1. Listeria monocytogenes
It is a small, coccoid, gram positive bacillus, measuring 1-3 mm in length and 0.5 mm width, with a tendency to occur in chains. They are often angled at the point of contact and may resemble diphtheroids or diplococci. Rough forms may be seen as long filaments. It exhibits a characteristic tumbling motility when grown at 25°C, but at 37°C is non-motile.This is because peritrichous flagella are produced at 20-30°C but not at 37°C. They are aerobic, facultatively anaerobic or microaerophilic. Growth can be improved at reduced O2 tension and with 5-10% CO2. It grow on ordinary media at 40-42°C, growth improved by the addition of glucose, blood. After 24 hours incubation at 35-370C Colonies are hemolytic. It is catalase positive.
It causes listeriosis and are widely distributed in nature.Foodborne transmission by improperly processed milk,cheese,meat and vegetables is the most common source of infection,survives high and low temperatures.Sometimes it is zoonotic and threatening to those with impaired immune systems.Listeriosis is a leading cause of infection in kidney transplant patients.In pregnant women the bacillus can cross the placenta,infect the foetus,is responsible for many cases of foetal damage.It may also present as abscesses,conjunctivitis,urethritis,pneumonia etc.
Diagnosis by isolation of bacillus from cervical and viginal secretions, CSF etc., Ampicillin is effective.
L. monocytogenes is widely distributed in nature. It has been isolated from mammals, birds, fish ticks and crustacea. It occurs as a saprophyte in soil, water and sewage. In humans it sometimes causes meningitis. Human infection is from contact with infected animals, inhalation of contaminated dust or ingestion of contaminated milk or food.
2. Alcaligenes faecalis
Gram negative, short, non-sporing bacilli which are strict aerobes and do not ferment sugars. They are motile, oxidase positive. It is a saprophyte found in water and soil contaminated with decaying organic matter. They are also commensals in the intestines of man and animals. Isolated from urine, pus, blood. Responsible for a typhoid like fever, urinary infections.
3. Chromobacterium violaceum
Gram negative, non-sporing, motile. They are facultative anaerobes growing on ordinary media and producing violet pigment soluble in ethanol and insoluble in water. They are oxidase negative, saprophytic. Human infections with skin lesions.
4. Flavobacterium meningosepticum
Gram negative, non-motile rod, produce a yellowish pigment. It is oxidase positive, proteolytic and weakly fermentative. It is a saprophyte and causes opportunistic infections. Responsible for meningitis in newborn infants. Infection in adult leads to a mild febrile illness.
5. Rat Bite Fever Organisms
RBF is caused by Streptobacillus moniliformis and Spirillum minor, RBF is characterized by relapsing fever, rash occurring days or weeks after a rat bite.
S. moniliformis is pleomorphic, Gram negative, non-motile bacillus. In cultures it grows as tangled chains of rods, with beaded swellings and develop into L-forms. Growth requires the presence of blood or other body fluids. It is catalase, oxodase, urease, indole negative. It ferments glucose.
S. moniliformis is present in the nose and throat of wild and laboratory rats. It results from bites and scratches of mice, squirrels, dogs, cats. It (RBF) begins as a localized inflammation at a bite site. In 1-3 days, headache begins and new lesions appear elsewhere, especially on palms and sides. Fever is intermittent. An arthritis that developes can permanently damage joints.
Spirillum minor is a short, actively motile bacterium. It is gram negative. The initial bite heals easily, but 7 to 21 days later it flares and forms an open ulcer. Chills, fever, inflamed lymph nodes accompany a red or dark purple rash that spreads out from the wound site. After 3-5 days symptoms subside, but they can return after a few days, weeks, months even years.
Diagnosis of both forms of RBF is made by dark field examination of exudates. Treatment is with streptomycin or penicillin.Technicians bitten by redents should disinfect the bite site seek medical treatment and be alert for rat bite fever symptoms.
It is a slender gram negative curved rod, they are typically comma shaped but may occur as ‘S’ or multispiral chains. Old cultures are coccoid and pleomorphic. They are non-sporing and motile. Growth occurs under microaerophilic conditions, 5% O2 being optimal. Many pathogenic species are thermophilic, growing well at 42°C. They are oxidase positive.
Two important strains are : C. jejuni (diarrhea)
C. fetus (Extraintestinal infection)
C. jejuni : It causes attacks of diarrhea worldwide. The infection is zoonotic, the source being food of animal origin, especially raw milk. It is part of the normal intestinal flora of domestic animals and birds, and is shed through their faeces. It can be isolated frequently from surface waters.
Infection occurs by ingestion of undercooked chicken, unpasteurised milk. The jejunum and ileum of small intestine are the primary sites of colonization, spread to colon and rectum. The incubation period is 1-7 days. The illness starts with fever, abdominal pain and watery diarrhea. Stool contains leucocytes and blood. Organisms are shedded even after recovery. Fluid and electrolyte replacement is required. Erythromycin can be prescribed.
Diagnosis by isolation of C. jejuni from stools and are plated on selective media. Colonies appear usually by 48 hours. They are non-hemolytic, grey or colourless, moist, flat, convex.
C. fetus : It causes infections abortions in several kinds of domestic animals. (cattle,sheep)
7. Helicobacter pylori
Spiral and is a bacterial cause of peptic ulcers and chronic gastritis and a probable cofactor of stomach cancer. It is able to survive the very acidic conditions of the stomach by generating ammonia from urea. The ammonia neutralize gastric acidity around the Helicobacter cells, thereby allowing the organisms to survive and reproduce. They colonize and multiply in the gastric mucosa above the epithelial layer of the stomach.
Peptic ulcers are lesions of mucus membranes lining the oesophagus, stomach or duodenum. The lesions are caused by the sloughing away of dead inflammatory tissue and exposure to acid, and eventually result in an excavation into the surface of the origan. Stomach inflammation may be so mild.
H. pylori is a Gram negative spiral rod, motile, grows on chocolate agar, pH 6-7, temp 37°C. It is oxidase, catalase, H2S positive. It is resistant to several antibiotics.
8. Legionella pneumophila
It is a weakly Gram negative, aerobic bacillus with fastidious nutritional requirements. It is a thin, non-capsulated bacilli. Most are motile. They grow on complex media. Growth is slow and take 3-6 days to appear. They are widely distributed. Legionellae survive and multiply inside free living amoebae and protozoa. Human infection typically by inhalation of aerosols produced by air conditioners.
Legionella causes Legionnaire’s disease. Most are free living in soil nad do not ordinarily cause disease. Some strains living as intracellular parasites of amoebas, these amoebas colonize cooling towers and other wet areas. Legionellosis is transmitted when organisms growing in soil or water become airborne and enter host/patients lungs as an aerosol. Once inhaled, the organisms are taken up into amoeboid phagocytes by phagocytosis. They thrive inside the acidic conditions of the phagolysosome, multiplying and eventually rupturing the cell.
After an incubation period of 2-10 days, the disease appears with fever, chills, headache, diarrhea, vomiting, fluid in the lungs, pain in the chest and abdomen, profuse sweating, mental disorders. When death occurs, it is usually due to shock and kidney failure.
Direct fluorescent antibosy tests,ELISA used in diagnosing.Erythromycin used in treatment.
Control of Legionella infections include maintaining adequate chlorine levels in all potable water sources and other reservoirs,periodic cleaning of surfaces in air conditions.