PROF. ARIMI SAMUEL MUTWIRI

As part of a study to assess zoonotic milk-borne health risks, seasonal survey data and unpasteurized milk samples were collected between January 1999 and February 2000 from randomly selected informal milk market agents (220 and 236 samples in the dry and wet seasons, respectively) and from households purchasing raw milk (213 and 219 samples in the dry and wet seasons, respectively) in rural and urban locations in central Kenya and screened for antibodies to Brucella abortus (B. abortus) and presence of Escherichia coli (E. coli) OI57:H7. The latter was assessed based on samples from consumer households only. Antibodies to B. abortus were screened using the indirect antibody Enzyme Linked Immunosorbent Assay (ELISA) and the Milk Ring Test (MRT). The presence of E. coli 0157:H7 was assessed by culture, biochemical characterisation, serological testing for production of verocytotoxin one (VTl) and two (VT2) and polymerase chain reaction (Pf.R) analysis for the presence of genes encoding for the toxins. The prevalence of antibodies to B. abortus varied considerably ranging from none in milk sold in small units and originating from intensive production systems to over 10% in samples that were bulked or originating from extensive production systems. E. coli 0157:H7 was isolated from two samples (0.8%), one of which produced VTl. All urban consumers (100%) and nearly all rural consumers (96%) of marketed milk boiled the milk before consumption, mainly in tea, thus greatly reducing chances of exposure to live pathogens and potential health risks.

Objectives: To investigate the level of contamination with C. jejuni of raw chicken and beef meats sold in Nairobi and to assess their potential as sources of campylobacter infections to man. Design: Dressed chicken and beef meat samples were randomly sourced from butcheries, markets and supermarkets in various parts of Nairobi over a period of two months. One hundred chicken and 50 beef samples were bacteriologically examined by selective enrichment and culture under microaerophilic environment. Thermophilic campylobacters were identified and characterised using standard physical and biochemical tests. Setting: Veterinary Public Health Laboratories, Kabete, University of Nairobi. Results: Thermophilic campylobacters were isolated from 77 (77%) poultry samples and one (2 %) beef sample. Isolation rate (85.3 %) was higher from chickens <24 hours old since slaughter than those >24 hours old. The beef isolate was 2% C. jejuni. Poultry samples yielded C. jejuni (59%), C. coli (39% and C. laridis (2%). Conclusion: These findings show that poultry meat sold at the counter is a major source of C. jejuni and C. coli, and that it is an important potential source of campylobacter infection. Proper cooking and hygienic handling before consumption is therefore essential.

Isolation rates for Listeria monocytogenes and the other Listeria spp. typically improve when samples are enriched in more than one primary enrichment medium. This study evaluated the abilities of two primary enrichment media, University of Vermont-modified Listeria enrichment broth (UVM) and Listeria repair broth (LRB), to recover different ribotypes of Listeria spp. from raw meat and poultry samples. Forty-five paired 25-g retail samples of ground beef, pork sausage, ground turkey, and chicken (160 samples) underwent primary enrichment in UVM and LRB (30 degrees C for 24 h) followed by secondary enrichment in Fraser broth (35 degrees C for 24 and 40 h) and plating on modified Oxford agar. After 24 h of incubation of 35 degrees C, 608 Listeria colonies from selected positive samples were biochemically confirmed as L. monocytogenes (245 isolates), L innocua (276 isolates), and L. welshimeri (89 isolates) and then ribotyped with the automated Riboprinter microbial characterization system (E. I. du Pont de Nemours & Co., Inc.). Thirty-six different Listeria strains comprising 16 L. monocytogenes (including four known clinical ribotypes), 12 L. innocua, and 8 L. welshimeri ribotypes were identified from selected positive samples (15 samples of each product type; two UVM and two LRB isolates per sample). Twenty-six of 36(13 L. monocytogenes) ribotypes were detected with both UVM and LRB, whereas 3 of 36 (1 L. monocytogenes) and 7 of 36 (3 L. monocytogenes) Listeria ribotypes were observed with only UVM or LRB, respectively. Ground beef, pork sausage, ground turkey, and chicken yielded 22 (8 L. monocytogenes), 21 (12 L. monocytogenes), 20 (9 L. monocytogenes), and 19 (11 L. monocytogenes) different Listeria ribotypes, respectively, with some Listeria ribotypes confined to a particular product. More importantly, major differences in both the number and distribution of Listeria ribotypes, including previously recognized clinical and nonclinical ribotypes of L. monocytogenes, were observed when 10 UVM and 10 LRB isolates from five samples of each product were ribotyped. When a third set of six samples per product type was examined from which two Listeria isolates were obtained by using only one of the two primary enrichment media, UVM and LRB failed to detect L. monocytogenes (both clinical and nonclinical ribotypes) in two and four samples, respectively. These findings stress the importance of using more than one primary enrichment medium and picking a sufficient number of colonies per sample when attempting to isolate specific L. monocytogenes strains during investigations of food-borne listeriosis.

A study on the role of dairy cooperative societies in providing services to small-holder dairy farmers in Kiambu district, Kenya, was carried out through interview to staff from various cooperative societies and farmers. The prices paid to farmers varied from Ksh. 5.00 to Ksh. 7.00 per litre and was influenced mostly by the proportion of milk the cooperative society was able to sell locally. The ability of the societies to provide input services increased with the number of members and the amount of cooperative levy charged on milk sales. The need for higher and more prompt payment for milk was a major concern to farmers while the provision of veterinary services was a secondary concern. It is concluded that both the recent deregulation of milk marketing and the withdrawal of many government technical services should influence dairy cooperative societies to assume a greater role in their areas.

A total of 152 strains of Campylobacter jejuni, C. coli, C. laridis and C. fetus subsp. fetus were tested for haemolysis on blood agar plates. Distinct haemolysis was detected in 92.% (96/104) of strains of C. jejuni and 21.7% (5/23) of strains of C. coli on sheep blood heart infusion agar after incubation for 4 d microacrobically at 42°C. Haemolysis was also detected on horse blood heart infusion agar. Haemolysis was not detected at 37°C except with one of 50 strains of C. jejuni tested at this temperature, which was weakly positive. Campylobacter laridis was not haemolytic; C. fetus subsp. fetus, which does not grow at 42°C, showed no haemolysis at 37°C. Blood agar (Oxoid, BA Base No. 2) was not suitable for testing for haemolysis by these organisms. A microaerobic gas mixture containing hydrogen is better than that containing nitrogen because the medium has a brighter colour, making haemolysis casier to detect. There was no synergistic haemolysis with Staphylococcus aureus or Streptococcus agalactiae. The plate haemolysis test as described here may aid differentiation within the thermophilic campylobacters