come into close contact with humans in public gardens and at their residence. Salmonellosis is considered the most important zoonoses in bacterial diseases that can be transmitted by the domestic pigeon, and their close interaction with humans, together with the observation that these birds are vectors for zoonotic agents (Vučemilo et al., 2003; Gonzalez-Acuna et al., 2007; Hoelzer et al., 2011), make them a public health risk. Rose et al. (2006) showed that pigeons can cover a maximum distance of 5.29 km; thus, they can spread pathogens locally in their environment. The Salmonella organism has frequently been isolated from pigeons in Europe, the United States, Japan, and South America (Vučemilo et al., 2003; Tanaka et al., 2005; Pedersen et al., 2006; Gonzalez-Acuna et al., 2007).

To determine the extent to which pigeons might harbor this pathogen and pose a risk to the human population in Egypt, we screened pigeons around Cairo for the presence of Salmonella relevant to public health.

Materials and Methods

This study was conducted in Egypt around Cairo (30° 3′ North, 31° 15′ East) over a 12-month period in 2010–2011. Forty-five random adult feral pigeons of both sexes were captured by net or cage traps that were distributed around urban areas and livestock premises, and the pigeons were delivered alive to the laboratory.

Fresh rectal swabs were collected and processed within 6 h of collection. Salmonella strains were isolated according to the Standard ISO-6579 method (Osman et al., 2010). For pre-enrichment of Salmonella, 2.5 g of each sample was homogenized in sterile bags with 22.5 mL of peptone buffered water (Oxoid CM509, Basingstoke, Hampshire, England) and incubated at 37°C for 18–24 h. Next, 0.1 mL of the pre-enriched culture in peptone buffered water was added to 10 mL of Rappaport–Vassiliadis broth (Becton Dickinson and Company, Sparks, MD) followed by additional incubation at 41.5°C for 24 h under aerobic conditions. A loopful of culture broth was then sampled from the selective enrichment Rappaport–Vassiliadis broth, streaked onto xylose–lysine–tergitol 4 agar (Merck), and incubated at 37°C for 24 h. Presumptive black colonies were selected from each plate and cultured on nutrient agar slants. Typical Salmonella colonies were selected, confirmed with the API 20E system (bioMérieux, Marcy l'Etoile, France), and were serotyped by using Denka-Seiken (Tokyo, Japan) antisera following Kauffman-White serotyping scheme (OIE, 2004).

The susceptibility of strains to antibiotics was evaluated by the disk diffusion method. The panel of antibiotic disks (Becton Dickinson) used in panel screens belonged to eight drug classes. Each isolate was inoculated onto Muller–Hinton agar (Difco Laboratories, Detroit, MI) and incubated at 37°C for 24 h according to National Committee for Clinical Laboratory Standards (CLSI, 2010), and the zones of inhibition were measured to assess resistance or susceptibility. The antimicrobial agents tested and their corresponding concentrations were as follows: ampicillin (10 mg), amoxicillin (20 mg), gentamicin (10 mg), neomycin (30 μg), streptomycin (10 mg), lincomycin (30 μg), chloramphenicol (30 mg), colistin (10 mg), tetracycline (30 mg), trimethoprim (5 μg), and sulfamethoxazole+trimethoprim (23.75+1.75 mg). In addition, resistance to three fluoroquinolones was tested: ciprofloxacin (5 μg), norfloxacin (5 μg), and nalidixic acid (30 mg) of broad-spectrum quinolone. Multidrug resistance isolate is defined as being resistant to two or more antibiotics belonging to different antibiotic classes (Hoelzer et al., 2010; Hauser et al., 2011).

Results and Discussion

The prevalence of Salmonella in the feces of the pigeons was 13.3% (6/45), highlighting their potential role as important carriers and spreaders of this zoonotic agent giving rise to public health problems if they were to be dispersed in the general human population. Serotyping indicated that Salmonella ser. Typhimurium recorded a prevalence of 8.9% (4/45) followed by Salmonella ser. Braenderup and Salmonella ser. Lomita (1/45; 2.2% for each) (Table 1).

In studies undertaken in different countries, a wide diversity in incidence and/or prevalence of Salmonella in pigeons was recorded (Vučemilo et al., 2003; Pasmans et al., 2004; Tanaka et al., 2005; Pedersen et al., 2006; Gonzalez-Acuna et al., 2007; Pasmans et al., 2008). Consequently, the diversity recorded between the prevalence of Salmonella in our study (13.3%) and the global prevalence rates (1.5%–30%) could be attributed to geographical location, serotype, and habitat (Hoelzer et al., 2011). Although Salmonella ser. Typhimurium is the only Salmonella serotype frequently associated with serious systemic disease in pigeons causing substantial mortality (Hoelzer et al., 2011), other serotypes have also been isolated (Tanaka et al., 2005; Hoelzer et al., 2011). Of note, Salmonella ser. Braenderup and Salmonella ser. Lomita have never been detected in pigeons before.

The frequency of resistance, particularly to lincomycin and streptomycin (100%), was evident by Salmonella ser. Typhimurium, Braenderup, and Lomita (Table 1). On the other hand, they were 100% susceptible to ciprofloxacin, colistin sulphate, and gentamicin. The findings suggest that multidrug resistance strains are more likely to be of clinical significance because they pose a public health risk to the human population in Egypt (Gebreyes et al., 2009). The absence of resistance to ciprofloxacin and norfloxacin among the isolates is of high significance since these two antimicrobials are the primary agents used against invasive salmonellosis in humans (Gebreyes et al., 2009). Our results indicate that the isolated nontyphoidal Salmonella from these birds, which could act as reservoirs for nontyphoidal Salmonella, are an important risk factor causing human gastroenteritis and bacteremia.