| Abstract: |
Summary and ConclusionListeria monocytogenes is a Gram-positive, facultative intracellular bacterium. It is ubiquitously distributed and grows in a wide variety of environments including soil, water, plant matter, diverse food items and intestinal tract of mammalian hosts.While L. monocytogenes infection often produces non-specific initial manifestations (eg, influ¬enza-like symptoms and gastroenteritis), it can have severe clinical consequences (e.g, meningitis, encephalitis, septicemia and occasional death) especially among susceptible population groups such as neonates, pregnant women, the elderly and immunocompro¬mized individuals.It is therefore vital that rapid, sensitive and specific laboratory procedures must be available for early detection and accurate identification of L. monocytogenes from nonpathogenic Listeria and other common bacteria.The conventional laboratory identification of L.monocytogenes had relied on lengthy in vitro culture followed by a series of phenotype-based biochemical tests. Apart from being slow and costly, sometimes they gave equivocal results.The obvious deficiencies in the phenotypic diagnostic methods had provided challenge for the development of technology that target the nucleic acids (DNA or RNA) instead of protein products of Listeria organisms.This work aimed to isolate and identify L.monocytogenes from different clinical specimens and food stuffs. In addition, to evaluate the accuracy of polymerase chain reaction in comparison to conventional methods of diagnosis.Sixty-six clinical specimens collected from three groups of patients: Neonates with early and late onset sepsis, aborted women & those presented with pre-term labour and patients showing clinical picture of septicemia and meningitis and 100 different food stuffs were from (milk, cheese and meat). Clinical specimens were cultivated on blood agar and on the other hand, food stuffs were inoculated into two enrichment media then cultivated on Oxford agar. Presumptively positive isolates by colonial morphology, Gram’s stain, catalase test, haemolysis on sheep blood agar and motility test were further identified to species level by 10300 API Listeria strips. PCR was done for all specimens to evaluate its accuracy in comparison to conventional methods of diagnosis. Antimicrobial susceptibility for all isolates was done.This study demonstrated the following results:1- Two cases (11.11%) among septicemic neonates, one case (8.3%) among aborted women and two (5.5%) from meningitis patients were positive for L.monocytogenes by conventional identification methods.2- The detection rate of L.monocytogenes by PCR in different clinical cases where (11.11%) in septicemic neonates, (8.3%) in aborted woman and (5.5%) among meningitis patients.3- No difference in detection rate of L.monocytogenes by conventional methods and PCR in clinical cases.4- Fourteen milk and cheese specimens (17.5%) were presumptively diagnosed as Listeria species on Oxford agar media and one (5.0%) from meat specimens. On further identification by API, four (5.0%) L.monocytogenes were from milk and cheese confirmed as positive.5- Six (7.5%) L.monocytogenes from 80 examined milk and cheese specimens were detected by PCR but no one detected by PCR from meat specimens.6- The conventional methods detect (4.0%) from 100 examined food samples versus (6.0%) detected by PCR as L. monocytogenes.7- No positive cases were detected by PCR among the clinical groups identified negative by conventional identification methods giving the test 100% specificity and 100.0% sensitivity with 100.0% and 100.0% +ve and –ve predictive value, respectively .8- Four food stuffs were detected as L. monocytogenes by conventional methods of dignosis while 6 were detected by PCR. Giving PCR technique 100% specificity, 66.7% sensitivity, 100.0% Positive predictive value, 97.9% Negative predictive value and 98.0% Accuracy.9- All isolates (100%) were sensitive to penicillin G and ampicillin followed by erythromycin where (90.9%) of isolates were sensitive followed by tetracycline (72.7%), vancomycin (63.6%) and amikacin& trimethoprime-sulfamethoxazole with sensitivity (54.5%). On contrary only 2 (18.2%) of isolates were sensitive to ofloxacin.In Conclusion:This study concluded that:1- Listeriosis is a public health hazard distributed in a diversity of environments.2- The use of 2 steps of enrichment media increase the isolation of Listeria monocytogenes from food samples.3- API Listeria 10300 provides rapid identification of Listeria on species level.4- The isolation of Gram positive rod from blood or CSF should never be regarded as a contaminant unless Listeria has been ruled out. As treatment differs considerably from other causes of meningitis, proper and timely diagnosis can have a great impact on the final outcome.5- PCR is deemed to be more reliable than conventional identification since it is based on stable genotypic characteristics rather than relying on biochemical or physiological traits, which can be genetically unstable.6- Penicillin G and ampicillin are used in treatment of listeriosis since all isolates were 100% sensitive to them.
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