Relationship of some biochemical characteristics of Staphylococcus aureus to enterotoxin production.

A total of 151 enterotoxigenic and 98 non-enterotoxigenic strains of Staphylococcus aureus were examined for production of coagulase, phosphatase, deoxyribonuclease, haemolytic activity, glucose and mannitol fermentation, typical growth on Baird-Parker medium, pigment production and growth under anaerobic conditions. Enterotoxigenic strains showed a higher tendency to demonstrate haemolytic activity, but none of the other biochemical properties could be correlated with the ability of the staphylococci to produce enterotoxins. It appears that other ancillary tests must be developed to be useful in the differentiation of enterotoxigenic and non-enterotoxigenic staphylococci.

Development and evaluation of dot-immunobinding assay for detection of scrub typhus infection in Leptotrombidium fletcheri (Acari: Trombiculidae).

A dot-immunobinding assay (DIBA) was compared with a direct fluorescent antibody technique (DFAT) for the detection of Rickettsia tsutsugamushi infection in Leptotrombidium fletcheri (Womersley & Heaslip). Laboratory colonies of infected and noninfected chiggers were examined. The relative proportions of positive, negative, and indeterminate results were significantly different between DIBA and DFAT for infected but not for noninfected chiggers. DIBA was more sensitive and had a better negative predictive value and a lower false negative percentage than DFAT. It was concluded that DIBA is a suitable alternative to DFAT for detecting scrub typhus infection in chiggers.

Enterotoxin production by Staphylococcus aureus strains isolated from humans, foods and animals in Malaysia.

Enterotoxin production by strains of Staphylococcus aureus isolated from human, food and animal sources was investigated. Of the 130 isolates studied, 27 (20.8%) were found to be enterotoxigenic. The most common enterotoxin detected from human sources was enterotoxin C whereas enterotoxin B occurred more frequently in staphylococcal strains of food origin. The 2 enterotoxigenic strains, from animals isolated from a dog and a goat, produced enterotoxins A and C, respectively. Enterotoxin E was not detected alone from any of the enterotoxigenic strains studied, but occurred together with other enterotoxins. The need to detect enterotoxin in staphylococcal strains and in suspected foods for the confirmation of staphylococcal food poisoning is discussed.

Pulsed-field gel electrophoresis as an epidemiologic tool in the investigation of laboratory acquired Salmonella typhi infection.

Strains of Salmonella typhi implicated in two separate cases of laboratory acquired infection from patients and the medical laboratory technologists who processed the patients' samples were analysed by pulsed-field gel electrophoresis. Although all four isolates were of bacteriophage type E1, PFGE was able to demonstrate that the strains responsible for the two laboratory acquired cases were not genetically related. The PFGE patterns of the isolates from the MLTs were found to be identical to those of the corresponding patients after digestion with restriction enzyme AvrII. This provided genetic as well as epidemiological evidence for the source of the laboratory acquired infections.

In-vitro susceptibility of Pseudomonas pseudomallei isolated in Malaysia to some new cephalosporins and a quinolone.

The current drugs recommended for treatment of melioidosis are tetracycline, chloramphenicol and cotrimoxazole. Unfortunately these drugs are not the drug of choice in an acutely ill patient with septicaemia prior to the availability of laboratory results. With the discovery of the new cephalosporins which have a broad spectrum of activity clinicians are using them either alone or in combination with other antibiotics in such critical situations. Hence, an in-vitro study was carried out on the susceptibility of 41 strains of P. pseudomallei isolated in Malaysia, to these new cephalosporins and a new quinolone. The results showed that all the cephalosporins tested had some activity on the strains tested, with ceftazidime being the most active drug. Pefloxacin had very poor activity. However, further clinical studies are required to determine the duration, dosage and in-vivo activity of the antibiotics.

Development and preliminary evaluation of an IgM dot-immunobinding assay (IgM-DIA) for rapid serodiagnosis of scrub typhus infection.

An IgM dot-immunobinding assay (IgM-DIA) was developed for the diagnosis of scrub typhus infection. The whole cell antigens of Karp, Kato and Gilliam strains of Rickettsia tsutsugamushi were immobilized onto nitrocellulose paper and reacted with patients sera. The presence of IgM R. tsutsugamushi specific antibody in the patient sera could be detected by the observation of a visible brown dot on the nitrocellulose paper. The IgM-DIA has a sensitivity of 90.4% and specificity of 81.4% as compared to the indirect immunoperoxidase test. The IgM-DIA is rapid, simple, cost-effective, does not require microscope or incubator. It is recommended as a rapid screening test for the diagnosis of scrub typhus infection in the field or rural area within the hyperendemic region.

