Klebsiella neonatal injections: mechanism of broadening aminoglycoside resistance

Abstract

Kanamycin resistance in eight strains of Klebsiellapneumoniae isolated during an outbreak of infection in a neonatal intensive care unit was found to be transferable and mediated by neomycin phosphotransferase. After gentamicin was used to control infections caused by kanamycin-resistant organisms, a strain resistant to gentamicin emerged. Gentamicin resistance in this ninth strain was not transferable and was accompanied by resistance to tobramycin, amikacin, and streptomycin. Enzymatic modifications of aminoglycosides other than neomycin and kanamycin could not be demonstrated either by filter binding assays or by electrophoresis of a radioactive aminoglycoside substrate. The strain with broad aminoglycoside resistance contained six plasmid deoxyribonucleic acid bands, none of which appeared to be different in molecular weight from plasmid deoxyribonucleic acid bands in strains isolated before the institution of gentamicin therapy. The broadening of resistance was accompanied by reduced uptake of radioactively labeled streptomycin and gentamicin. The relationship between aminoglycoside resistance and reduced drug transport in the absence of any enzymatic modification is discussed.The occurrence of drug-resistant Klebsiella pneumoniae as a cause of life-threatening disease in intensive care nurseries (1,10,16,17,23) remains a challenge in the management of this type ofselected patient population. Despite antibiotic therapy, drug-resistant K. pneumoniae strains can colonize the intestines and nasopharynx (2,8,24,26) and invade tissues and blood, causing lethal or potentially lethal infections (13,17,21,25). We report here the characteristics of nine strains of K. pneumoniae isolated from an outbreak ofinfection and compare the properties of these strains with those of other strains previously studied (23) in connection with neonatal infections. MATERIALS AND METHODSIsolation of strains. Strains of K pneumoniae were obtained from stool and blood specimens submitted to the clinical bacteriology laboratory at Confederate Memorial Medical Center, Shreveport, La., and were kindly referred to us by Ronald Silberman, Director of Microbiology. The biotype of each isolate was confirmed in our laboratory, and the serotype was determined at the Center for Disease Control, Atlanta, Ga.Antibiotic susceptibility testing and transfer ofresistance. The susceptibilities ofeach isolate were determined by measuring the minimal inhibitory concentrations (MICs) of antibiotics in tryptic soy broth (TSB) (Difco Laboratories, Detroit, Mich.) (23). The abilities of resistant strains to transfer specific resistance traits were determined by cocultivating isolates with a naladixic acid-resistant recipient strain of Escherichia coli, as previously described (23).Enzyme assays. Bacterial cell lysates were prepared by osmotic shock and/or sonication, as described by Haas and Dowding (15) for extraction of periplasmic contents. Aminoglycoside-modifying enzymes were assayed by the phosphocellulose paper binding method (15).

Two different types of fosfomycin resistance in clinical isolates of Klebsiella pneumoniae

“…Accordingly, it is presumed from these results that the impermeability-type FOM resistance in K. pneumoniae is due to membrane changes related to the uptake system of hexose phosphate [9,25]. Impermeability-type drug resistance other than FOM resistance has been described in other clinical isolates of bacteria, particularly K. pneumoniae [26], and P. aeruginosa [22,24,27,28].…”

Lipopolysaccharide changes in impermeability-type aminoglycoside resistance in Pseudomonas aeruginosa

“…Impermeability resistance is not restricted to P. aeruginosa, although it is much more common in that bacterium. It has been described in other clinical isolates of bacteria, particularly Klebsiella pneumoniae (12,22 Conjugation and transduction. Conjugation and transduction were performed as previously described (2,4,20), except that the transducing phage used was E79.tv2 (21).…”

“…Impermeability resistance is not restricted to P. aeruginosa, although it is much more common in that bacterium. It has been described in other clinical isolates of bacteria, particularly Klebsiella pneumoniae (12,22). Two aspects that make these types of isolates of importance are the very wide spectrum of aminoglycoside resistance (3) and the poor control of such strains by barrier nursing (29).…”

Antimicrobial agent susceptibility patterns of bacteria in hospitals from 1971 to 1982

“…Before 1946, 85% of Staphylococcus aureus strains were highly susceptible to penicillin; today, only 11% remain susceptible (12). The medical community has been warned repeatedly of major increases in bacterial resistance (23,28,34,39,41), with many reports citing the increased resistance of S. aureus to methicillin (1,4,5,7,8,11,19,41,44,49) and gentamicin (5,10,11,44,48), of Haemophilus influenzae to ampicillin (16,20,27,51), of gram-negative bacilli, especially Pseudomonas aeruginosa, to aminoglycosides (13,17,24,31,32,37,38,50), and the increasing multiple drug resistance among enterococci (30, 33). The new cephalosporins appear to be responsible for bacterial cross-resistance to several betalactam antibiotics and occasionally to the aminoglycosides (43).…”