Abnormal forms of bacteria produced by antibiotics

Analysis of Paradoxical Efficacy of Carbapenems against Carbapenemase-Producing Escherichia coli in a Murine Model of Lethal Peritonitis

The clinical benefit of carbapenems against carbapenemase-producing Enterobacteriaceae (CPE) remains in question. MICs of imipenem (IMP) and ertapenem (ERT) against isogenic derivatives of the wild-type strain Escherichia coli CFT073 producing KPC-3, OXA-48, or NDM-1 were 0.25, 2, 16, and 64 mg/liter for IMP and 0.008, 0.5, 8, and 64 mg/liter for ERT, respectively. Swiss ICR-strain mice with peritonitis were treated for 24 h with IMP or ERT. Despite a limited duration of time during which free antibiotic concentrations were above the MIC (down to 0% for the NDM-1-producing strain), IMP and ERT significantly reduced bacterial counts in spleen and peritoneal fluid at 24 h (P < 0.005) and prevented mortality. Several possible explanations were investigated. Addition of 4% albumin or 50% normal human serum did not modify IMP activity. Bacterial fitness of resistant strains was not altered and virulence did not decrease with resistance. In the presence of subinhibitory concentrations of ERT, growth rates of OXA-48, KPC-3, and NDM-1 strains were significantly decreased and filamentation of the NDM-1 strain was observed. The expression of bla _NDM-1 was not decreased in vivo compared to in vitro No zinc depletion was observed in infected mice compared with Mueller-Hinton broth. In conclusion, a paradoxical in vivo efficacy of IMP and ERT against highly resistant carbapenemase-producing E. coli was confirmed. Alternative mechanisms of antibacterial effects of subinhibitory concentrations of carbapenems may be involved to explain in vivo activity. These results are in agreement with a potential clinical benefit of carbapenems to treat CPE infections, despite high carbapenem MICs.

Escherichia coli spheroplasts in a Croatian patient misclassified by two urine sediment analysers as erythrocytes: case report

Introduction

It has already been reported that subinhibitory concentrations of β-lactam antibiotics can cause abnormal changes of bacterial forms, such as spheroplasts. Herein we report a case of Croatian male patient with Escherichia coli spheroplasts present in urine after treatment with tazobactam, on the tenth day of hospitalization. The aim of this report is to emphasize the inability of imaging based automated urine analysers to recognize some relatively uncommon forms of bacterial presentation in urine sediment.

Materials and methods

During routine urine analysis, unusual particles were observed in patient urine. Urine sediment was examined by two urine analysers: Atellica 1500 (Siemens, Germany) and Iris iQ200 (Beckman Coulter, USA). Additionally, urine was sent for culture testing to Microbiology department.

Results

Both urine analysers didn’t indicate presence of bacteria in urine sediment. Unusual particles observed on the tenth day were classified as erythrocytes by both instruments. Dipstick test showed blood trace and microscopic analysis revealed bacteria in urine. Urine culture was positive for Escherichia coli. Careful examination of urine sediment has confirmed that shapes present in urine were abnormal bacterial forms called spheroplasts.

Conclusions

Imaging based automated urine analysers are not able to recognize bacterial spheroplasts in urine sediment misclassifying it as erythrocytes. Microscopic examination remains the gold standard for urines with blood trace or negative blood, in which erythrocytes are reported by urine analyser in urine sediment. Failure to identify and follow up such cases may lead to inaccurate treatment decisions and puts patient safety at risk.

Morphological and ultrastructural changes in bacterial cells as an indicator of antibacterial mechanism of action

Efforts to reduce the global burden of bacterial disease and contend with escalating bacterial resistance are spurring innovation in antibacterial drug and biocide development and related technologies such as photodynamic therapy and photochemical disinfection. Elucidation of the mechanism of action of these new agents and processes can greatly facilitate their development, but it is a complex endeavour. One strategy that has been popular for many years, and which is garnering increasing interest due to recent technological advances in microscopy and a deeper understanding of the molecular events involved, is the examination of treated bacteria for changes to their morphology and ultrastructure. In this review, we take a critical look at this approach. Variables affecting antibacterial-induced alterations are discussed first. These include characteristics of the test organism (e.g. cell wall structure) and incubation conditions (e.g. growth medium osmolarity). The main body of the review then describes the different alterations that can occur. Micrographs depicting these alterations are presented, together with information on agents that induce the change, and the sequence of molecular events that lead to the change. We close by highlighting those morphological and ultrastructural changes which are consistently induced by agents sharing the same mechanism (e.g. spheroplast formation by peptidoglycan synthesis inhibitors) and explaining how changes that are induced by multiple antibacterial classes (e.g. filamentation by DNA synthesis inhibitors, FtsZ disruptors, and other types of agent) can still yield useful mechanistic information. Lastly, recommendations are made regarding future study design and execution.