In-vitro susceptibility of Burkholderia pseudomallei to cefoperazone-sulbactam combination.

Melioidosis is endemic in Malaysia. Emerging resistance with new and current antimicrobial agents has underscored the need to look further for new antimicrobial agents for the treatment of melioidosis. Hence, we evaluated the in-vitro susceptibility of fifty locally isolated strains of Burkholderia pseudomallei, the causative agent of melioidosis to cefoperazone-sulbactam combination using the method of NCCLS. All the fifty strains tested were susceptible in-vitro to cefoperazone-sulbactam. The MIC90 of the organism for cefoperazone-sulbactam was 4 mg/L. The results of our findings suggested that cefoperazone-sulbactam may be useful in the treatment of melioidosis.

Prevalence and antibiotic susceptibility of Ureaplasma urealyticum in Malaysian neonates with respiratory distress.

Ureaplasma urealyticum was isolated from the endotracheal aspirates of 39 (21.4%) of 182 neonates with respiratory distress requiring ventilatory support. Mycoplasma hominis was isolated from one (0.5%) neonate. Bacterial cultures were negative in 123 (67.6%) neonates. Antibiotic susceptibility test carried out on ten isolates of U. urealyticum showed that all the organisms were sensitive to erythromycin but resistant to lincomycin and sulfamethoxazole trimethoprim. All, except one, U. urealyticum were sensitive to tetracycline and minocycline. Two isolates were resistant to ciprofloxacin. This study showed that U.urealyticum was a common organism isolated from the endotracheal aspirates of neonates with respiratory distress.

Preliminary evaluation of the INDX DIP-S-TICKS with positive rickettsial samples in Malaysia.

Forty-four serum samples of various reactivities to rickettsial antigens demonstrated by the indirect immunoperoxidase technique were tested with INDX Dip-S-Ticks (INDX Integrated Diagnostics Inc., USA) Kit for the detection of tick borne diseases. The kit utilised Rickettsia rickettsii the causative agent of Rocky Mountain spotted fever (RMSF) as antigens. The samples positive for endemic typhus were also tested against R. typhi, the agent for endemic typhus by the same method. The aim of this study was to determine the extent of cross-reactivity of R. rickettsii with rickettsial infections in Malaysia. Nine out of 12 tick typhus, 4 out of 10 scrub typhus and 4 out of 12 endemic typhus samples cross reacted with R. rickettsii. Ten out of 12 endemic samples were positive with R. typhi by the same method. From the study, we concluded that the INDX Dip-S-Ticks Kit can be used as a rapid screening test to detect endemic and tick-borne rickettsial infections in Malaysia but a second serological test is strongly recommended on all weakly reactive cases.

An evaluation of the usefulness of a culture system for the detection of Ureaplasma urealyticum in the endotracheal aspirates of neonates.

In this study, we evaluated the usefulness of a culture system used in our laboratory for the detection of Ureaplasma urealyticum in the endotracheal aspirates of neonates. Ureaplasmal broth was used to enhance the growth of U. urealyticum followed by observation of colonies on A7 agar. Of the 68 samples of endotracheal aspirates tested, 60 gave positive indication of urease activity by the broth. However, only 14 yielded U. urealyticum colonies on A7 agar medium. Polymerase chain reaction detected U. urealyticum in 21 samples. The use of Ureaplasmal broth was therefore not specific for the diagnosis of U. urealyticum. We suggest that subculture onto agar medium or PCR is essential for definite identification of U. urealyticum.

Auxotypes and serogroups of tetracycline-resistant Neisseria gonorrhoeae isolated in Malaysia.

Between 1992 and 1994, 253 tetracycline-resistant Neisseria gonorrhoeae (TRNG) strains were isolated and characterized by auxotype and serogroup (A/S) classes to study TRNG prevalence in different years. TRNG accounted for 28.1, 42.5, and 51.9% of the strains isolated in 1992, 1993, and 1994, respectively, showing a significant increase in each successive year (chi square = 26.7, P < 0.001). There was no significant increase in penicillinase-producing TRNG, which accounted for 53.1, 53.8, and 63.2% of the TRNG isolates. The 253 TRNG isolates belonged to 53 A/S classes. Eighteen A/S classes not observed in 1992 were detected in 1993, and 11 A/S classes not observed in 1992 and 1993 were isolated in 1994, indicating dissemination of the tetracycline resistance gene among the N. gonorrhoeae strains in Malaysia. Its emergence and subsequent rapid spread are alarming. The plasmid is capable of self-transfer (S.A. Morse, S.R. Johnson, J.W. Biddle, and M.C. Roberts, J. Infect. Dis. 155:819-822, 1987), allowing further dissemination of tetracycline resistance.