Listeria Species Isolated from the Wastewater Samples of a Private and Tertiary Hospital in Ibadan and their Antibiotics Resistance Patterns

Introduction: In hospitals, a significant amount of water is consumed and equally, significant amounts of wastewater is disposed with high levels of contaminants, including disease-causing bacteria such as Listeria spp. have been found in wastewater effluent and surrounding freshwater bodies. Recent studies suggest that Listeria species readily survive conventional wastewater treatment processes even after tertiary treatment. This study was carried out to determine the antibiotic resistance pattern of Listeria spp. isolated from hospital wastewater (treated and untreated) from private and tertiary hospital samples in Ibadan and comment on the public health significance.

Materials and Methods: Hospital wastewater samples were collected between April and July, 2016. Listeria Selective Agar Base with Listeria Selective Supplement (Oxoid, UK) was used for the isolation of the Listeria species and the isolates were identified using standard conventional methods. Antimicrobial susceptibility testing was done against ampicillin (10 µg), cloxacillin (5 µg), amoxicillin (5 µg), streptomycin (10 µg), ceftriaxone (30 µg), chloramphenicol (30 µg), ciprofloxacin (5 µg), ofloxacin (5 µg), sulfamethoxazole-trimethoprim (25 µg) and tetracycline (30 µg) by the Kirby-Bauer disk diffusion method.

Results: A total of 96 Listeria spp. were isolated comprising L. monocytogenes 23 (24%), L. innocua 13 (13.5%), L. ivanovii 14 (14.6%) and other Listeria spp. 46 (47.9%). Furthermore, all the 96 (100%) isolates were resistant to ampicillin while all (100%) the L. monocytogenes and L. ivanovii showed resistance to both ceftriaxone and cloxacillin. In addition, all the L. ivanovii exhibited complete resistance to ciprofloxacin. Also, three (3.1%) isolates (L. monocytogenes, L. ivanovii and Listeria spp.) were resistant to a combination of eight antibiotics (sulfamethoxazole-trimethoprim, chloramphenicol, tetracycline, ampicillin, ceftriaxone, cloxacillin, amoxicillin and ciprofloxacin).

Conclusion: The observation from this study showed that the wastewater from both the private and tertiary hospitals could be a source of transmission of multi-drug resistant bacteria to human and animals. More so, the wastewater treatment processes did not reduce the load of the Listeria species.