Transformation of a plasmid encoding an adhesin of Staphylococcus aureus into a nonadherent staphylococcal strain.

Plasmid DNA was isolated and purified from a strain of Staphylococcus aureus demonstrating adherence to human epithelial cells, as determined by an assay quantitating adherence of radiolabeled S. aureus to HeLa cells in tissue culture. Other phenotypic characteristics of the donor strain are resistance to ampicillin and absence of hemolysis. A 23.5-kb (kilobase) plasmid was transformed into a nonadherent, ampicillin-sensitive, beta-hemolytic recipient of S. aureus, rendering it both ampicillin-resistant and adherent to a degree approaching that of the donor strain. Plasmid analysis of the donor and transformant strains revealed three identical EcoRI fragments of 7.6 kb, 6.5 kb, and 2.2 kb, together with a 3.6-kb EcoRI fragment in the transformant that demonstrated homology with the last 7.2-kb fragment in the donor. We conclude that an adhesin of S. aureus is encoded by this 23.5-kb penicillinase-encoding plasmid and that techniques of molecular genetics may be utilized to clarify the mechanisms of adherence of S. aureus.

Detection of cytomegalovirus antigen and antibodies in the urine of small infants and children.

The diagnostic efficacy of an enzyme immune assay to detect cytomegalovirus (CMV) antigen in the urine of infected infants and children was determined, and the effect that CMV-specific antibodies present in the urine have on the sensitivity of the test was ascertained. The antigen was detected in 84.4% of the CMV-culture-positive samples, while CMV-specific IgA was detected in 24% of CMV-culture-positive specimens. The absence of CMV-specific IgA correlated with detection of CMV antigen in the CMV-culture-positive urine specimens (p less than 0.05).

pH-dependent oxacillin tolerance of Staphylococcus aureus.

A proportion of clinical isolates of Staphylococcus aureus exhibit resistance to bactericidal activity of certain antibiotics, despite normal susceptibility to inhibition. This phenomenon is termed "tolerance." The methodology used to determine tolerance varies greatly. To clarify the relationship between laboratory methodology and tolerance, we determined the minimal bactericidal concentrations and minimal inhibitory concentrations for 20 clinical isolates by two methods. Inocula were prepared by either 3-h growth of the organism in Mueller-Hinton broth or overnight (22 to 24 h) cultures in Trypticase soy broth (BBL Microbiology Systems, Cockeysville, Md.). All inocula were plated for colony counts and tested for pH. An American Type Culture Collection (Rockville, Md.) reference strain was included in all tests for standardization. Tolerance was defined by the strictest criterion, i.e., a minimal bactericidal concentration/minimal inhibitory concentration ratio of greater than or equal to 100. With the first method, none of the 20 isolates displayed tolerance (mean inoculum pH, 7.15). When inocula were grown in Trypticase soy broth with overnight incubation, 35% (7 of 20) showed tolerance (mean inoculum pH, 6.22). There was a significant association between the decreased bactericidal capacity at high oxacillin concentrations and overnight incubation in Trypticase soy broth (P less than 0.01). We suggest that tolerance in staphylococci is in some way related to the pH value of the inoculating culture. Such pH-induced tolerance may have a clinical corollary in sequestered infections where the pH is acidic.

Pharyngeal carriage of group B streptococci: detection by three methods.

The prevalence of pharyngeal carriage of group B streptococci was evaluated in patients with and without the complaint of a sore throat by three methods (blood agar plates, Columbia CNA agar plates, and a selective enrichment broth containing gentamicin and nalidixic acid). The overall carriage rate of group B streptococci was 12%, and there was no significant difference between the two groups of patients. The selective broth medium was more sensitive than the two solid agar plate methods in detecting carriage, and 37% of all group B streptococci were recovered solely from the broth. Use of the broth alone would have permitted a 94% detection of the group B streptococcal carriers.