Yersinia pestis intracellular parasitism of macrophages from hosts exhibiting high and low severity of plague

BACKGROUND

Yersinia pestis causes severe disease in natural rodent hosts, but mild to inapparent disease in certain rodent predators such as dogs. Y. pestis initiates infection in susceptible hosts by parasitizing and multiplying intracellularly in local macrophages prior to systemic dissemination. Thus, we hypothesize that Y. pestis disease severity may depend on the degree to which intracellular Y. pestis overcomes the initial host macrophage imposed stress.

METHODOLOGY/PRINCIPAL FINDINGS

To test this hypothesis, the progression of in vitro infection by Y. pestis KIM62053.1+ of mouse splenic and RAW264.7 tissue culture macrophages and dog peripheral blood-derived and DH82 tissue culture macrophages was studied using microscopy and various parameters of infection. The study showed that during the early stage of infection, intracellular Y. pestis assumed filamentous cellular morphology with multiple copies of the genome per bacterium in both mouse and dog macrophages. Later, in mouse macrophages, the infection elicited spacious vacuolar extension of Yersinia containing vacuoles (YCV), and the filamentous Y. pestis reverted to coccobacillary morphology with genomic equivalents approximately equaling colony forming units. In contrast, Y. pestis infected dog macrophages did not show noticeable extension of YCV, and intracellular Y. pestis retained the filamentous cellular morphology for the entire experiment in DH82 cells or were killed by blood-derived macrophages. In addition, during the later stage of infection, Y. pestis infected mouse macrophages exhibited cell lysis whereas dog macrophages did not.

CONCLUSION/SIGNIFICANCE

Overall, these results support our hypothesis that Y. pestis in mouse macrophages can overcome the initial intracellular stress necessary for subsequent systemic infection. However, in dogs, failure of Y. pestis to overcome macrophage imposed stress may result in mild or in apparent disease in dogs.

Mechanisms to assess Gram stain interpretation proficiency of technologists at satellite laboratories

To address Gram stain interpretation proficiency in a satellite/centralized microbiology laboratory paradigm, two programs were devised. In quality assurance program 1, nonmicrobiology technologists at satellite laboratories were required to interpret standardized Gram-stained specimens of clinical material prepared by an experienced microbiologist at a central laboratory. In quality assurance program 2, clinical Gram stains prepared and read by the satellite laboratorians were reviewed by experienced microbiologists at the central laboratory. Satisfactory performance (94%) was achieved in quality assurance program 1. In contrast, quality assurance program 2 had a significantly lower overall performance (89%; P < 0.0001) due to poorer identification of host cells (93%) and bacteria (84%). A variety of intervention mechanisms, including continuous monitoring, resulted in overall performance improvement (P < or = 0.006). While a technologist challenge has educational merit, having a microbiologist review previously read slides is a better indicator of the technologist's Gram stain interpretation proficiency.

Atomic Force Microscopy Study of Different Effects of Natural and Semisynthetic β-Lactam on the Cell Envelope ofEscherichiacoli

The effects of native and semisynthetic beta-lactam on the surface of E. coli cells were investigated using tapping mode atomic force microscopy (AFM). These studies were done on both single cell and cell colonies. This allowed us to achieve a complete understanding of the effects, since previous related AFM analysis was only performed on single cells. Our results indicated that although amoxycillin and penicillin could both induce nanoporous damage to the envelope of E. coli, the distribution of the pores was different: those induced by penicillin were randomly distributed on the cell surface, while those induced by amoxycillin were far more numerous and mainly on the two ends of the cell. These findings could explain why the effect of amoxycillin is stronger than that of native penicillin. Ofloxacin was used as a control due to its inactive membrane, and no cell wall damages were observed. Our results demonstrate that AFM is a useful tool in discerning and verifying antibiotic mechanisms and can be helpful to explain the relationship between chemical structure and the function of antibiotics.

