Pseudomallei Group


The pseudomallei group include several opportunistic pathogens: P mallei, P. Pseudomallei. P cepacia, and P. picketti. P. mallei is the only non-motile member of the genus Pseudomonas and is the causative agent of glanders, a severe infection of horses that is occasionally transmitted to animal handlers. The disease is characterised by pneumonia and by necrosis of muccous membranes, skin, and lymphatics.

       P. pseudomallei is found in the soil and water in tropical areas. It is the causative agent of melioidosis, a disease which is prevalent in the tropical parts of Asia. The organism is usually inhaled and may remain dormant for several months or even years. Chronic pneumonia, resembling tuberculosis, may develop. The organism can also cause an acute suppurative infection in traumatised skin lesions and can progress to septicaemia. Patients usually respond to chloramphenicol, tetracycline, and trimethroprim-sulphonimides.

       P. cepacia has long been recognised as a pathogen for plants. In recent years, it had been associated with a number of hospital outbreaks. It can cause the same range of disease as P. aeruginosa, including pulmonary disease in cystic fibrosis patients. It is also resistant to a number of antimicrobial agents. Infections can usually be treated by chloramphenicol or trimethorim-sulphonimides and with some cephalosporins.



Other Nonfermenters




The genus acinetonacter consists of a single species A. calcoacetius. There are 2 variants: A. calcoacetius var anitratus oxidises glucose with production of acid, whereas var. lwoffi lacks this trait. These organisms are short gram-negative rods and are frequently found in pairs. They are non-motile (hence the name), grow only aerobically and are oxidase-negative. Acinetobacter can be found widely distributed in the environment and in the normal flora in approximately 10% of individuals. Nosocomial outbreaks of acinetobacter pneumonia and bronchitis have been reported. Intravenous catheterisation sometimes lead to septicaemia. Infections are usually treated with carbenicillin, co-trimoxazole, or kanamycin.





The flavobacterium are non-motile, slender gram-negative rods that form yellow colonies on most solid media. Flavobacteria are widely distributed in nature. F. meningosepticum can be highly virulent for the newborn infant, especially the premature. It has caused outbreaks of septicaemia and meningitis with a high mortality rate. These infections are usually attributed to contaminated hospital equipment and solutions. However, the organism has also been isolated from the female genital tract. Flavobacterium also causes bacteraemia in postoperative patients, although the illness is much milder. The organism has an unusual antibiotic sensitivity pattern for a gram-negative bacillus; it is resistant to aminoglycosides and penicillins but susceptible to erythromycin, rifampin and vancomycin.





Members of the genus moraxella are similar to acinobacter but are oxidase-positive and highly sensitive to penicillin. They are easily confused with Neisseria. Moraxella lacunata is a rare cause of conjunctivitis and corneal infections. M. osloensis, nonliquefaciens, and phenylpyruvica are members of the normal flora but may be involved in serious infections.





Achromobacter xylosoxidans is a motile oxidase-positive organism first described in 1971. It occurs in lower animals as well as free-living in nature. It has been associated with a variety of human diseases including meningitis, septicaemia, and otitis media.





Alcaligenes faeclis is oxidase-positive and usually motile. It may be encountered in the faeces or sputum as a harmless saprophyte but it has been associated with serious infections. As a contaminant of irrigation fluids and intravenous solutions, it has caused epidemics of urinary tract infections and postoperative septicaemia.