TABLE 1.
Summary of putative virulence factors for Acinetobacter spp.
| Model type and virulence factor(s) or gene(s), process, or organellea | Model | Outcome(s) | Reference |
|---|---|---|---|
| In vitro only | |||
| OmpA | Cell cytotoxicity | OmpA was administered to eukaryotic cells and induced cell death (note that endotoxin levels on the protein not reported) | 321 |
| OmpA | Complement lysis of OmpA mutant of A. baumannii 19606 vs wild type | OmpA mutant resisted alternative pathway complement lysis in vitro | 322 |
| OmpA | Knockout of OmpA in A. nosocomialis ATCC 17903 | The knockout had reduced biofilm formation and adherence to lung epithelial cells, with no difference in cytotoxicity | 323 |
| CpaA | Blood coagulation | Purified CpaA protease reduced coagulation of human plasma | 324 |
| BfmS | Various assays comparing BfmS mutant on ATCC 17978 background to the wild type | BfmS mutant had diminished biofilm formation, reduced adherence to cells, and sensitization to serum killing | 325 |
| Porins (CarO and OprD-like) | Growth rate, cytotoxicity of a clinical isolate vs ATCC 19606 strain (nonisogenic pair) | A clinical pan-drug-resistant isolate with reduced CarO and OprD-like expression grew more slowly and was less cytotoxic in a cellular assay | 326 |
| CFTR inhibitory factor (CiF) | Gene expression and function | Gene homologous to CiF from Pseudomonas aeuruginosa is found in A. nosocomialis and A. baumannii | 327 |
| Biofilm gene (LH92_11085) | Characterization of gene expression and biofilm formation in A. baumannii MAR002 | MAR002 overexpresses biofilm and has 25-fold increased expression of LH92_11085 | 328 |
| Oxidative resistance (KatG and KatE) | Mutants of A. baumannii and A. nosocomialis tested in vitro | Mutants had increased susceptibility to oxidative killing and neutrophil killing | 329 |
| Adherence, invasion, and cytotoxicity | 5 clinical isolates of A. baumannii and 6 clinical isolates of A. pittii tested in adherence, invasion, and cytotoxicity of lung epithelial cells | Adherence, invasion, and cytotoxicity not detected despite testing strains that had caused clinical disease | 84 |
| In vivo–invertebrate models | |||
| NfuA (iron acquisition scaffold protein) | NfuA knockout in ATCC 19606 strain vs wild-type strain | Knockout strain more sensitive to oxidative stress and modestly less lethal in Galleria | 312 |
| EntA (enterobactin precursor synthetic gene) | EntA knockout in ATCC 19606 vs wild-type strain | Knockout strain modestly less lethal in Galleria | 311 |
| Superoxide dismutase (SOD) | SOD knockout in ATCC 17978 vs wild-type strain | Knockout strain more sensitive to oxidative stress and less lethal in Galleria | 330 |
| TonB (energetics of nutrient uptake) | TonB mutant of ATCC 19606 vs wild-type strain | Variable impact on lethality in Galleria but impacted adherence to epithelial cells | 82 |
| OXA-40 gene (carbapenemase) | Clinical isolates with or without the OXA-40 gene | OXA-40-containing isolates appeared to kill Galleria more slowly | 331 |
| AbuO (outer membrane protein) | AbuO knockout of A. baumannii AYE (origin unclear) with infection in C. elegans | Knockout displayed increased susceptibility to antibiotics and disinfectant and modestly reduced lethality in C. elegans | 332 |
| SecA (iron acquisition) | Transposon mutant disruption of SecA in A. baumannii 19606 | Mutant displayed modest reduction in lethality in Galleria | 315 |
| pmrB (colistin resistance due to altered LPS charge) | Clinical isolate with spontaneous pmrB mutation | Mutant displayed no reduction in strain fitness, growth, or lethality in Galleria | 333 |
| lpxACD, pmrB (colistin resistance due to loss of LPS synthesis genes [lpx] or altered LPS charge [pmr]) | Clinical strains serially passaged on colistin | lpxACD mutants had growth defects and loss of virulence, whereas pmrB mutants had no change in growth or virulence in Galleria | 334 |
| Phospholipase D | Disruption of 3 phospholipase D genes in ATCC 19606 | Reduced virulence in Galleria | 335 |
| Type VI secretion system (T6SS) | T6SS was compared in ATCC 17978, a nonclinical isolate (DSM30011), and 3 clinical isolates | Only the nonclinical isolate expressed a highly functional T6SS, which played a role in colonization in Galleria | 336 |
| lpxD (colistin resistance due to loss of LPS synthesis) | Clinical isolate of A. noscomialis serially passaged in subtherapeutic colistin | lpxD mutant had modestly attenuated virulence in C. elegans | 337 |