Morphological changes induced by imipenem and meropenem at sub-inhibitory concentrations in Acinetobacter baumannii

Abstract Sub-inhibitory concentrations of imipenem and meropenem were evaluated for their ability to induce morphological changes with six strains of Acinetobacter baumannii isolated from patients with nosocomial pneumonia. Three strains were susceptible and three were resistant to carbapenems. The strains were grown in the presence of 0 (controls), 0.25x, 0.5x and 1x the MIC of both carbapenems for 4 h, and then examined after Gram's stain. Cells > or = 3 microm in size (spheroplasts) were considered to be altered. Both carbapenems induced significant numbers of spheroplasts compared to controls. Imipenem had more effect against susceptible strains, while meropenem had a greater effect against resistant strains.

Considerations relating to the epidemiology of human immunodeficiency virus infection: the impact of bacterial antigens and consequences for treatment

OBJECTIVE

A treatment for patients with human immunodeficiency virus/acquired immune deficiency syndrome (HIV/AIDS) is presented, which is based on an isopathic method that appears to be effective in eliminating bacterial antigens from the body. The concept is based on a new hypothesis concerning the outbreak and spread of AIDS in Africa and worldwide.

SUBJECTS AND DESIGN

Laboratory data are presented from five European and seven African patients with HIV.

RESULTS

Oral administration of ultra-low doses of a lysate of Staphylococcus aureus Cowan I (12c potency) resulted in a significant increase of CD4 T-cell subsets and CD4/CD8 ratios in patients with HIV infection as well as in advanced stages of HIV disease, concomitant with the improvement of clinical HIV-related symptoms.

CONCLUSIONS

Based on epidemiologic data, the beginning of the African AIDS epidemic is related-to time, place, and circumstances-to the initial large-scale introduction of antibiotics in areas of Central Africa that would later comprise the AIDS belt. It is concluded that certain antimicrobial agents can enhance the formation of persistent bacterial superantigens, which may indicate a link between asymptomatic HIV carriers and the development of AIDS. According to this view, superantigens and bacterial cell wall components remaining in the body after antibiotic treatment cause a permanent activation of the immune system and would thus favor T-cell infection and viral replication in HIV-infected individuals.

Postantibiotic effects and postantibiotic sub-MIC effects of erythromycin, roxithromycin, tilmicosin, and tylosin on Pasteurella multocida

When intermittent dosing is used during treatment, the concentrations of antibiotics fluctuate and subinhibitory concentrations may occur between doses. Postantibiotic effects (PAEs) and postantibiotic subinhibitory effects (PA SMEs) on bacteria may provide additional, valuable information for the rational use of a drug in clinical practice. In this study tilmicosin was the most active antibiotic tested against P. multocida type D with MICs ranging from 4-16 mg/l. Roxithromycin and tilmicosin induced a statistically significantly longer PAE than did tylosin against P. multocida types A and D (P < 0.05). The duration of PAEs and PA SMEs were proportional to the concentrations of drugs used for exposure. The PA SMEs were substantially longer than PAEs on P. multocida. Tilmicosin had a longer PA SME compared with erythromycin, roxithromycin and tylosin for P. multocida. The computerized incubator used in the present study provided an efficient and convenient determination of PAE and PA SME, allowing frequent measurements of the bacterial growth.

Pharmacodynamic effects of subinhibitory antibiotic concentrations

The pharmacodynamics of antibiotics have become increasingly important for the determination of optimal dosing regimens. Studies over the past decade have demonstrated marked differences in the time course of antimicrobial activity for different classes of antibiotics both in vitro, in animals and in human trials. One of the explanations for the success of intermittent dosing regimens has been the delay in regrowth after the concentration has fallen under the MIC, the so called postantibiotic effect (PAE). In addition to the PAE, the success of discontinuous dosing regimens may be attributed to both the function of a normal host defence and to the effects of subinhibitory antibiotic concentrations (sub-MICs). It has been shown that there is a difference between the effects of sub-MICs following a suprainhibitory dose (postantibiotic sub-MIC effect; PA SME) and the effects of sub-MICs (SME) alone. It seems that the PA SME is more clinically relevant compared with the PAE, since exposure to suprainhibitory concentrations will always be followed by sub-MICs in vivo. A long PA SME could indicate that longer dosing intervals may be used for that antibiotic /bacterial combination and together with the known effects of sub-MICs on bacterial virulence and the influence of the immune system, it may explain the efficacy of antibiotics with short half-lives even of they are given infrequently.

