Potential Human Pathogens (Bacteria) and their Antibiogram in Ready–to–eat Salads sold in Calabar, South-South, Nigeria
S Udo, I Andy, A Umo, M Ekpo
antibiogram, calabar, nigeria, pathogens, resistance, salads
S Udo, I Andy, A Umo, M Ekpo. Potential Human Pathogens (Bacteria) and their Antibiogram in Ready–to–eat Salads sold in Calabar, South-South, Nigeria. The Internet Journal of Tropical Medicine. 2008 Volume 5 Number 2.
A total of 150 ready –to-eat salad samples were collected from various sources in Calabar and analyzed bacteriologically using standard cultural methods. The samples included 50 from fast food centers, 50 from wedding reception parties and 50 from birthday reception parties all within Calabar metropolis between October 2006 and January 2007. All the bacterial isolates were characterized using the API system and subjected to antimicrobial susceptibility test using the Agar diffusion method. The probable human pathogens isolated were
Salad is a mixture of fresh vegetables and cream milk that provides a rich source of vitamins, minerals and dietary fiber of low fat and calories to the consumer. However, questions have been raised about the safety and microbiological quality of these food produce . Several outbreaks of human gastro-enteritis have been linked to the consumption of contaminated fresh vegetable salad .
In developing countries, there are serious concerns about the sanitation of ready to eat salads, particularly as potable water is seldom available at preparation venues and the fast food stands Washing of dishes and utensils is often with a single change of water in the same basin all day long . Health risks are associated with initial contamination and subsequent contaminations by the workers during handling while microbial proliferation occur during display. Salads are usually consumed without any pre-heat treatment and therefore the possibility of food poisoning exists .
The increasing availability of prepared vegetable salads reflects consumers demand for fresh, healthy, convenient and additive free foods that should be safe and nutritious. The survival of food borne pathogens is slightly enhanced once the protective epidermal barrier has been broken either by physical damage or by degradation by plant pathogens . These punctures can also promote the multiplication of pathogens especially at non-refrigerated temperatures . During salad preparation, raw vegetables are injured through peeling, slicing or shredding . These operations can transfer pathogenic microorganisms if present on the surface of fresh fruits and vegetables into the product. Most pathogens in salad do not cause product spoilage, even at relatively high populations. In the absence of spoilage signs, salads are consumed because they are perceived as safe. Several studies have associated outbreak of food poisoning with consumption of raw vegetable salads .
In recent years, salad has become a very popular component of menu served at birthday and wedding parties; they are also sold in fast food centers in most major cities in Nigeria. Media reports of unverified rampant cases of gastroenteritis following consumption of meals served with fresh vegetable salads have become serious public health concern. This study was therefore set up to evaluate the microbial quality of ready to eat salads commonly consumed in Calabar, South-South Nigeria The study will also address the profile of multiple drug resistance among isolates from ready to eat salads.
Materials and Methods
Study Location: Calabar, is the capital city of Cross River State and one of the fastest growing metropolis in Nigeria. In the last 9 years, the metropolis has been transformed from a mere sub-urban community to become Nigeria’s tourist destination. The hospitality industries have also experienced phenomenal growth with more sophisticated appetite. With Tinapa an international resort and shopping empire coming on stream well over ten million tourists are expected to visit Calabar every year. . The population of Calabar is approximately one million; the people are principally civil servants, traders, farmers and fishermen.
Sample Collection: Sampling for this study lasted between January 2007 and October 2007. A total of 150 salad samples were collected with 50 samples from fast food centers, birthday reception parties and wedding reception parties respectively. Only one sample each was collected from each location.
The samples were transported to the microbiology laboratory for processing on the same day of collection. Where delays were inevitable, the samples were stored at 4OC overnight and allowed to reach room temperature before they were processed.
One gram of thoroughly mixed salad sample was aseptically added to 18ml of sterile Thioglycollate broth (USP) and incubated overnight at 37OC. After 24 h. incubation, the thioglycollate broth was sub-cultured onto blood agar, chocolate agar, MacConkey agar and thiosulphate citrate bile salt agar (TCBS) plates All the plates were incubated aerobically except the blood agar plates which were incubated anaerobically with gas pack for 18-24 hr at 37 OC. The isolates were fully characterized using the API system.
Antimicrobial Susceptibility test
All the isolates that were potential human pathogens were subjected to antimicrobial susceptibility test using the agar diffusion method on Mueller Hinton agar  .The antimicrobial agents used and the disk concentrations were Benzyl penicillin 1.5 units, Ampicillin 25mcg, Tetracycline 10mcg/ 25mcg for gram positive and gram negative organisms respectively, Chloramphenicol 25mcg,Gentamicin 10mcg, Ciprofloxacin 10mcg,Cloxacillin 10mcg Cotrimoxazole 25mcg, Ceftazidine 10mcg, and Augmentin 30mcg. Laboratory maintained susceptible strains were used as controls in the susceptibility tests.
In this study a total of 150 salad samples were examined for bacterial contamination. In all, 85(56.67%) of the salad samples were contaminated with various bacterial species belonging to 5 genera, 3(60.0%) being gram negatives while 2(40.0%) were gram positives (see table1) below. A total of 35(41.18%) of the salad samples studied were contaminated with
In table 2 below is presented the Antimicrobial resistance profiles of the potential human pathogens isolated from fresh vegetable salads in Calabar, South-south Nigeria. The isolates showed variable resistance profiles ranging from 25.71% to 81.82% for
Multiple resistance to antibiotics was observed in all the isolates except among the
The number of documented outbreaks of human infections associated with the consumption of raw vegetables has increased in recent years . According to the report by the Center for Diseases Control and prevention (CDC) , the number of produce related outbreaks per year double between the periods1973-1987 and 1988-1992.During both periods, the aetiologic agents were known in more than 50% of the outbreaks.
In this study, the objective was focused on the isolation of potential pathogens in ready to eat salads. Surprisingly only five bacterial species were isolated. In a similar study reported by CDC, outbreaks with identified aetiology were predominantly of bacterial origin with
The isolation of
The high incidence of bacterial contamination of ready to eat salads reported in this study may partly be accounted for by the large numbers of people (usually friends or relations) deployed to assist during weddings, in the preparation of vegetable salads who may not observe basic sanitation requirements for processing produce that requires no pre-heating before consumption. Another reason may be the non- availability of water in good quantity and quality for washing and pre- disinfection of the fresh vegetables and fruits during mass production of salads as in weddings and birthday parties.
The low incidence of bacterial contamination and absence of
The susceptibility tests on the isolates were variable with the highest resistance rate of 81.82% and 25.71% as the lowest rate. An overall multiple resistant rate of 35.29% is reported in this study. This finding probably links the source of these isolates to humans who are commonly colonized by multiple drug resistant bacteria in this geographic region. 
It is concluded here that ready to eat salads contain various bacterial species that are potential human pathogens and that these organisms carry multiple drug resistant genes which are transferable to susceptible strains in humans that consume this produce. Due to worldwide emergence of old and new infectious agents and the fact that the world is now a global village, we advocate the establishment and enforcement of National microbiological standards for ready to eat fresh vegetable salads in Nigeria.
The technical assistance provided by Naomi Ngozi Onyemachi and the staff of Sufat Medilab and Diagnostic Services; Calabar is highly appreciated.
Dr. Sunde Moffat Udo PhD, FMLSCN Department of Med. Microbiology And Parasitology. University of Uyo Teaching Hospital. Uyo, Akwa Ibom State. Nigeria E-mail: firstname.lastname@example.org