| SurA1 (surface antigen protein) | Knockout of SurA1 from A. baumannii CCGGD201101 (an isolate from diseased chicks) | Knockout had decreased growth rate, increased killing in serum, and decreased virulence in Galleria | 338 |
| AdeRS (Acinetobacter drug efflux pump regulator) | Deletion of AdeRS from A. baumannii AYE or S1 | Knockouts had decreased biofilm formation; S1 but not AYE knockout had decreased virulence in Galleria | 103 |
| gacA and gacS (regulator genes), abaI (quorum sensing), paaA (phenylalanine catabolism) | ATCC 17978 and knockouts infected via blood in zebrafish embryos | Knockout strains had attenuated virulence in the zebrafish model, and the paaA knockout produced more phenylalanine, which triggered more neutrophil attraction to the site of infection | 81 |
| Multiple genes regarding stress response, osmotic stress, capsule, and LPS genes | Comparison of Acinetobacter strains in Galleria, including transposon disruptants | Galleria distinguished known avirulent (ATCC 17978) and virulent (5075) strains of A. baumannii, with the former causing some lethality and the latter 100% fatal. A. baylii ADP1 was less virulent than A. baumannii ATCC 17978. A variety of genes disrupted by transposon insertion in A. baumannii 5075 modulated mortality in Galleria. | 76 |
| In vivo–nonlethal vertebrate models | |||
| Serum/complement resistance | Clinical isolates in Long-Evans rat soft tissue infection (subcutaneous) | Sensitivity to complement correlated with rapidity of soft tissue clearance in vivo | 73 |
| Phospholipase D | C57BL/6 intranasal lung infection (>3 × 108 inoculum) with transposon mutant clinical CSF isolate 98-37-09 vs wild type | Disruption resulted in serum sensitivity and no difference in lung bacterial density, but the mutant strain had lower bacterial blood density following pneumonia | 57 |
| Heme consumption | Nonlethal intranasal infection with A. baumannii LAC-4 clinical isolate, treatment with an inhibitor of heme acquisition vs placebo | Mice infected with LAC-4 and treated with heme acquisition inhibitor had modestly reduced lung bacterial density and bacteremia | 313 |
| PTK and EpsA (capsular polysaccharide regulators) | Long-Evans rat soft tissue infection with knockouts on A. baumannii 307-0294 clinical isolate background vs wild type | Disruption resulted in diminished growth in human ascitic fluid, human serum, and rat soft tissue | 74 |
| OmpA, LpsB, GacA | Transposon mutant library of A. baumannii ATCC 17978 infected intranasally into C57BL/6 mice | CFU differences at 24 h detected for strains with mutations of various genes, including lpsB (LPS biosynthesis), ompA, and gacA | 89 |
| Outer membrane vesicles (OMVs) | Outer membrane vesicles purified from A. nosocomialis ATCC 17903 administered to cells in vitro and BALB/c mice intratracheally | OMVs were toxic to eukaryotic cells and triggered inflammatory cytokine production in mouse lungs | 339 |
| LipA (lipase) | Tail vein infection of DBA mice made neutropenic with cyclophosphamide and infected with LipA knockout in A. baumannii ATCC 17978 vs wild type | LipA knockout demonstrated reduced competition fitness during nonlethal infection in mice | 340 |
| gspD (type 2 secretion system [T2SS]) | Intranasal inoculation of C57BL/6 mice with A. nosocomialis M2 with knockout of gspD vs wild type | Modest differences in survival in Galleria and modest differences in bacterial densities during nonlethal infection in mice | 341 |
| AdeABC and AdeIJK (efflux pump regulators) | Intranasal and intraperitoneal infection of C57BL/6 mice with clinical isolate A. baumannii BM4587 or its isogenic Ade mutants | Increase in bacterial burden during intraperitoneal infection with the adeABC mutant, decreased with adeIJK mutant, no change after lung infection (intranasal) | 101 |
| Zur (zinc uptake regulator) | Intranasal infection of C57BL/6 mice with A. baumannii ATCC 17978 or a Zur knockout strain | No difference in lung bacterial burden, but liver burden lower for the Zur knockout strain | 319 |
| ZigA (zinc chaperone) | Intranasal infection of C57BL/6 mice with A. baumannii ATCC 17978 or a ZigA knockout strain | No difference in lung bacterial burden, but liver burden lower for the ZigA knockout strain | 320 |