Morphological changes (including filamentation) in Escherichia coli grown under starvation conditions on silicon wafers and other surfaces

Using a scanning electron microscope, pleomorphism (notably filamentation) was seen when Escherichia coli was grown under starvation conditions for 14 d on microporous silicon wafers, titanium, glass and plastic discs. Under these conditions, the 'standard', rod shaped cell (1-3 microns) failed to separate after division and filaments developed, some as long as 50 microns, with many showing bulbous tips. Filamentation began to occur 5 d after the imposition of starvation conditions. Dumbbell shaped cells were also observed, although apparent 'Y' and 'V'-shaped cells proved to be artefacts, caused by overlapping rods. The implications of the appearance of pleomorphism in E. coli, when grown under starvation conditions, is discussed in relation to its pathogenicity and growth in the environment.

New criteria for selecting the proper antimicrobial chemotherapy for severe sepsis and septic shock

The mortality rate resulting from severe bacterial sepsis, particularly that associated with shock, still approaches 50% in spite of appropriate antimicrobial therapy and optimum supportive care. Bacterial endotoxins that are part of the cell wall are one of the cofactors in the pathogenesis of sepsis and septic shock and are often induced by antimicrobial chemotherapy even if it is administered rationally. Not all antimicrobial agents are equally capable of inducing septic shock; this is dependant on their mechanism of action rather than on the causative pathogen species. The quantity of endotoxin released depends on the drug dose and whether filaments or spheroplast formation predominates. Some antibiotics such as carbapenems, ceftriaxone, cefepime, glycopeptides, aminoglycosides and quinolones do not have the propensity to provoke septic shock because their rapid bactericidal activity induces mainly spheroplast or fragile spheroplast-like bacterial forms.

Antibiotic-induced release of bacterial cell wall components in the pathogenesis of sepsis and septic shock: a review

This article reviews the new criteria for selecting the proper antimicrobial agent and dosage regimen for standard treatment of severe sepsis, with the intention of preventing septic shock. After introducing new concepts on the pathogenesis of sepsis and septic shock, the authors analyze the parameters of betalactam antibacterial activity, the antibiotic-induced release of bacterial endotoxin and the interrelationships between pharmacokinetics and pharmacodynamics of antibiotics in the search for an optimum dosage regimen of antimicrobial mono- or polytherapy for severely ill septic patients admitted to the intensive care unit.

Treated bacterial endocarditis as a histological mimic of fungal infection

Histological assessment of cardiac valve tissue contributes to the diagnosis of infective endocarditis and is of particular importance in cases in which no organism is cultured. Antibiotic treatment of bacterial endocarditis may lead to abnormal bacterial morphology and staining characteristics. Although in many cases the presence of some residual bacteria of normal appearance makes the diagnosis straightforward, in some only abnormal bacteria may be seen. Unless the appearances of these are interpreted with caution, the presence of larger spherical organisms with the staining properties of a yeast may lead to an erroneous diagnosis of fungal infection.

Atomic force microscopy: application to investigation of Escherichia coli morphology before and after exposure to cefodizime

Atomic force microscopy (AFM) is a recently developed technique that allows for the investigation of the surface morphology of a biological specimen at an unprecedented level of resolution. The aim of the present study was to explore some of the new opportunities offered by AFM by studying the morphological and surface alterations induced in Escherichia coli by supra-MICs and sub-MICs of a beta-lactam antibiotic (cefodizime). The underlying principle of AFM is the scanning and sensing of the topography of a sample by means of near-field microscopy that makes it possible to obtain simultaneous digital measurements of the x, y, and z coordinates of any point on the bacterial surface with great resolution (x and y, approximately 20 A; z, approximately 1 A). Unlike scanning electron microscopy, performance of AFM does not require a vacuum, drying to the critical point, or the coating of the bacterial surface with a metal layer. The digital storage of the information makes it easy to rotate the image, observe the bacterial surface and induced structural alterations from different points of view, and obtain a cross-section at any desired point with precise, automatic measurement of the heights and sizes of normal versus damaged bacteria. Use of the new and outstanding technique of AFM will make it possible for researchers to investigate biological samples immersed in biological fluids and will also make it possible for them to study the morphological alterations of living bacteria exposed to antibiotics as they are taking place.

