PhD Thesis
Members of the genus Campylobacter are known to cause more cases of human
gastrointestinal illness than any other bacterium worldwide. The organisms exist as normal
flora in the intestinal tracts of domestic and wild animals, more so in avian species.
Humans acquire Campylobacter infections from contaminated animal products,
particularly poultry meat, either directly or through cross-contamination of other food
products. Human infections are mostly attributed to Campylobacter jejuni and C. coli, the
former causing a larger proportion (85-90%) of all cases reported. In addition to
infections, campylobacteriosis is also associated with the emerging threat of antimicrobial
resistance as evidenced in isolates derived from different sources. An accurate picture of
the epidemiology of infections caused by Campylobacter and other aetiological agents is
lacking in developing countries due to the absence of regular surveillance programmes.
Consequently the present study was conducted in Morogoro Municipality, Eastern
Tanzania, to determine the molecular epidemiology and antimicrobial resistance of
thermophilic Campylobacter isolates from humans and animals. Specific objectives were;
1) To establish the prevalence of thermophilic Campylobacter infections in humans and
animals, 2) To determine the genetic relatedness of chicken and human derived
thermophilic Campylobacter isolates using DNA-based typing methods, 3) To evaluate the
antimicrobial resistance patterns in thermophilic Campylobacter isolates derived from
humans and animals; and 4) To identify risk factors for thermophilic Campylobacter
infections in humans. Stool samples were collected from 1195 human subjects; and fecal
samples from 1511 farm animals, 466 laboratory animals and 112 wild birds (Indian house
crows). Farm animals constituted chickens (n=1267), cattle (n=98), goats (n=81), sheep
(n=57), horses (n=5) and camels (n=3); whereas laboratory animals were composed of
guinea pigs (Cavia porcelllus, n= 30), mice (Mus musculus, n=160), rabbits (Oryctulagusiii
cuniculus, n=34) and rats (Rattus rattus, n=242). The Cape Town protocol was used for
isolation of thermophilic Campylobacter from stool and fecal samples. Campylobacter
isolates were identified by phenotypic and molecular techniques. The isolates were tested
for resistance against several antimicrobial agents using the disc diffusion method. Risk
factors for human infections with thermophilic Campylobacter were determined in an
unmatched case control study. Selected human and chicken derived Campylobacter jejuni
isolates were genotyped using flagellin A gene sequencing. In humans the prevalence of
thermophilic Campylobacter was 11.4% (n=1195). Symptomatic (12.9%) and young
individuals (16.7%) were more infected than asymptomatic (6.7%) and adults (10%),
respectively. Most (84.6%) of the isolates were C. jejuni and the remaining were C. coli;
and the difference was statistically significant at p≤0.05. Isolates had highest resistance
(95.6%) for colistin sulphate and lowest for ciprofloxacin (22.1%). Proportions of resistant
isolates for other antibiotics (azithromycin, erythromycin, tetracycline, cephalethin,
gentamycin, nalidixic acid, ampicillin, amoxycillin, norfloxacin and chloramphenicol)
ranged from 44.1% to 89%. Human infections with thermophilic Campylobacter were
associated with young age; and consumption of chicken meat, barbecue and pre-prepared
salad. In avians, thermophilic Campylobacter spp. were isolated from 44.0% and 20.5% of
the sampled chickens and crows respectively. The majority of isolates from both chickens
(87.6%) and crows (56.5%) were C. jejuni and the remaining were C. coli. The observed
difference in proportions of C. jejuni and C. coli isolates was statistically significant
(p≤0.05) in chickens but not in house crows. Chicken isolates had highest resistance to
Colistin sulphate whereas crow isolates showed highest resistance to azithromycin and
erythromycin. Lowest resistance was observed for gentamycin and ciprofloxacin for crow
and chicken isolates respectively. Among chicken isolates significantly high proportions
of C. coli were resistant to gentamycin, cephalothin, tetracycline, colistin sulphate and
chloramphenical. On the other hand a high proportion C. jejuni isolates were resistant toiv
nalidixic acid. Crow derived C. jejuni had significantly higher resistance to nalidixic acid,
cephalothin and ciprofloxacin than C. coli isolates from the same hosts. Among farm
animals thermophilic Campylobacter were detected from 18 (31.6%) sheep and 3/5 (60%)
of horses. Of the isolates 12 (57%) were C. jejuni; the remaining (43%) were C. coli. Of
the laboratory animals 8 (26.7%) guinea pigs and 3 (1.2%) rats were colonized with
Campylobacter. Four isolates from the guinea pigs were C. jejuni and the other 4 were C.
coli. From the rats two isolates were C. jejuni and one was C. coli. The isolates showed
high levels of antimicrobial resistance to erythromycin, norfloxacin colistin sulphate and
nalidixic acid in ascending order; whereas low levels of resistance were observed for
ciprofloxacin and gentamycin. Out of 55 sequenced isolates obtained from sporadic cases
of human illness and different categories of chickens, nine different flaA types (7, 36, 41,
51, 61, 62, 64, 105 and 111) were detected. Both C. jejuni isolates from humans and
chickens displayed a high degree of genetic diversity thereby suggesting weak clonality
among the tested isolates. Genetic relatedness of some isolates from human and avian
sources was however evident as on phylogenetic analysis some clusters contained both
human and chicken C. jejuni isolates. The work contained in this thesis contributes
significantly to the limited, available information on epidemiology and antimicrobial
resistance of human and animal Campylobacter infections in Tanzania. For the first time
the occurrence of Campylobacter infections in laboratory animals, antimicrobial resistance
of human derived Campylobacter isolates, risk factors for human Campylobacter
infections; and the population structure and relatedness of Campylobacter jejuni isolates
from humans and chickens in the country are provided. The observed clusters containing
isolates from human and avian sources confirm interspecies transmission of this zoonotic
pathogen. Information on antimicrobial resistance of Campylobacter isolates derived from
avian species in the country is also complemented. Control measures for colonization of
animals and occurrence of infections in humans with this particular bacterium species arev
warranted. Similarly strategies to stem emergency and spread of antimicrobial resistant
Campylobacter strains should be put in place.
Danish International Development Fund