| FeoB (ferrous iron transport), DDC (cell wall cross-linking), PntB (pyridine metabolism), FepA (enterobactin receptor) | Intravenous infection in CBA/J mice with a transposon mutant library of A. baumannii ATCC 17978 treated with cyclophosphamide to make them neutropenic, using competitive growth by spleen bacterial density, or in human serum, as read-outs | Defects in these genes altered competitive growth/relative bacterial density in the spleens or serum | 90 |
| In vivo–lethal vertebrate models | |||
| Inoculum mixed with porcine mucin | |||
| pmrB | Intraperitoneal infection in C57BL/6 mice with ≥108 organisms of pmrB mutant in A. baumannii ATCC 19606 vs wild type | pmrB mutant had lower bacterial density and less mortality | 59 |
| pmrB | Intraperitoneal infection in C57BL/6 mice with ≥107.9 organisms of a clinical spontaneous pmrB mutant of A. baumannii CR17 (cerebrospinal fluid strain) vs its pretreatment parent strain | pmrB mutant had reduced in vivo fitness in competition with wild type and lower mortality at low, but not high (i.e., >105) inocula | 342 |
| pmrA (altered LPS charge) | Intratracheal lung infection in Sprague-Dawley rats with a spontaneous mutant of A. baumannii respiratory clinical isolate vs its pretreatment isogenic strain | pmrA mutant had reduced lethality | 343 |
| Ciprofloxacin resistance (mutation not described) | Intraperitoneal infection in C57BL/6 mice with 106, 107, or 108 A. baumannii clinical strain serially passaged in subtherapeutic ciprofloxacin vs its parent | Ciprofloxacin-resistant strain induced lower mortality | 344 |
| Acinetobactin (iron siderophore) | Galleria as well as intraperitoneal infection in C57BL/6 mice with 106 or 105 A. baumannii acinetobactin knockouts in ATCC 19606 vs wild type | Knockout strain induced lower mortality in Galleria and in mice | 316 |
| PgILAb (O glycosylation) | Galleria and intraperitoneal infection with porcine mucin in BALB/c mice, using a PgIL knockout in ATCC 17978 vs wild type | Mutant less lethal in Galleria, and less competitive than wild type during growth in mice | 345 |
| pglC (capsule) | Intraperitoneal infection in BALB/c mice infected with pglC knockout in ATCC 17978 vs wild type | Capsule-deficient mutant strain was avirulent compared to wild type | 105 |
| Omp33 | Intraperitoneal infection in C57BL/6 mice with 106, 107, or 108 Omp33 knockout in A. baumannii 17978 vs wild type | Knockout strain displayed growth defect in vitro, and reduced lethality in mice | 171 |
| MapA (Omp33-36) | Intraperitoneal infection in C57BL/6 mice with Omp33-36 knockout in A. baumannii 17978 vs wild type | Knockout displayed a 12-h delay in death (but all mice died) | 346 |
| gacS (sensor kinase) and paaE (phenylacetic acid [PAA] catabolic pathway) | Intraperitoneal infection in BALB/c mice infected with knockouts in ATCC 17978 vs wild type | gacS and paaE mutant strains had attenuated mortality in mice | 347 |
| Infections in wild-type mice without porcine mucin | |||
| RecA (DNA damage repair) | Intraperitoneal infection in CD1 mice with 2 × 108 RecA knockout of A. baumannii ATCC 17978 vs wild type | RecA mutant was more sensitive to oxidative damage, macrophage killing, and heat exposure in vitro and caused mildly reduced lethality compared to wild-type strain (7% vs 20%) | 96 |
| pmrB, lpxA, lpxA, lpxC, lpxD (LPS genes) | Intraperitoneal infection in BALB/c mice with knockouts in A. baumannii 19606 vs wild type | lpx mutants had reduced in vitro growth while pmrB mutant did not; lpx mutants had attenuated virulence in both C. elegans and in mice, but pmrB mutant had attenuated virulence only in C. elegans and not in mice | 80 |
| OmpA | In vitro studies followed by tracheal aspiration pneumonia using Ab5075 strain in wild-type C57BL/6 mice | Transposon-disrupted OmpA strain was nonlethal in 5 mice, whereas 3 of 4 mice infected with wild-type died (note the small numbers of mice) | 100 |
| Capsule | Intraperitoneal infection of C57BL/6 mice with A. baumannii ATCC 17978 strains which were induced to overproduce capsule or strains with mutations in capsule production | Strains expressing enhanced capsule were resistant to serum/complement, and more lethal in mice | 107 |
| UspA (universal stress protein A) | Intranasal and intraperitoneal infection of C57BL/6 mice with UspA knockout in A. baumannii ATCC 17978 vs wild type | Modest difference in lung CFU during nonlethal infection and no significant difference in survival during intraperitoneal lethal infection | 348 |
a
CFTR, cystic fibrosis transmembrane conductance regulator; PTK, protein tyrosine kinase; DDC, d-Ala-d-Ala-carboxypeptidase.