Haemophilus influenzae infection of human respiratory mucosa in low concentrations of antibiotics

We examined the effects of 0.25 and 0.5 minimal inhibitory concentrations (MIC) of amoxicillin, loracarbef, and ciprofloxacin on the interaction of a clinical isolate of nontypable Haemophilus influenzae (NTHi) with human adenoid organ culture. Adenoid tissue was embedded in agar so that only the mucosal surface was exposed. Minimum essential medium containing NTHi with or without antibiotics was added to the organ culture and incubated with 5% CO2 at 37 degrees C for 24 h. The organ cultures (n = 6) were assessed for several parameters by light microscopy (LM) and transmission electron microscopy (TEM). Bacterial viable counts after 24 h were not significantly different in all organ cultures. Compared with uninfected controls at 24 h, infection with NTHi caused significant (p < 0.05) damage to epithelium as assessed by LM: reduced ciliary beat frequency (CBF), disruption of epithelium integrity, and reduced number of ciliated sites. TEM showed extrusion of cells from the epithelial surface, loss of cilia from ciliated cells, cytoplasmic blebbing, and mitochondrial damage. In the presence of 0.25 and 0.5 MIC of all three antibiotics, the mucosal damage was significantly less (p < 0.05). We conclude that in the presence of sub-MIC levels of amoxicillin, loracarbef, and ciprofloxacin, NTHi infection causes less functional (CBF) and structural damage.

Effect of subinhibitory concentrations of antibiotics on extracellular Shiga-like toxin I

Patients with diarrhea due to strains of enterohemorrhagic Escherichia coli (EHEC) (e. g. O157:H7) might be at a higher risk of developing hemolytic uremic syndrome when treated with antimicrobial agents. It has been suggested that this might be due to an increase of release or production of vero or shiga-like toxin from such organisms, possibly as a stress response to antimicrobial agents. The aim of this study was to detect such increases in extracellular toxin in vitro with a newly developed method that exposed EHEC to high sublethal concentrations followed by a recovery phase at progressively lower concentrations. Five strains of EHEC were exposed to continuously changing concentrations of ciprofloxacin, co-trimoxazole, cefixime and tetracycline. The amount of free shiga-like toxin I (SLT-I) released was compared to the amount released from inocula that were not exposed to antibiotics. There were significant differences between the five EHEC strains in the amount of toxin detected after exposure to antimicrobial agents (p less than 0.001). Equally important was the type of antibiotic (p less than 0.001), with ciprofloxacin inducing the largest increase ranging from 169 to 436%, followed by co-trimoxazole, cefixime and tetracycline. In addition, the increases in free toxin correlated with the concentration of the antibiotics (p less than 0.001). The association between antibiotic-induced increases in SLT-I produced by strains of EHEC and certain classes of antibiotics might influence the analysis of future epidemiological studies on risk factors for HUS.

Pharmacodynamic effects of subinhibitory concentrations of beta-lactam antibiotics in vitro

The pharmacodynamic effects of subinhibitory concentrations of different beta-lactam antibiotics were investigated. A postantibiotic effect (PAE) was induced for different bacterial species by exposure to 10x MIC of several beta-lactam antibiotics for 2 h in vitro. The antibiotic-bacterial combinations used in this study were imipenem-Pseudomonas aeruginosa, benzylpenicillin-Streptococcus pneumoniae and -Streptococcus pyogenes, cefcanel-S. pyogenes, ampicillin-Escherichia coli, and piperacillin-E. coli. After the induction of the PAE, the exposed cultures as well as the unexposed controls were washed and diluted. Thereafter, the cultures in the postantibiotic phase (PA phase) and the cultures not previously treated with antibiotics were exposed to 0.1, 0.2, and 0.3x MIC of the relevant drug and the growth curves were compared. When bacteria in the PA phase were exposed to sub-MICs, a substantial prolongation of the time before regrowth was demonstrated, especially in antibiotic-bacterial combinations for which a PAE was found. In contrast, sub-MICs on cultures not previously exposed to suprainhibitory antibiotic concentrations yielded only a slight reduction in growth rate compared with the controls. Thus, it seems important to distinguish the direct effects of sub-MICs on bacteria not previously exposed to suprainhibitory concentrations from the effects of sub-MICs on bacteria in the PA phase.

