Occurence, Civersity and Antimicrobial Susceptibility of Listeria Species From Retail Raw Beef and Goat Meat in Port Harcourt, Nigeria

ABSTRACT

Listeriosis has emerged as a disease of public health importance because of its clinical severity, high fatality and challenges to its control including resistance to antibiotics. Outbreaks reported in developing countries including Nigeria were associated with consumption of meat and meat products. However, previous work on Listeria in Nigeria focused on environmental samples. Hence, the need to ascertain the presence of Listeria in meat and their response to antimicrobial agents. The study was designed to investigate the occurrence, diversity, virulence and antimicrobial resistance of Listeria species in raw beef and goat meat in Port Harcourt, Nigeria as well as control of Listeria monocytogenes using plant extracts.

A total of 240 meat samples (122 beef and 118 goat), comprising flesh (72), kidney (60), intestine (38) and liver (70) were purchased from Choba, Rumuokoro and Rumuokwuta markets. Bacteria were isolated from the meat and tested for the presence of Listeria spp using Listeria selective media. Isolates were identified using conventional and molecular methods. The isolates were screened for susceptibility to selected antibiotics using disk diffusion method. Virulence genes and plasmid were screened using molecular methods. Thymus vulgaris L., Allium sativum L., Piper guineense Schum and Thonn, Monodora myristica (Gaertn) Dunal, Ocimum gratissimum L. and Xylopia aethiopica (Dunal) A. Rich were separately extracted with ethanol and water. Effects of the extracts (0.1-5.0%) were determined against L. monocytogenes (1× 108 cell/mL) in agar well diffusion, treated and untreated meat which served as control using standard methods. Data were analysed using descriptive statistics and ANOVA at p=0.05.

Eighty-one (33.8%) samples were positive for Listeria spp. Listeria isolates identified were L. monocytogenes (4), L. innocua (20), L. ivanovii (4), L. seeligeri (72), L. welshimeri (139), and L. grayi (71). All isolated Listeria were susceptible to gentamicin and vancomycin but resistant to amoxicillin (100%), augumentin (100%), cloxacillin (100%), tetracycline (88.5%), oxacillin (73.6%), erythromycin (43.7%), chloramphenicol (43.7%) and cotrimoxazole (33.3%). Virulence genes such as inlJ and inlC were detected in L. monocytogenes. Aqueous extract of P. guineense and T. vulgaris as well as ethanol extract of T. vulgaris inhibited L. monocytogenes growth at concentrations ranging from 1.0-5.0%, 0.5-5.0% and 0.1-5.0%, respectively. The reduction of L. monocytogenes attached to meat pieces varied during a 15 minutes immersion, ranging from 0.8 to 1.4 log10cfu/g. After 4-day storage at 30oC, L. monocytogenes exhibited significant higher growth in control samples compared to extract treated samples with initial population in log10 cfu/g increasing from 5.4-6.6 to 9.1-10.2 and 5.3-6.5 to 8.5-9.9 respectively. There was no significant difference between control and treated samples stored at 10oC for 15 days, although initial population increased from 5.4-6.6 to 8.5-8.8 log10cfu/g and 5.2-6.5 to 8.2-8.5 log10cfu/g respectively.

Presence of Listeria species was confirmed with Listeria monocytogenes having virulence characteristics. Thymus vulgaris had inhibitory potential against the growth of Listeria monocytogenes in meat and growth media. Thus, Thymus vulgaris can be employed as a control agent of Listeria pathogen in meat processing.