Cytology of primary versus secondary genital herpesvirus infection

Certain authors state that primary genital herpes infections mainly produce cells with ground-glass nuclei, whereas secondary infections produce a higher percentage of multinucleated or single cells with prominent intranuclear inclusions. The cervicovaginal smears of 11 patients with primary genital herpes infection and 16 patients with secondary infection were studied to determine the validity of this differentiation. The percentage per patient of virally infected cells containing distinct inclusions ranged from 0% to 35% in the primary herpes group and 0% to 100% in the secondary herpes group. In eight additional patients, the initial herpes simplex virus (HSV)-positive smear was compared with recurrent positive smears taken from 2 to 120 mo later. No statistical difference in the incidence of distinct inclusions in the infected cells was detected. Finally, primary rabbit kidney and the heteroploid A549 cell cultures were inoculated with herpes viruses and followed by fixation with several agents at various time intervals. Alcohol and Bouin's fixative favored the recognition of distinct inclusions, as did the duration of the infection.

Aminoglycoside resistance in Pseudomonas aeruginosa isolated from cystic fibrosis patients

The authors studied 30 gentamicin-resistant and 17 gentamicin-sensitive strains of Pseudomonas aeruginosa isolated from respiratory cultures of patients with cystic fibrosis from five United States cities for the presence of plasmids, cross-resistance to other aminoglycosides, and the production of aminoglycoside-modifying enzymes. Four of 30 resistant strains and 3 of 17 sensitive strains contained one or more plasmids. Aminoglycoside cross-resistance to tobramycin, amikacin, and netilmicin was seen in 21 of 30 gentamicin-resistant strains. Seven strains that had low-level gentamicin resistance (minimum inhibitory concentrations [MIC] = 8-32 micrograms/mL) were sensitive to one or more of the other three aminoglycosides. Two strains with high-level gentamicin resistance (MIC greater than or equal to 128 micrograms/mL) were sensitive to amikacin. These two strains, each containing three plasmids, were the only isolates of nine tested that produced an aminoglycoside-modifying enzyme with activity against gentamicin. None of the plasmids was transferable by conjugation. Four strains, three of which contained one or more plasmids, produced an aminoglycoside 3'-0-phosphotransferase II. The authors propose that the mechanism of gentamicin resistance in P. aeruginosa from patients with cystic fibrosis is not commonly plasmid-mediated and likely is due to membrane impermeability to aminoglycosides.

Evidence for a chromosomal site specifying amikacin resistance in multiresistant Serratia marcescens

We studied 21 strains of amikacin-resistant Serratia marcescens from three different U.S. cities, Twenty of the 21 strains contained conjugative R plasmids mediating gentamicin and tobramycin resistance. Amikacin-resistant S. marcescens from two cities predominated in protracted outbreaks. Conversely, the amikacin-resistant Charleston strain (serotype 02/03:nonmotile) was isolated from only four patients during an outbreak of gentamicin- and tobramycin resistant, amikacin-susceptible S. marcescens (serotype O19:O17). Five different representative amikacin-resistant S. marcescens, each containing a single conjugative plasmid, elaborated a nontransferable aminoglycoside (6')-N-acetyltransferase [AAC(6')] with similar substrate profiles in addition to other transferable aminoglycoside-modifying enzymes. One amikacin-resistant S. marcescens cured of its plasmid and another naturally occurring plasmid-free amikacin-resistant S. marcescens elaborated only AAC(6')-1. These data support the concept of a chromosomal locus in S. marcescens for AAC(6')-1 which commonly coexists with plasmid-mediated genes for aminoglycoside-modifying enzymes.

Characteristics of Serratia marcescens containing a plasmid coding for gentamicin resistance in nosocomial infections

Strains of gentamicin-resistant Serratia marcescens (GRSM) that originated in a crowded neurosurgical close observation unit (COU) became established during a 2.5-year interval at several affiliated hospitals in Charleston, South Carolina. Most patients with GRSM had colonization or infection of the urinary tract associated with indwelling bladder catheters. Infected patients in the COU more often had pyuria and less often received systemic steroids than COU patients not harboring GRSM. However, length of stay, use of urinary catheters, exposure to systemic antibiotics, and exposure to gentamicin were not significantly different between the two groups. Of the strains of GRSM, 92% contained a conjugative 41-megadalton plasmid tht encoded resistance to ampicillin, carbenicillin, tetracycline, kanamycin, gentamicin, and tobramycin and elaborated similar aminoglycoside 3-acetyltransferases. Seven 41-megadalton plasmids from outbreak strains and a 41-megadalton plasmid from a 1973 isolate of GRSM gave identical DNA fragments after restriction endonuclease digestion.

Activity of cephalosporins against methicillin-susceptible and methicillin-resistant, coagulase-negative staphylococci: minimal effect of beta-lactamase

Eight cephalosporins were tested for their activity against methicillin-susceptible and methicillin-resistant, coagulase-negative staphylococci and for their resistance to beta-lactamase from methicillin-resistant, coagulase-negative staphylococci. Susceptibility testing by the agar plate method was evaluated for the effect of inoculum size and duration of incubation. Methicillin-susceptible, coagulase-negative staphylococci were highly susceptible to the cephalosporins, with cephapirin and cepahlothin showing the greatest activity, followed by cefazolin and cefamandole. Methicillin-resistant, coagulase-negative staphylococci displayed nearly total cross-resistance to the cephalosporins. Resistance increased with increasing inoculum size. Beta-Lactamases produced by methicillin-resistant, coagulase-negative staphylococci had a minimal hydrolytic effect on cepahlothin, cephapirin, cefazolin, and cefamandole and no measurable effect on cefoxitin. There was no correlation between the anti-staphylococcal activity and resistance to beta-lactamases.

Evolution of multiple-antibiotic-resistance plasmids mediated by transposable plasmid deoxyribonucleic acid sequences

Two plasmid deoxyribonucleic acid sequences mediating multiple antibiotic resistance transposed in vivo between coexisting plasmids in clinical isolates of Serratia marcescens. This event resulted in the evolution of a transferable multiresistance plasmid. Both sequences, designated in Tn1699 and Tn1700, were flanked by inverted deoxyribonucleic acid repetitions and could transpose between replicons independently of the Excherichia coli recA gene function. Tn1699 and Tn1700 mediated ampicillin, carbenicillin, kanamycin, and gentamicin resistance but differed in the type of gentamicin-acetyltransferase enzymes that they encoded. The structural genes for these enzymes share a great deal of polynucleotide sequence similarity despite their phenotypic differences. The transposition of Tn1699 and Tn1700 to coresident transferable plasmids has contributed to the dissemination of antibiotic resistance among other gram-negative bacteria. These organisms have recently caused nosocomial infections in epidemic proportions.

Transposable plasmid deoxyribonucleic acid sequence in Pseudomonas aeruginosa which mediates resistance to gentamicin and four other antimicrobial agents

A 9.1 x 10(6)-dalton transposable deoxyribonucleic acid sequence resides within Pseudomonas aeruginosa plasmid R1033 and mediates resistance to gentamicin, streptomycin, sulfamethoxazole, chloramphenicol, and mercuric chloride. Transposability was demonstrated in Escherichia coli when this sequence, designated Tn1696, excised from R1033 and integrated into plasmid pMB8. Excision and insertion of Tn1696 occurred independently of the host Rec phenotype and may involve the 140-base pair, inverted deoxyribonucleic acid repeated region that flanks this sequence. Occurrence of a multiresistance transposon on a transferrable plasmid that has a broad host range may have serious epidemiological and therapeutic consequences.