Mechanisms of interaction among subinhibitory concentrations of antibiotics, human polymorphonuclear neutrophils, and gram-negative bacilli

Our hypothesis was that pretreatment of bacteria with subinhibitory concentrations (sub-MICs) of antibiotics enhances the susceptibility of the organisms to killing by human polymorphonuclear neutrophils (PMNs). Our purpose was to study a variety of drugs with different mechanisms of action and to determine whether the mechanism and locus of action altered the sub-MIC effect. The following outcome measures were used: ingestion and killing of bacteria by PMNs, bacterial killing in the absence of phagosome formation, and binding requirements of the bacteria to PMNs. The antibiotics used were representative of a variety of classes, including beta-lactams (piperacillin and imipenem) and quinolones (ciprofloxacin). Bacterial uptake and killing were measured by using standard techniques, and results were analyzed by using the analysis-of-variance technique and Dunnett's t test. Pretreatment of Escherichia coli with all drugs showed significantly enhanced killing of bacteria by PMNs, which was independent of ingestion by the phagocytes. Even in the absence of phagosome formation, statistically significant killing persisted with piperacillin-pretreated bacteria but not with imipenem- or ciprofloxacin-pretreated organisms. The opsonization experiments showed that contact between bacteria and PMNs was necessary for killing to occur. The sub-MIC effect appears to be independent of the locus or mechanism of action of the antibiotic. It results in enhanced killing by PMNs which is independent of ingestion and also may persist even in the absence of phagosome formation. Killing is dependent upon specific contact between bacteria and an intact phagocyte.

Mutations in cloned Escherichia coli P fimbriae genes that makes fimbriae-production resistant to suppression by trimethoprim

The effect of sublethal concentrations of trimethoprim on the expression of P fimbriae was tested in Escherichia coli HB101 recombinant strains. Fimbriation was inhibited at trimethoprim concentrations down to at least 1/64 of the minimal inhibitory concentration. However, the expression of the P fimbrillin by recombinant plasmids containing deletions in front of the fimbrillin gene did not respond to the inhibitory effect of trimethoprim indicating that trimethoprim may act at the level of gene regulation.

Graft infection and bacteremia with a tolerant L-form of Streptococcus sanguis in a patient receiving hemodialysis

I report a case of a tolerant L-form Streptococcus sanguis infection involving an artificial vascular access site that was probably acquired from a nonhuman source; this is the first report of such an infection in a human. Gram stains from the infected access site and blood cultures revealed an aberrant form which could only be recovered by passage through hypertonic sucrose media before being reisolated and subsequently identified as S. sanguis. The same organism was isolated from a pet dog of the patient. The organism was also felt to be tolerant to penicillin. The patient was successfully treated by removal of the artificial graft and intravenous erythromycin therapy. Microorganisms acquired from nonhuman sources are potential pathogens in the immunocompromised patient.

Demonstration of pathogenic bacteria in "sterile" inflammatory exudates

One hundred and twenty-seven exudates from inflammatory processes, judged sterile after incubation on standard isolation media, were further investigated. This involved the exclusion of slow-growing strains by a further 48 hours incubation of the primary plates and subcultures from hypertonic broth that had been inoculated concurrently with the initial cultures. Over 80% of otherwise sterile exudates grew presumptive pathogens only after passage through the hypertonic broth and no further isolations resulted from extended incubation of the primary cultures. A history of current, or recent, antibiotic therapy commonly accompanied the demonstration of these aberrant strains and clinical remission of symptoms usually followed fresh antibiotic therapy directed solely against the revertant isolates.

Effects of subminimal inhibitory concentrations of chloramphenicol, erythromycin and penicillin on group A streptococci

Group A streptococci strains were grown in broth containing subminimal inhibitory concentrations of chloramphenicol, erythromycin and penicillin, and tested for possible changes in colonial morphology, activity and amount of cellular and extracellular components. The following components were tested: T protein, M protein, opacity factor, lipoteichoic acid, hyaluronic acid, streptolysin S, streptolysin O, DNase, hyaluronidase and NADase. Sub-MICs of these drugs produced variable changes in the bacteria. They increased the amount of hyaluronic acid and hyaluronidase, decreased the amount of M protein, and enhanced phagocytosis and the release of lipoteichoic acid. The results indicate that sub-MICs of chloramphenicol, erythromycin and penicillin may affect the pathogenicity and toxinogenicity of group A streptococci.

Sublethal concentrations of antibiotics, effects on bacteria and the immune system

Biological specimens obtained from patients with infections that are treated with antibiotics at dosages that resulted in body fluid concentrations below those that are minimally inhibitory, exhibit abnormal forms of bacteria. Identical morphological changes can be induced in vitro when the parental normal forms of the bacteria. Identical morphological changes can be induced in vitro when the parental normal forms of the bacteria are exposed to subminimal concentrations of certain antibiotics. The phenomenon of induced abnormal morphology and ultrastructure has received consideration in terms of: (1) the relationship of the induced alterations of the specific bacterial species to the given antibiotic, (2) in vitro conditions required for antibiotic induced alterations, (3) the mechanisms of action; (4) immune responses to the abnormal forms, and (5) relationship between abnormal structure and the inhibition of bacterial replication. This review provides the reader with a description and the significance of current research in the above areas which together comprise the growing field of subinhibitory concentrations of antibiotics.

Anomalous cellular morphology and growth characteristics of Neisseria meningitidis in subminimal inhibitory concentrations of penicillin G

The effects of subminimal inhibitory concentrations of penicillin G on Neisseria meningitidis in the presence and absence of selected stabilizers were examined. Subminimal inhibitory concentrations of penicillin G decreased cell numbers and altered both colonial and ultrastructural morphologies of this meningococcus. Although these levels of penicillin did not have immediate adverse effects on cell mass increase, deoxyribonucleic acid synthesis, or the incorporation of [3H]leucine into protein, they did significantly alter the division rate and the integrity of the cell envelope. The inability of many of the abnormal membranous cell types produced in subminimal inhibitory concentrations of penicillin to form either complete or properly oriented division septa and the overproduction of cell wall material at such sites was indicative of the disruptive effects of this antibiotic on functions necessary for maintaining the normal division process. The addition of the stabilizers polyvinylpyrrolidone-40 and horse serum to the test medium diminished the effects of penicillin G as evidenced by a fourfold increase in the minimal inhibitory concentration. Moreover, such stabilizers maintained the association of the outer membrane with the peptidoglycan and inner membrane.

Properties of penicillin-binding proteins in Neisseria gonorrhoeae

The properties of penicillin-binding proteins (PBPs) of Neisseria gonorrhoeae were studied by comparing PBPs of clinical isolates of different penicillin susceptibility and by putting various beta-lactam antibiotics in competition with radioactive penicillin for PBP binding. Apparent molecular weights of the three major PBPs found were 87,000 (PBP 1), 59,000 (PBP 2), and 44,000 (PBP 3). Relative penicillin resistance was associated with decreased binding to PBP 2 and, to a lesser extent, to PBP 1. Cephaloridine and benzylpenicillin, which produced spheroplasts at minimal inhibitory concentrations, bound to all three PBPs. In contrast, antibiotics which produced a majority of enlarged but apparently intact cells bound only to PBP 2 (mecillinam) or to PBPs 2 and 3 (cephalexin) at their minimal inhibitory concentrations.

Morphological expressions of antibiotic synergism against Pseudomonas aeruginosa as observed by scanning electron microscopy

Antibiotic-induced changes in Pseudomonas aeruginosa were observed by means of a scanning electron microscope. Seven frequent and five less frequent morphological changes were noted. The frequent changes were: (i) elongation; (ii) chain formation; (iii) nub formation; (iv) spheroplasts; (v) surface holes or pits; (vi) super-elongation; and (vii) increased filamentation. The less frequent changes were: (i) rounded ends; (ii) streptococcal forms; (ii) stalked nubs; (iv) surface bulges; and (v) convoluted surfaces. A morphological equivalent of antibiotic synergism was found in which changes were noted due to synergistic combinations of antibiotics that were not observed when the antibiotics were used alone or when a nonsynergistic combination of antibiotics was used.

Aberrant forms of Escherichia coli in blood cultures: in vitro reproduction of an in vivo observation

Aberrant filamentous forms of Escherichia coli were observed on direct Gram stain of blood cultures from a patient being treated with the beta-lactam antibiotic cephalexin. After the institution of an alternative antibiotic regimen which included a different cell wall-active agent, E. coli of normal morphology was detected in blood cultures for an additional 48 h. Filamentous forms of E. coli could be reproduced reliably in vitro by incubating the organism in Mueller-Hinton broth containing various concentrations of cephalexin. Both supra- and subinhibitory concentrations of cephalexin resulted in filament formation after 4 h of incubation, whereas 24 h of incubation yielded intact filaments at only a narrow range of subinhibitory concentrations of cephalexin. In vitro comparison of the ability of cephalexin, cephalothin, ampicillin, and gentamicin to cause filamentous forms of E. coli showed that cephalexin and cephalothin produced pure filament formation after 4 h of incubation at subinhibitory concentrations of as low as one-fourth the minimum inhibitory concentration of the antibiotic. Ampicillin was not associated with pure filament formation at concentrations below the minimum inhibitory concentration, and gentamicin produced no filaments at any concentration. The effect of preincubation of E. coli with subinhibitory concentrations of cephalexin on subsequent minimum inhibitory concentrations of ampicillin was examined in an effort to develop an explanation for the persistent sepsis exhibited by the patient. No diminution of the activity of ampicillin by preincubation with cephalexin could be demonstrated. Other possible clinical implications of filamentous forms of gram-negative bacilli are discussed.

Killing of oxacillin-exposed staphylococci in human polymorphonuclear leukocytes

Twelve strains of Staphylococcus aureus isolated from patients and two collection strains were grown on membranes placed on agar containing subminimal inhibitory concentrations of oxacillin. Clusters of staphylococci held together by thick cross walls resulted. These organisms, as well as the same strains grown in the same way on drug-free medium (control), were eluted from the membranes and were incubated with human polymorphonuclear leukocytes (PMNs) from various donors. Phagocytosis was comparable for both staphylococci exposed to oxacillin and control staphylococci, but the killing effect was different. The staphylococci grown on membranes in the presence of oxacillin were less susceptible to killing than the control staphylococci, but the killing effect was different. The staphylococci grown on membranes in the presence of oxacillin were less susceptible to killing than the control staphylococci. After 0.5 and 1 h of incubation with PMNs, the killing rates for oxacillin-grown versus control staphylococci were 52 and 70% and 65 and 85%, respectively (P < 0.01). After 2 and 3 h of incubation, the killing was similar. Most clusters of staphylococci contain a few individual cells that are located in the center of the cluster and are surrounded by other staphylococci; therefore, they are protected from adverse agents in the environment. This could explain why the phagocytized clusters are less susceptible than control staphylococci to the killing effect of PMNs during the first hour of incubation. Oxacillin does not penetrate into PMNs and in the absence of the drug the cross walls lyse, liberating the constituent staphylococci. This coincides with the increase in the percentage of cluster killing by PMNs after 2 and 3 h of incubation.

Effects of subminimal inhibitory concentrations of Erythromycin, Clindamycin, and Pristinamycin on the penicillinase production of Staphlyococcus aureus

The influence of subminimal inhibitory concentrations of erythromycin, clindamycin, and pristinamycin on the penicillinase production of Staphylococcus aureus was tested in 12 strains. Of the 36 experiments performed, 16 (44%) showed a lack of influence, 10 (28%) displayed an increase, and 10 revealed a decrease in penicillinase activity. The maximal effect produced was generally induced by concentrations ranging from 1/4 to 1/32 the minimal inhibitory concentration, irrespective of the susceptibility of the strain to the drug. In spite of the fact that the drugs are closely related, they sometimes produced opposite effects on the same strain.

Aberrant form of Pseudomonas aeruginosa in sputum and cerebrospinal fluid causing infection in a compromised patient

A patient with non-Hodgkin's lymphoma developed meningitis due to an aberrant form of Pseudomonas aeruginosa observed on Gram stain. The organism was grown on primary isolation media without needing hypertonic media. The significance of aberrant forms in body fluids is discussed.